Influent Nitrate Research Articles

Effect of Organic Carbon on Tertiary Denitrification of the Secondary Effluent in Biofilters Packed with Suspended Carriers

Denitrifying biokinetics in biofilters packed with suspended carriers were evaluated under different empty bed residence times (EBRT) with ethanol or acetate as the electron donor. The two denitrifying biofilters removed nitrate (NO3––N) effectively after only 3–4 days operation. At EBRT of 30; 15 and 7.5 min, the NO3––N removal percentage was 84; 72 and 59% in the ethanol biofilter, and was 89; 70 and 62% in the acetate biofilter, respectively. With the influent NO3––N loading rate ranged from 0.4 to 1.8 g/(m2·d), the NO3––N removal loading rate increased with increasing influent NO3––N loading rates, and the system was substrate limited. While when the influent nitrate loading rate was above 3 g/(m2·d), the system was biomass limited. The half-order coefficients were 0.162; 0.175 and 0.274 (mg/L)1/2/min for the ethanol biofilter with the influent NO3––N concentration of 7.3–7.7 mg/L, and were 0.107; 0.165 and 0.303 (mg/L)1/2/min for the acetate biofilter with the influent NO3––N concentration of 6.8–8.0 mg/L. Denitrification efficiency varied slightly during the backwashing cycle, and the effect of backwashing on the effluent turbidity was relatively large, especially for the biofilter with ethanol as the organic carbon.

Treatment of Nitrocellulose Industry Watewaters by Upflow Denitrification Filter: Effect of Packing Media and Recirculation

The treatment of nitrocellulose industry wastewaters, characterized by high nitrate (1450–1990 mg/L) concentrations and low pH (1.45–1.57), was investigated by using denitrification filters. Methanol was added as external organic carbon source. The filter was filled with ceramic media and 50 to 100% effluent recirculation was applied. Alkalinity was produced during denitrification and increase in pH was observed. The system achieved 94–99% nitrate removal and effluent pH between 6.4 and 7.8, when pH of the influent wastewater was adjusted to 4. When the filter was filled with limestone media, 74 to 98% nitrate removal was achieved without any alkali addition. The denitrification rate was 229 mg NO3-N/m3/d. The two filters operated also in series, limestone filter being the first in the series receiving wastewater. The serial system was capable of reducing nitrate completely and neutralizing the pH into the weak alkali solution (7.08–7.82). The biologically produced alkalinity through denitrification could be beneficially used for the in situ neutralization and treatment of high influent nitrate containing acidic waters. These studies show that up-flow denitrification filters are suitable systems for treating acidic nitrocellulose industry wastewaters.

Research on denitrification efficiency of three types of solid carbon source

C/N rates can greatly influence efficiency of denitrification. It is difficult for current treated effluent to reach GB18918-2002 primary effluent standard because of its low C/N rate. To improve the efficiency of denitrification, the quality of effluent, and realize the waste recycling, this article selected magnolia leaves, loofah and degradable meal box as the solid carbon source and set different solid-liquid ratio of magnolia leaves for periodic denitrification stage to study the change of NO3--N, TN, COD, NO2--N, NH4+, PO43- and color. The results showed that in the condition of influent nitrate concentration of 40 mg/L, carbon dosage of 10 g, the reaction temperature of 25°C, the nitrate removal rates of magnolia leaves and loofah reached 89.0% and 96.8% respectively, rather higher than degradable meal box (56.3%). The TN removal rates of magnolia leaves (91.7%) and loofah (77.7%) were both higher than degradable meal box (53.9%), and the effluent TN concentration of loofah and degradable meal box reached 25.4 mg/L and 21.1 mg/L respectively, which couldn’t be discharged according to the primary effluent concentration standard of GB18918-2002. The released concentration of ammonia nitrogen and phosphate: loofah> magnolia> degradable meal box. The high solid-liquid ratio of magnolia leaves helped to improve the TN removal rate, which reached 75.0% (1:200) and 91.7% (1:100), but it caused higher released concentration of carbon, ammonia nitrogen and phosphate to effect system heavily. Under the integrated analysis, the low solid-liquid ratio (1:200) of magnolia leaves was more suitable to be the denitrification external carbon source.

