Abstract
This study was focused on the microbiological aspects of composting and on the behaviour of main prevalent microbial communities (non-pathogenic and selected pathogenic bacteria) during the composting process of municipal solid wastes and sewage sludge in a semi-industrial composting plant. Results showed that the dehydrogenase activity and Biomass C / Biomass N ratio showed a noticeable increase in the two windrows W1 (100% of municipal solid wastes) and W2 (60% of municipal solid wastes and 40% of dried sewage sludge) during the thermophilic phase (â¥45°C for 100 days) and marked a high microbial activity during this period of the composting process. During the thermophilic phase, the removal of faecal indicator bacteria is in order of 2 Ulog10, and a total absence of Staphylococcus aureus and Salmonella was observed. The re-emergence of faecal indicator bacteria at the end of the composting progress (cooling step) could constitute a major problem for the agricultural use of compost.
Highlights
Composting is basically a process of different organic solid wastes decomposition
Preparation of windrows: The study was performed in the composting plant of Beja located 100 km from the north of Tunis, using two types of windrows: (i) the first windrow W1 constituted with 100% of municipal solid wastes, and (ii) the second windrow W2 composed by weight of 60% of municipal solid wastes and 40% of dried sewage sludge
If the C/N ratio is above or below the optimum range (25-20), composting proceeds slowly and the excess carbon is converted to CO2 or the excess nitrogen is converted to ammonia, until the correct balance is restored
Summary
Composting is basically a process of different organic solid wastes decomposition. Release of heat and production of relatively stable organic compounds (humic substances) result from this process[1]. Initial decomposition is carried out by mesophilic microorganisms, which rapidly biodegrade the soluble and degradable compounds. As the temperature rises above 40°C, mesophilic microorganisms become less competitive and are replaced by thermophilic organisms[2]. High temperatures accelerate the breakdown of proteins, fats and complex carbohydrates such as cellulose and hemicellulose. As these high-energy compounds become exhausted, the compost temperature gradually decreases and mesophilic microorganisms once again take over the other types of microorganisms during the final phase of maturation
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