Effluent Nitrate Concentration Research Articles

NOB suppression by organic pollutants in mainstream single-stage partial nitrification/anammox (PN/A) process: Experimental evidence and modelling investigation

Effectively and stably suppressing nitrite oxidizing bacteria (NOB) under mainstream conditions is difficult for the wide application of the partial nitrification/anammox (PN/A) process. In this work, a continuous-flow single-stage PN/A reactor experiencing nitrate accumulation was restored by increasing the influent chemical oxygen demand (COD) concentrations. Experimental results showed that the total nitrogen removal efficiency quickly increased from 70 ± 2.54 % to 84 ± 1.21 % while effluent nitrate concentrations dropped from 30 ± 4.07 mg N/L to 10 ± 3.18 mg N/L following increasing the influent COD concentrations. A modified and calibrated mathematical model was employed to quantify the nitrogen conversion process and microorganism distributions under various influent COD levels. The detailed nitrogen metabolism network was calculated by labeling the source and sink of nitrite and nitrate. Simulation results revealed that influent COD suppressed NOB activity and enhanced anammox bacteria (AMX) activity in a short-term dynamic state while leading to the elimination of NOB and enrichment of the AMX under long-term pseudo-steady state. N-metabolism simulation results indicated that more nitrite (from 46.62 mg N/L to 55.05 mg N/L) was diverted to AMX with the assistance of heterotrophic bacteria (HET). NOB was outcompeted due to the dual pressure of competing with HET and AMX for oxygen and nitrite, respectively. Microbial analysis solidly supported these findings, showing that Candidatus_kuenenia, Thauera and Denitratisoma were enriched, while the relative abundance of Nitrospira decreased after COD addition. These findings demonstrate the potential of using organic pollutants to suppress and eliminate NOB, thereby enhancing the stability and efficiency of mainstream PN/A reactors.

Hybrid modelling of nitrogen removal by biofiltration using high-frequent operational data

ABSTRACT In this research, a parallel hybrid model is presented for the simulation of nitrogen removal by submerged biofiltration of a very large-size wastewater treatment plant. This hybrid model consists of a machine learning model and a mechanistic model that are combined to produce accurate predictions of water quality variables. The models are calibrated/validated using detailed and quality-controlled operational data collected over a period of 3.5 months in 2020. The mechanistic model applied is a modified activated sludge model that describes the biological, physical and chemical processes taking place in a biofilm reactor based on the domain knowledge of these processes. A three-layer feed-forward artificial neural network with a rectified linear activation function that aims to reduce the mechanistic model's residual error and then correct its output. The results show how the hybrid model outperforms and significantly reduces the size of the mechanistic model's prediction errors of the effluent nitrate concentration from a relative mean error of 12% for the mechanistic model to 2% for the hybrid model during training. The error on nitrate simulations increases to 8% during hybrid model testing, still significantly lower than the error of the mechanistic model. These results support future operational applications of hybrid biofilm models.

Biological treatment of N-methylpyrrolidone, cyclopentanone, and diethylene glycol monobutyl ether distilled residues and their effects on nitrogen removal in a full-scale wastewater treatment plant

Manufacturing processes in semiconductor and photonics industries involve the use of a significant amount of organic solvents. Recycle and reuse of these solvents produce distillate residues and require treatment before being discharged. This study aimed to evaluate the performance of the biological treatment system in a full-scale wastewater treatment plant that treats wastewater containing distillate residues from the recycling of electronic chemicals. Batch experiments were conducted to investigate the optimal operational conditions for the full-scale wastewater treatment plant. To achieve good nitrogen removal efficiency with effluent ammonia and nitrate concentrations below 20 mg N/L and 50 mg N/L, respectively, it was suggested to control the ammonia concentration and pH of the influent below 500 mg N/L and 8.0, respectively. In addition, the biodegradability of N-methylpyrrolidone, diethylene glycol monobutyl ether, and cyclopentanone distillate residues from the electronic chemicals manufacturing process were evaluated under aerobic, anoxic, and anaerobic conditions. N-methylpyrrolidone and cyclopentanone distillate residues were suggested to be treated under anoxic condition. However, substrate inhibition occurred when using cyclopentanone distillate residue as a carbon source with chemical oxygen demand (COD) levels higher than 866 mg/L and nitrate levels higher than 415 mg N/L. Under aerobic condition, the COD from both N-methylpyrrolidone and cyclopentanone distillate residues could be easily degraded. Nevertheless, a negative effect on nitrification was observed, with a prolonged lag time for ammonia oxidation as the initial COD concentration increased. The specific ammonia oxidation rate and nitrate production rate decreased under high COD concentration contributed by N-methylpyrrolidone and cyclopentanone distillate residues. Furthermore, the biodegradability of diethylene glycol monobutyl ether distillate residue was found to be low under aerobic, anoxic, and anaerobic conditions. With respect to the abundance of nitrogen removal microorganisms in the wastewater treatment plant, results showed that Comammox may have an advantage over ammonia oxidizing bacteria under high pH conditions. In addition, Comammox may have higher resistance to environmental changes. Dominance of Comammox over ammonia oxidizing bacteria under high ammonia condition was first reported in this study.

