Reuse of treated sewage effluent for cooling water make up: a feasibility study and a pilot plant study

Abstract

This investigation was aimed at developing an acceptable technology for using secondary effluent as cooling water makeup for inland manufacturing industry in Australia. Approximate economic evaluations were made for a number of pretreatment alternatives and for internal treatment with chemical conditioning agents. Internal treatment with biocide dosing appeared to be the most promising option. A portable pilot plant scale cooling tower/heat exchanger unit was constructed. The unit incorporated an on-line, differential pressure biofilm monitor together with automated control and data acquisition systems. The pilot plant was installed on site at a sewage treatment plant near Sydney. It was demonstrated that the use of TSE for cooling water makeup is technically feasible. The rate of biofilm growth observed using chlorinated secondary effluent directly from the sewage treatment plant as makeup water was similar to the rate of biofilm growth observed when potable water was used and supplementary chemical treatment was not introduced in either case. Excellent control of biofilm growth was observed in subsequent experiments when supplementary additions of simple chlorine or bromine chloride treatment systems were carried out. The pilot plant was operated successfully at 5 cycles of concentration without any other supplementary treatment being required.