Effectiveness and energy requirements of pasteurisation for the treatment of unfiltered secondary effluent from a municipalwastewater treatment plant

Abstract

Pasteurisation was investigated as a process to achieve high microbial quality standards in the recycling of water from unfiltered secondary effluents from a wastewater treatment plants in Melbourne, Australia. The relative heat sensitivity of key bacterial, viral, protozoan and helminth wastewater organisms (Escherichia coli, Enterococcus, FRNA bacteriophage, adenovirus, coxsackievirus, Cryptosporidium, and Ascaris) were determined by laboratory scale tests. The FRNA phage were found to be the most heat resistant, followed by enterococci and E. coli. Pilot scale challenge testing of a 2 ML/day pasteurisation pilot plant using unfiltered municipal wastewater and male specific coliphage (MS2) phage showed that temperatures between 69 °C and 75 °C achieved log reductions values between 0.9 ± 0.1 and 5.0 ± 0.5 respectively in the contact chamber. Fouling of the heat exchangers during operation using unfiltered secondary treated effluent was found to increase the energy consumption of the plant from 2.2 kWh/kL to 5.1 kWh/kL. The economic feasibility of pasteurisation for the current municipal application with high heat exchanger fouling potential can be expected to depend largely on the available waste heat from co-generation and on the efforts required to control fouling of the heat exchangers.