Synchronous in-situ sludge reduction and enhanced denitrification through improving electron transfer during endogenous metabolisms with Fe(Ⅱ) addition

The creation of large amounts of excess sludge and residual nitrogen are critical issues in wastewater biotreatment. This study introduced Fe(II) into an oligotrophic anaerobic reactor (OARFe) that was implemented to modify an anoxic-oxic process to motivate in-situ sludge reduction and enhance denitrification under an effective electron shuttle among organic matter, nitrogen, and Fe. The addition of 15 mg L−1 Fe(II) resulted in a sludge reduction efficiency reached 32.0% with a decreased effluent nitrate concentration of 33.3%. This was mostly attributed to the electron transfer from Fe(II) to organic matters and nitrogen species in OARFe. The participation of Fe(II) led to the upregulation of Geothrix and Terrimonas, which caused active organic matter hydrolysis and cell lysis to stimulate the release of extracellular polymeric substances (EPS) and substance transfer between each layer of EPS. The higher utilization of released bioavailable dissolved organic matter improved endogenous denitrification, which can be combined with iron autotrophic denitrification to realize multiple electron donor-based nitrogen removal pathways, resulting in an increased nitrate removal rate of 58.2% in the absence of external carbon sources. These functional bacteria associated with the transformation of nitrogen and carbon and cycling between ferrous and ferric ions were enriched in OARFe, which contributed to efficient electron transport occurred both inside and outside the cell and increased 2,3,5-triphenyltetrazolium chloride electronic transport system activity by 46.9%. This contributed to the potential operational costs of chemical addition and sludge disposal of Fe-AO being 1.9 times lower than those of conventional A2O processes. These results imply that the addition of ferrous ions to an oligotrophic anaerobic zone for wastewater treatment has the potential for low-cost pollution control.

Adapting to seasonal temperature variations: A dynamic multi-subunit strategy for sulfur autotrophic denitrification bioreactors

Elemental sulfur autotrophic denitrification (S0AD) processes are temperature-sensitive, presenting a substantial challenge for the practical implementation of S0AD bioreactors. In this study, a comprehensive methodology for designing and operating S0AD bioreactors was developed, effectively managing fluctuations in nitrogen removal efficiency caused by seasonal temperature variations. Initially, the nitrate removal rate was correlated with simulated on-site temperature and nitrate loading, revealing correlation coefficients of k1, k2, k3, and A as 5.42×10−4, −0.41, 0.04, and 0.13, respectively, to establish a mathematical model for predicting S0AD efficiency. Subsequently, by considering influence factors such as dissolved oxygen and dynamic sulfur consumption, the model was employed to accurately design a pilot-scale S0AD bioreactor for a case study. By utilizing an alternative multi-subunit operation, a stable effluent nitrate concentration of less than 8 mg-N/L was maintained throughout the year. Importantly, this approach resulted in a substantial reduction of 76.8% in excessive nitrate removal, sulfur consumption, and sulfate production. This study aims to provide an optimal design and operation strategy for the practical application of S0AD bioreactors, thereby enhancing reliability and cost-effectiveness in the face of seasonal temperature changes.

