Effluent Nitrogen Concentration Research Articles

Non-submerged attached growth process for domestic wastewater treatment: Influence of media types and internal recirculation ratios

This study is aimed to comprehend the treatment of non-submerged attached growth systems using bio-sponge, bio-cord, and bio-cloth media. Three reactors were set up with internal recirculation ratio of 1 (IR = 1) and similar media surface area. Bio-sponge and bio-cloth reactors showed removal of COD (79 vs. 76%) and NH4+–N (78 vs. 73%). While bio-cord treatment was deteriorated due to time-dependent process. Multiple linear regression revealed that alkalinity governed the formation degree of the anaerobic zone in bio-sponges, partially affecting nitrification. Increasing IR from 1 to 3 caused sloughing of the attached biomass and was positively correlated with effluent nitrite nitrogen concentration, indicating the sensitivity of nitrification to spatial distribution effects. In addition, bio-sponge system obtained superior performance at IR of 2 while bio-cloth one might be also an effective media for wastewater treatment if having good durability.

Efficient nitrogen removal from mainstream wastewater through coupling Partial Nitritation, Anammox and Methane-dependent nitrite/nitrate reduction (PNAM)

The application of partial nitritation and anammox to remove nitrogen from mainstream wastewater is of great interest because of the potential to reduce energy cost and carbon dosage. However, this process confronts a dilemma of relatively high effluent nitrogen concentration (>10 mg N/L), owning to the unwanted prevalence of nitrite-oxidizing bacteria (NOB) and the intrinsic nitrate production by anammox bacteria. Here, a novel technology, named the one-stage PNAM, that integrates Partial Nitritation, Anammox and Methane-dependent nitrite/nitrate reduction reactions, was developed in a single membrane biofilm reactor (MBfR). With feeding of synthetic mainstream wastewater containing ∼50 mg NH4+-N/L at a hydraulic retention time of 12 h, more than 95% nitrogen was removed in the established one-stage PNAM process at a practically useful rate of 0.1 kg N/m3/d. Microbial community characterization and in-situ batch tests revealed a sophisticated microbial structure consisting of ammonia-oxidizing bacteria (AOB), anammox bacteria, nitrite/nitrate-dependent anaerobic methane oxidation (n-DAMO) bacteria and archaea, and a small fraction of NOB and aerobic methanotrophs. The role of methane in removing nitrate was confirmed by switching on/off the methane supply, which relaxed the requirement for NOB suppression. In addition, the established system was relatively robust against temperature variations, evidenced by a total nitrogen removal efficiency above 80% at temperature as low as 14 ℃. The results provide a promising alternative for efficient nitrogen removal from domestic wastewater using methane as the sole carbon source.

From freshwater anammox bacteria (FAB) to marine anammox bacteria (MAB): A stepwise salinity acclimation process

An investigation into the effect of stepwise saline introduction (3–20 g·L−1 NaCl) on the anaerobic ammonium oxidation (anammox) process in a lab-scale sequencing batch reactor was carried out for 252 days by evaluating the changes in influent and effluent nitrogen concentrations, conductivity, microbial extracellular polymeric substances' (EPS) ionic content, as well as stresses due to salinity, via microbial ATP analysis. It was observed that, effluent nitrogen concentrations remained stable at low saline levels of 3 g·L−1 to 10 g·L−1. Nonetheless, midway through 10 g·L−1 and the preliminary phase of 15 g·L−1 salinity presented a very unstable, highly fluctuating as well as deteriorating effluent nitrogen concentrations. A more satisfactory nitrogen removal efficiency of 83.7 ± 5.9% was obtained at higher saline concentrations implying that, the adaptation mechanism to tolerate increasing salinity was taking place. Saline induced stress, which measures the variation in viable anammox bacteria, was correlative to the formation of EPS and changes in its cationic contents along the increasing salinity. Although the specific anammox activity (SAA) dropped by approximately 15% from the beginning of the process to the midpoint, the drop in SAA after the midpoint was not as drastic as the initial phase. A change in microbial aggregation and dominance proved the existence of new saline-dependent species that can withstand high saline stresses. Recovery from abrupt high saline shocks in batch experiment was seen to be almost impossible.

