WO2020144711A1

WO2020144711A1 - A process for the treatment of sewage

Info

Publication number: WO2020144711A1
Application number: PCT/IN2020/050023
Authority: WO
Inventors: Harshvardhan MODAK
Original assignee: Modak Harshvardhan
Priority date: 2019-01-10
Filing date: 2020-01-09
Publication date: 2020-07-16

Abstract

The present invention discloses a process for treatment of sewage employing membrane technology, which brings about recovery of reuse quality water to almost about 90% of original volume with least energy consumption as compared to that needed for traditional STP using aeration. It does not generate any sludge & occupies considerably less space per m3 of sewage. It can be easily installed in existing sewage treatment plants to accommodate incremental quantity of sewage. It gives an additional benefit of leaving behind a concentrated reject, which can be subjected to anaerobic digestion to recover biogas. The plate and frame configuration and the reverse osmosis technique is found to be giving the most preferred process characteristics. Thus applications of membrane technology helps to make available a significant quantity of clear colorless water suitable for reuse & concentrated sewage for recovery of biogas & electricity.

Description

Title:

A process for the treatment of sewage

Field of Invention

The present invention generally relates to a process for the treatment of sewage. More particularly the present invention relates to a process for the treatment of sewage which does not produce any sludge and eliminating the need for sludge disposal. Even more particularly, the present invention relates to application of membrane to split the sewage in two streams one, more than 70% of the original sewage volume as recovered & reuse quality water &another about 30% of original sewage volume as concentrated sewage.

Background of Invention:

Urban habitations like cities, towns, condominiums, townships etc. are populated by human beings & animals. The individuals living in the household for their own cleanliness & sanitation within households use water for flowing out their bath water, wash water, excreta etc. & together produce an effluent called sewage. Such sewage contains dissolved organic & inorganic substances, giving rise dissolved & un-dissolved pollutants, characterized by BOD, COD,TSS& TDS values. This sewage is taken away in pipelines to treatment units called Sewage Treatment Plants (STP), wherein it undergoes very many physico-chemical processes to destroy the above said pollutants to make the water as per prescribed environmental standards. Due to complexity of these processes & large electrical energy consumption, it becomes costly to treat the sewage. The burgeoning cost of electrical energy, other treatment & manpower cost, combined with its operational complexity is day by day making operations of STP a difficult proposition. The sewage does not get adequately treated in STPs& either the partially treated or untreated sewage is discharged in water bodies like rivers, ponds, lakes, streams or ground water to further pollute the water bodies which are potential sources of water. Pollution of such kind gives rise to diseases & health problems among population nearby the water bodies. The volumes of sewage created by population is millions of liters & the sheer large volume makes it more difficult to treat the sewage.

In addition, the STP operation brings about generation of large quantities of sludge, which is very difficult to dispose off. The aeration of sewage gives rise to growth of bacterial colonies, some of which die during the operations & have to be separated by clarification operations. The extended aeration again creates similar sludge. The same gives rise to a sludge, which is ridden with pathogenic bacteria. The sludge has to be left for a long time in sludge drying beds to remove water in it. The disposal of this sludge is a complex activity and is a problem faced worldwide.

However the sludge drying beds & all the other operating units together, create a very large footprint & occupies huge amount of land. Since the STPs have to be located in urban areas, where land is very costly, occupation of large parcels of land by STPs diminishes land availability for urban development. If the land is not available for expansion of existing or building new STPs, then it needs to be procured at large cost. Overall the entire traditional STP occupies huge quantity of land/m3 of input sewage. The traditional STP, once established at a location, cannot accommodate any extra quantity of sewage, over & above the designated capacity of that STP. Non-availability of adequate land prevents expansion of existing STPs & sewage needs to be released as it is into rivers.

The recovery of reuse grade water after traditional method of STP requires application of membrane system. The current state of art for sewage treatment uses membrane system for recovery of reuse grade water in sewage treatment, either within the aeration zone or after the aeration zone, which has deficiencies of its own.

