Simultaneous Nitrification And Denitrification Efficiency Research Articles

Enhanced denitrification performance and extracellular electron transfer for eletrotrophic bio-cathode mediated by anthraquinone-2, 6-disulfonate (AQDS) at low temperature

The slow electron transfer rate and low temperature are the bottleneck in biological denitrification process, and quinone electron shuttle (e.g. AQDS) has been confirmed as a viable approach to improve the efficiency of biological denitrification by accelerating electron transport. In this study, we employed the eletrotrophic bio-cathode with cold-tolerant to explore the mechanisms of extracellular electron transfer (EET) mediated by AQDS in simultaneous nitrification and denitrification (SND) for the first time. The results indicated that adding 0.5 mmol/L AQDS increased NH4+-N removal rate and SND efficiency by 18.1% and 17.9%, respectively, and the optimal hydraulic retention time (HRT) was shortened from 5 d to 3 d. The potential mechanism was that AQDS resulted in a 1.47-fold increase in the relative abundance of cathodic electroactive microorganisms, and the relative abundance of functional genes such as cytochrome c, flavin, cold acclimation and translocator increased by about 1.15–300.42%, which accelerated the transfer of extracellular electron and significantly improved the energy metabolism efficiency. In addition, AQDS may act as an electron shuttle to accelerate the electronic transition in long-distance electron transfer. In summary, this study expands our understanding of the role of AQDS in the SND process by bio-cathode under low temperature and provides an insight into the EET of eletrotrophic microorganisms with cold-tolerant.

Simultaneous nitrification and denitrification pattern in aerated moving-bed sequencing batch reactor: Choosing appropriate SRT for different COD/N ratios

ABSTRACT The effect of chemical oxygen demand (COD)/N ratio and sludge retention time (SRT) on the simultaneous nitrification and denitrification (SND) process in an aerated moving-bed sequencing batch reactor (A-MBSBR), for treating synthetic municipal wastewater, was studied. Three lab-scale reactors with SRTs of 5, 10, and 15 days were operated under COD/N ratios of 10 (phase 1) and 20 (phase 2). The high correlation coefficients between nitrification and denitrification efficiencies in both phases demonstrated that the denitrification efficiency in A-MBSBRs was strongly affected by nitrification efficiency (nitrate concentration). A high COD/N ratio of 20 in phase 2 provided suitable conditions for the increase and dominance of the population of heterotrophic bacteria over autotrophic nitrifiers, which led to weak nitrification (29.6–39.1%) and consequently weak denitrification (15.8–27.9%) in all reactors. In phase 2, increasing SRT from 5 to 15 days was beneficial for both nitrification and denitrification reactions. Therefore, the optimal SND efficiency in phase 2 was expected to be achieved under SRTs higher than 15 days. Under the COD/N ratio of 10 in phase 1, a better balance between the population of heterotrophs and autotrophs resulted in higher nitrification and denitrification efficiencies (44.4–62.7% and 26.3–42.8%, respectively). In phase 1, the highest and the lowest nitrification and denitrification efficiencies were obtained at SRTs of 10 and 5 days, respectively.

Exploring nutrient removal mechanisms in column-type SBR with simultaneous nitrification and denitrification

A comprehensive investigation utilized a column-type sequencing batch reactor (SBR) to efficiently remove nutrients throughout various phases of its operational cycle by forming granules. This study assessed the influence and mechanisms of a simultaneous nitrification and denitrification (SND) system employing a column-type sequential batch reactor (SBR). The primary focus was on elucidating the functional groups involved in nitrogen transformation and removal within the extracellular polymeric substances (EPS). The research findings demonstrate the superior performance of the SBR process compared to the control group. It achieved an impressive SND efficiency of 69%, resulting in a remarkable 66% total nitrogen removal. Furthermore, a detailed analysis unveiled that the SBR process had a beneficial impact on the composition and properties of EPS. This impact was observed through increased EPS content and enhanced capacity to transport, convert, and retain nitrogen effectively. Additionally, after initial acclimatization, the SBR process showed its effectiveness in removing nutrients (88–98%) and COD (93%) from the generated wastewater within a hydraulic retention time (HRT) of 6 h. A statistically significant difference between the treatments for the investigated mixing ratios was found by univariate analysis of variance (ANOVA). Machine learning (CatBoost model) was employed to understand each parameter’s relationship and predict the outcomes in measurable quantity. The findings of the SBR trials showed that the concentration of generated wastewater and the HRT impacted the treatment efficiency. However, the effluent may still need other physicochemical processes, such as membrane filtering, coagulation, electrocoagulation, etc., as post-treatment options, even though COD, nutrients, and turbidity have been entirely or significantly effectively removed. Overall, this work offers insightful information on the critical function of the SBR bacterial community in promoting SND.

