Industrial process water recycling:: Principles and examples

Recycling of industrial process water requires an adequate control of water quantities and qualities. A water balance has to be set up and the minimum water quality for each process has to be determined. This involves experimental determination of flows and concentrations, and a methodology to optimize the overall water consumption. This can be done either by rigorous methods or by '' common sense '' methods. The next step is the implementation of techniques for water recycling. Because quality standards differ significantly for each industrial activity, no general methods or techniques exist that can be applied in all cases. Two examples are discussed where water is regenerated and the water quality is evaluated in terms of influence on the process itself (1) process water in the textile industry, used for dyeing, and (2) water used in car washes. Wastewater from the textile industry is treated by nanofiltration. Effluents from car washes are treated by an integrated method consisting of ultrafiltration and biological treatment of the concentrate. Results indicate that water recycling is feasible in both cases, although in-depth studies are required to make an optimal membrane choice as a function of the proposed water quality, and to set up procedures to control membrane flux. In addition, further treatment of concentrates has to be considered in case membrane filtration is used in the regeneration step. (c) 2005 American Institute of Chemical Engineers.