Effects Of Temperature On Separate Treatment And Nitrifiers Accumulation With Reject Water

Reject water from municipal wastewater treatment plant(WWTP) is composed of supernatant discharged from the anaerobic digester,sludge thickener tank and sludge dewatering filtrate from sludge dewatering devices.Although the volume of reject water is small(olny 1%～2%of the flow rate),the nitrogen load is high(15%-25%of total load).WWTPs in China adopt the methond of recirculating reject water to the influent inlet,which causes the actual nitrogen load of the treatment system higher than the design load,so that there is an incomplete nitrification in WWTP.The reject water could be treated separately to produce a nitrifying biomass for bioaugmentation.nitrifiers would be treated separately in sequencing batch reactor(SBR),the nitrification performance and nitrifying biomass accumulation at different temperatures(20℃,25℃,30℃)were investigated respectively.Then the type and quantity of nitrifiers cultivated with reject water were investigated by fluorescent in situ hybridization(FISH),the effect of various temperatures on microbial community was analyzed.The results obtained showed that:(1) There was a low organic curbon removal rate,the everage removal efficiencies of TCOD,SCOD were 63.0%and 55.6%.The conventional activated sludg can achieve a excellent nitrification performance,the average remoal efficiencice of NH₄⁺-N was 99.3%.However there was a bad anti-nitrification ability,the average removal efficiencice of TN was only 24.3%during the experiment. And there was a remove rate of 25.5%with PO₄^3--P.When SBR operated steadily,the activated sludge had a compact structure,there were so many active protozoa that filamentous bacteria were not found.The settleability of sludge is very well and the average SVI was 70mg/L.(2) When temperature was cotrolled as 30℃,25℃and 20℃,The maximum ammonia utilized rate(AUR) of activated sludg were 25.7,40.7,33.4 mgNH₄⁺-N/gVSS.h respectively,and the maximum nitrite utilized rate(NUR) were 11.4,20.4,11.8 mgNO₂^--N/gVSS-h respectively.The nitrification rate was 326.0 mgN/gnitrifiers.h.Observed yield coefficieny(Y_obs) of nitrifiers would increase with temperature drop,there was a maximum as 0.138mg nitrifiers/mgN at 20℃.(3) Ammonia oxidizing bacteria(AOB) includes Nitrosococcus mobilis and Nitrosospira in activated sludge,At 25℃,the percentage of Nitrosococcus mobilis and Nitrosospira in AOB were 63%and 19%,while 70%and 1%at 20℃.Nitrite oxidizing bacteria(NOB) includes Nitrobacter,Nitrospira,Nitrococcus and Nitrospina gracilis. At 25℃,the percentage of Nitrobacter,Nitrospira and Nitrococcus in NOB were 64%,35%and1%while Nitrospina gracilis were not found.Then the percentage of Nitrobacter,Nitrospira,Nitrococcus and Nitrospina gracilis in NOB were 65%,19%,6%and 10%respectively.The percentage of AOB and NOB in total bacteria would increase when the temperature decreases,,at 25℃and 20℃,the percentage of ammonia oxidizing bacteria(AOB/DAPI) in activated sludge were 15.7%and 18.8% respectively,then the percentage of nitrite oxidizing bacteria(NOB/DAPI) were 12.9%and 14.4%respectively.