Simultaneous Nitrification And Denitrification Research Articles

Evaluation of nitrogen removal and the microbial community in a submerged aerated biological filter (SABF), secondary decanters (SD), and horizontal subsurface flow constructed wetlands (HSSF-CW) for the treatment of kennel effluent.

To ensure microbial activity and a reaction equilibrium with efficiency and energy saving, it is important to know the factors that influence microbiological nitrogen removal in wastewater. Thus, it was investigated the microorganisms and their products involved in the treatment of kennel effluents operated with different aeration times, phase 1 (7h of continuous daily aeration), phase 2 (5h of continuous daily aeration), and phase 3 (intermittent aeration every 2h), monitoring chemical and physical parameters weekly, monthly microbiological, and qualitative and quantitative microbiological analyzes at the end of each applied aeration phase. The results showed a higher mean growth of nitrifying bacteria (NB) (106) and denitrifying bacteria (DB) (1022) in phase with intermittent aeration, in which better total nitrogen (TN) removal performance, with 33%, was achieved, against 21% in phase 1 and 17% in phase 2, due to the longer aeration time and lower carbon/nitrogen ratio (15.7), compared with the other phases. The presence of ammonia-oxidizing bacteria (AOB), the genus Nitrobacter nitrite-oxidizing bacteria (NOB), and DB were detected by PCR with specific primers at all phases. The analysis performed by 16S-rRNA DGGE revealed the genres Thauera at all phases; Betaproteobacteria and Acidovorax in phase 3; Azoarcus in phases 2 and 3; Clostridium, Bacillus, Lactobacillus, Turicibacter, Rhodopseudomonas, and Saccharibacteria in phase 1, which are related to the nitrogen removal, most of them by denitrifying. It is concluded that, with the characterization of the microbial community and the analysis of nitrogen compounds, it was determined, consistently, that the studied treatment system has microbiological capacity to remove TN, with the phase 3 aeration strategy, by simultaneous nitrification and denitrification (SND). Due to the high density of DB, most of the nitrification occurred by heterotrophic nitrification-aerobic. And denitrification occurred by heterotrophic and autotrophic forms, since the higher rate of oxygen application did not harm the DB. Therefore, the aeration and carbon conditions in phase 3 favored the activity of the microorganisms involved in these different routes. It is considered that, in order to increase autotrophic nitrification-aerobic, it is necessary to exhaust the volume of sludge in the secondary settlers (SD), further reducing the carbon/nitrogen ratio, through more frequent cleaning, whose periodicity should be the object of further studies. Graphical abstract.

Prediction the performance of multistage moving bed biological process using artificial neural network (ANN)

Complexity, uncertainty, and high dynamic nature of nutrient removal through biological processes (BPs) makes it difficult to model and control these processes, forcing designers to rely on approximations, probabilities, and assumptions. To cope with this difficult task and perform an effective and well-controlled BP operation, an artificial neural network (ANN) algorithm was developed to simulate, model, and control a three-stage (anaerobic/anoxic and MBBR) enhanced nutrient removal biological process (ENR-BP) challenging real wastewater. The effect of surface area loading rate (SALR), organic matters (OMs), nutrients (N & P), feed flow rate (Qfeed), hydraulic retention time (HRT), and internal recycle flow (IRF) on the performance of the ENR-BP to fulfil rigorous discharge limitations were evaluated. Experimental data was used to develop the appropriate architecture for the AAN using iterative steps of training and testing. Significant removals of chemical oxygen demand (COD) (89.2 to 98.3%), NH4+ (88.5 to 98.9%), and total phosphorus (TP) (77.9 to 99.9%) were achieved at a total HRT of 13.3 h (HRTZ-1 = 3 h, HRTZ-2 = 6 h and HRTZ-3 = 5.3 h) and an IRF value of 1.75. The ENR-BP treatment mechanism relies on the use of OMs as a source of energy for phosphorus bio-uptake and the simultaneous nitrification and denitrification (SND) of nitrogen compounds. The removal efficiencies in the proposed ENR-BP were four fold higher than the suspended growth process and in the same order of magnitude of 5-stage Bardenpho-MBBR. The developed ANN-based model provides an efficient and robust tool for predicting and forecasting the performance of the ENR-BP.

