AbstractThe increasing cost of fossil fuels, combined with concerns about their impact on our environment has led to a renewed interest in hydrogen as a clean, sustainable, alternative energy vector. Using sewage biosolids as the substrate for fermentative hydrogen production offers several advantages over the use of other biomass sources. It is available at little or no cost and is abundant, being produced wherever there are human settlements, with 1.3 million tonnes (dry solids) per year currently being produced in the U.K alone.
This research demonstrated the feasibility of hydrogen production from sewage biosolids via anaerobic fermentation. To do this a number of issues specifically relating to the nature of sewage biosolids had to be addressed. Firstly, the solids content and rheology made automatic feeding difficult. The feedstock also contained high levels of indigenous microorganisms and a high ratio of insoluble to soluble carbohydrate.
To address these challenges, a novel reactor design using wide bore tubing and computer controlled pumping equipment was successfully used to construct a working continuously fed bio-reactor. A combination of heat treatment at 70°C for one hour and pre-treatment with a commercially available food processing enzyme mixture was found to be the most efficient method of inactivating competing microorganisms and improving substrate quality.
Hydrogen was successfully produced via batch fermentation of primary sewage biosolids which had undergone heat treatment and enzymatic digestion. When fermentation took place at pH 5.5 a peak hydrogen production rate of 3.75 cm3 min"1 was observed. At this pH the hydrogen yield was 0.37 mol H2 mol~ : carbohydrate, equivalent to 18.14 L H2 kg"1 dry solids. Fermentative hydrogen production from sewage biosolids was also demonstrated in a five litre, continuously fed bio-reactor for the first time. A comparison of different hydraulic retention times showed that hydrogen production was most stable at a HRT of 24 hours. A hydrogen producing fermenter was successfully linked to a methanogenic bio-reactor in a two stage digestion process.
|Date of Award
|Richard Dinsdale (Supervisor)
- Sewage sludge