Decentralised production of high purity biogas from pig slurry

Problem statement

Pig farms generate a large amount of waste. It is estimated that each animal produces an average equivalent to one and a half tubs of slurry per year.

Executive summary

The novelty lies in the possibility of decentralised recovery treatment and in the fact that the biogas produced is of high purity (biomethane) and can be injected directly into the natural gas network or used as automotive fuel.

Technology description

The valorisation strategy combines two sequential processes: biogas gas purification treatment and anaerobic digestion of livestock waste. The photosynthetic micro-organism used for this transformation is a purple phototrophic bacterium, capable of capturing the sun's infrared energy and feeding on the phosphorus, nitrogen and organic matter present in the slurry. Specifically, these bacteria can support high rates of nutrient assimilation and exhibit high tolerance to slurry toxicity. These organisms perform anoxygenic photosynthesis with carbon dioxide (CO2) and hydrogen sulphide (H2S) fixation, which allows high purity biomethane to be obtained.
The technology can be implemented on small farms, using the biomethane produced on the farm itself. For best performance, it is recommended to dilute/concentrate the slurry to ͂600 mg/L total nitrogen. The presence of volatile fatty acids improves CO2 fixation, thus allowing a purer biomethane.
The low phosphorus concentrations inherent in pig slurry are not significant in the performance of the process, but slightly improve the quality of the biomethane. Concentrations of 93.3% CH4 can be achieved, meeting most international standards for use as vehicle fuel.

Market deployment considerations

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Environmental considerations

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