Wastewater-treatment system could also produce electricity

Researchers in Scotland are hoping a new low-cost wastewater-treatment system for the developing world could also produce electricity.

A multi-disciplinary team led by Glasgow University has received £1m from the EPSRC to create a bacteria-based system for treating waste in areas on the outskirts of cities that have poor or no sewage facilities.

Scientists will bio-engineer bacteria to break down large amounts of solid waste using anaerobic digestion (without oxygen) in a reactor based on existing technology used by distilleries and pharmaceutical companies.

They hope to be able to capture the gas from the process to generate electricity. Because the system would not produce other waste products, they also hope it could improve wastewater treatment in the developed world.

An estimated one billion people worldwide live in peri-urban zones that only have open sewers and pit latrines rather than water-based sewage systems, principal investigator Dr Gavin Collins told The Engineer.

‘We can use anaerobic digestion where we can pump high volumes of high-solid wastewater in to achieve a much more efficient system and at the same time not pump energy into the system because it doesn’t need air.

‘The obvious alternatives are based on aerobic digestion like those used in developed countries. But these are unsustainable approaches where we don’t recoup any energy or useful products. Instead we put a lot of energy in and it costs a lot of money.

‘Conventional techniques also result in the production of huge volumes of excess sludge and new waste, which we also want to avoid.’

The project involves researchers from Brighton, Cranfield, Newcastle, Sheffield and Ulster universities and is expected to take four years to produce a prototype system.

Existing anaerobic systems are typically used to treat industrial wastewater with a low solid content. These expanded granular sludge bed (EGSB) reactors rely on the bacteria staying in the tank but high-solid waste would push them out.

‘Our hypothesis is that we can eco-engineer the bacteria so that they will stay in the system despite the fact that we’ll be pumping high-solid waste water through,’ said Collins.

Part of the challenge will be designing a system that will be socially and culturally acceptable, as well as practical, for populations in the developing world, he added.

The team has yet to work out how it will capture the gas from the system and needs to determine on what scale it can be feasibly and acceptably done in developing countries. It also has the challenge of getting the waste to the digesters.

If it can successfully build a high-rate solid-waste system, there might also be an opportunity to employ the technology in the developed world to treat the sludge produced by aerobic digestion.

‘We could radically increase the rate at which we treat sewage sludge in the UK, which is growing every year as we roll out more wastewater-treatment plants and is the biggest problem the water industry has in this country,’ said Collins.