EP2421798A2 - Water treatment - Google Patents

Water treatment

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Publication number
EP2421798A2
EP2421798A2 EP20100721545 EP10721545A EP2421798A2 EP 2421798 A2 EP2421798 A2 EP 2421798A2 EP 20100721545 EP20100721545 EP 20100721545 EP 10721545 A EP10721545 A EP 10721545A EP 2421798 A2 EP2421798 A2 EP 2421798A2
Authority
EP
European Patent Office
Prior art keywords
water
reverse osmosis
permeate
nanofilter
reject
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Withdrawn
Application number
EP20100721545
Other languages
German (de)
French (fr)
Inventor
Aljohani Mohammed
Original Assignee
Al-Mayahi Abdulsalam
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Priority to GB0906841A priority Critical patent/GB0906841D0/en
Application filed by Al-Mayahi Abdulsalam filed Critical Al-Mayahi Abdulsalam
Priority to PCT/GB2010/050648 priority patent/WO2010122336A2/en
Publication of EP2421798A2 publication Critical patent/EP2421798A2/en
Withdrawn legal-status Critical Current

Links

Classifications

    • CCHEMISTRY; METALLURGY
    • C02TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
    • C02FTREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
    • C02F1/00Treatment of water, waste water, or sewage
    • C02F1/44Treatment of water, waste water, or sewage by dialysis, osmosis or reverse osmosis
    • C02F1/441Treatment of water, waste water, or sewage by dialysis, osmosis or reverse osmosis by reverse osmosis
    • BPERFORMING OPERATIONS; TRANSPORTING
    • B01PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01DSEPARATION
    • B01D61/00Processes of separation using semi-permeable membranes, e.g. dialysis, osmosis or ultrafiltration; Apparatus, accessories or auxiliary operations specially adapted therefor
    • B01D61/02Reverse osmosis; Hyperfiltration ; Nanofiltration
    • B01D61/025Reverse osmosis; Hyperfiltration
    • BPERFORMING OPERATIONS; TRANSPORTING
    • B01PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01DSEPARATION
    • B01D61/00Processes of separation using semi-permeable membranes, e.g. dialysis, osmosis or ultrafiltration; Apparatus, accessories or auxiliary operations specially adapted therefor
    • B01D61/02Reverse osmosis; Hyperfiltration ; Nanofiltration
    • B01D61/025Reverse osmosis; Hyperfiltration
    • B01D61/026Reverse osmosis; Hyperfiltration comprising multiple reverse osmosis steps
    • BPERFORMING OPERATIONS; TRANSPORTING
    • B01PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01DSEPARATION
    • B01D2317/00Membrane module arrangements within a plant or an apparatus
    • B01D2317/02Elements in series
    • B01D2317/022Reject series
    • BPERFORMING OPERATIONS; TRANSPORTING
    • B01PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01DSEPARATION
    • B01D2317/00Membrane module arrangements within a plant or an apparatus
    • B01D2317/02Elements in series
    • B01D2317/025Permeate series
    • CCHEMISTRY; METALLURGY
    • C02TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
    • C02FTREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
    • C02F1/00Treatment of water, waste water, or sewage
    • C02F1/38Treatment of water, waste water, or sewage by centrifugal separation
    • CCHEMISTRY; METALLURGY
    • C02TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
    • C02FTREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
    • C02F1/00Treatment of water, waste water, or sewage
    • C02F1/44Treatment of water, waste water, or sewage by dialysis, osmosis or reverse osmosis
    • C02F1/442Treatment of water, waste water, or sewage by dialysis, osmosis or reverse osmosis by nanofiltration
    • CCHEMISTRY; METALLURGY
    • C02TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
    • C02FTREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
    • C02F1/00Treatment of water, waste water, or sewage
    • C02F1/44Treatment of water, waste water, or sewage by dialysis, osmosis or reverse osmosis
    • C02F1/444Treatment of water, waste water, or sewage by dialysis, osmosis or reverse osmosis by ultrafiltration or microfiltration
    • CCHEMISTRY; METALLURGY
    • C02TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
    • C02FTREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
    • C02F1/00Treatment of water, waste water, or sewage
    • C02F1/46Treatment of water, waste water, or sewage by electrochemical methods
    • C02F1/461Treatment of water, waste water, or sewage by electrochemical methods by electrolysis
    • C02F1/463Treatment of water, waste water, or sewage by electrochemical methods by electrolysis by electrocoagulation
    • CCHEMISTRY; METALLURGY
    • C02TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
    • C02FTREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
    • C02F2103/00Nature of the water, waste water, sewage or sludge to be treated
    • C02F2103/08Seawater, e.g. for desalination
    • CCHEMISTRY; METALLURGY
    • C02TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
    • C02FTREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
    • C02F2301/00General aspects of water treatment
    • C02F2301/08Multistage treatments, e.g. repetition of the same process step under different conditions
    • CCHEMISTRY; METALLURGY
    • C02TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
    • C02FTREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
    • C02F5/00Softening water; Preventing scale; Adding scale preventatives or scale removers to water, e.g. adding sequestering agents
    • C02F5/02Softening water by precipitation of the hardness
    • C02F5/06Softening water by precipitation of the hardness using calcium compounds
    • YGENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02ATECHNOLOGIES FOR ADAPTATION TO CLIMATE CHANGE
    • Y02A20/00Water conservation; Efficient water supply; Efficient water use
    • Y02A20/124Water desalination
    • Y02A20/131Reverse-osmosis
    • YGENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02WCLIMATE CHANGE MITIGATION TECHNOLOGIES RELATED TO WASTEWATER TREATMENT OR WASTE MANAGEMENT
    • Y02W10/00Technologies for wastewater treatment
    • Y02W10/30Wastewater or sewage treatment systems using renewable energies
    • Y02W10/37Wastewater or sewage treatment systems using renewable energies using solar energy

Abstract

The present invention relates to a water treatment system and process, and in particular a water treatment system, comprising: at least one reverse osmosis filter (10) comprising an inlet, a reject outlet and a permeate outlet; at least one means for removing dissolved contaminants (30) comprising an inlet, a reject outlet and a permeate outlet; at least one solids removal unit (40) comprising an inlet, a reject outlet and a permeate outlet; wherein the reject outlet from the at least one reverse osmosis filter is in fluid communication with the inlet of the at least one means for removing dissolved contaminants, and the permeate outlet from the at least one means for removing dissolved contaminants is in fluid communication with the inlet of the at least one solids removal unit.

Description

Water treatment
The present invention relates to a water treatment system and process. In particular the present invention relates to the treatment of brackish or sea water to produce potable water.
It is known that there are a number of existing problems and challenges in treating the reject from brackish water desalination plants using reverse osmosis. The present invention seeks to address at least some of these problems, and may allow the recovery of more fresh water, while making more environmental friendly reject effluents.
Freshwater recovery from Brackish Water Reverse Osmosis "BWRO" is limited to the membrane effectiveness, and the membrane effectiveness is linked to the potential scaling and fouling on the membrane. The present invention may provide an effective solution to such a problem, and may reach an overall freshwater recovery exceeding 95%, while producing a cleaner liquid reject that may be easily handled and treated by conventional techniques, such as solar pond evaporation or well re-injection. In addition, the present invention may allow the reduction, or elimination, of both heavy metals and radioactivity from the reject, easing its disposal and control; the heavy metals and radioactivity may be rejected in solid form.
