TECHNO-ECONOMIC ASSESSMENT FOR BIOGAS GENERATION FOR ENERGY USAGE FROM MUNICIPAL SEWAGE SLUDGE USING ACTI-ZYME AS DIGESTION CATALYST

A sewage plant with a capacity of 19 600 m3/day was considered for techno-economic assessment, with an operating efficiency of 60% and a life span of 20 years. $5.125/day of Acti-zyme were required for production of 12 769.69 kg/day for biogas costing $1.50/kg and 672.08 kg/day of bio-solids costing $16.00/50 kg. Capital budgeting techniques were then used for techno-economic assessment of sewage treatment recovering biogas and bio-solids. A net benefit of $5 656 363.92 per annum for using the Acti-zyme technology in sewage digestion was forecasted, whilst a net energy of 1 387.33 KWh was set to be produced. An investment of $22 199 501.40 was required for kick-starting the project. A positive net present value of $1 186 239.23 was realized with an internal rate of return of 17.6% and a payback period of 5.9 years. For breakeven to be realised, only 183 059.16 KWh must be produced. The techno-economic assessment indicated it is viable to treat sewage using Acti-zyme co-harnessing biogas and bio-solids as valued added products to an extent of making 0.04% to the Zimbabwe gross domestic product.