Enhancing Nitrification In Wastewater Treatment Plant Through Bioaugment

Reject water produced from sludge treatment process in wastewater treatment plant (WWTP) is of high ammonium concentration,low readily biodegradable organics and C/N ratio.Eventhough its flow rate is small(less than 1%of the total influent flow),the nitrogen load accounts for 15～25%of the total influent load.This study investigated the quality of reject water and its separate treatment firstly,and then examined the nitrifying biomass accumulation with reject water and the effect of bioaugmentation and predation on the microbial community and nitrification performance of the sewage treatment system.Finally,the microbial communities of three WWTPs in Xi'an were investigated by fluorescence in situ hybridization(FISH).The main results and Conclusions are as follows.(1) The TKN and TP concentration of the reject water was 494～946 and 72.1～124.8 mg/L respectively,and the ratio of SCOD/TKN was 0.25～0.84.(2) Reject water can be treated separately.A high level of nitrification and 99%of the average removal efficiency of ammonia can be achieved.Since the low biodegradability of COD in the reject water,the average removal efficiency of TCOD, SCOD and TN during the experiment was 66%,50%and 29.9%respectively.(3) In the nitrifying biomass accumulated with reject water,Nitrosomonas europaea/Nitrosococcus mobilis was the dominant ammonia oxidizing bacteria(AOB), Nitrobacter spp.was the dominant nitrite oxidizing bacteria(NOB).The temperature correction factors of ammonium utilized rate(AUR) and nitrite utilized rate(NUR) were 1.092 and 1.061 respectively;the K_N of AOB and NOB was,1.60±0.29mgNH₃-N/L, 2.78±0.30mgNO₂^--N/L respectively.The values ofÏ„_N and K_N of AOB were similar with that of the nitrifiers in WWTP,but the K_N of NOB was relative high.(4) Low SRT and temperature may increase the observed yield coefficieny(Y_obs) of nitrifiers,but,the HRT and A/O ratio had no evident effect on Y_obs. (5) Nitrification performance can be enhanced by the bioaugmentation.AUR increased more rapidly than NUR,so there was a nitrite accumulation after the bioaugmentation.(6) Bioaugmentation can increase the amount of nitrifiers quickly,and after the bioaugmentaion,the community structure was similar to the seed source,FISH analysis showed that Nitrosomonas europaea/Nitrosococcus mobilis lineage were the dominant AOB in all activated sludge samples,and the dominant NOB were Nitrospira spp.before the bioaugmentation,and then gradually transferred to Nitrobacter spp.(the dominant NOB in the seed source) after bioaugmentation.(7) The K-strategists(Nitrosospira,Nitrospira) were more vulnerable to predation pressure than the r-strategists(Nitrosomonas europaea,Nitrobacter),so the K-strategists were detected in the reactor without protozoa but not in the reactor with prozoa,and predation did not have a significant influence on nitrifiers performance.(8) Compared to reactors in lab-scale,a more diversified community of nitrifiers was observed in full scall WWTP.In the three WWTPs surveyed,Nitrosomonas europaea/Nitrosococcus mobilis was the dominant AOB,and there were quite amount of Nitrososipra coexisted;Nitrobacter spp.was the dominant nitrite oxidizing bacteria (NOB),Nitrososipra coexisted,and a few Nitrococcus,Nitrospina detected.In general,bioaugment with nitrifiers cultivated with reject water is an effective way to treat the reject water and to enhancing nitrifiers performance and microbial community in WWTP simultaneously.