Simultaneous carbon and nitrogen removal from anaerobic effluent of the cassava ethanol industry

This study investigated the simultaneous carbon and nitrogen removal from anaerobic effluent of cassava stillage using a lab-scale integrated system consisting of an upflow anaerobic sludge blanket (UASB) reactor and an activated sludge (AS) process. Simultaneous denitrification and methanogenesis (SDM) was observed in the UASB with nitrate recirculation. Compared with the blank reactor without recirculation, the overall chemical oxygen demand (COD) removal efficiencies in the combined system with nitrate recirculation were similar (80-90%), while the TN removal efficiencies were significantly improved from 4.7% to 71.0%. Additionally, the anaerobic COD removal efficiencies increased from 21% to 40% as the recirculation ratio decreased from 3 to 1. Although the influent nitrate concentrations fluctuated (60-140mgN/L), the nitrate removal efficiencies could be maintained at about 97% under different recirculation conditions. With the decreasing recirculation ratio from 3 to 1, the CH4 content in biogas improved from 2% to 40% while the N2 content reduced from 95.8% to 50.6%. The 16S rDNA sequencing results indicated that bacteria diversity in anaerobic SDM granular sludge was much higher than archaea. The effect of recirculation ratios on the bacterial and archaeal communities in SDM granular sludge could be further confirmed by the relative abundance of denitrifying bacteria.

Multilayer system of nanoscale zero valent iron and Nano-Fe/Cu particles for nitrate removal in porous media

Abstract This work studies the nitrate removal efficiency in porous media using nanoscale zero valent iron (nZVI) and modified surface of nZVI using Cu metal (known as bimetallic nano-Fe/Cu particles) in a multilayer system through an upflow packed sand column. The effect of multilayer and different thicknesses of nZVI/sand and nano-Fe/Cu particles on the nitrate removal performance was investigated. 10 g of nZVI and nano-Fe/Cu particles were introduced in each column with different layers configuration. The initial nitrate concentration was 45 NO3––N mg/L. The distribution of nitrate trapped inside the column was evaluated by measuring nitrate concentrations, not only at the column inlet and outlet, but also at various intermediate sampling ports along the depth of the column. The results showed that the best condition to remove nitrate among nZVI/sand columns was observed when using a single 10-cm high layer of nZVI/sand and more than 97% of influent nitrate was removed. Whereas in (nano-Fe/Cu)/sand columns, the optimum performance was noted when using double 5-cm high layers of (nano-Fe/Cu)/sand and a complete removal was attained (100%). Furthermore, nano-Fe/Cu particles showed better removal efficiency than nZVI for the treatment of nitrate in simulated groundwater. Based on the results obtained, it was concluded that using nZVI in the full length of porous media or using nano-Fe/Cu particles in multilayer porous media could enhance nitrate removal effectively.

Sulfide-Induced Dissimilatory Nitrate Reduction to Ammonium Supports Anaerobic Ammonium Oxidation (Anammox) in an Open-Water Unit Process Wetland.

