WO2019183221A1

WO2019183221A1 - Chemical cleaning for membrane filters

Info

Publication number: WO2019183221A1
Application number: PCT/US2019/023165
Authority: WO
Inventors: Thomas J. LEBEAU; Aaron J. Balczewski; Paul M. Gallagher; Joseph A. FURLONG
Original assignee: Evoqua Water Technologies Llc
Priority date: 2018-03-20
Filing date: 2019-03-20
Publication date: 2019-09-26

Abstract

Methods of treating water are disclosed. The method includes introducing water into a system containing a plurality of filter modules arranged in parallel for treatment. The method includes performing a cleaning cycle on a first set of the filter modules, the cleaning cycle including suspending operation of the first set of filter modules while maintaining operation of the second set of filter modules and backwashing the first set of filter modules. The method includes backwashing the filter modules with a first solution, draining the first solution, and backwashing the filter modules with a second solution which includes a cleaning agent. The method includes resuming operation of the first set of filter modules and performing a cleaning cycle on the second set of filter modules. Water treatment systems, methods of facilitating cleaning of filter modules, and methods of retrofitting water treatment systems are also disclosed

Description

CHEMICAL CLEANING FOR MEMBRANE FILTERS

CROSS REFERENCE TO RELATED APPLICATIONS

This application claims priority under 35 U.S.C. §119(e) to U.S. Provisional

Application Serial No. 62/645,502, titled“Chemical Cleaning for Membrane Filters,” filed on March 20, 2018, which is incorporated herein by reference in its entirety for all purposes.

FIELD OF TECHNOLOGY

Aspects relate to methods of cleaning a filtration apparatus. More particularly, aspects relate to methods of cleaning microfiltration or ultrafiltration membranes used for water filtration purposes.

SUMMARY

In accordance with one aspect, a method of treating water is provided. The method may comprise introducing water to a system comprising a plurality of filter modules arranged in parallel for treatment. The method may comprise performing a first cleaning cycle on a first set of the plurality of filter modules. The first cleaning cycle may comprise suspending operation of the first set of filter modules while maintaining operation of a second set of filter modules; backwashing membranes of the first set of filter modules with a first solution; draining down the first solution from the first set of filter modules; backwashing the membranes of the first set of filter modules with a second solution comprising a cleaning agent in the drained down state; purging the second solution from the membranes of the first set of filter modules; and resuming operation of the first set of filter modules. The method may comprise performing a second cleaning cycle on the second set of filter modules subsequent to the first cleaning cycle, the second cleaning cycle being analogous to the first cleaning cycle.

The first cleaning cycle may further comprise soaking the membranes in the second solution for a predetermined period of time prior to purging.

In accordance with certain embodiments, purging may comprise rinsing the membrane. The membrane may be rinsed with filtrate. The membrane may be rinsed via backwash.

In accordance with certain embodiments, purging may comprise neutralizing the second solution in place. A neutralization chemical may be introduced on a feed or filtrate side of the membranes. In accordance with certain embodiments, purging may further comprise at least partially draining down the first set of filter modules and refilling the first set of filter modules prior to resuming their operation.

In some embodiments, at least 25% of the tank may be filled with the second solution during backwashing.

In accordance with certain embodiments, purging may further comprise aerating the membranes.

The cleaning agent may be pulsed into the second solution.

The cleaning agent may comprise chlorine.

The first solution may comprise filtrate or gas.

In some embodiments, the first and second cleaning cycles may be configured to optimize performance of the system. Optimized system performance may pertain to at least one of: minimizing overall system downtime, minimizing a need for dedicated cleaning resources with respect to each set of filter modules, and maximizing functionality of equipment intrinsic to each set of filter modules.

In some embodiments, the first cleaning cycle may be performed between about 5 and 12 times in a 24 hour period. The maintenance wash may be performed at most about once every four days.

The method may further comprise measuring a backpressure value associated with the first set of filter modules and initiating the first cleaning cycle responsive to measuring a backpressure value that exceeds a threshold backpressure value.

In accordance with another aspect, there is provided a water treatment system. The water treatment system may comprise a plurality of filter modules arranged in parallel, each filter module comprising a plurality of membranes. The water treatment system may comprise a source of a first backwashing solution fluidly connected to each filter module.

The water treatment system may comprise a source of a second backwashing solution comprising a cleaning agent fluidly connected to each filter module. The water treatment system may comprise a controller configured to perform a first cleaning cycle on a first set of the plurality of filter modules, the first cleaning cycle comprising suspending operation of the first set of filter modules while maintaining operation of the remaining filter modules;

backwashing membranes of the first set of filter modules with the first backwashing solution; draining down the first backwashing solution from the first set of filter modules;

backwashing the membranes of the first set of filter modules with the second backwashing solution in the drained down state; purging the second backwashing solution from the membranes of the first set of filter modules; and resuming operation of the first set of filter modules. The controller may be configured to perform a second cleaning cycle on a second set of the plurality of filter modules subsequent to the first cleaning cycle, the second cleaning cycle being analogous to the first cleaning cycle.

The system may further comprise a pump operably connected to the controller and configured to deliver the first backwashing solution or the second backwashing solution to each filter module.

The system may further comprise a source of a neutralizing solution fluidly connected to each filter module.

The membranes may be hollow fiber membranes.

The membranes may be microfiltration or ultrafiltration membranes.

The first or second set of filter modules may be mounted in a single tank or on a single skid.

The first set of filter modules may share at least one of a common intake pump, tank, dosing pump, circulation pump, or distribution manifold.

The water treatment system may be a submerged tertiary filtration system.

The system may further comprise an aerator in fluid communication with each filter module.

The system may further comprise a pressure sensor associated with the first set of filter modules, wherein the controller is configured to initiate the first cleaning cycle responsive to measuring a backpressure value that exceeds a threshold backpressure value.

In accordance with another aspect, there is provided a method of facilitating cleaning of a plurality of filter modules arranged in parallel. Each filter module may include a filter membrane. The method may comprise, providing a controller configured to perform a first cleaning cycle on a first set of the plurality of filter modules, the first cleaning cycle comprising suspending operation of the first set of filter modules while maintaining operation of the remaining filter modules; backwashing membranes of the first set of filter modules with a first backwashing solution; draining down the first backwashing solution from the first set of filter modules; backwashing the membranes of the first set of filter modules with a second backwashing solution in the drained down state; purging the second backwashing solution from the membranes of the first set of filter modules; and resuming operation of the first set of filter modules. The controller may further be configured to perform a second cleaning cycle on a second set of the plurality of filter modules subsequent to the first cleaning cycle, the second cleaning cycle being analogous to the first cleaning cycle. The method may comprise operably connecting the controller to a first pump configured to introduce the first backwashing solution into the plurality of filter modules. The method may comprise operably connecting the controller to a valve configured to drain the first backwashing solution and the second backwashing solution from the plurality of filter modules. The method may comprise operably connecting the controller to a second pump configured to introduce the second backwashing solution into the plurality of filter modules.

In some embodiments, the method may further comprise providing a pressure sensor and installing the pressure sensor to measure backpressure associated with at least one filter membrane of the plurality of filter modules. The method may further comprise operably connecting the controller to the pressure sensor, the controller being programmed to control an automated cleaning cycle responsive the pressure sensor measuring a backpressure value which is outside tolerance of a target backpressure value range.

In accordance with yet another aspect, there is provided a method of retrofitting a system comprising a plurality of filter modules arranged in parallel. Each filter module may have a filter membrane, an inlet, and an outlet. The method may comprise fluidly connecting a source of a first backwashing solution to a pump configured to deliver the first backwashing solution to a first set of the plurality of filter modules. The method may comprise fluidly connecting a source of a second backwashing solution to the pump. The method may comprise operably connecting a controller to the pump. The controller may be configured to perform a first cleaning cycle on a first set of the plurality of filter modules, the first cleaning cycle comprising suspending operation of the first set of filter modules while maintaining operation of the remaining filter modules; backwashing membranes of the first set of filter modules with a first backwashing solution; draining down the first backwashing solution from the first set of filter modules; backwashing the membranes of the first set of filter modules with a second backwashing solution in the drained down state; purging the second backwashing solution from the membranes of the first set of filter modules; and resuming operation of the first set of filter modules. The controller may further be configured to perform a second cleaning cycle on a second set of the plurality of filter modules subsequent to the first cleaning cycle, the second cleaning cycle being analogous to the first cleaning cycle.

In some embodiments, the method may further comprise fluidly connecting a source of a neutralizing solution to the pump.

Still other aspects, embodiments, and advantages of these example aspects and embodiments, are discussed in detail below. Moreover, it is to be understood that both the foregoing information and the following detailed description are merely illustrative examples of various aspects and embodiments, and are intended to provide an overview or framework for understanding the nature and character of the claimed aspects and embodiments.

Embodiments disclosed herein may be combined with other embodiments, and references to “an embodiment,”“an example,”“some embodiments,”“some examples,”“an alternate embodiment,”“various embodiments,”“one embodiment,”“at least one embodiment,”“this and other embodiments,”“certain embodiments,” or the like are not necessarily mutually exclusive and are intended to indicate that a particular feature, structure, or characteristic described may be included in at least one embodiment. The appearances of such terms herein are not necessarily all referring to the same embodiment.

