Treatment Of Piggery Wastewater With Low C/N Ratio In A Wood-packed-bed A/O Process And The Mechanism For Denitrification

Manure-free piggery wastewater mainly contain pig urine and sty flushing water and is a typical a low COD-to-TN(C/N) ratio wastewater, with low in COD but high in NH4+-N concentration. If adopt the traditional denitrification process, not only the high cost, but also is difficult to achieve efficient and economical denitrification, in the absence of external carbon source. A wood-packed-bed A/O process using abandoned deadwood, which combined with the classic A/O nitrogen removal process and biofilter technology, was developed. The degradation of lignocelluloses, as a slow-release source of carbon, could supplement carbon source for microbial denitrogenation process to increase the efficiency of the pig wastewater treatment of biological denitrification. On the basis of the wood-packed-bed A/O process was successful launched and researched, further discussed the HRT and the aerobic and anaerobic volume ratio on the system processing efficiency, and analyzed the denitrification mechanism of the system.The reactor start-up process was at HRT 18.7 h and 32℃ and anaerobic zone and aerobic zone volume ratio was designed 3:1, with an internal recycle ratio of 200% and DO 1.5 mg/L in the aerobic zone, by gradually reducing raw wastewater dilution ratio and C/N ratio was ran. When the reactor performed steady in 80 d, fed with raw wastewater COD/TN ratio as low as 0.46, removal of COD, NH4+-N and TN averaged out about 66.5%, 93.6% and 89.0%. Respectively, load removal of TN above 0.22 kg/ m3.d was obtained, the nitrite accumulation rate(NAR) up to an average of 94.6%, and the effluent concentration of COD and NH4+-N is superior to the pollutant emission standard of the livestock and poultry breeding industry(GB 18596-2001).When the HRT gradually was decreased to 14.5 h stage by stage, removal of NH4+-N and TN still remained at 85% and 85% and the effluent was still superior to the standard(GB 18596-2001). When HRT was further reduced to 10.4 h, the NH4+-N and TN removal rate was reduced to about 77.8% and 72.1%, NH4+-N concentration in the effluent could still meet emissions requirements, but the TN up to 106.4 mg / L. After the anaerobic and aerobic area ratio was changed to 1: 1, even under the condition of HRT 8.3 h, NH4+-N and TN removal rate was still as high as 96.9% and 84.8%, load removal of TN reached 0.47 kg/ m3.d and the effluent quality fully met the emission requirements.Throughout the operation after successful launched the wood-packed-bed A/O process, the system indicated an excellent shortcut nitrification, and NAR had been remaining at more than 92.9%. Because of the compartment structure and layout of a fixed bed in the system, the four compartments had illustrated difference in pollutant removal and different functional microbial were separated in space. The anaerobic zone was the main function of COD removal and aerobic zone was main function of TN removal, avoiding the competition between heterotrophic bacteria and nitrobacteria to DO, thereby improved the efficiency of the system denitrification. TN removal in the reactor was mainly attributed to the shortcut nitrification-denitrification process with the packed wood as internal carbon source.