The present invention may be integrated with any existing brackish water reverse osmosis BWRO plant, and may enhance the performance of the plant via safer and optimal mode operations potentially increasing the life span of any BWRO plant.
The present invention may provide innovative solutions for problems in both water and environment fields in relation to the treatment of the reject from the BWRO plants.
According to one aspect of the present invention there is provided a water treatment system, comprising: at least one reverse osmosis filter comprising an inlet, a reject outlet and a permeate outlet; at least one means for removing dissolved contaminants comprising an inlet, a reject outlet and a permeate outlet; at least one solids removal unit comprising an inlet, a reject outlet and a permeate outlet; wherein preferably the reject outlet from the at least one reverse osmosis filter is in fluid communication with the inlet of the at least one means for removing dissolved contaminants, and preferably the permeate outlet from the at least one means for removing dissolved contaminants is in fluid communication with the inlet of the at least one solids removal unit. As such, a more efficient water treatment system may be provided that may provide up to 95% of the feed water as useful water, such as potable water.
Where the term "in fluid communication" is used to describe the interconnection between two entities such as an inlet (or outlet) and an outlet (or inlet) it is to be understood as including the possibility that fluid can flow between the two entities, namely the inlet (or outlet) and outlet (or inlet), either directly or indirectly or optionally via a third entity. For example, where an outlet is described as being in fluid communication with an inlet, the outlet may be considered as being located 'upstream' of the inlet (or alternatively, the inlet may be considered as being located 'downstream' of the outlet), and the resulting direction of the fluid flow to be from outlet to inlet.
The solids removal unit may be a suspended-solids separation unit.
Preferably, the system further comprises a further such reverse osmosis filter, wherein preferably the permeate outlet of said solids removal unit is in fluid communication with the inlet of said further such reverse osmosis unit.
Preferably, the system further comprises at least one nanofilter comprising an inlet, a reject outlet and a permeate outlet; wherein preferably the reject outlet from the at least one reverse osmosis filter is in fluid communication with the inlet of the at least one nanofilter, and the preferably reject outlet from the at least one nanofilter is in fluid communication with the inlet of the at least one means for removing dissolved contaminants.
Preferably, the permeate outlets from the at least one nanofilter and the at least one solids removal unit are in fluid communication. More preferably, the permeate outlets from the at least one nanofilter and the at least one solids removal unit are in fluid communication with the inlet of said further such reverse osmosis filter.
Preferably, the system further comprises a solar pond, and the preferably reject outlet of said further such reverse osmosis filter is in fluid communication with said solar pond or a source water well.
Preferably, the system further comprises a pump, wherein preferably the permeate outlets from the at least one nanofilter and the at least one solids removal unit are in fluid communication with the inlet of said pump, and the preferably outlet of said pump is in fluid communication with the inlet of said further such reverse osmosis filter.
Preferably, the nanofilter is adapted to provide at the permeate outlet 30% to 70% of the water entering the inlet of said nanofilter, preferably 40% to 60%, and more preferably 50%. Preferably, the nanofilter is adapted to filter particles within the size range of 0.01 μm to 0.001 μm.
Preferably, the at least one means for removing dissolved contaminants comprises an electrocoagulation unit. More preferably, the electrocoagulation unit comprises at least one anode and cathode pair, and preferably a DC power supply connected to said electrodes to generate polymeric hydroxides to enable coagulation of the contaminants. Yet more preferably, the electrodes are iron and aluminium. Preferably, the electrocoagulation unit is adapted to generate gas via electrolysis to utlise buoyancy forces to remove contaminants.
Preferably, the solids removal unit comprises at least one of: sand filtration SF, microfiltration (MF), ultrafiltration (UF), rotary vacuum drum filtration (RVDF), and sedimentation using a mixing tank and a settling tank, adapted to utilise gravity separation, wherein preferably said settling tank is larger than said mixing tank. Preferably, the means for removing dissolved contaminants comprises a chemical additives unit. More preferably, the chemical additives unit is adapted to utilise lime and soda ash.
According to a further aspect of the present invention there is provided a method of treating water comprising: removing contaminants using a reverse osmosis filter; removing dissolved contaminants from the water; removing solid contaminants from the water; wherein the dissolved contaminants are removed from the reject water from the reverse osmosis filter, and the solid contaminants are removed from the permeate water subsequent to removing the dissolved contaminants.
According to a further aspect of the present invention there is provided a water treatment system, comprising: at least one nanofilter comprising an inlet, a reject outlet and a permeate outlet; means for feeding a proportion of the permeate outlet into said inlet; and means for placing said water treatment system in fluid communication with a water reverse osmosis treatment plant; wherein the inlet to the at least nanofilter is preferably adapted to be placed in fluid communication with the reject outlet from the water reverse osmosis treatment plant, and the permeate outlet of said nanofilter is preferably adapted to be placed in fluid communication with the water reverse osmosis treatment plant.
Preferably, said feeding means comprises at least one valve and a pump.
Preferably, the system further comprises a pump in fluid communication with the reject from said water reverse osmosis treatment plant and said inlet of the nanofilter.
Preferably, the permeate outlet of said nanofilter is adapted to be placed in fluid communication with the inlet of a first stage of the water reverse osmosis treatment plant. Preferably, the permeate outlet of said nanofilter is adapted to be placed in fluid communication with the inlet of a second stage of the water reverse osmosis treatment plant.
Preferably, the permeate outlet of said nanofilter is adapted to be placed in fluid communication with the permeate outlet of the water reverse osmosis treatment plant.
According to a yet further aspect of the present invention there is provided a method of treating water, comprising: nanofiltering the water to produce reject water and permeate water; feeding a proportion of the permeate water into the inlet of the nanofilter; and placing said water treatment system in fluid communication with a water reverse osmosis treatment plant; wherein the inlet to the at least nanofilter is preferably adapted to be placed in fluid communication with the reject outlet from the water reverse osmosis treatment plant, and the permeate outlet of said nanofilter is preferably adapted to be placed in fluid communication with the water reverse osmosis treatment plant.
According to a yet further aspect of the invention, chemicals such as soda and /or lime may be added to the feed of the Electrocoagulation EC unit. This may enhance the separation process of dissolved contaminants as solids, which can then be treated further in a similar way to that proposed above.
The invention extends to methods and/or apparatus substantially as herein described with reference to the accompanying drawings.
Each feature disclosed in the description, and (where appropriate) the claims and drawings may be provided independently or in any appropriate combination.
Any feature in one aspect of the invention may be applied to other aspects of the invention, in any appropriate combination. In particular, method aspects may be applied to apparatus aspects, and vice versa. These and other aspects of the present invention will become apparent from the following exemplary embodiments that are described with reference to the following figures in which:
Figure 1 shows a schematic illustration of a typical Brackish Water Reverse
Osmosis (BWRO) plant;
Figure 2 shows a schematic illustration of a BWRO plant using
Electrocoagulation to treat the reject stream;
Figure 3 shows a schematic illustration of a BWRO plant using chemicals to treat the reject stream;
Figure 4 shows a schematic illustration of a BWRO plant using nanofiltration within the process;
Figure 5 shows a schematic illustration of a variation of the BWRO plant shown in Figure 4; and Figure 6 shows a schematic illustration of a further variation of the BWRO plant shown in Figure 4.
