Comparison between aerated static piles and vermicomposting in producing co-compost from rural organic wastes and cow manure

In this study, the process of producing compost from rural separated solid wastes using aerated static piles (ASP) and vermicomposting was investigated which was carried out from September 2015 to January 2016. A combination of waste ingredients, conditions, processing duration, analysis of key parameters (moisture, pH, temperature and C/N ratio) governing the process, the quality of the final product and economic assessment was considered. Six piles were created in the ASP method, and six piles were loaded in vermicomposting pits in which the Eisenia foetida species was used. Three piles in each method (odd piles) contained 100% putrescible wastes, while the rest of three piles (even piles) contained 75% putrescible wastes and 25% cow dung. The total coliform reductions in both kinds of waste compositions were observed. Heavy metals such as lead, cadmium and nickel were not found in any of the piles. Comprehensive statistical analysis, including the comparison of the variables, correlation among variables and analysis of variance, was performed for the measured parameters. Comparing the final product with standards showed that composting proceeded satisfactorily in both methods. There were no issues such as bad smells or rodents during the study. An approximate chemical empirical formula calculated for the organic fraction of the composts generated in vermicompost pits and ASP was C15.1H22.4O7.7N and C15.2H21.5O14.3N, respectively. Economic assessment showed that net present value in the internal rate of return for producing compost using aerated static piles was equal to 12.4%; for vermicomposting, it was 5.4%.