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The use of seawater treatment and injection to increase oil recovery is extensively practiced worldwide. Seawater can be treated at different levels to provide the required water quality compatible with the reservoir for pressure maintenance. In this respect, membrane technologies including ultrafiltration, nanofiltration and reverse osmosis can be used for fines, sulphates and salt removal respectively. The use of subsea treatment systems built on these filtration technologies is proposed as an alternative to bulky and heavy conventional topside systems. Subsea systems can eliminate the need for expensive floating facilities that often have space and weight restrictions. For a reliable operation of a subsea system it is required to verify the filtration membranes performance at water depths that can reach 3000 m (300 bar and 4°C). Laboratory tests of hollow fiber ultrafiltration (UF), spiral-wound nanofiltration (NF) and spiral-wound reverse osmosis (RO) membrane modules were performed at simulated deep-water conditions to assess their integrity and performance. A high-pressure dynamic testing system, with precision temperature and pressure control was built to enable accurate measurements. Short and long-term dynamic tests, including pressure cycling fatigue tests, were performed by operating membrane modules at the simulated subsea environment (300 bar and 4°C). Static tests were also performed to assess the impact of deep subsea conditions on membrane module structural integrity and membrane physical properties. The results indicate that the tested UF, NF, and RO membrane modules are promising for deep subsea applications. The mechanical integrity and membrane module performance were maintained within the predefined acceptable limits at both static and dynamic test conditions. These promising results are a big step towards the technical feasibility of using membrane technology for subsea seawater injection systems.

In order to demonstrate the impact of ultrafiltration (UF) on the fouling rate and cleaning intervals of nanofiltration (NF) membranes in seawater sulfate removal application, GE conducted a two-year long demonstration in Singapore. GE's ZW700B UF and SWSR NF membranes were used for this study. The evaluation was conducted in two phases. During Phase 1, pretreated seawater with SDI between 2.5 and 4.5 was used as feed. During Phase 2, water was pre-treated with the ZW700B UF membrane to yield an SDI of less than 2, before being fed to the NF sulfate removal unit. In Phase 1, the SWSR-440-ft2 NF membrane showed >99.8% sulfate removal. The membrane also showed very good resistance to fouling; validating the low-fouling properties of the SWSR membrane due to its unique three-layer construction and low surface roughness (typically 10 nm or lower). When the feed water SDI increased to 4, the feed pressure and pressure drop increased but the fouling rate remained low. The unit only needed one chemical cleaning after six months of operation. As expected, chemical cleaning at high pH temporarily reduced the sulfate rejection to 99.7%; but sulfate rejection recovered to 99.8% within two weeks of operation. The temporary increase can be explained by opening of the NF membrane pores due to high pH. In Phase 2, UF pre-treatment reduced the average SDI to 1.7 and the feed particle count by more than 96%. The NF sulfate removal unit operated more than three months without any noticeable fouling; fouling rate remained low even when the recovery was increased to 80%. Sulfate rejection remained at 99.7% to 99.8%. These results confirm that ZW700B UF pretreatment will reduce NF cleaning frequency and increase the life time of NF membranes. Lower cleaning frequency will lead to lower chemical consumption, lower chemical cost and increased system availability. UF pretreatment will also allow for higher NF Flux and recovery which will reduce the footprint and weight of SRU systems. GE's ZW700B UF system did not show any decrease in membrane permeability during the duration of the pilot. Membranes were cleaned and recovered by conducting regular backwashes as well as two chemically enhanced backwash cycles at different time intervals.

The MBR technology has evolved rapidly over the past two decades with significant gains in performance and reliability, and reductions of costs. While the MBR process is recognized for providing superior effluent quality in a small footprint, it carries additional operating costs associated with the membrane system, including the periodic replacement of the membranes which have a life shorter than the civil components of the plant. The methodology used to determine membrane life was to analyze the entire data set of ZeeWeed MBR membranes shipped to North American sites over the period of 15 years since their commercial introduction. This analysis shows that membrane life for the current generation product should be greater than 10 years. The analysis also considered the various mechanisms of aging and end-of-life triggers. It was determined that a slow increase in operating pressure and the need for more frequent chemical cleaning should be the dominant end-of-life trigger with the current product. The most effective method for membrane replacement is a planned campaign where a fixed portion of the plant, typically dictated by the membrane train configuration, is replaced on an annual basis in the period of time around the anticipated life of the membranes.