Liquid-gas phase transition enables microbial electrolysis cell to treat organic pollution and synchronously remediate nitrate-contaminated groundwater via hydrogenotrophic denitrification

Groundwater denitrification is challenged by a lack of electron donors and usually requires additional energy input or chemical agents. MEC can convert organic pollution into clean electron donor (hydrogen) through a gas-liquid phase transition. In this study, the MEC was combined with permeable bio-reactive barrier (PRB) as a hybrid system to achieved simultaneous organic waste removal, hydrogen production and groundwater remadition via long-distance hydrogenotrophic denitrification by biogas. The semi-hydrophobic PTFE-coated granular activated carbons (GAC) and hydrophilic GAC were filled as two kinds of biocarriers in PRBs, in which the hydrophobic PTFE surface coating improved hydrogen utilization. The PTFE-coated GAC maked the denitrification performance of PRB insensitive to hydrogen partial pressure within the tested range of 0.01–0.04 MPa and achieved effluent nitrate concentration of <20 mg L−1 within 12 h (The Water Quality Standard for Drinking Water Sources in China). The gas production in MECs was actively pumped to PRBs and spontaneously achieve negative pressure on the MEC side and positive pressure on the PRB side. The actively pumping of biogas induced negative pressure in MEC and positive pressure in PRB. The negative pressure improved current density by 18.6 ± 0.7% in MECs and the MEC-PRB hybrid system achieved a nitrate removal of 85.0 ± 0.8% in actual groundwater with an effluent concentration of 15.0 ± 0.8 mg L−1 at 72 h. This work demonstrated the feasibility of matching MEC and PRB as a novel hybrid system for organic pollution degradation and effective nitrogen removal in electron-donor-lacking groundwater.

Effect of plant-self debris on nitrogen removal, transformation and microbial community in mesocosm constructed wetlands planted with Myriophyllum aquaticum

Aquatic macrophytes debris decomposition could release pollutants and nutrients into the water of constructed wetlands (CWs), but their role in nitrogen removal and transformation remains poorly understood. The present study investigated the effects of plant-self debris on nitrogen removal and microbial communities in mesocosm CWs planted with Myriophyllum aquaticum. During the 68-day operation, the plant debris addition did not change the mean removal efficiency of ammonium (NH4+-N) and total nitrogen (TN) of CWs but showed significant differences over the operation time. The NH4+-N and organic nitrogen released from the plant debris decomposition affected the nitrogen removal. The plant debris decreased the effluent nitrate concentration and N2O emission fluxes of the CWs with the increased abundance of denitrifying bacterial genera, indicating that plant debris decomposition increased the denitrification activities via dissolved organic carbon release. High-throughput sequencing indicated that the plant debris altered the distribution and composition of the microbial community in the sediments. Proteobacteria was the dominant phylum (28–52%), and the relative abundance of denitrifying bacteria genera was significantly higher in the sediments with debris addition (37–40%) than in the non-addition (6.6–7.7%). The present study provided new insights into the role of macrophytes in pollutant removal and the plant management strategy of CWs.

Mass-Balance Process Model of a Decoupled Aquaponics System

Highlights A mass balanced process model for a large, decoupled aquaponics system was developed in SuperPro Designer. The flows of N, P, and C were determined over the course of a full year of system operation. On average, tilapia assimilated 21.6% of the input nitrogen, while cucumber plants only assimilated an average of 2.81%. The model was suitable for long-term system simulation but was not effective at predicting short term effects. Abstract. Aquaponics presents a viable solution to water pollution from aquaculture by utilizing nitrate- and phosphate-rich effluent for crop production. The objective of this study was to develop a mass-balanced process model based on a pilot-scale aquaponics facility growing Nile tilapia (Oreochromis niloticus) and cucumbers (Cucumis sativus) in Auburn, Alabama. This enabled a better understanding of how key elements partition among different downstream processes, ultimately affecting nutrients available to plants or discharged to the environment. Data were collected from a pilot scale decoupled aquaponics system for a full calendar year and included weekly water quality, direct GHG emissions, and water flows. Bio-solids, fish mass, and plant mass were also quantified and underwent elemental analysis. Together, these measurements were used to create stoichiometric equations for mass partitioning. The resulting stoichiometry was used to develop a mass-balanced process model constructed in SuperPro Designer software. Four separate variations of the model were developed, one for each season. The model showed that 21.6% of input nitrogen was assimilated by tilapia and only 2.81% by plants, while 33% of input phosphorus was assimilated by tilapia and 2.6% by plants. Modeled effluent concentrations of nitrate from the fish tank, clarifier, and plants averaged 440, 441, and 307 mg L-1, respectively, compared to average measured values of 442, 406, and 298 mg L-1. Modeled effluent phosphate concentrations from the fish tank, clarifier, and plants were 25, 27, and 20 mg L-1 of phosphate, respectively, over the course of one year, while average measured values were 30, 31, and 26 mg L-1. The model was not suitable for predicting short term system changes. The constructed model shows promise in predicting long-term changes in system outputs based on upstream operational changes and is effective for simulation and scenario analysis. Keywords: Aquaponics, Mass balance, Nitrogen, Phosphorus, Process Model.

