Accelerating Aerobic Sludge Granulation Through Effluent Sludge Conditioning And Feeding Back Into SBRs

Aerobic granular sludge(AGS)has been regarded as a new biological treatment technology due to its many advantages of good settling ability,higher biomass and capacity to withstand shock loadings.However,Long startup time of AGS greatly limited the development and application of this technology.This research investigated the effects of accelerating sludge granulation by effluent slusge conditioning with natural drying,adding FeCl3 or CaCl2 and feeding back into SBRs.The results demonstrated that rapid sludge granulation could be achieved through returning the effluents sludge using external conditioning,and also granular sludge reactor run long term,efficiencies of adding FeCl3 or CaCl2 conditioning and rapid granulation were better than natural drying,the results areas follow:(1)External conditioning of effluent sludge.The effluent sludge were adjusted with natural drying for 72 h,and resulted in extracellular polymers(EPS)increasing from 109.4 mg/gVSS to 158.61 mg/gVSS,moisture content and SOUR decreasing from 0.97 and 14.2 mgO2/gVSS·h to 0.52 and 5.26 mgO2/gVSS·h,not dense and large aggregates formed.However,the sludge adjusted for 24 h with adding 0.1 g FeCl3/g dried sludge(DS)and 0.1 g CaCl2/DS,EPS increased to 360.5 mg/gVSS,180.3 mg/gVSS,moisture content reduced to 0.45 and 0.55,respectively.SOUR decreased to 4.25 mgO2/gVSS·h and 4.3 mgO2/gVSS·h.Cohesive and intensive aggregates formed by adding FeCl3 or CaCl2.Compaere to adding CaCl2,adding FeC13 contributed to form more denser and smaller aggregates.EPS of effluent sludge quickly improved through external conditioning and promoted sludge aggregating.(2)Rapid granulation.Aerobic granules were got on 37 d through gradually shortening settling time,MLSS,SVI30,SVI30/SVI5 and the average particle size were 3.713 g/L,46.4 mL/g,0.90 and 1.16 mm,respectively.Granules were obtained on 23 d through feeding back 7 times effluent flocs adjusted with normal method from 15th d(1.75±0.05 g/L)everyday,MLSS,SVI30,SVI30/SVI5 and the average particle size were 4.665 g/L,47.4 mL/g,0.93,and 2.8 mm;granules were obtained on 17 d through feeding back 3 times its effluent flocs adjusted with adding FeCl3 from 13th d(1.75±0.05 g/L)everyday,and MLSS,SVI30,SVI30/SVI5 and the average particle size were 6.0 g/L?45.5 mL/g?1.0 and 2.5 mm;aerobic granules were obtained on 20 d through feeding back 5 times its effluent flocs adjusted with adding CaCl2 from 13th d(1.75±0.05 g/L)everyday,and MLSS,SVI30,SVI30/SVI5 and the average particle size were 5.7 g/L?45.0 mL/g?1.0 and 3.5 mm.Compaered to convetional granualation method,feeding back external conditioning ofeffluent sludge can shorten granulation time of 14-23 d in startup phase.Despite feedback the same amount aggregates,frequency and sludge ganualation time are different due to the aggregates with different properties using different formed methods.(3)Pollutants'removal efficiencies.In the initial phase,COD and NH4+-N removal rates of R1-R4 were fluctuated,especially feeding back sludge feedback result in decreasing the removal efficiencies of R2-R4 to 80%and 70%.When feeding back ended and aggregates activity recovered,granular sludge formated and stabilized,COD and NH4+-N removal efficiencies improved.(4)Bacterial analysis.Strain analysis(eg.Condition with CaCl2)indicated bacterial abundance of effluent sludge after adding CaCl2 has not changed significantly and the diversity has changed greately.Compared to the inoculation(AGS1),the abundance and diversity of acclimated sludge(AGS5)had significantly reduced,but the species abundances and diversities of feeding back sludge(AGS2),the initial stage of granular sludge form(AGS3)and stability(AGS4)did not significantly change.The dominant bacteria of seeding sludge,Probacteria and its subsequent bacteria {?-Proteobacteria,Rhodocyclales,Rhodocyclaceae and Thauera)enriched in the process of CaCl2 regulating,and become the main group.These species not only can secrete a large number of EPS for rapid granulation,also can degrade COD and nitrogen in wastewater.(5)Mechanism of rapid granulation.The feeding back sludge were broken into aggregates and flocs by hydraulic shear force.Smaller aggregates with good settling ability stayed in the SBRs and induced microbes grow on its surface gradually for rapid sludge granulation.Bigger aggregates with compact structure and intensity didnot break up and stayed in the SBRs,microorganism gradually adapt to its own structural environment and recovery,these sludge tended to regulate and became aerobic granules with the action of shear force.However,the flocs were still washed out at shortened settling time,collected,disposed and returned to SBRs for-accelerating sludge granulation.In conclusion,rapid granulation and long-term stable operation can be achieved through effluent sludge external conditioning(natural drying,adding the FeCl3 or CaCl2)and feeding back into SBRs under 2 min settling time.And this method is simple,low energy(surface gas velocity of0.44 cm/s),decrease sludge emissions.