Pasteurisation disinfection using waste heat

Pasteurisation - ie, the rapid heating and cooling of food (usually liquid) - has been used since the late 1800s to treat and disinfect milk. Now, a version of the process will be used in Australia for a different purpose - treating recycled water.

A wastewater pasteurisation project will be conducted at Melbourne’s Western Treatment Plant over a period of one year. It was initiated by the Australian Water Recycling Centre of Excellence (AWRCE) and will be led by Victoria University with support from the Australian Water Quality Centre, Melbourne Water, Carollo Engineers, Pasteurization Technology Group (PTG) and WJP Solutions. PTG and Carollo Engineers have previously trialled recycled water pasteurisation in California at the Santa Rosa’s Laguna and the Ventura Wastewater Treatment Plants.

In March, Ventura Water was honoured at the 2013 WateReuse California Annual Conference for its use of PTG’s technology in a pilot program at the Ventura Wastewater Reclamation Facility. At this point it was estimated that by going full-scale, the technology could save the City of Ventura over $750,000 a year in energy and operational costs; now that the trial has been completed, this number is expected to be even higher. This is because the process can be run using waste heat from biogas or from on-site electricity generation.

PTG’s integrated systems use natural gas combined with biogas (a natural by-product of wastewater treatment) as fuel to drive a turbine (or turbines) to generate electricity. The hot exhaust air from the turbine (usually wasted) is then passed through a series of heat exchangers that increase the temperature of the wastewater to a level that disinfects it. The water is cooled to a safe level by transferring the heat of the disinfected water to the incoming water - re-using the energy over and over.

“In a sense, you’re getting something for nothing - disinfection from waste heat,” said Victoria University Research Fellow Dr Peter Sanciolo, who is leading the research.

This is in comparison to Australia’s current water disinfection processes, such as UV followed by free chlorination, which Dr Sanciolo says are energy- and cost-intensive. Melbourne Water’s Dr Judy Blackbeard said, “Initial estimates indicate that if these two treatment processes are replaced with pasteurisation, the operating costs of pasteurisation are likely to be only 60% of those for UV and free chlorination. A similar reduction in capital costs can be expected.”

But Dr Sanciolo noted that although pasteurisation was successful in California, the economics of the process vary from site to site, hence the need to trial it for the Australian water industry. Dr Mara Wolkenhauer, Program Manager, Research & Development at AWRCE, explained that cost savings would be lower if a facility had to generate its own biogas; on the other hand, if it already generated biogas through wastewater treatment, or had a biogas-fuelled power plant on site, it would not have to pay for the  additional energy requirement to heat the wastewater.

Dr Sanciolo said scientists are currently testing our wastewater to see what temperature and time conditions are required to kill the water’s many different types of microbial contaminants. Once the trial proper gets underway, it will be used to develop monitoring protocols to ensure the process works properly. It will also be an important demonstration for Australian regulatory authorities, showing that the water can be treated to a very high standard suitable for crop irrigation and industrial use.

AWRCE CEO Mark O’Donohue said: “If successful, the project will demonstrate that pasteurisation can reduce treatment costs and energy requirements, and simplify the recycled water disinfection process, under rigorous conditions required by Australian Departments of Health.”

With thanks to Dr Judy Blackbeard, Dr Peter Sanciolo and Dr Mara Wolkenhauer.