Evolution of clostridia and streptomycetes in full-scale composting facilities and pilot drums equipped with on-line temperature monitoring and aeration

The evolution of sporulating bacteria in full-scale composting facilities with online temperature monitoring has been poorly studied, although organic matter recycling increases. We analysed Clostridium perfringens and sulphite-reducing clostridia (SRC) by cultivation, and streptomycetes by real-time PCR in five full-scale, temperature-monitored and aerated composting processes, and two pilot-scale drum composters. Facilities composted woodchips, sawdust, peat, or bark amended sludge or source-separated biowaste. Streptomycetes genes of 0.21-110 × 10⁷ copies/g feed increased fast to 0.019-33 × 10⁹ copies/g, and then were equal or decreased. SRC of 0.06-2.2 × 10⁷ cfu/g feed decreased to 0-600 cfu/g, with re-growth in two facilities. End products were clean of C. perfringens, detected in sludge composts. Although processes contained large quantities of spore-forming bacteria, in the best facilities end products had the high quality. Temperature (>55 °C, >2d) was not related to the end compost quality, but relations between waste and bulking agent qualities, aeration, and processing time should be better controlled.