Dairy wastewater processing and automatic control for waste recovery at the municipal wastewater treatment plant based on modelling investigations

Based on the calibrated model for an Anaerobic-Anoxic-Oxic (A2O) municipal wastewater treatment plant (WWTP), this research investigated and proposed feasible solutions, control system configurations and optimal operating conditions for the dairy wastewater processing. The steady state study on adding different daily amounts of dairy wastewater in the WWTP water line revealed the most efficient amount to be treated by finding a minimum of the total nitrogen concentration in the water effluent. The dynamic investigations on adding different daily amounts of diary wastewater demonstrated the incentives of the proposed cascade control system configurations, based on the ammonia or nitrates concentration control in the aerated reactors, associated to nitrates and nitrites concentration control in the anoxic reactor. The best periods of time and duration for scheduling the dairy wastewater processing were searched and found. Preliminary results showed the incentives of the additional dairy wastewater distribution during 2 h, at the highest influent concentration moments. Further investigations, relying on the genetic algorithm optimization method revealed that better daily scheduling of the dairy wastewater addition may be obtained. Compared to normal operation, the optimal scheduling program of the dairy wastewater treatment showed an overall performance index improvement of 13.36%, when the daily 1:52 p.m. moment of time and the duration of about 1 h program, found by optimization, were applied. Results demonstrate the dual incentives of the carbon and nutrients recovery, associated to the energy and effluent quality benefits on WWTP operation.

Pruning stormwater biofilter vegetation influences water quality improvement differently in Carex appressa and Ficinia nodosa

The maintenance of stormwater biofilter vegetation is conducted under local guidelines, which often include seasonal pruning. However, the effects that pruning has on water quality improvement remain unknown. This study used experimental columns to investigate the effects of pruning on effluent concentrations of nitrogen, phosphorus, and metals when planted with two common biofilter plant species, Carex appressa and Ficinia nodosa. Effluent was monitored in pruned, non-pruned, and unplanted control columns during a 70-day regrowth period, with monthly composite water sampling encompassing the flushed saturated zone water and effluent of each column to best represent a biofilter during a storm event. Differences between pruning treatments and the control were often species-specific and varied with nutrient type. No significant differences between treatments were found for total phosphorus, but pruning treatments affected nitrogen oxide removal in later sampling dates for F. nodosa, but not C. appressa. Total N and P removal ranged from 77 to 88% and 66–93 %, respectively, by both pruned and non-pruned plants. The overall amount of N and P removed in the pruned biomass was 2.1–3.5 times more than the estimated amount removed from the influent by the regrowth of the pruned columns alone during the regrowth period. Consequently, the amount of nutrients removed via pruning may significantly impact long-term removal. Cadmium, copper, lead, and zinc effluent concentrations were similar between treatments with removal efficiencies over 95 %. Overall, pruning appears to affect water quality improvement, but optimal pruning practices that may enhance long-term removal should be investigated further.

Denitrification mechanism and artificial neural networks modeling for low-pollution water purification using a denitrification biological filter process

Low-pollution water treatment is an important process for improving surface water quality. In the present study, a denitrification biological filter (DNBF) was used to treat synthetic low-pollution water, representing the typical water present in a heavily polluted urban seasonal river. The feasibility of alkali treated corncob as a denitrification slow-release carbon source was investigated. Furthermore, the performance of DNBF with different media (ceramsite, quartz sand and polypropylene plastics) and operating conditions was studied. The DNBF denitrification mechanism was analyzed and an artificial neural network model was established to predict the water quality of DNBF treated low-pollution water effluent. Results showed that when the alkali treated corncob dosage was 20 g and hydraulic retention time (HRT) was 2 h, the denitrification efficiency of DNBF with ceramsite as the filter medium was highest (≥94.7% for nitrate nitrogen and ≥ 85.6% for total nitrogen), with the effluent total nitrogen concentration meeting Class IV of the Environmental Quality Standard for Surface Water (GB 3838-2002, China). The total nitrogen removal efficiency increased with increasing HRT (0.5–2.0 h) and alkali treated corncob dosage (0–20 g). The denitrification rates established for DNBF with different media were ranked in the following order: ceramsite medium DNBF > polypropylene plastic medium DNBF > quartz sand medium DNBF. The relative abundance of denitrifying bacteria was highest (10.07% for quartz sand medium DNBF, 13.92% for polypropylene plastic medium DNBF and 23.13% for ceramsite medium DNBF) in the lower layer of the DNBFs, indicating that denitrifying bacteria are concentrated in the lower layer of the up-flow DNBF. Environmental factors (nitrite nitrogen, nitrate nitrogen, water temperature and pH) were found to affect the DNBF microbial community structure. The established artificial neural network model accurately predicted the effluent nitrogen concentration in DNBF treated low-pollution water. DNBF provides a feasible system for the treatment of heavily polluted urban seasonal rivers, achieving high total nitrogen removal efficiency using a low cost and easy operation method.