Performance of sulfur-based autotrophic denitrification process for nitrate removal from permeate of an MBR treating textile wastewater and concentrate of a real scale reverse osmosis process

Textile is one of the industrial sectors generating the highest amount of wastewater with various polluting substances. Lately, water reuse in textile industries, especially, with the reverse osmosis (RO) process following membrane bioreactor (MBR) treatment has been applied more commonly. In this study, an autotrophic sulfur-based denitrifying column performance was evaluated, for the first time, for nitrate reduction from permeate of a lab-scale MBR receiving real textile wastewater and from the concentrate stream of a real scale-RO plant used for recovering water from textile wastewater. Nitrate concentration in the MBR effluent and RO concentrate averaged 35 ± 3 and 12 ± 2 mg-N/L, respectively. With the sulfur-based column bioreactor, quite high (≥90%) denitrification performances were attained both for MBR effluent and RO concentrate up to nitrate loadings of 0.432 and 0.12 g-N/(L.d), respectively. COD present in wastewater was not utilized in the column bioreactor, which illustrates no or minimal contribution of heterotrophic denitrification. Alkalinity concentration in the wastewater was enough to buffer the acid formation during autotrophic denitrification. Sulfate was generated accompanied by nitrate reduction and sulfide was formed at low nitrate loadings. In the batch tests, the denitrification rates for the MBR effluent and RO concentrate were 0.31 and 0.28 g-N/(g-VSS.d), respectively, which were relatively higher than the ones observed for the synthetic nitrate-contaminated groundwater. Autotrophic sulfur-based denitrification is a promising and robust process alternative even for textile RO concentrate with high concentrations of salinity, non-biodegradable COD, and color.

Effect of Bio-Electrochemical Treatment of Hydroponic Effluent on the Nutrient Content

This study examined the effect of bio-electrochemical treatment processes on nitrogen and phosphorus removal, but it also evaluated the impact of the treatment processes on the concentration of other nutrients present in hydroponic effluent. A bio-electrochemical reactor (BER) was used in the experiment to treat effluent from the hydroponic cultivation of tomatoes. It was stated that the nitrogen removal efficiency decreased with increasing current density. The study showed that an electric current density of 0.63 A/m2 ensured the lowest effluent nitrate concentration. The nitrogen removal efficiency ranged from 41.6%-R1 (density of 0.63 A/m2) to 8.9%-R4 (density of 5 A/m2). Electric current density higher than 1.25 A/m2 resulted in lower total nitrogen removal efficiency. The total phosphorus removal efficiency increased with increasing electric current density. The phosphorus removal efficiency was the lowest—95.1%—in the R1 reactor, whereas it was the highest in R4—99.1%. The concentration of the other elements in the effluent was determined. The content of molybdenum, boron, sulphates, and potassium did not meet the acceptable norms for discharging hydroponic effluent into the environment. The study showed that bio-electrochemical processes taking place in BER caused secondary contamination of hydroponic wastewater with molybdenum ions.

Optimization Removal of COD and Nitrogen at Different Hydraulic Retention Times in Biocord-Integrated Fixed-Film Activated Sludge Syste

Although conventional activated sludge has been demonstrated to be a feasible approach for extracting nitrogenous chemicals and organic pollutants from wastewater, it still has a number of drawbacks. In this research, a pilot-scale biocord-integrated fixed-film activated sludge (Biocord-IFAS) reactor fed with actual domestic wastewater was operated to examine the effect of varying hydraulic retention time (HRT) on the COD and nitrogen removal. The type of material employed in this study is fibrous polypropylene (biocord), which is a major difference. The contribution of the Biocord-IFAS to COD removal efficiency reached 94.2% at HRT of 8 h and gradually decreased to 82.9% when HRT was reduced to 4 h. During the investigation period, a slight decrease in nitrification was found at a shorter HRT. The NH4+-N removal efficiencies at HRTs of 10, 8, 6, and 4 h were 97.8%, 98.7%, 97.1%, and 96.3%, respectively. The average effluent nitrate concentration was 5.3 mg/L with HRTs from 10 to 6 h, but over 30 mg/L with an HRT of 4 h. The SEM analysis results show that microorganisms have formed on the biocord surface. The results of this research have demonstrated the potential application of IFAS reactors in bioremediation procedures employing biocord material with great processing efficiency.