Open-water unit process wetlands host a benthic diatomaceous and bacterial assemblage capable of nitrate removal from treated municipal wastewater with unexpected contributions from anammox processes. In exploring mechanistic drivers of anammox, 16S rRNA gene sequencing profiles of the biomat revealed significant microbial community shifts along the flow path and with depth. Notably, there was an increasing abundance of sulfate reducers (Desulfococcus and other Deltaproteobacteria) and anammox microorganisms (Brocadiaceae) with depth. Pore water profiles demonstrated that nitrate and sulfate concentrations exhibited a commensurate decrease with biomat depth accompanied by the accumulation of ammonium. Quantitative PCR targeting the anammox hydrazine synthase gene, hzsA, revealed a 3-fold increase in abundance with biomat depth as well as a 2-fold increase in the sulfate reductase gene, dsrA These microbial and geochemical trends were most pronounced in proximity to the influent region of the wetland where the biomat was thickest and influent nitrate concentrations were highest. While direct genetic queries for dissimilatory nitrate reduction to ammonium (DNRA) microorganisms proved unsuccessful, an increasing depth-dependent dominance of Gammaproteobacteria and diatoms that have previously been functionally linked to DNRA was observed. To further explore this potential, a series of microcosms containing field-derived biomat material confirmed the ability of the community to produce sulfide and reduce nitrate; however, significant ammonium production was observed only in the presence of hydrogen sulfide. Collectively, these results suggest that biogenic sulfide induces DNRA, which in turn can explain the requisite coproduction of ammonium and nitrite from nitrified effluent necessary to sustain the anammox community.IMPORTANCE This study aims to increase understanding of why and how anammox is occurring in an engineered wetland with limited exogenous contributions of ammonium and nitrite. In doing so, the study has implications for how geochemical parameters could potentially be leveraged to impact nutrient cycling and attenuation during the operation of treatment wetlands. The work also contributes to ongoing discussions about biogeochemical signatures surrounding anammox processes and enhances our understanding of the contributions of anammox processes in freshwater environments.

Optimizing sulfur-driven mixotrophic denitrification process: System performance and nitrous oxide emission

Nitrate contamination of groundwater has been recognized as a significant environmental problem world widely. Sulfur-driven mixotrophic denitrification has been demonstrated as a promising groundwater treatment process, which though plays an important role in nitrous oxide (N2O) emissions, significantly contributing to the overall carbon footprint of the system. However, the current process optimizations only focus on nitrate removal and excess sulfate control, with the N2O emission being ignored. In this work, an integrated mathematical model was proposed to evaluate the N2O emission as well as the excess sulfate production and carbon source utilization in sulfur-driven mixotrophic denitrification process. In this model, autotrophic and heterotrophic denitrifiers use their corresponding electron donors (sulfur and organic matter, respectively) to reduce nitrate to nitrogen gas, with each modeled as three-step denitrification (NO3− to N2 via NO2− and N2O) driven by sulfur or organic matter to describe all potential N2O accumulation steps. The developed model, employing model parameters previously reported in literature, was successfully validated using N2O and sulfate data from two mixotrophic denitrification systems with different initial conditions. Modeling results revealed substantial N2O accumulation due to the relatively low autotrophic N2O reduction activity as compared to heterotrophic N2O reduction activity, explaining the observation that higher carbon source addition resulted in lower N2O accumulation in sulfur-driven mixotrophic denitrifying system. Based on the validated model, optimizations of the overall system performance were carried out. Application of the model to simulate long-term operations of sulfur-driven mixotrophic denitrification process indicates that longer sludge retention time reduces N2O emission due to better retention of active biomass. High-level total nitrogen removal with significant N2O emission mitigation, appropriate excess sulfate control and maximized COD utilization can be achieved simultaneously through controlling the influent nitrate and COD concentrations.

Role of nitrite in the competition between denitrification and DNRA in a chemostat enrichment culture

Denitrification and dissimilatory nitrate reduction to ammonium (DNRA) are two microbial processes that compete for oxidized nitrogen compounds in the environment. The objective of this work was to determine the role of nitrite versus nitrate as terminal electron acceptor on the competition between DNRA and denitrification. Initially, a mixed culture chemostat was operated under nitrate limitation and performed DNRA. Stepwise, the influent nitrate was replaced with nitrite until nitrite was the sole electron acceptor and N-source present. Despite changing the electron acceptor from nitrate to nitrite, the dominant process remained DNRA and the same dominant organism closely related to Geobacter lovleyi was identified. Contrary to previous studies conducted with a complex substrate in marine microbial communities, the conclusion of this work is that nitrate versus nitrite as electron acceptor does not generally control the competition between DNRA and denitrification. Our results show that the effect of this ratio must be interpreted in combination with other environmental factors, such as the type and complexity of the electron donor, pH, or sulfide concentrations.