Figure 1 shows a typical BWRO plant comprising the following:
1. Feed water from the well
2. Pre-treatment unit consists of sand filter and MF, it could be substituted by UF or any convenient method
3. Chemical conventional additives such as acids or anti-sealants
4. High pressure pump 5. First stage RO membranes
6. Second stage RO membranes
7. Permeate water from first stage and second stage
8. Reject
In the process flow diagram shown in Fig. 1 , brackish water or underground water enters the BWRO plant via line 1. Unit 2 is a pre-treatment unit which could be a sand filter (coarse filtration) and microfiltration MF. Unit 2 could be substituted by an Ultra Filter UF. The filtrate stream can be treated by well- measured chemical dosages such as acids and anti-sealants taken from multi- feeder chemical unit 3 from where the chemicals are injected into filtrate stream. Outlet stream from the pump 4, enters the first-stage RO membranes unit 5 where can be separated to a permeate water 7, and reject stream at a sufficiently high pressure to enter the second-stage membranes unit 6. Normally unit 6 has fewer membranes than unit 5. The whole rejected stream from the plant could be collected only via line 8 whereas the total permeate could be collected from the both permeates of unit 5 and unit 6 via line 7.
Figure 2 shows a BWRO plant using Electrocoagulation (EC) to treat the reject stream, comprising the following main units:
10. Last- stage RO membranes for an existing or new BWRO plant 20. RO or NF membrane after EC treatment 30. Electrocoagulation (EC) unit
40. Suspended solid separation unit (sand & MF, RVDF or UF) 50. High pressure pump.
Stream 1 1 , the last stage feed stream, enters unit 10, which is the previous RO membrane. The reject stream 12 from unit 10, which is in general a second or third stage RO membrane array, enters the EC unit 30, in which it will be treated via an external electrical power supply which is not shown in this diagram. The solid precipitate can be discarded via line 32 in case of any sedimentation within unit 30 whereas the stream comprising less suspended particles exits via line 31 to enter the appropriate separation unit 40. Unit 40 could be a sand filter combined with MF or UF or Rotary Drum Filter or RVDF or plate-and-frame filter press. The aim of Unit 40 is to provide liquid stream 42, with solid particles with a diameter of less than 1 μm and acceptable by RO or NF filtration 20 without causing any operational damage. The solid content or sludge can be discarded via line 41. The Liquid stream 42 is pushed by a high pressure pump 50, to enter RO or NF membranes 20, via Line 51. Reject stream 21 , leaves unit 20, to a solar pond or to be re-injected back to a well, or can be treated by any other method (not shown in the diagram). Permeate can be collected via Line 22. Freshwater can be collected in the case where unit 20 is a RO membrane, whereas it can be recycled back to the feed via line 13 in the case where unit 20 is NF. Figure 3 shows a BWRO plant using chemicals to treat the reject stream, comprising the following main units:
1 10. Last-stage RO membranes for an existing or new BWRO plant 120. RO or NF membrane after chemical treatment 130. Chemical treatment unit, normally soda-lime process
140. Suspended solid separation unit (sand & MF, Rotary Drum or
RVDF or UF)
150. High pressure pump.
Stream 1 11 , last stage feed stream enters unit 1 10, which is the previous RO membrane in a BWRO plant. The permeate can be collected via line 1 14. The reject stream 1 12 from unit 1 10 enters the chemical treatment unit 130 in which it will be treated, using chemical additives facility 131. The solid precipitates from the unit can be discarded via line 132 whereas the less suspended particles leave via line 133 to enter the appropriate liquid-solid separation unit 140. Unit 140 could be an UF or sand filter combined with MF or RVDF. The aim of unit 140 is to result in liquid stream 142 having solid particles of diameter of less than 1 μm, which are acceptable by RO filtration 120 without causing any operational damage. The solid content or sludge can be discarded via line 141. The Liquid stream 142 is pushed by a high pressure pump 150, to enter RO or NF membranes 120, via line 151. Reject stream 121 leaves unit 120 to a solar pond or to be re-injected back to a well, or can be treated by other known method which are not shown in the diagram. Permeate can be collected via line 122. A freshwater can be collected in case unit 120 is a RO membrane, whereas it can be recycled back to the feed via line 1 13 in case unit 120 is NF.
Figure 4 shows a BWRO plant using nanofiltration within the process comprising the following main units:
210 NF membrane
220 and 230 High pressure pumps
240 and 250 Valves
All other units are the same as for Figure 1 and are located on the top part of drawing and divided from the bottom part by the dotted line. In the process flow diagram shown in Fig. 4 the reject stream 152 is taken from conventional BWRO plant as illustrated in Fig.1 and enters the Nanofiltration membranes unit 210 via line 231 after been pumped by the pump 230. Rejected stream from unit 210 is collected via stream 212. Permeate stream 211 is divided into two streams via appropriate valves 240 and 250 which can be regulated to control the process through mixing. First stream 251 could be recycled to the unit 210 via line 221 after having been pumped by pump 220. Second stream 241 enters the BWRO plant at a point prior to the main pump 4. Alternatively, or in addition, stream 241 could enter between stages of the BWRO (which is not shown in this figure) which may result in better operational modes. It could also be mixed with the permeate produced by the main plant in order to prepare good quality potable water.
Figure 5 shows a schematic illustration of a BWRO plant using nanofiltration within the process, comprising the following main units:
310. Pre-treatment unit
320. Chemical additives unit, such as acids and antiscalants.
330. High pressure pump
340. First stage RO membranes 350. NF membrane
360. High pressure pump
370. Second stage RO membranes
In the process flow diagram shown in Fig. 5, a brackish water desalination plant consists of NF membranes unit 350 is in between a first-stage RO membranes unit 340 and a second-stage RO membranes unit 370. Brackish water enters coarse and micro filtration pre-treatment unit 310 via line 31 1. Unit 310 could be a sand filter and micro filter, UF or RVDF. Then, the filtrate stream 312 enters the high pressure pump 330. Well-measured chemicals dosages such as anti- sealants are taken from tank 320 and injected into stream 312 via line 321.
Outlet stream 331 from the pump 330 enters the first-stage RO membranes unit
340 where it can be separated into a permeate or product water via line 342 and reject stream via line 341 at an enough high pressure to enter the NF membranes unit 350. The reject of the NF unit 350 is taken via line 351 for disposal. Permeate stream 352 is pumped by a pump 360 to enter a second- stage RO membranes unit 370 via line 361. The reject stream from RO unit 370 is discarded via line 371 whereas permeate is collected via line 372 and combined with line 342 to make the whole permeate stream of the plant.
Figure 6 shows a schematic illustration of a BWRO plant using a nanofiltration NF - Electrocoagulation EC optimal cost process comprising the following main units:
410 Last-stage RO from BWRO 420 NF unit 430 EC unit
440 Suspended solids removal unit 450 High pressure pump 460 Extra RO unit
In the process flow diagram shown in Fig. 6 the reject stream 41 1 from the last stage RO 410 which is a part of a BWRO plant, enters NF unit 420. Permeate from unit 420 can be collected via line 421 whereas the reject is taken via line 422 to enter the EC unit 430. Some of separated solids within the EC unit 430 can be discarded via line 431 but the high suspended-solids content stream 432 leaves EC to a further solid removal unit 440 which it could be sand filter and microfiltration or rotary vacuum-drum filter RVDF or ultra filtration UF or mixing tank followed by settling tank and microfiltration. All these alternatives of unit 440 can result in fewer suspended solids of average size more (or possibly not more) than 1 μm via line 442 whereas the solids or sludge can be discarded via line 441. Both the permeate stream 421 from unit 420 and stream 442 are mixed then enter the high pressure pump 450 to enter an extra RO unit 460 via line 451. The permeate from unit 460 can be collected via line 461 whereas the final reject from the plant can be collected via line 462 and sent to a suitable treatment unit such as solar pond.
