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

• Published in: Desalination Vol. 74; pp. 51 - 67
• Main Authors: Applegate, Lynn E., Erkenbrecher, Carl W., Winters, Harvey
• Format: Journal Article
• Language: English
• Published: Elsevier B.V 1989
• ISSN: 0011-9164; 1873-4464
• DOI: 10.1016/0011-9164(89)85042-8

Surface seawater RO plant using Permasep R 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.