Nitrogen Removal Using Combined Ultracompact Biofilm Reactor-Packed Bed System

A predenitrification system consisting of an ultracompact biofilm reactor (UCBR) and a packed bed column was used for removing nitrogen from synthetically simulated wastewater. The UCBR column was maintained under aerobic conditions to favor nitrification process, while the packed bed column was operated under an anoxic environment for denitrification process. A peristaltic pump was used to recycle fluid between the anoxic-packed bed and aerobic-UCBR columns to facilitate nitrogen removal. Five recycle ratios (R) were investigated, namely, 3, 4, 5, 6, and 10. The highest average total nitrogen (TN) removal rate was achieved at R = 4. The NH4+–N, TN, and chemical oxygen demand (COD) removal rates at this R were 0.56±0.05?kg NH4+–N/m3/day, 0.39±0.09?kg TN/m3/day, and 1.83±0.18?kg COD/m3/day, respectively. It was noted that poor nitrification in the UCBR was accompanied by a corresponding reduction in overall TN removal efficiency. This observation suggested that nitrification process was the limiting step for TN removal in this setup. Thus, the performance of this predenitrification system could be enhanced by optimizing the performance of the nitrification process.     

Optimization of Biological Nutrient Removal in a Membrane Bioreactor System

The main objective of the present study is to develop a modified membrane bioreactor (MBR) system for the treatment of municipal wastewater for the enhanced biological removal of nitrogen (N) and phosphorus (P) simultaneously with the ultimate goal of optimizing the two processes. The paper will address the implementation and optimization of the MBR process with respect to biological characteristics, operational performance, and effluent quality. The system utilizes anoxic P uptake and nitrification–denitrification in a MBR. Following optimization, the system achieved 99% chemical oxygen demand (COD), 98.4% NH3–N, 77.5% TN, and 96.3% P removal producing effluent biological oxygen demand, COD, NH3–N,NO3–N,NO2–N, and P of <3, 3, 0.4, 5.8, 0.050, and 0.18?mg/L, respectively.     

Comparative Study between a Hybrid System and a Biofilm System for the Treatment of Ammonia and Organic Matter in Wastewaters

The efficiency of two similar gas-lift bioreactors, a biofilm reactor and a hybrid circulating floating bed reactor (CFBR), were studied and compared. In the biofilm CFBR the biomass grew preferably adhered on a plastic granular support, whereas in the hybrid CFBR both suspended biomass and biofilms were allowed to grow in the reactor. COD/NH4+ ratio (COD=chemical oxygen demand) was manipulated between 0.0 and 8.0?g/g, maintaining the ammonia influent concentration around 50?mg N–NH4+/L, the ammonia loading rate at 0.9?kg N–NH4+/m3?day and the hydraulic retention time at 1.36?h. At low COD/NH4+ ratio (0 and 0.5?g/g) both systems behaved similarly, achieving ammonia removal percentages higher than 95%. In the biofilm CFBR a reduction of the nitrification percentage from 95 to 20% was observed when a COD/N–NH4+ ratio up to 8?g/g was applied in the influent. However, at the same operational conditions, the nitrification process in the hybrid CFBR was slightly affected. In the hybrid-CFBR reactor heterotrophs growing in suspension consumed the COD source faster than those growing in biofilms as was monitored. The growth of heterotrophic microorganism in suspension had a beneficial effect for the nitrifying population growing in the biofilm of the hybrid CFBR. Nitrifying activity of the biofilm was not limited by the presence of heterotrophs consuming dissolved oxygen, displacing the nitrifying bacteria or creating mass transfer resistance as was observed in the biofilm CFBR.     