Optimal influent N-to-P ratio for stable microalgal cultivation in water treatment and nutrient recovery

Species specific nitrogen-to-phosphorus molar ratio (NPR) has been suggested for green microalgae. Algae can store nitrogen and phosphorus, suggesting that the optimum feed concentration dynamically changes as function of the nutrient storage. We assessed the effect of varying influent NPR on microalgal cultivation in terms of microbial community stability, effluent quality and biokinetics. Mixed green microalgae (Chlorella sorokiniana and Scenedesmus sp.) and a monoculture of Chlorella sp. were cultivated in continuous laboratory-scale reactors treating used water. An innovative image analysis tool, developed in this study, was used to track microbial community changes. Diatoms proliferated as influent NPR decreased, and were outcompeted once cultivation conditions were restored to the optimal NPR range. Low NPR operation resulted in decrease in phosphorus removal, biomass concentration and effluent nitrogen concentration. ASM-A kinetic model simulation results agreed well with operational data in the absence of diatoms. The failure to predict operational data in the presence of diatoms suggest differences in microbial activity that can significantly influence nutrient recovery in photobioreactors (PBR). No contamination occurred during Chlorella sp. monoculture cultivation with varying NPRs. Low NPR operation resulted in decrease in biomass concentration, effluent nitrogen concentration and nitrogen quota. The ASM-A model was calibrated for the monoculture and the simulations could predict the experimental data in continuous operation using a single parameter subset, suggesting stable biokinetics under the different NPR conditions. Results show that controlling the influent NPR is effective to maintain the algal community composition in PBR, thereby ensuring effective nutrients uptake.

Carbon Aerogel Coated Air-cathode Bioelectrochemical System for Simultaneous Nitrogen and Phosphorus Removal

The modern bio-electrochemical technologies can convert the energy stored in the chemical bonds of biodegradable organic materials into renewable electrical bioenergy through the catalytic reactions of the microorganisms while treating the wastewaters. The present research has been conducted to study the efficiency of the single-chamber bio electrochemical system with carbon aerogel catalyst as a new, simple and inexpensive approach to remove and recover the valuable but polluting nutrients (nitrogen and phosphorus) from municipal wastewaters and also determines the optimal conditions to scale up the system in countries with hot, dry climates. In the present study, the bacterial consortium was isolated from the sediments of local lagoons, and the municipal wastewater was used as the substrate. During the six months of cell operation, the effluent of BES showed a 54.9% decrease in nitrate concentration and a 59.8% decrease in total N and 90% of phosphate removed from wastewater, the total nitrogen and total phosphate concentration in effluent were 28.9 ± 24.3 mg/l. and 13 ± 46.8 mg/l, respectively. The maximum removal of COD was 80%, and the maximum power density was 1.82mW/m2. Carbon aerogel as a novel material with suitable absorbance and resistance to oxidation by urban wastewater pH can be coated on electrodes to facilitate the Oxidation Reduction reactions and electricity transmission

Taxonomic and functional variations in the microbial community during the upgrade process of a full-scale landfill leachate treatment plant — from conventional to partial nitrification-denitrification