The effect of chlorine dioxide ( ClO2 ) pretreatment on subsequent treatment processes (coagulation, flocculation, sedimentation, filtration, and ozonation) was studied at pilot-scale at the Upper San Leandro Water Treatment Plant near Oakland, Calif. Potential impacts of ClO2 on the distribution system were also studied at bench scale using simulated distribution system (SDS) tests. Pilot trials were conducted with one train operating without ClO2 pretreatment (Train 1) and the other with a ClO2 dose of between 0.6 and 1.0 mg∕L (Train 2). Comparison between Trains 1 and 2 showed that ClO2 pretreatment resulted in a 0.1–0.2 NTU decrease in settled water turbidity when compared to no pretreatment. ClO2 pretreatment also resulted in a small (0.01 cm−1 ) decrease in ultraviolet absorbance at 254 nm . Following sedimentation, about 60% of the applied ClO2 formed chlorite ( ClO2− ) , with 10–20% forming chlorate ( ClO3− ) . Ozonation immediately converted all residual ClO2 and ClO2− to ClO3− . There was no sig...

The purpose of this study was to quantify the potential level of protection that secondary disinfection may provide in response to an intrusion event. Although several uncertainties exist regarding intrusion events, this study presents an analysis of the inactivation provided by disinfectant residuals by using a distribution system model, inactivation and disinfectant decay models, and conservative assumptions based on available data. A variety of conditions were modeled, including a range of water quality parameters (pH, temperature); inactivation of two microorganisms, Giardia and E. coli O157:H7; and intrusion water dilution ratios. Despite the assumptions inherent in the model, several generalizations were derived from the study. A free chlorine residual of 0.5 mg∕L may be insufficient to provide adequate control of disinfectant-resistant Giardia even at low pH (6.5) and high temperature (25°C) conditions that enhance chlorine effectiveness. For E. coli, an organism of “average” disinfectant resistanc...

The overall objective of this study was to investigate the impact of blending membrane-treated water treatment plant (WTP) residuals with plant-filtered water on finished water quality in terms of biostability and disinfectant by-product (DBP) formation. Filter backwash water (FBWW) was treated with a pilot-scale ultrafiltration (UF) membrane to produce permeate that was blended with plant-finished water. The batch studies involved storing samples for a specified time with a disinfectant residual to simulate residence time in the distribution system. Both chlorinated and non-chlorinated FBWW streams were evaluated, and the experimental design incorporated free chlorine, monochloramine, and chlorine dioxide in parallel to a model system that did not receive a disinfectant dose. The results of the study found that blending 10% UF-treated FBWW with plant-filtered water did not have an impact on water biostability as monitored with heterotrophic plate counts (HPCs) or DBP concentrations as monitored by TTHM and HAA5 concentrations. However, the presence of preformed THM and HAA species found in chlorinated FBWW streams may result in higher levels of initial DBP concentrations in blended water matrices, and could have a significant impact on finished water quality in terms of meeting specific DBP guidelines or regulations.

Excessive algal growth in drinking water sources like lakes and reservoirs is responsible for filter-clogging, undesirable taste and odor, disinfection-by-product formation and toxin generation. Although various methods are currently being used to control algal bloom, their successes are limited. Some water utilities routinely use copper sulfate to control excessive algal growth. But there is a growing concern against its use mainly because it is non-specific to target algae and kills many non-target species. In this study, the scope of using UV-radiation to control algal growth was assessed using Microcystis aeruginosa as test species. A UV-dose of 75 mW s cm(-2) was found to be lethal to M. aeruginosa. A smaller dose of 37 mW s cm(-2) prevented growth for about 7 days. It was found that UV-radiation may increase the specific gravity of the cells and thus may adversely affect the ability of the cells to remain in suspension. Three days after a UV-dose of 75 mW s cm(-2), almost all the cells settled to the bottom of the incubation tubes, whereas all the unirradiated cells remained in suspension. It was also observed that UV-radiation on algal extracellular products has a significant residual effect and can contribute to algal growth control. The extent of residual effect depends on the UV-dose and can continue even for 7 days. UV-radiation was found to produce H2O2 in the microM level concentration. But at such level, H2O2 itself is not likely to cause the residual effect that was found in this study.