In-vessel composting systems : microbial and compost dynamics

Abstract

Organic matter represents more than one third of the waste produced worldwide and is a major contributor to the acute shortage of acceptable land fill sites. Composting significantly reduces the volume of organic waste and is an environmentally sound way of recycling this waste into valuable soil conditioner. The traditional process of composting heaped material is cheap and simple but slow (taking up to 140 days). In addition, the problems associated with odor and vermin make this process less attractive, especially in areas of high density living. Heap systems can be managed to a limited extent by regular mixing and moisture addition but it is difficult to manipulate the microbial communities successfully. Continuous in-vessel composting systems are increasingly being used for on-site composting of organic matter due to their ease of use and manageability. Hot Rot continuous in-vessel composting system acquired and set up by ANU Green at the ANU campus in Canberra is one such system. The aim of this study was to characterize the microbial communities present in the system and the physical and chemical makeup of the material being composted. This was accomplished by using 16S rDNA-PCR followed by DGGE, 454 pyro- sequencing and standard chemical analyses such as the carbon and nitrogen content, pH, electrical conductivity and temperature. Experimental manipulations of the system, such as varying the residence time of the material in the vessel and seeding the input with the finished product were trialed. The results of these experiments showed that the material exiting the composting system rarely met the Australian standards for compost and that additional maturation of the material was required. High throughput sequencing using the 454 platform provided considerable insight into the bacterial diversity present in the system and into the changes in the bacterial communities during the composting process under the experimental conditions. Importantly, the results also showed that the elimination of pathogens occurred regardless of the operating temperature and that elevated temperatures likely slowed the composting process. Consideration should be given to revising the relevant Australian standards so that they reflect the different composting regimes used in Australia. Show more