蚯蚓引入垂直流-水平潜流湿地混流系统处理沼液的效果

为了避免或减少人工湿地处理厌氧发酵液发生堵塞,并提高系统处理效果,该试验将蚯蚓引入到垂直流湿地系统中,并与水平潜流湿地构成混流系统,用来处理厌氧发酵液。结果表明:采用蚯蚓垂直流湿地-水平潜流湿地混流系统处理厌氧发酵液,在进水平均有机负荷达1.82 kg/(m~2·d),水力负荷10、20 cm/d的条件下,对化学需氧量、总磷、总悬浮固体的去除率达到了90%以上,氨氮去除率达80%以上,总氮去除率也维持在60%以上。提高水力负荷对污染物的消减量更有优势,水平潜流湿地对总氮的消减优于蚯蚓生态湿地。2种水力负荷下,混流湿地出水化学需氧量、氨氮、总磷、总悬浮固体均能达到《畜禽养殖业污染物排放标准》要求。蚯蚓使混流系统对化学需氧量、氨氮、总凯氏氮的去除分别提高了2%、12%、4%,同时具有同步处理污水污泥,缓解湿地堵塞的效果,处理水质基本达标,处理污泥的成本也大大降低,因此具有很大应用潜力。

Treatment efficiencies of biogas slurry by earthworm-constructed vertical flow and horizontal subsurface flow constructed wetlands system

Anaerobic digestion slurry is wastewater with a characteristics of high solid content, high organic loads and hard for biodegradation. In this paper, Earthworm-constructed Vertical Flow (EVF) and Horizontal Subsurface Flow (HF) Constructed Wetlands System was designed based on the ecological functions of earthworms. The aim of this research was to investigate the potential of integrating earthworms into the vertical flow constructed wetlands to determine if they could mitigate clogging problems as well as to improve the wetland treatment performances. The Constructed Wetlands Systems were filled with sand and ceramsite as the main media. In this paper, hybrid constructed wetland system (a vertical flow wetland and followed by a Horizontal Subsurface Flow Constructed Wetland) was constituted to process anaerobic digestion slurry. Earthworms were added in the VF, a VF without earthworms was set as a contrast at the same time. We also set up two hydraulic loading 10, 20 cm/d, so there were four hybrid constructed wetland systems. After the system was in a stable performance mode, anaerobic digestion slurry was pumped into the systems. Effluents from each sample point were sampled and tested every six days during the two-month operation. Treatment efficiencies and the clogging were determined. Research results showed that when the average influent organic load reached 1.82 kg/(m2·d), hydraulic loading 10, 20 cm/d, COD removal efficiency reached 90%, TP removal efficiency reached 94% and SS removal efficiency reached 97%, ammonium removal rate reached more than 80%, and the total nitrogen removal efficiency was also maintained above 60%. Adding earthworms in 1st stage (VF), COD, ammonia nitrogen, total phosphorus can meet emission standards under hydraulic loading 10, 20 cm/d. On the other hand, after the treatment of the Horizontal Subsurface Flow (HF) constructed wetland, COD, ammonia nitrogen, total phosphorus, Suspended solid (SS) can meet emission standards. Adding earthworms increased removal of COD, NH4-N, TKN by 2%, 12%, 4%, respectively when the hydraulic loading was 10 cm/d. Improving the hydraulic load reduced greater amount of pollutants but the treatment efficiency decreased. Thus the processing costs were greatly reduced by improving the hydraulic load on the premise of effluent standards. The performance of horizontal subsurface flow wetlands in mitigating TN and TP was better than earthworm-constructed vertical flow wetland. Earthworms had the effect of synchronous treatment of sewage sludge and mitigating clogging. As such sludge handling cost would be greatly reduced, and therefore Earthworm-constructed Vertical Flow and Horizontal Subsurface Flow Constructed Wetlands System have great potential applications in treating anaerobic digestion slurry.