Maturity and hygiene quality of composts and hygiene indicators in agricultural soil fertilised with municipal waste or manure compost

Abstract

Composts produced from municipal source separated biowaste (Biowaste), a mixture of biowaste and anaerobically digested sewage sludge (Biosludge) and cattle manure (Manure) were examined for their maturity and hygiene quality. The composts were applied to a potato crop in 2004 and to a barley nurse crop of forage ley in 2005 in a field experiment. Numbers of faecal coliforms, enterococci, clostridia and Salmonella in field soil were determined 2 weeks and 16 weeks after compost applications. Municipal compost batches chosen based on successful processing showed variable maturity during field application, and the need to evaluate compost maturity with multiple variables was confirmed. The numbers of faecal coliform were similar in all compost types, averaging 4.7 and 2.3 log ₁₀ CFU g^-1 in the first and second years, respectively. The highest number of enterococci was 5.2 log₁₀ CFU g^-1, found in Manure compost in the first year, while the highest clostridia numbers were found in Biosludge compost, averaging 4.0 log₁₀ CFU g ^-1 over both years. Except for one case, less than 2.4 log₁₀ CFU g^-1 of faecal coliforms or clostridia were found in compost-fertilised soil, while the numbers of enterococci were mostly higher than in unfertilised soil (<4.2 or <3.2 log₁₀ CFU g^-1, respectively). No hygiene indicator bacteria were present in compost-fertilised potato at harvest. Overall, compost fertilisations caused rather small changes in the counts of hygiene indicators in the field environment.