Because of the low access to biodegradable organic substances used for denitrification, the partial nitrification-denitrification process has been considered as a low-cost, sustainable alternative for landfill leachate treatment. In this study, the process upgrade from conventional to partial nitrification-denitrification was comprehensively investigated in a full-scale landfill leachate treatment plant (LLTP). The partial nitrification-denitrification system was successfully achieved through the optimizing dissolved oxygen and the external carbon source, with effluent nitrogen concentrations lower than 150 mg/L. Moreover, the upgrading process facilitated the enrichment of Nitrosomonas (abundance increased from 0.4% to 3.3%), which was also evidenced by increased abundance of amoA/B/C genes carried by Nitrosomonas. Although Nitrospira (accounting for 0.1%–0.6%) was found to stably exist in the reactor tank, considerable nitrite accumulation occurred in the reactor (reaching 98.8 mg/L), indicating high-efficiency of the partial nitrification process. Moreover, the abundance of Thauera, the dominant denitrifying bacteria responsible for nitrite reduction, gradually increased from 0.60% to 5.52% during the upgrade process. This process caused great changes in the microbial community, inducing continuous succession of heterotrophic bacteria accompanied by enhanced metabolic potentials toward organic substances. The results obtained in this study advanced our understanding of the operation of a partial nitrification-denitrification system and provided a technical case for the upgrade of currently existing full-scale LLTPs.

A Study on the Improvement of Nitrogen & Phosphorus Removal of a Sequence Batch Reactor with Internal Circulation and Multi-Step Addition

Objectives:The purpose of this study is to increase the denitrification and phosphorus removals by the oxygen control of the anaerobic or anoxic period using the circulation of the supernants through the settled sludge and multi-step addition of raw wastewater during the operation of the internal circulation sequence batch reactor (ICSBR).Methods:The internal circulation pipe at the bottom of SBR is installed to circulate the supernatant into the settled sludge layer to create anoxic condition of non-aeration period instead of a stirrer in a SBR. And it is attempted to develope the SBR that properly uses the organic materials of the raw wastewater as a carbon source by the feeding the raw wastewater at a suitable time of the reaction period.Results and Discussion:Dissolved oxygen (DO) concentration of the reactor decreases more rapidly with an internal circulation to which the uniform pressure division method is applied, increasing the efficiency of about 40%. As the multi-step addition of raw wastewater proceeds, the nitrogen concentration of effluent is lowered and the C/N (Carbon/Nitrogen) ratio is higher, the nitrogen removal rate is higher.Conclusions:Circulating the supernatant to the bottom through settle sludge was effected to properly control the dissolved oxygen in the reaction tank, thereby improving the denitrification efficiency by about 68%. Even the higher the C/N ratio at the step addition can be expected the higher the nitrogen removal, it is noteworthy that the optimum feeding ratio of the multi-step addition may be different depending on the C/N ratio.

Mass and heat balances for biological nitrogen removal in an activated sludge process: to couple or not to couple?

ABSTRACT Models adapt constantly, usually increasing the degree of detail describing physical phenomena. In water resource recovery facilities, models based on mass and/or heat balances have been used to describe and improve operation. While both mass and heat balances have proven their worth individually, the question arises to which extent their coupling, which entails increased model complexity, warrants the supposedly more precise simulation results. In order to answer this question, the need for and effects of coupling mass and heat balances in modelling studies were evaluated in this work for a biological nitrogen removal process treating highly concentrated wastewater. This evaluation consisted on assessing the effect of the coupling of mass and heat balances on the prediction of: (1) nitrogen removal efficiency; (2) temperature; (3) heat recovery. In general, mass balances are sufficient for evaluating nitrogen removal efficiency and effluent nitrogen concentrations. If one desires to evaluate the effect of temperature changes (e.g. daily, weekly, seasonally) on nitrogen removal efficiency, the use of temperature profiles as an input variable to a mass balance-based model is recommended over the coupling of mass and heat balances. In terms of temperature prediction, considering a constant biological heat generation term in the heat balance model provides sufficient information – i.e. without the coupling of mass and heat balances. Also, for evaluating the heat recovery potential of the system, constant biological heat generation values provide valuable information, at least under normal operating conditions, i.e. when the solids retention time is large enough to maintain nitrification.

