| With the rapid development of economy, large amount of wastewaters are emitted, in which a large number of industrial wastewater, agricultural wastewater and domestic sewage contain nitrogen. Nitrogen pollution has already seriously threated the living environment and the physical and mental health of human beings. It is urgent that nitrogenous pollutants should be removed from wastewaters. Due to the high efficiency and cost effectiveness, anaerobic ammonium oxidation (ANAMMOX) process has drawn much attention in the field of environmental engineering. However, the slow growth of anaerobic ammonium oxidizing bacteria (AAOB) severly restricted the full-scale application of ANAMMOX process. Using the wastewaters with different nitrogen concentrations as the treatment objects, this study revealed the performance of ANAMMOX-EGSB (expanded granular sludge bed) reactor. Commencing from the microbial consortium and the characteristics of growth and metabolism of ANAMMOX enrichment culture (hereafter referred as enrichment culture), this study revealed the working mechanisms of AAOB and associated bacteria. The main results are as follows:(1) The performances of ANAMMOX-EGSB reactors at high and low substrate concentrations were revealed.①The performance of ANAMMOX-EGSB reactor at high substrate concentrations was revealed. The ANAMMOX-EGSB reactor was suitable to treat strong ammonium-containing wastewaters. When the influent nitrogen concentrations were up to1429.1mgN/L, the nitrogen loading rate (NLR) and nitrogen removal rate (NRR) were as high as22.87kgN/(m3·d) and18.65kgN/(m3·d), respectively, moreover, the NRR was still on the rise. The enrichment culture in the reactor had high substrate conversion rates. The theoretical ammonium, nitrite and nitrogen specific conversion rates were381.2,304.7and731.7mgN/(gVSS·d), respectively. The enrichment culture possessed great substrate affinity and excellent substrate tolerance. The half-saturation constant (KS) values for ammonium, nitrite and nitrogen were36.75,0.657and29.26mg N/L and the inhibition constant (Ki) values for ammonium, nitrite and nitrogen were887.1,13942.1and1779.6mg N/L.②The performance of ANAMMOX-EGSB reactor at low substrate concentrations was revealed. The ANAMMOX-EGSB reactor had an excellent performance to meet the Chinese integrated wastewater discharge standard (GB8978-1996) in which the ammonium concentration should be lower than15mg/L. When the effluent ammonium concentrations was11.90mgN/L which was lower than15mgN/L, the NLR, NRR and nitrogen remove efficiency (NRE) were27.31kgN/(m3·d),25.86kgN/(m3·d) and94.68%, respectively. The enrichment culture had high specific substrate conversion rate (qmax) and great substrate affinity. The qmax for ammonium, nitrite and nitrogen were907.13,841.76and1810.10mg N/(g VSS-d), the KS for ammonium, nitrite and nitrogen were2.69,0.44and3.11mg N/L which were significantly stronger than those reported in the similar studies.(2) The microbial characteristics of ANAMMOX enrichment culture were investigated.①The growth and metabolism characteristics of ANAMMOX enrichment culture at different NLRs were explored. The results showed that the enrichment culture presented starved, suitable and inhibitory phase along with the increase of substrate supply. The change rates of biomass in the starved, suitable and inhibitory phase were-6.1×10-3gVSS/(gVSS·d),1.45×10-2gVSS/(gVSS·d) and-5.78×10-2gVSS/(gVSS·d), respectively. The substrate conversion rates for survival were0.05kgNH4+-N/(kgVSS·d),0.07kgNO2--N/(kgVSS·d) and0.12kgN/(kgVSS·d); the substrate conversion rates for maximum growth were0.21kgNH4+-N/(kgVSS·d),0.24kgNO2--N/(kgVSS·d) and0.45kgN/(kgVSS·d), respectively. In different phase, the specific ammonium, nitrite and nitrogen conversion rates were as follows:starved phase-0.03,0.04,0.07kgN/(kgVSS·d); suitable phase-0.22,0.23,0.45kgN/(kgVSS·d); inhibitory phase-0.08,0.10,0.18kgN/(kgVSS·d). In suitable phase, the VSS accumulation rate showed a linear correlation with the substrate (ammonium, nitrite and nitrogen) removal rate and product (nitrate) formation rate, the correlation coefficients were0.94,0.92,0.93and0.90, the yield of enrichment culture was0.14gVSS/(gNH4+-N),0.12gVSS/(gNO2--N) and0.70gVSS/(gNO3--N), the yield of EPS was0.11gEPS/(gNH4+-N),0.09gEPS/(gNO2--N) and0.55gEPS/(gNO3--N).