Functional microorganisms and enzymes related nitrogen cycle in the biofilm performing simultaneous nitrification and denitrification

Simultaneous nitrification and denitrification (SND) is a potential energy-saving process in wastewater treatment while the nitrogen removal mechanism is still unclear due to the lack of information about the functional microbes and enzymes. Sequencing batch biofilm reactors were implemented to achieve efficient SND. Eight nitrogen removal related microorganisms out of the top abundant 20 microbial community and reference species were used to construct a phylogenetic tree. Functional enzymes and modules analysis were investigated to reveal the SND pathway: in the aerobic part of the biofilm, ammonia oxidation was catalyzed by complete ammonia oxidizers while in the inner anoxic part, denitrification, dissimilatory nitrate reduction (DNRA) and nitrogen fixation (NF) cooperated to stimulate nitrate removal. These results provide a practical aeration control strategy to achieve SND and indicate that DNRA and NF are important nitrogen removal pathways that should not be ignored in the SND mechanism.

Salt effect on MUCT system performance of nitrogen and phosphorus removal

The effect of salinity on biological nitrogen and denitrifying phosphorus removal was investigated in a Modified University of Cape Town (MUCT) system. Removal rates of COD, NH4+-N, NO3−-N, NO2−-N, phosphorus and the sludge characteristics at salt concentrations (0.0, 3.2, 6.4, 11.2 and 16.0 g L−1) were analyzed. With the salt concentration increasing, all the COD, NH4+-N, TN and TP removal rates exhibited a trend of decline, and exhibited an initial reduction and subsequent increase at every stage of salt concentration. NH4+-N, TN and TP removal rates were 92.7%, 51.5% and 67.2% in 16 g L−1 salt concentration, respectively. And they were outperformed the literature reported and acceptable in practical applications. When the salinity of wastewater changed from 0.0 to 16.0 g L−1, the biomass yield coefficients increased from 0.0794 to 0.126 g VSS/g COD. Increased salinity had a detrimental effect on phosphorus-accumulating organisms (PAOs) and denitrifying PAOs (DPAOs) (especially DPAOs). Therefore, phosphorus removal gradually depended on PAO. The simultaneous nitrification and denitrification (SND) rate and nitrogen removal rate (including nitrification rate, denitrification rate, and total nitrogen removal rate) gradually decreased with the increased salinity.

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 removal of organic matter and nitrogen compounds from landfill leachate by aerobic granular sludge

ABSTRACT This study aimed at investigating the treatment of landfill leachate using the aerobic granular sludge process in a lab-scale sequential batch reactor (SBR-AGS). The leachate from a giant sanitary landfill localized in the State of São Paulo (Brazil) exhibited high concentration of organic matter (COD 5,300 ± 78 mg L−1) and total nitrogen (TKN 2,630 ± 355 mg L−1). Comparatively, the leachate was added to wastewater in three different volumetric ratios (5, 10 and 20%) and the mixtures were characterized over treatment. The results indicated that there were no significant changes in the behaviour of the biological process even at the highest leachate ratio. The granulation of the aerobic sludge occurred after 90 days of operation and the granules had a diameter of 485–1585 μm. SBR-AGS exhibited removal efficiency of 87–89% for organic matter and at least 98% for total nitrogen, regardless of the leachate ratio. The treated effluent that received 20% of leachate showed 2.7 mg L−1 ammonia and 1.1 mg L-1 nitrate. This study shows that SBR-AGS was able to form large granules, thus promoting a simultaneous nitrification and denitrification (SND) process. We highlighted that SND occurred in low dissolved oxygen concentrations (< 1.5 mg L−1) for 120 days, without compromising aerobic granule integrity. These results suggest that the aerobic granular sludge process is a promising alternative for the co-treatment of landfill leachate and domestic wastewater under tropical climate conditions and its use should be encouraged.