Potential of sulfide-based denitrification for municipal wastewater treatment

Wastewater treatment through anaerobic carbon removal followed by sulfide-based denitrification for nitrogen removal offers significant advantages over conventional processes in terms of decreased sludge production and reduced energy requirements. While the process has been demonstrated to treat wastewater with very high sulfate concentrations resulting from saline water supply, this contribution assesses the potential of sulfide-based denitrification for a broader range of municipal wastewater characteristics. A mass balance-based calculation procedure was presented to determine the optimal recycle ratio and the corresponding effluent nitrogen concentrations in a pre-denitrification system. The calculation procedure was first validated with experimental data from literature and was then applied to various scenarios. The latter showed that legal effluent requirements may be achievable only for specific municipal wastewater streams with a low nitrogen concentration and an elevated sulfate content (>42 g S m−3), e.g. close to the sea, or if a significant amount of biodegradable carbon enters the anoxic reactor to stimulate auxiliary heterotrophic denitrification. A stoichiometric calculation illustrated that even with external carbon addition to supplement the sulfide-based denitrification, the total sludge production and aeration energy could still be reduced compared to a scenario with purely heterotrophic denitrification. Finally, it was shown that a broader range of wastewater types could be treated when applying nitrification-denitrification over nitrite instead of over nitrate, due to the lower sulfide and carbon requirements for the reduction of nitrite.

Trimethylamine abatement in algal-bacterial photobioreactors.

Trimethylamine (TMA) is an odorous volatile organic compound emitted by industries. Algal-based biotechnologies have been proven as a feasible alternative for wastewater treatment, although their application to abate polluted air emissions is still scarce. This work comparatively assessed the removal of TMA in a conventional bacterial bubble column bioreactor (BC) and a novel algal-bacterial bubble column photobioreactor (PBC). The PBC exhibited a superior TMA abatement performance compared to the conventional BC. In this sense, the BC reached a removal efficiency (RE) and an elimination capacity (EC) of 78% and 12.1g TMA m-3h-1, respectively, while the PBC achieved a RE of 97% and a EC of 16.0g TMA m-3·h-1 at an empty bed residence time (EBRT) of 2min and a TMA concentration ~500mgm-3. The outstanding performance of the PBC allowed to reduce the operating EBRT to 1.5 and 1min while maintaining high REs of 98 and 94% and ECs of 21.2 and 28.1gm-3·h-1, respectively. Moreover, the PBC improved the quality of the gas and liquid effluents discharged, showing a net CO2 consumption and decreasing by ~ 30% the total nitrogen concentration in the liquid effluent via biomass assimilation. A high specialization of the bacterial community was observed in the PBC, Mumia and Aquamicrobium sp. being the most abundant genus within the main phyla identified. GraphicalAbstract.

Variable-timing, fixed-rate application of cattle biogas effluent to rice using a leaf color chart: microcosm experiments in Vietnam

ABSTRACT Livestock production plays a leading role in agricultural land-use change. Producing biogas from livestock waste and subsequently using the biogas effluent as fertilizer for crops is a promising option to solve environmental problems resulting from expanding livestock production. However, it is difficult to promptly and accurately measure the nitrogen (N) concentration of effluent for farmers in developing countries, making precise N management difficult. The objectives of the current study were (1) to evaluate the feasibility of variable-timing, fixed-rate application of cattle biogas effluent using a leaf color chart (LCC) for rice (Oryza sativa L.) and (2) to determine the optimum LCC threshold for grain yield. We conducted two microcosm experiments in the Mekong Delta of Vietnam in 2018 using eight treatments of N-fertilizer application. In the Zero treatment, we applied no N. In the Estd treatment, we split-applied N as effluent (E) at fixed rate and timing as the standard method. In E2.75, E3.00, E3.25, E3.50, and E3.75, we applied effluent whenever the LCC value went below 2.75, 3.00, 3.25, 3.50, and 3.75, respectively. In U3.25, we applied N as urea (U) whenever the LCC value fell below 3.25. The total effluent-N application rate ranged from 90 to 210 kg N ha−1 season−1. Rice growth was normal but there was a substantial yield gap between the two microcosm experiments due to the seasonal difference in solar radiation. Rice yield tended to increase with increasing LCC threshold. There was a positive linear relationship between LCC and chlorophyll content (SPAD) values (R 2 = 0.73–0.79). Grain yield was well explained (R 2 = 0.70–0.89) by the seasonal mean LCC or SPAD value. Plant total N uptake increased with increasing LCC threshold, but the three calculated indices of N use efficiency (NUE) – apparent N recovery, agronomic NUE, and internal NUE – were not always improved with a higher LCC threshold. Our results showed that the tested variable-timing, fixed-rate strategy for the application of cattle biogas effluent was feasible and the optimum LCC threshold for grain production was 3.75 under the current microcosm conditions.

