Partial nitritation and anammox of a livestock manure digester liquor and analysis of its microbial community

A swim-bed reactor for partial nitritation with polymeric coagulant treatment and an UASB reactor for anammox were applied to the treatment of livestock manure digester liquor. The partial nitritation was maintained for 32 days under a 1.6 kg N/m³/d nitrogen loading rate (NLR) with an average conversion efficiency of 51%, and achieved 1.65 kg N/m³/d of the maximum nitrite production rate under 2.58 kg N/m³/d of NLR. Although 200 mg/L of TOC remained in the effluent of the partial nitritation reactor, the anammox nitrogen removal rate was not significantly decreased and a relatively high rate of 2.0 kg N/m³/d was obtained under a NLR of 2.2 kg N/m³/d. 16S rRNA gene analysis showed that Nitrosomonas and KSU-1 were dominant in the partial nitritation and anammox reactor, respectively. The results of this study demonstrated that the partial nitritation-anammox process has possibility of applying to the nitrogen removal of livestock manure digester liquor.     

Stimulating denitrification in a stream mesocosm with elemental sulfur as an electron donor

The heavy use of fertilizers in agricultural lands can result in significant nitrate (NO₃⁻) loadings to the aquatic environment. We hypothesized that biological denitrification in agricultural ditches and streams could be enhanced by adding elemental sulfur (S^o) to the sediment layer, where it could act as a biofilm support and electron donor. Using a bench-scale stream mesocosm with a bed of S^o granules, we explored NO₃⁻ removal fluxes as a function of the effluent NO₃⁻ concentrations. With effluent NO₃⁻ ranging from 0.5 mg N L⁻¹ to 4.1 mg N L⁻¹, NO₃⁻ removal fluxes ranged from 228 mg N m⁻² d⁻¹ to 708 mg N m⁻² d⁻¹. This is as much as 100 times higher than for agricultural drainage streams. Sulfate (SO₄²⁻) production was high due to aerobic sulfur oxidation. Molecular studies demonstrated that the S^o amendment selected for Thiobacillus species, and that no special inoculum was required for establishing a S^o-based autotrophic denitrifying community. Modeling studies suggested that denitrification was diffusion limited, and advective flow through the bed would greatly enhance NO₃⁻ removal fluxes. Our results indicate that amendment with S^o is an effective means to stimulate denitrification in a stream environment. To minimize SO₄²⁻ production, it may be better to place S^o deeper in the sediment layer.     

Denitrifying sulfide removal and carbon methanogenesis in a mesophilic, methanogenic culture

The inhibitory effects of 90-189 mg l⁻¹ of sulfide and 25-75 mg-N l⁻¹ of nitrate on methanogenesis were investigated in a mixed methanogenic culture using butyrate as carbon source. In the initial phase of 90 mg l⁻¹ S²⁻ test, autotrophic denitrification of nitrate occurred with sulfide as the electron donor. Then the sulfate-reducing strains converted the produced sulfur back to sulfide via heterotrophic oxidation pathway. Methanogenesis was not markedly inhibited when 90 mg l⁻¹ of sulfide was dosed alone. When 25-75 mg-N l⁻¹ of nitrate was presented, initiation of methanogenesis was seriously delayed. Nitrogen oxides (NO_x), the intermediates for nitrate reduction via denitrification pathway, inhibited methanogenesis. The 90 mg l⁻¹ of sulfide favored heterotrophic dissimilatory nitrate reduction to ammonia (DNRA) pathway for nitrate reduction. Possible ways of maximizing methane production from an organic carbon-rich wastewater with high levels of sulfide and nitrate were discussed.     

