The NWaste2H2 team at the University of Leeds have demonstrated an innovative process for producing hydrogen at anaerobic digestion (AD) plants processing for example food and agricultural wastes or sewage sludge. AD yields three main products: biogas, digestate solids and digestate liquids (liquor).
The hydrogen production process
In the NWaste2H2 process, ammonia is recovered from the liquor and converted to hydrogen alongside another hydrogen carrier - the methane fraction of the biogas. This occurs via three key reactions: ammonia decomposition, steam methane reforming and water-gas shift.
If implemented at wastewater treatment plants, the recovery of ammonia for this purpose also diverts it from conventional wastewater treatment, simultaneously saving both energy and greenhouse gas emissions.
Establishing feasibility
We carried out multi-faceted analysis including extensive process modelling, experimental hydrogen production, carbon lifecycle assessment and economic analysis which found that it is feasible to introduce this process into a significant number of AD plants across the UK.
We developed a case-study for an example wastewater treatment plant serving 750,000 people which found that hydrogen could be produced and prepared as fuel for buses with a levelised cost of £4.90/kg which is competitive with other sources of green hydrogen and has a discounted pay-back period of just 5.7 years.
A lifecycle analysis of greenhouse gas emissions also showed that the process could save up to 17.2 kg carbon dioxide equivalent per year for each person served by the treatment facility. This saving would come from the replacement of diesel buses and the reduced nitrous oxide emissions from biological treatment.
For more information on this project please email Dr Valerie Dupont via V.Dupont@leeds.ac.uk.