In one embodiment, and as shown in Fig 6, there is provided a method of treating a reject of BWRO plant to produce more fresh water, said method comprising treating a reject initially by first nanofiltration NF and then the reject from first NF is treated by an Electrocoagulation EC unit. providing a first NF of any available NF membrane to achieve certain permeate recovery between 30-70%. providing the reject of first unit which represent 70 - 30% of the main reject from the BWRO plant, introducing the reject of first unit to a second Electrocoagulation EC unit, in said second unit, the reject stream from said first unit can be treated, most of divalent ions, heavy metals, soluble radioactive isotopes, silica, small- size suspended solids, soluble organics and mono monovalent ions be converted to a big- size solid particles, from said second unit, a part of big-size solid particles can be separated and discarded by gravity , from said second unit, the liquid stream with high suspended solids is taken to a third suspended- solids removal unit to separate the suspended solids to sufficient degree to be treated in a fourth RO unit , from said third unit, solids can be separated and discarded in a solid or sludge form. from said forth unit, permeate is collected and considered as a high quality water whereas the reject is send to a solar pond , well reinjection or to any suitable disposal method. the feed of said forth unit could be a blend of the liquid stream from third unit and the permeate of first unit and a part of the permeate from the first unit could be recycled back to the BWRO plant prior to any RO membrane array.
In a further embodiment, as shown in Fig 2, there is provided a method of treating a reject from BWRO plant exclusively by EC and suspended-solids removal process followed by RO unit.
In a further embodiment, shown in Figures 4 and 5, there is provided a method of treating a reject from BWRO plant exclusively by NF with or without extra RO unit. NF unit could be integrated in between RO stages of the BWRO plant.
In a further embodiment, in Figure 3, there is provided a method of treating a reject from BWRO plant partially or totally by chemical treatment (soda-lime process) followed by extra RO unit. Background
Groundwater is becoming rare, insufficient and costly in most MENA (Middle
Eastern and North African) countries as well as in many places around the world. In most arid areas water supplies are of a poor quality, and the supply of good quality water is becoming a daily problem which reaches urgency in peak periods. In such areas and circumstances, in order to respond to such a local drinking, irrigation and industrial water demand, both reject from desalination plants, and effluents of wastewater treatment plants, become a precious resource to be re-explored, re-treated and converted into a vital source of water via an appropriate separation process.
With increasing awareness of the importance of water desalination activities, technology has been developed in parallel to solve the several problems associated with the pre-treatment of sea and brackish water, the efficiency of the membrane in RO plants, the toxicity of the reject and its impact on the environment, etc.
While chemical pre-treatment has been eliminated and substituted by anti- sealants, energy efficacy been raised, membrane technology has been improved, and the process slightly upgraded, no higher freshwater recovery has been reached, and most importantly no reduction in toxic and harmful content of reject water from BWRO has been recorded.
In the following paragraphs, the treatment problems are described and the limits of existing solutions in both brackish and reject waters RO processes are highlighted.
Water quality problems and limits in membrane technologies: Membrane-based separation processes have been shown to have a huge potential for the treatment of a variety of waters and wastewaters by acting in line with strict legislation regulating acceptable standards in potable water quality and wastewater discharges worldwide. Microfiltration (MF), ultrafiltration (UF), nanofiltration (NF) and reverse osmosis (RO) have been increasingly utilized for water and wastewater treatment projects. They are used to remove suspended solids and reduce the content of organic and inorganic substances in filtered waters. In BWRO, the biggest challenge of conventional spiral membrane technology for instance, is how to extract more water from the reject without being limited by solubility of cautiously soluble salts in the brine.
Despite the many prior proposed brackish water desalination processes using reverse osmosis RO, a steady problem of membrane plugging always restrains a higher permeate recovery. Accordingly, RO membrane operation is often not well matched to the high allowed pressure that could be applied on membrane to overcome the osmotic pressure. This is particularly the case in many BWRO plants where the precious and depletable underground water has generally been wasted by solar evaporation in solar ponds hence loosing all possibilities to reach the ultimate water recovery ratios. Besides, there will be a harmful impact on the environment associated with the relatively large brine disposal area.
In contrast to sea water, underground water has certain constituents that have a high tendency to scale, foul and enhance a biological growth on the membrane, causing severe damage to the latter.
The scaling in the RO desalination processes for both Seawater Reverse Osmosis "SWRO" and BWRO occurs when the concentration of scale forming ions (hardness ions) exceeds the saturation points (solubility limit) at which after a certain time, scale nucleation starts followed by the precipitation of scale. Anti-sealants are normally added to interfere with the nucleation process, therefore preventing up to a certain concentration and temperature level the scale formation. Thus, allowing for the operation of the brackish and seawater desalination plants at high saturation of potentially precipitated ions.
Indeed one of the biggest challenges in BWRO processes is that underground waters contains high silica contents, 20-60 mg/l, naturally dissolved from the rocks which leads to a very high silica content above the saturation limit at the final stage of separation. Silica (SiO2 silicon dioxide), generally, is an anion. The chemistry of silica is complex and to some extent unpredictable. Silica content in water reports the total concentration of silicon (as silica) without detailing what the silicon compounds are. The "Total Silica" content of water measured in mg/L is composed of "Reactive Silica" and "Unreactive Silica". Reactive silica (e.g. silicates SiO4) is dissolved silica that is a little ionized and has not been polymerized into a long chain. It is preferable to handle this form of silica in desalination plants rather than unreactive silica. Reactive silica is used in all RO projection software programs that are normally produced by RO membrane producers. Reactive silica, though it has anionic features, is not considered as an anion in terms of balancing a water analysis but it is counted as a part of the total TDS (total dissolved solids). Unreactive silica is undesired Silica, polymerized/colloidal silica, acting more like a solid than a dissolved ion.
Silica can occur in both colloidal and polymerized forms. Polymerized silica (essentially silicon dioxide) can occur naturally in the form of, for example quartz or agate, and can also result from the saturation level of reactive silica being exceeded. Although the colloidal form can in principle be removed by a RO there is a risk of the front-end of the RO becoming fouled. However, solid particles with a diameter of less than 1 μm (colloidal silica can have particle diameters as small as 0.008 μm) are typically acceptable by RO or NF filtration units without causing any operational damage. The standard test used to determine the Silt Density Index (SDI) is an example of a test which can be used to screen for potentially problematic particles as it can detect particles of a diameter of 0.45 μm or greater and can therefore detect particulate silica compounds such as clays, silts and sand which are usually 1 μm or larger. The skilled person will understand that these particle sizes are not absolute but rather illustrative of the upper/lower bounds of particle sizes which are considered in various filtration steps.
The solubility of reactive silica is on average limited to 200-300% with the use of a silica dispersant (antiscalant). Reactive silica solubility increases with increasing temperature, increases at a pH less than 7.0 or more than 7.8, and decreases in the existence of iron which operates as a catalyst in the polymerization of silica. Silica scaling becomes a problem when any water system becomes over- saturated with dissolved and colloidal silica. Silica scaling can then become a problem for the efficient use of high-recovery BWRO.
