BIOGAS PRODUCTION FROM WASTE TEA LEAVES AS A WASTE MANAGEMENT STRATEGY AT DL KOISAGAT TEA FACTORY NANDI HILLS (KENYA)

Abstract

Most tea factories in Kenya utilize wood as the main source of energy. Wood is burned in boilers to produce steam that is used in unit operations in tea processing. The firewood produce stack gases that are emitted into the environment. DL Koisagat tea factory uses approximately 12 tons of wood daily, taking into consideration numerous tea factories in the country, contributing to rapid deforestation. Waste tea leaves from these factories are used as compost manure and the rest discarded on the surface. Decomposition of these dumped waste produces methane into the environment and affect the quality of ground water through coloration. Considering environmental degradation caused by tea factories it prompt the need for waste management and alternative sources of energy. Waste tea leaves can be anaerobically digested in a batch reactor to produce methane which is a clean source of energy and also reduce and reuse of waste from the factory. The study aim at determining the quantity of waste tea produced daily in the factory. Also determining the optimum conditions of retention time, pH, and temperature required in generation of methane gas. The factory waste tea leaves quantity was determined by measuring the weight of daily sweepings using industrial crane scale (KERN HFB). Waste tea leaves from the factory was mixed homogeneously with cow dung (inoculum) and fed into the digester. The digestion process took place under varying conditions of retention time, pH and temperature. The gas collected was pumped into gas samplers using vacuum pump for analyzing in the Gas chromatograph (FID) within 48 hours for methane quality determination. It was found that DL Koisagat produces approximately 2,847.00kg of waste tea leaves per month. The optimum conditions for biogas production from waste tea were pH of 7, temperature of 37oC and retention time of 20 days. Though the highest yield of methane was obtained at pH of 5, temperature of 50oC and retention time of 20 days, these conditions also promote production of high quantities of carbon dioxide gas. This impurity limits the quality of methane by hindering its combustion. Based on the results of the study, it was concluded that waste tea leaves produces biogas with 19% methane. From monthly production of waste tea, there is sufficient biomass for biogas production and also waste tea leaves from the factory have the potential to produce methane. The optimum conditions of pH, temperature and retention time have the potential to generate biogas from waste tea. Methane produced contains impurities of carbon dioxide, ammonia and hydrogen sulphide gases. Purification process of methane increases the cost of production.