Enhancing Nitrification In Pilot-scale Municipal Wastewater Treatment Plant Through Bioaugmentation

Reject water produced from sludge treatment process in wastewater treatment plant(WWTP) is of high ammonium concentration. Even though its flow rate accounts for only 1~2% of the total influent flow, the nitrogen load accounts for 15~25% of the total influent load. O/A reactor was used to treat reject water and enrich nitrifier and then the enriched nitrifier was bioaugmented to the WWTP(A2O) to enhance its nitrification. The research contents performed in this study contains: nitrifying biomass accumulation with reject water and the nitrifier community and its kinetic parameters, the removal of pollutant of the bioaugmented WWTP, nitrification recovery of the bioaugmented A2 O pilot plant after seasonal deterioration, the effect analysis of enhancing nitrification through bioaugmentation. In addition, the reforming of biological phosphorus removal in the fourth WWTP was conducted according to the operation of the A2 O pilot WWTP. The main results and conclusions are as follow.(1) O/A Continuous Stirred-Tank Reactor(CSTR) was used to treat reject water, the influent NH4+-N increased from 45 mg/L to 400 mg/L, compared with sequencing batch reactor, the treatment of reject water in CSTR was more stable. The yield coefficient of the nitrifier was 0.12 mg nitrifiers/mg N and the concentration of nitrifier in the activated sludge was 197.9 mg nitrifiers/gVSS, the proportion of nitrifier to total bacteria was 22.67%, Nitrosomonas europaea /Nitrosococcus mobilis was the dominant ammonia oxidizing bacteria(AOB) and Nitrobacter was the dominant nitrite oxidizing bacteria(NOB). The temperature correction factors of AOB and NOB were 1.061 and 1.071, respectively. The Ks of AOB and NOB were 1.3052±0.2208 mg NH4+-N/L and 1.1000±0.0700 mg NO2--N/L, respectively.(2) The change of temperature and solid retention time(SRT) had no effect on the removal of TCOD and the average effluent maintained at 47 mg/L, which met the discharge standards requirements of < 60mg/L. The release of phosphorus in the secondary settler was the reason for the high effluent concentration of phosphorus. Anarobic△P/△HAc ratio was 0.39 in the anaerobic phosphorus activity batch tests, which was similar to the theoretical value. To enhance the anoxic phosphorus uptake rate was important for the removal of phosphorus for the anoxic/aerobic phosphours uptake rate ratio accounted for 70%.(3)The NH4+-N removal efficiency of the WWTP increased from 40% to 84% and the corresponding specific ammonium utilizing rate(SAUR) and specific nitrite utilizing rate(SNUR) increased 72% and 100% when the temperature increased from 12°C to 15°C with the same SRT. The removal efficiency increased to nearly 100% and the SAUR and SNUR were 6.3 mg NH4+-N/gVSS h and 6.5 mg NO2--N/gVSS at 18 °C. Bioaugmentation can shorten the recovery time of nitrification performance after seasonal deterioration.(4) The removal efficiency of NH4+-N and the nitrifier activity increase nearly one fold after bioaugmentation at low temperature and short SRT, the proportion of AOB and NOB to total bacteria increased 2.83 and 3.71 fold; The contribution of bioaugmentation to the nitrification rate range from 9.3% to 32%; The dominant AOB and NOB was similar to those in the reject water treatment system.(5) Through the adjustment of return sludge ratio and influent distribution ratio and the shut of return mixed liquid, the rate of anaerobic phosphorus release rate increased 30%, the phosphorus removal efficiency increased 50%.In conclusion, bioaugmentation with nitrifiers cultivated with reject water is an effective way to treat reject water and to enhance nitrification performance in WWTP simultaneously.