The Influence of Atmospheric Pressure and Organic Loading on the Sustainability of Simultaneous Nitrification and Denitrification

In high-altitude regions, a diminished atmospheric oxygen content significantly impairs the aeration efficiency of municipal wastewater, posing a challenge to sustainable wastewater management. Consequently, conventional biological wastewater treatment methods necessitate elevated energy consumption in high-altitude areas, rendering them economically and environmentally unsustainable. The simultaneous nitrification and denitrification (SND) process, owing to its minimal oxygen requirements, emerges as a promising and sustainable solution in low-pressure environments. Additionally, owing to the unique lifestyle and natural conditions in plateau regions, the organic loading in municipal wastewater is often low. To comprehensively assess the impact of low pressure and organic loading on the SND process, three laboratory-scale reactors were implemented. This study revealed that low pressure and the introduction of organic matter enhanced both nitrogen removal performance and SND efficiency. The sludge volume index decreased by 93.5%, indicating a substantial improvement in the microbial aggregation ability and the formation of a more favorable SND sludge structure. 16S rRNA sequencing results demonstrated alterations in the microbial community structure due to low pressure and the addition of organic matter, leading to a substantial increase in the abundance of nitrifying and denitrifying bacteria. Furthermore, the prediction results of functional genes indicated the upregulation of genes related to the nitrification and denitrification processes with decreasing pressure and the addition of organic matter. This enhancement underlines the improved microbial nitrogen removal function. This study underscores the positive influence of low pressure and organic loading on the SND system, thereby substantially enhancing the economic and environmental sustainability of the SND process in plateau regions.

Effect of dissolved oxygen concentration on performance and mechanism of simultaneous nitrification and denitrification in integrated fixed-film activated sludge sequencing batch reactors

Integrated fixed-film activated sludge (IFAS) is a superior system for achieving simultaneous nitrification and denitrification (SND), however, the impact of dissolved oxygen (DO) has not been fully elucidated. Therefore, this study investigated the effect of DO concentration on performance and mechanism of SND in IFAS system. Results showed that IFAS outperformed control systems and achieved optimal SND performance at a DO concentration of 0.5 mg/L, with an SND efficiency of 88.51% and total nitrogen removal efficiency of 82.78%. Typical cycles analysis demonstrated limited-DO promoted SND performance. Further analysis implied biofilms exhibited high biomass and denitrification activity with decreasing DO. Microbial community analysis revealed low DO concentrations were responsible for abundant functional groups and genes associated with SND and promoted unconventional nitrogen removal pathways. Moreover, co-occurrence network analysis elucidated microbial interactions, responses to DO, and keystone genera. This study helps understanding the roles of DO for enhanced SND in IFAS.

Process optimization of a moving bed bioreactor undergoing simultaneous nitrification and denitrification for wastewater in the absence of organic carbon

ABSTRACT Moving bed bioreactors are efficient for the removal of nitrogen effluents by simultaneous nitrification and denitrification (SND), which is particularly challenging for effluents with low C/N ratio due to insufficient carbon available for denitrification. The addition of external organic carbon in such cases increases treatment costs. Endogenous degradation of biomass offers a cost-effective and persistent source of carbon. Internal carbon leads to low denitrification rates and optimizing the biomass content leads to a sustainable solution for treating such effluents. The present study aims to optimize the process of SND using endogenous carbon by investigating the effect of operational parameters like dissolved oxygen, influent ammonium (NH4–N) loading, hydraulic retention time (HRT) and carrier filling ratio (CFR). The synthetic wastewater used in the study does not inherently contain any organic carbon, thus indicating the responsible carbon for denitrification to be of internal origin. Using a novel carrier for multispecies biofilm development, initial NH4–N concentration variation showed an insignificant effect on SND efficiency. At higher loading, nitrite accumulation due to incomplete denitrification was observed. The effect of CFR was investigated in a range of 20–35%, beyond which non-homogeneous mixing was caused in the reactor. Under controlled DO and temperature of about 5 mg/L and 28 ± 2°C, respectively, an optimum filling ratio of 35% was finalised, resulting in an SND efficiency of 97.9% at 22 h HRT for high influent NH4–N concentration of 500 mg/L. Bacteriological species identification revealed the coexistence of nitrogen-fixing, aerobic nitrifying and anaerobic denitrifying bacteria in the biofilm growing on the biocarrier. Mechanism of SND occurring in aerobic moving bed bioreactors: Laboratory-scale aerobic Moving Bed Bioreactor setup for a continuous study evaluating the influence of operational parameters on SND Occurrence of aerobic and anoxic zones in biofilm grown on the surface of novel carriers due to diffusional gradient of dissolved oxygen

