A promising approach of reject water treatment using a tidal flow constructed wetland system employing alum sludge as main substrate

摘要

This study examined a novel reuse of alum sludge, an inescapable by-product of drinking waterntreatment process when aluminium salt is added as a coagulant, as the main medium in a laboratory-nscale multi-stage constructed wetland (CW) system for reject water treatment. Such reject water is anmain concern in municipal wastewater treatment plant (MWWTP) for increasing the organic andnnutrient loading. A ‘tidal flow’ strategy was employed to enhance the wetland aeration to stimulatenorganic matters (OM) and ammoniacal-nitrogen (N) oxidation while the ‘step feed’ operation wasnadopted to supply the necessary amount of carbon source for denitrification. The results reveal thatnalum sludge acting as P adsorbent can secure the P removal. Meanwhile, high removals of N and OMncan also be obtained due to the active bacteria growth on the alum sludge surface. The results shownthat average removal efficiencies of 65.4± 12.3% for chemical oxygen demand (COD), 67.8±9.2%nfor five-day biochemical oxygen demand (BOD5), 33.6±17.0% for N and 99.5±0.49% for P can benachieved over a period of 190 days. This indicates that novel reuse of alum sludge as medium in CWnsystem can provide a promising approach for reject water treatment. Therefore, it will significantlynreduce the amount of pollutant feedback through reject water recycling in a MWWTP.