| Aerobic granular sludge technology, partial nitrification technology anddenitrifying phosphorus removal technology are the hot spots for wastewatertreatment at home and abroad. In this study, the cultivation of aerobic granules fornitrogen and phosphorus removal by seeding conventional activated sludge werestudied and the effect of environmental factor on the performance of granules werealso studied. On this basis, a new process called granular two-sludge system wasestablished in this paper which is fundamentally based on the technique ofdenitrifying phosphorus removal. The two-sludge system with simultaneous nitrogenand phosphorus removal consists of sequencing batch reactors (SBR) is workingunder alternating anaerobic/anoxic conditions and an aerobic SBR using granularsludge. This process realizes a combination of granulation technology, denitrifyingphosphorus and nitrogen removal technology and has the characteristics described asfollows:(1) aerobic granules exhibit advantages of excellent settleability, highbiomass and high efficiency of nitrogen and phosphorus removal;(2) the system issimplified without sludge return and solves the contradiction of different SRT ofnitrifying bacteria and PAOs;(3) anoxic stage saves oxygen consumption and reducessludge production.There are three parts in this paper:(1) Study of partial nitrifying granular sludge in SBRâ‘ Cultivation of partial nitrifying granular sludge: Conventional partialfloccular activated sludge were successfully achieved granulation in80cycles (19days) under the conditions of temperature30C, dissolved oxygen (DO)2.0mg/L,sludge retention time (SRT)15days by increase of the settling time and optimizationof aerobic duration in SBR. pH was monitored and used to control aeration in order toavoid excess aeration. Average diameter of the aerobic granular sludge was between1.5-2.0mm. The nitrite accumulation ratio (NO2--N/NOx--N) was over95%as theshort-cut process was operated stably. The granules showed very good capability ofCOD removal with80%and ammonia removal with95%. Enrichment of ammoniaoxidizing bacteria was quantified by fluorescence in situ hybridization (FISH)analysis as17.8%of the total bacteria,on the contrary, the density of NOB decreasedto be0.6%. FA inhibition effect and real-time control were the main factors for stablepartial short-cut nitrification.â‘¡Cultivation of granules with nitrite oxidizing bacteria and reaction dynamicsstudy: In this study, a sequencing batch reactor (SBR) was developed to enrich nitriteoxidizing bacteria granular sludge fed with nitrite inorganic wastewater in SBR continuously under the condition of temperature25C, dissolved oxygen (DO)2.0mg/L, settling-time2mins. After130-day operation, sludge flocs becamegranulated with an average diameter of0.72mm. Long-term monitoring of the reactorperformance revealed that steady nitrite oxidation was achieved with the nitrite levelin the effluent almost undetectable. FISH results reported that Nitrospira is thedomitant bacteria. The Monod equation was used to describe their nitrite utilizationrate and the kinetic coefficients were calculated to be Vs=30.94mg/(g VSS h) and Ks=8.19mg/L.â‘¢Effect of COD/N ratio on the granulation process and microbial populationsuccession: Four identical sequencing batch reactors, R1, R2, R3and R4wereoperated with various initial COD/N ratios ranging from0/200,200/200,400/200and800/200. Aerobic granules were successfully cultivated in R2and R3. Differently,granules in R2had compact structure, regular shape, strong intensity and high specificnitritation rate and nitrifying bacteria population.â‘£Short-term effects of temperature and free ammonia (FA) on ammoniumoxidization in granular and flocculent system: The results showed that the rate ofammonium oxidation in both cultures increased significantly as temperatureincreasing. The specific ammonium oxidation rate with the granules was2-3timeshigher than that with flocs at the same temperature. Nitrification at various FAconcentrations and temperatures combination exhibited obvious inhibition inammonium oxidation rate when FA was90mg/L and temperature dropped to10C inthe two systems. However, the increase in substrate oxidation rate of ammonia at30Cwas observed. The results suggested that higher reaction temperature was helpful toreduce the toxicity of FA. Granules appeared to be more tolerant to FA attributed tothe much fraction of ammonia oxidizing bacteria (AOB) and higher resistance to thetransfer of ammonia into the bacterial aggregates.(2) Study of aerobic granular sludge enriched with phosphorus accumulatingorganisms for phosphorus removal in SBRâ‘ Cultivation of aerobic granular sludge enriched with phosphorusaccumulating organisms and filamentous overgrowth controlling: By decreasing thesettling time,aerobic granules enriched with phosphorus accumulating organisms(PAOs) are cultivated under alternate anaerobic/aerobic conditions in a SBRinoculated with conventional activated sludge. The system underwent three phases:rapid start-up with synthetic wastewater, stabilization with real domestic wastewaterand enrichment of PAOs by increasing P/COD and stabilized during the next360cycles. Filamentous sludge bulking happened during start-up phase and readilybiodegradable organics in synthetic wastewater was considered to be the main reasonfor filamentous overgrowth in aerobic granules. It was ultimately controlled through changing the substrate from synthetic wastewater to real domestic wastewater. Thematured aerobic granules had an approximately spherical shape with a size of0.8mm,SVI of17-30ml/g. The average PO43--P removal efficiency was above90%. FISHanalysis showed that PAOs accounted for about51.48%of the total bacteria.â‘¡Effects of anoxic condition on phosphorus release of the phosphorusaccumulating microbial granules: It was investigated in batch testes using acetate andpropionate as carbon source by adding different levels of NO3--N and NO2--N in theinitial anaerobic stage. The results showed that nitrate addition had no obviousinhibition effect on phosphorus release. Phosphorus release and denitrificationsimultaneously occurred in the presence of nitrate accompanying VFAs increased andphosphorus release rate decreased. This phenomenon demonstrated a competition fororganic substrate under an anoxic condition between PAOs and ordinary heterotrophicdenitrifying bacteria with equal opportunities. Nitrite accumulation was observed ingranular system. Batch tests of NO2--N with different pH value showed that FNA,rather nitrite, had a strong stimulation effect on P-release. The P-release rate exhibited4times increase when FNA concentration was higher than0.004mg HNO2-N/L. And,VFA uptake rate and PHA synthesis mass were observed to decrease by53%and70%.The mechanism of nitrite toxicity associated with its effect on bacterial membranesand energy generation was that PAOs need release more energy to provide adequateproton motive force.â‘¢Nitrogen and phosphorus removal performance of granular two-sludgesystem: In this study, the effect of HRT on nitrogen and phosphorus removal wasinvestigated in the two-sludge system. The results found that COD removal rate wasless affected; the average COD effluent concentration was35.2mg/L. The increaseingHRT of aerobic nitrifying SBR can achieve complete ammonia oxidation and reducetotal nitrogen concentration in effluent. Similarly, a corresponding reduction ofphosphorus in effluent can be attained by increasing the HRT of anoxic stage. Theeffect of influent C/P/N ratio on the two-sludge system was also studied. With theinfluent C/P ratio gradually increasing, the phosphorus release capacity increased.When influent C/P ratio was at20/1, phosphorus removal capacity remained at90%and average effluent phosphorus concentration of0.75mg/L. But when the C/P ratioincreased to40/1, the effluent phosphorus concentration was higher to3.8mg/L. In all,it is expected that this study can optimize simultaneous biological nitrogen andphosphorus removal process to the greatest extent via the aerobic granular media.
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