PERFORMANCE OF SUBSURFACE FLOW CONSTRUCTED WETLAND FOR DOMESTIC WASTEWATER TREATMENT

Constructed wetlands (CW) have recently emerged as efficient technology for secondary treatment of wastewater in developing countries because of its low cost, ease operation, maintenance and generally good performance. At present there are a number of small scale units of CW for wastewater treatment in Tanzania but information on their performance is scarce. This study investigated the removal efficiency of fecal bacteria indicators, inorganic nutrients and Biochemical Oxygen Demand (BOD) from wastewater by a CW at the University of Dar es Salaam. The CW received wastewater from a primary facultative pond and was a monoculture system planted with Phragmites mauritianus (> 10 years old) with one unplanted cells as control. The results showed significantly (P < 0.001) higher removal of fecal indicator bacteria, in planted than in unplanted cells. Thus, the overall E. Coli and Fecal coliform percentage removal were 92.9±6.05 % and 93.2±6.13 % in planted cells as compared to unplanted cell which were 75.2±21.3 % and 58.7±21.2%, respectively. The BOD5 values in influent was also significantly (P < 0.001) reduced (71 ± 6.2%) in effluent of planted cells than in unplanted cells where the average percentage removal averaged 45 ± 3.3%. Similarly, nutrients were significantly (P < 0.001) removed in planted cells compared to unplanted cells. The results of this study show that plants enhanced the removal process and that the CW are efficient in wastewater treatment, supporting the ideas put forward by several researchers on the usefulness of these systems in developing countries. The system continues to perform efficiently for long time which signifies its cost effectiveness. It is recommended that CW be promoted for sewage treatment in a strategy to reduce wastewater pollution in Tanzania