Anaerobic ammonium oxidation process in an upflow anaerobic sludge blanket reactor with granular sludge selected from an anaerobic digestor

The purpose of this work was to evaluate the development of the anammox process by the use of granular sludge selected from a digestion reactor as a potential seed source in a lab-scale UASB (upflow anaerobic sludge blanket) reactor system. The reactor was operated for approximately 11 months and was fed by synthetic wastewater. After 200 days of feeding with NH₄ ⁺ and NO₂ ⁻ as the main substrates, the biomass showed steady signs of ammonium consumption, resulting in over 60% of ammonium nitrogen removal. This report aims to present the results and to more closely examine what occurs after the onset of anammox activity, while the previous work described the start-up experiment and the presence of anammox bacteria in the enriched community using the fluorescencein situ hybridization (FISH) technique. By the last month of operation, the consumed NO₂ ⁻N/NH₄ ⁺-N ratio in the UASB reactor was close to 1.32, the stoichiometric ratio of the anammox reaction. The obtained results from the influentshutdown test suggested that nitrite concentration would be one key parameter that promotes the anammox reaction during the start-up enrichment of anammox bacteria from granular sludge. During the study period, the sludge color gradually changed from black to red-brownish.     

Differential distribution of ammonia- and nitrite-oxidising bacteria in flocs and granules from a nitrifying/denitrifying sequencing batch reactor

A lab-scale sequencing batch reactor was operated with alternating anoxic/aerobic conditions for nitrogen removal. Flocs and granules co-existed in the same reactor, with distinct aggregate structure and size, for over 180 days of reactor operation. Process data showed complete nitrogen removal, with temporary nitrite accumulation before full depletion of ammonia in the aerobic phase. Microbial quantification of the biomass by fluorescence in situ hybridisation showed that granules contained most of the nitrite-oxidising bacteria (NOB) whereas the ammonium-oxidising bacteria (AOB) seemed to be more abundant in the flocs. This was supported by microsensor measurements, which showed a higher potential of NO₂⁻ uptake than NH₄ uptake in the granules. The segregation is possibly linked to the different growth rates of the two types of nitrifiers and the reactor operational conditions, which produced different sludge retention time for flocs and granules. The apparent physical separation of AOB and NOB in two growth forms could potentially affect mass transfer of NO₂⁻ from AOB to NOB, but the data presented here shows that it did not impact negatively on the overall nitrogen removal.     

Pyridine degradation characteristics of a newly isolated bacterial strain and its application with a novel reactor for the further treatment in pyridine wastewater

A pyridine-degrading strain Gemmobacter sp. ZP-12, isolated from an activated sludge, was able to use pyridine as the sole carbon and nitrogen source for the growth. The strain could effectively degrade pyridine and remove TOC over a wide range of initial pyridine concentrations. The pyridine degradation rate for 100, 500, 1000, 1500 and 2000 mg/L was 2.90 ± 0.17; 13.72 ± 0.21, 20.40 ± 0.24, 31.09 ± 0.26, 27.63 ± 0.17 mg/L/h, respectively. During the pyridine degraded, a large amount of NH₄⁺-N was released and accumulated. The accumulation of NH₄⁺-N increased with the increase of pyridine concentration. For further removing the NH₄⁺-N producing in pyridine degradation, an aerobic-moving bed biofilm reactor coupled with intermittent-aeration membrane biological reactor (a-MBBR-IMBR) was constructed, in which the strain and the aerobic / anoxic mixed sludge combined to remove the pollutants in the wastewater containing 500 mg/L pyridine. After 96 h of operation, the final TOC removal efficiency was 96.5 ± 1.05 %. The average residual concentration of NO₃⁻-N and NH₄⁺-N was respectively 9.09 ± 4.13 mg/L and 7.85 ± 3.88 mg/L. The study provides a viable option for treating pyridine wastewater.     