Simultaneous nitrification and denitrification in continuous flow MBBR with novel surface-modified carriers

ABSTRACT Moving-Bed Biofilm Reactor (MBBR) process is an ideal preference for simultaneous nitrification and denitrification (SND) attributing to the longer sludge age and aerobic/anoxic microenvironment along biofilm. However, conventional carriers generally exhibit negative charge and surface hydrophobicity, which are unbeneficial for biofilm formation. In this study, novel surface-modified carriers with favourable hydrophilicity (surface contact angle dropped to 60.2 ± 2.3°) and positive surface charge (+11.7 ± 1.1 mV, pH 7.0) were prepared via polymer blending and implemented for SND in continuous flow MBBR system. Results indicated SND started up quickly with more biomass in MBBR filled with surface-modified carriers. At the operation condition of low dissolved oxygen level (0.75 ± 0.25 mg/L), pH of 7.5 ± 0.5, 23 ± 2°C and C/N ratio of 7, COD, NH4 +-N and TN removal efficiencies were 90.5%, 88.6% and 76.6% respectively in MBBR filled with surface-modified carriers, which ensured the effluent met the first grade A of the Discharge Standard of China. On the contrary, COD, NH4 +-N and TN removal efficiencies were 89.7%, 82.3% and 60.4% respectively in the control reactors filled with conventional polyethylene carriers. The worse performance of the control reactor was mainly attributed to the less biomass and lower functional bacteria abundance developed on conventional carriers. Moreover, novel carriers provided a favourable niche for more types of functional bacteria, of which autotrophic nitrification, anoxic denitrification, heterotrophic nitrification and aerobic denitrification co-existed and participated in nitrogen removal.

Simultaneous nitrification and denitrification in biofilm of a model distribution pipe fed with disinfected reclaimed water

Simultaneous nitrification and denitrification (SND) in a model distribution pipe (DP) fed with actual reclaimed water was studied in this experiment. The water quality, microbial activity, bacteria community as well as the surfaces of biofilm were analysed and observed along the model DP, which had been operated for more than three years. The results exhibited that the nitrogen loss appeared in 65.6 % of the samples and an observable increase in pH value and a measurable decrease in organic carbon occurred along the flow course. The highest nitrification activity arose at the forepart of DP, which indicated nitrifiers of biofilm in DP appeared low susceptible to residual chlorine. Meanwhile, the higher denitrification activity was inclined to appear in the middle section of DP and the obvious gas pores existed on the biofilm surfaces of DP. Finally, the clone analysis revealed that Nitrospirae and Nitrosomonadales were the dominant nitrifiers while some potential denitrifiers such as Pseudomonas, Flavobacteria, Sphingobacteria, and Acinetobacter were also detected along the model DP. Briefly, SND could happen in the DP fed with the reclaimed water even under a certain amount of residual chlorine existed in the influent. A complicated microbial community, including typical nitrifiers and denitrifiers, was involved in the biofilm system of the DP, which played a key role in SND. The paper revealed that the end-water quality tended to stable after a long delivery for reclaimed water due to SND, which is helpful to the designers and managers of the water resource.

Effects of deoxygenation pretreatment and dissolved oxygen adjustment on performance of double-layer-packed sequencing biofilm batch reactor treating secondary effluent under low temperature

To meet the increasing stringent discharge standards, many wastewater treatment plants (WWTPs) are impelled to execute tertiary treatment, among which advanced nitrogen removal is still the key. An effective alternative for advanced nitrogen removal is sequencing biofilm batch reactor (SBBR), whose performance is closely related to dissolved oxygen (DO). In this study, the effects of deoxygenation pretreatment during anoxic phase and DO adjustment during aerobic phase on performance of double-layer-packed SBBR treating a typical carbon-lacked (COD/TN = 2.0, dominated with ammonium) secondary effluent under low temperature (15 °C) were investigated. It was found that deoxygenation pretreatment via adding sulfite had no significant impact on organics/phosphorus removal or nitrification but significantly improved denitrification. The deoxygenation stimulated nitrite accumulation leading to a higher simultaneous nitrification and denitrification (SND) rate. Similarly, with the increase of DO during aerobic phase, nitrification capacity increased while denitrification intensity decreased. When DO ≥ 3.5 mg/L, total ammonium nitrogen (TAN) in final effluent met the first A standard (GB 18918-2002, China). When DO at 2.5 mg/L, a highest denitrification intensity was observed while neither TAN nor total nitrogen (TN) in final effluent met the discharge standards probably mainly due to low temperature and carbon shortage. Among all the tests, FA and FNA were not the main causes for nitrite accumulation. The above findings might be helpful in guiding practical applications.

