Evaluation of a constructed wetland for removal of some physicochemical and microbiological contaminants from wastewater in a residential tertiary institution in Nigeria

摘要

Covenant University is a residential tertiary institution in Canaan land, a large faith based facility, whose population can be more than 75,000 during Sundays religious activities in Ota, Ogun State, Nigeria. Sewage from this community is treated by a series of constructed wetland located in the University, with its effluent discharging into a canal that empties into River Iju. This river is used by several hundreds of thousands of people downstream. The effluent flows through six sets of constructed wetlands, each with four chambers and the treatment process in the wetlands was evaluated by its adequacy and efficiency. Input and output of the system were monitored. Results indicated that the series of wetland reduced the total dissolved solids (TDS) by only 8% and conductivity by 11%, while the pH was constant at 6.8. The microbiological test results indicated a 99% reduction in the most probable number of coliforms (MPN) from 1,600 cfu/100 mL. The constructed wetland achieved 85%, 79%, 52%, 79%, 66% and 83% reduction for coliform, staphylococcus, salmonella, salmonella and shigella, total viable count, and fungi, respectively. Results of the colony units/mL, cfu/mL, for these parameters, obtained at both upstream and downstream and at the point of discharge into the canal compared with those at the effluent point showed adequacy of removal of contaminants by the constructed wetland series. The efficiency of the wetlands can be enhanced further by slowing the flow rate and increasing the number of wetland chambers. Further work is required to determine the rate of recovery of the polluted canal water.