Natural Coagulant-enhanced Aerobic Granular Sludge Formation And Its Performance Effects

Aerobic activated sludge is the existing mainstream water treatment process,but it has the defects of large fluctuation of effluent quality and large amount of residual sludge.Aerobic Granular Sludge(AGS)has the advantages of bacterial coupling,superior settling performance and high shock load resistance,and is regarded as the future mainstream process in the 21 st century.However,the long and time-consuming formation of AGS has limited its application to some extent.The formation of enhanced AGS can be achieved by regulating the reactor operating parameters and influent conditions,but there are drawbacks such as the inability to adjust in real time and the complexity of operation;while the effective and simple way to promote sludge granulation is to add Polyaluminium Chloride(PAC),but PAC has the risk of biological toxicity and environmental damage.To address the technical challenge of long time consuming AGS formation,this paper proposes a green and convenient strategy to enhance the formation and performance of AGS.By using Starch-based Natural Coagulant(SNC)extracted from discarded pineapple nuclei as a new enhancement strategy and PAC as a control group,we investigated the changes of AGS properties,pollutant removal efficiency,microbial community characteristics and heavy metal adsorption performance during the granulation process to investigate the enhancement efficiency of SNC on AGS and its,The main findings of this study are summarized as follows.The main findings of this study are summarized as follows.SNC type AGS and PAC type AGS were formed at 21 d and 28 d,respectively,and matured at 42 d and 56 d.The SNC type AGS was formed earlier and had a more uniform particle size distribution.The SVI and MLSS of SNC-type AGS changed more slowly than that of PAC-type AGS during the forming process,and the EPS content of SNC-type AGS was higher than that of PAC-type AGS.The surface morphology of SNC-type AGS and PAC-type AGS were significantly different from each other in terms of the surface scanning electron microscopy observation of AGS,and their strengthening and forming mechanisms were also different.In terms of the coagulation strengthening mechanism,the coagulation of PAC mainly relies on the electrical neutralization effect and the roll trapping net sweeping effect.In contrast,SNC mainly relies on polymer adsorption and bridging.In terms of the AGS formation mechanism,both PAC-type and SNC-type AGS have multiple hypotheses of action,but the forms of action are different.Both SNC-type and PAC-type AGS had good COD and NH4+-N removal effects,and the removal effect of SNC-type AGS was better than that of PAC-type.After particle formation,the TIN effluent concentration of AGS was lower than 15 mg-L-1,and AGS achieved Simultaneous Nitrification and Denitrification(SND).From the typical cycle,the nitrification of SNC-type and PAC-type AGS was intense,and SNC could be released by AGS after adsorption,which transiently increased the COD concentration in water.The Shannon and ace indices of microorganisms increased during the granulation of sludge,and the microbial diversity and total number of species were higher in AGS than inoculated sludge.In contrast,the microbial communities of SNC-type and PACtype AGS showed significant differences at the phylum level,phylum level,and genus level.At the phylum level,the relative abundance of Actinobacteriota and Chlorflexi was higher in PAC-type AGS than in SNC-type AGS,while the relative abundance of Proteobacteria and Bacteroidota was higher in SNC-type AGS than in PAC-type AGS,and the relative abundance of γ-Proteobacteria at the phylum level.SNC-type AGS >PAC-type AGS;relative abundance of α-Proteobacteria: PAC-type AGS > SNC-type AGS.at the genus level,the anaerobic denitrifying Azoarcus was the dominant genus for SNC-type AGS,and the heavier Micropuina was the dominant genus for PAC-type AGS.secretors of EPS Paracoccus and Zoogloea had higher relative abundance of SNC type and therefore SNC promoted the formation of AGS more effectively.For the metabolic pathway analysis,Metabolism was the main functional metabolic pathway of activated sludge.the relative abundance of Amino acid metabolism showed a decreasing trend during the formation of AGS.Citric acid cycle was the main energy metabolic pathway of AGS,and the abundance of citric acid cycle was greater in SNCtype AGS.The adsorption performance of both PAC and SNC type AGS had good adsorption effect on Ni2+,and there were differences in their adsorption performance,with the adsorption efficiency of PAC type AGS being better for Ni2+ concentrations from 0 to25 mg-L-1,and the adsorption performance of SNC type AGS being better for Ni2+concentrations from 100 to 150 mg-L-1.The results of model fitting showed that the adsorption of Ni2+ by both PAC-type and SNC-type AGS was based on physicalchemical adsorption,and the adsorption amount and rate of SNC-type were larger than those of PAC-type.FT-IR results showed that a large number of hydroxyl,carboxyl and amino groups existed in both SNC-type and PAC-type AGS,which combined with Ni2+adsorption in the adsorption process and achieved the effective removal of Ni2+.At the same time,SNC can strengthen the functional groups in AGS and improve the adsorption performance of AGS.In summary,compared with PAC,SNC has the advantages of being green,cheap and efficient,and is an effective strategy to strengthen the granulation of activated sludge.