The relationship between energy production and simultaneous nitrification and denitrification via bioelectric derivation of microbial fuel cells at different anode numbers

In this study, three microbial fuel cells (MFCs) with different numbers of anodes (i.e., 1A, 3A, and 5A) were constructed to study the effects of a multi-anode (MA) system on power generation performance and nitrogen (N) removal from low carbon (C)/N wastewater. The maximum power density of 3A-MFC was 236.7 mW m−3, which was 2.6-fold and 1.2-fold that of 1A-MFC and 5A-MFC, respectively. The 3A-MFC system produced the highest total energy output in one cycle, approximately 41.7 mW h, which was 1.5-fold and 1.3-fold that of 1A-MFC and 5A-MFC, respectively. 3A-MFC also had the highest total N (TN) removal efficiency (71.1 ± 3.9%) and simultaneous nitrification and denitrification (SND) rate (93.5 ± 2.4%). An analysis of electron flow distribution in the 3A-MFC biocathode showed that electro-autotrophic denitrification accounted for 19% of the total denitrification in the last 135 h. Thereafter, the relationships between TN removal, anode number, and bioelectricity were systematically evaluated. TN removal efficiency had a good linear relationship with energy production (R2 = 0.97539); TN removal was mainly dependent on SND. Generally, the MA-MFC configuration proposed in this study produced more electrical energy and improved TN removal by enhancing nitrification and heterotrophic and electro-autotrophic denitrification of the biocathode. The proposed method is therefore effective for enhancing N removal.

Coupling of electricity generation and denitrification in three-phase single-chamber MFCs in high-salt conditions

High-salt conditions reduce the efficiency of electricity generation and nitrogen removal in microbial fuel cells (MFCs). In this work, we propose a three-phase single-chamber MFC (TP-MFC) by setting up a phase with immobilized cells in a conventional bipolar single-chamber MFC (common MFC). Cells from Halomonas were used as the immobilized phase, because these cells secrete the compatible solute ectoine and exhibit simultaneous nitrification and denitrification (SND). This enhanced the efficiency of SND and subsequent electricity generation under high-salt conditions. The average voltage of TP-MFC generated during the stable period in the presence of 30 g/L NaCl was 439.3 mV, which was 55.2% higher than that generated in common MFC. In addition, the N-removal rate of TP-MFC at 72 h was 63.4%, which was 38.4% higher than that of common MFC. The 16S rRNA diversity analysis showed an improved abundance of Pseudomonas, Acinetobacter, Alcaligenes, and Halomonas in TP-MFC, indicating that the ectoine secreted by immobilized Halomonas conferred substantial salt-tolerance on the electrogenic bacteria growing in a high-salt environment. This paper establishes an efficient and convenient method for improving the salt tolerance of microbial flora in MFCs, which is of great significance for the application of MFCs in high-strength wastewater treatment.

Effects of the carbon/nitrogen (C/N) ratio on a system coupling simultaneous nitrification and denitrification (SND) and denitrifying phosphorus removal (DPR)

ABSTRACT Simultaneous nitrification and denitrification (SND) were coupled with a denitrifying phosphorus removal (DPR) to achieve simultaneous nutrient and carbon removal. With influent chemical oxygen demand (COD), ammonia-N (NH4 +-N), and total phosphorus (TP) concentrations of 250, 50, and 8 mg/L, the SND-DPR coupled system achieved stable nutrient removal efficiency of COD, NH4 +-N, TN and TP were 91.8 ± 1.7%, 88.4 ± 1.8%, 64 ± 3.3% and 99.2 ± 0.6%, respectively. Enhancing the C/N ratio strengthened the storage of intracellular polymers and provided sufficient intracellular carbon sources for phosphorus uptake. The nutrient removal efficiency reached the highest level at a C/N ratio of 5, and no advantage was observed after increasing the C/N ratio to 7. Nutrients were mainly removed during the aerobic stage at a low DO concentration as well during the anoxic stage, which helped achieve concurrent nitrification and denitrification by ordinary heterotrophic organisms (OHOs), promote denitrifying and aerobic phosphorus removal, and conserve organic carbon demand and energy consumption for aeration. The system was limited for DO in the aerobic stage at a low DO concentration, resulting in a deficiency in electron acceptors (O2 and NO3 –N) and limiting the subsequent promotion of phosphorus uptake and TN removal. The limited DO content in the low DO stage was the key factor involved in enhancing the nutrient removal efficiency along with the increasing influent C/N ratio.

