TECHNO-FEASIBILITY OF A PLANT TO CAPTURE 8TPD OF METHANE GAS FROM SEWAGE SLUDGE

Abstract

Currently, there is an increase in amounts of sewage sludge and disposal routes are limited posing a great threat to the environment, at the same time, economic hardships in production of electricity have also led to constant load shedding and higher electricity rates nationwide. This study was conducted to develop a plant to capture methane gas from sewage sludge for electricity generation with minimized human intervention so as to cab the above stated effects.72% of methane gas was captured from sewage sludge over a 15 day period. Mass and energy balances for the methane capturing plant showed that a throughput of approximately 617 kg/hr sewage sludge would give the stated amount of methane. This amount of methane gas when converted to electrical energy would also sustain Harare`s daily electrical consumption of 1600MW. Process conditions were observed to be at mesophillic temperature of 37ᴼC- 40ᴼC.The bio digester as the major piece of equipment was designed with an installed carrying capacity of 10 tons of sewage sludge. Based on design calculation, the digester was predicted to produce up to 8 tons per day of methane and 1125 kg of organic fertilizer from the digestate. An economic analysis was also carried out and the process proved to be viable economically as it has a payback period of 3 years for a unit cost of $2.50 /kg and is most likely not to face bankruptcy as shown by low capital gear ratio. This project proved to be technically and economically viable as it also supports the Zim Asset in providing a benefit to the nation