Combined removal of sulfur compounds and nitrate by autotrophic denitrification in bioaugmented activated sludge system

An autotrophic denitrification process using reduced sulfur compounds (thiosulfate and sulfide) as electron donor in an activated sludge system is proposed as an efficient and cost effective alternative to conventional heterotrophic denitrification for inorganic (or with low C/N ratio) wastewaters and for simultaneous removal of sulfide or thiosulfate and nitrate. A suspended culture of sulfur-utilizing denitrifying bacteria was fast and efficiently established by bio-augmentation of activated sludge with Thiobacillus denitrificans. The stoichiometry of the process and the key factors, i.e. N/S ratio, that enable combined sulfide and nitrogen removal, were determined. An optimum N/S ratio of 1 (100% nitrate removal without nitrite formation and low thiosulfate concentrations in the effluent) has been obtained during reactor operation with thiosulfate at a nitrate loading rate (NLR) of 17.18 mmol N L(-1) d(-1). Complete nitrate and sulfide removal was achieved during reactor operation with sulfide at a NLR of 7.96 mmol N L(-1) d(-1) and at N/S ratio between 0.8 and 0.9, with oxidation of sulfide to sulfate. Complete nitrate removal while working at nitrate limiting conditions could be achieved by sulfide oxidation with low amounts of oxygen present in the influent, which kept the sulfide concentration below inhibitory levels.     

以N-甲基吡咯烷酮(NMP)为电子供体进行反硝化的可行性及实验研究

【目的】利用N-甲基吡咯烷酮(N-methylpyrrolidone, NMP)作为电子供体进行反硝化实验,以实现废水资源化。【方法】分别将NMP废水和葡萄糖作为电子供体加入到模拟的城市污水处理尾水中进行反硝化,比较2种电子供体去除硝酸盐的规律。同时考查NMP在反硝化过程中的氮素释放规律,并对所释放的氮素进行后续处理。最后再对它们作为电子供体时的反硝化污泥采用高通量测序,从微生物群落的角度分析NMP作为电子供体时其作用机理是否相同。【结果】当以NMP为电子供体时,硝酸盐氮的去除速率比葡萄糖为电子供体时要快67%。在8 h的反硝化结束后,剩余的硝酸盐氮、累积的亚硝酸盐氮和NMP本身所释放氨氮之和的总氮,与葡萄糖为电子供体时相近。【结论】NMP废水可以作为电子供体用于城镇污水处理厂的深度脱氮。对2种碳源所驯化的反硝化污泥样品进行高通量分析表明,NMP与葡萄糖作为电子供体用于反硝化反应时,相关的作用机理是不同的。该项研究结果对利用含氮杂环化合物作为电子供体进行反硝化具有重要的理论指导意义。     

Nitrogen-removal bioreactor capable of simultaneous nitrification and denitrification for application to industrial wastewater treatment

A bioreactor system with 30 packed gel envelopes was installed in a thermal power plant for the removal of nitrogen from ammonia-containing desulfurization wastewater. Each envelope consisted of double-sided plate gels containing Nitrosomonas europaea and Paracoccus denitrificans cells with an internal space in between for injecting an electron donor. The envelope can remove ammonia from wastewater in a single step. When the wastewater was continuously treated with the bioreactor system, it removed 95.0% of the total nitrogen in the inlet, and the total nitrogen concentration in the outlet was below 9.0 mg L⁻¹. The maximum nitrogen removal rate was 6.0 g day⁻¹ per square meter of the gel area. The maximum utilization efficiency of the injected ethanol for denitrification was 98.4%, and the total organic carbon concentration in the outflow was maintained at a low level. Since the bioreactor system could use the electron donor effectively, it was not necessary to use an additional aerobic tank to remove the electron donor and a settling tank to segregate the surplus sludge containing bacteria from wastewater. Our concept of using packed gel envelopes would be highly effective for constructing a simple and efficient nitrogen removal system capable of simultaneous nitrification and denitrification.     

Effect of sulfide concentration on autotrophic denitrification from nitrate and nitrite in vertical fixed-bed reactors

Autotrophic denitrification coupled with sulfide oxidation represents an interesting alternative for the simultaneous removal of nitrate/nitrite and sulfide from wastewaters. The applicability of such bioprocess is especially advantageous for the post treatment of effluents from anaerobic reactors, since they usually produce sulfides, which can be used as endogenous electron donor for autotrophic denitrification. This study evaluated the effect of sulfide concentration on this bioprocess using nitrate and nitrite as electron acceptors in vertical fixed-bed reactors. The results showed that intermediary sulfur compounds were mainly produced when excess of electron donor was applied, which was more evident when nitrate was used. Visual evidences suggested that elemental sulfur was the intermediary compound produced. There was also evidence that the elemental sulfur previously formed was being used when sulfide was applied in stoichiometric concentration relative to nitrate/nitrite. Nitrite was more readily consumed than nitrate. For both electron acceptors and sulfide concentrations tested, autotrophic denitrification was not affected by residual heterotrophic denitrification via endogenic activity, occurring as a minor additional nitrogen removal process.     

