Preliminary investigation of the performance of an anaerobic baffled reactor and a constructed wetland with different media in treating faecal sludge and greywater

Abstract

Emerging worldwide challenges such as urbanization, climate change, water scarcity and poor sanitation are pushing for development of viable alternative technologies to reduce on the impacts resulting from these challenges. Nature-based solutions such as anaerobic baffled reactors (ABR) and constructed wetlands (CWs) look to be feasible choices because of their low cost in operation and maintenance. This study sought to assess the performance of an ABR and a CW, with pumice and plastic media in co-treating septage and grey water. Despite the fact that the present treatment plants in Kampala can manage 400 m3/d and 200 m3/d, the study was driven by the significant volume of faecal sludge (FS) originating from various sections of Kampala city (900m3/d) and its neighbouring regions (150 m3/d). In order to achieve the study goal of evaluating the efficiency of an ABR and CW in the treatment of septage and grey water, septage from Lubigi treatment plant and grey water from Makerere Africa hall were characterized and the ABR was fed with a mixture of septage and grey water in an optimal mix ratio of 1:1.17. The performance of the ABR-CW was monitored to assess the pilot-plants performance in removing the various pollutants. The removal efficiencies of 89.34±688.69 %, 95.92±1114.62%, 85.07±764.15%, 72.71±106.21% and 71.12±7.39% for chemical oxygen demand (COD), biochemical oxygen demand (BOD5), total suspended solids total (TSS), TN and TP respectively, were achieved in the ABR (HRT of 73.9hrs). The effluent from the ABR was subjected to further treatment in the CW units each with floating mat, plastic and pumice media. The COD removal efficiencies of 91.66±146.75%, 95.64±135.87% and 94.17±139.86% were obtained in the floating mat, plastic and pumice media, respectively. Similarly, TSS had removal efficiencies of 83.56±286.07%, 83.75±292.34% and 84.31±292.17% respectively and TN had removal efficiencies of 88.27±95.19%, 89.88±74.2% and 90.91±74.43% respectively. Parameters such as pH (7.28±0.83, 7.3±0.5 and 7.31±0.72) and turbidity (40.25±16.43 mg/L, 30.88±9.4 mg/L and 30.13±10.66 mg/L) met the national effluent discharge standards across all the three media as well as the concentration of electrical conductivity (956.88±449.79 mg/L) in pumice. Basing on the performances, the combination of the ABR-CW with a pumice media performed well although the effluent did not meet the national effluent discharge standards. Therefore, the effluent required further treatment by increasing the hydraulic retention time of the influent or reducing the amount of septage fed into the plant and its performance monitored.