Hence there is a need of a process for sewage treatment in order to make STP operations simpler, occupying less space or making it possible to use within existing STPs & also making it one-step process, a Membrane Technology is used without any aeration step (using RO or NF membranes). The application of membranes at this stage, splits the sewage into two streams. Viz. more than 70% of the original sewage volume as recovered & reuse quality water & about 30% of original sewage volume as concentrated sewage, containing most of the dissolved & un-dissolved, suspended matter. The reuse quality water can be then either mixed with incoming raw water in a Water Treatment Plant (WTP) to further purify it or directly use as such, depending on end use &application. The second stream of concentrated sewage can be digested in anaerobic reactor to produce biogas, which is a source of energy. The slurry after digestion is a good fertilizer. This is an instantaneous process and the quality of recovered water complies with environmental standards.

Objects of the Invention:

The primary object of the present invention is to provide a process for the sewage treatment to recover more than 70% of the original volume of sewage directly as reusable water, without any aeration, creation of sludge & occupying large land parcel OR also to upgrade existing STP to accommodate incremental quantity of sewage at that location, without further treatment.

Another object of the present invention is to provide a process for the sewage treatment for extracting large portion of reuse quality water (more than 70% of the original volume of sewage), which is colourless & has BOD<10, COD< 50 & TDS <100 & without pathogen contamination. Yet another object of the present invention is to provide a process for the sewage treatment for producing a concentrate sewage stream as the reject suitable for generation of biogas by anaerobic digestion.

Summary of the Invention

Accordingly the process of the present invention employs the membrane technology comprising of four techniques viz. Reverse osmosis (RO), Nano- fdtration (NF), Ultra-filtration (UF) & Microfiltration (MF). The membranes themselves have different materials of constructions. In addition, the methods in membrane technology can be carried out using three different types of configurations, viz. Spiral wound, Hollow Fiber & Plate & Frame. The results in terms of volume proportions & characteristics of the two streams produced on application of membrane technology to sewage vary depending on type of membrane technology, material of construction of the membrane & the internal configuration of construction of membrane system.

The present invention employs the membrane technology to the sewage to split into two streams viz. Permeate & Reject.

The technique of Microfiltration (MF) &Ultra-filtration (UF) were not very useful for producing permeate water of desired reusable quality. MF only cut off the suspended solids, whereas UF only cut off suspended solids as well as limited portion of dissolved substances.

Permeate obtained using nano-filtration (NF) was colorless water. Permeate obtained using RO was also colorless& had maximum cut off of the original characteristics (TDS, COD, BOD & TSS) of the starting sewage. Both these permeates can pass the minimum standards prescribed by pollution board for discharge into water bodies or reuse. The application of membrane technology, which produced a reject, brought about reduction in the volume of the original sewage, with concomitant concentration of the dissolved contents.

The membrane technology can reduce such volume only at the expense of pumping energy(electrical), which is less compared to the energy required for aeration of sewage to bring about identical reduction in characteristics of COD, BOD & TDS. The reject after processing through membranes (NF & RO) are verified for anaerobic digestion & are found to give good results in terms of biogas generation.

The residue after anaerobic digestion was found to be a good fertilizer. The Total Suspended Solids (TSS) in such sewage under study produced choking & fouling of the membranes resulting into reduction in and stoppage of flow rate of permeate & reject. However, the Plate & Frame configuration modules gave the best results in terms of continuity of flow rate & its revival after back flushing or chemical cleaning.

Detailed description of the invention:

Process of Application of Membrane Technology to sewage

The sewage under study was first pre-filtered to remove any large size floating matter. Taking the sewage in a reservoir. Then pumping the sewage through a sand-filter suitable to reject any suspended particle of more than lOOmicron size. Pumping the output again through a cartridge filter suitable to reject any suspended particle of more than ten micron size. Pumping the said sewage into the membrane module by using a centrifugal pump. The sewage needs to be suitably pre treated with the help of sand filter and cartridge filter before pushing it into the membrane module. Increasing the pressure of the said effluent & monitoring and controlling the pressure using combination of valves, a high pressure reciprocating pump, a pulsation dampner & pressure gauges, which forms a part of membrane system.

Pumping the above effluent into the membrane module containing the membranes, having two tubes to carry the streams of reject andpermeate. Controlling the pressure controlled the flow into the membranes.

