Study On Cultivation And Treating Digested Piggery Wastewater With Aerobic Granular Sludge In SFSBR

Aerobic granular sludge has its own characteristics of hierarchical structure,with aerobic zone,oxygen zone and anaerobic zone,can achieve simultaneous nitrification and denitrification only in a reactor.It has the potential advantages for treating the high strength digested piggery wastewater containing organics,nitrogen and phosphorus.Moreover,the step-feed sequencing batch reactor(SFSBR)is an enhanced nitrogen removal system,characterized by a multiple anoxic feeding for supplying the organic carbonsource to denitrifiers,with the combination of aerobic granular sludge can further improve the effect of total nitrogen removal.Using sodium acetate as the simulated wastewater,the effects on aerobic sludge granulation and its performances were investigated with different step-feed modes(R1 is one-step influent,R2 is two-step influent,R3 is three-step influent)in this experiment.Results show that,on the condition of low water temperature(15±2?),mature aerobic granular sludge can cultivated in the three reactors by improving influent loads,reducing settling time gradually and adding some metal ions,but there are differences in the granulation process,granule size,characteristics of microbial community structure and other performances.When mature granules had cultivated,the possibility about treating digested piggery wastewater with aerobic granular sludge in SFSBR(R1,R2)had investigated.Results show that,under the new and complicated condition,aerobic granular sludge had experienced adaptation period and proliferation period,and its physical properties,characteristics of microbial community structure and effluent quality were significantly changed.The growth rate of microbial increasing when microbes had adapted to the new environment,and mixed liquor suspended solids(MLSS)of R1,R2 increased gradually to 4706 and 5310 mg·L-1,and sludge volume index(SVI)of the sludge measured for 5 minutes(SVI5)decreased gradually to 47.5 and 60.5 m L·g-1,respectively.Even on the condition of low water temperature(11±1 ?),the phenomenon of shortcut simultaneous nitrification and denitrification can be found in the two SFSBRs,and the effluent quality were good.The chemical oxygen demand(COD)and concentration of ammonia nitrogen,total nitrogen,total phosphorus about effluent of R1 were 309,67.5,176.0 and 14.2 mg·L-1,and corresponding removal rate were 74.7%,82.0%,53.4% and 53.5%,respectively.The chemical oxygen demand(COD)and concentration of ammonia nitrogen,total nitrogen,total phosphorus about effluent of R2 were 323,73.2,188.2 and 13.3 mg·L-1,and corresponding removal rate were 73.6%,80.5%,50.1% and 56.4%,respectively.Observations carried out by scanning electron microscopy(SEM)showed that the mature aerobic granular sludge formed in R1 was ellipsoidal or spherical with smooth surface,and structure was denser,better settling performance,more stable.However,the mature aerobic granular sludge formed in R2 was ellipsoidal with rough surface,and structure was loose,worse settling performance,worse stable.It may be due to the aging of aerobic granular sludge formed in R2.To keep the activity of aerobic granular sludge system,should be discharged out the aging and oversize mature aerobic granular sludge regularly,so can make sure the new small granular sludge has enough nutrients and become mature gradually.Besides,the microbial population of aerobic granular sludge became more diverse,bacillius bacteria was the dominant microorganism,a few coccus,no filamentous.