Effects of biocarrier type and size on the performance of nitrification and simultaneous nitrification and denitrification

Four soft polyurethane biocarriers with different sizes and a hard polypropylene biocarrier were selected to evaluate the effects of material type and size on the nitrification and simultaneous nitrification and denitrification (SND) performance of the aerobic moving bed biofilm reactors (MBBR) in treating synthetic coking wastewater under different organic loading rates (OLR, 0.95, 0.65, 0.49 kg COD m−3 day−1). The attached biomass concentrations of the polyurethane biocarriers were 1.65 ± 0.15 g L−1, almost twice that of the polypropylene one (0.76 ± 0.05 g L−1), while the differences in the suspended biomass concentrations were relatively small (1.48 ± 0.18 g L−1 and 1.28 ± 0.06 g L−1, respectively). The SND efficiency of 32.43% ± 5.15% for all five MBBRs was achieved at an OLR of 0.95 kg COD m−3 d−1, which decreased to 8.48% ± 5.25% and 4.35% ± 2.99%, respectively, at lower OLRs. It was clear that OLR was an important factor affecting the SND performance. The MBBR using the smallest polyurethane biocarrier (10 mm × 10 mm × 10 mm) achieved complete nitrification at an OLR of 0.65 kg COD m−3 day−1, while the other ones achieved it at a lower OLR (0.49 kg COD m−3 day−1). The smallest polyurethane biocarrier exhibited a higher specific ammonium oxidizing rate (SAOR, 0.071 ± 0.007 g NH4+-N g−1 VSS day−1) than the other ones (0.045–0.050 g NH4+-N g−1 VSS day−1 for the larger size polyurethane ones and 0.023 ± 0.002 g NH4+-N g−1 VSS day−1 for the polypropylene one). Miseq analysis revealed that Nitrosomonas and Nitrospira were respectively the dominant AOB and NOB in all MBBRs. The polyurethane biocarriers enriched AOB and NOB in the biofilms as much as 14.6 and 9.7 times, while the polyethylene one only enriched them 3.8 and 2.2 times. Thus, the polyurethane biocarrier with smaller size was advantageous for improving nitrification capacity.

Optimization of synthetic domestic wastewater treatment performance in anoxic/aerobic sequencing batch reactor with zeolite addition

In this study, treatment performance was investigated based on chemical oxygen demand (COD), ammonium nitrogen (NH4 +-N), total inorganic nitrogen (TIN) and simultaneous nitrification and denitrification (SND) parameters in a zeolite-added anoxic/aerobic sequencing batch reactor. Response surface methodology (RSM) was used to model treatment performance, determine the impact of operating conditions, and optimize them. The effect of zeolite size, dosage and COD/NH4 +-N (C/N) ratio as operating parameters were evaluated in the central composite design (CCD). Variance analysis (ANOVA) results of the quadratic model, high coefficients of determination and low values of the root mean square error (RMSE) for dependent variables indicated the validity of the model in predicting experimental results. The desirability function showed that optimum conditions were 0.80 mm for zeolite size, 3.05 g/L for zeolite dosage and 9.8 for C/N. Under these conditions, the maximum COD, NH4 +-N, TIN removal efficiencies and SND efficiency were 92.85%, 93.3%, 77.33% and 82.96%, respectively. The results of the study showed that the most effective independent variable on dependent variables was the C/N ratio.

