Lynn E. Applegate

New chloroamine process to control aftergrowth and biofouling in permasepR B-10 RO surface seawater plants

Abstract Surface seawater RO plant using PermasepR B-10 permeators typically use chlorination-dechlorination in the pretreatment system to control biological activity. For such plants, bacterial aftergrowth and biofouling in the B-10 permeators can occur when the water temperature rises above 25°C. The bacterial aftergrowth can be significant, requiring frequent disinfection and cleaning of the permeators which reduces the efficiency to the RO plant. Using bacteria isolated from Middle East B-10 RO plants, aftergrowth in a model seawater system was extensively studied over a pH range of 6 to 8 and a temperature range of 150° to 35°C. Both planktonic (growth in solution) and periphytic (growth on surfaces) studies clearly showed that the degradation of humic acid (as well as other organics) by chloride accelerated aftergrowth. The bacterial aftergrowth was influenced by pH and temperature and was directly proportional to the availability of assimilable organic compounds. Chlorine degradation of humic acid in seawater produced these assimilabl organic compounds which led to bacterial aftergrowth and biofouling. The degree of humic acid degradation by chlorine was dependent on pH, temperature and the concentration of chlorine. Chloramine, a disinfectant which was generated in situ, was extensively examined as an alternative to chlorine. Chloramine was a better disinfectant and did not degrade humic acid. In addtion, significantly less aftergrowth was observed in the chloramine process (chloramine followed by neutralization with sodium bisulfite). B-10 permeators were found to be completely compatible with the chloramine process. Even brief exposure of B-10 permeators to chloramine did not significantly affect the Ro performance. The chloramine process is a significant discovery that should control biofouling in seawater RO plants.

Monitoring and control of biological activity in Permasep® seawater RO plants

Abstract For seawater RO plants, biological activity is dependent on site-specific factors such as temperature, organic and inorganic nutrients, pollution and surface water runoff. These site-specific factors are discussed along with the effect of biofouling (accumulation of slime and biomass) on RO performance, proper monitoring techniques for biological activity, pretreatment of source water to control biological fouling, cleaning to remove slime and biomass and procedures for proper storage of RO plants during shutdown to prevent biofouling. Microbiological analyses are used to measure the biological activity. Although numerous microbiological techniques are available for the analysis of water and wastewater, it is critical that the appropriate ones be used for seawater. Clearly, direct microscopy is the best method to measure the biological activity. Routine monitoring of the biological activity must be performed to determine the efficacy of the pretreatment system and to give early indications of any biofouling in the B-10 permeators. Based on the data obtained from routine monitoring, value judgements can be made with respect to operational changes needed in the pretreatment and the need to disinfect and clean the B-10 permeators. The biological activity in Permasep® B-10 seawater permeators can be controlled by using proper precautions, the proper pretreatment of the source water and adherence to proper operating procedures. Control of the biological activity in Permasep® B-10 seawater RO plants will significantly enhance long-term successful performance of the permeators.

The Phenomenological Characterization of DP-1 Membranes

During the past few years, great interest and active research have been directed to desalination of brackish water and seawater via reverse osmosis. Until recently cellulose acetate membranes were the only practical desalinating membranes developed; however, with the discovery of permselective, aromatic, nitrogen-containing polymeric membranes by Richter and Hoehn[1], a whole new class of practical reverse osmotic membranes is available. These new membranes are superior to cellulose acetate membranes with respect to their permeation characteristics and polymer properties.