Influencing Mechanism Of Influent Organics Content On Formation Of Aerobic Granular Sludge

Aerobic granular sludge(AGS)is a promising technology for biological wastewater treatment.The special compact and stratified structure of AGS induces the outstanding settling ability,good biomass retention high resistance to harsh conditions.However,the formation mechanism of AGS is still unclear.The influent organics content is an important factor that affecting the formation of AGS,while the correlations of quorum sensing(QS),extracellular polymeric substances(EPS),and the microbial community composition during the granulation under different influent organics contents still lack systematic investigation.This study aimed to comprehensively investigate the influencing mechanism of different influent organics contents on the formation of AGS.The changes of physicochemical properties,pollutant removal performance,microbial community structure and N-Acyl homoserine lactone(AHL)were discussed.The correlations of AHL with extracellular polymeric substances(EPS)and the relative abundance of microorganisms were analyzed to interpret the microbiological essence of AGS formation influenced by different influent organic matter concentration.It provides a theoretical basis for the rapid formation and long-term operation of AGS from the perspective of AHL-mediated QS under different influent organics contents.In this study,the influent COD contents of the sequencing batch reactors were set as 100,250,500,1000,1500 and 2000 mg/L,respectively.The effects of the different contents of influent organics on physicochemical properties and treatment efficiency of AGS were investigated.The results showed that the increase of influent organics content was conducive to the rapid formation of AGS and the increase of sludge particle size.The influent COD contents of 100 mg/L and 2000 mg/L required 90 and 10 days respectively to initially form AGS,and the particle size was 235.79 ?m and 1055.89 ?m at the 100 th day,respectively.Tightly-bound EPS(TB-EPS)was the main EPS component under all influent organics contents.When the influent COD concentration was in the range of 500-1500 mg/L,increasing the concentration of inlet organic matter could promote the accumulation of tightly-bound extracellular proteins(TB-PN)and tightly-bound extracellular polysaccharides(TB-PS)in AGS.The ratios of TB-PN to TB-PS in aerobic granulation under different influent organics contents gradually increased,which proved that TB-PN was the key component of aerobic granulation.The increasing ratio of TB-PN to TB-PS was a key indicator of aerobic granulation.In the R4 reactor under an influent COD content of 1000 mg/L,t he AGS had the best settleability,and the SVI5 and SVI30 values were just 31.38 m L/g.The Illumina Miseq high-throughput sequencing was adopted to analyze the shift of microbial composition in the formation of AGS under different influent organics contents.Results showed that EPS-producing bacteria were enriched in all R1-R6 reactors with contents of 29.24%,58.71%,69.91%,48.65%,43.45% and 34.83,respectively.Pseudoxanthomonas,Comamonas,Acidovorax and Thauera were the main EPS producers under the influent organics content of 100 mg/L(R1).Zoogloea,Flavobacterium and Acidovorax were the main EPS producers under higher influent COD contents.Glycogen accumulation organism Micropruina remained stable during the whole granulation in all reactors,which was closely related to the sludge settleability.When the COD was 1000 mg/L,the mature AGS had the highest relative abundance of Micropruina(6.99%)and the lowest sludge volume indice.The influent organics contents had little effect on the dominant species of ammonia-oxidizing bacteria during aerobic granulation,but had a great influence on the dominant species of nitrite-oxidizing bacteria.The relative abundance of heterotrophic bacteria increased and that of autotrophic nitrifiers declined when the influent organics content was more than 1000 mg/L,when the influent ammonium was mainly removed via the assimilation.The influent organics content affected the microbial community diversity during the formation of AGS.The substrate competition mechanism enabled the higher diversity and abundance of microorganism in AGS under low influent organics contents.The ultra-high performance liquid chromatography-tandem mass spectrometry and correlation analysis were used to investigate the effect and the interac tion mechanism of influent organics content on the QS in AGS.Results showed that the influent organics affected the spatial and temporal distribution of AHL.N-Butyryl homoserine lactone and N-Hexanoyl homoserine lactone in water phase,and N-Decanoyl homoserine lactone and N-Dodecanoyl homoserine lactone in sludge phase were the main AHL types at all influent organics contents,which promoted the initial formation of AGS.The amount and ratio of TB-PN and TB-PS had significantly positive correlations with several types of AHLs.Influent organics content affected the microbial community composition and the responding AHL secretion,and then the secretion of TB-PN and TB-PS under the regulation of QS was influenced.Finally,the different influent organics contents lead to the different formation process of AGS.Under an influent COD content of 100 mg/L,the autotrophic nitrifying bacteria had high correlation with the AHLs,while the denitrifying and carbohydrate degrading bacteria closely correlated with the AHLs under higher COD contents in the AGS systems.