Anaerobic digestion is the breakdown of organic wastes and waste water by microorganisms. This produces a useful fuel known as biogas (methane). The biogas industry is booming in countries throughout the world including China, India, Brazil and the US. Anaerobic digestion works well in warmer climates for generating renewable energy from waste and treating wastewater. But it is slightly more challenging for countries with colder climates.
Anaerobic vs aerobic
The UK is an international leader in anaerobic digestion and the second largest producer in Europe. But since the UK does not have an ideal climate for microorganisms to break down wastes, particularly for wastewater, other more expensive methods are used instead like aeration.
Three percent of all electricity generated in the UK is used to treat wastewater, half of that is used for aeration.
Dr Jan Dolfing and colleagues from the School of Civil Engineering and Geosciences tested how bacteria from much colder climates in the Arctic and Lake Geneva in Switzerland, could be used for anaerobic digestion in the UK.
“Treating wastewater using aeration involves pumping a lot of air as the bacteria in these big reactors use oxygen to break down the waste. This degrades compounds in the waste, but uses a lot of energy. Anaerobic digestion could potentially be used to treat wastewater in the UK at lower cost, but the bottleneck is doing it at low temperature”, says Dr Dolfing.
Cold adapted microorganisms
Jan’s research team collected bacteria that live just below the surface of the soil in the Arctic and lake bed of Lake Geneva to be taken back to their lab in Newcastle University. The microorganisms were kept alive in a half litre of biomass and a half litre of wastewater. Funding from the Institute for Sustainability was key to keeping the microorganisms alive for the project and testing them at temperatures as low as 4C.
Once the bacteria were placed in a temperature controlled incubator with wastewater in the lab they gradually started producing methane from it. This experiment confirmed that cold adapted microorganisms can treat wastewater at low temperatures.
“We were happy if 8C worked but there wasn’t much difference in waste degradation between 4C, 8C or 15C for these bacteria”, says Dr Dolfing. Variations in productivity of different bacteria were observed depending on where they were collected.
“The bacteria from the middle of Lake Geneva were not very active when they were fed only wastewater, but this is likely because they had never been exposed before”, says Dr Dolfing.
Researchers decided to travel to the outfall of a sewage treatment plant in Lausanne to collect cold adapted bacteria that also love waste. In collaboration with a group of Russian scientists aboard a submarine they were able to travel to the bottom of the lake to take samples for their research at Newcastle University.
In collaboration with Northumbrian Water, Jan and his research team are currently working on large scale anaerobic digesters using the bacteria from Lausanne. In anaerobic digestion there is usually a community of different organisms involved, for example, one species to convert the waste into something that can be eaten by another species to produce methane.
Jan and his team will be looking at ways to exploit cooperation between different organisms to develop methods for starting anaerobic digestion at low temperatures, potentially a boon for the UK wastewater treatment industry. In future there may also be scope for anaerobic digestion in much colder climates.
“Fundamentally, there shouldn’t be a problem with anaerobic digestion in extremely cold environments like the Arctic because the carbon cycle also works there as well. If an animal dies there for example eventually it decays. Bacteria can be active at low, even at sub-zero temperatures as long as they are in liquid water,” says Dr Dolfing.
This research is from the project ‘Towards Energy Neutral Treatment of Municipal Wastewater’ funded through our Responsive Mode Funding call.