The Effect Of Iron Ion Concentration In Wastewater On Activated Sludge Yield

In recent years,around the hotspot issues such as shortage of natural resources,global warming,and serious pollution of aquatic environment,countries around the world have stopped treating the excess sludge of sewage treatment plants as waste.How to reduce sludge treatment has become a global focus environmental issue.The sludge yield coefficient is an important index in the process of sludge reduction,and is a key indicator to measure the amount of residual sludge in the biological treatment system.Its essence is the ratio of microbial conversion of organic matter?COD?in activated sludge to its own quality.As an enzyme activator in microbial cells,metal elements play a vital role in the growth and metabolism of microorganisms.A large number of studies have shown that the increase of the sludge yield coefficient may be related to the content of metal ions.If the quantitative ratio between the two can be found,the decrease of the sludge yield coefficient can be controlled by changing the metal ion content of the influent,so as to achieve the purpose of sludge reduction.Therefore,based on the sequential batch reactor?SBR?treatment system,this paper studied the characteristics of activated sludge,the apparent sludge yield coefficient(Y_obs),extracellular polymer and sludge dewatering with different concentrations of Fe³⁺in the influent.At the same time,the impact of performance was analyzed and discussed the changes of microbial community structure and functional flora,in order to provide a theoretical basis for further research on sludge reduction and residual sludge dewatering treatment.The results show that the activated sludge has a good sediment ability when the concentration of Fe³⁺is in the range of 0.02?70mg/L,when the concentration of Fe³⁺is more than 80mg/L,SV₃₀0 and SVI begin to rise,and the activated sludge undergoes viscous expansion and sedimentation the performance deteriorates.The proliferation range of Fe³⁺on activated sludge is 10³0mg/L,MLSS,V_MLSS,MLVSS and V_MLVSSLVSS show an upward trend within this range.When the concentration of Fe³⁺is 30mg/L,Y_obsbs reaches the maximum value,which is 0.90mgMLVSS/mgCOD,and the microorganism's own multiplication rate is the largest,which will lead to the maximum sludge production.There may be two mechanisms for the removal of COD by activated sludge with added Fe³⁺:when Fe³⁺content is small,the degradation of microorganisms is dominant,as Fe³⁺continues to increase,the flocculation and adsorption of Fe³⁺play a major role;The average COD during the entire process The removal rate is about 85±6%,so Fe³⁺in the range of 0.02¹00mg/L has no significant effect on the average removal rate of COD.Under the action of Fe³⁺,polysaccharide is the dominant component that determines EPS content Fe³⁺is in the range of 0.02?40mg/L,with small polysaccharide content,less EPS secretion,and better dewatering performance of sludge.Statistical analysis shows that the correlation between polysaccharide and CST is more significant than that of protein.The content of polysaccharide directly affects the dewatering of sludge.Controlling the Fe³⁺concentration to less than 30mg/L can avoid the maximum sludge production and sludge inhibition interval,and achieve the purpose of larger COD removal rate and smaller sludge production,and less EPS secretion,low polysaccharide content,activated sludge can achieve better sludge dewatering performance.Five groups of samples with Fe³⁺concentrations of 0.02mg/L,10mg/L,30mg/L,70mg/L,and 80mg/L were selected,and the high-throughput sequencing method was used to study and analyze the microbial community structure and the dominant flora under different Fe³⁺content Variety.The results showed that the abundance of biomes gradually decreased with the increase of Fe³⁺concentration,and the uniformity and diversity of microbial flora of activated sludge are higher under the action of Fe³⁺at 30mg/L,while the Fe³⁺concentration of70mg/L and 80mg/L will reduce the diversity of microbial population.At the phylum level,Patescibacteria has a strong tolerance to Fe³⁺,and the Fe³⁺concentration of 70mg/L and80mg/L can still maintain a large advantage,with a relative abundance of up to 78.7%;The relative abundance of Planctomycetes is basically stable in the range of Fe³⁺concentration of0.02?30mg/L,which is maintained at 27.2?28.6%,but it is detected at high concentrations of Fe³⁺of 70mg/L and 80mg/L,the relative abundance is as low as 1.7%;The relative abundance of Proteobacteria decreased from 20.4%to 11.6%with the increase of Fe³⁺concentration,indicating that its dominance will be gradually suppressed.At the level of class,Fe³⁺can continue to stimulate the growth of Saccharimonadia belonging to the Patescibacteria phylum,increasing its relative abundance from 26.8%to 78.7%;Planctomycetacia has the same trend as Planctomycetes,that is,the high concentration of Fe³⁺is severely suppressed,and the relative abundance drops to 1.5%when Fe³⁺is 80mg/L;Fe³⁺has the same effect on Alphaproteobacteria and Proteobacteria,when the Fe³⁺concentration increases from 0.02 to30mg/L,the relative abundance of Alphaproteobacteria decreases 60%.At the genus level,Bradyrhizobium and Brevifollis showed a high tolerance to Fe³⁺,at the highest Fe³⁺concentration of 80 mg/L,they still had abundances of 5.7%and 3.6%respectively;and the abundances of Pirellul and Gemmata belonging to the Phytophthora reached 7.5%and 3.6%at a concentration of 30 mg/L Fe³⁺,but at a higher Fe³⁺concentration of 80 mg/L,it was suppressed to a greater extent,with abundances of only 0.29%and 0.27%.What can be determined is that under the action of 30mg/L of Fe³⁺,Planctomycetes?Planctomycetacia?Pirellul and Gemmata,the microbes of this level and the corresponding class and genus levels can maintain the maximum advantage under this concentration,which may be the reason why the activated sludge yield coefficient is maximum at the concentration of 30mg/L Fe³⁺.