The highest silica content in the reject from last stage RO can not usually exceed 240 mg/l, even when using very efficient anti-sealants. Therefore, the overall water recovery from water with a high silica feed between 40-60 mg/l is limited to a maximum recovery between 80-85% though the total dissolved solids (TDS) in the reject, may be relatively low. For instance, some reject from BWRO may contain a TDS value as low as 5,000 mg/l, while the silica content is as high as 240 mg/l. Therefore, it is necessary to find practical solutions to extract more fresh water by removing as much silica as possible.
Another very important issue in brackish water treatment is the high content of heavy metals and soluble radioactive isotopes, which most conventional plants do not treat or decontaminate. These elements are captured in the reject stream, which end up being released in to nature causing all the consequent environmental damages.
A usage of the Electrocoagulation EC process:
Generally, Electrocoagulation "EC" is one of the separation methods that has been recently developed and commercialized to remove unwanted contaminants in waste water - either by chemical reaction and precipitation or by causing colloidal materials to join together and then be removed by electrolytic flotation. Electrocoagulation techniques operate by applying a direct current that generates sacrificial electrode ions into the flow. The electrochemical system may be able to cope with a variety of wastewater treatments such as paper pulp mill waste, metal plating, tanneries, canning factories, steel mill effluent, slaughter houses, chromate, lead and mercury laden effluents, as well as domestic sewage. These wastewaters could be treated and converted to clear, clean, odourless and reusable water for different applications. Generally, especially in domestic sewage treatment, the treated water will have better value and characteristics than the raw water from which it had originated. During the EC process, the electrical current is introduced into water via parallel plates built of different metals that are chosen to optimize the removal process. The most regular plate materials are iron and aluminium. According to Faraday's Law, metal ions can be split off or sacrificed into the solution. Those metal ions tend to form metal oxides that may electromechanically attract to some or all of the contaminants that have been destabilized. EC is a complex process relating many chemical and physical observable facts that use consumable electrodes (Fe/AI) to provide ions into the water flow.
Fe/AI is dissolved from the anode making equivalent metal ions, which instantly hydrolyze to polymeric iron or aluminium hydroxide. These polymeric hydroxides are first-rate coagulating agents. The consumable (sacrificial) metal anodes produce polymeric hydroxides in the surrounding area of the anode. Coagulation occurs when these metal cations come together with the negative particles carried toward the anode by electrophoretic motion.
In general, contaminants in wastewater during the EC process are treated either by chemical reactions and precipitation or by physical and chemical attachment to colloidal materials being generated by the electrode dissolving. Then, the newly-formed solid particles can be removed by electroflotation, sedimentation, and filtration. EC can generate coagulation agents in situ. By contrast, in conventional coagulation process, coagulation chemicals are added.
In the EC process, the deterioration mechanism of the contaminants, particulate suspension, and cracking of emulsions may be summarized as follows:
1 ) Packing together the disband double layer around the charged species by the interactions of ions generated by oxidation of the sacrificial anode.
2) Charging to neutralize the ionic species present in wastewater by counter ions produced by the electrochemical dissolution of the sacrificial anode. These counter ions may decrease the electrochemical dissolution of the sacrificial anode. These counter ions also can decrease the electrostatic interparticle repulsion to the extent that the van der Waals attraction predominates, therefore coagulation can be generated and furthermore a nil net charge results in the process. 3) Floe formation: the floe shaped as product of coagulation forms a sludge blanket that carries the suspended solids in the flow and causing coagulation. A zero net charge outcomes in the process, and as result of coagulation, an enhanced separation process can be achieved when it generates a sludge blanket that captures and bridges colloidal particles such as silica that are still remaining in the aqueous stream.
Water is also electrolyzed in a parallel reaction producing minute gas-bubbles of oxygen at the anode and hydrogen at the cathode. The generated gases in the form of tiny bubbles can work to be a focus for the flocculated particles and float the flocculated pollutants to the surface through natural buoyancy.
To understand more, a simple Electrocoagulation EC reactor is fabricated of one anode and one cathode. When an electrical potential is applied from an external power source, the anode material goes through oxidation, while the cathode will be subjected to reduction or reductive deposition of elemental metals. The electrochemical reaction with metal M as anode may be summarized as follows.
At the anode:
M(s) -> M(aq) n+ + ne 2H2P(D-* 4H+(aΨ + 02(g) + 4e
At the cathode: M(aq) n+ + ne * M(s)
When iron or aluminum electrodes are used, the generated Fe(aq) +3 or Al(aq) +3 ions will immediately undergo unstructured reactions to produce corresponding hydroxides and/or polyhydroxides. These compounds have strong attraction for dispersed particles as well as counter ions to cause coagulation. The gases generated at the electrodes may interfere with and cause flotation of the coagulated materials. To improve the performances of an EC, it may be necessary to interchange the polarity of the electrode from time to time. In general, a two-electrode EC cell is not suitable for wastewater treatment because of an effective rate of metal dissolution, and so the use of large surface areas electrodes is required.
A performance development has been achieved by using EC cells either with monopolar electrodes or with bipolar electrodes. The parallel arrangement basically consists of pairs conductive metal plates located between two parallel electrodes and a DC power source.
There are two EC arrangments. A monopolar EC arrangement means that electrodes with cells in series are electrically similar to a single cell arrangement but with many electrodes and interconnections with the main power supply. In this arrangement each pair of "sacrificial electrodes" is internally connected with each other, and has no interconnection with the outer electrodes. This durable setup may also require a resistance box to regulate the flow current and a multimeter to read the current values. For example, the arrangement of four electrodes could be described as: (+ , -, +, - ) and for six electrodes as:( +, -, +, -, +, - ) and so on. This arrangement means that all electrodes are connected directly to the power supply.
A bipolar EC arrangement means that the sacrificial electrodes are placed between the two parallel electrodes without any electrical connection. The two monopolar outer electrodes inside the bipolar arrangement are connected to the electric power source with no interconnections between the sacrificial electrodes of the system. This cell arrangement provides an easy setup, in which the neutral sides of the conductive plate are transformed to charged sides, which have reverse charge compared with the parallel side beside it. The sacrificial electrodes are identified as bipolar electrodes. For example, the arrangment of four electrodes could be described as: (+ , 0, 0, - ) and for six electrodes as:( +, 0, 0, 0, 0, - ) and so on. This arrangement means that only the outer electrodes are connected directly to the power supply whereas the other electrodes are affected by electrical potential indirectly. This arrangement can take different possibilities depending on many design features and various operation modes. In the Electrocoagulation process, the suspended, emulsified or dissolved contaminants in an aqueous medium can be destabilized by means of introducing an electrical current which provides the electromotive force to drive the chemical reactions betweens ions and particles. While reactions are driven or forced, the elements or formed compounds will move toward the most stable state. As a result, this state of stability can produce a solid that is less colloidal and less emulsified and/or less soluble than the compound at equilibrium values. The contaminants form hydrophobic statuses then precipitate and can simply be removed by a number of secondary separation techniques.
The electrocoagulation process treats heavy metals, viruses, bacteria, pesticides, arsenic, MTBE, cyanide, BOD, TDS, and soluble radioactive isotopes when it separates soluble solids from the water molecules in a solid form. The EC process is used to treat sewage, dairy effluents, plating shop wastes, and contaminated soil.
