Membrane biofouling is a common occurrence in water treatment plants that utilize reverse osmosis (RO). As bacteria and biofilm material build up on the membrane surface, it becomes more difficult for clean water to permeate through the membrane, and more pressure is required to produce the same amount of water. When pressures become critically high, membranes must be cleaned. This process is expensive in terms of chemical cost, labor, and downtime. Even after membranes have been cleaned, they can re-foul quickly if the cleaning did not effectively remove the biofilm. The water treatment plant in Dunedin, FL, which uses RO for treating groundwater, has experienced membrane biofouling since it began operation in 1992. Without the means to systematically evaluate a multitude of cleaning strategies on the bench scale, cleaning optimization must be conducted on the production skid level, which restricts the evaluation of alternative protocols. This problem is typical for many RO plants. The objectives of this project are: (1) using a multi-level and systematic approach, develop cleaning strategies for biofouled membranes that will lead to improved cleaning and decreased operational costs; (2) develop other cleaning strategies that will add to the scientific knowledge base; (3) quantify the effects of improved protocols; and (4) determine the policy implications of developed protocols in terms of cost suitability to Dunedin and elsewhere in Florida. This project consists of three phases, with phases progressively more similar to the water production environment. In the first phase, a series of bench tests were performed in the laboratory. Fouled membrane swatches were soaked and agitated in different cleaning solutions for different lengths of time, at different temperatures and pH. Protein and carbohydrate assays were then performed on both the cleaning solution and the membrane swatch to determine which conditions yield most complete removal of protein and carbohydrate from the membrane surface. Results indicate that carbohydrate removal does not appear to depend strongly on pH or temperature. Protein removal increases with increasing pH and is slightly greater at higher temperatures. The second phase of testing employed a 4"x6" stainless steel flat-sheet module in which cleanings were performed under different conditions to document corresponding changes in water flux and salt rejection. Operational parameters were based on pertinent literature and optimization results from Phase 1. Results indicate that water flux increases in response to cleaning at increasing pHs and increasing temperatures with best performances occuring after 30 minutes of cleaning. Salt rejection appears to decrease with pH. The most effective cleaning protocols, determined through trials in Phases 1 and 2, were put to the test again in Phase 3 where cleanings were performed on a specially constructed single-element cleaning system (for 8.5" x 40" elements), designed to clean a membrane element in isolation. This phase also served as final verification of new cleaning protocols before implementation on the production scale. Results from this phase were inconclusive due to mechanical problems. A multi-level, systematic cleaning evaluation leads to better understanding of the dependence of biofilm material removal and membrane performance on critical factors such as temperature, pH, time of cleaning, and chemical dose, which results in improved cleaning protocols and ultimately cost savings to RO water utilities such as Dunedin.

Yes / Reverse Osmosis (RO) process accounts for 80% of the world desalination capacity. Apparently, there is a rapid increase of deploying the RO process in seawater desalination due to its high efficiency in removing salts at a reduced energy consumption compared to thermal desalination technologies such as MSF and MED. Among different types of membranes, spiral would membranes is one of the most used. However, there is no in-depth study on the performance of spiral wound membranes in terms of salt rejection, water quality, water recovery and specific energy consumption subject to wide range of seawater salinity, temperature, feed flowrate and pressure using a high fidelity but a realistic process model which is therefore is the focus of this study. The membrane is subjected to conditions within the manufacturer's recommendations. The outcome of this research will certainly help the designers selecting optimum RO network configuration for a large-scale desalination process.

Yes / Reverse osmosis (RO) is becoming one of the most promising technologies used in wastewater treatment because it offers high rate of contaminant rejection and lower energy consumption in comparison with other thermal treatment processes. Earlier research by the same authors in respect of a distributed one-dimensional mathematical model for a single spiral-wound RO membrane module based on the solution-diffusion model has been used in this paper to simulate the rejection of NDMA (N-nitrosodimethylamine) from wastewater in a series of seven RO elements full-scale treatment plant. Firstly, the applicability of this model has been evaluated using a simulation study and the results have been compared against experimental data gathered from the literature for a given plant. Secondly, further simulation and analysis studies are carried out to assess the performance of the plant for NDMA rejection and recovery rate under different operating conditions of feed pressure, flow rate, and concentration. For the studied RO configuration, it is concluded that a maximum of 55.1% NDMA rejection can be achieved, which confirms the remaining issue of lower NDMA rejection.

Syftet med den här studien var att undersöka en alternativ slamningsreducerande teknik till spolning, som effektivt kan ta bort biologisk påväxt. Ultraljud undersöktes som en möjlig metod för att ta bort igenslamningen från omvänd osmos med ett spirallindat membran. Tidigare forskning har föreslagit att ultraljud skulle kunna vara effektivt på platta membran men inte på spirallindade membran, på grund av packningsdensiteten som spirallindan medför. Därför genomfördes inom denna studie försök med spirallindade membran och ultraljud, för att få en förståelse av dess effekter inom det spirallindade membranet. För det första undersöktes tidsberoendet av ultraljud, vilket visade liknande resultat som tidigare forskning, att ultraljudet uppnådde effekt inom några minuter. För det andra behandlades två membran en gång om dagen under 12 dagar, med undantag för dag 6 och 7. Ett behandlades med ultraljud och ett med spolning, och den mikrobiologiska kontamineringen i permeatet analyserades sedan. Det ultraljudsbehandlade membranet producerade mindre kontaminering under de 12 dagarna. Det krävs dock fler experiment och analyser för att bekräfta detta, eftersom tidsbegränsningar inte möjliggjorde repetitioner. En ekonomisk utvärdering genomfördes också för att undersöka möjligheten att implementera ultraljud i kommersiell skala. Den ekonomiska aspekten är en avvägning mellan vattenkostnad och energikostnad, som är beroende av geografiskt läge. Överlag indikerar resultaten att det sparade vattnet kostar mer än den energi som krävs, vilket är fördelaktigt för implementering av ultraljudsbehandling. Sammanfattningsvis visade ultraljudsbehandlingen bättre resultat än spolning inom några minuter, och hade även en ekonomisk fördel, men kostnaden för energi till vatten är beroende av geografisk plats. / The purpose of this study was to investigate an alternative fouling mitigation technique to flushing, that can efficiently remove biological fouling. Ultrasound was investigated as a possible method of removing fouling from a reverse osmosis spiral wound membrane. Previous research had suggested ultrasound to be efficient on flat sheet membranes but not on spiral wound membranes, due to the packing density. Therefore, this study conducted experiments on spiral wound membranes with ultrasound, as to get an understanding of its effects within the spiral wound membrane. Firstly, the time dependency of ultrasound was investigated, and showed similar results to that of previous research, that the ultrasound was efficient within a matter of minutes. Secondly, two membranes were subject to treatment once a day over the span of 12 days, with an exception for days 6 and 7. One was treated with ultrasound and one with flushing, and the microbiological contamination in the permeate was then analysed. The ultrasonically treated membrane produced less contamination throughout the 12 days. However, more experiments and analysis would be required to confirm this, as time constraints did not allow for repetitions. An economic assessment was also performed, as to evaluate the feasibility implementing ultrasound on a commercial scale. This is a weigh-off between water cost and energy cost, which is dependent on geographical location. Overall, the results indicate that the water saved costs more than the energy required though, which is favourable for the implementation of ultrasonic treatment. To conclude, the ultrasonic treatment showed better results than flushing within a matter of minutes, and also economically had an advantage but the cost of energy to water is relative to geographical location.