Isolation and Characterization of Pseudoxanthomonas sp. Strain YP1 Capable of Denitrifying Phosphorus Removal (DPR)

A bacterial strain (designated as YP1) was isolated from an aerobic granular sequence batch reactor (SBR) performing simultaneous nitrogen and phosphorus removal. Based on the morphological, biochemical characteristics, and phylogenetic analysis of 16S rRNA gene sequence, YP1 was identified as Pseudoxanthomonas sp. strain. Strain YP1 was confirmed to have the ability to conduct denitrifying phosphorus removal (DPR). The optimal conditions for YP1 were pH 8.0, phosphorus (PO₄^3?-P) concentration of 8.0 mg/L, sodium citrate as carbon source, and nitrate nitrogen (NO₃^?-N) concentration of 30 mg/L. The functional genes including ppk and ppx, narG and narA, nirS and nirK were amplified for understanding the DPR pathways. The results provide more information about denitrifying polyphosphate-accumulating organisms (DPAOs) in aerobic granular sludge (AGS) and lay the foundations for full-scale DPR.     

Screening and characterization of an aerobic nitrifying-denitrifying bacterium from activated sludge

Taking advantage of the good biocompatibility and high efficiency of nitrogen removal with microbes, nitrifying and denitrifying bacteria, are becoming increasingly more widely used for wastewater treatment and prevention of eutrophication. In this research, an aerobic nitrifying-denitrifying bacterium was successfully screened from activated sludge and identified as Pseudomonas sp. (CCTCC No M2010209) by the 16S rDNA sequence. The activity verification confirmed its nitrifying-denitrifying capability of removing ammonium, nitrate and nitrite nitrogen. The types of carbon sources and carbon-nitrogen ratio greatly influenced the removal efficiency of NH₄ ⁺-N and NO₃ ⁻-N. When the initial concentrations of NH₄ ⁺-N and NO₃ ⁻-N in synthetic wastewater were less than 70 and 50 mg/L, the nitrogen removal rates reached 94 and 90% in 9 h, respectively. Preliminary comparisons of nitrogen removal capacity between this isolate and other commercial preparations in the treatment of synthetic wastewater revealed its promising potential to be used in the actual wastewater treatment.     

Rapid start-up and performance of denitrifying granular sludge in an upflow sludge blanket (USB) reactor treating high concentration nitrite wastewater

Denitrifying granular sludge reactor holds better nitrogen removal efficiency than other kinds of denitrifying reactors, while this reactor commonly needs seeding anaerobic granular sludge and longer period for start-up in practice, which restricted the application of denitrifying granular sludge reactor. This study presented a rapid and stable start-up method for denitrifying granular sludge. An upflow sludge blanket (USB) reactor with packings was established with flocculent activated sludge for treatment of high concentration nitrite wastewater. Results showed mature denitrifying granular sludge appeared only after 15 days with highest nitrogen removal rate of 5.844 kg N/(m³ day), which was much higher than that of compared anoxic sequencing batch reactor (ASBR). No significant nitrite inhibition occurred in USB and denitrification performance was mainly influenced by hydraulic retention time, influent C/N ratio and internal reflux ratio. Hydraulic shear force created by upflow fluid, shearing of gaseous products and stable microorganisms adhesion on the packings might be the reasons for rapid achievement of granular sludge. Compared to inoculated sludge and ASBR, remarkable microbial communitiy variations were detected in USB. The dominance of Proteobacteria and Bacteroidetes and enrichment of species Pseudomonas_stutzeri should be responsible for the excellent denitrification performance, which further verified the feasibility of start-up method.     

Anammox bacteria enrichment in upflow anaerobic sludge blanket (UASB) reactor

We investigated the anaerobic ammonium oxidation (anammox) reaction in a labscale upflow anaerobic sludge blanket (UASB) reactor. Our aim was to detect and enrich the organisms responsible for the anammox reaction using a synthetic medium that contained low concentrations of substrates (ammonium and nitrite). The reactor was inoculated with granular sludge collected from a full-scale anaerobic digestor used for treating brewery wastewater. The experiment was performed during 260 days under conditions of constant ammonium concentration (50 mg NH₄/⁺-N/L) and different nitrite concentrations (50∼150 mg NO₂-N/L). After 200 days, anammox activity was observed in the system. The microorganisms involved in this anammox reaction were identified as CandidatusB. Anammoxidans andK. Stuttgartiensis using fluorescencein situ hybridization (FISH) method.     

