Enhancing Nitrification In A~2/O System Through Augmenting Nitrifiers Enriched By Reject Water

Reject water of wastewater treatment plant (WWTP) is of high ammoniumconcentration and low C/N ratio. Traditionally, reject water is recycled to and retreatedwith the influent by wastewater treatment. Although the flow rate of reject water issmall, but it is of high ammonium concentrations which makes actual ammonianitrogen load much higher than designed, which made it difficult to meet the statestandards of NH4--N and TN in effluent.In this paper, nitrifiers are enriched with reject water and then added into themunicipal sewage treatment system for enhancing its nitrification. In this procedure,O/A process is employed for nitrifier accumulation, while municipal wastewatertreatment is achieved by an A2/O reactor.Ammonia nitrogen removal efficiency of O/A system is99%, and the treatment ofreject water was achieved. In a steady state, the average specific ammonia utilizing rate(SAUR) and nitrite utilizing rate (SNUR) are15.32mgNH4+-N/(gVSS·h) and22.28mgNO2--N/(gVSS·h) respectively, which is much higher than the nitrification activityof general municipal wastewater treatment system. The halfsaturation constant forammonia oxidizing bacteria is1.3052±0.2208. And the halfsaturation constant fornitrite oxidizing bacteria is1.1012±0.0733. The temperature correction factor forammonium and nitrite oxydising organisum is1.072and1.027respectively, close tothat of the nitrifiers in WWTPs.The average removal efficiency of COD, NH4+-N and PO43--P was77%、95%and90.3%for the A2/O system in steady state. The COD and NH4--N concentration reached level A of discharge standard of pollutants for municipal wastewater treatmentplant (GB18918--2002). The sludge bulking of the system can be attributed to lowtemperature, and it is proved that the sludge bulking caused by excessive proliferationof microthrix parvicella by the means of microscope observation and microbialstaining.Compared with the sludge retention time (SRT), nitrification rate and thehydraulic retention time (HRT) of aerobic zone in the fourth WWTP in Xi’an, thenitrification activity of the bioaugmented A2/O system was higher, which indicatedthat nitrifier augmentation has an obvious effect on the nitrification of the system.The full-scale experiment had been done in the fourth WWTP, Xi’an. Anaerobicenvironment of anaerobic zone was destroyed by high NO3--N concentration. At thesame time, insufficient carbon source which supplied to phosphorus release decreasedthe removal efficiency of phosphorus. By reducing the recycling ratio of mixture liquorand the amount of nitrate into the anaerobic zone, the phosphorus releasing anduptaking rate had been improved. The PO43--P removal efficiency increased to78%instable state. The process adjustment achieved the purpose of cultivation andenrichment of PAO meanwhile, the removal of COD and NH4+-N was not affectedprincipally. The activity of PAO showed that the acetic acid consumed was not used forbiological phosphorus release, which may be the reason for the unstable phosphorusremoval.