Constructed mangrove wetland as secondary treatment system for municipal wastewater

摘要

Intermittent subsurface flow mangrove microcosms were constructed to investigate their capabilities in treating primary settled municipal wastewater collected from a local sewage treatment work in Hong Kong SAR and the effect of hydraulic retention time(HRT).The study was carried out in a greenhouse and without any tidal flushing or tidal cycle,with half of the tanks planted with Kandelia candel and half without any plants.The removal percentages of dissolved organic carbon(DOC),ammonia-N,inorganic-N and total Kjel-dahl nitrogen in the planted systems were 70.43-76.38%,76.16-91.83%,47.89-63.37% and 75.15-79.06%,respectively,significantly higher than in the unplanted system during the 6-month treatment period.More than 97% ortho-phosphate and 86.65-91.83% total phosphorus were removed by the planted microcosms.The HRT of 10 days had better removal than that of 5 days,and the best performance was obtained in the planted microcosms with 10 days of retention time.During the 6-month experimental period,the concentrations of all forms of nitrogen in the treated effluent were within the standards for effluents discharged into Group B inland waters and coastal zone with open waters.In terms of phosphorus,the effluents met the standards for effluents discharged into Group A inland waters.These results suggest that it is feasible to use the constructed mangrove wetland without tidal flushing as a secondary treatment process for municipal wastewater.