BRIEF DESCRIPTION OF THE DRAWINGS

Various aspects of at least one embodiment are discussed below with reference to the accompanying figures, which are not intended to be drawn to scale. The figures are included to provide an illustration and a further understanding of the various aspects and embodiments, and are incorporated in and constitute a part of this specification, but are not intended as a definition of the limits of any particular embodiment. The drawings, together with the remainder of the specification, serve to explain principles and operations of the described and claimed aspects and embodiments. In the figures, each identical or nearly identical component that is illustrated in various figures is represented by a like numeral. For purposes of clarity, not every component may be labeled in every figure. In the figures:

FIG. 1 shows an embodiment which enables solution delivery to the shell side of a hollow fiber membrane and permeation through to the lumen side;

FIG. 2 shows an embodiment which enables solution delivery to the lumen side of a hollow fiber membrane with the shell side at least partially drained/filtered down first;

FIG. 3 shows an embodiment which enables solution delivery to lumen side of a hollow fiber membrane while water containing solid remains on the shell side;

FIG. 4 shows the test profiles of maintenance clean and definition of cleaning efficiency, according to one embodiment;

FIG. 5 shows the membrane performance recovery with different tested methods, according to one embodiment;

FIG. 6 shows the relative chemical cleaner consumption for a number of cleaning methods, according to one embodiment; FIG. 7 is a box diagram of a system for water treatment, according to one embodiment;

FIG. 8A is a graph of system performance after a chemically enhanced backwash, according to one embodiment; and

FIG. 8B is a graph of permeability after a chemically enhanced backwash, according to one embodiment.

DETAILED DESCRIPTION

Microfiltration and ultrafiltration membrane filters may be used in municipal drinking water treatment and wastewater treatment. Surface waters may contain inorganic

contaminants, for example, iron and magnesium. Surface waters may contain higher concentrations of inorganic contaminants during weather related events such as storm events or snow melts. Certain surface waters may contain significant concentrations of natural foulants, such as algae. Wastewater may contain contaminants including, for example, organic contaminants, inorganic contaminants, and biological contaminants. These contaminants may foul membranes, increasing transmembrane pressure and resistance and decreasing permeability. Fouling events may require periodic membrane module cleaning procedures to continue adequate water treatment.

One membrane configuration for membrane modules is hollow fiber. Hollow fiber modules are often operated in dead-end mode when filtering or with only a small crossflow.

In such systems, physical and chemical cleaning operations may be carried out periodically to remove retained solids and foulants from the membrane bundles. A physical cleaning operation including a backwash may be carried out about once or twice an hour and last for between about 2 and 5 minutes. A maintenance wash performed by introducing a chemical cleaning agent may be conducted once a day or once every few days and last for between about 45 and 60 minutes. A full chemical cleaning operation may be conducted once or twice a month and last for between about 3 and 8 hours.

With a typical microfiltration or ultrafiltration operation, transmembrane pressure (TMP) is the main driving force for the filtration process. As the process progresses and filtered water permeates through the membrane, most of the solid contaminants are retained either on the membrane surface, forming a fouling layer or as plugs in the membrane pores blocking filtration. The presence of a fouling layer or plugged pores or both can significantly increase the transmembrane pressure and ultimately the filtration energy consumption. Scheduled backwashes with either filtrate or gas can partially reclaim the membrane permeability. However, with these methods it is known that foulants may continue to build up on the membrane surface and in the pores. Successive backwashes may sometimes not remove all the deposited material, and consequently over time there is deterioration in filter permeability.

Cleaning protocols may be supplemented by the use of chemical cleaning agents. The general criteria for selecting a chemical cleaning method may include, for example, to achieve a good recovery of membrane permeability, to minimize the amount of chemical cleaning agent required and the resultant amount of waste generated, and to allow ease of operation. In some embodiments, a cleaning agent may be selected based on the composition of the feed stream. For instance, membrane modules treating water containing inorganic contaminants may be cleaned with acidic cleaning agents. One example is industrial wastewater containing inorganic foulants. For example, acidic cleaning agents may be used in association with phosphate recovery operations. Membrane modules treating surface waters containing foulants such as algae may be cleaned with chlorine-based cleaning agents.

Membrane modules treating wastewaters with organic contaminants and/or biological contaminants may be cleaned with chlorine-based cleaning agents. The cleaning agent may be chlorine-based, acidic, alkaline, and/or caustic. Exemplary cleaning agents include ammonium bifluoride, sodium hypochlorite, and others.

One cleaning method involves immersing the membranes in a chemical cleaning solution for a period of time. The chemical reactions may dissolve the solids accumulated on the membrane surface and plugged in the pores. The cleaning effect may be facilitated by injecting air to scour membranes or by recirculating the chemical solution. This method may be used for full chemical recovery of membrane performance. However, a significant volume of chemical solution may be required and the process may generate large volumes of chemical waste.

In other methods to control permeability deterioration, chemical cleans (maintenance cleans) are frequently carried out with membrane filters. US 5,403,479, incorporated herein by reference in its entirety for all purposes, describes one such method of carrying out such a process. Briefly, a cleaning solution may be introduced into the lumen of a hollow fiber membrane, and recirculated at low flow at a pressure below the membrane bubble point. The cleaning solution may permeate through membrane pores under low transmembrane pressure and at a low rate. Diffusion of the cleaning solution through the membrane may occur even when fluid is held in the fibers at no velocity but under pressure. During the course of cleaning, the membrane is typically immersed in water. This method requires storage of a volume of chemical solution sufficient to fill the permeate lines and for recirculation. During the recirculation process, an increasing amount of chemical solution may penetrate through the membrane pores from the lumen side to the feed side.

Another method of conducting a membrane clean involves repeatedly back-pulsing membranes with a chemical cleaner, as described in US 6,045,698, incorporated herein by reference in its entirety for all purposes. Similar methods of chemical cleaning backwash for submerged membrane systems are disclosed in US Patent Application Publication Nos.

20010052494 Al, 20030146153A1, 20040007525A1, International Application Publication No. W00108790A1 and US Patent No. 6,547,968, each of which is incorporated herein by reference in its entirety for all purposes.

The second and third methods mentioned above generally use less volume of chemical solution than the first method, but they require that the chemical solution be of very high quality and free of solids because the solution is introduced into the permeate side.

As disclosed herein, membrane filters may be treated by a chemically enhanced backwash. Membrane modules may undergo regularly scheduled backwashes. In some embodiments, all scheduled backwashes may be chemically enhanced. In other embodiments, a fraction of the scheduled backwashes may be chemically enhanced. For example, in some embodiments, every other scheduled backwash may be chemically enhanced. In other embodiments, every third, fourth, fifth, sixth, seventh, eighth, ninth, tenth, eleventh, or twelfth scheduled backwash may be chemically enhanced.

Chemical cleaning backwash can be continuous or pulsed, and can be carried out after the membrane tank is drained, while the membrane tank is draining, or even without draining the membrane tank prior to the chemical backwashes. The chemical solution may be delivered to the system via a header at the top of the membranes by pump when the membranes are oriented vertically. The chemical cleaning solution may be forced under pressure through the membranes to the lumen side. Repeated back-pulses may bring the biofilm in the permeate lines back to membranes.

Conventionally, membrane modules are emptied of liquid after a physical cleaning backwash to remove the dirty water containing solids. In some embodiments, membrane modules may be emptied prior to performing a chemically enhanced backwash. A chemical cleaning solution may be introduced to the emptied membrane module after the scheduled physical backwash. The membrane module may be filled with the chemical cleaning solution and soaked for a period of time. The membrane module may be filled between about 25% and about 75% with the chemical cleaning solution for soaking. For example, the membrane module may be filled about 25%, about 50%, or about 75% with the chemical cleaning solution for soaking. After a period of time, the membrane modules may be refilled with fresh feed. The fill can be performed from the feed side, the filtrate side, or both. The liquid in the membrane module may then be drained from the system to rinse out the chemical cleaning solution or may be neutralized in place. The modules may be refilled to resume normal filtration.

Thus, in some embodiments, the chemically enhanced backwash may be performed during a scheduled physical cleaning backwash. The chemically enhanced backwash may be performed prior to draining the physical cleaning backwash fluid. The chemically enhanced backwash may be performed before refilling the module with fresh feed. During the chemically enhanced backwash, the filter module may be soaked with the cleaning solution for a period of time. The period of time may be, for example, between about 2 and about 20 minutes. The cleaning solution may be rinsed by soaking or backwashing with a rinsing solution or fresh feed. The cleaning solution may be drained before resuming operation. In some embodiments, operation is resumed without draining the cleaning solution. A neutralization solution may be introduced from the feed or filtrate side to neutralize certain cleaning agents.

