Effect of Waste Separation on the Composting of Organic Waste Fraction from Domestic Solid Waste

Abstract

In Nigeria, due to lack of sanitary landfills and general poor attitude towards waste management, various types of wastes such as: commercial, hospital, construction and domestic wastes are mixed and transported in open trucks to unprotected open dumpsites. This is likely to interfere with degradation of biodegradable wastes by non-biodegradable components, which are non-permeable to water and gases. These factors are needed by biodegrading materials for adequate decomposition. This study therefore, evaluates the effect of waste separation on natural biodegradation of solid domestic waste. Domestic waste samples were obtained from three different households at Rivers State University campus senior staff quarters, Port Harcourt, Nigeria and were sorted and categorised into biodegradable (organic), mixed fractions (inorganic and organic) and non-biodegradable. These were composted in open containers and monitored. Samples were withdrawn biweekly and analysed for microbiological and some physicochemical parameters for a period of 12 weeks. Morphological and biochemical characteristics were used for identification of isolates. Statistical analyses of the results were performed using SPSS version 21. Results of total heterotrophic bacterial counts in the biodegradable fraction of the wastes recorded the highest counts that ranged from 8.2±0.01x105 to 8.5±0.01x1806Cfu/g followed by the mixture, that ranged from 8.1±0.02 x104Cfu/g to 6.4 ±0.01x105Cfu/g, paper waste that ranged from 5.0 ±0.00 x103 to 6.7 ±0.01 x104Cfu/g, metal waste; ranging from 4.0 ±0.00 x 102 to 4.7±0.01 x103Cfu/g, plastics waste; ranging from 2.1±2.8 x103 to 4.3 ±0.02 x 102Cfu/g and glass waste that ranged from 4.0 ±0.00 x102 to 4.7±0.01 x 103Cfu/g. The following bacterial genera were identified: Bacillus, Providentia, Proteus, Staphylococcus, Escherichia, Enterobacter, Pseudomonas, Klebsiella, Streptococcus, Micrococcus, Citrobacter, Acetobacter, Serratia, and Chryseobacterium. Fungi identified belong to the following genera: Aspergillus, Penicillium, Mucor, Rhizopus, Saccharomyces, Alternaria, Chlamydosporium, Fusarium and Candida. At the end of the monitoring period, 50% of the biodegradable category, 31% of the mixed category and 17% of the paper waste were degraded. The other categories, metals, plastics and glass did not show differences in weight loss during the monitoring period. Results of statistical analyses revealed that there was significant difference in the decomposition rate of the biodegradable and mixed wastes samples at P<0.05, when compared to the other categories. Hence, waste separation into biodegradable and non-biodegradable categories enhanced the maximum rate of degradation of the organic portion and this would reduce the amount of wastes at dumpsites/landfills.