Conserving the total volume of the system and operating in recycle mode i.e. the reject & permeate streams were put back into the original reservoir. Whenever needed, the sample is withdrawn from the relevant tube for analysis. Further measuring the volume collected by timing a stopwatch enabled the monitoring of the flows.

In one embodiment of the present invention, sewage was subjected to each type of three different configurations containing the RO Membranes, viz. Spiral wound, hollow fiber & plate & frame. The resultant samples were analyzed for TDS & COD. The volume percentage of each stream to the original was also verified. In one embodiment of the present invention, sewage was subjected each type of the four types of membrane technology, viz. RO, NF, UF & MF. The resultant samples were analyzed for TDS & COD. The volume percentage of each stream to the original was also verified.

Example 1:

(TDS & COD values in ppm)

Example 2:

Taken Only for Plate & Frame Type:

Experimental Details

The set up consisted of a barrel with bottom discharge port for storage of pre filtered raw untreated sewage (obtained from local municipal sewage treatment plant); a valve connected to the bottom of the barrel reservoir with an extended pipe for connection to the pump; heavy duty flexible rubber hose connected to the input of a centrifugal pump; output of pump connected to a suitable screw valve to regulate pressure of the pump, output of the regulator valve connected to a single module of membranes of suitable type; all the connections by using suitable flexible rubber hose with screw clips to fasten the hose properly; two output ports of the membrane modules are again connected by flexible rubber hoses with screw clips for proper connection, both the rubber hoses connecting membrane module ports are put back into the same barrel reservoir. The sampling of the output streams is done by intermittently lifting them & collecting the liquid sample into a beaker & sent for testing. The sample collected needs to be sufficient for checking, appearance, TDS & COD. The sample is checked for volumetric flow per minute by using a stop watch. The volume collected is checked &measured with respect to time on stop watch to estimate the volumetric quantity recovered for the set of operating parameters to further estimate percentage recovery of the particular stream i.e. either permeate or reject. During the whole experiment the system is in re -circulating mode i.e. both the permeate & reject streams are sent back to the same reservoir, such that the original volume in the same is maintained both in terms of quantity & quality. This is called experimental mode & is maintained only for experimental set up. (The set up can be in user mode, wherein the reject & permeate are collected separately. However the volume of the filtered sewage needs to be constantly replenished to maintain the continuous flow.) The same experimental set up is used for various type of membranes (viz. microfiltration, ultra-filtration, nano-filtration & reverse osmosis). The membrane modules mentioned earlier, contained the different membranes described in the last sentence. The various readings recorded for each type of membrane mentioned earlier, are compiled in Table 1, given below. In conclusion of these experiments, it was inferred that in regard to the substrate under investigation i.e. pre-filtered raw untreated sewage, if processed by reverse osmosis or nano-filtration membrane, can yield clear recycle grade purer water at more than 70% of the original sewage volume & the balance being concentrated sewage of about 30% of the original sewage volume. On analyzing the COD contents of the concentrated stream, which is about 30% of the original volume of sewage, it was inferred that the COD values exceeded lOOOppm. On account of these high values of COD, it could be inferred that the material can be used for anaerobic digestion to produce biogas. (It is well known that lower COD values do not sustain anaerobic digestion to produce biogas.)

Table 1: Results of processing of pre-filtered untreated raw sewage by membranes.

The results in Table 1 are average outcome of number of runs. The parameters were chosen for quicker analysis to facilitate quicker verification of the quality of permeate & reject streams. Apart from these parameters, the permeate samples from nano-filtration & Reverse Osmosis were also given to check for microbiological contamination as shown by results in Table 2, wherein the microbiological contamination was checked only for Reverse Osmosis. Even after keeping the permeate for few hours, the level of water purity did not greatly alter.

