Markus Busch

How different is the composition of the fouling layer of wastewater reuse and seawater desalination RO membranes

To study the effect of water quality and operating parameters on membrane fouling, a comparative analysis of wastewater (WW) and seawater (SW) fouled reverse osmosis (RO) membranes was conducted. Membranes were harvested from SWRO and WWRO pilot plants located in Vilaseca (East Spain), both using ultrafiltration as pretreatment. The SWRO unit was fed with Mediterranean seawater and the WWRO unit was operated using secondary effluent collected from the municipal wastewater treatment plant. Lead and terminal SWRO and WWRO modules were autopsied after five months and three months of operation, respectively. Ultrastructural, chemical, and microbiological analyses of the fouling layers were performed. Results showed that the WWRO train had mainly bio/organic fouling at the lead position element and inorganic fouling at terminal position element, whereas SWRO train had bio/organic fouling at both end position elements. In the case of WWRO membranes, Betaproteobacteria was the major colonizing species; while Ca, S, and P were the major present inorganic elements. The microbial population of SWRO membranes was mainly represented by Alpha and Gammaproteobacteria. Ca, Fe, and S were the main identified inorganic elements of the fouling layer of SWRO membranes. These results confirmed that the RO fouling layer composition is strongly impacted by the source water quality.

Backwashing pressurized ultrafiltration using reverse osmosis brine in seawater desalination and its potential costs savings

This paper discusses the feasibility of using reverse osmosis concentrate to backwash ultrafiltration membranes in the seawater reverse osmosis desalination space. Brine is produced through DOW FILMTEC™ reverse osmosis elements and it backwashed every 90 min to DOW™ ultrafiltration membranes. A side-by-side validation is done for 15 d using two parallel ultrafiltration and reverse osmosis integrated systems. One line uses brine for backwashing, while the other uses conventional filtrated water. The optimization is proven to have the same cleaning efficiency than the conventional backwashing methods and no precipitation is observed in the fibers. An additional validation period that uses reverse osmosis brine during backwashes and only two backwash steps is also carried out successfully. These steps are the previously identified backwash top with air scour and forward flush. Fibers also show an excellent integrity after the whole experimental period. A model is built in order to analyze the backwash efficiency of the optimized conditions and the transmembrane pressure increases during the filtration cycle. The results show the same fouling tendency for the line operating with brine and the line operating with filtrated water. The efficiency of the ultrafiltration process is improved from 88 to 98% thanks to this optimization together with the previous researches. This represents filtrating 96 min extra per day and a reduction of 100% in the filtrated water used during backwashes. The chemical equivalent concentration is also optimized from 0.28 to 0.06 mg/L NaClO thanks to the adjustment of the chemically enhanced backwash frequency. This accounts for a 7.1% savings in the ultrafiltration step and for a 1.2% savings in the whole desalination process.

Optimizing seawater operating protocols for pressurized ultrafiltration based on advanced cleaning research

Abstract This paper is part of a global research project conducted by Dow Water & Process Solutions to optimize the efficiency of ultrafiltration processes. After an initial identification of the backwash as the key opportunity to increase the efficiency of the process, a study based on its optimization is developed. Main emphasis is given to the sequence and subsequent number of steps involved in the backwash. The ultimate goal is thus to increase the availability and recovery of the process while still attaining a high cleaning effect during the backwash. This optimization is done through the realization of various experiments using DOW™ Ultrafiltration SFP-2660 outside-in polyvinylidene difluoride (PVDF) membranes following an exhaustively planned factorial design of experiments. The factors being assessed are the steps normally performed during a backwash. These are the air scour (AS/D), the draining (D), the backwash top (BWT) with or without air scour, the backwash bottom (BWB) and the forward flush...