Evolution of clostridia and streptomycetes in full-scale composting facilities and pilot drums equipped with on-line temperature monitoring and aeration Aija Rainisalo, Martin Romantschuk, Merja H. Kontro ⇑ Helsinki University, Department of Environmental Sciences, Niemenkatu 73, 15140 Lahti, Finland article info Article history: Received 16 March 2011 Received in revised form 30 May 2011 Accepted 30 May 2011 Available online 12 June 2011 Keywords: Clostridia Streptomycetes Composting Full-scale facilities Pilot drums abstract The evolution of sporulating bacteria in full-scale composting facilities with online temperature monitor- ing 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 Â 10 7 copies/g feed increased fast to 0.019–33 Â 10 9 copies/ g, and then were equal or decreased. SRC of 0.06–2.2 Â 10 7 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. Ó 2011 Elsevier Ltd. All rights reserved. 1. Introduction The municipal solid waste management is under the develop- ment towards the increased recycling of organic wastes to soil fer- tilizer, instead of incineration, or use in landfills blamed for pollution incidents and enhanced greenhouse gas production. The soils progressively lose organic matter in the intensive cultivation and through water runoff. In the municipal waste management, the sewage sludge, manure, yard wastes, and municipal, source- separated and sorted organic wastes are transported for the anaer- obic or aerobic processing (Giusti, 2009; Epstein, 1997). The aero- bic microbial waste treatment called composting efficiently transforms organic material to humus-like substances concomi- tantly with hygienization of harmful microbes. The composting proceeds from the active mesophilic decomposition generating heat to the thermophilic phase, and finally in the curing phase the less susceptible carbon fractions are mineralised into a stable humic product (Epstein, 1997). The increase in the organic material flow to composting has resulted in the construction of large pro- cess units with sometimes inadequately developed stages, leading to odour emissions under anaerobic conditions, low process tem- peratures, and immature end products without hygienization. The industrial, full-scale composting facilities typically have closed tunnel or drum process units for the initial phases of com- posting, while the curing of compost occurs in windrows. In the beginning of composting, the dense waste material is usually mixed with the bulking agent to enhance the oxygen flow into the compost mass, and in the end of the process the coarse bulking agent is removed by sieving. The typical bulking agents include wood chips, sawdust, bark, and peat. The temperature within the compost mass determines the rate of biological processes, plays the selective role in the evolution and succession of microbial com- munities, and is related to the hygienization of harmful microbes (Giusti, 2009; Epstein, 1997). According to the health rules con- cerning animal by-products not intended for human consumption, a composting plant must be equipped with a closed composting reactor having temperature monitoring without bypass possibility. The maximum compost particle size is 12 mm and minimum tem- perature in material 70 °C for 60 min. The other standardised pro- cess parameters may be provided when the applicant ensures minimisation of biological risks (European Commission, 2002, 2006). The composting process often involves activities of micro- organisms presenting health risks to the general population. The workers in composting facilities are exposed to, e.g. bioaerosols, airborne microbes and spores, microbial volatile organic com- pounds and mycotoxins (Epstein, 1997; Poulsen et al., 1995). According to hygiene requirements for processing animal by-prod- ucts, Clostridium perfringens must be absent from 1 g of product di- rectly after the heat treatment (European Commission, 2002, 0960-8524/$ - see front matter Ó 2011 Elsevier Ltd. All rights reserved. doi:10.1016/j.biortech.2011.05.087 ⇑ Corresponding author. Address: Helsinki University, Department of Ecological and Environmental Sciences, Niemenkatu 73, 15140 Lahti, Finland. Tel.: +358 9 19120309; fax: +358 9 19120331. E-mail address: merja.kontro@helsinki.fi (M.H. Kontro). Bioresource Technology 102 (2011) 7975–7983 Contents lists available at ScienceDirect Bioresource Technology journal homepage: www.elsevier.com/locate/biortech