In one embodiment, EC can treat the reject of a BWRO plant to separate some of its solutes in a solid shape. EC can provide a high level of separation for most of the divalent ions existing in the reject such as calcium, magnesium, sulphate and carbonate with a removal rate of between 20% to 70%. It can also provide very high removal rate for silica exceeding 90%. Heavy metal and soluble radioactive isotopes can be removed with an excellent rate as high as 99%. Solids can be separated and discarded from the EC in different down- stream methods. For example, the suspension effluent from the EC may be treated further by mixing and settling, then the precipitates can be discarded as a sludge or solid.
In general, the EC effluent has floating coagulated solids as a layer lifted by buoyancy force on the surface of the collection tank linked to the EC directly whereas the heavy solids go down to the bed of the tank. Technically, solids could be collected from the top and bottom of the tank. More practically, mixing the contents of this tank following to the EC allows very efficient settling in a further tank if it has enough residence time to settle. Because of the need for sufficient residence time the size of the settling tank will be bigger than the mixing tank. Preferably, using the mixing and settling tanks after the EC will provide highest solid separation. In the case of using those tanks, a micro filtration MF could be enough to achieve a filtrate with non-soluble contents of size less than 1 μm. This option can provide the filtrate from MF which is considered to be accepted as a feed for an extra RO membrane unit.
Ultra filtration UF could be used to treat the effluent extracted directly after the EC or after the mixing or settling tanks. UF permeate is considered to have smaller suspensions size in comparison with microfiltration MF so that it can provide better feed to RO membrane. Regularly, UF requires back washing by clean water to enhance the filtration process. In most other industrial processes rather than EC, the UF back wash reject after cleaning the membranes is thrown out, however in EC it could be recycled back to the main feed of the EC and saving any water that was used in the backwashing. Indeed, using UF with EC has the benefits of saving the backwashing water and providing high quality water that can be fed to RO plant.
A rotary vacuum drum filter (RVDF) can be integrated with EC to achieve an efficient filtration process which provides less than 0.5μm suspended solids that is considered good enough as a feed for RO. Similarly to UF, a rotary vacuum drum filter can be used soon after the EC or following the settler. Using a rotary vacuum drum filter later than the settler may reduce the power consumption and the use of Diatomaceous earth (DE) material which is generally used as consumable entry to cover the surface of the rotary drum and discarded continuously from the covering layer subsequent to precipitating the suspended solids on the DE face. Through the precipitating process of the suspended solids on the DE coating, a built-in blade or knife removes a controlled-thickness layer from the DE material continuously. So that the DE material should be added to re-cover the rotary drum cylinder periodically before the DE material is removed or vanished completely. The consumption rate of DE is according to the precipitating rate of the solids on the outer surface of the DE and the operation modes of the process.
Accordingly, the outlet filtrate from any of the above-mentioned filtration options, should be fed to RO or NF membranes. By this means more fresh water can be extracted from BWRO reject. For example, potable or fresh water with high quality may be collected from the reject treatment with the highest permeate recovery up to 90%. This percentage means the recovery from and after treating BWRO reject solely by this invention.
This combined process using EC treatment followed by RO to take care of the reject from BWRO may give the highest overall BWRO permeate recovery exceeding 95% and may allow heavy metals, toxic materials and radioactive pollutants to be discarded in a solid state. For example, if the reject of an existing BWRO plant with a permeate recovery of 80% is treated by this method to extract 80% fresh water, this means that the overall plant recovery is 96%. The final reject from the last RO following the EC which consists of less than 5% of the main feed from the well can be easily treated by any conventional method such as solar pond evaporation or underground re- injection with minimal, or nil, pollution.
Using the NF to replace the final RO membranes following the EC may provide higher flow rate for the reason that NF membrane flux has a higher value than the RO. That means the NF filtration process can be achieved at a lower operating pressure and providing a higher permeate value leading to fewer membranes for the same output.
The advantages of using NF to replace the RO are to allow some useful minerals in its permeate that can be mixed then with the permeate from the main BWRO membranes getting a well controlled and high quality potable water. The permeate from the NF can be recycled back to the process prior to any RO array such as a first, second and/or a third stage of the BWRO plant. Specifically, recycling the permeate with a lower TDS from NF to the final RO array in the main BWRO plant may enhance its performance with less potential scaling.
Chemical treatment and chemical ore-treatment:
A lime softening process is used as a pre-treatment in BWRO in which calcium and magnesium is partially precipitated as calcium carbonate and magnesium hydroxide respectively. Through the precipitation process, magnesium hydroxide forms larger floe that more readily adsorbs or catches silica particles in water. A significant amount of silica can be eliminated by way of the precipitation of common hardness cations, particularly when magnesium hydroxide is generated in the lime softening process.
Usually, silica concentration of raw water is reduced during a lime-soda softening process in which calcium, and magnesium concentrations are also decreased. So that the lime softening process could be considered an effective method to reduce soluble and insoluble silica in the feed water prior to BWRO plant, although its primary purpose is to control water hardness.
Conventionally, a lime and soda ash softening process is utilized with BWRO plants where lime (Ca(OH)2) and soda ash (Na2COs) are used. Accordingly, the total hardness can be reduced and thus prevent scaling and fouling of the RO membranes.
The Lime-Soda softening process can mainly remove carbon dioxide; carbonate hardness, calcium non-carbonate hardness and magnesium non- carbonate hardness.
Removal of carbon dioxide takes place according to thef following reaction:
CO2 + Ca(OH)2 → CaCO3 j + H2O
The carbonate hardness of calcium and magnesium as bicarbonates can be precipitated and discarded as calcium carbonate and magnesium hydroxide by the addition of lime (calcium hydroxide Ca(OH)2). At first, magnesium bicarbonate is transformed to magnesium carbonate. Since magnesium carbonate is soluble, excess lime is added to precipitate it as magnesium hydroxide whereas the pH is raised above 10.
Ca(HCO3)2 + Ca(OH)2 → 2CaCO3J+ 2H2O Mg(HCO3)2 + Ca(OH)2 → CaCO3 |+ MgCO3 + 2H2O MgCO3 + Ca(OH)2 →CaCO3 1+ Mg(OH)2 1 The non-carbonate hardness caused by calcium sulfate and calcium chloride existing in water can be precipitated and discarded as calcium carbonate as a result of the addition of soda ash (sodium carbonate (Na2CO3)).
CaSO4 + Na2CO3 → CaCO3 1+ Na2SO4
CaCI2 + Na2CO3 → CaCO3 1+ 2NaCI
The non-carbonate hardness caused by magnesium sulfate and magnesium chloride can be precipitated and discarded as magnesium hydroxide via the addition of lime, (calcium hydroxide Ca(OH)2). These reactions make calcium non-carbonate hardness, CaCI2 and CaSO4. Therefore, soda ash must be added to precipitate these calcium non-carbonate hardness, CaCI2 and CaSO4, to calcium carbonate as follow.
MgCI2 + Ca(OH)2 →Mg(OH)2 j+ CaCI2
CaCI2 + Na2CO3 →CaCO3 1+ 2NaCI MgSO4 + Ca(OH)2 → Mg(OH)2 j+ CaSO4 CaSO4 + Na2CO3 →CaCO3 1+ Na2SO4
Throughout the lime softening process, silica can be reduced significantly. This is by reason of the attachment of silica on the surface of the precipitated magnesium ions whereas at high pH values calcium-magnesium silicates can also be formed and precipitated.