Comparison research on denitrification efficiency of two types of solid carbon source

C/N rates can greatly influence efficiency of denitrification. It is difficult for current treated effluent to reach GB18918-2002 primary effluent standard because of its low C/N rate. To improve the efficiency of denitrification, the quality of effluent, and realize the waste recycling, this article selected magnolia leaves and degradable meal box as the solid carbon source for periodic denitrification stage to study the change of NO3--N, TN, COD, NO2--N, NH4+, PO43- and color. The results showed that in the condition of influent nitrate concentration of 40 mg/L, carbon dosage of 10 g, the reaction temperature of 25°C the nitrate removal rates of magnolia leaves and degradable meal box reached 89.0% and 56.3% respectively, and the TN removal rates reached 91.7% and 53.9% respectively. But in the aspect of final treated effluent COD concentration level, magnolia leaves experiment (608 mg/L) was much higher than the degradable meal box (78 mg/L). Besides, the accumulation of nitrite, the released concentration of ammonia nitrogen and phosphate of magnolia leaves experiment were also higher than the degradable meal box. Under the integrated analysis, the magnolia leaves are more suitable than the degradable meal box as the denitrification external carbon source.

Evaluation of Mechanistic Models for Nitrate Removal in Woodchip Bioreactors.

Woodchip bioreactors (WBRs) are increasingly being applied to remove nitrate from runoff. In this study, replicate columns with aged woodchips were subjected to a range of measured flow rates and influent nitrate concentrations with an artificial stormwater matrix. Dissolved oxygen (DO), nitrate, and dissolved organic carbon (DOC) were measured along the length of the columns. A multispecies reactive transport model with Michaelis-Menten kinetics was developed to explain the concentration profiles of DO, nitrate, and DOC. Four additional models were developed based on simplifying assumptions, and all five models were tested for their ability to predict nitrate concentrations in the experimental columns. Global sensitivity analysis and constrained optimization determined the set of parameters that minimized the root-mean-squared error (RMSE) between the model and the experimental data. A k-fold validation test revealed no statistical difference in RMSE for predicting nitrate concentrations between a zero-order model and the other multispecies reactive transport models tested. Additionally, the multispecies reactive transport models demonstrated no significant differences in predicting DO and DOC concentrations. These results suggest that denitrification in an aged woodchip bioreactor at constant temperature can effectively be modeled using zero-order kinetics when nitrate concentrations are >2 mg-N L-1. A multispecies model may be used if predicting DOC or DO concentrations is desired.

Performance of the dominant bacterial species and microbial community in autotrophic denitrification coupled with iron cycle in immobilized systems

We used three stable reactors to investigate the rates of nitrate removal coupled with iron cycle and the subsequent influence of the reaction on bacterial communities. The iron-reducing bacterium Klebsiella sp. FC61 was immobilized on the reactor columns of the experimental groups B (only Klebsiella) and C (Klebsiella+magnetite). With the fluctuation of Fe2+ to Fe3+ (iron cycle), the average nitrate removal efficiency increased from 73.22% to 93.91% and 86.92% to 97.84% in groups B and C, respectively, as the influent nitrate concentration decreased from 40 to 10mg/L. However, the average rate of nitrate removal showed the opposite trend (from 2.08mg/L/h to 0.67mg/L/h and 2.41mg/L/h to 0.69mg/L/h in groups B and C, respectively) as the influent nitrate concentration decreased. Analysis of microbial distribution and community structures indicated that the population of Klebsiella sp. increased in groups B (from 18.21% to 41.21%) and C (from 25.43% to 46.80%) and contributed to the effective removal of nitrate in the reactors.

Pyrosequencing reveals microbial community dynamics in integrated simultaneous desulfurization and denitrification process at different influent nitrate concentrations

