Total Nitrogen Removal Performance Research Articles

Intensified partial nitrification and microbiome response in a membrane pulsing-aerated biofilm reactor

Membrane aerated biofilm reactor (MABR) has been developed as an energy-saving process for nitrogen removal in municipal sewage treatment, even in high ammonia wastewater. However, the impact of aeration pattern on biofilm microbiome assemblage and nitrification is not well understood. In this study, MABR and membrane pulsing-aerated biofilm reactor (MpABR) were established for partial nitrification under high ammonium loadings. The MABR and MpABR exhibited a 95 % nitrite accumulation rate (NAR), with over 60 % ammonium removal and nitrite conversion achieved after the start-up phase. The MABR and MpABR gradually adapted to the substantial increase in ammonium loading (350 mg NH4+-N·L-1), resulting in stable and high NAR (96 %), ammonium removal efficiency (70 %), and nitrite conversion efficiency (67 %). Orthogonal experiments revealed that ammonium loading rate (ALR) was the primary factor regulating nitrite conversion and oxygen levels. A moderate ALR was preferable to achieve ideal partial nitrification and energy saving. Furthermore, the integrated MpABR-anaerobic ammonium oxidation (Anammox) maintained high total nitrogen (TN) removal (> 90 %) under high ALR conditions. Microbiome analysis revealed that nitrifiers (Nitrosomonas) and denitrifiers (Stenotrophomonas and Arenimonas) alternately dominated the biofilms at different stages. These findings highlight the potential for achieving efficient partial nitrification effects using a MpABR. The excellent TN removal performance of the MpABR-Anammox suggests its wide applicability in energy-efficient wastewater treatment.

Insights on biological phosphorus removal with partial nitrification in single sludge system via sidestream free ammonia and free nitrous acid dosing

The sidestream sludge treatment by free ammonium (FA)/free nitrous acid (FNA) dosing was frequently demonstrated to maintain the nitrite pathway for the partial nitrification (PN) process. Nevertheless, the inhibitory effect of FA and FNA would severely influence polyphosphate accumulating organisms (PAOs), destroying the microbe-based phosphorus (P) removal. Therefore, a strategic evaluation was proposed to successfully achieve biological P removal with a partial nitrification process in a single sludge system by sidestream FA and FNA dosing. Through the long-term operation of 500 days, excellent phosphorus, ammonium and total nitrogen removal performance were achieved at 97.5 ± 2.6 %, 99.1 ± 1.0 % and 75.5 ± 0.4 %, respectively. Stable partial nitrification with a nitrite accumulation ratio (NAR) of 94.1 ± 3.4 was attained. The batch tests also reported the robust aerobic phosphorus uptake based on FA and FNA adapted sludge after exposure of FA and FNA, respectively, suggesting the FA and FNA treatment strategy could potentially offer the opportunity for the selection of PAOs, which synchronously have the tolerance to FA and FNA. Microbial community analysis suggested that Accumulibacter, Tetrasphaera, and Comamonadaceae collectively contributed to the phosphorus removal in this system. Summarily, the proposed work presents a novel and feasible strategy to integrate enhanced biological phosphorus removal (EBPR) and short-cut nitrogen cycling and bring the combined mainstream phosphorus removal and partial nitrification process closer to practical application.

Evaluation of nitrogen removal and nitrous oxide turnovers in granule-based simultaneous nitrification and denitrification system

Nitrous oxide (N2O) is an inevitable intermediate generated during the nitrogen removal process of granule-based simultaneous nitrification and denitrification (SND) system. In order to alleviate N2O production while maintaining a desired total nitrogen (TN) removal level in this system, a comprehensive evaluation of the contribution pathways and process parameters affecting N2O turnovers is keenly required. Therefore, mathematical models were applied to evaluate the impact of operating conditions and unravel potential mechanisms on TN removal performance and N2O production. Simulation results show that higher N2O production (11.6 %–14.2 %) occurs at higher dissolved oxygen (DO) concentrations, lower chemical oxygen demand (COD) levels, longer hydraulic retention time (HRT) and larger granule size in the granular SND system. The relative conversion rates of nitrogenous components in different regions within the granule influence N2O turnovers, with the nitrification process occurring only in the region 200 μm inward from the granule surface and denitrification working throughout the entire granule. In the inner region of the granule (0–300 μm), the heterotrophic bacteria (HB) denitrification pathway dominates N2O production as a source of N2O. While in the outer region (300–450 μm), HB denitrification acts as a sink for N2O and regulates N2O turnovers (i.e. production and reduction of N2O) together with the hydroxylamine (NH2OH) pathway that is the main contributor of N2O production. Moreover, simultaneous adjustment of multiple operating parameters within a certain range can lower the N2O production factor (<0.5 %) while achieving the desired TN removal efficiency (>80 %), resulting in a feasible N2O mitigation strategy.

Supercritical Water Oxidation of Aniline, Nitrobenzene, and Indole: Effect of Catalysts on Nitrogen Conversion Mechanism

Certain undesired N-containing products like ammonia, nitrate, and organic-N species have become the roadblocks to supercritical water oxidation (SCWO) application. This study examined the mechanisms for total nitrogen (TN) removal by catalytic SCWO. By comparing pseudo-first order kinetic constants of TN removal, our findings showed that heteropolyacids took a significant part in TN removal for nitrobenzene, and Cu(NO3)2 achieved the best TN removal performance for aniline, nitrobenzene, and indole since both Cu(II) and NO3- could accelerate N2 formation via the reduction of nitrate and the oxidation of ammonia by NO2. and .OH. Distribution of N-containing species revealed that adding catalysts could generally facilitate the conversion of nitrogen gas from organic-N, while it cannot accelerate N2 production from ammonia and nitrate. According to the DFT result, conceivable degradation pathways of aniline, nitrobenzen, and indole were proposed involving denitrification, ring-open, and mineralization.