Insight into the roles of microalgae on simultaneous nitrification and denitrification in microalgal-bacterial sequencing batch reactors: Nitrogen removal, extracellular polymeric substances, and microbial communities

This study explored the influence and mechanism of microalgae on simultaneous nitrification and denitrification (SND) in microalgal-bacterial sequencing batch reactors (MB-SBR). It particularly focused on nitrogen transformation in extracellular polymeric substances (EPS) and functional groups associated with nitrogen removal. The results showed that MB-SBR achieved more optimal performance than control, with an SND efficiency of 68.01% and total nitrogen removal efficiency of 66.74%. Further analyses revealed that microalgae changed compositions and properties of EPS by increasing EPS contents and improving transfer, conversion, and storage capacity of nitrogen in EPS. Microbial community analysis demonstrated that microalgae promoted the enrichment of functional groups and genes related to SND and introduced diverse nitrogen removal pathways. Moreover, co-occurrence network analysis elucidated the interactions between communities of bacteria and microalgae and the promotion of SND by microalgae as keystone connectors in the MB-SBR. This study provides insights into the roles of microalgae for enhanced SND.

Performance and microbial mechanism of eletrotrophic bio-cathode denitrification under low temperature

Insufficient amount of carbon in wastewater and low temperatures hinder the use of biological nitrogen removal for purification of wastewaters. Nitrogen removal using cold-tolerant electrotrophic cathodic microbes is a novel and unique autotrophic denitrification technique in which electrical current, not chemicals, is used as a source of electrons. In this study, integrated MFC (RW) and open-circuit MFC (RO) were cultured and acclimatized in stages at a low temperature (10 °C) to impart cold tolerance to electrotrophic cathodic microbes, investigate the effectiveness of simultaneous nitrification and denitrification (SND) process, and address the possible mechanism of microbial action. The results showed that (i) microbial communities in the RW system were successfully enriched with the cold-tolerant electrotrophic cathodic microbes after five stages, and (ii) the degree of NH4+-N removal and SND were 75.50% and 81.91%, respectively, but the respective values in the RO system were only 40.47% and 54.01%. The desirable SND efficiency was obtained in RW at a DO of ∼0.6 mg/L, a current of ∼20 mA, and pH ∼7.0. In RW, Thauera, Pesudomonas, and Hydrogenophaga were the main electrotrophic cathodic denitrifying bacteria with cold tolerance capable of degrading ammonia, nitrate, and nitrite through autotrophic denitrification and cathodic-driven bio-electrochemical denitrification. Besides, for RW, results from high throughput sequencing analysis revealed that the abundance of genes related to energy production and conversion, amino acid transport, and metabolism, signal transduction, environmental adaptation, and enzymatic activity (AMO, HAO, NAR, NIR, NOR, and NOS) were significantly higher than the corresponding parameters of the RO system. This may explain the reason behind RW having excellent ammonia and TN removal performance at low temperatures.

Shifts of microbial community structure along substrate concentration gradients in immobilized biomass for nitrogen removal

Immobilized biomass technology has been regarded as an effective strategy to enhance simultaneous nitrification and denitrification (SND) in existing aerobic biological wastewater treatment processes. Nevertheless, the mechanisms of SND in an aerobic immobilized biomass need to be proven. In this study, waste sludge from municipal wastewater treatment plants was immobilized by cellulose triacetate as bioplates, and an immobilized bioplate reactor (IBPR) was successfully established for nitrogen removal tests. The SND efficiency of the IBPR was increased 18% under the intermittent aeration (IA) mode compared with that under the continuous aeration (CA) mode. During IA operation, the IBPR achieved 96% COD removal and 76% NH4+-N removal, with 71% SND. The results of microbial community analysis by high-throughput sequencing showed that nitrogen-related functional bacteria were more abundant in the bioplates than in the attached biofilms. The colocalization of nitrifiers and denitrifiers in the bioplates was observed, and the microbial community of nitrogen-related functional bacteria clearly shifted with the substrate concentration gradients.