Integrated simultaneous desulfurization and denitrification (ISDD) process has proven to be feasible for the coremoval of sulfate, nitrate, and chemical oxygen demand (COD). In this study, we aimed to reveal the microbial community dynamics in the ISDD process with different influent nitrate (NO3−) concentrations. For all tested scenarios, full denitrification was accomplished while sulfate removal efficiency decreased along with increased influent NO3− concentrations. The proportion of S0 to influent SO42− maintained a low level (5.6–17.0%) regardless of the increased influent NO3− concentrations. Microbial community analysis results showed that higher influent NO3− concentrations affected the microbial community structure greatly. Phyla Proteobacteria, Spirochaetae, Firmicutes, Synergistetes, and Chloroflexi dominated in all the community compositions, of which Proteobacteria exhibited a clear difference among eight microbial samples. Members of δ-Proteobacteria, with 16S rRNA gene sequences related to Desulfobulbus, were clearly decreased at influent NO3− = 3000 and 3500 mg/L, suggesting an inhibitory effect of NO3− on sulfate reduction. In contrast, as influent NO3− concentration increased, microbial community was notably enriched in γ-Proteobacteria and ε-Proteobacteria, which revealed the enrichment of 16S rRNA gene sequences related to Pseudomonas (γ-Proteobacteria), and Arcobacteria and Sulfurospirillum (ε-Proteobacteria).

Continuous fixed-bed column study for the removal of nitrate from water using chitosan/alumina composite

A continuous adsorption study in a fixed-bed column was conducted for the removal of nitrate from water by using chitosan/alumina composite as an adsorbent. The effects of influent nitrate concentration, flow rate, and bed depth on the adsorption characteristics of adsorbent and column performances were evaluated at room temperature and original pH of the solution. The results revealed that the breakthrough curves are significantly affected by the variation of flow rate, initial concentration and bed depth. The nitrate removal efficiency increased with increase in bed height and decreased with increase in influent nitrate concentration and flow rate. The breakthrough time increased with increase in bed height. Thomas and Yoon-Nelson kinetic models were applied for the analysis of adsorption kinetics. The model data confirmed that both models are fitted well with the experimental results of continues fixed-bed column adsorption study. Bed-depth service time (BDST) model was used to study the effect of bed depth on breakthrough curves and to predict the time required for breakthrough. The model data revealed the applicability of the BDST model for the present system. The result show that chitosan/alumina composite can be used in fixed bed column for the removal of nitrate from water.

Effect of nitrate concentration, pH, and hydraulic retention time on autotrophic denitrification efficiency with Fe(II) and Mn(II) as electron donors.

The role of electron donors (Fe(2+) and Mn(2+)) in the autotrophic denitrification of contaminated groundwater by bacterial strain SY6 was characterized based on empirical laboratory-scale analysis. Strain SY6 can utilize Fe(2+) more efficiently than Mn(2+) as an electron donor. This study has shown that the highest nitrate removal ratio, observed with Fe(2+) as the electron donor, was approximately 88.89%. An immobilized biological filter reactor was tested by using three levels of influent nitrate (10, 30, and 50 mg/L), three pH levels (6, 7, and 8), and three levels of hydraulic retention time (HRT; 6, 8, and 12 h), respectively. An optimal nitrate removal ratio of about 95% was achieved at pH 6.0 using a nitrate concentration of 50 mg/L and HRT of 12 h with Fe(2+) as an electron donor. The study showed that 90% of Fe(2+) and 75.52% removal of Mn(2+) were achieved at pH 8.0 with a nitrate concentration of 50 mg/L and a HRT of 12 h. Removal ratio of Fe(2+) and Mn(2+) is higher with higher influent nitrate and HRT. A weakly alkaline environment assisted the removal of Fe(2+) and Mn(2+).

Nitrate and phosphate removal from agricultural subsurface drainage using laboratory woodchip bioreactors and recycled steel byproduct filters

