Study On Rural Piggery Wastewater Treatment With Tidal Flow Constructed Wetland

Constructed wetland is a human design and construction sewage treatment technology which is on the basis of simulation of natural wetland ecosystem. Compared with conventional wastewater treatment technologies, constructed wetland treatment process has many good advantages, including higher treatment efficiency, lower investment and operating cost, simpler equipment, more convenient operation and management, landscaping and so on. However, continuous stream operating mode of traditional wetland could not supply sufficient oxygen for organic matteroxygenolysis and ammonia nitrogen removal in system. The bed would show an anoxic and anaerobic environment, which is not conducive to the effective removal of contaminants.Tidal flow constructed wetland is a new type of modified constructed wetlandtreatment technology which is based on the traditional constructed wetland.It adopts a operating mode of "intermittent influent, instantaneous effluent",hence, the tidal flow system is periodically filled with water and drained dry. During operating, depend on the change ofsaturated infiltration surface,it generatessubstratevoidsuction in the bed, causing to oxygen forced to inhale to the bed.This operating mode would significantlyimprove oxygen transfer volume and effective utilization rate of oxygen. Thus, treatment effect of wetland would be strengthen.Rural piggery wastewater has high organic matter concentration, high nitrogen and phosphorus content. Base on the characteristics, in this study, a small-scale experimental unit of the tidal flow constructed wetland system was constructed to studythe removal efficiency of pollutants in wastewater and analyze influence factors during operating. The results of the study are as follows:(1)By adopting "U-type" tidal flow constructed wetlandoperating mode, the system exhibited good nitrogen, phosphorus and organic matter removal effect. Under the hydraulic loading of 0.62m3/(m2·d) and operating cycle 6h, the average removal rates for COD, NH4+-N and TP reached 89.6%, 71.37% and 92.61%, respectively. Operation mode of tidal flow provided sufficient oxygen for the system.(2)By adopting Al sludge as substrate of constructed Wetland, the system showed quite good removal effect. During reaction period, under 11mg/L influent TP, the removal rate for TP reached more than 90%.(3)Under different influent C/N ratio condition, the removal rates for COD had no significant difference, each C/N ratio reachedover 85%. NH4+-N removal rate showed a rising trend with the C/N ratio. When C/N ratio was 7, the removal rates for NH4+-N reached 72.28%, which was the highest.(4)Compared with operation mode of completely risingwastewater through Peristaltic pump, adopting "U" tidal flow wetland bed design,implementgravity flow of wastewater, the system could save nearly half of electricity. The method achieved effect of reducing energy consumption.(5)After five months of operation,the system appeared water infiltrated slowly, upper substrate ponding and water flow rate decreased.By analyzing cause clogging,measures of filler backwash effectively solved the problem of clogging of the substrate.