Biowaste to bioenergy with a biofactory

The development of the bioenergy space as part of creating a circular economy is seeing research into turning waste into energy. SUEZ Australia and New Zealand is part of that transition.

Wastewater treatment plants (WWTPs) provide opportunities for completing a circular economy for wastewater. Around the world, SUEZ is working with water utilities, local councils, and industrial water users to help convert waste into energy, thus closing the loop in a circular economy.

With rising energy prices and the need to reduce our activities’ carbon footprint, SUEZ is innovating to transform non-recyclable waste and sewage sludge into local, renewable energy that supports the ecological transition in local areas. SUEZ is also exploring technologies for capturing, storing, and using carbon dioxide, which will help achieve carbon neutrality.

People like Zdravka Doquang, Innovation Officer at SUEZ, are leading the charge in developing biofactories. She has been working in the water and wastewater industries for more than 20 years.

“When we think about bioenergy in the wastewater treatment space, we think of bioenergy as the production of biogas or a biosolid with a sufficient calorific power to be used as fuel for energy recovery,” Doquang said. “This represents the first brick of the Biofactory and the circular economy concept. SUEZ has been working on this for more than 15 years.”

Challenges around bioenergy

There are many challenges associated with bioenergy projects. The primary one is to maximise the production of biogas. This requires directing as much carbon as possible to the digestor by optimising the primary treatments with enhanced settling.

“The bioenergy production process results in the capacity to combine several treatment steps smartly,” she said. “To optimise the biogas production method, we need to optimise the digestion process. Different reactors and configurations are possible and have been developed by SUEZ. These processes have subsequently been implemented in different projects worldwide.”

Anaerobic digestion (AD) generates positive externalities, but its profitability depends on the evolution of the biomethane feed-in tariff in the coming years. Developing a profitable AD will depend highly on complementary revenues (e.g., higher biogas production, digestate recovery, carbon dioxide recovery, hydrogen production, green certificates, VFAs production) and CAPEX/OPEX optimisation.

Rachael Nuttall, the Head of Major Projects Development & Sales, SUEZ Australia & New Zealand, believes in using biomethane as a green gas source.

“Biomethane reinjection into the existing framework is an emerging practice in Australia and is currently being trialled,” Nuttall said. “In Europe, we see biomethane schemes everywhere. It’s even at the level of local councils and farmers creating biomethane with their digesters. We are looking forward to being able to deliver biomethane projects in Australia.”

Global learnings

As SUEZ has expanded its influence into different bioenergy projects, there is always a lot to learn.

“Each and every business case is site-specific, and there is no one-size-fits-all treatment line,” said Doquang. “There are different factors to account for issues such as WWTP characteristics, sewage effluent classifications, local regulations, local demands, and opportunities for bioenergy use.”

Bioenergy can be used for electricity generation, heating, biomethane for injection into the grid, and a range of other opportunities.

“For example, one of the Australian water recycling plants has a two-stage mesophilic anaerobic digestor (MAD) operating at 37°C,” Doquang said. “This allows SUEZ to produce up to nine per cent more biogas compared to a single-stage MAD. Furthermore, the two-stage configuration allows biological hydrolysis optimisation. We’ve put this in place in Nice (France) and Okhla (India) to tackle land footprint constraints.”

There’s also the option of operating the hydrolysis at a higher temperature, ideally above 140°C. With the right equipment, SUEZ has seen a further 20 per cent more biogas at projects in Mapocho (Chile), Panama and Dijon (France).

“To transform sludge into biosolid with high calorific value, we need to increase the sludge dryness with thermal drying or ultra-dewatering to create bio-coal,” said Doquang. That dewatering process is critical to maximising energy production. Whether it is dewatered on-site or pre-dried is a site-specific decision.

“Finally, to produce green electricity from sludge incineration, SUEZ implements either an Organic Rankine Cycle (ORC) technology or a vapour turbine.”

Biofactories and the future

In partnership with SA Water, SUEZ recently ran its inaugural Innovation Day in Australia, having held it in other parts of the world in previous years. A focus was on the implementation of biofactories.

“The key takeaway from the Innovation Day was that a biofactory exists within an ecosystem,” said Stephanie Clarke, the V.P. for Growth & Innovation, SUEZ Australia and New Zealand. “When viewed through this lens, we recognise it’s environmental, economic, and social impacts. SUEZ is looking to create value from the incoming wastewater at the plant. . To maximise the potential for reuse, we delved into various considerations during the biofactory workshop, beginning with site specificity. Apart from just available space and existing processes, we also needed to consider proximity to communities, and potential users and markets for the resources.”

SUEZ has a variety of technologies to implement for different projects and is always looking for different organisations to partner with. This collaborative approach is fundamental to our accumulated expertise in the field.

“We have treatment plant technology, resource recovery technology, and waste-to-energy technology, but how do we work together with our clients to maximise the impact, given the location?” asked Clarke. “If we think about it holistically, it can be an effective way to address the problem.”

SUEZ will continue to work and invest in renewable energy and resource generation projects and the reduction of carbon dioxide emissions.

“Ideally, we want to implement breakthrough and game-changing technologies allowing biomass conversion to biomethane. That way, we can achieve even higher green gas production and, ultimately, close the loop for a circular economy,” said Clarke.

For more information, visit https://www.suez.com/en/