Denitrification of high nitrate wastewater in a cloth strip bioreactor with immobilized sludge

Denitrification of synthetic high nitrate wastewater containing 40,000?ppm NO₃ (9,032?ppm NO₃-N) was achieved using immobilized activated sludge in a column reactor. Active anoxic sludge adsorbed onto Terry cloth was used in the denitrification of high nitrate wastewater. The operational stability of the immobilized sludge system was studied both in a batch reactor and in a continuous reactor. The immobilized sludge showed complete degradation of different concentrations of NO₃-N (1,129, 1,693, 3,387, 6,774, and 9,032?ppm) in a batch process. The reactors were successfully run for 90?days without any loss in activity. The immobilized cell process has yielded promising results in attaining high denitrifying efficiency.     

Nitrogen removal performance in a novel combined biofilm reactor

Experiments have been performed to investigate the nitrogen removal performance in a novel combined biofilm reactor using synthetic wastewater. In the reactor, one cubic box was separated by two baffles into three zones: aerobic zone, buffering zone and anoxic zone. Nitrification and denitrification were supposed to be mainly accomplished in the aerobic and anoxic zones, respectively. When the influent total nitrogen (TN) and organic carbon loadings were averaged at 0.093 and 0.40 kg/m³/d, 84% TN removal efficiency was achieved by adjusting the aeration rate and the configuration of the reactor. Continuous experimental results demonstrated that NH₃-N removal efficiency increased by adjusting the clapboards of the reactor at a certain aeration rate. Energy produced by aeration was used for liquid recycle, so TN could be more efficiently removed at lower cost in this reactor.     

Development of a fixed-bed anammox reactor with high treatment potential

A plug-flow type anaerobic ammonium oxidation (anammox) reactor was developed using malt ceramics (MC) produced from carbonized spent grains as the biomass carriers for anammox sludge. Partial nitrified effluent of the filtrate from the sludge dehydrator of a brewery company was used as influent to a 20 L anammox reactor using MC. An average volumetric nitrogen removal rate (VNR) of 8.78 kg-N/m³/day was maintained stably for 76 days with 1 h of HRT. In a larger anammox reactor (400 L), an average VNR of 4.84 kg-N/m³/day could be maintained for 86 days during the treatment of low strength synthetic inorganic wastewater. As a result of bacterial community analysis for the 20 L anammox reactor, Asahi BRW1, probably originating from the wastewater collected at Asahi Breweries, was detected as the dominant anammox bacterium. These anammox reactors were characterized by a high NH₄-N removal capacity for low strength wastewater with a short hydraulic retention time.     

Analysis of the characteristics of short-cut nitrifying granular sludge and pollutant removal processes in a sequencing batch reactor

Aerobic granular sludge is a new type of microbe auto-immobilization technology; in this paper, short-cut nitrification and denitrification were effectively combined with the granular sludge technology. Simultaneous nitrification and denitrification granules were developed in a sequencing batch reactor (SBR) using synthetic wastewater with a high concentration of ammonia nitrogen at 25 °C with a dissolved oxygen concentration above 2.0 mg/L and a 15 days sludge retention time. The characteristics of the sludge and the removal efficiency were studied, and the removal mechanisms of the pollutants and the process of short-cut nitrification were analyzed. The average granule diameter of the granular sludge was 704.0 μm. The removal rates of pollutants and the accumulation rate of nitrite in the SBR were studied. During treatment of wastewater with a high concentration of ammonia nitrogen, simultaneous nitrification, and denitrification and the stripping process could contribute to the removal of total nitrogen. The high pH value, the high concentration of free ammonia, and the delamination of granular sludge were the main factors contributing to the short-cut nitrification property of granular sludge in the reaction process.     

