红树林人工湿地对生活污水的净化效果

Three identical belts (length : 33 m, width : 3 m, depth : 0.5 m) of subsurface-flow wetland were constructed, and each was planted with one of three different mangrove plants [one exotic mangrove species (Sonneratia caseolaris) and two native species (Kandelia obovata and Aegiceras corniculatum)]. The hydraulic loading rate was 5 m³ · d⁻¹ and the hydraulic retention time was three days. The study was lasted for 2 years. The average removal efficiencies were 65%, 74%, 53%, 52%, 67% and 70% for chemical oxygen demand (COD_cr), biochemical oxygen demand (BOD₅), total nitrogen (TN), ammonia-nitrogen (NH₃-N), total phosphorus (TP) and soluble phosphate (SP), respectively. The treatment efficiency was positively correlated with plant growth. At the beginning of the study, S. caseolaris had the fastest growth and best purification efficiency. However, half of S. caseolaris were dead due to an accidental spillage of herbicides few months after the start, the treatment efficiency of S. caseolaris was then dropped and became lower than that of A. corniculatum and K. obovata. More than 80% of total coliform and fecal colifoπn were removed and no significant differences were found among the three mangrove species, but the average concentrations in the treated effluents were still higher than the discharge standard set by the state government. The results indicated that a post-treatment process to remove coliforms must be included if the mangrove constructed wetland is used for domestic sewage treatment. As for S. caseolaris, further research is needed to understand its sensitivity to chemicals and low temperature.