Pilot Study on Start-up and Stable Operation at Low Temperature Based on Denitrifying Phosphorus Removal

In order to understand the denitrifying and phosphorus removal characteristics of denitrifying phosphate-accumulating organisms (DPAOs), a pilot scale (20 m3) denitrifying and phosphorus removal experiment was carried out using a modified University of Cape Town (UCT) process at low temperatures of (6-16)℃. The test results show that at such temperatures, the hydraulic retention time (HRT) is 20 h and the solids retention time (SRT) is 35 days, and the modified UCT process can start up successfully and run steadily. When running steadily, the system can maintain nitrogen and phosphorus removal rates of 60%±5% and 80%±5%, respectively. The effluent concentrations of chemical oxygen demand (COD), ammonium nitrogen (NH4+-N), total nitrogen (TN), and total phosphorus (TP) were 20, 5, 11, and 0.5 mg·L-1, respectively, which meet the first A emission standard of "Pollutant Discharge Standard for Urban Sewage Treatment Plant" (GB 18918-2002). In order to further investigate the characteristics of nitrogen and phosphorus removal in the system, the reflux ratio from the aerobic tank to the anoxic tank was increased to 150%. After the system was stabilized, it obtained higher nitrogen and phosphorus removal rates of 80%±10% and 90%±5%, respectively. Among them, denitrifying phosphorus removal in the anoxic tank accounted for 80%±4% of the total biological phosphorus removal. The average effluent concentrations of COD, NH4+-N, TN, and TP were 19.55, 0.1, 7.8, and 0.15 mg·L-1, respectively, which meet the Beijing Standard A discharge standard.

Impacts of salt shocking and the selection of a suitable reversal agent on anammox.

In this study, an anaerobic ammonium oxidation (anammox) reactor, which was inhibited by a salinity of 50 g NaCl L-1 during a long-term experiment, was rapidly restarted by decreasing the salinity to 20 g NaCl L-1 and adding biomass. The effects of exposure time and shock concentrations on the anammox reactor indicate that anammox granular sludge has a high tolerance to salinity and strong ability for self-recovery. The nitrogen removal efficiency was higher than 50% after exposure to 50 g NaCl L-1 for 66 h. To shorten the time taken for effluent nitrogen concentrations to attain national standards (GB18918-2002) after the anammox reactor was shocked with NaCl, reactor performance (i.e., recovery) after the addition of K+, glycine betaine, Fe2+, and hydroxylamine were compared after the reactor was inhibited by 80 g NaCl L-1. The results indicate that hydroxylamine was the best reversal agent. The recovery time of the anammox reactor could be shortened by 50% following the addition of hydroxylamine. The most favorable NH2OH-N/NO2--N concentration ratio for improving nitrogen removal of anammox was 1:11. The abundances of Planctomycetes and its genera Candidatus Kuenenia and Brocadiaceae_g_unclassified increased after repeated salinity shock-recovery phases, indicating that Candidatus Kuenenia and Brocadiaceae_g_unclassified are able to adapt to NaCl shocking and recovery.

Effects of different substrates on nitrogen and phosphorus removal in horizontal subsurface flow constructed wetlands.

This study aimed to explore the nitrogen and phosphorus removal performance of the horizontal submerged constructed wetland (HSCW) with Ti-bearing blast furnace slag (T). Another two HSCWs, with the converter steelmaking slag (G) and the stone (S) as wetland substrates, respectively, were simultaneously running as control. The results showed that the nitrogen and phosphorus removal capacities of the T-HSCW were generally better than those of another two HSCWs. When the hydraulic retention time (HRT) was 6days, the effluent concentrations of ammonia nitrogen (NH4+-N) and total nitrogen (TN) were 6.66mgL-1 and 14.02mgL-1, respectively, and the removal rates of NH4+-N and TN reached 77.54% and 71.07%, respectively. The T-HSCW had better removal efficiency of phosphorus. The effluent concentration of total phosphorus (TP) was lower than 0.3mgL-1, and the maximum removal rate could reach 98%. Through the characterization of the three substrates before and after experiments, it was found that the removal of nitrogen and phosphorus by T and G mainly relied on chemical adsorption, while S mainly relied on physical adsorption. Ti could also promote the absorption of nitrogen by plants and increase the nitrogen removal capacity of T-HSCWs.