Influence of static mixer on the development of aerobic granules for the treatment of low-medium strength domestic wastewater

The present work investigates the feasibility of aerobic granulation for the treatment of low-medium strength domestic wastewater for long-term operation and effects of a static mixer on the properties and removal performances of the aerobic granules formed. The static mixer was installed in a sequential batch reactor to provide higher hydrodynamic shear force in enhancing the formation of the aerobic granules. Aerobic granules were successfully formed in the domestic wastewater, and the granulation treatment system was sustained for a period of 356 days without granules disintegration. Subsequent to the installation, aerobic granules with a low SVI30 of 41.37 mL/gTSS, average diameter 1.11 mm, granular strength with integrity coefficient 10.4% and regular shape with minimum filamentous outgrowth were formed. Mineral concentrations such as Fe, Mg, Ca and Na as well as composition of protein and polysaccharide in tightly bound-extracellular polymeric substance of the aerobic granules were found to be higher under the effect of the static mixer. However, no significant improvement was observed on the TCOD, NH4+-N and TSS removal performance. Good TCOD and TSS removal performance of above 85% and 90%, respectively and moderate NH4+-N removal performance of about 60% were observed throughout the study. Higher simultaneous nitrification and denitrification (SND) efficiency of 56% was observed after the installation of the static mixer, as compared to 21% prior. Therefore, it may be concluded that the installation of the static mixer significantly improved the properties of aerobic granules formation and SND efficiency but not the TCOD, NH4+-N and TSS removal performance.

Factors affecting simultaneous nitrification and denitrification (SND) in a moving bed sequencing batch reactor (MBSBR) system as revealed by microbial community structures.

The effects of biological factors including dissolved oxygen (DO), pH, carbon/nitrogen (C/N) and hydraulic retention times (HRT) on the performance of simultaneous nitrification and denitrification (SND) in a moving bed sequencing batch reactor (MBSBR) were investigated. A low DO was found to be advantageous to the SND in that nitrification was not inhibited, while pH and C/N ratio were shown to have positive effects on SND, and HRT needed to be controlled in a suitable range. A desirable SND efficiency was obtained at a DO of 2.5 mg L-1, pH of approximately 8.0, C/N ratio of 10 and HRT of 10h in the MBSBR. High-throughput sequencing analysis showed that different operating conditions impacted microbial communities, resulting in different nitrogen removal mechanisms. Autotrophic and heterotrophic nitrification together contributed to the good nitrification performance, while denitrification was conducted by combined anoxic and aerobic processes. Furthermore, the results of principal component analyses (PCA) and the abundance of the predominant nitrification and denitrification genera both showed that DO and HRT might be regarded as the dominant variable factors influencing community structure analysis during SND, while the linear discriminant analysis (LDA) effect size (LEfSe) algorithm showed differences in abundance among the biofilm microbial communities with different DO. Overall, the results of this study improve our understanding of the bacterial community structure with different operating conditions in MBSBRs.

Electron transfer pathways and kinetic analysis of cathodic simultaneous nitrification and denitrification process in microbial fuel cell system

Microbial fuel cell (MFC) is an innovative bioconversion technology for wastewater treatment accompanied with electricity recovery. In this study, a kinetic model was developed base on Activated Sludge Model No.1 (ASM1) to describe electron transfer pathways during the simultaneous nitrification and denitrification (SND) process in the biocathode system of a dual-chamber MFC. The batch running of the dual-chamber MFC system showed that it produced a power density up to 2.96 W m−3 within 48 h, the achieved SND efficiency and autotrophic denitrification ratio in the cathodic denitrification process were up to 87.3 ± 0.8% and 69.5 ± 6.6%, respectively. Meanwhile, by integrating nitrification, autotrophic denitrification, heterotrophic denitrification, organic carbon oxidation, and oxygen reduction in the cathode, the model was able to precisely fit the concentration variations of NH3–N, dissolved oxygen (DO) and chemical oxygen demand (COD) during the cathodic SND process (R2 ≥ 0.9876). The cathode electrons tended to be completely utilized with the increase of autotrophic denitrification ratio in the cathodic denitrification process. When the nitrification rate was enhanced, the autotrophic denitrification would prevail in the competition with the heterotrophic denitrification. In summary, the developed model was confirmed to be effective and reliable for describing the electron transfer pathways and predicting the performance of the nitrogen removal reactions during the cathodic SND process in a double-chamber MFC.

Simultaneous nitrification and denitrification in an aerobic biofilm biosystem with loofah sponges as carriers for biodegrading hydrolyzed polyacrylamide-containing wastewater.

