Development of Advanced Composting Technologies for Municipal Organic Waste Treatment in Small Communities in Newfoundland and Labrador

Zhang, Baiyu and Lye, Leonard and Kazemi, Khoshrooz and Lin, Weiyun (2013) Development of Advanced Composting Technologies for Municipal Organic Waste Treatment in Small Communities in Newfoundland and Labrador. Project Report. The Harris Centre.

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Abstract

Municipal Solid Waste (MSW) is one of the major fractions of the solid waste in Canada. From 2002 to 2008, Canadian municipal solid waste disposal has increased from 769 kilograms to 777 kilograms per capita. Among the provinces, Newfoundland and Labrador (NL) has one of the highest waste disposal levels per capita in the country. According to the Multi Materials Stewardship Board (MMSB), it is estimated that more than 400,000 tonnes of municipal solid waste (MSW) materials are generated each year in this province and organic waste makes up as much as 30% of all waste generated. To properly manage MSW generated, the Provincial Solid Waste Management Strategy has been identified in 2002, aiming to reduce the amount of waste going into landfills by 50 per cent. Composting has been regarded as an efficient and effective way to deal with the organic waste and helps work toward achieving the provincial 50 per cent waste reduction goal. It also creates rich organic soil that can enhance lawns and gardens. Therefore, MSW composting has been listed as one of the six new environmental standards applied to new waste management systems in NL. However, NL comprises more than 200 small communities without access to the central composting facility. For those areas, small-scale composting technologies are desired to manage their MSW so as to reduce collection and transport costs and eliminate the other environmental contamination during transportation. Composting is a biological process that is affected by chemical and physical factors. The lack of understanding of the complexity of biological, chemical, and physical processes can result in malfunction of a composting system. The microbial and physicochemical environment in composting can be affected by the diversity of microbial population, temperature, bulking agent, aeration, and chemical properties of raw material such as the C/N ratio and moisture content. Interactions among biological, chemical, and physical factors are crucial to the comprehensive understanding of the composting process, and thus viable for process control and system optimization. This project aims at developing composting technologies applicable to northern communities in NL, and conducting system optimization to increase the composting efficiency and improve compost quality. Six composting reactors (50×20×25 cm) were designed and manufactured. Six mixers were installed in each reactor. An inlet was designed to provide air through a vacuum pump. A perforated plate with holes was installed for air distribution in the system. The exhaust gas was monitored by a gas monitoring system and then discharged into a flask containing H2SO4 solution (1 M) to absorb the NH3. To prevent heat loss, heat insulating layers were designed and applied to cover the reactor thoroughly. Reactors were filled with food waste as raw material. Factorial design was applied, with sixteen runs conducted, to optimize the operational factors including moisture content, aeration, bulking agent, and C/N ratio. Each composting run lasts 30 days. The effect of main factors and their interactions on composting process was investigated by measuring temporal variations of enzyme activities (dehydrogenase, β-glucosidase, and Phosphomonoesterase), germination index (GI), pH, electrical conductivity (EC), temperature, moisture, ash content, oxygen uptake rate (OUR), and C/N ratio during composting. Experimental results showed that the breakdown of organic matter by microbial activities led to increase in the temperature of the composting material. As composting progresses, the amount of degradable matter decreased and the temperature declined. When most of the organic matter was consumed, the temperature in the reactor dropped to the ambient temperature. The OUR can express biological activities during composting and biological stability at the end of composting. The OUR values showed strong correlation with temperature. The maximum OUR was observed concurrently with the maximum temperature. The pH value was low at the first stage due to the accumulation of organic acids, and increased gradually while organic acids were consumed by microorganisms. The EC values increased in all runs as a result of cation concentration increment. Moisture content showed descending trends in all runs due to the evaporation under high temperature. As a result of decomposition of organic matter by composting, the organic matter decreased and ash content increased in all runs. Although the GI data showed notable fluctuation during composting, it started to increase at the end of the composting process. In most of the runs, the peaks of dehydrogenase activity as an indicator of biological activity were observed with the maximum temperature and OUR value simultaneously. The β-glucosidase activity showed with high values at the themophilic phase and after the temperature drop. In addition, high activity of phosphomonoesterase accrued during the thermophilic phase. Results of the factorial design indicated that aeration rate, moisture content, and bulking agents affect the maximum temperature significantly. Aeration rate has significant influence on the maximum OUR. The C/N ratio and the interaction between aeration rate and bulking agent have major impact on GI. Moisture content is an important factor affecting the cumulative dehydrogenase and the β-glucosidase activity. The C/N ratio influences the β-glucosidase activity as well. The output of this research can help to design the small-scale composting system for MSW management in small communities in NL, and provide a solid base of technical and scientific knowledge for system operation.

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