| Aerobic Granular Sludge(AGS)has high biodiversity and abundance,superior settling performance,outstanding impact load resistance and anti-toxicity capability,and can efficiently decontaminate a variety of water quality environments including industrial wastewater and domestic wastewater,and the process facility has a small footprint and low capital operation costs,which is a hot topic in the field of water treatment.It is a hot spot for research in the field of water treatment.However,AGS has problems such as slow granulation speed,long cycle time,poor mechanical strength and decontamination stability after granulation,which restrict its further promotion and development.As a polysaccharide extracted from the natural environment,sodium alginate is made into crystal nuclei for the cultivation of AGS,which can provide both crystal nuclei for free microorganisms to attach and grow("crystal nuclei theory")and polysaccharides(PS),the main component of extracellular polymers,to enhance the adhesion between bacterial colloids("(EPS)theory),which can promote the formation and stabilization of AGS under the combined effect of the two theories.In this study,based on the "nucleation theory" and "EPS theory",we investigated the suitable nucleation preparation and dosing scheme,determined the optimal influent organic loading rate(OLR)and C/N ratio,and combined with the microbial community analysis,we investigated the effects of sodium alginate nucleation on The effect of adding sodium alginate nuclei on the pelletizing effect and pollutant removal performance of aerobic granular sludge was investigated.All of them are to provide technical and theoretical support and develop new ideas for the design and optimization of aerobic granular sludge process performance.The main conclusions are as follows.(1)Using hydraulic shear force and calcium ion coupling,a mixture of 20 g/L sodium alginate and 5 g/L sodium carbonate sprayed into a pressurized spray bottle in a calcium chloride solution(concentration 20 g/L)maintained in a cyclonic state can effectively form spherical sodium alginate nuclei,and after 12 h of pure water immersion,the formed nuclei can recover their complete shape and physical and chemical properties after pure water immersion,drying and dehydration and ultrasonic shock.The nuclei were soaked in pure water,dried and dehydrated,and ultrasonically shaken.When 0.04～0.08 g/L(dry weight)of sodium alginate nuclei were added to the inoculated activated sludge,the balance between hydrophilic polysaccharide and microbial proliferation could be better achieved,and the granulation effect was better than 90%,and the formed AGS had good sedimentation performance and ability to remove pollutants in water.(2)It was found that the proliferation rate of filamentous bacteria had a positive correlation with the OLR of the influent water,and with the increase of OLR,the proportion of filamentous bacteria inside and on the surface of the AGS increased significantly,the particles tended to be loose,the particle size increased,and the settling performance decreased,and when the OLR was controlled in the range of 1.2～2.5kg/(m3·d),the AGS formed in the reactor had a complete and dense particle shape and good decontamination performance.The C/N ratio can influence the granulation effect and decontamination performance by regulating the microbial activity,and when the C/N ratio is controlled at 10～15,the AGS with complete particles,uniform particle size(1.5～2.5 mm)and good settling performance can be formed.(3)Under the optimum influent OLR and C/N ratio conditions,the test group with additional crystal nuclei had better sludge activity than the control group,with the activated sludge specific oxygen consumption rate(SOUR)reaching 22.48 mg O2/g MLVSS·h and sludge concentration(MLSS)reaching 1285 mg/L,while the SOUR and MLSS of the control group were only 9.6 mg O2/g MLVSS·h and 325 mg/L.At the same time,AGS could be formed in 5 d in the additional crystal nucleus test group,and the mature AGS particles were uniformly distributed with filamentous,rod-shaped and spherical bacteria on the surface,and the particle size could reach1.4-2.6 mm,which was three times larger than that of the crystal nucleus,and the EPS concentration was as high as 450 mg/g MLSS,and it had highly efficient decontamination ability,including the removal of COD removal rate was more than80% and NH4+-N removal rate was nearly 100%,while the control group was only40% and 60%.The sodium alginate nuclei significantly enhanced the granulation effect and microbial activity of AGS through its spherical shape,bioadhesion and biofriendliness,while obtaining better fouling removal performance.(4)Microorganisms promoted AGS pelletization by secreting EPS in the early stage of the reaction,and EPS was consumed as a carbon source by microorganisms as the nutrients in the sludge aging reactor decreased,thus the EPS content in all experimental groups showed a trend of increasing and then decreasing during the reaction cycle.The influent C/N ratio had less effect on EPS secretion during AGS pelletization,and high EPS content and PN/PS ratio were obtained for all AGS at maturity.The effect of influent OLR on PS content was more significant,and PN/PS showed a decreasing trend with increasing OLR,leading to a weakening of sludge hydrophobicity and gradual loosening of sludge particles.The results showed that EPS content,PN/PS ratio and AGS granulation effect and structural stability all showed a good positive correlation.The recovery of sodium alginate in the remaining sludge can be achieved by using high temperature-sodium carbonate extraction method,and the recovery rate can reach 27%～87%.(5)In the AGS formed by the addition of sodium alginate nuclei,more abundant microbial species could be formed,and in the phylum level community structure,Proteobacteria,Actinobacteria and Bacteroidetes were the dominant phylum.Among them,genera related to biological denitrification such as Hydrogenophaga,Shinella,Paracoccus and Flavobacterium were the dominant species,which made AGS with good nitrogen removal ability;while polysaccharide bacteria such as Micropruina spp.and The presence of dominant strains such as Micropruina and Nakamurella forms a competitive relationship with phosphorus-polymerizing bacteria,resulting in the limitation of the biological phosphorus removal process of AGS. |
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