Anaerobic Digestion and the generation of biogas for electricity production, is becoming commonplace across the UK and Europe, but with a wide range of feedstocks being used, from poultry manure to household waste, operating an Biogas plant is far from easy.

The key is to maximise the available nutrient content of the feedstock and release as much energy as possible in the AD reactor, by breaking down complex organic compounds into simple monomers.

It is vital to maintain stable and neutral conditions inside the reactor for healthy bacterial operation, and to avoid variations in the feedstock.

Increasing Biogas Output from a number of Feedstock’s

Research has shown that a thermochemical pre-treatment Biogas feedstock’s using a combination of lime and temperature, massive gains in gas output can be achieved, whether you are using poultry manure or maize the results are quite astonishing!

Household / Municipal Waste Feedstock; Biogas output up 172%

This feedstock has to undergo a number of pre-treatment steps to remove materials that would be harmful to the AD Reactor, generally solids such as metals, plastics and sands which are removed through mechanical means.

It is also typical to introduce a temperature treatment stage prior to the AD reactor in order to facilitate hydrolysis, as this feedstock is inherently variable and contains a range of complex organic material that the AD bacteria will be unable to process.

Recent work has indicated that a combination of temperature and lime addition can greatly increase the biogas output by increasing the breakdown of the feedstock’s complex organics into readily soluble monomers that will improve the efficiency of the anaerobic treatment.

The optimal pre-treatment for breakdown of the complex organics was found to be 3% liquid lime per % dry solids with a residence time of 6 hours at approx 40 deg C.

The highest methane yield under anaerobic digestion of the pre-treated waste was 0.15 m3CH4/kg volatile solids (VS), 172.0% of the control. Under that condition the soluble COD and VS removal were 93.0% and 94.0%, respectively. The results have shown that chemical pre-treatment with lime, followed by anaerobic digestion, provides the best results for stabilizing the feedstock

 

Ref; Effect of alkaline pretreatment on anaerobic digestion of solid wastes.

López Torres M1, Espinosa Lloréns Mdel C.