Woodchip bioreactors have been increasingly used as an edge-of-field treatment technology to reduce the nitrate loadings to surface waters from agricultural subsurface drainage. Recent studies have shown that subsurface drainage can also contribute substantially to the loss of phosphate from agricultural soils. The objective of this study was to investigate nitrate and phosphate removal in subsurface drainage using laboratory woodchip bioreactors and recycled steel byproduct filters. The woodchip bioreactor demonstrated average nitrate removal efficiencies of 53.5–100% and removal rates of 10.1–21.6 g N/m3/d for an influent concentration of 20 mg N/L and hydraulic retention times (HRTs) of 6–24 h. When the influent nitrate concentration increased to 50 mg N/L, the bioreactor nitrate removal efficiency and rate averaged 75% and 18.9 g N/m3/d at an HRT of 24 h. Nitrate removal by the woodchips followed zero-order kinetics with rate constants of 1.42–1.80 mg N/L/h when nitrate was non-limiting. The steel byproduct filter effectively removed phosphate in the bioreactor effluent and the total phosphate adsorption capacity was 3.70 mg P/g under continuous flow conditions. Nitrite accumulation occurred in the woodchip bioreactor and the effluent nitrite concentrations increased with decreasing HRTs and increasing influent nitrate concentrations. The steel byproduct filter efficiently reduced the level of nitrite in the bioreactor effluent. Overall, the results of this study suggest that woodchip denitrification followed by steel byproduct filtration is an effective treatment technology for nitrate and phosphate removal in subsurface drainage.

Enhanced removal of nitrate from water using amine-grafted agricultural wastes

Adsorption using low-cost adsorbents is a favourable water treatment method for the removal of water contaminants. In this study the enhanced removal of nitrate, a contaminant at elevated concentration affecting human health and causing eutrophication of water, was tested using chemically modified agricultural wastes as adsorbents. Batch and fixed-bed adsorption studies were performed on corn cob and coconut copra that were surface modified by amine-grafting to increase the surface positive charges. The Langmuir nitrate adsorption capacities (mgN/g) were 49.9 and 59.0 for the amine-grafted (AG) corn cob and coconut copra, respectively at pH6.5 and ionic strength 1×10−3M NaCl. These values are higher than those of many commercially available anion exchange resins. Fixed-bed (15-cm height) adsorption capacities (mgN/g) calculated from the breakthrough curves were 15.3 and 18.6 for AG corn cob and AG coconut copra, respectively, for an influent nitrate concentration 20mg N/L at a flow velocity 5m/h. Nitrate adsorption decreased in the presence of sulphate, phosphate and chloride, with sulphate being the most competitive anion. The Thomas model fitted well to the fixed-bed adsorption data from four repeated adsorption/desorption cycles. Plug-flow model fitted well to the data from only the first cycle.

Optimizing Hydraulic Retention Times in Denitrifying Woodchip Bioreactors Treating Recirculating Aquaculture System Wastewater.

The performance of wood-based denitrifying bioreactors to treat high-nitrate wastewaters from aquaculture systems has not previously been demonstrated. Four pilot-scale woodchip bioreactors (approximately 1:10 scale) were constructed and operated for 268 d to determine the optimal range of design hydraulic retention times (HRTs) for nitrate removal. The bioreactors were operated under HRTs ranging from 6.6 to 55 h with influent nitrate concentrations generally between 20 and 80 mg NO-N L. These combinations resulted in N removal rates >39 g N m d, which is greater than previously reported. These high removal rates were due in large part to the relatively high chemical oxygen demand and warm temperature (∼19°C) of the wastewater. An optimized design HRT may not be the same based on metrics of N removal rate versus N removal efficiency; longer HRTs demonstrated higher removal efficiencies, and shorter HRTs had higher removal rates. When nitrate influent concentrations were approximately 75 mg NO-N L ( = 6 sample events), the shortest HRT (12 h) had the lowest removal efficiency (45%) but a significantly greater removal rate than the two longest HRTs (42 and 55 h), which were N limited. Sulfate reduction was also observed under highly reduced conditions and was exacerbated under prolonged N-limited environments. Balancing the removal rate and removal efficiency for this water chemistry with a design HRT of approximately 24 h would result in a 65% removal efficiency and removal rates of at least 18 g N m d.