In this embodiment, the existing facilities of the chemical pre-treatment in a BWRO can be used as a post chemical treatment for its reject. Recently, most of the chemical pre-treatment facilities had not been used because of utilizing chemical additives such as anti sealants achieving the same permeate recovery with quite high cost reduction.
Consequently, the reject from any conventional BWRO can be further treated via chemical treatment using the soda lime process as described above. The sludge produced from the soda lime treatment of reject can be handled and treated exactly in the same manner for BWRO plant. The chemical consumption rate may be the same as that of full chemical treatment of the reject with the chemical pre-treatment of the feed in the BWRO with same flow rate and recovery. The soda lime treatment for reject could be achieved in equipment with a smaller size due to lower flow rate. The less - suspended solid contents are usually clarified by sand filtration and microfiltration before it is fed to an extra RO to extract more fresh water from the reject.
Soda lime treatment process could treat part of BWRO reject which contains high silica between 150- 250 mg/l. Accordingly, this part of reject is treated by soda lime to reduce its silica content to 30-60 mg/l and then fed to conventional RO or NF. The permeate from RO or NF with very low silica level below 5 mg/l is mixed with the other part which was not treated in such percentage to minimize silica content to a certain acceptable level not exceeding 60 mg/l. The mixed stream with silica content below 60 mg/l can be further treated by another RO or NF with a recovery up to 75%. Lower silica content can provide higher recovery. The permeate from the final RO may be used as potable water whereas the permeate from the NF may be recycled back to the process to enhance the performance of membranes and reduce the amount of main feed to the plant with the same recovery before treating the reject partially with soda lime.
NF & RO processes:
The RO process deals with separation of all ionic size particles in the range of 0.001 μm or less. The NF Membrane falls in-between the RO and UF separation range, and is suited for the separation of particle sizes in the range of 0.01 μm to 0.001 μm. In addition to the rejection of neutral particles according to their sizes, as is the case with the MF and UF membranes, the NF rejection of inorganic matter is accomplished by their electrostatic interaction with the negatively charged membrane. Furthermore, the degree of rejection by the NF membrane is lesser for mono-valent ions, such as Cl, Na+, than for the divalent SO4=I Mg++ and Ca++. So that utilizing NF is very effective in the hardness removal from low salinity water. Nowadays the NF low salinity water purification process is gaining approval as a major drinking water softening treatment, replacing in many cases, the conventional lime softening treatment. Dual nanofiltration (NF) and seawater desalination processes have been developed in Saudi Arabia. The seawater feed proceeding to RO membranes is first pretreated/partially and pre-desalinated by the nanofiltration process. The NF pre-treatment can avoid sea water reverse osmosis (SWRO) membrane fouling by the removal of turbidity and bacteria, and can prevent also scaling of the plant by removal of scale forming hardness ions. This can significantly lower the required pressure to operate BWRO plant by reducing TDS of seawater feed. This pre-treatment modifies the seawater feed chemistry with the net result of increasing SWRO potable water yield and permeate recovery ratio. Similarly, it allows for the operation of SWRO without the addition of antiscalants. Nanofiltration NF can be used for the pre-treatment seawater in Multi stage Flash (MSF), Multi Effect Distillation (MED) desalination plants to allow the plant operation, without fear of scaling, fouling and foaming.
It has been shown that the use of NF and RO contributes significantly to a decrease in TDS, salinity, hardness, nitrates, cyanides, fluorides, arsenic, heavy metals, colour and organic compounds, e.g., total organic carbon (TOC), biological oxygen demand (BOD), chemical oxygen demand (COD), total organic halides (TOX), trihalomethanes (THM), THM forming potential (THMFP), and pesticides. In addition, the elimination of bacteria, viruses, turbidity and total suspended solids (TSS) from surface water, groundwater, and seawater may be achieved perfectly.
The removal of divalent cations (water softening), natural colour, trihalomethanes precursors and reduction of total dissolved solids (TDS) can be accomplished by nanofiltration (NF). Furthermore, RO has an ability to remove all types of pathogens.
Combined NF & EC process: Both NF and EC are described in detail above. In a further embodiment, a combination of NF followed by EC is utilised. This combined process starts initially by treating the reject of such BWRO in a NF unit in which the inlet flow rate can be split into permeate and reject streams. The separation degree or recovery ratio in the NF unit generally depends on many aspects such as, feed osmotic pressure, feed ingredients & chemistry, applied pressure, membrane characteristics, scaling awareness and permeate degree and quality.
Accordingly, in the NF, the reject and permeate ratios can vary from 20 - 80%. This means that the reject from NF may be between 20 - 80% of the feed, preferably 30 - 70%, and more preferably 50%.
In the case of 50% ratio, the flow rate value of reject stream represents half of feed that entered the NF at beginning. The reject stream enters the EC unit which means that the EC capacity is 50% less than the capacity of EC standing alone to treat the whole stream for a BWRO plant.
Up till now, the cost and the foot-print of a complete EC process standing alone to treat the reject of BWRO plant as was described above, is higher than the NF process proposed above, for the same target and flow rate.
Therefore, treating the BWRO reject by NF then treating the reject of NF which consists of about half of the main reject by EC will reduce both the investment costs and operational costs in comparison with treating the main reject with standing-alone EC as proposed above.
After treating 50% of the reject by EC and after removing its suspended solids via an efficient solids removal method, the permeate should be mixed again with the permeate stream of the NF.
The follow-on stream after mixing should not have any suspended solids above 1 μm; therefore, it can be treated easily with extra RO avoiding any membrane plugging and producing high permeate ratio exceeding 70%. By other means, the mixed stream treated by RO has almost the same flow rate for the main reject stream minus any solids amount that had been discarded from the process by EC and solids removal units. The process combination of NF followed by EC could provide a good option to recycle some of the NF permeate and/or EC permeate back to the process before entering any RO stage within the BWRO plant. This option could provide better membrane performance and safer operation.
In an alternative embodiment, chemicals such as soda and /or lime may be added to the feed of the Electrocoagulation EC unit. This may enhance the separation process of dissolved contaminants as solids, which can then be treated further in similar ways to those proposed above.

Claims

Claims
1. A water treatment system, comprising: at least one reverse osmosis filter comprising an inlet, a reject outlet and a permeate outlet; at least one means for removing dissolved contaminants comprising an inlet, a reject outlet and a permeate outlet; and at least one solids removal unit comprising an inlet, a reject outlet and a permeate outlet; wherein the reject outlet from the at least one reverse osmosis filter is in fluid communication with the inlet of the at least one means for removing dissolved contaminants, and the permeate outlet from the at least one means for removing dissolved contaminants is in fluid communication with the inlet of the at least one solids removal unit.
2. A system according to Claim 1 , further comprising a further such reverse osmosis filter, wherein the permeate outlet of said solids removal unit is in fluid communication with the inlet of said further such reverse osmosis unit.
3. A system according to Claim 1 or 2, further comprising at least one nanofilter comprising an inlet, a reject outlet and a permeate outlet; wherein the reject outlet from the at least one reverse osmosis filter is in fluid communication with the inlet of the at least one nanofilter, and the reject outlet from the at least one nanofilter is in fluid communication with the inlet of the at least one means for removing dissolved contaminants.
4. A system according to Claim 3, wherein the permeate outlets from the at least one nanofilter and the at least one solids removal unit are in fluid communication.
5. A system according to Claim 4, when dependent on Claim 2, wherein said permeate outlets from the at least one nanofilter and the at least one solids removal unit are in fluid communication with the inlet of said further such reverse osmosis filter.
