Solid waste composting and the application of compost for biosurfactant production

Kazemi, Khoshrooz (2017) Solid waste composting and the application of compost for biosurfactant production. Doctoral (PhD) thesis, Memorial University of Newfoundland.

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Abstract

In Canada, about 9 million tonnes of residential waste with over 40% of organic waste was disposed every year. Another major source of organic waste in Canada is from the seafood processing industry. For effective organic waste management, composting serves as a sound, cost-efficient and environmental friendly measure. The selection of bulking agents is of primary importance to adjust the moisture and carbon/nitrogen (C/N) ratio of organic waste during composting. Therefore, initially, the performance of locally available bulking agents (i.e., sawdust and peat in Newfoundland and Labrador (NL)) during organic municipal solid waste (MSW) composting was evaluated. Results indicated that to generate a high temperature and a longer duration of high temperature to kill pathogens and sterilize the compost, peat was considerably more effective. A design of experiment (DOE) based methodology was then adopted to investigate the effects of multiple factors including C/N ratio, moisture content (MC), type of bulking agent (BA) and aeration rate (AR) and their interactions on the maturity, stability and toxicity of compost product. For the first time, enzyme activities were used as indices of maturity and stability during the course of a DOE based composting. The results provided guidance to optimize a MSW composting system that will lead to increased decomposition rate and the production of more stable and mature compost. Thirdly, the feasibility of using enzyme activities for indicating the state of marine fish waste composting was also examined. A good correlation among enzyme activities and different physiochemical parameters including oxygen uptake rate (OUR), C/N ratio, and germination index (GI) led to the conclusion that enzyme activities could be feasible indicators of the state and evolution of the composting process. Raw materials contribute about 30% of the biosurfactant production cost. Evaluation of the feasibility of using fish waste compost (FWC) extract as an unconventional substrate for biosurfactant production was highly desirable to refine the utilization of FWC and achieve the economical biosurfactant production. In this study, the nutrient extraction from FWC was achieved by enzyme hydrolysis and optimized using response surface methodology (RSM). The extract was used to produce biosurfactants by Rhodococcus erythropolis sp. P6-4P and bacillus sp. N3-1P strains. FWC extract showed a good potential as an unconventional source of nutrient for microbial growth. The obtained biosurfactants showed excellent properties with high surface tension reduction, high emulsification activity, and exhibited a high level of stability. The research outputs can contribute to the technical and scientific knowledge to design and operate composting system to manage the organic MSW and fish waste by achieving a double benefit of waste reduction while producing marketable products. Additionally, the products and the bioprocess can be of great value to both scientific understanding and industrial applications.

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