Reducing membrane fouling through molecular microbiology analysis & decision support systems.

Biofouling of membranes presents one of the greatest operational challenges to water treatment and reuse. This paper will centre on a case study of a membrane treatment application at a rural water authority in the state of Louisiana, USA. The water that was supplied to residents had traditionally carried a high amount of organic material and color. In the past, organics were oxidized and broken down by chlorination prior to passing through prefilters and then a set of membrane filters. However, this practice resulted in the formation of disinfection by-products (DBPs) such as Trihalomethanes (THMs) and Haloacidic Acids (HAAs). The utility therefore sought to remove pre-chlorination but complete removal of pre-oxidation resulted in severe membrane fouling and eventual failure.

This paper will demonstrate how proactive biological monitoring using 2nd Generation ATP (Adenosine Triphosphate) testing was able to guide mitigation activities and optimize several design modifications to provide improved plant operation and product water quality. The information provided allowed operations staff to diagnose the fouling issue as a biological problem and subsequently optimize pre-treatment, cleaning, and membrane system configuration. To date, the results of these modifications have included far lower microbial content in treated water, enhanced biostability resulting in the ability to maintain chlorine residual for a longer period, and thousands of dollars per month in electricity savings due to reduced fouling and the head loss that occurs across fouled membranes. The paper will also present process control practices including a discussion of decision support systems including the Membrane Biofouling Index (MBI).