An effective scale control program for seawater RO is widely recognized as an important factor in... more An effective scale control program for seawater RO is widely recognized as an important factor in ensuring trouble free and cost effective operation. This is especially important under the high feed water pH and temperature conditions found in Southern Europe and Middle East. In addition, regulatory issues concerning maximum acceptable boron levels in drinking and irrigation water necessitate the growing need to operate plants at higher feed water pH. Operating at increased pH increases boron rejection but also increases the scaling tendencies of the water. This can lead to calcium carbonate and magnesium hydroxide precipitation in the membranes. A complete scale control program needs to control calcite and brucite saturation at the maximum operating reject pH and temperature. Antiscalant chemistry, optimum dose rate as well as accurate monitoring and control of the scale inhibitor are key factors in long-term cost effective " scale free " operation. This paper details the operating strategies and scale control issues related to both single and two pass seawater RO plants operating at elevated feed water pH and temperature.
Reverse Osmosis is finding increasing use for the treatment of municipal and industrial wastewate... more Reverse Osmosis is finding increasing use for the treatment of municipal and industrial wastewaters due to the growing demand for high quality water in large urban areas. The growing success of membranes in this application is related to improved process designs and improved membrane products. Key factors which have been determined to result in successful operation of large-scale plants will be discussed. Factors which play a key role in the use of RO membranes include ultra or microfiltration pretreatment, low fouling membranes, flux rate, recovery and control of fouling and scaling. In particular, high flux rates can be used when UF or MF pretreatment is used. These technologies remove most of the suspended particles that would normally cause heavy fouling of lead elements. Typically, fluxes in the range of 17-21 lmh lead to cleaning frequencies in the range of 3-4 months. By combining the use of membrane pretreatment and chloramination of the feed water through chlorine addition, two of the primary sources of RO membrane fouling can be controlled. The use of chloramine has become a proven means to control biofouling in a membrane for wastewater applications. The other significant problems for RO membranes result from organics fouling by dissolved organics and scaling due to saturation of marginally soluble salts. The former can be a significant problem for membranes, due to the strong attraction forces. To some extent, these can be mitigated by making the membrane surface more hydrophilic or changing the charge of the membrane surface. To minimize fouling, many plants are turning to low fouling membranes. Extensive studies have demonstrated that the membrane surface is hydrophilic, neutrally charged over a broad pH range, and more resistant to organic adsorption. Also, an analysis of the potential scaling issues will be reviewed. In particular, calcium phosphate has been found to be one of the key scalants that will limit RO system recovery rate. Calcium phosphate concentrations can reach high values in many wastewaters, and scaling of this compound is not often modeled in most RO projection software. Various process options will be presented to evaluate the most economic means of avoiding phosphate scaling. Finally, data from major RO wastewater treatment plants will be presented to show how the RO membranes operate under actual conditions, utilizing many of these design features. Long-term data from the 2.6 mgd Bedok demonstration Plant demonstrate that the RO membranes operate consistently on wastewater. Experiences from the 8.5 mgd (32,000 m3/day) Bedok and 10.5 mgd (40,000 m3/day) Kranji plants will also be presented. These large plants started operation in the fall of 2002 and have demonstrated an effective means to reclaim high quality water from difficult source waters, such as municipal wastewaters.
This review for literature published in 2009 contains information related to membrane processes f... more This review for literature published in 2009 contains information related to membrane processes for municipal and industrial applications. This review is a subsection of the Treatment Systems section of the annual Water Environment Federation literature review and covers the following topics: pretreatment, membrane bioreactor (MBR) configuration, design, nutrient removal, operation, industrial treatment, fixed film and anaerobic membrane systems, reuse, microconstituents removal, membrane technology advances, membrane fouling, and modeling. ———————
The effects of cyclic changes in feed water temperature and pressure on permeate flux, solute rej... more The effects of cyclic changes in feed water temperature and pressure on permeate flux, solute rejection, and compaction in spiral wound composite polyamide seawater reverse osmosis membranes were examined with pure water and 4% NaCl solutions. A membrane permeability hysteresis or memory effect due to the up and down temperature and pressure sequences was only seen with the saline water
Boron contamination of permeate in seawater RO desalination is commonly prevented by increase of ... more Boron contamination of permeate in seawater RO desalination is commonly prevented by increase of the concentrate pH level in a rather elaborate multi-pass processing system. The reason for this cumbersome processing is the need to control the scale precipitation tendency induced by the pH increase. The lack of sufficient information on the scaling propensity of seawater at various supersaturation levels
Induction time data in CaCO3 precipitation were determined by an electrochemical technique. The a... more Induction time data in CaCO3 precipitation were determined by an electrochemical technique. The alkaline environment surrounding the cathode surface promotes CaCO3 precipitation. The data were measured using simulated sea water solutions without the interfering presence of magnesium ions. The effect of current intensity on induction time was successfully correlated by a modified form of the classical nucleation equation. Data indicating
It is sometimes necessary to dose into a desalination feed stream a caustic solution to achieve a... more It is sometimes necessary to dose into a desalination feed stream a caustic solution to achieve a controlled pH increase, as, for example, in the application of boron suppression measures. To restrict the size of the caustic feed system, the NaOH is dosed from a high concentration solution. The solution is injected at the center of the raw water feed
RO seawater systems that operate on a surface feed water originating from an open intake source r... more RO seawater systems that operate on a surface feed water originating from an open intake source require an extensive pretreatment process in order to control membrane fouling. Considerations of long-term performance stability lead to a design concept of operation at a low permeate ...