In such embodiments, overall downtime of the membrane system may be reduced. The chemically enhanced backwash may eliminate or reduce the need for the longer scheduled daily maintenance washes. In some embodiments, the maintenance washes may be performed every other day. In some embodiments, the maintenance washes may be performed every three days. In some embodiments, the maintenance washes may be performed every four days. In some embodiments, the maintenance washes may be performed every five days. Maintenance washes may be reduced for as long as the membrane performance is stabilized. For instance, maintenance washes may be withheld until the transmembrane pressure, permeability, and/or resistance exceeds a threshold value. In an exemplary embodiment, the threshold value for transmembrane pressure may be, for example, about 4 psi, about 3 psi, or about 2 psi. In an exemplary embodiment, the threshold value for permeability (normalized to 20 °C) may be, for example, about 15 gfd/psi, about 12.5 gfd/psi, or about 10 gfd/psi. In an exemplary embodiment, the threshold value for resistance may be, for example, about 1 m ¹, about 2 m ¹, or about 3 m ¹. Scheduled chemically enhanced backwashes may stabilize the membrane for a longer period of time as compared to performing physical backwashes and a daily chemical maintenance wash. The daily downtime of each membrane module as a result of chemically enhanced backwashing (on a day without a maintenance wash) may be less than 30 minutes, less than 20 minutes, or less than 10 minutes. The reduced daily downtime may be achieved by performing a chemically enhanced backwash every 5-20 hours. In some embodiments, the downtime for each chemically enhanced backwashing may be less than 20 minutes, less than 15 minutes, less than 10 minutes, or less than 5 minutes. Each membrane module may undergo between about 1 and 6 chemically enhanced backwashes a day. In some

embodiments, each membrane module may undergo one, two, three, four, five, six, seven, or eight chemically enhanced backwashes.

The number of daily chemically enhanced backwashes may be determined based on a concentration of the cleaning agent in the chemical solution. In some embodiments, the number of chemically enhanced backwashes and/or concentration of cleaning agent in the chemical solution may be sufficient to stabilize at least one of transmembrane pressure, resistance, and permeability. The number of chemically enhanced backwashes and/or concentration of cleaning agent in the chemical solution may be sufficient to stabilize transmembrane pressure of a membrane module to be between about 0.1 and 4 psi, for example, between about 2 and 3 psi or between about 1 and 3 psi. The number of chemically enhanced backwashes and/or concentration of cleaning agent in the chemical solution may be sufficient to stabilize permeability (normalized to 20 °C) of a membrane module to be between about 5 and 15 gfd/psi, for example, between about 7.5 and 10 gfd/psi or between about 10 and 12.5 gfd/psi. The number of chemically enhanced backwashes and/or concentration of cleaning agent in the chemical solution may be sufficient to stabilize resistance of a membrane module to be between about 0.1 and 2 m ¹, for example, between about 1 and 2 m ¹.

In some embodiments, a concentration of the cleaning agent in the chemical solution used for the chemically enhanced backwash may be between about 10% and about 50% of a concentration of the cleaning agent in the solution used for the maintenance wash. For example, a concentration of the cleaning agent in the chemical solution used for the chemically enhanced backwash may be about 10%, about 20%, about 25%, about 30%, about 40%, or about 50% of the concentration of the cleaning agent in the solution used for the maintenance wash. In an exemplary embodiment, a chemical solution used for the chemically enhanced backwash may have a concentration of cleaning agent of between about 100 ppm and 500 ppm, for example, between about 200 ppm and about 300 ppm or between about 100 ppm and about 200 ppm. The chemical solution used for the chemically enhanced backwash may have a concentration of cleaning agent of about 100 ppm or about 250 ppm. In an exemplary embodiment, a chemical solution used for the maintenance wash may have a concentration of cleaning agent between about 250 ppm and about 1000 ppm, for example, between about 500 ppm and about 1000 ppm. The chemical solution used for the

maintenance wash may have a concentration of cleaning agent of about 500 ppm. The concentration of the cleaning agent in any chemical solution may be selected based on the characteristics of the water to be treated, for example, based on a concentration of contaminants or total suspended solids (TSS).

There are trade-offs between the concentration of chemical cleaning agent in the chemically enhanced backwash solution and the frequency of chemically enhanced backwashes. For instance, cost may be considered when determining the concentration of chemical agent and frequency of backwashes. In some embodiments, an increase in chemical agent concentration may be correlated with a decrease in frequency of chemically enhanced backwashes needed to stabilize the membrane. Other considerations for selecting the concentration of the chemical solution include maintaining a lower transmembrane pressure, better handling fluctuations in feed composition, stabilizing filtrate output for a downstream process (for example, a post-treatment process), and reducing overall downtime of the system.

In general, a greater concentration of cleaning agent in the solution used for the chemically enhanced backwash may stabilize the membrane for a longer period of time. In an exemplary embodiment, a chemical solution having 100 ppm chlorine may be introduced every 5, 6, or 7 backwashes occurring every 20-25 minutes. In an exemplary embodiment, a chemical solution having 200 ppm chlorine may be introduced every 6, 7, or 8 backwashes occurring every 20-25 minutes. In an exemplary embodiment, a chemical solution having 250 ppm chlorine may be introduced every 7, 8, or 9 backwashes occurring every 20-25 minutes. In an exemplary embodiment, a chemical solution having 300 ppm chlorine may be introduced every 8, 9, or 10 backwashes occurring every 20-25 minutes. Such exemplary embodiment may stabilize a membrane module for at least about 3, 4, or 5 days, depending on the concentration of contaminants in the feed water and the type of membrane.

The reduced daily downtime from performing less maintenance washes may minimize flow balancing and system resource availability problems that conventional systems experience. In particular, the reduced downtime may be beneficial for larger systems with a plurality of membrane modules. Conventionally, larger systems may not be able to perform frequent chemical cleaning operations due to large downtimes. The methods disclosed herein may alleviate downtime of the system.

According to one aspect, there is provided a method of cleaning a porous polymeric membrane having a feed side and a permeate side comprising introducing a fluid containing a cleaning agent to the permeate side of a membrane, allowing the cleaning agent to contact the permeate side of the membrane for a predetermined time, and contact the pores of the membrane.

The cleaning agent may contact the permeate side under static pressure.

According to another aspect, there is provided a method of cleaning a porous polymeric membrane having a feed side and a permeate side comprising introducing a fluid containing a cleaning agent to the feed side of a membrane; applying a transmembrane pressure to force the fluid containing the cleaning agent from the feed side to the permeate side of the membrane; allowing the cleaning agent to contact the permeate side of the membrane for a predetermined time, and contact the pores of the membrane.

The transmembrane pressure may be a small differential pressure.

According to another aspect, there is provided a method of cleaning a porous polymeric membrane having a feed side and a permeate side comprising providing a feed side fluid in contact with the feed side of the membrane; introducing a fluid containing a cleaning agent to the permeate side of a membrane; allowing the cleaning agent to contact the permeate side of the membrane for a predetermined time to contact the pores of the membrane and diffuse into the feed side fluid.

The solution diffusion may be driven by a concentration gradient between the feed side fluid (for example, low in concentration of cleaning agent) and the lumen side fluid containing the cleaning agent. In some embodiments, the feed side fluid contains no cleaning agent.

The methods may further include applying a pressure to the fluid containing a cleaning agent on the permeate side to dislodge, where present, dissolved and undissolved solid from the membrane pores. Such pressure may be applied in a pulsed fashion. In one embodiment, the source of pressure may be compressed air at a pressure not more than the membrane's bubble point.

The methods disclosed herein may, in some embodiments, be preceded by a backwash.

The methods disclosed herein may also be followed by a backwash, for example, prior to the recommencement of filtration. In certain embodiments, for example, responsive to a determination that further cleaning is desired, the methods may be repeated in cycles.

The cleaning methods described herein may be applied to pressurized membrane filtration or immersed membrane filtration systems. The membranes can be microfiltration, ultrafiltration or nanofiltration membrane, and can be either capillary or flat sheet membranes.

In some embodiments, the membrane may be an ultrafiltration or microfiltration membrane.

In some embodiments, the membranes may be hollow fiber membranes, having a lumen side (permeate side) and a module or shell side (feed side). A plurality of hollow fiber membranes may be housed inside a module housing.

A plurality of the membranes may be arranged in aligned bundles. The modules may be potted at the ends of the bundles, creating a plurality of lumen spaces inside the hollow fibers and a contiguous space on the outer or shell side of the hollow fibers. The lumens may be arranged so that filtered water accumulates therein and is passed from the plurality of lumens into a combined filtration stream.

The fluid may be water.

In accordance with certain embodiments, the fluid containing a cleaning agent may be introduced to the lumens of these hollow fiber membranes. In other embodiments, the fluid containing a cleaning agent may be introduced to the shell side of the membrane, for example, by partially filling the shell side of the module before being transported into the lumens.

The fluid containing the diffusible cleaning agent may be retained in the membrane permeate side without applied pressure or with slight applied pressure. A pressure approximately equal to the static head pressure may be applied.

