Aerobic Granulation At Low Load And The Effect Of Heavy Metal On The Aerobic Granules

Domestic wastewater contains low organic concentration,complex composition, a large number of heavy metals and toxic chemicals,which inhibits biological treatment of toxic substances.To solve the problem,the granular sludge was tried to cultivable with the synthetic domestic wastewater.During the granulation,the formation process,and removal mechanism of COD and NH₄⁺-N was studied in detail, in addition,microbial community characteristics and metabolic activity were investigated;the effect of two soluble heavy metal ions(Cu²⁺ and Ni²⁺) on aerobic granule treatment performance,microbial metabolic activity,and functional diversity of microbial communities was investigated.Aerobic granulation with synthetic low-concentration domestic wastewater was determined to provide a theoretical foundation for the treatment of actual domestic wastewater.Aerobic granulation was achieved at low organic loading rate(OLR) 1.05-1.68 kgCOD/(m³Â·d).During the process,brown flocculent become yellow sludge filamentous bacteria at first,to 70 days,4-10 mm black filamentous granules appeared, sludge volume index(SVI) decreased to 70 mL/g from 228 mL/g.The granules composed of a variety of filamentous bacteria,had an excellent settling ability with the settling velocity at 38-65 m/h,much higher than the settling velocity of activated sludge.After granulation,removal efficiencies of COD and NH₄⁺-N were over 95%, the effluent concentration of COD and NH₄⁺-N were stabilized at 5 mg/L and 3 mg/L, respectively.Microbial community diversity was analyzed by Biolog methods.The result of average well color development(AWCD),substrate richness(S) and Shannon's diversity index(H) shows that granule microbial metabolic activity is higher than that of sludge;the result of principal component analysis(PCA) shows that microbial communities of different sludge have significant differences.The effects of Cu²⁺ and Ni²⁺ on wastewater treatment performance,the heterotrophic community activity and diversity of aerobic granules were investigated in sequencing batch reactor(SBR).Three parallel lab-scale SBR systems were operated.One was used as a control unit,while the other two received 5 mg/L and 15 mg/L Cu²⁺ and Ni²⁺ ions,respectively.Cu²⁺ severely inhibited the proliferation of aerobic granule,greatly reduced the COD and NH₄⁺-N removal rate,resulting in high and unstable effluent COD and NH₄⁺-N concentration,while NO₃-N concentration significantly reduced,and NO₂^--N concentration appeared a significant peak during the 5-29 days;Ni²⁺ stimulated the growth of aerobic granule,and slightly inhibited COD and NH₄⁺-N removal efficiency.Cu²⁺ severely inhibited the dehydrogenase activity(DA),while Ni²⁺ stimulated DA to some extent.Cu²⁺ and Ni²⁺ stimulated the growth of extracellular polymer substances(EPS).Through PCA,it can be seen that significant differences exist in the variety and degree of carbon source utilization by the five kinds of sludge samples,community structure and function change in diversity.The result shows that the toxic effect of Cu²⁺ on the microbial community was greater than that of Ni²⁺.