Biofilm stratification during simultaneous nitrification and denitrification (SND) at a biocathode

The aeration of the cathode compartment of bioelectrochemical systems (BESs) was recently shown to promote simultaneous nitrification and denitrification (SND). This study investigates the cathodic metabolism under different operating conditions as well as the structural organization of the cathodic biofilm during SND. Results show that a maximal nitrogen removal efficiency of 86.9 ± 0.5%, and a removal rate of 3.39 ± 0.08 mg N L⁻¹ h⁻¹ could be achieved at a dissolved oxygen (DO) level of 5.73 ± 0.03 mg L⁻¹ in the catholyte. The DO levels used in this study are higher than the thresholds previously reported as detrimental for denitrification. Analysis of the cathodic half-cell potential during batch tests suggested the existence of an oxygen gradient within the biofilm while performing SND. FISH analysis corroborated this finding revealing that the structure of the biofilm included an outer layer occupied by putative nitrifying organisms, and an inner layer where putative denitrifying organisms were most dominant. To our best knowledge this is the first time that nitrifying and denitrifying microorganisms are simultaneously observed in a cathodic biofilm.     

Nitrogen transformations under different conditions in open ponds by means of microalgae-bacteria consortium treating pig slurry

Four open ponds inoculated with microalgae-bacteria consortium treating different swine slurries (fresh and anaerobically digested) were evaluated in terms of nitrogen transformation under optimal and real conditions of temperature and illumination. Ammonium complete depletion was not achieved. Ponds operated under real conditions presented lower ammonium removal. Elimination capacities were around 26 mg N/L d and were subsequently increased with increasing inlet ammonium loading rate. Different nitrogen transformation was observed depending on substrate source. When anaerobically digested slurry was fed to the ponds, nitrification followed by biomass uptake and denitrification were the main nitrogen transformation taking place depending on inlet ammonium loading rate and operational conditions. Ponds fed with fresh slurry exhibited denitrification as the main nitrogen removal mechanism for the pond operated under real conditions while under optimal conditions stripping, denitrification and biomass uptake contributed similarly. Therefore, this study confirmed that the so-claimed nitrogen recovery by microalgae biomass is frequently overestimated.     

Microbial community analysis of an aerobic nitrifying-denitrifying MBR treating ABS resin wastewater

A two-stage aerobic membrane bioreactor (MBR) system for treating acrylonitrile butadiene styrene (ABS) resin wastewater was carried out in this study to evaluate the system performance on nitrification. The results showed that nitrification of the aerobic MBR system was significant and the highest TKN removal of approximately 90% was obtained at hydraulic retention time (HRT) 18 h. In addition, the result of nitrogen mass balance revealed that the percentage of TN removal due to denitrification was in the range of 8.7-19.8%. Microbial community analysis based on 16s rDNA molecular approach indicated that the dominant ammonia oxidizing bacteria (AOB) group in the system was a β-class ammonia oxidizer which was identified as uncultured sludge bacterium (AF234732). A heterotrophic aerobic denitrifier identified as Thauera mechernichensis was found in the system. The results indicated that a sole aerobic MBR system for simultaneous removals of carbon and nitrogen can be designed and operated for neglect with an anaerobic unit.     

Cascade bioreactor with submerged biofilm for aerobic treatment of Tunisian landfill leachate

A bioreactor cascade with a submerged biofilm is proposed to treat young landfill leachate of jbel chakir landfill site south west from capital Tunis, Tunisia. The prototype was run under different organic loading charges varying from 0.6 to 16.3 kg TOC m⁻³ day⁻¹. Without initial pH adjustment total organic carbon (TOC) removal rate varied between 65% and 97%. The total reduction of COD reached 92% at a hydraulic retention time of 36 h. However, the removal of total kjeldahl nitrogen for loading charges of 0.5 kg N m⁻³ day⁻¹ reached 75%. The adjustment of pH to 7.5 improved nitrogen removal to a rate of 85% for loading charge of 1 kg N m⁻³ day⁻¹. The main bacterial groups responsible for a simultaneous removal of organic carbon and nitrogen belonged to Bacillus, Actinomyces, Pseudomonas and Burkholderia genera. These selected isolates showed a great capacity of degradation at different leachate concentrations of total organic carbon.     