The cleaning solution may be any conventional cleaning solution, including, for example, acidic, basic or neutral cleaning solutions. The cleaning solution may be oxidative or reductive, depending upon the origin of the foulant. The cleaning agent may also be inorganic or organic. Certain cleaning agents include dissolved halogens, such as chlorine, or dissolved oxidative or reductive agents, such as sulfite based reagents. The cleaning agents may be chelating agents, such as citric acid or EDTA. To facilitate wetting out and dissolving the foulant, a small amount of surfactant may be added to the cleaning solution.

In a membrane system, the method of delivery of chemical cleaner may vary according to the system design. For example, in some membrane filtration systems the chemical cleaner may be delivered to the feed side of the membrane. If so, the requirement on the water used to prepare the chemical solution in terms of solid content is not particularly stringent and the cleaning solution may be re-used for several times. This, however, may require a chemical storage tank and a chemical transfer pump. This delivery method may be found, for example, in large membrane systems. In other membrane systems, the delivery of the chemical cleaner may be to the permeate side to further reduce the volume of chemical solution and improve ease of operation. A dosing pump may be used in such circumstances. The methods disclosed herein may be adapted to handle either feed side or lumen side dosing.

It should be noted that even though certain embodiments are described herein with reference to hollow fiber polymeric microfiltration and ultrafiltration membranes arranged in bundles and housed in modules, and certain embodiments are described herein with reference to maintenance clean for pressurized membrane filtration system with an outside-in filtration mode, one of ordinary skill in the art would appreciate that the disclosure is not limited to such embodiments. The disclosure may, for example, encompass a different filter membrane and/or an inside-out filtration mode. The disclosure may, for example, be applied to pressurized membrane arrays with minimal changes.

Backwash may be performed prior to any maintenance wash. In a typical backwash process of a hollow fiber membrane, for example, a liquid may be forced through the membrane from the lumen side, either by gas pressure or pumped by further liquid. As part of the backwash process, the shell side may be either drained, partially drained, or filled with liquid during the backwash and prior to any cleaning solution being introduced.

A procedure for carrying out a backwash may include an initial filtering down or draining down process. Filtering down may be achieved with compressed air at a pressure below the membrane bubble point entering the shell side as the filtration driving force to push the shell-side liquid through the membrane and into the lumen. Filtering down may continue until the shell side liquid level is at least less than half of the shell side liquid holding volume. In the case where no backwash is carried out before the clean, filtering down may be carried out as the initial step of the maintenance wash. The shell side liquid level may be down to the lowest level that filtering down with compressed air can achieve, which in most cases is usually just above the lower module potting. Filtering down means the shell side volume may be greatly reduced and any maintenance wash solution can thus enter the system without the necessity of draining the shell side. For immersed membrane filtration processes, no compressed air is required to perform filtering down. Following the drain down or filtering down, a liquid backwash can be carried out, for example, with air scouring. The liquid backwash can be achieved in different ways. One method involves an air pushed backwash. In such a method, compressed air below the membrane bubble point may enter the lumen and push the filtrate through the membrane in the reverse direction to the filtration direction. The filtrate retained in the lumen at the end of filtration or filtering down may be used for the backwash. In some embodiments, only the filtrate retained in the lumen may be used for the backwash. Following the backwash, the lumen may be empty and ready to receive the chemical cleaning solution.

Membranes requiring maintenance washes are usually covered with a layer of fouling materials and some of the membrane pores may also be plugged. Backwashing may be employed to at least partially remove such pore blockages and fouling layer, enabling cleaning solution to reach a greater percentage of the membrane surface. When maintenance washing is used without backwashing, the cleaning solution may diffuse through the membranes via unblocked pathways which may be present as a result of regions of less fouled membrane surface and unblocked membrane pores. With sufficient air pressure, filtrate in the lumen may flow through membrane pores at reasonable velocity, removing at least some fouling materials on the membrane surface and opening a portion of blocked pores. This method may enable chemical solutions, when introduced, to reach a greater percentage of membrane pores.

At end of any pre-maintenance wash backwash, the shell side liquid can be either drained or retained as part of the backwash process. Because of the reduced shell side liquid volume achieved by prior filtering down, the shell side liquid volume before maintenance wash is generally less than half of the total shell side liquid holding volume, even when drain down is removed from the end of the backwash sequence. Drain down of the shell side liquid before maintenance wash is optional.

Alternatively, before maintenance wash, the membrane may not be backwashed. In some embodiments, the shell side may be filtered down or drained down to reduce the shell side volume before the delivery of maintenance wash solution.

Depending on the particular method chosen, the chemical solution may be either delivered to the shell side, for example, via a lower CIP (Cleaning-In-Place) manifold or to the filtrate (lumen) side, for example, via a lower filtrate/CIP manifold, or both in a sequence.

In the methods disclosed herein, the solution flow rate may be low (for example, on the order of 0.1 - 4.0 m³/h per module, depending on module size) for the lumen side chemical delivery. The solution flow rate may be selected to minimize the negative transmembrane pressure which may occur during this stage. The maximum cleaning solution volume used in the clean may be no more than the lumen volume, shell volume, or both (plus any pipe holding or tidal volume) depending on the particular delivery method. The cleaning solution volume may be selected for controlling chemical solution consumption.

Cleaning solutions may be delivered by any existing pump connected to the appropriate fluid volumes, for example, the plant CIP pump. If the cleaning solution is mainly delivered to the lumen side, the cleaning solution usage may be very low. In such cases, the cleaning solution can be stored in a sealed storage tank and compressed gas may be used as a delivery tool to push the solution from the storage tank into the lumens of the hollow fiber membranes. In such embodiments, if the storage tank is fitted with a fluid level sensor, or if the storage tank volume is similar to the total lumen volume, control of solution volume delivered to the system can be simplified.

Once cleaning solution is delivered to the system, the CIP pump may be stopped or the gas pressure source may be removed. Depending on the chemical used in the clean, if desired, the shell side and lumen side may be vented via upper manifolds during the soaking period or periodically vented during the soaking period. When vented, shell side aeration may be used to mix the chemicals and improve the contact between the chemical and the membrane. When the solution is dosed to the filtrate (lumen) side, shell side aeration may be used when the solution diffused through membrane wall and reaches the shell side. The solution diffuses through membrane pores to reach the side where there is little or no liquid or where the concentration of cleaning agent in solution is low.

When both the shell side and lumen side are filled, the chemical cleaning agent may diffuse into the membrane pores via a concentration gradient. Membrane pores may be soaked in solution for a period of time. The period of time may be on the order of 30 seconds to 20 minutes for a typical chemically enhanced backwash. A longer time, for example, greater than 20 minutes, may be used for a maintenance wash. A shorter time, for example, between 5 and 10 minutes, may be used for a chemically enhanced backwash. If desired, the shell side and lumen side may be vented via upper manifolds during the soaking period or periodically vented during the soaking period. Humidity loss due to vaporization in the lumen or shell side is typically very low and membrane pores are kept wet with cleaning solution.

If desired, a backwash may be carried out to remove the remaining cleaning solution from the system prior to resuming filtration.

In some embodiments, there is provided a filtration system including at least one group or set of filter membrane modules. The groups of filter membrane modules may be arranged in parallel to allow continuity of operation during a cleaning cycle of one group of filter membrane modules. Typically, large systems have several membrane units which may be termed cells, units, skids, arrays, and may comprise a group of membrane modules that operate together and are mounted on a single tank or a single skid. The group or set of filter modules may be mounted in a single tank or on a single skid.

The system may be fluidly connectable or fluidly connected to a source of water to be treated. The source of water to be treated may include groundwater, surface water, municipal wastewater, or industrial wastewater. The system may be fluidly connectable or fluidly connected to a source of a chemical cleaning agent. In some embodiments, the chemical cleaning agent may be pulsed into a solution. The solution may be, for example, system filtrate. The system may be fluidly connectable or fluidly connected to a source of a neutralizing solution. The system may be fluidly connectable or fluidly connected to a source of a fresh feed. In certain embodiments, the source of the fresh feed may be the source of the water to be treated. In certain embodiments, the system may include a recirculation line to deliver drain down liquid to an inlet of the filter module. In such embodiments, the source of the fresh feed may include filter module drain down liquid. The system may include a recirculation line to deliver filtrate to one or more sources of solution.

The system may be fluidly connectable to a post-treatment subsystem. In some embodiments, the filtrate of the water treatment system may be delivered to a post-treatment subsystem, for example, a reverse osmosis treatment unit, an ion exchange unit, or an electrodialysis unit.

The system may include components, such as pumps, tanks, dosing pumps, circulation pumps, and distribution manifolds which may be shared between the groups of filter membrane modules. The system may include a controller programmed to allocate shared components efficiently and minimize overall downtime. The system may simplify cleaning processes such that the components do not require allocation to an individual filter module for extended periods of time and reduce redundant membrane units.

The system may further comprise an aerator in fluid communication with each filter module. The aerator may be fluidly connectable to, for example, a source of a gas. The aerator may be configured to apply the gas to the membrane to dislodge solid foulants. In some embodiments, the source of the gas may include one or more of air, oxygen, gaseous chlorine, ozone, nitrogen, methane, or any other gas suitable for a particular application. The aerator may be a device as described in US Patent No. 9,573,824, incorporated herein by reference in its entirety for all purposes. The aerator may be a device for providing a pulsed fluid flow such that, in use, the fluid flow moves past the surfaces of the membrane. The aerator may be configured to provide a regular cyclic pulsed fluid flow. The aerator may be configured to provide a randomly generated pulsed fluid flow.

