Water and materials recovery from fertilizer industry acidic effluents by membrane processes

Recent developments in membrane technology are promising as regards drastic reduction of effluents from process plants, through cleaning and recycling polluted streams until recently considered untreatable. This paper outlines specific R & D activities in this direction. Results are reported, of a study in progress, towards recycling various effluent streams from a fertilizer industrial complex with the use of RO membrane technology. The scope of this study is to determine the technical and economic feasibility of a dual process target: a) Concentrating selected effluent streams containing valuable compounds and reusing them in fertilizer production processes; at present, the cost of treatment (before release) of these environmentally offensive streams is high. b) Obtaining high quality membrane permeate water to be used in steam production, and for improving cooling-water quality, thus minimizing fresh water consumption. Two specific examples are discussed: one of a stream rich in nitrate and ammonium ions and another of a highly acidic effluent, rich in fluorosilicic and fluoride ions. Results from bench and short-term pilot scale tests are encouraging with regard to the technical feasibility of membrane processes for achieving the targets set. These test results are further used to determine membrane rejection characteristics, to guide the selection of appropriate membranes, and to determine the process concentrate and permeate quality (as a function of recovery) as well as the necessary pretreatment. Preliminary economic evaluations are also summarized which take into account the benefits from materials and water reuse, and from the significantly reduced loads of the ion-exchange facility (for water demineralization) and of the final wastewater treatment plant. These results suggest that the application of membrane technology is promising for more efficient and environmentally friendlier plant operation.