| Activated sludge is the most widely using method for aerobic wastewater treatment.The microorganisms in activated sludge take the responsibility of degradation and removal of pollutants in wastewater.Understanding and identification of sludge and its microbial properties is of great significance for the study of the operation process of activated sludge process.In order to understand the changes of properties/functions of activated sludge and microorganisms in aerobic biological treatment,and also the possibility of achieving selective separation based on the properties/functions of sludge,the following studies were conducted:Firstly,this study proposed the microbial apoptosis-like decay in sludge and the apoptosis-like decayed cells distribution evaluation approach.obtained by the method of enrichment of screening key pollutants in coking wastewater phenol degradation of two strains of microorganism Ochrobactrum sp.and Micrococcus sp.,and puts forward the sludge bacteria as a model class apoptosis of microbes in a recession,and puts forward the mainly fluorescence staining and flow cytometry in the sludge microbial detection method of the distribution of apoptosis cells.The properties of activated sludge with different settling velocities which were separated by gravity were characterized.Mean particle size,settling velocity,EPS distribution composition,sludge activity,apoptosis-like decay,microbial community structure and microbial function variation of aerobic pool activated sludge in gravity field was investigated.In order to simplify composition of sludge,all of the sludge in the reactor were divided into three types of sludge according to mean floc size,the proportion of constituent sludge were calculated by particle size distribution.Finally,the phase distribution of three types of sludge with different particle sizes in the fluidized bed was simulated by computational fluid dynamics(CFD).The main conclusions of this study are as follows:1.AVF was found to be in low efficiency in staining bacterial cells directly.In view of this,treatments of lysozyme,ethanol,high-temperature sterilization and combined were designed to verify the reason of low efficiency of dyeing.Then,the staining of phosphatidylserine(PS)on the surface of bacterial cell membrane by AVF was found to be hindered by bacterial cell wall.However,ethanol and lysozyme treatment can be used to maintain the original PS externalization state of cell membrane while removing the staining barrier of cell wall,and PS can be successfully stained by AVF.Bacterial apoptosis-like decay cells increased with the extension of starvation time,which revealed that apoptosis-like decay occurred in bacterial cells during starvation,and the distribution of apoptosis-like decay cells could be used as an indicator to measure the degree of microbial decay.Ethanol-lysozyme treatment combined with AVF staining also had a good identification effect on the degradation of actual sludge.2.Heterogeneity of aggregation ability,microbial decay and functional variation were found distributed in gravity-separated sludge,slowly settling sludge was suspected to decay from fast settling sludge and medium settling sludge.(1)It is found that the heterogeneity of sludge accumulation capacity is distributed in the sedimentation process of gravity field.The study on the properties of sludge F,M and S with three different settling velovities(<5 m/h,5 m/h-10 m/h,>10 m/h)which separated by gravity indicated the flocculation of sludge F was larger than sludge M and sludge S.It was found that due to the high protein/polysaccharide(PN/PS)in EPS,the sludge with large particle size and fast sedimentation had a stronger flocculation hydrophobicity and a weaker water-binding ability than the sludge with small particle size and slow sedimentation.The aggregation effect in the interparticle interaction of sludge S was less than that of the other two kinds of sludge.However,the aggregation effect in the interparticle interaction of sludge F was greater than that of the other two kinds of sludge.The analysis of the internal interaction between particles shows that sludge F has a stronger coagulation effect than sludge S.Therefore,judging from the indicators of sludge,average particle size and SVI,large particle size sludge with rapid settlement has a more compact structure.(2)It was found that the pollutant removal capacity and activity of sludge were distributed in the sludge with different sedimentation rates.The activity of the three kinds of sludge was F >M >S.The apoptotic decay degree and microbial community structure of the gravity field separated sludge were analyzed for investigation of the physiological status and functional distribution of microorganisms in the sludge.Among the three kinds of sludge,the apoptosis-like decayed cells distribution(ALDCD)in sludge S were 19.52% which was the highest among three kinds of sludge,and the sludge F were 16.88%,indicating sludge S was relatively decayed sludge.There was a significant diversity difference among the three kinds of sludge microbial diversity.Sludge F and sludge S had the furthest distance in the community diversity,it can be considered that the microbial diversity distribution of sludge M is a transition from sludge F to sludge S.Function prediction analysis also found that the relative abundance of OTUs related to degradation of pollutants and biological oxidation such as digestion and absorption of carbohydrates,cytochrome P450,citric acid cycle,energy metabolism,the function of pyruvate metabolism and oxidative phosphorylation in the of sludge F 2.0%-31.6% higher than the sludge M and S,further confirmed that the sludge F with the fastest settling velocity has the highest function of wastewater treatment,and sludge S with a slowest settling velocity has the weakest functions of wastewater treatment.3.Separation of properties could be realized by fluid field in fluidized bed,leading to improving the efficiency of wastewater treatment.(1)It was found that there was heterogeneity in sludge activity,particle size distribution,SVI and other sludge properties at different depths(0.5 m,1.5 m and 2.5 m)in the fluidized bed separation area.The sequence of activity,SVI,apoptosis-like decayed cells distribution,volume weighted mean particle size of the three types of sludge were found distribute gradiently in separation zone in fluidized bed.According to the distribution of sludge particle size,the sludge composition was simplified,and the sludge in the reactor was assumed to be composed by three groups of sludge with different particle size: 10.56-81.42 ?m,81.42-104.63 ?m and 104.63-257.94 ?m and named a,b and c,respectively.Microbial community analysis showed that most dominant microorganisms in sludge were aerobic or facultative.The abundance of the key indicated bacteria for treating coking wastewater such as Ignavibacterium and Thiobacillus in sludge S2.5 were the highest while the microorganisms in the sludge S0.5 were dominant by the anaerobic bacteria.This showed that the environment of S0.5 on the top of separation zone was anaerobic,and the sludge was no longer adapt to the environment of the coking wastewater aerobic biodegradation.(2).Based on the study of sludge heterogeneity and microbial degradation,the feasibility of selective separation of degraded and degraded sludge in reactor was explored.Computational fluid dynamics(CFD)numerical simulation shows that there is a relative concentration of small particle size sludge in local space in the fluidized bed separation area.And an efficient in-situ separation of sludge with different particle size was achieved in the fluidized bed separation zone.Taking the position of the outer wall of the separation zone for an example,when the depth of the separation zone is 1.18-1.21 m,the phase proportion of different sludge remains relatively constant.The volume phase distribution of the sludge with little particle size(10.56-81.42 ?m)increased from 25.7% to 41.3%.In a self-designed three-phase internal circulating aerobic fluidized bed,decayed sludge can be preferentially discharged from the fluidized bed while mature and stable sludge can be preferentially retained.In practical application,under the condition of constant SV30 control,the activity and concentration of total sludge will be increased by 4.48% and 4.77% respectively.Comparing with non-selective discharge of excess sludge,the total sludge treatment capacity of the system will be increased by 9.47%. |
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