The Investigation Of Pollutant Removal And Sludge Reduction By Activated Sludge Under Low Oxygen Concentration

The activated sludge process is currently the most widely used and the mostpromising wastewater treatment technology, which treats more than90%of municipalsewage and about50%industrial wastewater of the world. However, during wastewatertreatment,there are a few disadvantages: the first problem is the sludge bulking, which isthe most common problem of the activated sludge process; the second problem is aboutenergy consumption, the electric bill accounts for about1/3of the total operating costsduring the municipal wastewater treatment plant; the third problem is the remainingsludge due to the proliferation of microorganisms, a large amount of sludge is generatedduring the treatment process,and the disposal of the excess sludge costs higher than50%of total operating costs For the three disadvantages occurred during the activatedsludge process, many scientists have carried out extensive research，that is filamentoussludge bulking in low dissolved oxygen(DO)condition. The core of the process is tocontrol artificially the activated sludge wastewater treatment system run in low DOcondition, and the level of the sludge bulking do not result in the serious sludge loss；Meanwhile the low DO level means low power consumption for aeration; many expertshave found that sludge production was reduced under low DO condition;and so theremaining sludge is reduced too. In order to better understand the potential of the lowDO sludge process, it is necessary tomake the further research.This paper studied the theremoval efficiency for contaminants, sludge reductioneffect, ts stability,the mechanisms and the mathematical modeling of the low DOactivated sludge process. The research has focused on the removal efficiency forcontaminants and the influential factors,the effect of sludge reduction and themechanismin in low DO situation. Besides, we analyzed the presence ofmicroorganisms and profiles of extracellular enzyme from a microscopic point of viewin low DO situation，and built a mathematical model to understand the mechanism ofactivated sludge process in low DO condition from a macro perspective. The mainresults are as follows:Compared with the conventional activated sludge process, the greatestdisadvantage present in the low dissolved oxygen activated sludge process is that itsstability is not strong and is prone to bulking. According to the research, sludge reactorwas in a steady bulking state by low DO adaptation training, it was the first time for analyzing the existence of a stable state from a mathematical point of view，and itshowed that the low dissolved oxygen activated sludge process reduced the energyconsumption, and could effectively remove contaminants in influent, and had short-cutnitrification characteristics. the removal efficiencies of NH4+-N, PO43--P and CODwere all more than95%, and removal rate of total nitrogen exceeded70%, andnitrosation rate was over80%, Altogether， the removal efficiencies for thesecontaminants in low dissolved oxygen activated sludge process were greater than thosein the control, namely, the activated sludge process. Moreover, the obtained results haveshowed that the activated sludge process for the removal of pollutants would beinhibited in low temperatures, and low dissolved oxygen would further aggravate theadverse effects, and SRT varied within a certain range would not reduce the removal ofpollutants.Compared with the conventional activated sludge process, sludge yield wasreduced13.3%in low dissolved oxygen activated sludge process, in order to study thenature of this phenomenon, we divided sludge reduction into three parts, according tothe difference of activated sludge and hydrolysis kinetic parameters, EPS, etc., the firstdifference is the nature of the sludge, the second difference is the sludge dynamics, thethird aspect is the difference of hydrolysis. Though these differences, we analyzed themechanism of the reduction of sludge. It was concluded that the real sludge yields weredecreased under long-term low DO conditions and sludge endogenous oxygen uptakerate and the decay rate also become low, and under the combined action, the activatedsludge yield was reduced, sludge yield was reduced by13.3%compared to control,and the contribution of low real sludge yield was16%, and the sludge decay contributed84%.Long-term low dissolved oxygen levels would lead tothechangesofmicroorganisminsludge and exhibits some remarkable characteristics, andthese characteristics are the core of the activated sludge-the special nature of themicroorganisms constituting the appearance, In low DO process, the removal of organicmatter, nitrogen and phosphorus and sludge reduction are the particularity ofmicroorganisms, Therefore, in order to clearly understand the difference between lowDO process and the control, we analyzed the influence on microbial reactor and sludgecharacteristics of extracellular enzymes in low DO conditions using454pyrosequencingfrom the microscopic point of view,It was found that the microbial communities ofbacteria from low dissolved oxygen sludge samples and the reference system both showed a higher diversity，totally18,368bacterial sequences genus, the dominantbacteria weredetectedProteobacteria, with50.86%of the total low dissolved oxygensludge sequence and68.55%of the total reference bacterial system sludge samplesequence. The major of the Actinobacteria of the sludge sample in low dissolved oxygenwas Acidobacteria, BD1-5, Bacteroidetes, Candidate_division_SR1,Candidate_division_TM7、Chlorobi、Firmicutes et.al. The major of the Actinobacteriaofthe reference sludge sample was Chloroflexi、Nitrospirae、Proteobacteria et.al.Base on the current framework of the model ASM3，Using material balancetheory, and through analysis of kinetic parameters of unique biological process underlow DO sludge process, first proposed and established the low DO referenceSBR-ASM3-SMP model, besides， with sludge SRT was variable Preliminarilysimulated and discussed the impact of sludge real yield rate, sludge decay to waterquality, active sludge, sludge accumulation of inert particles, etc. during the changesSRT. It was also Found that pH, HRT, SRT, yHwould all cause greater impact on thenature of the sludge and water of sludge, the advantages of low DO sludge lies in lowerpH and longer HRT, which can maintain and even improve pollutant degradation ratewhile reducing sludge yield.