Ammonia removal from a waste air stream using a biotrickling filter packed with polyurethane foam through the SND process

This paper presents the results of a bench-scale biotrickling filter (BTF) on the removal of ammonia gas from a waste stream using a simultaneous nitrification/denitrification (SND) process. It was found that the developed BTF could completely remove 100 ppm ammonia from a waste stream, with an empty bed retention time of 60 s and 98.4% nitrogen removal through the SND process under the tested conditions. It was elucidated that both autotrophic and heterotrophic bacteria were involved in the nitrogen removal trough the SND process in the BTF. Additionally, the elimination capacity of total nitrogen by the BTF increased from 3.5 to 18.4 g N/m³ h with an inlet load of 20.6 g N/m³ h (73.6%). The findings of this study suggest that the BTF can be operated to attain complete ammonia removal through the SND process, thereby making the treatment of ammonia-laden gas streams both short and cost-effective.     

Effect of infiltration rate on nitrogen dynamics in paddy soil after high-load nitrogen application containing N tracer

Flooded paddy fields perform many ecological and conservation functions and are also reported to facilitate livestock waste disposal. Paddy field infiltration rates are important for nitrogen dynamics. A laboratory study was conducted to compare the effects of infiltration rate on nitrogen dynamics including nitrogen leaching, soil adsorption, microorganism assimilation, plant uptake and denitrification. Two infiltration rates were applied to paddy soil: 18.6 ± 10.3 mm d⁻¹ (High Infiltration Columns: HIC) and 4.49 ± 3.15 mm d⁻¹ (Low Infiltration Columns: LIC). Total nitrogen load was 484 kg-N ha⁻¹, with the ammonium ion form including basal fertilizer and a double supplemental fertilizer application. A (¹⁵NH₄)₂SO₄ tracer was applied in each infiltration rate as supplemental fertilizer.Nitrification and denitrification, plant uptake, soil adsorption, and leaching differed between infiltration rates. Compared with high nitrate concentration in HIC soil water, little nitrate appeared in the LIC, and it maintained relatively higher soil water ammonium concentrations long after application. The ¹⁵N assimilated by rice and contained in the LIC soil was higher than in the HIC, suggesting that low infiltration is beneficial to nitrogen assimilation, adsorption and fixation. Although loss of nitrogen via leaching was higher in the HIC than the LIC, it accounted for only 3.94% of total ¹⁵N input. About 69.4% of total ¹⁵N input was unaccounted for in the HIC, whereas 38.3% of total ¹⁵N input was unaccounted for in the LIC. According to the denitrification rate calculated from changes in ²⁹N₂/²⁸N₂ and ³⁰N₂/²⁸N₂ ratios, the denitrification rate after HIC application was higher than the LIC, reaching a maximum rate of 2.9 g m⁻² d⁻¹. This suggests that high infiltration rate enhances nitrification and denitrification, with most of the unaccounted inputted ¹⁵N in the HIC was probably lost through nitrification and denitrification.     

Autotrophic denitrification and inhibitory effect caused by the injection of spent sulfidic caustic in a modified Ludzack-Ettinger process

As spent sulfidic caustic (SSC) from petroleum plants contains a high concentration of alkalinity and sulfur compounds, SSC can be applied in sewage treatment system as an electron donor for autotrophic denitrification. In our previous study, the reuse of SSC in the biological nitrogen process was successful, and some neutralization may be required for stable treatment performance. In this study, the pH of SSC was neutralized to 12.0 from 13.3, and the modified Ludzack-Ettinger process was conducted for 90 days with the municipal wastewater. Some toxic effects of SSC on microorganisms were tested via a specific oxygen uptake rate (SOUR) assay. According to the SOUR assay, as compared with no SSC injection condition, SOUR was reduced by approximately 5.4% when 4 mL SSC/L was injected and the effective concentration of a toxicant causing 50% inhibition of the microorganism’s activity (EC₅₀) was 22.6 mL/L. During the days of operation, the COD removal and nitrification efficiency were over 53.0 and 98.2%, respectively. The TN removal efficiency was 56.6% and the nitrogen removal rate (NRR) was 0.15 kg/m³·d when the hydraulic retention time (HRT) in the anoxic tank was 3 h. The ratio of nitrifying bacteria was unaffected by the HRT, and Nitrobacter spp. and Nitrospira genus existed at similar ratios. The ratio of T. denitrificans increased after the injection of SSC and was approximately 6.5%.     