Isolation and niche characteristics in simultaneous nitrification and denitrification application of an aerobic denitrifier, Acinetobacter sp. YS2

The ecological niche of aerobic denitrifiers in activated sludge is little studied, but this determines the performance of these bacteria in reactors. Acinetobacter sp. YS2 isolated from a treatment process for petrochemical wastewater and showed excellent nitrogen removal performance. In the nitrification and denitrification process, the removal efficiencies of NH4+-N and NO3−-N were 87.81% and 88.20% at 24 h, respectively, and nitrogen balance analysis indicated that the proportions of nitrogen removal by gaseous nitrogen were 37.58% and 46.45%, respectively. During simultaneous nitrification and denitrification (SND) treatment of synthetic petrochemical wastewater in a sequencing batch reactor (SBR), aerobic denitrifiers became the dominant species and the proportion reached 87.44% in the microbial community. The removal efficiencies of NH4+-N and TN were 99.46% and 80.36% over 5 days, respectively. This research has shown that aerobic denitrifiers can become the dominant species in the applications of SND treatment for petrochemical wastewater.

A novel feedforward control strategy for simultaneous nitrification and denitrification (SND) in aerobic granular sludge sequential batch reactor (AGS-SBR)

The nitrogen removal in the aerobic granular sludge sequential batch reactor (AGS-SBR) can be achieved by the simultaneous nitrification and denitrification (SND) mode, or by the separated nitrification and denitrification stages. The SND offers a simpler operation structure than the separated nitrification and denitrification. Based on the mathematical simulation, a novel control strategy was put forward to adjust the DO (dissolved oxygen) concentration to achieve the SND under dynamic fluctuated influent conditions in AGS-SBR. The control strategy aimed to achieve a small accumulation of NH4+ at the end of the aeration cycle (NH4+ setpoint value), as previous research has indicated that keeping the small NH4+ setpoint value would guarantee the optimal condition for total nitrogen (TN) removal. The SBR aeration cycle was divided into several equal control intervals. The DO was adjusted in every control interval to reach the NH4+ set point. The results revealed that the control strategy was able to maintain the NH4+ setpoint value and achieve satisfactory TN removal. The control interval should be less than 30 min to prevent deviation of NH4+ concentration from its setpoint value. A minimum aeration duration of 3 h was required to achieve satisfactory SND.

Simultaneous nitrification and denitrification process using novel surface-modified suspended carriers for the treatment of real domestic wastewater

Moving-bed biofilm reactor (MBBR) is a well-established technology for simultaneous nitrification and denitrification (SND). In MBBR, biofilm development and pollutant removal performance are strictly governed by the physico-chemical properties of the carriers. In this study, novel surface-modified carriers with enhanced hydrophilicity (surface contact angle of 60.2 ± 2.3°) and positively-charged surfaces (+11.7 ± 1.1 mV, pH 7.0) had been prepared successfully via polymer blending, and they had also been implemented in SND system for the treatment of real domestic wastewater. Results showed that accelerated startup of SND with more biomass on the carriers was observed in MBBR system filled with surface-modified carriers. At low DO level (0.6–0.8 mg L−1) and low C/N ratio (≤5), highly efficient organics removal and SND performance could be achieved with COD removal, TN removal and SND efficiencies of 79.3–85.7%, 62.0–75.9% and 58.5–71.8%, respectively. The efficient performance of SND in MBBR system filled with surface-modified carriers was mainly attributed to the coexistence of enriched mixtrophic nitrifiers and denitrifiers like autotrophic nitrifers (Nitrosomonas, Nitrospira, Nitrobacter), heterotrophic nitrifers (Rudaea), aerobicdenitrifiers (Dokdonella, Terrimonas), anoxic denitrifiers (Gemmobacter, Ottowia, Methyloversatilis, Thermomonas) and N2O producer (Mesorhizobium).