An exemplary embodiment of a system is shown in FIG. 7. System 1000 may include a plurality of filter modules arranged in parallel. The filter modules may be arranged into a first set of filter modules 1010 and a second set of filter modules 1020. System 1000 includes two sets of filter modules, but the system may include as many sets as necessary to reduce or eliminate overall system downtime. The system may include a source of a first backwashing solution 100 to perform the physical backwash. The system may include a source of a second backwashing solution 200 to perform the chemically enhanced backwash. The system may include a source of a neutralizing solution 300. The system may include pumps 110 and 120 configured to deliver the backwashing and neutralizing solutions to the filter modules.

System 1000 includes one pump associated with each set of filter modules. However, a single pump may be provided and fluid may be directed to each set of filter modules by one or more valves. The system may include an aerator 400 in fluid communication with each filter module. For simplicity, aerator 400 is shown in fluid communication with a single filter module, but the aerator may be in fluid communication with a set of filter modules or all filter modules. The system may include a plurality of aerators, as necessary. The system may further include sensor 600 configured to measure a parameter of the feed stream. The system may include sensor 650 configured to measure a parameter of the filter module. The system may include controller 500 operably connected to sensors 600 and 650. The membrane configurations disclosed herein may be part of a submerged tertiary water treatment system.

Methods of treating water disclosed herein may comprise introducing the water to be treated to the system as described herein. A cleaning cycle may be performed on a first group of filter modules while at least one second group of filter modules continues operation. After the cleaning cycle of the first group is completed, the filter modules may resume operation. The second group of filter modules may then be subjected to an analogous cleaning cycle while the first group of filter modules continues operation. The cleaning cycles may be configured to optimize performance of the system.

Optimized system performance may be associated with minimizing filter module downtime. Filter module downtime may be measured as an average daily downtime of each filter module. The cleaning cycles may be configured to reduce filter module downtime by reducing a frequency with which the longer maintenance wash is performed on each filter module. In certain embodiments, overall system downtime may be measured as the total amount of time in a day when the system is not treating water. Overall system downtime may be optimized by isolating a group of filter modules for the scheduled cleaning cycle. Another group of filter modules may continue operation, thus reducing or minimizing an amount of time that the system is not treating water. In some embodiments, system downtime may be eliminated by controlling performance of sets of filter modules. In other embodiments, system downtime may be reduced as compared to a system which performs daily

maintenance washes on each filter module.

Optimized system performance may be associated with delivering a constant filtrate stream to a downstream process. The filtrate may be delivered to a post-treatment unit which requires a constant feed stream. By minimizing downtime, the downstream post-treatment process may be enhanced. In some embodiments, the filtrate may be treated by reverse osmosis, ion exchange, or electrodialysis.

In some embodiments, at least some of the drain down fluid may be recirculated to an inlet of the system for treatment and to avoid the disposal of waste fluids. The system may be operated as a zero waste discharge system, such that all or substantially all of the drain down fluid is recirculated to an inlet of the system.

The system may be arranged such that equipment is shared among filter modules. Optimized system performance may be associated with minimizing a need for dedicated cleaning resources with respect to each filter module or each set of filter modules. A pump may be associated with a group of filter modules. By isolating cleaning procedures for each group of filter modules, performance by shared equipment may be optimized.

The system may be arranged such that equipment is shared among groups of filter modules. Optimized system performance may be associated with maximizing functionality of equipment intrinsic to each set of filter modules. For instance, pumps may be associated with more than one backwashing fluid. Valves may be installed to direct a selected fluid to a shared pump. Thus, footprint may be reduced by maximizing functionality of one or more system components.

Conventionally, longer maintenance washes are performed daily or every other day. By using the methods described herein maintenance washes may be performed at most every 2-5 days, such that each filter module may be subjected to a maintenance wash at most every 2-5 days. Physical backwashes may be performed between every 15-30 minutes. In some embodiments, physical backwashes may be performed between every 20-25 minutes.

Physical backwashes may last between 2-10 minutes. Every 5-10 backwashes may be chemically enhanced, as previously described. Chemically enhanced backwashes may last between 5-15 minutes. Each filter module may be subjected to between about 2 and about 15 chemically enhanced backwashes in a day. For example, each filter module may be subjected to between about 5 and about 12 chemically enhanced backwashes in a day.

A chemically enhanced backwash may be performed prior to and in association with a physical backwash. In general, a physical backwash may include backwashing a membrane with a feed solution. The membrane may be backwashed with filtrate. In some embodiments, the membrane may be backwashed with gas. The physical backwash may be followed by draining down the backwashing solution. The membrane may then be backwashed with a chemical cleaning solution in the drained down state. The chemical cleaning solution may be purged from the filter module to complete the chemically enhanced backwash.

In some embodiments, the membrane may be soaked in the chemical cleaning solution for a predetermined period of time. The filter module may be filled to between about 25% and about 75% capacity with the chemical solution for soaking. For instance, the filter module may be filled to about 25%, about 30%, about 35%, about 40%, about 45%, about 50%, about 55%, about 60%, about 65%, about 70%, or about 75% for soaking. The membrane may be soaked for between about 5 and 15 minutes before purging the chemical solution from the filter module. For instance, the membrane may be soaked for about 5 minutes, about 7 minutes, about 10 minutes, about 12 minutes, or about 15 minutes before purging. The predetermined period of time may be selected based on one or more of the concentration of contaminants or TSS in the feed water, the fouling on the membrane, and the type of membrane.

Purging may comprise rinsing the membrane. The membrane may be rinsed with new feed water. The membrane may be rinsed with fresh water. The membrane may be rinsed with filtrate. In some embodiments, the membranes may be rinsed by introducing the rinsing fluid through the permeate side. For instance, the membrane may be rinsed by backwashing. The membranes may be rinsed by introducing the rinsing fluid through the retentate side. For instance, the membrane may be rinsed by filling the filter module and soaking the membrane in rinsing fluid for a predetermined period of time.

Purging may include at least partially draining down the chemical cleaning solution. In some embodiments, purging may include draining down the filter module to remove all or substantially all the chemical cleaning solution. The filter module may be refilled with fresh feed prior to resuming operation.

Purging may include neutralizing the chemical cleaning solution. In certain embodiments, purging may include neutralizing the chemical solution without draining all or substantially all the chemical solution. In other embodiments, purging may include neutralizing remnants of the chemical solution after draining down all or substantially all the chemical solution. Neutralization may include introducing a neutralization chemical on a feed or filtrate side of the membrane. For instance, the neutralization chemical may be introduced by backwashing. The neutralization chemical may be introduced on a feed side and allowed to soak the membrane for a predetermined period of time.

In an exemplary embodiment, the wastewater may be municipal wastewater containing ammonia. The chemical cleaning solution may include free chlorine. Residual chlorine in the system is desirable for downstream treatment. After backwashing with the chemical cleaning solution, chloramine is formed. The backwashing fluid containing chloramine may be kept in the filter module, without draining or rinsing, for resumed filtration.

In some embodiments, the membrane may be aerated. For instance, purging may include aerating the membrane, as described in US Patent No. 9,573,824, incorporated by reference in its entirety for all purposes. Briefly, an intermittent or pulsed fluid flow may be provided along a membrane surface to remove dislodged fouling materials. The pulsed fluid flow may be cyclic, for example, cycling between on and off every 3 to 10 seconds. The cyclic pulsed fluid flow may have regular intervals, for example, 3 seconds on/3 seconds off,

5 seconds on/5 seconds off, or 10 seconds oh/10 seconds off. In other embodiments, the pulsed fluid flow may be randomly generated and/or irregular. The aeration fluid may include, for example, air, oxygen, gaseous chlorine, ozone, nitrogen, methane, or any other gas suitable for a particular application.

In one exemplary embodiment, the method may include aerating a filter module during a soak period of the chemical cleaning solution. For example, a cleaning agent including chlorine may be deactivated by oxygen. Thus, aeration may occur during a soaking period, prior to backwashing the membrane with the chemical cleaning solution.

The chemically enhanced backwash may include back-pulsing the cleaning solution into the membrane, as described in US 6,270,671, incorporated herein by reference in its entirety for all purposes. A back-pulse through a membrane may be used to clean the surface of the membrane and removed built up layers of precipitate from the wall of the membrane.

Back-pulsing may include a high pressure application of a fluid to a wall of a membrane. In some embodiments, back-pulsing may comprise applying pressurized air as the motive force. Either at predetermined intervals or on demand, a high pressure back-pulse may be applied to the outer surface of a membrane. The back-pulse may serve to dislodge any scale or caked-on precipitate that has formed a layer that is either too thick or too dense to provide optimal filtration results. Other methods of removing precipitate include, for example, increasing the rate of flow or decreasing the pressure differential across the membrane. Such methods may increase performance.

