Assessment of the status and performance of horizontal subsurface flow constructed wetlands for industrial wastewater treatment in Tanzania

Three horizontal subsurface flow constructed wetlands (HSSF-CWs) evaluated in northern Tanzania were from the meat, winery, and paper industries. The winery and paper industry CWs exhibited surface flow, while the meat industry CW did not. This difference was attributed to inadequate pretreatment, hydraulic, and organic overloads. Poor design also contributed to the issue, as the design flow rates exceeded those suggested by Darcy’s law, resulting in system clogging. The clogged HSSF-CWs produced poor effluent due to insufficient contact time and area between the wastewater, microorganisms, and rhizosphere. The winery industry effluent met Tanzania and WHO standards for BOD (29±1.41 mgO2/L), P (3.68±0.81 mgP/L), and FC (3.2±0.1 log unit) but did not comply with COD (137.5±116.67 mgO2/L), NO3-N (44.75±32.17 mgN/L), and NH3-N (41.05±2.9 mgN/L). The paper industry effluent met standards for NH3-N (0.12±0.17 mgN/L), P (0.22±0.26 mgP/L), and FC (3.4±0.1 log unit) but did not meet the standards for BOD (59.69±0.44 mgO2/L), COD (72.5±31.82 mgO2/L), and NO3-N (96.5±12.02 mgN/L). The meat industry effluent met standards for NO3-N (18.6±10.75 mgN/L) and FC (3.6±0.3 log unit) but failed to meet standards for BOD (59.5±14.85 mgO2/L), COD (160.5±89.8 mgO2/L), P (29.49±3.79 mgP/L), and NH3-N (57.6±23.19 mgN/L). Therefore, proper design of HSSF-CWs requires adherence to Darcy’s law and ensuring adequate information on production. Moreover, for a properly designed HSSF-CW to remain functional and have a long lifespan, regular monitoring, including water quality analysis, is essential. published by the Journal of Biodiversity and Environmental Sciences | JBES