Submitted by: Amar Neku
Supervisors:
1. Dr. Shashi Shankar Rajbanshi (Member)
2. Mr. Mahesh Prasad Bhattarai (Member)
Abstract
A highly polluted city like Kathmandu should utilize its ubiquitous organic waste (ca. 70 % of total volume) as a valuable resource before the waste creates problems. In a country like Nepal, where there is no well-developed mechanism for integrated solid waste management, large-scale waste management systems are impossible in the immediate future. Nevertheless, there is a need for a system where private and individual initiatives can contribute to the management of municipal solid waste (MSW). In this context, it is a worthwhile experiment to evaluate the performance of home composters made of plastic tanks. The home composters considered here were designed by considering the different aspects of known composting ecosystems. The materials used for studying the composting process include organic fraction of municipal solid waste, garden waste, agriculture waste, and vegetable market waste. Their carbon to nitrogen (C/N) ratio and moisture content were examined to determine the proportion of each of these wastes in the final mixture. The carbon to nitrogen ratio and moisture content of starting material (day 0) were adjusted to 24.3 % and 55 % (wet weight), respectively. The composting matrix was taken out from the tanks on day 125 and kept in a windrow system for further maturation.
The highest mean temperature reached 610C on day 4. A gradual decrease in temperature was then observed until the temperature stabilized at 2.50C above the ambient temperature on day 60 and thereafter. The carbon dioxide evolution rate (CER) reached the maximum average value of 13.5-gkg-1 dry weight day-1 on day 17, and decreased to 4.3 units on day 60. However, the CER slightly increased to 5.9-g kg-1 dry weight day-1 on day 150 due to the introduction of the windrow system on day 125. The carbon to nitrogen (C/N) ratio declined logarithmically to values 12.1 and 9.2 on day 60 and 150, respectively. The five day bio-chemical oxygen demand (BOD5) of water extracts of the compost decreased logarithmically from an average value of 49.5 g O2 kg-1 dry weight on day 1 to 7 g O2 kg-1 dry weight on day 60. Eventually, it reached to the value of 6.6 g O2 kg-1 dry weight on day 150. The germination index (GI) of fenugreek (Trigonella foenum-graecum) seeds on water extracts of the compost increased from 45 % of the control on day 1 to 71.6 % of the control on day 60. Eventually, it reached 82.2 % of the control on day 150. The average pH increased gradually from 6.9 on day 1 to 8 on day 60. Then, it stabilized at 7.9 on day 150. The electrical conductivity (EC) increased from 1.5 dS m-1 on day 1 to 2.8 dS m-1 on day 60. The EC then slightly declined to 2.5 dS m-1 on day 150. The nutrient values in terms of NPK (Nitrogen, Phosphorous, and Potassium) of the compost were found as 1.3, 0.3, and 3.5 % of dry weight, respectively. A distinct positive correlation was observed between total carbon versus BOD5. In contrasts to this, the C/N ratio versus GI was negatively correlated.
The composting process performance of the passively aerated home composters was satisfactory in terms of maintaining aerobic condition, removing heat through ventilation, and pasteurizing the pathogens inherent to the organic wastes. The time required for the active decomposition and maturation was approximately 60 and 115 days, respectively. The quality of the compost product met the ranges of standard NPK values given in the literature.