Pollutant Removal Efficiency In Upflow Microaerobic Reactor For Treating Piggery Wastewater With Low C/N Ratio

Manure-free piggery wastewater was identified as high ammonium(NH4+-N) and low chemical oxygen demand/total nitrogen(C/N) ratio. Open discharge or disposal of piggery wastewater without treatment has a potential health effect and significant adverse effect on the environment and human health. The nitrogen removal is a common problem and has been considered a major challenge in piggery wastewater treatment. The novel microaerobic biological treatment technology including upflow microaerobic sludge reactor and upflow microaerobic biofilm reactor were constructed in the present study. And the effect of wastewater characteristic and reflux ratio on the performance of UMBR and the effect of temperature decrease on the performance of UMSR was investigated. According to the quality of the wastewater fluctuated following the breeding seasonality, sequencing batch reactor(SBR) was introduced as a pretreatment for a feasible influent C/N ratio for the subsequent microaerobic treatment.The SBR used in the present study had a good bearing capacity to the piggery wastewater quality fluctuation with seasonal change. The manure-free piggery wastewater with different influent NH4+-N concentration and C/N ratio treated by the SBR could maintain a feasible C/N for subsequent microaerobic treatment by adjusting aeration time. In the early stage of aeration time, the dissolved oxygen(DO) in the SBR was used to oxidizing organic matter, resulting in a rapid decrease of chemical oxygen demand(COD). And after COD decreased to a certain degree, the residual DO was used to NH4+-N oxidation, and a nitrite(NO2--N) accumulation was observed. According to the previous study about the effect of C/N ratio on the UMSR, the aeration time of the SBR was set to satisfy effluent C/N ratio as low as possible. When influent NH4+-N was lower than 400 mg·L-1 and C/N ratio averaged at 1.2-2.0, the aeration time was suggested 30 minutes. When influent NH4+-N was about 200-250 mg·L-1 and C/N ratio averaged at 3.0-4.5, the aeration time was suggested at 3.0-4.5 minutes.The UMSR had a better pollutant removal including COD, NH4+-N, TN and TP treating manure-free piggery wastewater with low C/N ratio at HRT 8 h, reflux ratio 45:1 and 27℃, and the pollutant in effluent could met the standard required by the Ministry Environmental Protection of China. When the temperature was 23℃, the removal load of NH4+-N, TN and COD averaged 0.71, 0.64 and 0.55 kg·m-3·d-1. But when the temperature further decreased to 20℃, although the NH4+-N removal in the UMSR could maintain at a better performance, the anammox bacteria was inhibited due to the low temperature. The TN removal was only 78.0% in the UMSR with an obvious NO2--N accumulation. Meanwhile, the COD removal was decreased to 53.4% with the temperature decreasing.The DO range in the UMBR was 0.20-0.70 mg·L-1 controlled by refluxing aerated effluent with the reflux ratio decreased from 45:1 to 25:1 by stages. No negative impact on COD removal had been found with a well NH4+-N oxidation. But the anaerobic ammonium oxidation would be inhibited by a DO above 0.70 mg·L-1 and resulted in a decrease in TN removal when reflux ratio was 45:1. The average COD, NH4+-N and TN removal load reached 0.60, 0.94 and 0.91 kg·m-3·d-1, respectively, with the HRT 8 h, DO 0.40 mg·L-1 and the reflux ratio 35:1 at 27℃. Obviously, the filler allowed more activated sludge to grow as biofilm in the UMBR and could construct suitable microenvironments for chemoheterotrophic bacteria, ammonia oxidizing bacteria, autotrophic and heterotrophic denitrifiers, separately. And the diversity of physiological groups of bacteria laid the foundation for the excellent pollutant removal in the microaerabic process.