Simultaneous nitrification and denitrification (SND) during treating hydrolyzed polyacrylamide (HPAM) containing wastewater were explored in an aerobic biofilm reactor biosystem. Here, loofah sponges as the environment-friendly and low-cost material were applied as the carriers in this biosystem. The removal efficiencies of HPAM and total nitrogen (TN) reached 43.6% and 54.3%, respectively, after 120days stabilized running periods. Moreover, the structure of loofah sponges affected anaerobic microenvironment significantly which was indispensable for realizing a high-performance of SND. Key microorganisms in this biosystem included nitrobacteria, denitrobacteria and HPAM-biodegrading bacteria. The abundance of nitrobacteria and denitrobacteria on the biofilm was increased by 17.2% and 15.3%, respectively, through cultivation. Meanwhile, the biotransformation mechanisms of HPAM and diverse valence of nitrogen under different chemical oxygen demand (COD)/N and dissolved oxygen (DO) conditions were investigated. When COD/N and DO were 8:1 and 2mg/L, HPAM biodegradation, SND efficiency and TN removal achieved their maximum, and the values were 54.3%, 92.3% and 60.1%, respectively. Key enzyme activities also reached their maximum in this condition. The optimal COD/N and DO was pivotal to achieve the high-performance of SND, and it was closely correlated with HPAM biodegradation. Meanwhile, SND could facilitate the biotransformation of HPAM.

Simultaneous nitrification and denitrification (SND) bioaugmentation with Pseudomonas sp. HJ3 inoculated for enhancing phenol and nitrogen removal in coal gasification wastewater.

A simultaneous nitrification and denitrification (SND) bioaugmention system with Pseudomonas sp. HJ3 inoculated was established to explore the potential of simultaneous phenol and nitrogen removal in coal gasification wastewater (CGW). When the concentration of influent chemical oxygen demand (COD) and total phenols (TPh) was 1,765.94 ± 27.43 mg/L and 289.55 ± 10.32 mg/L, the average removal efficiency of COD and TPh at the stable operating stage reached 64.07% ± 0.76% and 74.91% ± 0.33%, respectively. Meanwhile, the average removal efficiency of NH4 +-N and total nitrogen (TN) reached 67.96% ± 0.17% and 57.95% ± 0.12%, respectively. The maximum SND efficiency reached 83.51%. Furthermore, SND bioaugmentation performed with good nitrification tolerance of phenol shock load and significantly reduced toxic inhibition of organisms. Additionally, the microbial community analysis indicated that Pseudomonas sp. HJ3 was the predominant bacterium in the SND bioaugmentation system. Moreover, the indigenous nitrogen removal bacteria such as Thauera, Acidovorax and Stenotrophomonas were enriched, which further enhanced the nitrogen removal in the SND bioaugmentation system. The results demonstrated the promising application of SND bioaugmentation for enhancing simultaneous phenol and nitrogen removal in CGW treatment.

The combined effect of dissolved oxygen and COD/N on nitrogen removal and the corresponding mechanisms in intermittent aeration constructed wetlands

In this study, the combined effect of dissolved oxygen (DO) and COD/N on nitrogen (N) removal as well as the corresponding mechanisms were investigated in aerated constructed wetlands (CWs). At each investigated COD/N level, the ammonium removal efficiency increased as DO concentration increased. However, the highest total N removal efficiency occurred at different DO concentration at each COD/N level. The results of functional gene analysis and cyclic N profile studies indicated that DO supply and COD/N influence the N removal performance, which is not only exert a direct effect on nitrification-denitrification process, but also change N removal pathway in intermittent aerated CWs. At a relatively high influent COD/N of 20, the simultaneous nitrification and denitrification (SND) via nitrite was almost the exclusive N removal pathway at all investigated DO concentration. With the decrease of COD/N from 20 to 2 at DO of ∼1.8, ∼3.5 and ∼6.0 mg/L, SND efficiency all decreased, however, its decreasing rate was much higher at relatively high DO level of ∼6.0 mg/L than that at DO levels of ∼1.8 and ∼3.5 mg/L. In comparison, a simultaneously partial nitrification, anammox and denitrification was established at DO of ∼0.8 mg/L along with reducing influent COD/N.

