Comparative effectiveness of engineered wetland systems in the treatment of anaerobically pre-treated domestic wastewater

A study was carried out to assess the effectiveness of engineered wetland systems (EWSs) in the treatment of domestic wastewater pre-treated in an upflow anaerobic sludge blanket (UASB) reactor in the tropics. Relative advantages of using different wetland plants were also assessed. The EWS had three units using river sand media. One bed was left unplanted and used as a control while each of the remaining beds was planted with either Typha latifolia (cattail) or Colocasia esculenta (cocoyam). The EWS was able to remove well phosphorus, sulphate, ammonia, and COD. Mean removals of phosphorus (as orthophosphate) were 51% for the control unit, 69% for the T latifolia unit, and 75% for the C. esculenta unit. Mean removals of sulphate were 46% for the control unit, 72% for the T latifolia unit, and 77% for the C. esculenta unit. Mean removals of ammonia were 63% for the control unit, 74% for the T latifolia unit, and 75% for the C. esculenta unit. Mean removals of COD were 65% for the control unit, 79% for the T latifolia unit, and 75% for the C. esculenta unit. This study demonstrated that the EWS can effectively treat anaerobically pre-treated UASB reactor effluent. As such, when coupled to a UASB reactor, the EWS is a promising alternative to the traditional septic tank/soakaway coupled systems widely used for treating domestic wastewater. This study reaffirms the accepted notion that wetland plants enhance the performance of wetland systems. However, in this study, no significant performance difference was observed between the two planted EWS units. (c) 2004 Elsevier B.V. All rights reserved.