Evaluation of passive solar heating and alternative flow regimes on nitrate removal in denitrification beds

Denitrification beds are a simple and relatively inexpensive technology for removing nitrate from point source discharges. To date, operational beds have used wood media as the carbon source, as it provides a sustained nitrate removal rate (2-10 g N m⁻³ of media d⁻¹) while maintaining permeability. In pilot-scale (2.9 m⁻³) denitrification beds receiving municipal wastewater effluent dosed with KNO₃, we looked at improving nitrate removal by using alternative carbon media (maize cobs) and increasing bed temperature through passive solar heating. The influence of flow regime (horizontal-point, horizontal-diffuse, downflow and upflow) on short-circuit flow was also investigated.The long-term nitrate removal rate (21.8 g N m⁻³ d⁻¹) of the maize cob beds over the 15-month period of the trial was 2-11-fold higher than sustained removal rates reported by other researchers for wood-based beds. While passive solar heating raised the mean bed temperature by 3.4 °C, it did not cause a measurable increase in the nitrate removal rate due to the variability in the removal rate exceeding the expected increase due to temperature.Horizontal flow had more short-circuiting than vertical flow. Short-circuiting in the horizontal flow was attributed to flow being concentrated near the top surface due to the buoyancy effect of warmer water. Greater short-circuiting in the solar heated horizontal and upflow beds than in the corresponding unheated beds was attributed to the buoyancy effect being more pronounced in the solar heated beds.Overall, downflow was deemed the most effective of the four tested flow regimes. It provided the highest increase in bed temperature due to solar heating, had the highest nitrate removal rate in the latter part of the trial and had more plug-flow characteristics. While passive solar heating raised bed temperature, we were unable to demonstrate a significant difference (at 95% CL) in nitrate removal rate between the unheated and solar heated beds because of the high variability in nitrate removal rate and the increase in short-circuiting in the solar heated horizontal and upflow beds.     

Application of low intensity ultrasound to enhance the activity of anammox microbial consortium for nitrogen removal

In this study, effect of low intensity ultrasound on the activity of anammox microbial consortium for nitrogen removal was investigated through batch experiments at the same irradiation frequency of 25 kHz. Total nitrogen removal rate increased by about 25.5% when ultrasound intensity of 0.3 w cm⁻² was applied at an optimal irradiation time of 4 min, and further experiments demonstrated that this effect could last for about 6 days. Analysis of extracellular polymeric substances indicated that the maximum increase of carbohydrate, protein and total extracellular substances was obtained on the first day after ultrasound, which was 28.8%, 30.5% and 29.7%, respectively. As the time prolonged, the production rate of extracellular carbohydrate, protein decreased gradually. Transmission electron microscopy observation demonstrated that ultrasounded cell wall of anammox microbial consortium became thinner resulting in increased release of extracellular substances. The results suggested that application of low intensity ultrasound may enhance the activity of anammox microbial consortium and ultimately the potential for nitrogen removal.     

Stoichiometry of biological nitrogen transformations in wetlands and other ecosystems

The stoichiometric equations of ammonification, nitrification and denitrification have demonstrated that the nitrogen cycle in nature is rather complicated. The mechanisms of biological nitrogen transformations are very important for analysis, design, operation and optimal control of natural ecosystems or engineered systems for nitrogen removal, and accurate stoichiometric equations can help in the maintenance of these environments. In this study, the new stoichiometric equations of intermediate nitrification, and heterotrophic and autotrophic denitrification with sulfur as the electron donor have been developed and discussed. The parameter values of f(s) (the fraction of electron donor coupled to cell synthesis) in stoichiometric equations of nitrification and denitrification are calculated according to experimental results implied in previously reported stoichiometric equations. Some new stoichiometric relationships of nitrification and denitrification, such as the O(2) demand for nitrifications, chemical oxygen demand/N ratios and the yield coefficients for denitrifications have been established. The pathway steps of nitrification and denitrification have been discussed.     

