Assessment of Eco-environmental Impact of Harvesting Greenhouse Gas from Bio-waste: A Case of Wastewater Treatment Plant

Abstract

Aim: To determine economic and environmental impacts of greenhouse gas harvesting from bio-waste generated at wastewater treatment plant. Study Design: Quantitative experimental research for anaerobic digestion using a prototype bio digester. Place and Duration of Study: Case study of Kaunda square wastewater treatment plant in Lusaka city of Zambia. The duration of study was one year inclusive of research proposal writing. Methodology: Two Anaerobic Digestion (AD) experiments were conducted; alongside was control experiment-c. The first experiment-a used a balloon as means of biogas collection while experiment-b used water displacement technique. Each experiment used 9.6kg feedstock (on dry basis) into a 40 litres prototype bio digester and subjected to AD for 30days hydraulic retention time (HRT). Results: Total biomass potential available as feedstock at kaunda square wastewater treatment ponds was found to be 483,947kg per annum.  The 9.6kg biomass feedstock used in experiments A and B produced 0.0179  and 0.0165  of biogas respectively leading to 0.0172  as average monthly biogas production. Scaling-up these experimental findings of using 9.6kg feedstock to produce 0.0172  biogas, resulted in Kaunda square wastewater treatment plant with feedstock potential of 483,947kg yielding 868.43Kg (755,156.78 liters) of biogas production per annum. Total amount of greenhouse gases (GHGs) of environmental importance came from the summation of contributions of methane and carbon dioxide and expressed as carbon-dioxide equivalents . The value of the two GHGs was found to be  with direct effect on global warming and climate change while the digestate had its economic value in agricultural use where the potential stood at 9,662 by 50kg bags of nitrogen/sulphur rich organic fertilizer per annum. Conclusion: Energy harvesting through harvesting of greenhouse gases from bio-waste can lead to reduction in emission of greenhouse gases, reduce energy deficit and improve food security through soil preservation.