Nitrification Performance and FISH Detection in Startup-test of Biofilm Culturing of Suspended Carrier
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The startup-test of the aerobic moving bed biofilm reactor for the domestic wastewater treatment is used to study and analyze the changes of the main pollutants in the different periods of time during the startup-test,and the bacteria of nitrifier in the biofilm was examined.The results show that the biofilm can be cultured successfully in the nineteenth day when the temperature is 20 to 30 ℃ and the DO is 3.0～4.0 mg/L,NH4+-N removal efficiency reaches 88%,and there is no any accumulation of the nitrite in the effluent.Fluorescent in situ hybridization analysis indicates the nitrobacteria within the biofilm change as time goes.The ammonia oxidizing bacteria and the nitrite-oxidizing bacteria occupy about 14% and 10% of the total eubacteria number in the 15th day biofilm,respectively,and in the 27th day biofilm,the ammonia oxidizing bacteria and the nitrite-oxidizing bacteria occupy about 22% and 19% of the total eubacteria number,respectively.In the late startup process,the nitrifying bacteria have a greater proliferation.Keywords:
Nitrifying Bacteria
Oxidizing agent
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The characteristics of nutrient removal in hybrid biofilm reactor(HBR) and sequencing batch reactor(SBR) were compared to determine the contribution of suspended sludge and biofilm in HBR to nitrogen and phosphorus removal.Under 0.8 kgCOD/(m3·d),the HBR had higher nitrogen and phosphorus removal efficiency.The removal rates of NH3-N,TN and TP were 96%,92% and 94% respectively,which were higher than those in SBR.In the HBR,suspended sludge played an important role in nitrification and biofilm played an important role in denitrification and phosphorus removal.The biofilm was mainly composed of extracellar polymeric substances(EPS),cell clusters,holes and channels.The biofilm grew in good condition,a large number of cocci and bacilli interspersed among structural frame of filamentous bacteria adhered to the surface of suspended carriers.FISH results showed that many phosphate-accumulating bacteria(PAO) and ammonia-oxidizing bacteria(AOB) existed on the surface of biofilm.The percentages of AOB and PAO amongst total microorganisms were 9.4% and 13.7%,respectively.The bacteria improved the removal efficiency of nutrients in HBR.
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The dynamic transition of bacterial community structure in a biofilm was monitored by the fluorescence in situ hybridization (FISH) technique and subsequent image analysis. Heterotrophic bacteria that had occupied the outer layer were gradually decreased whereas ammonia-oxidizing bacteria (AOB) gradually increased their growth activity and extended their existence area to the outer layer of the biofilm through the gradual reduction of the C/N ratio. The spatial organization of AOB in the biofilm dynamically changed responding to the environmental conditions such as pH fluctuation and lack of dissolved oxygen (DO) and had great influence on the nitrification activity. The accumulation of nitrite was observed at lower DO concentration, which might be due to the property that nitrite-oxidizing bacteria (NOB) possess of higher Km values for oxygen than AOB.
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This study investigated the nitrifying community structure in a single‐stage submerged attached‐growth bioreactor (SAGB) that successfully achieved stable nitrogen removal over nitrite of a high‐strength ammonia wastewater. The reactor was operated with intermittent aeration and external carbon addition (methanol). With influent ammonia and total Kjeldahl nitrogen ranging from 537 to 968 mg/L and 643 to1510 mg/L, respectively, 85% nitrogen removal was obtained, and effluent was dominated by nitrite (NO 2 − /NOx >0.95). Nitrifying community analysis using fluorescence in situ hybridization (FISH), with a hierarchical set of probes targeting known ammonia‐oxidizing bacteria (AOB) within beta‐proteobacteria, showed that the AOB community of the biofilter consists almost entirely of members of the Nitrosomonas europaea/eutropha and the Nitrosococcus mobilis lineages. Image analysis of FISH pictures was used to quantify the identified AOB, and it was estimated that Nitrosomonas europaea/eutropha‐like AOB accounted for 4.3% of the total volume of the biofilm, while Nitrosococcus mobilis‐like AOB made up 1.2%; these numbers summed up to a total AOB fraction of 5.5% of the total volume on the biofilm. Nitrite‐oxidizing bacteria (NOB) were not detectable in the biofilm samples with probes for either Nitrospira sp. or Nitrobacter sp., which indicated that NOB were either absent from the biofilters or present in numbers below the detection limit of FISH (<0.1% of the total biofilm). Nitrite oxidizers were likely outcompeted from the system because of the free ammonia inhibition and the possibility that the aeration period (from intermittent aeration) was not sufficiently long for the NOB to be released from the competition for oxygen with heterotrophs and AOB. The nitrogen removal via nitrite in a SAGB reactor described in this study is applicable for high‐ammonia‐strength wastewater treatment, such as centrate or industrial wastes.
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The biofilm characteristics of a novel three-phase reactor, the circulating bed reactor (CBR), were studied using industrial prototype fed with primary and secondary settled effluent in conditions of tertiary N and secondary C+N nitrification. The results showed a high nitrification rate close to the intrinsic values for N and C+N conditions: up to 2 and 0.6 kgN-NH4 m-3 d-1, or 1.88±0.26 and 0.22±0.07 gN g-1 PR d-1, respectively. The application of an integrated approach for biofilm analysis enabled the better understanding of biofihn dynamics. The biofilm remained relatively thin, below 100 μm, indicating an effective control of the biofilm development. Protein, measured by the conventional colometric method and pyrolysis-GCMS, was the major fraction accounting for up to 35% of the biomass dry weight and 58% of the biopolymer content. The polysaccharide's fraction remained very low (<3%). The ribosomal RNA probes analysis confirmed the predominance of bacterial cells in the CBR biofilm (80–86% of bacteria versus the universal probe) showing a high proportion of nitrifying bacteria accounting for up to 50% and 27% in the N and C+N removal respectively. Nitrosomonas predominated in tertiary nitrification whereas carbon input led to the appearance of other ammonia oxidizers. This particular composition was characterized by a high state of oxidation of the biomass, expressed by the low COD/DW ratio of about 0.85. In conclusion, it can be stated that this new three-phase bioreactor ensures a high nitrification rate through an effective biofilm control promoting the development of bacterial cells, especially nitrifying bacteria, and minimizing exopolysaccharides production.
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