Effects of simultaneous denitrification and desulfurization and changes of microbial community structure with corncob solid slow-release carbon source under different S/N ratios

Industrial wastewaters contain high concentrations of sulfate and nitrate. Methanol, ethanol, and acetic acid are often used as the external carbon sources to remove pollutants in wastewater. However, they carry a hefty price. In this study, using low-cost corncob as solid slow-release carbon source, we investigated the effects of different S/N ratios (5:8, 5:5, and 5:2) on simultaneous denitrification and desulfurization, and microbial community structure under continuous flow conditions. Results showed that nitrate concentration in effluent was maintained below 5 mg/L throughout the experiment. Concurrently, 34.89%, 73.59%, and 88.22% of sulfate was removed, respectively, at the beginning of each stage, without the release of hydrogen sulfide. Microbial community analysis showed that heterotrophic denitrifying bacteria, sulfate-reducing bacteria, autotrophic denitrifying bacteria, and hydrolyzing bacteria co-existed in the reactor at different S/N ratios. In particular, the relative abundance of autotrophic denitrifying bacteria increased with the increase of S/N ratio. Furthermore, the copies of key functional genes of nirK, nirS, dsrA, and dsrB also reached the highest when S/N ratio was 5:2. Therefore, simultaneous denitrification and desulfurization by using solid slow-release carbon sources provided theoretical references for practical applications.

Start-up of mainstream anammox process through inoculating nitrification sludge and anammox biofilm: Shift in nitrogen transformation and microorganisms

The feasibility of starting up mainstream single-stage partial nitrification-anammox (SPNA) system by inoculating nitrification sludge and anammox biofilm was investigated. The SPNA system treating low-strength synthetic wastewater was rapidly started up with TN removal efficiency of 88.5 ± 1.8% and effluent nitrate concentration of 7.2 ± 1.2 mg/L. Both the abundance and maximum activity of nitrite oxidizing bacteria (NOB) in flocs decreased obviously. Interestingly, the abundance of anaerobic ammonium oxidizing bacteria (AnAOB) in flocs increased from 0.213% to 0.346% despite the sludge retention time (SRT) of flocs decreased to 60 days, the AnAOB in biofilm was 0.434%. That meant AnAOB gradually enriched in flocs and accounted for a fairly high proportion. The inhibition of NOB, partial denitrification and increased aerobic_chemoheterotrophy function in flocs might be the main reasons for AnAOB enrichment. The possibility of simultaneous fermentation, partial denitrification and anammox reaction was predicted in biofilm, further improving the stability of the system.

Assessment on the treatment of nitrogen contaminant by constructed wetland exposed to different concentrations of graphene oxide

The environmental effect of two-dimensional carbon-based graphene oxide (GO) is an emerging worry as it becomes more widely used. The present work investigated the effects of GO (0.5 and 5 mg/L) on nitrogen transformation in constructed wetlands (CWs). GO could be effectively captured by CWs, but it was harmful to nitrogen removal. GO delayed dynamic time of nitrogen transformation with slight increases in ammonia and nitrate effluent concentrations, resulting in nitrogen removal reducing from 59.24% to 51.51–54.12% (p < 0.05). GO showed the selective influence on key enzyme involved in nitrogen transformation. It caused 33% and 37% inhibitions on ammonia monooxygenase (at 0.5 and 5 mg/L GO) and nitrate reductase (only at 0.5 mg/L GO), but 153% stimulations on urease at 5 mg/L GO. The evidence at molecular level showed that GO reduced abundances of amoA, anammox, and nirS gene, which was determined by GO concentration, contact time, and target gene. 5 mg/L GO produced more obvious reductions on relative abundances of denitrification genes (narG, napA, nirK, qnorB, and nosZ) after 120 days. The shifts in microbes related to nitrogen transformation were also observed after GO feeding, but collaborative microbial pathways were still presented including ammonia-oxidizing bacteria (Nitrosomonas and Nitrosospira), nitrite-oxidizing bacteria (Nitrospira), denitrifying bacteria (Sphingomonas, Arenimonas, Rhodopseudomonas, Rhodanobacter), heterotrophic nitrification aerobic denitrification bacteria (Bacillus, Acidovorax, Dechloromonas, Acidovorax), and nitrogen-fixing bacteria. The denitrification was rate-limiting TN removal process due to insufficient carbon sources and dominant aerobic environment in CWs. The present work deepened understanding of variations in ecological functions of CWs when they encountered nano-pollution.