Biofilm producing indigenous bacteria isolated from municipal sludge and their nutrient removal ability in moving bed biofilm reactor from the wastewater

In the present study, improved moving bed biofilm reactor (MBBR) was applied to enhance the nutrient removal ability of the municipal wastewater. A total of 18 indigenous bacterial isolates were screened from the sewage sludge sample and nitrate reductase, nitrite reductase and hydroxylamine oxidase was analyzed. The strains Pseudomonas aeruginosa NU1 and Acinetobacter calcoaceticus K12 produced 0.87 ± 0.05 U/mg and 0.52 ± 0.12 U/mg hydroxylamine oxidase, 1.023 ± 0.062 U/mg and 1.29 ± 0.07 U/mg nitrite reductase, and 0.789 ± 0.031 U/mg and 1.07 ± 0.13 U/mg nitrate reductase. Nitrogen and phosphate removal improved by the addition of nutrient sources and achieved > 80% removal rate. pH and temperature of the medium also affected nutrient removal and improved removal was achieved at optimum level (p < 0.05). MBBR was designed with R1 (aerobic), R2 and R3 (anoxic) reactors. MBBR reactors removed acceptable level phosphorus removal properties up to 7.2 ± 3.8%, 42.4 ± 4.6%, and 84.2 ± 13.1% in the R1, R2, R3 and R4 reactors, respectively. Denitrification rate showed linear relationship at increasing concentrations nitrogen content in the reactor and denitrification rate was 1.43 g NO₂-N /m²/day at 1.5 g NO₂-N /m²/day. Dehydrogenase activity was assayed in all reactors and maximum amount was detected in the aerobic biofilm reactor. Based on the present findings, MBBRs and the selected bacterial strains are useful for the degradation domestic wastewater with minimum working area.     

Nitrifying granules cultivation in a sequencing batch reactor at a low organics-to-total nitrogen ratio in wastewater

It is possible to cultivate aerobic granular sludge at a low organic loading rate and organics-to-total nitrogen (COD/N) ratio in wastewater in the reactor with typical geometry (height/diameter = 2.1, superficial air velocity = 6 mm/s). The noted nitrification efficiency was very high (99%). At the highest applied ammonia load (0.3 ± 0.002 mg NH₄⁺–N g total suspended solids (TSS)⁻¹ day⁻¹, COD/N = 1), the dominating oxidized form of nitrogen was nitrite. Despite a constant aeration in the reactor, denitrification occurred in the structure of granules. Applied molecular techniques allowed the changes in the ammonia-oxidizing bacteria (AOB) community in granular sludge to be tracked. The major factor influencing AOB number and species composition was ammonia load. At the ammonia load of 0.3 ± 0.002 mg NH₄⁺–N g TSS⁻¹ day⁻¹, a highly diverse AOB community covering bacteria belonging to both the Nitrosospira and Nitrosomonas genera accounted for ca. 40% of the total bacteria in the biomass.     

Treatment of old landfill leachate with high ammonium content using aerobic granular sludge

Background

Aerobic granular sludge has become an attractive alternative to the conventional activated sludge due to its high settling velocity, compact structure, and higher tolerance to toxic substances and adverse conditions. Aerobic granular sludge process has been studied intensively in the treatment of municipal and industrial wastewater. However, information on leachate treatment using aerobic granular sludge is very limited.

Methods

This study investigated the treatment performance of old landfill leachate with different levels of ammonium using two aerobic sequencing batch reactors (SBR): an activated sludge SBR (ASBR) and a granular sludge SBR (GSBR). Aerobic granules were successfully developed using old leachate with low ammonium concentration (136 mg L^?1 NH₄ ⁺-N).

Results

The GSBR obtained a stable chemical oxygen demand (COD) removal of 70% after 15 days of operation; while the ASBR required a start-up of at least 30 days and obtained unstable COD removal varying from 38 to 70%. Ammonium concentration was gradually increased in both reactors. Increasing influent ammonium concentration to 225 mg L^?1 N, the GSBR removed 73 ± 8% of COD; while COD removal of the ASBR was 59 ± 9%. The GSBR was also more efficient than the ASBR for nitrogen removal. The granular sludge could adapt to the increasing concentrations of ammonium, achieving 95 ± 7% removal efficiency at a maximum influent concentration of 465 mg L^?1 N. Ammonium removal of 96 ± 5% was obtained by the ASBR when it was fed with a maximum of 217 mg L^?1 NH₄ ⁺-N. However, the ASBR was partially inhibited by free-ammonia and nitrite accumulation rate increased up to 85%. Free-nitrous acid and the low biodegradability of organic carbon were likely the main factors affecting phosphorus removal.