Enhancing the nitrogen removal from swine wastewater digested liquid in a trickling biofilter with a soil layer

Trickling biofilters (TFs) allow for a simultaneous nitrification and denitrification (SND) process, and offer a favorable solution for the treatment of swine-wastewater digested liquid due to their simple operation and low cost. In this study, a soil trickling biofilter (STF) was developed to enhance nitrogen removal. A gravel trickling filter (GTF) and a woodchip trickling filter (WTF) were also constructed and operated synchronously to demonstrate the advantage of micron-sized media. The results showed that the STF had a higher ammonium nitrogen (NH4+-N) removal capacity of 21.4%, 24.9%, and 18.3% in comparison to the GTF when the influent NH4+-N was 192.9 mg L−1, 500.2 mg L−1 and 802.1 mg L−1, respectively. The total nitrogen (TN) removal capacity of the STF was 104.6%, 89.4%, and 37.5% higher than that of the WTF. Thus, the addition of micron-sized soil to TF could increase the systemic nitrogen removal capacity.

Enhanced carbon and nitrogen removal in an integrated anaerobic/anoxic/aerobic-membrane aerated biofilm reactor system.

A pilot-scale anaerobic/anoxic/aerobic-membrane aerated biofilm reactor (A2/O-MABR) system was constructed to enhance carbon and nitrogen removal. The effects of major operating parameters including the nitrate recycling ratio (R), sludge recycling ratio (r), and aerobic tank dissolved oxygen (DO) concentration on the system performance were investigated. The average removal efficiencies of the chemical oxygen demand (COD), ammonium nitrogen (NH4+-N), and total nitrogen (TN) were 89.0 ± 3.2%, 98.8 ± 1.3%, and 68.5 ± 4.2%, respectively, and their effluent concentrations were averagely 22.6 ± 7.3, 0.32 ± 0.2, and 13.3 ± 1.2 mg L−1. The suspended sludge and biofilm in aerobic tank facilitated the simultaneous nitrification and denitrification (SND) processes. Indeed, unique biofilm layered structure and abundant microbial community in the biofilm on MABR would enhance nitrogen removal. Compared with the A2/O system, the A2/O-MABR system exhibited higher nitrifying bacteria oxygen uptake rate (OUR) of 58.1 and 54.5 mgO2 per gMLSS per h in suspended sludge and biofilm, respectively, and the lower mixed liquor suspended solid (MLSS) concentration of 1800 mg L−1. Moreover, high-throughput sequencing indicated that putative nitrogen removal bacteria such as Thauera and Paracoccus could be effectively enriched in the biofilm. Since the volume proportions of the anaerobic, anoxic, aerobic and settling tank in the existing A2/O system of the WWTP was not changed, the A2/O-MABR system was simple and practical for the upgrading of A2/O system.

Performance Study of Concentrated Circular Channels System (Orbal) for Removing Nutrients from Domestic Wastewater

A biological nutrient removal was investigated as a continuous flow (orbal) system to study the efficiency of system for removing phosphor and nitrogen compounds, and to predict the effect of internal and external recirculation rates on its performance. The pilot plant consisted of three concentric circular channels: outer, intermediate and inner in capacities of 24, 16.8 and 8.7 m3 respectively. The last sedimentation basin has sludge return system to the outer channel. Pilot plant also has an internal cycle to return the mixed liquor from the inner channel to the intermediate one. Continues Flow was used to feed the plant with raw municipal wastewater from Al-Khadraa residential quarter at an average flow rate of 66.7 m3/day. The plant was equipped with a modified surface aeration system operating in total power equal to 0.48 kW to achieve the required dissolved oxygen concentrations in the outer, middle, and inner channels: 0.38, 1.3, and 2.4 mg /L respectively. The three-channel was operated on two levels of returned activated sludge (RAS): 60% and 80%. It has three levels of internal cycle (IR): 100%, 150% and 200%. The results showed: the total removal efficiencies of phosphorous, and ammonia were in the range of: (93.3% - 88.5%) and (93.5% - 92.4%), respectively. The results meet the Iraqi standards for wastewater disposal into rivers. This study revealed there is no significant correlation between removal efficiency of ammonia with the internal and external recirculation ratios, while the effluent phosphor concentrations significantly affected by RAS and IR ratios. This study adopted the hypothesis: the process of simultaneous nitrification and denitrification (SND) occurs in the outer channel, while the phosphorus removal by the pilot plant was performed by the mechanism of enhanced biological phosphorous removal (EBPR).

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.