Researchers at the University of South Wales (USW) are part of a new project that will engineer the world’s first full-scale two-stage anaerobic digestion system producing biohydrogen from wastewater biosolids – which will help to cut the production of millions of tonnes of carbon by-products a year.

USW is working with Dwr Cymru Welsh Water, Marches Biogas, AD Ingenuity and the University of Bath to demonstrate this process with sewage biosolids. Funding for the feasibility and design stage of the project has been made available from the government’s Hydrogen BECCS Innovation Programme funded through the Net Zero Innovation Portfolio (NZIP), which aims to provide funding to support innovation in hydrogen BECCS (bioenergy with carbon capture and storage) technologies.

BIOHYGAS is a novel two-stage biohydrogen/biomethane anaerobic digestion system which can increase energy recovery from biodegradable wastes by up to 37%, compared with existing waste treatment processes.

Together with partners, this project will look at the feasibility of using the BIOHYGAS process for the conversion of thermal hydrolysed sewage biosolids to hydrogen at full scale in a working wastewater treatment site by converting a 2,200m3 digester system to a two-stage digestion system.

Wastewater biosolids are an abundant low-cost feedstock, with the infrastructure for its collection and treatment already in place. Annually, 1.5 million tonnes of wastewater biosolids are produced in the UK which could be converted to 143 million kg of hydrogen with a value of £891m and a carbon saving of 1.6 million tonnes per year.

USW’s innovative approach uses a two-stage digestion system.

In stage one, anaerobic bacteria will be used to produce hydrogen directly from sewage biosolids in a reactor which is much smaller and faster than a conventional anaerobic digester, minimising both the capital and operational expenditure requirements. In stage two, the output from the hydrogen bioreactor is fed to a conventional methane digester. In lab-based experiments the two-stage digestion system operating on a food co-product showed methane yields increased by 37% compared to the single stage digester. This BIOHYGAS project will investigate the potential of using sewage biosolids in such a system and produce a design for use at full scale.

The project will evaluate the potential hydrogen yield obtained when methane from this system is sent to a steam methane re-former for conversion to fuel cell grade hydrogen. The project will also determine the additional value of using the carbon dioxide, which is co-produced in both digestion stages as a preservative gas in food packaging.

The BIOHYGAS project itself will focus on the two-phase digestion process and will work closely with Dwr Cymru Welsh Water exploring the possibilities of implementing steam methane reforming (which converts methane to hydrogen) in the recently funded HyValue project.

If the feasibility study is successful, the BIOHYGAS process will be applied to a full-scale methanogenic digester treating up to 14 tonnes of dry solids per day, which will be a world first and will make the UK a world leader in the production of hydrogen from sewage biosolids.

Professor Alan Guwy, from the Sustainable Environment Research Centre at the University of South Wales, said:

“Research already carried out by USW, together with the ability to work closely with the partners on this project, presents a unique opportunity to demonstrate this advanced form of biohydrogen enhanced anaerobic digestion system at full scale at a working treatment plant.

“After 20 years of working on biohydrogen systems, it offers a landmark opportunity to deploy a full-scale demonstration plant – converting wastewater to hydrogen at a Dwr Cymru Welsh Water site.”

Dr Jaime Massanet-Nicolau, also from the Sustainable Environment Research Centre at the University of South Wales, said:

“This project is a unique chance to build and operate the world’s first full-scale, two-stage system producing biohydrogen from wastewater biosolids.”