Fertilisers from biogas plants pose only a minor risk to food safety


<p>The end products, or digestates, of biogas plants can be used as fertilisers and soil improvers. Biogas plant end products, however, may contain hazardous organic compounds which are released into the soil during fertilisation. Some of the agents may also accumulate in food products. It is unlikely that agricultural use of biogas plant digestates would cause any notable risk to food safety.</p>

The risk to food safety caused by any organic compounds contained in biogas plant end products is probably minimal. Although they may be released into the soil when biogas plant digestates are being used as fertilisers, the compounds only accumulate in plants and food of animal origin in very small amounts.

In a joint project, the Finnish Food Safety Authority Evira and MTT Agrifood Research Finland studied the occurrence of hazardous organic compounds in biogas plant digestates, and evaluated the risk to food safety caused by such compounds. The project examined digestates produced from various waste materials, such as waste water sludge, municipal biowaste, by-products from food industry, and animal manure.

Most compounds break down quickly

Hazardous organic compounds were found in every digestate examined. The concentrations measured were at the same level as those in other European countries.

"Most of the compounds examined break down in the soil relatively quickly. In the case of most agents there is little accumulation from the soil into foodstuffs, or else they enter the soil in such small quantities that accumulation in plants or food of animal origin is relatively insignificant. Any risk to food safety is therefore likely to be minimal," says Kimmo Suominen, Senior Researcher from Evira's Risk Assessment Research Unit.

Further research on biogas plant digestates is needed

Certain brominated (organic bromine-containing) flame retardants such as PBDE (polybrominated diphenyl ether) compounds – used in furnishing fabrics, among others – and perfluorinated alkyl compounds – used, for example, as water repellents in textiles – persist in the environment.  These can accumulate in soil as a result of frequent and long-term use of biogas plant digestates, and also have the tendency to accumulate in foodstuffs. 

"More information is needed on the behaviour of these agents in the food production chain. The calculated soil burden of almost all compounds examined after a single addition of biogas plant digestate was the same order of magnitude as, for example, the atmospheric deposition with rain in Finland or other Nordic Countries. The soil burden of PBDE compounds after a single addition of digestate may be even thousand-fold compared to the atmospheric deposition presented in the literature," Suominen points out.

View the study and its chemical compound groups

The results of the research project have been published in the MTT report (abstract in English).
Marttinen, S., Suominen, K., Lehto, M., Jalava, T., Tampio, E.
Occurrence of hazardous organic compounds and pharmaceuticals in biogas plant digestate and evaluation of the risk to the food production chain.
BIOSAFE project final report. MTT Report 135, 2014.

A scientific peer-reviewed article of the subject has also been published
Suominen, K., Verta, M., Marttinen, S. 
Hazardous organic compounds in biogas plant end products – soil burden and risk to food safety. Science of the Total Environment 2014: Vol. 491–492, pp. 192–199.

More on this subject Biogas plants can refine fertilisers for agricultural use

Further information:
Senior Researcher Kimmo Suominen, tel. +358 40 8279 715


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