Comparison of Two Model Concepts for Simulation of Nitrogen Removal at a Full-Scale Biological Nutrient Removal Pilot Plant

The experimental studies conducted at the Hanover-Gümmerwald pilot wastewater treatment plant (WWTP) focused on minimizing nitrogen loads discharged during stormwater events. The data collected during the plant operation were used for a long-term process simulation. The aim of this study was to compare predictive capabilities of two different mechanistic models (ASM2d and ASM3P) in terms of nitrogen removal. The influent wastewater composition was generated using on-line measurements of only three parameters (COD, N–NH4+, P–PO43?) and the model predictions were primarily compared with on-line data (concentrations of N–NH4+, N–NO3?) originating from the aerobic zone of the bioreactor. The simulation results confirmed the experimental data concerning the capabilities of the system for handling increased flows during stormwater events. The predicted peaks of N–NH4+ at the line with the quadruple dry weather flow rate were normally exceeding 8?g?N?m?3 (similar to the observations), whereas no (or minor) peaks of N–NH4+ were predicted for the line with the double dry weather flow rate. The relationships between ASM2d and ASM3P predictions for N–NH4+ and N–NO3? were highly correlated (r2 = 0.83–0.99) with the slopes remaining close to 1.0. Both models appear to be equally suitable for practical applications in common municipal WWTPs.     

Operational Optimization and Mass Balances in a Two-Stage MBR Treating High Strength Pet Food Wastewater

A two-stage membrane bioreactor (MBR) system was evaluated for the treatment of high strength pet food wastewater characterized by oil and grease, chemical oxygen demand (COD), biochemical oxygen demand (BOD)5, total suspended solids (TSS), total Kjeldahl nitrogen (TKN), NH4–N, and TP concentrations of 2,800, 25,000, 10,000, 4,500, 1,650, 1,300, and 370?mg/L, respectively, to meet stringent surface discharge criteria of BOD5, TSS, and NH4–N of <10?mg/L, and TP of <1?mg/L. Pretreatment of the dissolved air flotation effluent with FeCl3 at a dose of 3.5?g/L, corresponding to a Fe:P molar ratio of 1.3:1 affected TP, TSS, volatile suspended solids (VSS), COD, BOD5, and TKN reductions of 88, 72, 75, 11, 11, 36, and 17%, respectively. The two-stage MBR operating at a total hydraulic retention time of 5.3?days comprising 2.5?days in the first stage and 2.8?days in the second stage, and solids retention time of 25?days in the first stage consistently met the criteria despite wide variations in influent characteristics. Very high COD and BOD5 removal efficiencies of 97.2 and 99.8% were observed in the first stage, with an observed yield of 0.14?gVSS/gCOD. A modular approach for the quantification of simultaneous nitrification denitrification (SND) in the first-stage MBR was developed and verified experimentally. The model indicated that on average, 21% of the influent nitrogen was removed by SND and predicted nitrogen loss with an accuracy of 72%. Complete nitrification of the residual organic nitrogen and ammonia was achieved in the second-stage MBR.     

Effect of Dynamic Loading on Biological Nutrient Removal in a Pilot-Scale Liquid-Solid Circulating Fluidized Bed Bioreactor

A pilot-scale liquid-solid circulating fluidized bed (LSCFB) bioreactor was employed for biological nutrient removal from municipal wastewater at the Adelaide Pollution Control Plant, London, Ontario, Canada. Lava rock particles of 600?μm were used as a biomass carrier media. The system generated effluent characterized by <1.0?mg NH4–N/L, <6.0?mg NO3–N/L, <1.0?mg PO4–P/L, <10?mg TN/L, and <10?mg SBOD/L at an influent flow of 5?m3/d, without adding any chemicals for phosphorus removal and secondary clarification for suspended solids removal. The impact of the dynamic loading on the LSCFB effluent quality and its nutrient removal efficiencies were monitored by simulating wet weather condition at a maximum peaking factor of 3 for 4 h. The achievability of effluent characteristics of 1.1 mg NH4–N/L, 4.6 mg NO3–N/L, 37 mg COD/L, and 0.5 mg PO4–P/L after 24 h of the dynamic loading emphasize the favorable response of the LSCFB to the dynamic loadings and the sustainability of performance without loss of nutrient removal capacity.     