In accordance with certain embodiments, there is provided a method of facilitating cleaning of the filter modules. The method may include providing a controller, as previously described. The method may include operably connecting the controller to a pump configured to backwash the filter membrane with the feed stream. The method may additionally include operably connecting the controller to a pump configured to backwash the filter membrane with the chemical cleaning solution. In certain embodiments, the pumps may be a shared resource. Thus, the same pump may be configured to backwash the filter membrane with the feed stream and with the chemical cleaning solution. A valve may be provided upstream from the pump to selectively direct the backwashing solutions as required. The valve may additionally be operably connected to the controller. In some embodiments, the method may further comprise operably connecting the controller to a valve configured to drain the backwashing solutions from the filter module.

In some embodiments, the method may comprise providing a sensor, as previously described herein. The method may comprise installing the sensor to measure the desired parameter from one or more of the feed stream, the solution within the filter membrane, or the treated water exiting the filter membrane. The method may further comprise operably connecting the controller to the sensor to control an automated physical backwash, chemically enhanced backwash, maintenance wash, or full chemical cleaning operation, as previously described.

In accordance with certain embodiments, there is provided a method of retrofitting a water treatment system, as previously described. The method may include fluidly connecting a source of a backwashing solution to a pump configured to backwash the filter membrane. In some embodiments, the pump may be fluidly connected to a source of a feed stream. The pump may be fluidly connected to a source of a chemical cleaning solution. The pump may be fluidly connected to a source of a neutralizing agent. The method may further include operably connecting a controller to the pump, as previously described.

Methods may further include providing and/or installing a sensor, an aerator, a valve, or any additional pumps, as previously described herein.

The system may include a controller configured to perform one or more cleaning cycle on a set of filter modules. For instance, the controller may be configured to suspend operation of a set of filter modules while maintaining operation of an alternate set of filter modules. The controller may be configured to perform any one or more of backwash membranes, drain down solutions in membrane modules, purge filter modules, aerate membranes, introduce fresh feed into the filter module, introduce a neutralizing agent into the filter module, and soak the membrane for a period of time, as described in more detail herein. The controller may be configured to resume operation of the set of filter modules, for example, after completion of the cleaning cycle. The controller may additionally be configured to perform a cleaning cycle on an alternate set of filter modules subsequent to the cleaning cycle performed on the first set of filter modules. The cleaning cycles performed on different sets of filter modules may be analogous or may be different. The cleaning cycles performed by the controller may include physical backwashes, chemically enhanced backwashes, maintenance washes, and full chemical cleaning operations.

The system may include one or more pump, valve, or other component operably connected to the controller. In some embodiments, a pump may be operably connected to the controller and configured to deliver a selected backwashing fluid to each filter module. For instance, the pump may be configured to deliver fresh feed or a cleaning agent to the filter module, as operated by the controller. In certain embodiments, the pump may be configured to deliver a neutralizing solution to the filter module, as operated by the controller. The controller may be configured to operate the cleaning cycles to optimize performance of the system, as previously described. The system may operate by controlling one or more valve configured to fluidly connect a source of a solution to a common pump and/or to the filter module.

The system may further comprise a pressure sensor associated with the selected set of filter modules. The controller may be configured to initiate a cleaning operation responsive to measuring a backpressure or transmembrane pressure value that exceeds a threshold value or falls outside a stabilized range, as previously described. The threshold backpressure value may be selected based on the type of filter module. In general, the threshold backpressure value may be selected based on the type of membrane. The controller may be configured to suspend the cleaning operation responsive to the pressure sensor measuring a pressure value that is within tolerance of a target stabilized pressure value, as previously described herein. The tolerance may be, for example, within 10%, 9%, 8%, 7%, 6%, 5%, 4%, 3%, 2%, or 1% of the target backpressure value.

The system may include a pressure sensor associated with each set of filter modules. In such embodiments, the controller may be configured to perform the cleaning cycle on a given set of filter modules responsive to the measurement of the backpressure or transmembrane pressure value associated with the same set of filter modules. In alternate embodiments, the system may include a single pressure sensor associated with one or more set of filter modules configured to measure an average backpressure or transmembrane pressure for the system. In such embodiments, the controller may be configured to perform the cleaning cycle in series on one or more set of filter modules responsive to the

measurement of the backpressure or transmembrane pressure value of the overall system.

The system may further comprise a permeability sensor associated with the selected set of filter modules. The controller may be configured to initiate a cleaning operation responsive to measuring a permeability value that exceeds a threshold value or falls outside a stabilized range, as previously described. The threshold permeability value may be selected based on the type of filter module. In general, the threshold permeability value may be selected based on the type of membrane. The controller may be configured to suspend the cleaning operation responsive to the permeability sensor measuring a permeability value that is within tolerance of a target stabilized permeability value, as previously described herein. The tolerance may be, for example, within 10%, 9%, 8%, 7%, 6%, 5%, 4%, 3%, 2%, or 1% of the target permeability value.

The system may include a permeability sensor associated with each set of filter modules. In such embodiments, the controller may be configured to perform the cleaning cycle on a given set of filter modules responsive to the measurement of the permeability value associated with the same set of filter modules. In alternate embodiments, the system may include a single permeability sensor associated with one or more set of filter modules configured to measure an average permeability for the system. In such embodiments, the controller may be configured to perform the cleaning cycle in series on one or more set of filter modules responsive to the measurement of the permeability value of the overall system.

The system may further comprise a resistance sensor associated with the selected set of filter modules. The controller may be configured to initiate a cleaning operation responsive to measuring a resistance value that exceeds a threshold value or falls outside a stabilized range, as previously described. The threshold resistance value may be selected based on the type of filter module. In general, the threshold resistance value may be selected based on the type of membrane. The controller may be configured to suspend the cleaning operation responsive to the resistance sensor measuring a resistance value that is within tolerance of a target stabilized resistance value, as previously described herein. The tolerance may be, for example, within 10%, 9%, 8%, 7%, 6%, 5%, 4%, 3%, 2%, or 1% of the target resistance value.

The system may include a resistance sensor associated with each set of filter modules. In such embodiments, the controller may be configured to perform the cleaning cycle on a given set of filter modules responsive to the measurement of the resistance value associated with the same set of filter modules. In alternate embodiments, the system may include a single resistance sensor associated with one or more set of filter modules configured to measure an average resistance for the system. In such embodiments, the controller may be configured to perform the cleaning cycle in series on one or more set of filter modules responsive to the measurement of the resistance value of the overall system.

The system may additionally include one or more of a temperature sensor, a flow meter, a flux sensor, a feed turbidity sensor, and a sensor configured to measure

concentration of contaminants and/or TSS in the incoming feed water. The sensors may be operably connected to the controller. The controller may be configured to adjust treatment of the water based on one or more of these parameters.

Methods of treating water and/or methods of operating the one or more components of the systems disclosed herein are described in the following exemplary protocols.

Examples

The systems and methods described herein will be further illustrated through the following examples, which are illustrating in nature and are not intended to limit the scope of the disclosure.

Prophetic Example 1: Partly fill shell side of membrane with chemical cleaning solution

The chemical solution may be introduced through the shell side, for example, via the lower feed manifold. The solution may enter the shell side with all the shell outlet valves closed, i.e. in dead-end filtration mode, forcing the cleaning solution to the lumen side. If the pressure is not high enough to push the cleaning solution to the permeate side, additional transmembrane pressure may be supplied by injecting compressed gas, as in a pressure filtration process, or by suction, as in an immersed membrane filtration process. The shell side may be only partially filled with membrane cleaning solution. The minimum delivery volume of solution to the shell side may be slightly more than the lumen volume plus the permeate manifold volume. The consumption of chemical and filtrate of this method is significantly less than that of a conventional cleaning method where the shell side is filled with the chemical solution.

This method may include backwashing and then emptying both shell and lumen sides. Cleaning solution may enter the shell side via a lower CIP valve. If the shell side upper CIP return valve is closed and the lumen CIP return valve is opened, the CIP solution is forced by the shell side pressure to enter lumen side once the CIP solution level in the shell side is above the lower potting level. A compressed air pocket may also formed above shell side liquid level. Depending on the shell side pressure, the CIP pump may only run for short period of time, enabling the pressure from the air pocket to continue to press solution to lumen side. Additional transmembrane pressure may be supplied when necessary. Depending on the mixing of solution prior to entering the shell side, the filtration of membrane cleaning solution may just fill the lumen or be extended to send some solution back to the CIP tank or recirculation pipe loop. Alternatively, the CIP solution can be pushed into the shell side by compressed air eliminating a short running cycle of the CIP pump.

After the lumen side is filled up with the chemical solution, the shell side and lumen side vent valves may then be opened to equalize the pressure. After the lumen side pressure is close to the shell side pressure, the shell side vent valve may be opened while the lumen side vent valve can be either opened, closed, or opened periodically to control the diffusion process. When the lumen side vent valve is opened periodically, the valve may be opened briefly during the initial stage of soaking. During the whole soaking period, the lumen side can be vented for 1-10 times, with each time lasting from ls to 10 mins. The solution in the lumen side may slowly diffuse through the membrane. The diffusion process may be aided by static pressure in the lumen side when lumen side vent valve is opened. The membrane may be partially soaked in the solution, and capillary effect may help to hold solution within the membrane wall.