Table 2: Microbiological Status of Sewage Processing ICFU: Colony Forming Unit)

There was no detectable contamination. (This was expected, since the output water from membranes is known to cut off any microbiological contamination to make it sterile.) Reusability of water recovered from Membranes

The quality of permeate water was assessed for its reusability. For the sake of comparison, the Indian standard for potable water (IS 10500 2012

[http://cgwb.gov.in/Documents/WQ-standards.pdf]) were referred, which indicate them to be as follows: TDS <500, Color: Clear transparent & COD <50ppm. The FAO standard for irrigation (http ://w ww . fao . org/3/T0234E/T0234E01 .htm ) indicates that TDS<2000 is suitable for irrigation. The standards for sewage treatment prescribed by Indian Central Pollution Control Board (Ref; https://kspcb.gov.in/Notification_05122015_4976.pdf) for COD are<50ppm. Thus on review of these various standards, we can infer that the product water recovered from membrane processing of pre-filtered untreated raw sewage can be used various non-potable purpose like irrigation. Irrigation water is in short supply at many places all over world. The sewage treatment in a treatment plant has to be done by carefully maintaining a treatment protocol. If not done so the sewage may remain untreated or undertreated. However the untreated or under treated sewage discharged outside cannot be used for irrigation. Thus it is better, instead of leaving the sewage treatment to the personal skills of operators, it is better to be processed by membranes to recover major quantity of sewage as reuse quality water. Membrane process does not require elaborate treatment protocol. Once the sewage is pumped through membranes, the processing automatically happens to recover major quantity of reuse quality water & concentrated reject. (The reject , which contains COD of more than 1500ppm, can sustain anaerobic digestion. (Ref: p. 987, Metcalf & Eddy [2004]) after anaerobic digestion yields biogas for energy generation & fertilizer.) The Central Pollution Control Board, India has published the discharge standards for treated sewage, which is given in Table 3 below. It is available at

(http://wvvw.cpchenvis.nic.in/envis newsletter/ENVIS%20Newsletter%20Jan%20 -%20Apr%202015.pdf) .This will indicate that the values of sewage processed by membranes compares very well with the standards prescribed by Central Pollution Control Board of India.

Time taken for membrane processing

Whereas the traditional processing of sewage requires considerable residence time to undergo treatment for primary aeration, primary clarifier, extended aeration & secondary clarifier followed by tertiary treatment for passing through activated carbon & chlorination etc.; the membrane processing is instantaneous. In other words, as soon as pre-filtered, raw untreated sewage passes through membranes, it is instantaneously split into two streams, viz. permeate (i.e. recycle grade water) & reject, which is concentrated sewage, suitable for anaerobic digestion to produce biogas & fertilizer. Thus membrane based processing saves considerable amount of time for any given quantity of pre -filtered untreated raw sewage.

Functions controlled by Microprocessor

The membrane unit can be run in both manual as well as microprocessor controlled format. The parameters to be controlled manually consist of monitoring of input flow & pressure, measuring conductivity of the permeate output, measuring flow of the permeate, periodic stoppage of the membrane process& switching over to washing cycle of the membranes, restarting of membrane processes after certain period of washing, switching over to weekly cleaning of membranes by special cleaners, washing of the membranes after cleaning by special cleaners is over, constant monitoring of the flow & stopping the unit if proper flow is not obtained due to blockage or any other fault etc. All these monitoring & controls can be automated by incorporating microprocessors. A programmable logic can be fed to the microprocessor such that all the above parameters are effortlessly controlled & operated by the same. Thus it is more convenient to incorporate microprocessor. However, if there are constraints for expenditure then the manual mode can be adopted.

Brief Description of drawings:

Figure 1 explains the schematic drawing of the sewage treatment according to the present invention.

Detailed description of the drawings:

Figure 1 further explains the sewage is pre-filtered to remove any large size floating matter. Taking the sewage in a sewage reservoir (1) . Then pumping the sewage through a sand-filter (6) suitable to reject any suspended particle of more than lOOmicron size. Pumping the output again through a cartridge filter (9) suitable to reject any suspended particle of more than ten micron size. Pumping the said sewage into the membrane module (13) by using a centrifugal pump. The sewage needs to be suitably pre treated with the help of sand filter and cartridge filter before pushing it into the membrane module (13).

Increasing the pressure of the said effluent & monitoring and controlling the pressure using combination of valves, a high pressure pump (10), a pulsation dampner (11) & pressure gauges, which forms a part of membrane system.