Conclusion

The results from this research suggested that aerobic granular sludge have advantage over activated sludge in leachate treatment.

     

Identification of bacteria coexisting with anammox bacteria in an upflow column type reactor

Anammox process has attracted considerable attention in the recent years as an alternative to conventional nitrogen removal technologies. In this study, a column type reactor using a novel net type acrylic fiber (Biofix) support material was used for anammox treatment. The Biofix reactor was operated at a temperature of 25°C (peak summer temperature, 31.5°C). During more than 340 days of operation for synthetic wastewater treatment, the nitrogen loading rates of the reactor were increased to 3.6 kg-N/m³/d with TN removal efficiencies reaching 81.3%. When the reactor was used for raw anaerobic sludge digester liquor treatment, an average TN removal efficiency of 72% was obtained with highest removal efficiency of 81.6% at a nitrogen loading rate of 2.2 kg-N/m³/d. Results of extracellular polymeric substances (EPS) quantification revealed that protein was the most abundant component in the granular sludge and was found to be almost twice than that in the sludge attached to the biomass carriers. The anammox granules in the Biofix reactor illustrated a dense morphology substantiated by scanning electron microscopy and EPS results. The results of DNA analyses indicated that the anammox strain KSU-1 might prefer relatively low nutrient levels, while the anammox strain KU2 strain might be better suited at high nutrient concentration. Other types of bacteria were also identified with the potential of consuming dissolved oxygen in the influent and facilitating survival of anammox bacteria under aerobic conditions.     

Importance of the operating pH in maintaining the stability of anoxic ammonium oxidation (anammox) activity in moving bed biofilm reactors

Two bench-scale parallel moving bed biofilm reactors (MBBR) were operated to assess pH-associated anammox activity changes during long term treatment of anaerobically digested sludge centrate pre-treated in a suspended growth partial nitrification reactor. The pH was maintained at 6.5 in reactor R1, while it was allowed to vary naturally between 7.5 and 8.1 in reactor R2. At high nitrogen loads reactor R2 had a 61% lower volumetric specific nitrogen removal rate than reactor R1. The low pH and the associated low free ammonia (FA) concentrations were found to be critical to stable anammox activity in the MBBR. Nitrite enhanced the nitrogen removal rate in the conditions of low pH, all the way up to the investigated level of 50 mg NO₂-N/L. At low FA levels nitrite concentrations up to 250 mg NO₂-N/L did not cause inactivation of anammox consortia over a 2-days exposure time.     

Reactivation of effluent granular sludge from a high-rate Anammox reactor after storage

In this study, effluent sludge from a high-rate Anammox reactor was used to re-start new Anammox reactors for the reactivation of Anammox granular sludge. Different start-up strategies were evaluated in six upflow anaerobic sludge blanket (UASB) reactors (R₁–R₆) for their effect on nitrogen removal performance. Maximal nitrogen removal rates (NRRs) greater than 20 kg N/m³/day were obtained in reactors R₃–R₅, which were seeded with mixed Anammox sludge previously stored for approximately 6 months and 1 month. A modified Boltzmann model describing the evolution of the NRR fit the experimental data well. An amount of sludge added to the UASB reactor or decreasing the loading rate proved effective in relieving the substrate inhibition and increasing the NRR. The modified Stover–Kincannon model fit the nitrogen removal data in the Anammox reactors well, and the simulation results showed that the Anammox process has great nitrogen removal potential. The observed inhibition in the Anammox reactors may have been caused by high levels of free ammonia. The sludge used to seed the reactors did not settle well; sludge flotation was observed even after the reactors were operated for a long time at a floating upward velocity (F_s) of greater than 100 m/h. The settling sludge, however, exhibited good settling properties. Scanning electron microscopy showed that the Anammox granules consisted mainly of spherical and elliptical bacteria with abundant filaments on their surface. Hollows in the granules were also present, which may have contributed to sludge floatation.     