Bioaugmentation with Nitrifying Bacteria Acclimated to Different Temperatures

A nitrifying biomass was produced from anaerobic sludge dewatering liquors for the purpose of bioaugmentation of sequencing batch reactors (SBRs). Nitrification of centrate was conducted at four temperatures (10, 20, 25, and 30°C) while the seeded SBRs were operated at 10°C with a solids retention time of approximately 4 days. The SBRs did not exhibit any nitrification before the onset of seeding. When the hydraulic retention time (HRT) was 24 h, partial removal of NH3–N occurred when seed acclimated to 20, 25, and 30°C was added. When the HRT was 12 h, only the SBR seeded with nitrifying biomass acclimated to 10°C achieved 50% NH3–N removal. Complete removal of NH3–N was not achieved in any of the seeded SBRs. The degree of NH3–N removal in the seeded SBRs was dependent on the initial temperature of the seed, and the observed growth rates of the nitrifying bacteria were inversely proportional to the change in temperature.     

Horizontal-Flow Biofilm System with Step Feed for Nitrogen Removal

The aim of this study was to develop a simple biological system suitable for the treatment of dairy parlor wash waters. A novel horizontal-flow biofilm system with step feed was designed, constructed, and tested in the laboratory for organic carbon removal, nitrification, and denitrification of a synthetic dairy wastewater with average filtered chemical oxygen demand (CODf) of 2,060?mg/L, total nitrogen (TN) of 288?mg/L, and ammonia nitrogen (NH4–N) of 127?mg/L. The novel biofilm system consisted of two reactor units placed on top of one another, each comprising a stack of horizontal plastic sheets. Part of the wastewater was pumped onto Sheet 1 (top feed) and the remainder onto Sheet 11 (step feed) and flowed over the horizontal sheets down through the system. Three hydraulic loading rates were examined: 32.3, 25.1, and 19.3?L/m2?day, based on the top plan area, and the respective removals of CODf were 96, 96, and 97% and of TN, 86, 83, and 75% were achieved. The system was simple and cheap to construct and operate.     

Response of Soil Water Chemistry to Simulated Changes in Acid Deposition in the Great Smoky Mountains

Watershed recovery from acidic deposition, such as the Noland Divide Watershed in the Great Smoky Mountains National Park, is difficult to predict because of complex biogeochemical processes exhibited in soils. Laboratory soil columns and in?situ pan lysimeters were used to investigate soil solution response to simulated reductions in acid deposition. Controlling for influent SO42-, NO3-, and NH4+ concentrations in the column experiments, effluent pH declined similarly to 4.4 among five experimental scenarios from an initial pH of approximately 4.7 and 6.1. Influent-effluent chemical comparisons suggest nitrification and/or SO42- desorption controls effluent pH. Sulfate adsorption occurred when SO42- influent was greater than 25??μmol?L-1 and desorption occurred below 15??μmol?L-1, which would equate to approximately a 61% reduction in current SO42- deposition levels. Base cation depletion occurred in column experiments, in which 64–60??μmol?L-1 Ca2+ and 24–27??μmol?L-1 Mg2+ reductions were measured. Cation depletion rates were pH dependent, primarily caused by soil cation exchange and not weathering. In these soils with base saturation below 7%, complete Ca2+ and Mg2+ depletion was estimated as 90 to 140?years. Protons released by SO42- desorption via ligand exchange are expected to cause further base cation depletion, thereby delaying watershed recovery. Field experiments found SO42- sorption dynamics to be limited by kinetics and hydrologic interflow rates, illustrating how precipitation intensity can influence ion transport from soil to stream. Results from this study provide important information for predicting watershed recovery in the future and suggest needs for further research.     

Aerated Rock Filters for Enhanced Ammonia and Fecal Coliform Removal from Facultative Pond Effluents

Rock filters used to treat effluents from waste stabilization ponds do not remove ammonia as they are anoxic. A pilot-scale aerated rock filter was investigated, in parallel with an unaerated control, over an 18-month period to determine whether aeration provided conditions within the rock filter for nitrification to occur. Facultative pond effluent containing ～ 10?mg NH4–N/L was applied to the filters at a hydraulic loading rate of 0.15?m3/m3?day during the first 8?months and at 0.3?m3/m3?day thereafter. The results show that the ammonia and nitrate concentrations in the effluent from the aerated filter were <3 and ～ 5?mg?N/L, respectively, whereas the ammonia concentration in the effluent from the control filter was ～ 7?mg?N/L. Fecal coliforms were reduced in the aerated filter to a geometric mean count of 65?per?100?mL; in contrast the effluent from the control filter contained 103–104 fecal coliforms per 100?mL. Aerated rock filters are thus a useful land-saving alternative to aerobic maturation ponds.     