Soil Water Infrastructure to Eliminate Off-Site Nutrient Migration and Support Farm Profitability

Nutrient migration from agricultural land to freshwater resources is a fundamental global concern. The Department of Agriculture at Southeast Missouri State University has installed technology to research aspects of nutrient migration and propose mitigation strategies. The installed technologies include: 1) controlled subsurface drainage and irrigation technology, 2) a denitrification bioreactor to reduce nitrate concentrations in tile-drainage effluent, 3) an off-season water storage reservoir to capture and retain nitrate-bearing tile-drain effluent which will be applied as in-season liquid fertilizer, 4) riparian buffers, and 5) cover crops. For our beef livestock operation, we are installing a constructed wetland to capture nutrient-laden runoff from manure amended pastures associated with a confined feeding facility. Modern pasture management and row-crop nitrogen research augment the environmental stewardship potential of these infrastructures, while preserving farm profitability. The goal is to demonstrate that environmental stewardship, agriculture production and farm profitability are synergistic and may be explicitly demonstrated to the agriculture community.

Zeolite amended bioretention media improves nitrogen removal from stormwater

AbstractBioretention cells alleviate stormwater toxicity by permeation through soil media. Amending bioretention materials may result in increased chemical pollutant removal while maintaining hydraulic properties. Zeolite was tested in bioretention media for zinc, copper, phosphorus, ammonium, and nitrate removal from synthetic stormwater in a column study. Ecolite did not improve metal or phosphorus removal; however, significantly lower effluent concentrations of ammonium (p &lt; .001) and nitrate (p = .014) were measured compared with the standard media. The standard media averaged a 70% reduction in ammonium concentration, while mixtures containing 10 and 20% Ecolite per volume averaged 86 and 87% reduction, respectively. All media leached higher nitrate concentrations than the influent stormwater. Ecolite significantly increased the saturated hydraulic conductivity by up to 55% (p &lt; .001). The inclusion of Ecolite in bioretention cells may be practical in areas with nitrogen‐impaired watersheds.

Pyrite-activated persulfate oxidation and biological denitrification for effluent of biological landfill leachate treatment system

The feasibility of pyrite as catalysts in the persulfate oxidation and electron donor for subsequent bacterial denitrification was investigated. The results demonstrated that pyrite-activated persulfate oxidation could efficiently degrade the organic matter in the effluent of biological landfill leachate treatment system, and COD removal efficiency of about 45% was achieved at the optimum parameters: pH = 6, pyrite dosage = 9.28 mM, dimensionless oxidant dose = 0.25. Among the dissolved organic matter, hydrophobic dissolved organic carbon (HO DOC), humic acids and building blocks were the main components. After the pyrite-activated persulfate oxidation, humic acids and HO DOC were primarily degraded, followed by building blocks, while low molecular weight neutrals were probably the degradation products. In the subsequent biological process, nitrate reduction was satisfactorily accomplished with autotrophic denitrification as the main pathway. When the influent nitrate concentration was about 180 mg L−1, the effluent nitrate concentration was stable below 20 mg L−1 with the nitrogen removal rate of about 108 mg L−1 d−1. To sum up, the pyrite-activated persulfate oxidation and the following biological denitrification was a feasible application in the effluent of biological landfill leachate treatment system.

