Understanding the COD mass balance in waste stabilization ponds (Uganda)

Due to their capability to remove pathogens and organic matter, coupled with cost efficiencies in terms of operation and maintenance, waste stabilization ponds (WSPs) remain a viable option for the treatment of wastewater, especially in areas where temperatures are favourable. Effective co-treatment of wastewater and faecal sludge (FS) is also feasible in combination with appropriate settling or thickening infrastructure for FS. This research sought to develop a Chemical Oxygen Demand (COD) mass balance for the treatment of wastewater and FS at National Water & Sewerage Corporation (NWSC). Triggered by the inconsistent performance of WSPs at NWSC with regard to meeting the national discharge standards, and considering COD as the major parameter of interest to gain insights into WSPs functionality, performance improvement recommendations were generated. Following sampling campaigns, analysis and field measurements at 2 WSP sites in the cities of Entebbe and Arua, one which was co-treating wastewater and FS, it was concluded that understanding not just the value of a parameter but also the COD fractions is crucial when designing a treatment facility. The mass balance of COD further presented resource recovery options in the form of biogas and biofuels which could be subjects of further study to determine their valorization.