Biological treatment of industrial wastewater by a membrane bioreactor

Wastewater originating from chemical industries may contain compounds that could adversely affect the treatment processes, mainly the biological process, by either toxic or inhibition effects. The objectives of this study were to evaluate practical possibilities to upgrade existing wastewater treatment facilities by operating aerobic treatment based on membrane bioreactor (MBR) technology. Three different industries were included in this study: a paper mill that operates raw solid separators followed by anaerobic treatment; a food production plant that operates oil and grease separators, chemical flocculation, and dissolved air flotation; and port fuel facilities that include gravity oil separators. In all the above cases the biological treatment was exposed to different problems, which included: (a) the possible presence of deflocculating materials such as starch and biocides, in the case of the paper mill; (b) residual hydrophobic compounds that may affect diffusion through biosolids surfaces in the food plant; and (c) organic matter characterized by low biodegradability (hydrocarbons), in the case of the fuel port facilities. The experimental work in this study indicated that biological treatment of industrial wastewater containing contaminants characterized by hydrophobicity and/or by low biodegradability could be successfully performed by MBR configuration, obtaining effluent of high quality. However, these particular types of industrial wastewater would require the adaptation of the MBR operation conditions, by lowering cell residence time and mixed liquor volatile suspended solids (MLVSS) in the bioreactor and by increasing the amounts of excess biosolids accordingly.