6. A system according to any of Claims 2 to 5, further comprising a solar pond, wherein the reject outlet of said further such reverse osmosis filter is in fluid communication with said solar pond.
7. A system according to any of Claims 2 to 6, wherein the reject outlet of said further such reverse osmosis filter is in fluid communication with a source water well.
8. A system according to any of Claims 3 to 7, further comprising a pump, wherein the permeate outlets from the at least one nanofilter and the at least one solids removal unit are in fluid communication with the inlet of said pump, and the outlet of said pump is in fluid communication with the inlet of said further such reverse osmosis filter.
9. A system according to any of Claims 3 to 8, wherein said nanofilter is adapted to provide at the permeate outlet 30% to 70% of the water entering the inlet of said nanofilter, preferably 40% to 60%, and more preferably 50%.
10. A system according to any of Claims 3 to 9, wherein said nanofilter is adapted to filter particles within the size range of 0.01 μm to 0.001 μm.
1 1. A system according to any of the preceding claims wherein said at least one means for removing dissolved contaminants comprises an electrocoagulation unit.
12. A system according to Claim 11 , wherein said electrocoagulation unit comprises at least one anode and cathode pair, and a DC power supply connected to said electrodes to generate polymeric hydroxides to enable coagulation of the contaminants.
13. A system according to Claim 12, wherein said electrodes are iron and aluminium.
14. A system according to Claim 11 , 12 or 13, wherein said electrocoagulation unit is adapted to generate gas via electrolysis to utlise buoyancy forces to remove contaminants.
15. A system according to any of the preceding claims, wherein said solids removal unit comprises sand filtration.
16. A system according to any of the preceding claims, wherein said solids removal unit comprises microfiltration.
17. A system according to any of the preceding claims, wherein said solids removal unit comprises ultrafiltration.
18. A system according to any of the preceding claims, wherein said solids removal unit comprises a rotary vacuum drum filter.
19. A system according to any of the preceding claims, wherein said solids removal unit comprises a mixing tank and a settling tank, adapted to utilise gravity separation, wherein said settling tank is larger than said mixing tank.
20. A system according to any of the preceding claims, wherein said means for removing dissolved contaminants comprises a chemical additives unit.
21. A system according to Claim 20, wherein said chemical additives unit is adapted to utilise lime and soda ash.
22. A method of treating water comprising: removing contaminants using a reverse osmosis filter; removing dissolved contaminants from the water; removing solid contaminants from the water; wherein the dissolved contaminants are removed from the reject water from the reverse osmosis filter, and the solid contaminants are removed from the permeate water subsequent to removing the dissolved contaminants.
23. A method according to Claim 22, further comprising removing further contaminants, from the permeate water subsequent to removing the solid contaminants, using a second such reverse osmosis filter.
24. A method according to Claim 22 or 23, further comprising removing further contaminants from the reject water from the first said reverse osmosis filter using at least one nanofilter, and subsequently removing dissolved contaminants from the reject water from said nanofilter.
25. A method according to Claim 24, further comprising mixing the permeate water from said nanofilter, and the permeate water after the removal of solid contaminants.
26. A method according to Claim 25, when dependent on Claim 23, further comprising removing further contaminants from said mixed water using said second such reverse osmosis filter.
27. A method according to any of Claims 23 to 26, further comprising treating the reject from said second reverse osmosis filter using a solar pond.
28. A method according to any of Claims 23 to 27, further comprising injecting the reject from said second reverse osmosis filter into a source water well.
29. A method according to any of Claims 22 to 28, wherein said dissolved contaminants are removed using an electrocoagulation unit.
30. A method according to Claim 29, wherein said electrocoagulation unit comprises at least one anode and cathode pair, and a DC power supply connected to said electrodes to generate polymeric hydroxides to enable coagulation of the contaminants.
31. A method according to Claim 29 or 30, wherein said electrocoagulation unit is adapted to generate gas via electrolysis to utlise buoyancy forces to remove contaminants.
32. A method according to any of Claims 22 to 31 , wherein said solid contaminants are removed using at least one of the following: sand filtration, microfiltration, ultrafiltration, a rotary vacuum drum filtration, and sedimentation.
33. A method according to any of Claims 22 to 32, wherein said dissolved contaminants are removed using chemical additives.
34. A method according to Claim 33, wherein said chemical additives are lime and soda ash.
35. A water treatment system, comprising: at least one nanofilter comprising an inlet, a reject outlet and a permeate outlet; means for feeding a proportion of the permeate outlet into said inlet; and means for placing said water treatment system in fluid communication with a water reverse osmosis treatment plant; wherein the inlet to the at least nanofilter is adapted to be placed in fluid communication with the reject outlet from the water reverse osmosis treatment plant, and the permeate outlet of said nanofilter is adapted to be placed in fluid communication with the water reverse osmosis treatment plant.
36. A system according to Claim 13, wherein said feeding means comprises at least one valve and a pump.
37. A system according to Claim 13 or 14, further comprising a pump in fluid communication with the reject from said water reverse osmosis treatment plant and said inlet of the nanofilter.
38. A system according to Claim 13, 14 or 15, wherein the permeate outlet of said nanofilter is adapted to be placed in fluid communication with the inlet of a first stage of the water reverse osmosis treatment plant.
39. A system according to Claim 13, 14 or 15, wherein the permeate outlet of said nanofilter is adapted to be placed in fluid communication with the inlet of a second stage of the water reverse osmosis treatment plant.
40. A system according to Claim 13, 14 or 15, wherein the permeate outlet of said nanofilter is adapted to be placed in fluid communication with the permeate outlet of the water reverse osmosis treatment plant.
41. A method of treating water, comprising: nanofiltering the water to produce reject water and permeate water; feeding a proportion of the permeate water into the inlet of the nanofilter; and placing said water treatment system in fluid communication with a water reverse osmosis treatment plant; wherein the inlet to the at least nanofilter is adapted to be placed in fluid communication with the reject outlet from the water reverse osmosis treatment plant, and the permeate outlet of said nanofilter is adapted to be placed in fluid communication with the water reverse osmosis treatment plant.
42. A method according to Claim 41 , wherein said feeding uses at least one valve and a pump.
43. A method according to Claim 41 or 42, wherein the permeate water of said nanofilter is mixed with the feed water to a first stage of the water reverse osmosis treatment plant.
44. A method according to Claim 41 , 42 or 43, wherein the permeate water of said nanofilter is mixed with the feed water to a second stage of the water reverse osmosis treatment plant.
45. A method according to any of Claims 41 to 44, wherein the permeate water of said nanofilter is mixed with the permeate water of the water reverse osmosis treatment plant.
46. A water treatment system as substantially herein descirbed with reference to Figure 2, 3, 4, 5 or 6.
47. A water treatment method as substantially herein described with reference to Figure 2, 3, 4, 5 or 6.
48. A system according to Claim 11 , 12, 13 or 14, or any of claims 15 to 19 or 36 to 40 when dependent on any of claims 1 1 , 12, 13 or 14, wherein said electrocoagulation unit is adapted to receive chemicals such as soda and /or lime as a feed.
49. A method according to Claim 29, 30 or 31 , further comprising the addition of chemicals such as chemicals such as soda and /or lime to the feed of the electrocoagulation unit.
EP20100721545 2009-04-21 2010-04-21 Water treatment Withdrawn EP2421798A2 (en)

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