Pumping the above effluent into the membrane module (13) containing the membranes, having two tubes to carry the streams of concentrated sewage (15) and permeate (14). Controlling the pressure controlled the flow into the membranes. Conserving the total volume of the system and operating in recycle mode i.e. the reject & permeate streams were put back into the original reservoir. Whenever needed, the sample is withdrawn from the relevant tube for analysis. Further measuring the volume collected by timing a stopwatch enabled the monitoring of the flows. Following Table No. 3 describes the legends used in the drawings and their description

Definitions:

Permeate: One of the output streams of membrane unit, which in this case is purified sewage.

Reject: Other output stream of the membrane unit, into which all the cut off impurities are carried.

Sewage: The effluent from domestic units, arising out of cleaning, washing, bathing, sanitary functions of humans.

Sludge: The residue arising at 2 stages in sewage treatment unit, first at primary clarifier, which removes all the suspended solids & second at secondary clarifier, which removes all the dead excess bacteria in activated sludge process.

Membrane: A semi-permeable sheath of a thin pliable sheet of material forming a barrier or lining. The pore size of the same decides the type of membrane. The pore size is very small of just few Angstrom units.

Set desired parameters: The set desired parameters in the context of the present invention are pressure of the pump and flow of the incoming sewage

Advantages:

• Being a quick physical process, it is not subject to human error or supervision.

• Process of the present invention does not produce any sludge, thus removing any need for sludge disposal operation & expenses.

• Occupies much less area/m³ of input sewage.

• Once established for a designated capacity, can accommodate higher quantity of input sewage, merely by adding suitable membrane modules.

• Electricity requirement is less since the aeration or extended aeration is not done. & many pumps are not required to pump the liquid into many reservoirs.

• The process of the present invention eliminates the need of clarifier.

• The process for treatment of sewage has ability to produce biogas for generation of electrical/ thermal energy, which is absent in traditional STP.

Claims

Claims: 1/ We claim,

1. A process for the treatment of sewage comprising;

- a sewage reservoir (1) for accumulating the incoming sewage;

- a mechanical filter (2) for removing debris like leaves, twigs of tree or plastics;

- a floating matter disposal (3) for collecting such debris;

- a filtered sewage reservoir (4) for accumulating the filtered sewage after the mechanical filtration;

- a pump (5) to pump the filtered sewage to sand filter (6) for removing coarse and suspended solids for filtration in Coarse suspended solid disposal (7);

- a second pump (8) to pump the sewage output of sand filter (6) into the cartridge filter (9) for removing finer suspended matter;

- a pulsation dampner (11) for maintaining a steady flow of sewage without pressure surges;

- a microprocessor control (12) to monitor pressure, volume/unit time and conductivity of the sewage flow;

- membrane module (13) for modifying the sewage to the set desired parameters and for separating sewage into permeate (14) and reject (15);

- an anaerobic digester (16) for further digestion and generating biogas.

2. A process for the treatment of sewage as claimed in claim 1, further comprising

- removing any large size floating matter, - accumulating the sewage in a sewage reservoir (1),

- pumping sewage through a sand-filter (6) suitable to reject any suspended particle of more than lOOmicron size,

- pumping the output again through a cartridge filter (9) suitable to reject any suspended particle of more than ten micron size,

- pumping the said sewage into the membrane module (13) by using a centrifugal pump,

- increasing the pressure of the said effluent & monitoring and controlling the pressure using microprocessor control (12), a pulsation dampner (11),

- pumping the above pre treated effluent into the membrane module (13) containing the membranes,

- conserving the output volume and operating in recycle mode i.e. putting the reject & permeate streams back into the original reservoir (1) to identify the set desired parameters.

3. The membrane module (13) as claimed in claim 1; is selected from spiral wound, tube type and plate and frame membrane modules.

4. The membrane module (13) as claimed in claim 3; is particularly plate and frame membrane module.

5. A process for the treatment of sewage as claimed in claim 1, characterized in that said plate and frame membrane module (13), splits the incoming pre-filtered sewage into permeate (14) as a recycle grade water of desired analytical parameters & concentrated sewage (15) as reject.

6. The plate and frame membrane as claimed in claim 4, is further positioned after the primary filtered sewage reservoir (4) in such a manner that the requirement of aeration is eliminated.