Co-composting of municipal solid waste and dewatered faecal sludge: a case study of Kumasi

An experimental waste management option - co-composting, was conducted to examine the feasibility of composting the large volume of organic portion of the solid waste and human excreta generated daily within the Kumasi metropolis and to assess the quality of the product to be utilized as fertilizer (organic manure), soil ameliorant, land cover as well as ensuring promotion of better environmental and sanitary conditions in the city. Market waste (Mw) and Household waste (Hw), which together make a huge contribution to the solid wastes generated in the metropolis, were used in mixtures with Dewatered Faecal sludge (DFs) in a ratio of 3:1 as raw materials for windrow composting (i.e. Mw/DFs as pile I and Hw/DFs as pile Ill respectively) at a co-composting plant built at Buobai, a suburb of Kumasi. Three replicate mixtures of each treatment were raised as the main treatment. Similarly, three replicates each of the market and household wastes without faecal sludge additions serving as unmodified experimental controls were also raised (i.e. Mw and Hw as Piles II and IV respectively). These were monitored in 10 weeks during decomposition for: microbial population dynamics, physical and chemical changes within the mixtures. Biological components monitored were population changes in: total bacteria, total fungi, E. coli Clostridium and helminthes eggs (Ascaris). Temperature evolutions and fluctuations, pH changes and moisture fractions of the mixtures (piles) were also followed as physical parameters. Finally, changes in chemical concentration involving heavy metals (Pb, Mn, Cu, Zn, Fe) and macronutrients - plant nutrients required in greater quantity (C, N, C, N, P, K) as well as C/N ratio were monitored during the period of decomposition. The relationship between each main treatment and the control on all the parameters monitored! was statistically analyzed. The results revealed good microbial and physiochemical conditions of the products at the end of the 10th week process. There was a drastic reduction in the populations of all pathogenic mesophilic and thermophilic microorganisms considered. The reduction in the populations was reflective in all the products with Ascaris achieving between 90-98 % in the piles: 315.00, 6.00, 50.67 and 5.00 /g in piles I, II, III and IV respectively hence, both conventional and co-composting methods are equally effective approaches in improving product quality as far as microbial destruction is concerned. Temperature of the final products relatively assumed ambient values; 30.1. 33.1. 33.0. and 29.0 °C in piles I, II, III and IV respectively while pH levels attained, ranged between that of slightly acidic and basic matrices; (6.93- 8.02). Appreciable high macronutrient levels for example, nitrogen concentrations in the co-composting products of piles I and III (1.52 and 0.93 %) compared with that of the conventional mixtures; piles II and IV (0.38 and (3.28 % respectively) were recorded. In a similar extent, heavy metals concentrations recorded were higher in piles I and III mixtures as compared to piles II and IV; Zn and Fe recording relatively the highest levels of heavy metal contaminants in all the piles: (Zn: l67.62, 78.75, 6l.0, 17.28 ppm and Fe: 492.80, 284.25, 274.6, 60.2 ppm in piles I, II, III, IV respectively). However, the overall heavy metal concentrations in the final products were within tolerable limits making them safer for application baring any other harmful factors. In conclusion, having undergone a smooth decomposition, drastic microbial reduction and appreciable retention of chemical nutrients to support soil fertility among other uses (especially in piles I and III), the products show that co-composting provides an efficient approach in waste treatment methods and improved compost quality It is therefore recommended as a suitable waste management option for adoption by Kumasi Metropolitan Assembly (KMA) other Metropolitans as well as the various District Assemblies in the country.

Source: KNUST