Effect of pH on elemental sulfur conversion and microbial communities by autotrophic simultaneous desulfurization and denitrification

ABSTRACTpH has an important influence on the elemental sulfur accumulated in an autotrophic simultaneous desulfurization and denitrification process. The influent nitrate to sulfide (N/S) mole ratio was set to 0.5, 0.67, 1.0, 1.33 and 2.0 with a 200 mg/L sulfide concentration. The effect of pH on elemental sulfur conversion and microbial communities was studied. Sulfide removal was achieved to the extent of 98% under near-neutral and weak base conditions after 24 h of reaction. The conversion rate of elemental sulfur was 29.41% under the near-neutral condition. The weak base condition led to greater formation of sulfate, and the nitrate used by the microorganisms was transformed mainly to N2 with a removal rate of 96%. Increasing the retention time from 24 to 48 h caused the removal rate of nitrate increased from 63.58% to 90% under the near-neutral condition. Sulfurovum sp. was the functioning bacterial species, and bands 1 and 2 represent different species of Sulfurovum sp. in the system according to the PCR-DGGE analysis of the microbial community structure. The functional bacteria represented by band 1 produced mainly sulfate, but the functional bacteria represented by band 2 produced mainly elemental sulfur.

A novel elemental sulfur-based mixotrophic denitrifying membrane bioreactor for simultaneous Cr(VI) and nitrate reduction

This study aims at investigating the simultaneous nitrate and chromate reduction by combining the advantages of sulfur-based autotrophic denitrification, heterotrophic denitrification and membrane bioreactor (MBR) technologies. A laboratory-scale MBR equipped with hydrophilic flat sheet polyethersulfone (PES) membranes (0.45μm) was used to evaluate the performance of mixotrophic denitrification at varying nitrate and Cr(VI) concentrations. Methanol was supplied at C/N (mg methanol/mg NO3−-N) ratio of 1.33. In the absence of Cr(VI), almost complete denitrification of 50mg/L NO3−-N was obtained and the methanol requirement (3.60±0.9mg COD/(mg NO3−-N)) for heterotrophic denitrifiers, was quite close to the theoretical value (3.7mg COD/(mg NO3−-N)). Around 54% of the influent nitrate was denitrified by heterotrophs and the rest (56%) was denitrified by autotrophic sulfur oxidizers. The effluent sulfate averaged around 200mg/L, which was below than the theoretical sulfate concentration if autotrophic denitrification process was used alone. Autotrophic denitrification activity completely ceased at 5mg/L Cr(VI), but heterotrophic denitrification did not show any inhibition. Almost complete chromate and nitrate reduction was observed at 1mg/L Cr(VI). MBR was operated for around 200days and a weekly physical membrane cleaning was enough at a flux of 15 LMH.

Tertiary nitrogen removal for municipal wastewater using a solid-phase denitrifying biofilter with polycaprolactone as the carbon source and filtration medium

Tertiary nitrogen removal technologies are needed to reduce the excess nitrogen that is discharged into sensitive aquatic ecosystems. An integrated solid-phase denitrification biofilter (SDNF) was developed with dual media to remove nitrate and suspended solids (SS) from the secondary effluent of municipal wastewater treatment plants. Biodegradable polymer pellets of polycaprolactone (PCL) served as the biofiltration medium and carbon source for denitrification. Long-term continuous operation of the SDNF was conducted with real secondary effluent to evaluate the denitrification performance and effects of influent nitrate loading rates (NLR) and operating temperatures. The results indicated that both nitrate and SS were effectively removed. The SDNF had a strong tolerance for fluctuations in influent NLR, and a maximum denitrification rate of 3.80 g N/(L·d) was achieved. The low temperature had a significant impact on nitrogen removal, yet the denitrification rate was still maintained at a relative high level to as much as 1.23 g N/(L·d) even at approximately 8.0 °C in winter. Nitrite accumulation and excessive organics residue in the effluent were avoided throughout the whole experiment, except on occasional days in the lag phase. The observed biomass yield was calculated to be 0.44 kgVSS/kgPCL. The microbial diversity and community structure of the biofilm in the SDNF were revealed by Illumina high-throughput sequencing. The special carbon source led to an obvious succession of microbial community from the initial inoculum (activated sludge from aerobic tanks), and included a decrease in microbial diversity and a shift in the dominant groups, which were identified to be members of the family Comamonadaceae in the SDNF. The SDNF developed in this study was verified to be an efficient technology for tertiary nitrogen removal from secondary effluent.