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.
Highlights
Recycled water is widely used in Australia for various purposes such as toilet flushing, domestic gardening, irrigation of parks and sportsgrounds, and in peri-urban agriculture
Water for the laboratory scale testing was collected at two levels of maturation and biological treatment, from the second pond (P2) and the 10th pond (P10) in the Western Treatment Plant (WTP)
The data indicates that Enterococci and E. coli could serve as a conservative surrogate for bacteria in general, with Enterococci being the more conservative surrogate
Summary
Recycled water is widely used in Australia for various purposes such as toilet flushing, domestic gardening, irrigation of parks and sportsgrounds, and in peri-urban agriculture. Due to the high risk of direct human exposure to the water, or to incidental ingestion of the water, the highest level of treatment (Class A) is required for this recycled water. Class A water are determined by a quantitative microbial risk assessment (QMRA), consistent with the Australian Guidelines for Water Recycling [1]. The ability of a treatment process to render the water safe to use for a specific purpose is a key feature of the QMRA. Other key features of the QMRA are the feed water quality and variability, the likely level of exposure, and infection rates of pathogens
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