Renewable Energy Ecosystem in a Wastewater Treatment Plant

How long has the project been operational:

The Bristol WWTP, built in the 1960s, is the foundation of GENeco’s innovative activities. Since GENeco took over the operation of this WWTP in 2008, it has been at the centre of GENeco’s bid to become more sustainable and help others to do the same.

It was in this year that the sewage sludge anaerobic digestion process was split in to two phases. By providing optimal conditions for bacteria responsible for the production of acetic acid and methane in separate reactors the volumes of methane (biogas) produced can be maximised. In addition, two-phase digestion can produce a compliant digestate (bio-fertiliser) without the need for any secondary storage. This process optimisation allowed GENeco to convert two secondary storage tanks into anaerobic digesters.

In 2012, GENeco built the UK’s only food waste recycling facility to be co-located on a WWTP. The food waste recycling facility was able to utilise the two anaerobic digesters GENeco had released through optimisation of the sewage sludge anaerobic digestion process. GENeco’s food waste recycling facility processes 40,000 tonnes of food waste per year, converting this waste into useable resources, biogas and bio-fertiliser.

GENeco produces more biogas than it required to satisfy its heat and power requirements. GENeco identified that the excess biogas produced would be better utilised if converted to biomethane than if used as fuel for a combined heat and power (CHP) engine. This is because energy efficiency in GENeco’s CHP engines are on average 33% electrical efficiency and 38% heat efficiency, whereas energy efficiency in GENeco’s biomethane generation plant is 98%. In 2014 GENeco opted to install a biomethane generation plant, which uses high-pressure water to strip CO2 and other contaminants from the biogas to produced biomethane. This biomethane generation plant converts enough biogas into biomethane to power 7,000 homes every year, and the plant is currently injecting around 1,000m3/hr of renewable gas into the national gas grid.

In 2015 GENeco employed real-time monitoring system (Bentley’s AssetWise Amulet) to help them further optimise biogas production and to reduce the consumption of chemicals and raw materials. AssetWise Amulet enhances process-monitoring capabilities of the plant by combining raw data signals and lab analysis results into useable performance parameters. Visualisation of these parameters has been configured into supervisory dashboards to achieve efficient process operation.

To further its bid to create a sustainable circular economy within Bristol, GENeco is launching the UK’s first food waste collection vehicle (the “Bio-Bee”) which will be powered by biomethane produced from food waste and sewage. Compared to diesel equivalents, this ground-breaking refuse truck is quieter, produces <90% less ‘well-to-wheel’ CO2, and has measurable reductions in particulate matter (PM) and NOx emissions. The Bio-Bee will be used to collect the food waste that feeds the anaerobic digesters.

In addition to biogas, the anaerobic digestion process produces bio-fertiliser, with which GENeco provides a safe and sustainable source of nutrients to the agricultural industry. It facilitates significant crop yields and improves soil condition whilst reducing the industry’s carbon footprint and reliance on inorganic fertilisers.

How long the project took from concept approval to implementation: Ongoing since 2008

Organisation: GENeco

Funding: Private company