Rural domestic wastewater treatment in constructed ditch wetlands: Effects of influent flow ratio distribution

Constructed wetlands (CWs) are a sustainable technology used to remove pollutants from wastewater; however, their low total nitrogen (TN) removal efficiency remains a pressing issue. Constructed ditch wetland systems (CDWs) differ from CWs in being narrow and shallow. This study observed the performance of CDWs throughout their operational period and investigated the causes of their low TN removal rates. To enhance TN removal, we propose an approach where the inflow is divided into two parts with different influent flow ratios. Four systems were trialed in parallel to examine the effects of the influent flow ratio distribution on organics removal and nitrogen transformation. A flow ratio of 1:2 was considered optimal following comparison of the four experimental CDWs. The removal efficiencies of chemical oxygen demand (COD) and TN in the control CDW (influent flow ratio 3:0) during winter were 91.15% and 25.87%, respectively, whereas the removal efficiencies of the best-performing CDW (influent flow ratio 1:2) were 91.59% and 50.40%, respectively. Based on an analysis of nitrogen transformation, a model of effluent TN and nitrate nitrogen concentration in the four CDWs was constructed.

Model-based evaluation of a trickling filter facility upgrade to biological nutrient removal

This article presents the feasibility evaluation and preliminary design of a wastewater treatment plant upgrade supported by simulation. The existing facility was based on trickling filters, and the objective of the upgrade was to achieve nutrients removal. The proposed solution modifies the existing primary clarifier to host an anaerobic-anoxic suspended growth reactor, which is an alternative that, to our knowledge, has not been proposed or explored so far. The trickling filters would remain as aerobic reactors. In this study, the novel treatment scheme has been assessed for the first time, through model simulations. The modified treatment train was simulated, showing that the anoxic zone is able to denitrify satisfactorily achieving the required effluent nitrogen concentration. However, to promote biological phosphorus removal, an additional aerobic zone combined with a bypass of activated sludge from the anoxic zone to the first trickling filter is needed, in order to provide aerobic conditions to the phosphate accumulating organisms. Several combinations of additional aerobic volume and sludge bypass flowrate were found to successfully achieve both nitrogen and phosphorus removal, using the existing facilities without the need for new reactors neither implementing modifications that could put the trickling filters' physical integrity at risk. The novel treatment scheme could be applied in other cases with similar flowsheet in the same context.

Novel two stage partial denitrification (PD)-Anammox process for tertiary nitrogen removal from low carbon/nitrogen (C/N) municipal sewage

High nitrate (NO3−-N) concentration in the effluent of wastewater treatment plants (WWTPs), cannot meet the increasing stringent discharge limits. Hence, the tertiary treatment is necessary to lower the total nitrogen concentration. In this study, an innovative partial denitrification (PD)-Anammox process was applied to remove the nitrate nitrogen (20–40 mg N/L) from secondary effluent. The nitrate wastewater were firstly fed to PD sequencing batch reactor (SBR, 10 L) to produce nitrite along with the low carbon/nitrogen ratio (C/N) municipal sewage (NH4+ of 57.8 mg N/L, COD of 175.8 mg/L), then the effluent from SBR was pumped to the anaerobic sludge blanket (UASB, 3.2 L) performing anammox for further nitrogen removal. The integrated process was operated for 224 days with the secondary effluent to municipal sewage volume ratio of 2.9–6. The results suggested that an excellent nitrate removal efficiency of 97.9% was achieved, and the mean removal efficiency of NH4+-N and COD from municipal sewage were 95.2% and 81.6%, respectively, leading to the total nitrogen and COD concentration in the final effluent as low as 4.0 mg N/L and 30.1 mg/L, respectively. Anammox was the main nitrogen removal pathway with a mean proportion of 78.2%, and Candidatus_Brocadia was identified as the dominating genus. Furthermore, it was found that a minor nitrous oxide (N2O) was produced in the integrated process. The PD-Anammox process was verified to be economically and environmentally feasible for retrofitting of existing plants.