Process of simultaneous hydrogen sulfide removal from biogas and nitrogen removal from swine wastewater

The feasibility of a new flowchart describing simultaneous hydrogen sulfide removal from biogas and nitrogen removal from wastewater was investigated. It took 30 days for the reactor inoculated with aerobic sludge to attain a removal rate of 60% for H₂S and NO_x–N simultaneously. It took 34 and 48 days to attain the same removal rate for the reactor without inoculated sludge and the reactor inoculated with anaerobic sludge respectively. The reactor without inoculated sludge still operated successfully, despite requiring a slightly longer startup time. The packing material was capable of enhancing the removal efficiency of reactors. Based on the concentration of NO_x–N and H₂S in the effluent, the loading rate and the ability of the system to resist shock loading, the performance of the reactor filled with hollow plastic balls was greater than that of the reactor filled with elastic packing and the reactor filled with Pall rings.     

Effect of influent substrate ratio on anammox granular sludge: performance and kinetics

Effect of influent substrate ratio on anammox process was studied in sequencing batch reactor. Operating temperature was fixed at 35 ± 1 °C. Influent pH and hydraulic retention time were 7.5 and 6 h, respectively. When influent NO₂ ^?-N/NH₄ ⁺-N was no more than 2.0, total nitrogen removal rate (TNRR) increased whereas NH₄ ⁺-N removal rate stabilized at 0.32 kg/(m³ d). ΔNO₂ ^?-N/ΔNH₄ ⁺-N increased with enhancing NO₂ ^?-N/NH₄ ⁺-N. When NO₂ ^?-N/NH₄ ⁺-N was 4.5, ΔNO₂ ^?-N/ΔNH₄ ⁺-N was 1.98, which was much higher than theoretical value (1.32). The IC₅₀ of NO₂ ^?-N was 289 mg/L and anammox activity was inhibited at high NO₂ ^?-N/NH₄ ⁺-N ratio. With regard to influent NH₄ ⁺-N/NO₂ ^?-N, the maximum NH₄ ⁺-N removal rate was 0.36 kg/(m³ d), which occurred at the ratio of 4.0. Anammox activity was inhibited when influent NH₄ ⁺-N/NO₂ ^?-N was higher than 5.0. With influent NO₃ ^?-N/NH₄ ⁺-N of 2.5–6.5, NH₄ ⁺-N removal rate and NRR were stabilized at 0.33 and 0.40 kg/(m³ d), respectively. When the ratio was higher than 6.5, nitrogen removal would be worsened. The inhibitory threshold concentration of NO₂ ^?-N was lower than NH₄ ⁺-N and NO₃ ^?-N. Anammox bacteria were more sensitive to NO₂ ^?-N than NH₄ ⁺-N and NO₃ ^?-N. TNRR would be enhanced with increasing nitrogen loading rate, but sludge floatation occurred at high nitrogen loading shock. The Han-Levenspiel could be applied to simulate nitrogen removal resulting from NO₂ ^?-N inhibition.     

Enrichment and granulation of Anammox biomass started up with methanogenic granular sludge

A sequencing batch reactor (SBR) seeded with methanogenic granular sludge was started up to enrich Anammox (Anaerobic Ammonium Oxidation) bacteria and to investigate the feasibility of granulation of Anammox biomass. Research results showed that hydraulic retention time (HRT) was an important factor to enrich Anammox bacteria. When the HRT was controlled at 30 days during the initial cultivation, the SBR reactor presented Anammox activity at t = 58 days. Simultaneously, the methanogenic granular sludge changed gradually from dust black to brown colour and its diameter became smaller. At t = 90 days, the Anammox activity was further improved. NH₄⁺-N and NO₂⁻N were removed simultaneously with higher speed and the maximum removal rates reached 14.6 g NH₄⁺-N /(m³ _reactor·day) and 6.67 g NO₂⁻-N /(m³ _reactor·day), respectively. Between t = 110 days and t = 161 days, the nitrogen load was increased to a HRT of 5 days (70 mg/l NH₄⁺ and 70 mg/l NO₂), the removal rates of ammonium and nitrite were 60.6% and 62.5% respectively. The sludge changed to red and formed Anammox granulation with high nitrogen removal activity.