A low volumetric exchange ratio allows high autotrophic nitrogen removal in a sequencing batch reactor

Sequencing batch reactors (SBRs) have several advantages, such as a lower footprint and a higher flexibility, compared to biofilm based reactors, such as rotating biological contactors. However, the critical parameters for a fast start-up of the nitrogen removal by oxygen-limited autotrophic nitrification/denitrification (OLAND) in a SBR are not available. In this study, a low critical minimum settling velocity (0.7 m h⁻¹) and a low volumetric exchange ratio (25%) were found to be essential to ensure a fast start-up, in contrast to a high critical minimum settling velocity (2 m h⁻¹) and a high volumetric exchange ratio (40%) which yielded no successful start-up. To prevent nitrite accumulation, two effective actions were found to restore the microbial activity balance between aerobic and anoxic ammonium-oxidizing bacteria (AerAOB and AnAOB). A daily biomass washout at a critical minimum settling velocity of 5 m h⁻¹ removed small aggregates rich in AerAOB activity, and the inclusion of an anoxic phase enhanced the AnAOB to convert the excess nitrite. This study showed that stable physicochemical conditions were needed to obtain a competitive nitrogen removal rate of 1.1 g N L⁻¹ d⁻¹.     

Denitrification, nitrate turnover, and aerobic respiration by benthic foraminiferans in the oxygen minimum zone off Chile

Population density, nitrate turnover, and oxygen respiration of benthic foraminiferans were investigated in the oxygen minimum zone (OMZ) off the Chilean coast. Live foraminiferans were found predominantly in the upper 3 mm of the sediment, and the nitrate accumulating species Nonionella cf. stella and Stainforthia sp. dominated with a combined standing stock of 2.0 × 10⁶ Rose Bengal stained specimens m^− 2. The rate of denitrification in cells of N. cf. stella analyzed with nitrous oxide microsensors during acetylene inhibition was 84 ± 33 pmol C individual^− 1 d^− 1. Multiplied with the standing stock of N. cf. stella and Stainforthia sp. this yielded a minimum benthic denitrification rate of 173 µmol N m^− 2 d^− 1 by foraminiferans. Foraminiferal denitrification, which seemed to account for almost all benthic denitrification at the investigated site will be overlooked by most conventional methods measuring benthic denitrification. Compared to the denitrification rates, the potential rates of nitrate accumulation and oxygen respiration by N. cf. stella were an order of magnitude higher (864 pmol N individual^− 1 d^− 1 and 760 ± 87 pmol C individual^− 1 d^− 1, respectively), which seems an adaptation to the infrequent availability of nitrate and oxygen in the sediment surface.     

Sulfide oxidation under chemolithoautotrophic denitrifying conditions

Chemolithoautotrophic denitrifying microorganisms oxidize reduced inorganic sulfur compounds coupled to the reduction of nitrate as an electron acceptor. These denitrifiers can be applied to the removal of nitrogen and/or sulfur contamination from wastewater, groundwater, and gaseous streams. This study investigated the physiology and kinetics of chemolithotrophic denitrification by an enrichment culture utilizing hydrogen sulfide, elemental sulfur, or thiosulfate as electron donor. Complete oxidation of sulfide to sulfate was observed when nitrate was supplemented at concentrations equal or exceeding the stoichiometric requirement. In contrast, sulfide was only partially oxidized to elemental sulfur when nitrate concentrations were limiting. Sulfide was found to inhibit chemolithotrophic sulfoxidation, decreasing rates by approximately 21-fold when the sulfide concentration increased from 2.5 to 10.0 mM, respectively. Addition of low levels of acetate (0.5 mM) enhanced denitrification and sulfate formation, suggesting that acetate was utilized as a carbon source by chemolithotrophic denitrifiers. The results of this study indicate the potential of chemolithotrophic denitrification for the removal of hydrogen sulfide. The sulfide/nitrate ratio can be used to control the fate of sulfide oxidation to either elemental sulfur or sulfate.