An optional post-aeration may also be applied. This aeration may help to suspend foulants loosened or removed by solution.

The above fill-lumen and back-diffusion procedure can be repeated when necessary to achieve a higher cleaning efficiency.

An optional post membrane cleaning backwash may also be used after the soak. A full backwash may be undertaken, at the end when the shell side chemical waste is fully discharged. In some embodiments, chemical cleaning solution drained from shell side can be reused by draining to a CIP tank.

Filtration may then be resumed. The methods disclosed herein may significantly reduce the chemical and chemical waste volume, typically by more than 50%. The repeated lumen-fill and back-diffusion procedures help to enhance the cleaning efficiency without additional chemical. FIG. 1 shows a method with both the shell side and the lumen empty. The shell side is partially filled with cleaning solution and then pressurized so that the liquid passes into the lumen.

Prophetic Example 2: Fill permeate side of membrane with chemical solution while shell side at least partially drained/filtered down

Chemical cleaning solution may be delivered to fill the membrane lumen (permeate side) and therefore the chemical and filtrate consumption may be reduced.

As an initial step, the membrane may be backwashed via a method described above. This leaves the lumen side empty and the shell side either empty or partially empty. The membrane lumen side may then be ready for receiving the chemical cleaning solution. In case the membrane lumen side is not empty through backwashing, the chemical solution has to be delivered under pressure to displace permeate remained in the membrane lumen.

The lumen may then be filled with a chemical cleaning solution. The chemical dosing pump or the CIP pump may be used to introduce the membrane cleaning solution to the lumen side, for example, via lower filtrate/CIP valves. Any extra solution can exit the lumen side via upper filtrate/CIP valves returning to the CIP tank. During the chemical delivery, shell side upper CIP valve may be either opened or closed. When the lumens are filled with chemical solution, the shell side vent valve may be opened and the lumen side vent valve may be either opened, closed, or opened periodically. When the lumen side vent valve is opened periodically, the valve may be opened briefly during the initial stage of soaking. During the whole soaking period, lumen side can be vented for 1 - 10 times and each time last from 5s to 10 mins. Chemical diffusion may occur until the chemical concentration at lumen and shell sides are equalized.

While the shell side is empty or partially empty, part of the solution in the lumen side may slowly diffuse through the membrane pores, for example, aided by static pressure in the lumen side when lumen side vent valve is opened. During this process, both shell side and lumen side may be partially empty. The capillary effect may help to hold solution within membrane wall. The process of soaking and diffusion may be carried out for a predetermined time, until the membrane is as clean as desired, or until most of the cleaning solution is consumed. The lumen fill procedure with chemical cleaning solution may be repeated when necessary after the solution in the lumen side is diffused to shell side and consumed.

Alternatively solution diffused into shell side can be pushed back to lumen side by applying compressed air to the shell side. This method may be repeated if necessary.

FIG. 2 shows a method in which solution is introduced to lumen side while shell side is fully or partially drained.

Prophetic Example 3: Fill permeate side of membrane with chemical solution and shell side not drained

This method is similar to the one described in prophetic example 2, with the exception that the shell side may not be filtered down. If the solid containing water remains on the shell side (tank not drained as shown in FIG. 3), the chemical solution may diffuse through membrane pores to the shell side under concentration gradient. The diffusion rate may be comparatively uniform along the membrane module. The diffusion process may continue until the chemical concentration on both sides reaches equilibrium.

The lumen fill procedure with chemical cleaning solution may be repeated when necessary after the chemical concentration in the lumen side is reduced to certain level. An optional post-aeration may also be used. This aeration may help to suspend foulants loosened or removed by solution.

An optional post membrane cleaning backwash may also be used after the soak. A full backwash may be performed after discharge of the chemical waste.

Filtration may then be resumed.

FIG. 3 shows a schematic illustration of this method. The lumen may be filled with water or other fluid and the cleaning solution introduced into the lumen. The cleaning species may diffuse through the membrane from a region of higher concentration in the lumen to a region of lower concentration in the shell side.

FIGS. 1-3 show a schematic diagram of the piping and instrumentation employed for the various methods.

In the figures, Pl is the feed pump and P2 is the CIP pump. P2 can be substituted by a small solution storage vessel with compressed air inlet on top of the vessel. SV1 is a pump which supplies scouring air if aeration is required. SV2 is a pump which supplies compressed drain down air to assist fast drain down at shell side or filtering down. SV3 is a pump which supplies compressed liquid backwash air to push filtrate in the lumen through membrane pores in a reverse direction to the filtration direction. AV1 is the lower feed valve and AV2 is upper feed valve. AV4 is the lower shell side drain valve and A V5 is the upper shell side return valve.

In the method shown in FIG. 1, the cleaning solution may be delivered to the shell side. The shell side may be partly filled with Chemical Solution and the solution may be allowed to penetrate to the permeate side under TMP.

In the exemplary embodiment, when the CIP pump starts to deliver the cleaning solution to the shell side, AV7 and AV3 are opened while AV5 is closed. The pressure on the shell side increases slowly, and some chemical solution penetrates to the lumen side under pressure. The chemical delivery stops when the solution level on the shell side reaches between the lower potted head and mid of the module, or membrane lumen is filled up with chemical solution. If the pressure on the shell side is not high enough to push the solution to the lumen side, compressed air can be injected to the shell side via SV2. After soaking for a predetermined period of time, a backwash can be performed to push the remaining chemical solution on the permeate side back to the shell side. It is preferred that compressed air is introduced through SV3 to push the remaining solution in the lumen back to the shell side.

In the methods of prophetic examples 2 and 3, the cleaning agent is dosed to the lumen side. During the dosing stage, AV9 and AV3 are both opened, and AV5 on the shell side outlet can be either opened or closed (FIGS. 2 and 3). The chemical delivery stops after the permeate side is filled up with the solution. The chemical solution then penetrates through the membrane pores. In the method of prophetic example 2, the penetration goes on by liquid static pressure and the chemical solution diffuses back to the shell side. The diffusion is only driven by the concentration gradient as the shell side is full (FIG. 3). Again a backwash may be performed after a period of diffusion. Prophetic Example 4: Chemically enhanced backwash with aeration

A method as described above may be performed to physically backwash the membrane. The backwash fluid may be drained down. An empty tank liquid backwash may be performed for an extended period of time with the chemical solution pulsed in the backwash stream. The tank may be filled up to 25% during the chemical backwash. The tank may then be refilled with feed. The membrane may be aerated. The chemical solution may be drained down and neutralized. The membrane may be rinsed. Filtration may then be resumed. Prophetic Example 5: Chemically enhanced backwash without aeration

A method as described above may be performed to physically backwash the membrane. The backwash fluid may be drained down. An empty tank liquid backwash may be performed for an extended period of time with the chemical solution pulsed in the backwash stream. The tank may be filled up to 25% during the chemical backwash. The chemical solution may be drained down and neutralized. The membrane may be rinsed.

Filtration may then be resumed.

Prophetic Example 6: One- third tank soak with chemical cleaning solution

A method as described above may be performed to physically backwash the membrane. The backwash fluid may be drained down. A chlorine-containing chemical cleaning solution may be slowly introduced backwards through the fibers into the empty tank. The tank may be filled up to 33%-34% during the chemical backwash. The chemical cleaning solution may be allowed to soak for a period of time. The chemical solution may be drained down. Optionally, the membrane may be flushed with liquid backwash during the drain. Filtration may then be resumed.

The method of prophetic example 6 may be performed for treatment of wastewater filtration systems in which the cleaning chemical is free chlorine and the wastewater contains an ammonia residual. In such cases, the ammonia will generally combine with free chlorine from the cleaned cell. The need for extensive rinsing of the cell after the chemically enhanced backwash will typically be avoided. Free chlorine being carried downstream in the filtrate as chloramine will form from the combination of ammonia and fee chlorine.

Example 1: Efficiency of a maintenance wash

A six-module Memcor® CMF-L pilot system (Evoqua Water Technologies,

Pittsburgh, PA) was used for comparative testing. A 30 minute filtration was followed by a gas pushed physical backwash without a chemical agent. The recycle was repeated several times before a maintenance wash was carried out.

As shown in FIG. 4, the membrane fouling rate is determined by an increase in the membrane resistance. After filtering for 30 minutes, the membrane resistance increased. The physical backwash can partially reduce the membrane resistance. However, the physical backwash did not fully recover the membrane's permeability and the trend of resistance continued to rise. A maintenance wash was performed to further reduce the membrane's resistance and better recover the membrane's permeability. A general trend is depicted in the graph of FIG. 4.