An effective scale control program for seawater RO is widely recognized as an important factor in... more An effective scale control program for seawater RO is widely recognized as an important factor in ensuring trouble free and cost effective operation. This is especially important under the high feed water pH and temperature conditions found in Southern Europe and Middle East. In addition, regulatory issues concerning maximum acceptable boron levels in drinking and irrigation water necessitate the growing need to operate plants at higher feed water pH. Operating at increased pH increases boron rejection but also increases the scaling tendencies of the water. This can lead to calcium carbonate and magnesium hydroxide precipitation in the membranes. A complete scale control program needs to control calcite and brucite saturation at the maximum operating reject pH and temperature. Antiscalant chemistry, optimum dose rate as well as accurate monitoring and control of the scale inhibitor are key factors in long-term cost effective " scale free " operation. This paper details the operating strategies and scale control issues related to both single and two pass seawater RO plants operating at elevated feed water pH and temperature.
Reverse Osmosis is finding increasing use for the treatment of municipal and industrial wastewate... more Reverse Osmosis is finding increasing use for the treatment of municipal and industrial wastewaters due to the growing demand for high quality water in large urban areas. The growing success of membranes in this application is related to improved process designs and improved membrane products. Key factors which have been determined to result in successful operation of large-scale plants will be discussed. Factors which play a key role in the use of RO membranes include ultra or microfiltration pretreatment, low fouling membranes, flux rate, recovery and control of fouling and scaling. In particular, high flux rates can be used when UF or MF pretreatment is used. These technologies remove most of the suspended particles that would normally cause heavy fouling of lead elements. Typically, fluxes in the range of 17-21 lmh lead to cleaning frequencies in the range of 3-4 months. By combining the use of membrane pretreatment and chloramination of the feed water through chlorine addition, two of the primary sources of RO membrane fouling can be controlled. The use of chloramine has become a proven means to control biofouling in a membrane for wastewater applications. The other significant problems for RO membranes result from organics fouling by dissolved organics and scaling due to saturation of marginally soluble salts. The former can be a significant problem for membranes, due to the strong attraction forces. To some extent, these can be mitigated by making the membrane surface more hydrophilic or changing the charge of the membrane surface. To minimize fouling, many plants are turning to low fouling membranes. Extensive studies have demonstrated that the membrane surface is hydrophilic, neutrally charged over a broad pH range, and more resistant to organic adsorption. Also, an analysis of the potential scaling issues will be reviewed. In particular, calcium phosphate has been found to be one of the key scalants that will limit RO system recovery rate. Calcium phosphate concentrations can reach high values in many wastewaters, and scaling of this compound is not often modeled in most RO projection software. Various process options will be presented to evaluate the most economic means of avoiding phosphate scaling. Finally, data from major RO wastewater treatment plants will be presented to show how the RO membranes operate under actual conditions, utilizing many of these design features. Long-term data from the 2.6 mgd Bedok demonstration Plant demonstrate that the RO membranes operate consistently on wastewater. Experiences from the 8.5 mgd (32,000 m3/day) Bedok and 10.5 mgd (40,000 m3/day) Kranji plants will also be presented. These large plants started operation in the fall of 2002 and have demonstrated an effective means to reclaim high quality water from difficult source waters, such as municipal wastewaters.
This review for literature published in 2009 contains information related to membrane processes f... more This review for literature published in 2009 contains information related to membrane processes for municipal and industrial applications. This review is a subsection of the Treatment Systems section of the annual Water Environment Federation literature review and covers the following topics: pretreatment, membrane bioreactor (MBR) configuration, design, nutrient removal, operation, industrial treatment, fixed film and anaerobic membrane systems, reuse, microconstituents removal, membrane technology advances, membrane fouling, and modeling. ———————
The effects of cyclic changes in feed water temperature and pressure on permeate flux, solute rej... more The effects of cyclic changes in feed water temperature and pressure on permeate flux, solute rejection, and compaction in spiral wound composite polyamide seawater reverse osmosis membranes were examined with pure water and 4% NaCl solutions. A membrane permeability hysteresis or memory effect due to the up and down temperature and pressure sequences was only seen with the saline water
Boron contamination of permeate in seawater RO desalination is commonly prevented by increase of ... more Boron contamination of permeate in seawater RO desalination is commonly prevented by increase of the concentrate pH level in a rather elaborate multi-pass processing system. The reason for this cumbersome processing is the need to control the scale precipitation tendency induced by the pH increase. The lack of sufficient information on the scaling propensity of seawater at various supersaturation levels
Induction time data in CaCO3 precipitation were determined by an electrochemical technique. The a... more Induction time data in CaCO3 precipitation were determined by an electrochemical technique. The alkaline environment surrounding the cathode surface promotes CaCO3 precipitation. The data were measured using simulated sea water solutions without the interfering presence of magnesium ions. The effect of current intensity on induction time was successfully correlated by a modified form of the classical nucleation equation. Data indicating
It is sometimes necessary to dose into a desalination feed stream a caustic solution to achieve a... more It is sometimes necessary to dose into a desalination feed stream a caustic solution to achieve a controlled pH increase, as, for example, in the application of boron suppression measures. To restrict the size of the caustic feed system, the NaOH is dosed from a high concentration solution. The solution is injected at the center of the raw water feed
RO seawater systems that operate on a surface feed water originating from an open intake source r... more RO seawater systems that operate on a surface feed water originating from an open intake source require an extensive pretreatment process in order to control membrane fouling. Considerations of long-term performance stability lead to a design concept of operation at a low permeate ...
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