| Aerobic granular sludge technology is known as one of the most promising wastewater biological treatment technologies in the 21st century,with the properties of shock-load resistance,toxic resistance,simultaneous removal of nitrogen and phosphorus,rapid settlement,less footprint et al in the respect of wastewater treatment,and is also an effective means of recycling resources from sewage.Two sequential batch reactors(SBR)were utilized to investigate the effects of organic load fluctuation and N/S ratio on the granulation of aerobic granular sludge under low organic load conditions,and the granulation mechanism of the inoculated aerobic granules for granulation was also explored.The granulation process and the characteristics of impact loading resistance were verified by using the model of organic loading up and down,meanwhile,the enriched microbial community structure was sequenced.By changing the N/S ratio,the granulation process was controlled,and the microbial community structure before and after granulation was investigated for comparable analysis.Finally,partial aerobic granular sludge was inoculated to accelerate the granulation process,and the physicochemical properties of the internal granulation mechanism were analyzed.Through analyzing the experimental results,the main conclusions are as follows:(1)In the low organic load range,the increase of organic load rates(OLRs)could accelerate the formation of AGS.However,the stability of cultivated AGS was not great,and when OLRs were reduced,it would easily lead to large particles becoming fragment.The OLRs changes within the range,which would induce the variation of the removal effect of COD and TP.In the low organic load range,the rise and fall of OLRs will not affect the removal of COD,but would weaken the activity of autotrophic microorganisms by affecting the change of particle structure,and affect the activity of phosphorus accumulating bacteria.TP removal increased gradually during re-granulation,indicating that the change of particle size was correlated with TP removal rate.(2)Under low organic loading range and different nitrogen and sulfur loading,active sludge from flocs to granule was realized in the SBR reactor on the 72nd day.Most of the particles were within 0.4-0.8 mm.The mature AGS had good settling performance(SVIs was 36.51 mL/g),and the biomass was maintained at 4.678±0.5 g/L.In the process of granulation,the influent NH4+-N load were maintained at 0.18 kg/(m3.d)and adding sulfide load gradually decreased from 0.09 kg/(m3·d)to 0.0225 kg/(m3·d)for stabilization,and the corresponding nitrogen/sulfur increased from 2:1 to 8:1.The examining results showed the microorganisms in the inoculated sludge could adapt to the changes of the environment caused by the added sulfide.When the nitrogen/sulfur ratio was 8:1,the growth of filamentous bacteria in the inoculated flocculent activated sludge was controlled and the sludge no longer inflated.The removal rates of COD,NH+4-N,TN and TP after granulation were 95.51%,98.33%,61.29%and 25.57%.respectively.Under the full aeration mode,the influent sulfide will be rapidly oxidized to sulfate ions.High sulfate ions concentration will affect the performance of phosphorus accumulation bacteria and denitrifying bacteria,and then affect the concentration of TN and TP in the effluent.Paracoccus and Meganema can survive normally at high sulfate ion concentrations.(3)Under the low organic loading,two different ways to cultivate AGS with/without(S1/S2)inoculating AGS,,found that S1 at the beginning of the operation showed better degradation ability,COD、NH4+-N、TP removal rate to an average of 91.61,92.47,and 43.87%(S1),86.76,85.21,and 39.03%(S2),MLSS in S1 increased to 1079±16 mg/L,and S2 is 1911±27.7 mg/L.The variation of EPS components in the granulation process revealed that humiclike acids played a very important role in the granulation process,and the groups of hydroxy in EPS enriched dramatically,and the comparison was more obvious in S2 reactor.Paracoccus and Unclassified_Cytophagales were the dominant bacterial genera enriched by microbial community analysis in the granulation process of AGS under low organic load.Paracoccus can significantly improve the nitrogen and phosphorus removal efficiency of the system,and the unclassified_Cytophagales are enriched in the high dissolved oxygen environment.In summary,influent OLRs which was manipulated within low OLRs range in the measures of first increasing and then decreasing will affect the granular stability,further contributing to decreasing removal efficiency of nitrogen,phosphate.When adopted the differential ratio of nitrogen to sulfur for culturing granules,it was claimed that when introduced of sulfur load of 0.0225 kg/(m3·d),reactors could remain steady,but this load would contribute to the low nitrogen and phosphate removal capacity.With/without partial granular sludge could assist sludge granulation,and optimized the initial pollutants removal ability,providing novel viewpoint and idea for application of aerobic granular sludge technology. |
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