The efficiency of a maintenance wash is defined as:

MC Efficiency (Ri -R₂)/(RI-RO)

Where: Ro is Resistance straight after the last full chemical clean;

Ri is Resistance straight after the last physical backwash before maintenance wash; and

R₂ is Resistance after the previous maintenance wash

FIG. 5 shows the maintenance wash efficiency with different methods, where:

MCO is a conventional cleaning method with shell side fully filled of cleaning solution;

MC1 is the method of prophetic example 1 described above, where the shell side is partially filled of cleaning solution;

MC2 is the method of prophetic example 2 described above, where the shell side is drained and the cleaning solution fills the permeate side; and

MC3 is the method of prophetic example 3 described above, where there is no shell side drain and the cleaning solution fills the permeate side.

FIG. 6 illustrates the relative chemical solution consumption compared to the conventional method. Example 2: Performance after a chemically enhanced backwash

Chemically enhanced backwash was performed at a wastewater treatment pilot plant. The pilot plant was scheduled to perform a physical backwash every 22 minutes. The chemically enhanced backwashes were performed by the method as described in prophetic example 4.

In a first test run, a chemical backwash with 100 ppm sodium hypochlorite solution was performed on every 6^th physical backwash. The chemically enhanced backwash was performed between about 10-11 times in a 24 hour period. The chemically enhanced backwash was performed about every 2.2 hours. The maintenance wash was performed about once every four days.

During the course of treatment, the transmembrane pressure ranged from about 2 psi to about 14 psi. The permeability (normalized to 20 °C) was below 12 gfd/psi. A spike in feed turbidity was believed to have caused increase in transmembrane pressure and permeability.

In a second test run, a chemical backwash with 250 ppm sodium hypochlorite solution was performed on every 8^th physical backwash. The protocols result in about the same cost for the chemical solution. The chemically enhanced backwash was performed between about 8-9 times in a 24 hour period. The chemically enhanced backwash was performed about every 2.9 hours. The maintenance wash was performed about once every four days.

During the course of treatment, the transmembrane pressure ranged from about 1 psi to about 6 psi. the permeability (normalized to 20 °C) was below 14 gfd/psi.

FIG. 8A shows measurements for transmembrane pressure, resistance, flux, and temperature for a 24 hour period of the second test run immediately following a maintenance wash. FIG. 8B shows permeability and permeability normalized to 20 °C for the same 24 hours period as FIG. 8 A. As shown in FIGS. 8A-8B, each of transmembrane pressure, resistance, and permeability can be stabilized for 24 hours with periodic chemically enhanced backwashes. The stabilization of these parameters means a maintenance wash is not needed after 24 hours. In a conventional treatment, transmembrane pressure, permeability, and resistance would increase within 24 hours, requiring a maintenance wash.

Accordingly, the methods of chemically enhanced backwashing described herein may stabilize the membrane and reduce the frequency of maintenance washes.

Claims

1. A method of treating water, comprising:

introducing water to a system comprising a plurality of filter modules arranged in parallel for treatment;

performing a first cleaning cycle on a first set of the plurality of filter modules, the first cleaning cycle comprising:

suspending operation of the first set of filter modules while maintaining operation of a second set of filter modules;

backwashing membranes of the first set of filter modules with a first solution; draining down the first solution from the first set of filter modules;

backwashing the membranes of the first set of filter modules with a second solution comprising a cleaning agent in the drained down state;

purging the second solution from the membranes of the first set of filter modules; and

resuming operation of the first set of filter modules; and

performing a second cleaning cycle on the second set of filter modules subsequent to the first cleaning cycle, the second cleaning cycle being analogous to the first cleaning cycle.

2. The method of claim 1, wherein the first cleaning cycle further comprises soaking the membranes in the second solution for a predetermined period of time prior to purging.

3. The method of claim 1, wherein purging comprises rinsing the membranes.

4. The method of claim 3, wherein the membranes are rinsed with filtrate.

5. The method of claim 3, wherein the membranes are rinsed via backwash.

6. The method of claim 1, wherein purging comprises neutralizing the second solution in place.

7. The method of claim 6, wherein a neutralization chemical is introduced on a feed or filtrate side of the membranes.

8. The method of claim 1, wherein purging further comprises at least partially draining down the first set of filter modules and refilling the first set of filter modules prior to resuming their operation.

9. The method of claim 1, wherein about 25% of the tank is filled with the second solution during backwashing.

10. The method of claim 1, wherein purging further comprises aerating the membranes.

11. The method of claim 1, wherein the cleaning agent is pulsed into the second solution.

12. The method of claim 1, wherein the cleaning agent comprises chlorine.

13. The method of claim 1, wherein the first solution comprises filtrate or gas.

14. The method of claim 1, wherein the first and second cleaning cycles are configured to optimize performance of the system and optimized system performance pertains to at least one of: minimizing overall system downtime, minimizing a need for dedicated cleaning resources with respect to each set of filter modules, and maximizing functionality of equipment intrinsic to each set of filter modules.

15. The method of claim 1, wherein the first cleaning cycle is performed between about 5 and 12 times in a 24 hour period.

16. The method of claim 1, further comprising measuring a backpressure value associated with the first set of filter modules and initiating the first cleaning cycle responsive to measuring a backpressure value that exceeds a threshold backpressure value.

17. A water treatment system, comprising:

a plurality of filter modules arranged in parallel, each filter module comprising a plurality of membranes;

a source of a first backwashing solution fluidly connected to each filter module; a source of a second backwashing solution comprising a cleaning agent fluidly connected to each filter module; and a controller configured to:

perform a first cleaning cycle on a first set of the plurality of filter modules, the first cleaning cycle comprising:

suspending operation of the first set of filter modules while

maintaining operation of the remaining filter modules;

backwashing membranes of the first set of filter modules with the first backwashing solution;

draining down the first backwashing solution from the first set of filter modules;

backwashing the membranes of the first set of filter modules with the second backwashing solution in the drained down state;

purging the second backwashing solution from the membranes of the first set of filter modules; and

resuming operation of the first set of filter modules; and

perform a second cleaning cycle on a second set of the plurality of filter modules subsequent to the first cleaning cycle, the second cleaning cycle being analogous to the first cleaning cycle.

18. The system of claim 17, further comprising a pump operably connected to the controller and configured to deliver the first backwashing solution or the second backwashing solution to each filter module.

19. The system of claim 17, further comprising a source of a neutralizing solution fluidly connected to each filter module.

20. The system of claim 17, wherein the membranes are hollow fiber membranes.

21. The system of claim 17, wherein the membranes are microfiltration or ultrafiltration membranes.

22. The system of claim 17, wherein the first or second set of filter modules are mounted in a single tank or on a single skid.

23. The system of claim 17, wherein the first set of filter modules share at least one of a common intake pump, tank, dosing pump, circulation pump, or distribution manifold.

24. The system of claim 17, wherein the water treatment system is a submerged tertiary filtration system.

25. The system of claim 17, further comprising an aerator in fluid communication with each filter module.

26. The system of claim 17, further comprising a pressure sensor associated with the first set of filter modules, wherein the controller is configured to initiate the first cleaning cycle responsive to measuring a backpressure value that exceeds a threshold backpressure value.

27. A method of facilitating cleaning of a plurality of filter modules arranged in parallel, each filter module including a filter membrane, the method comprising:

providing a controller configured to:

suspending operation of the first set of filter modules while maintaining operation of the remaining filter modules;

backwashing membranes of the first set of filter modules with a first backwashing solution;

backwashing the membranes of the first set of filter modules with a second backwashing solution in the drained down state;

resuming operation of the first set of filter modules; and

perform a second cleaning cycle on a second set of the plurality of filter modules subsequent to the first cleaning cycle, the second cleaning cycle being analogous to the first cleaning cycle;

operably connecting the controller to a first pump configured to introduce the first backwashing solution into the plurality of filter modules; operably connecting the controller to a valve configured to drain the first backwashing solution and the second backwashing solution from the plurality of filter modules; and

operably connecting the controller to a second pump configured to introduce the second backwashing solution into the plurality of filter modules.

28. The method of claim 27, further comprising providing a pressure sensor and installing the pressure sensor to measure backpressure associated with at least one filter membrane of the plurality of filter modules.

29. The method of claim 28, further comprising operably connecting the controller to the pressure sensor, the controller being programmed to control an automated cleaning cycle responsive the pressure sensor measuring a backpressure value which is outside tolerance of a target backpressure value range.

30. A method of retrofitting a system comprising a plurality of filter modules arranged in parallel, each filter module having a filter membrane, an inlet, and an outlet, the method comprising:

fluidly connecting a source of a first backwashing solution to a pump configured to deliver the first backwashing solution to a first set of the plurality of filter modules;

fluidly connecting a source of a second backwashing solution to the pump; and operably connecting a controller to the pump, the controller configured to:

perform a first cleaning cycle on the first set of the plurality of filter modules, the first cleaning cycle comprising:

suspending operation of the first set of filter modules while

maintaining operation of the remaining filter modules;

resuming operation of the first set of filter modules; and perform a second cleaning cycle on a second set of the plurality of filter modules subsequent to the first cleaning cycle, the second cleaning cycle being analogous to the first cleaning cycle.

31. The method of claim 30, further comprising fluidly connecting a source of a neutralizing solution to the pump.