INCREASE IN BIOGAS PRODUCTION FROM PREDIGESTED AQUATIC PLANT USING HUMAN URINE AS ENHANCER

Abstract

Water hyacinth, an aquatic plant, due to its rapid growth, is easily available and is used for treatment of variety of waste water and is also a good biogas producer, due to its high water content, soft organic matter and a favorable C/N ratio. The aim of the present study is to assess the anaerobic biodegradability of water hyacinth – both thermo-chemical pretreated and untreated. Human urine is used as an enhancer of the gas production. It increases the gas production rate and decreases the total gas production time as per the following reaction CH3COOH + NH3 CH4 + CO2 + NH3. It also, supplies the nitrogen for bacterial growth. The temperature and human volume is taken as the parameter. Water hyacinth, collected from local pond is cut into pieces and treated with sodium hydroxide and then heated in a pressure cooker for 15 mins. The P H is maintained at 10. Then the material is kept for 7 days in facultative condition. The experiment is then conducted by taking 100 gm of the substrate, the human urine of varying volume and inoculum in a conical flask. The human urine volume and temperature is varied in different experiment. The gas produced is collected in the gas burette by water displacement. It has been observed that, pretreatment reduces the time for hydrolysis step in the conversion of complex water hyacinth organic matter in order to increase the soluble organic constituents. Gas production started within 7 days. With increase in urine volume upto 150 ml, the gas production is increased and beyond which it is decreased due to the accumulation of ammonia. The production rate increases upto 41 o C. The gas production is quantified as first order reaction as per black box model. The reaction rate constant is seen to fit the Arrhenius equation in a better way. The rate expression is seen to be function of both temperature and urine volume.