Improving Wastewater Nitrogen Removal and Reducing Effluent NOx - -N by an Oxygen-Limited Process Consisting of a Sequencing Batch Reactor and a Sequencing Batch Biofilm Reactor

Abstract A series of reactors including a sequencing batch reactor (SBR) and a sequencing batch biofilm reactor (SBBR) were used for nitrogen removal. The aim of this study was simultaneous removal of NH4+-N and NOx–-N from synthetic wastewater. In the novel proposed method, the effluent from SBR was sequentially introduced into SBBR, which contained 0.030 m3 biofilm carriers, so the system operated under a paired sequence of aerobic-anoxic conditions. The effects of different carbon sources and aeration conditions were investigated. A low dissolved oxygen (DO) level in the biofilm depth of the fixed-bed process (SBBR) simulated the anoxic phase conditions. Accordingly, a portion of NH4+-N that was not converted to NO3–-N by the SBR process was converted to NO3–-N in the outer layer of the biofilm in the SBBR process. Further, simultaneous nitrification and denitrification (SND) was achieved in the SBBR where NO2–-N was converted to N2 directly, before NO3–-N conversion (partial nitrification). The level of mixed liquid suspended solids (MLSS) was 2740 mg/l at the start of the experiments. The required carbon source (C: N ratio of 4) was provided by adding an internal carbon source (through step feeding) or ethanol. Firstly, as part of the system (SBR and SBBR), SBR operated at a DO level of 1 mg/l while SBBR operated at a DO concentration of 0.3 mg/l during Run-1. During Run-2, the system operated at the low DO concentration of 0.3 mg/l. When the source of carbon was ethanol, the nitrogen removal rate (RN) was higher than the operation with an internal carbon source. When the reactors were operated at the same DO concentration of 0.3 mg/l, 99.1 % of the ammonium was removed. The NO3–-N produced during the aerobic SBR operation of the novel method was removed in SBBR reactor by 8.3 %. The concentrations of NO3--N and NO2–-N in the SBBR effluent were reduced to 2.5 and 5.5 mg/l, respectively. Also, the total nitrogen (TN) removal efficiency was 97.5 % by adding ethanol at the DO level of 0.3 mg/l. When C:N adjustment was carried out SND efficiency at C:N ratio of 6.5 reached to 99 %. The increasing nitrogen loading rate (NLR) to 0.554 kg N/m3 d decreased SND efficiency to 80.7 %.

Simultaneous nitrification and denitrification in the activated sludge systems of continuous flow

ABSTRACTThis study has investigated the biological nitrogen removal by simultaneous nitrification and denitrification (SND) processes in a system of continuous flow activated sludge (AS) process. The investigation had four stages and evaluated the system behavior under different solid retention times (SRT), food-to-mass (F/M) ratios and dissolved oxygen (DO) concentrations. The data showed that the concentration of DO 0.5±0.2 mgO2/L did not affect the growth of heterotrophic bacteria (2.2–3.1 d−1 at 20°C) and autotrophic nitrifying bacteria (0.16–1.94 d−1 at 20°C), resulting in values very close to those obtained in conventional AS processes. The chemical oxygen demand (COD) removal was over 90% in all stages. The decrease in SRT from 37.2 to 27.8, 19.0 and 10.0 days had no significant influence on the development of SND. In the stage where the carbon/nitrogen (C/N) ratio was 4.3 mgCOD/mgN L, SND efficiency was of 55%. In the following stages, the C/N ratio was increased and it was possible to achieve efficiencies higher than 98% SND. Overall, the data showed that appropriate controls of carbon and nitrogen input are required to achieve an efficient SND. An established SND technology can save operation time and energy, and might replace the traditional two stages: biological nitrification and denitrification process.

Enhanced nitrogen removal from coal gasification wastewater by simultaneous nitrification and denitrification (SND) in an oxygen-limited aeration sequencing batch biofilm reactor

Simultaneous nitrification and denitrification (SND) for treating coal gasification wastewater (CGW) was achieved successfully in a lab-scale sequencing batch biofilm reactor (SBBR) by oxygen-limited aeration. SND efficiency increased gradually with the concentration of dissolved oxygen (DO) decreased from 4.5mg/L to 0.35mg/L. The maximum SND efficiency of 81.23% was obtained at DO concentration of 0.35mg/L, and the corresponding removal efficiency of NH4+-N and TN reached 76.91% and 70.23%, respectively. Meanwhile, COD was removed significantly and toxic compounds were degraded into biodegradable substances, which relieved effectively the inhibition on nitrogen removal. The results indicated that oxygen-limited condition performed greater toxic compounds and nitrogen removal compared with the aerobic condition. Furthermore, the results of scanning electron microscopic (SEM) and microbial community structure confirmed robust biofilm formation provided a suitable anoxic micro-environment for co-existence of nitrifying and denitrifying bacteria and organics degradation bacteria in the reactor at oxygen-limited condition.