Cultivation Of Shortcut Nitrifying Granular Sludge And Its Efficiency And Mechanism For Treating Ammonium–nitrogen-rich Wastewater

With the aggravation of water eutrophication and the increase in national emission standards,the levels of ammonium nitrogen in wastewater should be reduced.Conventional biological denitrification technologies are used for treatment of medium-and low-concentration ammonium–nitrogen wastewater.However,these technologies are inapplicable for high-concentration ammonium–nitrogen wastewater because of their high energy consumption,low efficiency,and low denitrification rate with the carbon source.To address these limitations,scholars have used shortcut nitrification,a common feature of the new denitrification technology(such as Single reactor for High activity Ammonia Removel Over Nitrite(SHARON)and Anaerobic Ammonium Oxidation(ANAMMOX)),because of its low cost and low sludge yield.Granular sludge is characterized by high microbial concentration,good sedimentation,high impact load,and survival from bacteria with long generation time.It has the potential of high efficiency and low energy consumption processing for treatment of ammonium-nitrogen-rich wastewater.This study used shortcut nitrification with aerobic granular sludge technology and a self-designed reactor to determine the cultivation strategies on the formation process of shortcut nitrification granular sludge(SNGS).The mechanism of the organic components and metal ions of extracellular polymeric substances(EPS)during granular sludge formation was studied.Main factors affecting pollutant removal and storage of SNGS were discussed.The removal way of total nitrogen was studied during aerobic granular sludge treatment of ammonium-nitrogen-rich wastewater.Aeration intensity,mode and reactor structure influence the formation of SNGS.Aerobic nitrifying granules were successfully cultivated in a sequencing batch reactor(SBR)reactor through 90 d's operation.Under the same conditions of wastewater,reciprocating strong and weak aeration mode(R2)is beneficial to SNGS formation than that in large aeration mode(R1,350 l/h)and little aeration mode(R3,40 l/h).The reactor with the new structure(R4)is more beneficial to SNGS formation than that in large aeration mode(R1,350 l/h).The intensity and mode of aeration and the structure of the reactor minimally affected the COD removal.Furthermore,R3 led to high efficiency for removing ammonium–nitrogen,and the effluent ammonium concentration was below 30 mg/L.Appropriate storage methods can help maintain the integrity and activity of granular sludge.The particle size,EPS content,and tolerance to free ammonia(FA)of the granular sludge decreased after 4-week storage under different conditions(15 °C with intermittent aeration,4 °C,-20 °C,and-80 °C).Low-temperature storage can maintain the ammonium conversion and nitrification capacity of SNGS.Based on the study of the distribution of metal ions in EPS,tightly(TB-EPS)and loosely(LB-EPS)of different sludge particle size,and then analyzed organic functional groups characteristics in EPS of the SNGS,and the ion-exchange method was used to preliminarily determine the existence of metal ions in EPS.The EPS of the SNGS contain high amounts of metals ions including Ca,Mg,K,and Zn.The mineral fraction contents are high in TB-EPS,and the metal contents in the EPS vary with changes in the polysaccharide(PS)and protein(PN)content of the sludge particles.The PS content in SNGS slightly changed,and the content of PN and metal ions,namely,Ca,Mg,K,and Zn,increased gradually with particle size.The metal ions in the EPS exist not only in the form of easy exchange ion but also in the form of difficult exchange ion or precipitation of inorganic salts.The presence of metal ions decreased the Zeta potential of the EPS and thus promoted the sludge accumulation.Hydraulic retention time(HRT),influent ammonium nitrogen concentration,and dissolved oxygen(DO)level affect the removal of pollutants in SNGS.The effect of ammonium removal was affected by HRT,while the effect of COD removal was little by HRT.When the average concentrations of influent ammonium nitrogen and COD are 445.44 and 240 mg/L,respectively,the HRT decreased from 10.00 to 7.14 and the average removal rate of ammonium nitrogen decreased from 97.62% to 71.19%,and the average removal rate of COD was 90.00%.The PS concentration decreased by 41.21%,the PN content increased by 24.36%,and PN/PS increased nearly by 1 time with increasing ammonium concentration.The DO level slightly affected the removal of ammonium nitrogen and COD in SNGS.The DO level influenced the removal of total nitrogen.When the DO levels are 6-7 mg/L,4-5 mg/L,and 2-3 mg/L,the average influent concentrations of ammonium–nitrogen and COD are 296.49 and 227.96 mg/L,respectively.The average removal rates of ammonium–nitrogen and COD are More than 98.18% and 84.29%,whereas the average removal rate of total nitrogen increased from 24.60% to 42.81%.The nitrogen removal pathway is unclear during treatment of ammonium–nitrogen-rich wastewater by using SNGS.In this regard,the removal of total nitrogen during aeration stripping,heterotrophic denitrification,and Anammox was determined.The dynamic changes in the contents of ammonium,nitrite,and nitrate nitrogen in EPS were analyzed,and the structure characteristics of the microbial population in the SNGS were evaluated by high throughput sequencing.Aeration stripping and heterotrophic denitrification contributed to the removal of total nitrogen during aerobic granular sludge treatment of ammonium-nitrogen-rich wastewater.The adsorption(retention)of EPS on ammonium,nitrite,and nitrate nitrogen would underestimate the denitrification capacity of aerobic granular sludge.The EPS accounted for 32.94% of the total nitrogen adsorbed and 72.29% of the total nitrogen loss during heterotrophic denitrification and anaerobic ammonium oxidation processes.The microbial population was abundant in the SNGS.The dominant bacteria belong to Proteobacteria and Bacteroidetes.The influent ammonium nitrogen concentration affected the microbial community structure of the SNGS.Nitrosomonas was the only ammonium-oxidizing genus detected in the granular sludge samples.Bacteria belonging to this genus exhibit potential denitrifying function,such as heterotrophic simultaneous nitrification,aerobic denitrification,and autotrophic denitrification bacteria.