②The effects of high substrate concentration on the granulation of ANAMMOX enrichment culture were revealed. The ammonium and nitrite are both substrates of AAOB, but they will become inhibitors when their concentrations exceed a certain level. The substrate concentrations exceeded the inhibitory threshold concentration could result in the physiological changes of AAOB which were an important factor for enrichment culture (granular sludge) dispersal. The inhibitory effects of nitrite were greater than those of ammonium, the inhibitory threshold concentration of nitrite to AAOB was around100mgN/L. The dispersal of granular sludge directly resulted in poor settleability (the settling velocity decreased form73.73m/h to16.49m/h), some sludge were washed-out which lead to the deterioration of reactor performance [the NRR decreased from21.81kgN/(mj-d) to16.97kgN/(m3·d)]. By rinsing out the residual substrate from the reactor and then re-running the reactor from low substrate concentrations, the enrichment culture could reform granular sludge (the settling velocity increased to60.59m/h) and reactor performance also could recover [the NRR went up to22.51kgN/(m3·d)].③The microbial consortia of two different enrichment cultures were studied. The two enrichment cultures were derived from two ANAMMOX-EGSB reactors which were operated with two different operation modes-high concentration with low flow rate (R1) and high flow rate with low concentration (R2). The microbial populations of enrichment cultures in R1and R2were different. The enrichment culture in R1was white and reddish, in which the cell morphology was various, the predominant bacteria were cocci, filamentous bacteria and bacilli, and the shape of cell inclusion was various and irregular. The enrichment culture in R2was red. Compared to the enrichment culture in R1, the cell morphology of enrichment culture in R2was more consistent, predominant bacteria were cocci and bacilli, rarely filamentous bacteria were observed, and shape of cell inclusion was consistent but irregular. The results from PCR-DGGE analysis showed that the fingerprints of the two enrichment cultures were significantly different. The bands of enrichment cultures in R2were more than the bands of enrichment culture in R1, which meant the microbial species of enrichment culture in R2were more than those of enrichment culture in R1. The number of bacteria in two enrichment cultures was obviously different. By using quantitative PCR to analyze the number of bacteria and AAOB in enrichment cultures, it was found that both of the bacterial gene copies and AAOB hzs gene copies in enrichment culture (R2) were more than those in enrichment culture (R1). However, the proportion of AAOB to the total bacteria in enrichment culture (R1)(61.10±6.5%) was higher than the proportion of AAOB to the total bacteria in enrichment culture (R2)(34.27±3.7%). The results from the fluorescence in situ hybridization (FISH) showed that, in the two enrichment cultures, the predominant AAOB were Candidatus Kuenenia stuttgartiensis and Candidatus Brocadia anammoxidans.④Two associated bacteria in the ANAMMOX enrichment culture were isolated and studied. The strains ZU-H and ZU-I were isolated from the enrichment culture and were identified as Castellaniella defragrans and Castellaniella denitrificans in phylum Proteobacteria. Strain ZU-I had denitrification activity but no ANAMMOX activity. The denitrification rates of strain ZU-I were3.94×10-2mgC/(mg protein-h) and1.08×10-2mgN/(mg protein-h), the consumed COD/N in denitrification was5.47:1. As an associated bacterium, stain ZU-I was able to form capsule, which was helpful to the formation of ANAMMOX aggregates. Strain ZU-I was Gram-negative, heterotrophic, facultatively anaerobic and had rich diversity of carbon source. It was found from the study of microbial consortium that the isolation source contained the bacteria in Burkholderiales, which meant strain ZU-I was able to live in the enrichment culture and could use organic matters very well. |
PDF Full Text Request