Enhanced landfill leachate treatment in sequencing batch biofilm reactors (SBBRs) amended with zeolite and biochar

AbstractBACKGROUNDBiological treatment of landfill leachate is inhibited by high concentrations of ammonia and recalcitrant organic matter. This study investigated the addition of natural adsorbent materials, zeolite (clinoptilolite) and biochar, to enhance biological treatment of landfill leachate in sequencing batch biofilm reactors (SBBRs). Three bench‐scale SBBRs were set up with varying types of biofilm support media: (i) lightweight expanded clay aggregate (LECA) as a control (C‐SBBR); (ii) LECA + zeolite (CZ‐SBBR); and (iii) LECA + zeolite + biochar (CZB‐SBBR). SBBRs were operated with alternating anoxic and aerobic stages to promote total nitrogen (TN) removal via nitrification/denitrification.RESULTSExcellent TAN removal (&gt;99%) was achieved in all three SBBRs throughout the study, most likely as a result of the favorable environmental conditions and long hydraulic retention time (HRTs) applied (nine or more days). Biochar addition in CZB‐SBBR resulted in significantly higher chemical oxygen demand (COD) (61–83%) and color (82–95% as UV456) removals compared with C‐SBBR (42–44% for COD and 28–33% for color) and CZ‐SBBR (34–45% for COD and 20–35% for color). High effluent nitrate (NO3−) concentrations initially were observed in CZB‐SBBR, most likely due to limited organic carbon availability for denitrification. However, after &gt;1 year of operation, NO3− accumulation declined and TN removal of 81% was achieved, indicating that the main nitrogen removal pathway shifted from simultaneous nitrification/denitrification to partial nitritation/anammox.CONCLUSIONSZeolite/biochar amended SBBRs are a promising approach for enhanced landfill leachate treatment. © 2021 Society of Chemical Industry (SCI).

A pressurized hydrogenotrophic denitrification reactor system for removal of nitrates at high concentrations

A pressurized hydrogenotrophic denitrification reactor to remove nitrate from groundwater was recently presented. To enable treatment of nitrate-concentrated brines, we demonstrate here the removal of high nitrate concentrations without nitrogen gas accumulation in the reactor’s headspace over time. In order to eliminate nitrogen gas build up in the pressurized reactor’s headspace, the main unsaturated flow pressurized reactor was connected to an external degassing unit via liquid recirculation. Pressurized liquid from the main reactor was intermittently discharged to the degassing unit where dissolved N2 gas effervesced and escaped to the atmosphere. The degassed effluent water was continuously recirculated back to the main reactor to maintain steady-state nitrogen and hydrogen gas partial pressures. Denitrifying rates of up to 6 g N/L-reactor/d were achieved in the reactor system under freshwater and brine conditions. Nitrate removal was over 97 %, with nitrate effluent concentrations lower than 10 mg N/L for influent concentrations of about 400 mg N/L. The reactor system maintained steady-state nitrogen and hydrogen gas partial pressures using low external recirculation rates at low reactor total pressures (< 5 atm). At high denitrification rates, dissolved nitrogen concentrations in the reactor were super saturated (125–150%) while on the other hand, dissolved hydrogen was undersaturated (30–60%) due to intense bacteria uptake from the water. These dynamic conditions reduced the external recirculation flow requirement for degassing and resulted in much better hydrogen utilization than expected (greater than 93 %).

Cold temperature increases nitrate accumulation in pilot-scale surface flow constructed wetlands with high rates of nitrogen removal

Nitrogen dynamics were studied over 3 years in pilot-scale surface flow constructed wetlands (SFCWs) treating three strengths of ammonium-rich swine wastewater. A high removal rate of ammonium (1.2–2.9 g m−2 d−1) and total nitrogen (1.5–3.5 g m−2 d−1) was achieved from highstrength wastewater in the SFCWs. Nitrate concentration was significantly higher (p < 0.01) in the effluent than in the influent, and the increased nitrate concentration did not significantly affect ammonium removal in the SFCWs. The effluent nitrate concentration showed annual cyclical changes and could be described using a harmonic regression equation over time (y = a + b sin (2π/365.25 t + c); R2 = 0.152–0.566). The multiple regression equation (R2 = 0.200–0.551) indicated that water temperature and oxidation reduction potential were the primary factors affecting nitrate accumulation in the SFCWs. The abundance of nitrification functional genes (amoA in ammonia-oxidizing archaea and bacteria) was higher in spring and winter than in summer. The abundance of denitrification functional genes (narG, nirK, nirS, and nosZ) was higher in summer than in spring and winter. At cold temperatures (5–10 °C), nitrate accumulated significantly in the water column rather than in the sediments and the potential nitrification rates increased slightly, suggesting the importance of nitrogen transformation in the water column during nitrogen removal. These results are helpful for selecting targeted seasonal intensification strategies to improve the SFCWs performance.