红树林人工湿地对生活污水的净化效果

Purification efficiency of domestic wastewater by mangrove constructed wetlands

建立3条结构相同的潜流人工湿地带(长×宽×高为33 m×3 m×0.5 m),带内分别种植外来种海桑和本地种秋茄、桐花树,水力负荷为5 m3·d-1,停留时间约3 d,连续2年监测。结果表明:各湿地带对CODcr、BOD5、TN、NH3-N、TP和SP的平均去除率分别为65%、74%、53%、52%、67%和70%;不同红树植物湿地带的去除能力不同,且与植物生长状况相关;湿地运行初期,海桑生长速度最快,其去污能力最强;其后海桑受到化学试剂的影响死亡1/2,其去污能力显著低于桐花树和秋茄;各湿地带对肠道菌群的去除率均高于80%,不同植物之间无显著差异,但出水中的菌体数量远高于国家污水排放标准,应结合其他措施(如氯化消毒等)处理肠道菌群;红树林是比较理想的人工湿地净化植物,但外来种海桑对化学试剂、低温等不良环境敏感,生长不稳定,需进一步探讨红树林作为人工湿地净化植物的可行性。

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 corniculaturn） ]. 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 （CODcr） , biochemical oxygen demand （BODs ）, total nitrogen （TN）, ammonia-nitrogen （NH3-N）, total phosphorus （TP） and soluble phosphate （SP）, respectively. The treatment efficiency was positively correla- ted 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 coliform were removed and no significant differences were found among the three man- grove 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.