Simultaneous Removal of Nitrogen and Phosphorous from Municipal Wastewater Using Continuous-Flow Integrated Biological Reactor

A pilot-scale experiment was carried out to study the simultaneous removal of nitrogen and phosphorous from municipal wastewater by an innovative continuous-flow integrated biological reactor (CIBR) process. A three-phase separator was used in the CIBR process, which not only saved energy consumption of sludge returning, but also solved the sludge–gas separating problem. The optimal working condition was 2?h aeration, 1?h agitation, and 1?h settling, with an energy consumption of 0.23?kW?h/m3. The average removal of chemical oxygen demand (COD), ammonia nitrogen (NH4+–N), total nitrogen (TN), and total phosphorus (TP) under the optimal conditions were 72.87, 75.23, 61.25, and 68.25%, respectively. The distributing rules of dissolved oxygen, pH, mixed liquid suspended solid, COD, NH4+–N, NO3?–N, TN, and TP in each phase of CIBR was studied. It was indicated that the appropriate condition was created for the simultaneous removal of nitrogen and phosphorus in the integrated reactor. The study demonstrated the feasibility of using CIBR process for simultaneous removal of nitrogen and phosphorus at the average temperature 12.2°C.     

Electroremediation of Naphthalene in Aqueous Solution Using Alternating and Direct Currents

The key objectives of this study were to evaluate the use of an alternating current (AC) for the degradation of naphthalene in spiked aqueous solutions and to investigate the effect of current density on the degradation rates of naphthalene. Direct current (DC) was also used to compare the rates of degradation. Sodium chloride (NaCl) and anhydrous sodium sulfate (Na2SO4) were used as the supporting electrolytes. Degradation rates and byproducts formed were investigated when DC and AC were separately passed through naphthalene solutions. A square wave AC, having a frequency equal to 0.1?Hz was used. Naphthalene solutions having an initial concentration of about 20?mg/L ( ～ 0.15?mM) were subjected to an AC peak current density and DC density of 6?mA/cm2, using NaCl as the supporting electrolyte. An approximate 65% reduction in the concentration of naphthalene was observed after a period of 48 h when DC was applied. Degradation was almost 100% when the AC was applied during the 48-h period. The effect of current density on the electrochemical degradation rate of naphthalene in aqueous solution was also investigated at alternating and direct current densities of 1, 3, and 6?mA/cm2 using Na2SO4 as the supporting electrolyte. AC peak current densities of 1, 3, and 6?mA/cm2 resulted in overall conversions of 77, 87, and 95%, respectively, of naphthalene in solution. The corresponding values for DC application were 95% for all current densities while the initial degradation rates were greater at higher DC densities. Based on the degradation products formed, hydroxylation is believed to be the key mechanism for the degradation of naphthalene.     

High Rates of Ammonia Removal in Experimental Oxygen-Activated Nitrification Wetland Mesocosms

While constructed treatment wetlands are very efficient at polishing nitrate from secondary effluent, they are much less effective at removing ammonia. A key factor that limits ammonia oxidation via biological nitrification in vegetated wetlands is low levels of dissolved oxygen. This study evaluated the effectiveness of side-stream oxygenation to enhance ammonia removal in replicate surface-flow experimental mesocosms containing wetland sediment and plants (Typha spp.). Mesocosms had a water volume of 29.5 L, a hydraulic retention time of 5 days, and a hydraulic loading rate of 4.3 cm/d, and were loaded with synthetic secondary effluent contain 10 mg-N/L of ammonia. Relative to nonoxygenated controls, oxygenation increased ammonia removal rates by an order of magnitude. Areal removal rates increased from 40?mg-N/m2/d to 450?mg-N/m2/d, concentration removal efficiency increased from 10 to 95%, and area-based first-order removal rates increased from <2?m/year to 50–75 m/year. Ammonia removal rates in oxygenated mesocosms were 2- to 4-fold higher than rates reported for full-scale constructed wetlands treating secondary effluent. Results show that oxygen-activated nitrification wetlands, a hybrid of conventional oxygenation technology and wetland ecotechnology, hold promise in economically enhancing rates of ammonia removal and shrinking the wetland area needed to polish ammonia-dominated secondary effluent. Further study is needed to confirm that oxygenation can promote high rates of ammonia removal at the field scale.     

