| Aerobic Granular Sludge(AGS)is a self-fixed aggregate with multiple biological gradients.Compared with the traditional activated sludge method,aerobic granular sludge has the advantages of good sludge settling performance,high pollutant removal capacity,and good environmental adaptability.However,it has problems such as easy destruction of internal cavity structure,structural instability and slow growth rate,which hinder the practical application of aerobic granular sludge technology.Therefore,this study aims to shorten the granulation time,improve the strength and stability of granule structure,and provide a crystal nucleus skeleton for the growth and stable operation of aerobic granular sludge by constructing NZVI/AC composites with synergistic adsorption and electrical conductivity,and investigate the growth characteristics,pollutant removal characteristics and microbial community structure change characteristics of NZVI/AC skeleton-based aerobic granular sludge.Three key parameters are optimized in the preparation process,namely,activated carbon particle size,m(Fe0):m(AC)and stirring intensity,and designed a three-factor two-level orthogonal experiment to prepare four groups of NZVI/AC materials,and compared their electrical conductivity and adsorption performance by SEM observation,conductivity test and BET analysis.Finally,the best group with 200 mesh particle size of activated carbon,m(Fe0):m(AC)= 3:5 and stirring speed of 1000 r/min was preferentially selected by functional assignment and orthogonal calculation.The optimized NZVI/AC composite has a regular spherical shape,a two-dimensional mesoporous structure and a relatively uniform pore size distribution,with a BET specific surface area of 214.1482 m2/g and a total pore volume of0.276264 cm3/g,which makes it have strong adsorption properties and provides the possibility to promote sludge aggregation and thus accelerate the formation of aerobic granular sludge.mg/L NZVI/AC composite was added to pure water,the conductivity of pure water increased from 2.11 μS/cm to 58.2 μS/cm,which increased the electrical conductivity by 26 times,significantly improving the conductivity of the solution and providing conditions for accelerating the electron transfer efficiency of pollutant removal.The NZVI/AC skeleton-based aerobic granular sludge was constructed and its growth characteristics were investigated.The results showed that the granulation process of the NZVI/AC skeleton-based aerobic granular sludge was divided into three stages,namely the initial adsorption rapid growth period(0-20 d),the deceleration growth period(20-60 d)with the synergistic effect of adsorption and microbial growth,and the stabilization period(60-80 d).The average particle size of the aerobic granular sludge reached 0.371 mm in the first 20 d,which was 101.63% higher than that of the blank group in R0.The sludge concentration of the NZVI/AC skeleton-based aerobic granular sludge was higher than that of the blank group,and the settling performance was greatly improved compared with that of the blank group.The structural strength of the granular sludge was greatly enhanced by the introduction of NZVI/AC skeleton material,which increased the polysaccharide secretion by nearly 56% compared to the blank group,thus increasing the intercellular adhesion and enhancing the structural strength of the granules,and the lower TB-PN/PS made the granules more stable.The pollutant removal characteristics of NZVI/AC skeleton-based aerobic granular sludge were investigated,and the results showed that the removal of COD,nitrogen and phosphorus by NZVI/AC skeleton-based aerobic granular sludge was enhanced compared with the blank group,with COD removal rates basically higher than 95%,ammonia nitrogen removal rates basically able to reach 100%,total nitrogen concentration reduced to 11.23 mg/L,significantly enhanced compared with the blank group by 42%,and the total phosphorus removal rate reached 80%.The organic removal and SND efficiency in the complete cycle were investigated,and the results showed that the COD degraded to 37.63 mg/L in 30 min,while the blank group decreased to 40.63 mg/L only in 60 min;the SND efficiency in the first hour was 80.4%,while the blank group was only 56.4%,and the simultaneous nitrification denitrification of granular sludge formed after the introduction of NZVI/AC skeletal material was enhanced.The ability of simultaneous nitrification and denitrification formed by the introduction of NZVI/AC skeleton material was enhanced.To further clarify the key microorganisms causing changes in the physicochemical properties of sludge and pollutant removal during the pellet formation process,the structural change characteristics of microbial community of NZVI/AC skeleton-based aerobic granular sludge were investigated.The results showed that the abundance and diversity of the microbial community were lower than those of the blank group,and the enrichment of the dominant bacteria made the system enhanced;the addition of NZVI/AC skeleton material promoted the enrichment of Proteobacteria,the key bacteria for nitrogen removal,in the aerobic granular sludge system,and its relative abundance was 26.53% higher than that of the blank group;the enrichment of iso-oxygenic nitrification-aerobic reverse sludge in the NZVI/AC skeletonbased aerobic granular sludge system was 26.53% higher than that of the blank group.The NZVI/AC skeleton-based aerobic granular sludge system was well enriched in HN-AD bacteria Thauera and EPS-secreting Zoogloea bacteria,with a significant advantage over the blank group.The enrichment of HN-AD bacteria allowed the simultaneous nitrification and denitrification,thus improving the SND efficiency.The higher abundance of Zoogloea promoted the secretion of EPS,especially polysaccharides,which increased the intercellular adhesion and the structure of the NZVI/AC skeleton-based aerobic granular sludge was enhanced.Research has shown that the NZVI/AC skeleton-based aerobic granular sludge has shortened granulation time and greatly enhanced the structural strength and stability of the granules with the synergistic effect of adsorption and electrical conductivity of the composite material,and the pollutant removal effect is significantly improved and the functional microorganisms are well enriched.This is a feasible solution to the problem of unstable aerobic granular sludge structure and slow growth rate,which has certain practical application value. |
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