Sanitation of blackwater via sequential wetland and electrochemical treatment

Abstract

The discharge of untreated septage is a major health hazard in countries that lack sewer systems and centralized sewage treatment. Small-scale, point-source treatment units are needed for water treatment and disinfection due to the distributed nature of this discharge, i.e., from single households or community toilets. In this study, a high-rate-wetland coupled with an electrochemical system was developed and demonstrated to treat septage at full scale. The full-scale wetland on average removed 79 ± 2% chemical oxygen demand (COD), 30 ± 5% total Kjeldahl nitrogen (TKN), 58 ± 4% total ammoniacal nitrogen (TAN), and 78 ± 4% ortho-phosphate. Pathogens such as coliforms were not fully removed after passage through the wetland. Therefore, the wetland effluent was subsequently treated with an electrochemical cell with a cation exchange membrane where the effluent first passed through the anodic chamber. This lead to in situ chlorine or other oxidant production under acidifying conditions. Upon a residence time of at least 6 h of this anodic effluent in a buffer tank, the fluid was sent through the cathodic chamber where pH neutralization occurred. Overall, the combined system removed 89 ± 1% COD, 36 ± 5% TKN, 70 ± 2% TAN, and 87 ± 2% ortho-phosphate. An average 5-log unit reduction in coliform was observed. The energy input for the integrated system was on average 16 ± 3 kWh/m3, and 11 kWh/m3 under optimal conditions. Further research is required to optimize the system in terms of stability and energy consumption.