Performance Of Wood Soil Infiltration Treatment On Piggery Wastewater And Analysis Of Functional Bacteria

Piggery wastewater contains lots of COD, NH4+-N and TP. If it is discharged without any treatment, it will cause environmental pollution. This research carried out a study of improving process based on soil infiltration treatment(SIT), constructing a wood soil infiltration treatment(WSIT) by doping wood-chips into the soil infiltration treatment. At the meanwhile, this research optimized the starting method and operating condition of the reactor, and discuss ed the microbiological mechanism of nitrogen removal.There were three WSITs with the same volume in the study. There were 5 clapboards evenly in from bottom to top No. 1 WSIT with the wood and soil ratio 1:3. No. 2 WSIT was not set clapboard and filled by wood and soil for 1:3. No. 3 WSIT was not set clapboard but filled by the wood and soil separator for 1:4. Under the surface hydraulic loading of 0.2 m3/m2?d and 25℃ condition, three WSIT could successfully start in about 40 days and stabilized, however their removal of each contaminant were different. No. 1 WSIT’s removal ratio of COD, NH4+-N and TN was about 67.3%, 87.7% and 24.7%, respectively. And No. 2 WSIT was about 61.0%, 84.9% and 35.2%, No. 3 WSIT was about 68.5%, 94.5% and 45.0%. The remove of clapboards weakened the oxygen exchange with the outside. However it didn’t reduce the removal capacity of COD and NH4+-N. Instead it strengthened the denitrification. At the meanwhile, the soil ratio increased, the internal biomass increased, thereby the removal capacity of NH4+-N and TN was enhanced. The change of surface hydraulic loading had little effects on COD removal efficiency. But it made the NH4+-N and TN removal capacity reduced remarkablely when the surface hydraulic loading was 0.3 m3/m2?d. The removal ratio of NH4+-N and TN dropped to 80.8% and 37.9% respectively.The wood in the WSIT, not only improved the mechanical strength of the packed bed, so that it could withstand high surface hydraulic load, but also played a certain role in sustained release carbon. Due to a serious shortage of carbon in the piggery wastewater, the removal of TN was more a short-denitrification process. After influent NH4+-N was oxidized into NO2--N, one part was reduced to gaseous nitrogen, the other part was further oxidized to NO3--N flowing out of the system.In WSIT, the microbial population in the surface was low, which might be caused by either the uneven distribution of nutrients or ammonia concentration inhibition. At 0.2 m the copy number of bacteria was only 3.55×107 copies/μL. And microbes mainly gathered in the region 0.4-1.0 m, which was the main area of wasterwater contaminants removal. The population of denitrification bacteria and AOB changed similarly. It showed that the removal of nitrogen in WSIT relied mainly on short-denitrification process. And the maximum copy number of denitrification bacteria and AOB were about 2.67×107 and 4.70×107 copies/μL, respectivley. In the region of 1.0-1.2 m, the lack of nutrients was the limiting factor for microbial growth. It caused the microbial population reduced. The copy number of the total microbial was about 1.03×108 copies/μL.