Microbial fouling of reverse-osmosis membranes used in advanced wastewater treatment technology: chemical, bacteriological, and ultrastructural analyses

Abstract

Biofouling of reverse-osmosis membranes was investigated at an advanced wastewater treatment facility. Cellulose diacetate membranes operated for .apprx. 4000 h became uniformly coated with a mucilaginous fouling layer. The fouling material was .apprx. 93% water by weight; .apprx. 90% of the dehydrated residue was organic in composition. Ca, P, S and Cl were the major inorganic constituents detected. Protein and carbohydrate represented as much as 30 and 17%, respectively, of the dry weight of the biofilm. Bacteriological plate counts indicated up to 5.6 .times. 106 colony-forming units/cm2 of membrane surface. Accumulation of [3H]glucose in the biofilm and measurement of ATP indicated that the fouling bacteria were metabolically active in situ. The genus Acinetobacter and the Flavobacterium-Moraxella group were the major generic groups associated with the feedwater surface of the membrane; Acinetobacter, Pseudomonas-Alcaligenes and Bacillus-Lactobacillus predominated on the permeate water surface. EM revealed that the biofilm on the feedwater surface of the membrane was 10-20 .mu.m thick and was composed of several layers of compacted bacterial cells, many of which were partially or completely autolyzed. The bacteria were firmly attached to the membrane surface by an extensive network of extracellular polymeric fibrils. Polyester (Texlon) support fibers located on the permeate surface of the reverse osmosis membranes were sparsely colonized, suggesting bacterial regrowth in the product water collection system.