Carbon Abatement in Wastewater Stabilization Ponds Case Study of Dandora Waste water stabilization Ponds in Kenya

Abstract

Wastewater treatment plants (WWTPs) operate on natural processes in removal of Biochemical oxygen Demand (BOD), Oxygen chemical (COD), nutrients organic carbon, and pathogenic microorganisms from wastewater. Wastewater treatment produce considerable amount of greenhouse gases largely methane during their operations. Reducing these emissions from the treatment process and the contribution of the wastewater treatment plants is important in reducing green house gas effects into the environment. This can also allow recuperating energy, and nutrients, thus reclaiming of treated wastewater in less developed countries can be of importance in boosting the energy sources as well as improve in Economies of these countries. It is therefore important to understand how these emissions can be computed and get documented. This research has attempted to estimate and compute the greenhouse gases, primarily methane, emissions from Dandora Sewage Treatment Plant (DSTP) in Nairobi Kenya using the Intergovernmental Panel in Climate Change (IPCC) Guidelines (1996) and IPCC Good Practice Guidance (2000).Operations data from year 2007 to year 2013 was obtained from Nairobi City Water and Sewerage Company (NCWSC), the operator at the plant and analysed to determine the average BOD loading rate and flows to the Plant as well as the BOD removal rate across the anaerobic ponds from which the amount of methane being generated by the DSTP was computed. The average BOD loading rate and effluent to and from the anaerobic ponds of DSTP was 454.11mg/l and 120.82 mg/l respectively between year 2007 and 2013.This was 88.7% of the design capacity of 512mg/l. The plant received an average of 83,648.30 m3/day which was 52.28% of the design capacity of 160,000m3/day from year 2007 to year 2013.This represented a BOD mass loading of 37,985.53kg/day against a designed capacity of 81,920kg/day which was 46.37%.Thus DSTP has been operating at about 50%. The plant generated an average of 11.29m3/day of methane from year 2007 to year 2013 at the current flows and can generate an average of 14.1m3/day of methane at a full capacity of 160,000m3/day at a BOD loading of 512mg/l. Methane generated from the anaerobic ponds at the plant can be collected using floating covers and be used to generate electricity that can be imported into the national grid at a feed in tariff ,be used in operations of the plant or be sued for carbon credits. This would increase revenue to the operator as well as prevent methane being released into the atmosphere as it is the case now.