Automated Separation and Conductimetric Determination of Inorganic Nitrogen

Experiments were conducted for the evaluation of a continuous flow conductimetric method that measures the inorganic nitrogen compounds ammonia (NH3) and combined nitrite (NO2?) and nitrate (NO3?). Approximately 300 analyses were performed using the method during experiments to estimate the method detection level, to determine the bias and precision, and to determine the equivalency of the method to others found in Standard Methods. An estimated method detection level of 0.01 mg N∕L (NH3–N, NO3?–N, or NO2?–N) was measured. Precision values for ammonia and nitrate standards at concentrations ranging from 0.1 to 75 mg∕L NH3–N or NO3?–N did not exceed 5.5 and 4%, respectively. Recovery values for ammonia and nitrate standards at the same concentration range did not exceed 104.8 and 103%, respectively. At concentrations of 0.05 mg∕L NH3–N or NO3?–N, the precision values were 12.5 and 11%, respectively, which were high relative to others obtained in this study but are within the range of values reported in Standard Methods.     

Nitrification Modeling in Pilot-Scale Chloraminated Drinking Water Distribution Systems

A suspended growth nitrification model was developed to describe nitrification dynamics in terms of chloramine, ammonia, nitrite, nitrate, and nitrifying bacteria concentrations in pilot-scale chloraminated drinking water systems. The model provided a semimechanistic base to study the regrowth and persistence of nitrifiers in chloraminated distribution systems. Results showed that the developed suspended growth model, without a biofilm nitrification component, was able to simulate and predict nitrification episodes in the pilot-scale systems. In the restricted low nutrient drinking water environment, growth kinetic parameters for nitrifiers were estimated to be significantly lower than ranges reported in the literature. The maximum specific growth rate and ammonia half-saturation constant for ammonia oxidizing bacteria were estimated to be 0.46?day?1and 0.023?mg NH3–N/L, respectively. In addition, an estimated reaction rate of 70±32?L/(mg?HPC?day) between chloramines and soluble microbial products suggests that heterotrophic growth can be a significant contributor to chloramine decay in some chloraminated distribution systems.     

Electrochemical Reduction of 2,4-Dinitrotoluene in a Continuous Flow Laboratory Scale Reactor

An electrochemical laboratory scale reactor was used to treat 2,4-dinitrotoluene (DNT). Experiments were conducted by using a graphite carbon cylinder impregnated with glassy carbon (zero porosity) as the cathode and a platinum wire as the anode. All experiments were conducted under anoxic conditions. Initially, experiments simulating batch conditions were conducted to obtain the optimum operating conditions for the reactor. During this batch-mode study, the effect of various parameters such as applied current, electrolyte concentration, and type of electrolyte on the reduction of DNT were evaluated. Results showed that the rates of DNT reduction increased with an increase in current or concentration of electrolyte. Based on the results obtained from the batch simulation experiments, continuous flow experiments were conducted at three different currents and one electrolyte concentration. The ionic strength of the feed solution was maintained at 0.027 M. A current of 200 mA (current density 0.088 mA/cm2) provided a stable reduction of DNT at the 80% level for a period of 14 days after which reactor cleaning was necessary for removal of suspended solids that were formed within the reactor. End products determined for the experiments showed 80–100% molar balance closure.     

