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Utility capturing biogas to improve energy efficiency

Melbourne Water’s Western Treatment Plant (WTP) is one step closer to becoming energy positive thanks to a new approach to anaerobic lagoon covers.

Although harvesting biogas from wastewater ponds for energy conversion is nothing new at the WTP, a unique and innovative design is helping capture more gas.

New covers have been installed at the plant’s 55 East and 25 West anaerobic lagoons. WTP Treatment and Resources Manager Jenelle Watson said the installations are part of a larger plan to convert biogas for energy use at the plant.

“We have considerable population growth in Melbourne, and the growth in wastewater load results in more production of biogas at the site. We are pursuing this opportunity with the expansion of our onsite power station to make use of that extra resource now being captured,” she said

WTP Energy Futures Principal Ken Baxter said the lagoons’ unique configuration is helping the utility produce more gas, offering a strong case for expansion of its onsite power station.

“Theoretically, we should be getting about 60% methane in our biogas composition, but at WTP we are getting a lot more. This is because of the configuration of our lagoons and the long retention of biological materials,” Baxter said.

“We get a return from that gas by taking it to the power station and using it as a fuel. We are generating enough electricity to cover our plant requirements. We actually have additional gas produced beyond what the current power station can utilise.

“We have a project under development to expand the power station. That will result in upsizing the current power station by 40-60%, which will make the plant an exporter of power.”

It’s estimated that the new covers collect approximately 110,000m³ of biogas per day, amounting to approximately $3.5 million in savings per year.

Watson said the new segmented cover design utilised for the 55 East lagoon, which allows for easier maintenance and pumping, is also part of the plant’s odour management.

“When it came to replacing the 55 East lagoon cover, we wanted to try something new that would enable us to lower the impact on our odour profile,” she said.

“Not only do the segmented covers help capture the biogas, but they are also a part of our odour management on site. With monolithic covers, if you take the whole cover off you obviously have a much bigger impact than if you only take off part of a cover.”