EFFECTS OF THE DEGRADATIVE ABILITY OF MIXED MICROORGANISMS ON COMPOSTING DOMESTIC FOOD WASTES

Abstract

This project was proposed to assess the degradative activity of mixed microbial cultures on domestic food wastes (DFW) for composting. The domestic food wastes were inoculated with the mixture of the microorganisms, left to decompose for 42 days at ambient temperature (28oC) during which samples were taken at 7-day intervals for microbial and physicochemical analyses (proximate, minerals and anti-nutrient) using standard microbial and chemical methods. Different species of fungi namely Aspergillus flavus, Aspergillus fumigatus, Rhizopus nigricans, Varicosporium elodeae, Trichoderma roseum, Penicillium italicum and Rhizopus nigricans were found to inhabit the domestic food wastes. The test bacteria were obtained from the Department of Microbiology of the Federal University of Technology, Akure and were confirmed to be Lactobacillus delbrueckii, Geobacillus stearothermophilus, Bacillus megaterium, Lactobacillus jensenii, Bacillus sphaericus, Macromonnas mobilis, Azotobacter, Listeria monocytogenes and Kurthia species. The composts were used to grow maize plants using pre-planting and post-planting application methods. Height of each shoot, number of leaves and the height of the plant were determined. The microbial load showed that DFW sample inoculated with Azotobacter and Penicillium italicum had the highest cell count (2.7x107 cfu/ml) while DFW sample inoculated with Kurthia species and Aspergillus niger had the lowest microbial load of (1.2 x 104 sfu/ml) at week 6. The proximate composition of the composts revealed that the moisture contents of the treated samples ranged between 60.34 ± 0.01% and 69.05 ± 0.02%. The ash, carbohydrate, crude protein, fat and crude fibre contents of the compost samples ranged from 6.02 ± 0.02% to 15.25 ± 0.02%, 21.17 ± 0.01% to 28.37 ± 0.02%, 6.56 ± 0.01% to 8.56 ± 0.02%, 0.76 ± 0.01% to 2.15 ± 0.01% and 1.36 ± 0.01% to 2.04 ± 0.02% respectively. The macronutrients (nitrogen, phosphorus, potassium, calcium and magnesium), had the highest values of 1.36 ± 0.01%, 0.55 ± 0.01%, 0.73 ± 0.02%, 1.59 ± 0.01% and 1.73 ± 0.15ppm, for samples inoculated with Varicosporium elodeae + Rhizopus nigricans, Bacillus megaterium + Lactobacillus jensenii, Listeria monocytogenes + Aspergillus niger and Lactobacillus delbrueckii + Geobacillus stearothermophilus respectively, while the micronutrients (iron, manganese, zinc and copper) had values of 0.02 ± 0.01ppm, 0.01 ± 0.01/ppm, 0.02 ± 0.01ppm and 0.04 ± 0.01ppm respectively for DFW inoculated with Bacillus megaterium + Lactobacillus jensenii, Varicosporium elodeae + Rhizopus nigricans, Lactobacillus delbrueckii + Geobacillus stearothermophilus and Azotobacter + Penicillium italicum, being the lowest at week 6. There was a significant reduction in the antinutritional contents of the composts. Effect of the composts on the maize plant showed that there was a positive effect of the compost on the growth of the maize