Nitrification at Low Oxygen Concentration in Biofilm Reactor

A nitrification process under low dissolved oxygen (DO) concentration is proposed in a completely stirred biofilm reactor. The reactor was fed with a synthetic wastewater containing 250 mg NH4–N∕L. A stable nitrite accumulation in the effluent was obtained during >110 days' operation; NO2–N:(NO2–N + NO3–N) in the effluent reached >90% under 0.5 mg DO∕L. Ammonium was completely converted and NH4–N in the outlet was as low as 5 mg∕L. A transient increase of the DO concentration in the reactor induced a complete conversion of ammonia and nitrite to nitrate after only 2 days. A return to a low DO concentration again induced nitrite accumulation. These results show that the nitrite oxidizers were always present in the reactor but were outcompeted at low DO concentration, due to their lower affinity for oxygen, compared with ammonia oxidizers. Nitrite accumulation could also be favored by free nitrous acid accumulation inside the biofilm.     

Single-Submerged Attached Growth Bioreactor for Simultaneous Removal of Organics and Nitrogen

The use of a single-unit, single-zone submerged attached growth bioreactor (SAGB) for the combined removal of carbonaceous organics and nitrogen from a municipal wastewater was demonstrated. A nitrification efficiency of 97% was achieved at a total organic loading of 3.47?kg?bCOD/m3?day. The total nitrogen loading varied from 0.2?to?0.3?kg?N/m3?day and resulted in effluent total nitrogen concentrations ranging from 4.2?to?8.5?mg/L. Concurrent denitrification was achieved at rates ranging from 0.077?to0.29?kg?N/m3?day. This single-unit SAGB, by providing dual treatment capacities, represents a cost-effective option that is particularly attractive for facilities with limited space and budget for system upgrade.     

Simultaneous Nitrogen and Phosphorus Removal from High-Strength Industrial Wastewater Using Aerobic Granular Sludge

Aerobic granular sludge technology was applied to the simultaneous nitrogen and phosphorus removal from livestock wastewater that contains high concentrations of nitrogen and phosphorus (TN: 650?mg/L; TP: 125?mg/L). A lab-scale sequencing batch reactor was operated in an alternating anaerobic/oxic/anoxic denitrification mode. Granular sludge was first formed using synthetic wastewater. When livestock wastewater was diluted with tap water, the shape and settleability of aerobic granular sludge were maintained even though livestock wastewater contained suspended solids. Simultaneous nitrification, denitrification, and phosphate uptake were observed under an aerobic condition. However, when nondiluted livestock wastewater was used, the diameter of granular sludge and the denitrification efficiency under an oxic condition decreased. When the concentrations of nitrogen and phosphorus in wastewater increased, hydraulic retention time (HRT) increased resulting in a decrease in selection pressure for granular sludge. Therefore, the sustainment of granular sludge was difficult in livestock wastewater treatment. However, by applying a new excess sludge discharge method based on Stokes’ law, the shape of granular sludge was maintained in spite of the long HRT (7.5?days). To select large granular sludge particles, excess sludge was discharged from the upper part of settled sludge because small particles localized there after settling. Finally, excellent nitrogen and phosphorus removal was accomplished in practical livestock wastewater treatment. The effluent concentrations of NH4–N, NOx–N, and PO4–P were <0.1, 1.4, and 1.2?mg/L, respectively.     

Improvement of Submerged Biofilter Process by Bioelectrochemical Method

A bioelectrochemical method was applied to a submerged biofilter process to improve its nitrogen removal performance. Packed beds of activated carbon submerged into the aerobic tank of the submerged biofilter process were used as the electrodes and support for attached microbial growth. The experiments were conducted under different temperatures, dissolved oxygen (DO) concentrations and electric currents. The results showed that nitrification and denitrification rates were enhanced by supplying oxygen and hydrogen, respectively, from the substratum through electrolysis of water. The nitrification and denitrification rates were increased with increasing electric current. The effects of electric current on nitrification and denitrification rates were clearly shown under lower bulk liquid DO concentration. There was an optimum DO concentration to give the largest nitrogen removal rate in the bioelectrochemical compartment. The optimum DO concentration was in the range of 1.5–2.0 g∕m3.