Floating Wetlands for Sustainable Drainage Wastewater Treatment

The preservation of water resources in modern urbanized society is a major concern. In this study, a floating constructed wetland (FWT) pilot plant was designed and constructed for the treatment of a polluted wastewater drain. A series of experiments were run continuously for a year in pilot-scale FWTs in a semi-arid area located in Egypt’s Delta. Four aquatic plant species (Eichhornia, Ceratophyllum, Pistia stratiotes, and Nymphaea lotus) were used to assess the performance of FWTs for pollutant removals, such as biochemical oxygen demand (BOD), chemical oxygen demand (COD), total suspended solids (TSS), total nitrogen (TN), total phosphorus (TP), electrical conductivity (EC), and total dissolved solids (TDS), from drainage wastewater to reuse the treated effluent in irrigation practices. The FWT systems were fed drainage tainted water on a weekly basis, and the concentrations and removal efficiency were assessed in the experiments. The average reduction in BOD, COD, TSS, TDS, TN, EC, and TP were 76–86%, 61–80%, 87–95%, 36.6–44.1%, 70–97%, 37–44%, and 83–96%, respectively. ANOVA with Post-HOC t-tests show that the Eichhornia, Pistia stratiotes, and Nymphaea lotus have the highest BOD and COD removal performance, whereas Pistia stratiotes and Nymphaea lotus have the highest TN and TP removal performance. In all cases, the Nymphaea lotus performed well in terms of pollutant removal. In addition, a design procedure for a FWT systems is presented. For wastewater treatment, FWT systems have proven to be a low-cost, long-term option.

Nitrogen removal from summer to winter in a field pilot-scale multistage constructed wetland-pond system

A pilot-scale multistage constructed wetland-pond (MCWP) system with a "pre-ecological oxidation pond, two-stage horizontal subsurface flow constructed wetland (HSCW) and surface flow constructed wetland (SFCW) as the core and postsubmerged plant pond" as the process was used to treat actual polluted river water in the field, and the variation in nitrogen removal from summer to winter was investigated. The results showed that the average total nitrogen (TN) removal efficiency in the MCWP was approximately 40.74%. The significant positive correlation between the daily highest temperature and the TN removal efficiency of the whole system was fitted with a nonlinear curve (R2 = 0.7192). The TN removal load rate in the HSCWs was 2.7–3.7 times that in the SFCW. The SFCW, which had high-density plants (35 plants/m2), increased the proportion of nitrogen removed by plant harvesting and microbial function. The TN transformed by Iris pseudacorus L. accounted for 54.53% in the SFCW. Furthermore, bacteria completed the nitrogen cycle in the SFCW through a variety of nitrogen removal pathways. This research not only investigated the TN removal performance in an MCWP system but also made it possible to predict the TN removal efficiency according to the daily highest temperature from summer to winter in the field.

Simultaneous hydrogen sulfide removal and wastewater purification in a novel alum sludge-based odor-gas aerated biofilter

A novel alum sludge-based odor-gas aerated vertical flow biofilter (Al-OAF) was developed, which aims to removal the pollutants in wastewater and simultaneously to eliminate H2S generated from wastewater treatment facility. Three lab-scale parallel columns were operated in batch model while intermittently aerated with 200 ppm H2S (Al-OAF), air (Al-AF) and unaerated (Al-F, as blank), respectively. The pollutants in wastewater and the effluent H2S concentration from Al-OAF were monitored regularly. Results showed that three columns presented a high removal efficiency (>98%) of total phosphorus (TP) and a completed removal of H2S (100%) in Al-OAF. Al-OAF and Al-AF could enhance the removal efficiency of chemical oxygen demand (COD) of 94.3 ± 3.0, 94.8 ± 1.9%, and total nitrogen (TN) of 86.2 ± 14.2, 91.6 ± 5.4%, respectively. In particular, there was no significant difference regarding the COD, TN removal performances between the “H2S driven” Al-OAF and the “air driven” Al-AF. The H2S removal mechanism lies in the alum sludge ability of H2S adsorption and the reaction by the biofilm in the biofilter. This demonstrates that the novel Al-OAF (aerated with waste gas) would be a promising “wise choice” for intensified biofilter with dual-goals of simultaneous wastewater purification and H2S elimination.

Intensified constructed wetlands for the treatment of municipal wastewater: experimental investigation and kinetic modelling.

This study reports organics and nutrient removal performances of the intensified constructed wetlands, i.e., tidal flow-based microbial fuel cell (MFC) and tidal flow wetlands that received municipal wastewater. The wetland systems were filled with organic (coco peat, biochar) or waste (Jhama brick, steel slag) materials, planted with Phragmites australis or Chrysopogon zizanioides (Vetiver) species, and operated under three flood periods: 8, 16, 24 h. Input ammonia nitrogen (NH3-N), total nitrogen (TN), phosphorus (P), chemical oxygen demand (COD), and biochemical oxygen demand (BOD) load across the wetland systems ranged between 3-27, 12-78, 0.1-23, 36-1130, and 11-281 g/m2day, respectively; mean removal percentages were 60-83, 74-84, 95-100, 94-98, and 93-97%, respectively, throughout the experimental run. The wetland systems achieved similar organics and P removals; operational and media variation did not influence removal kinetics. All wetland systems achieved the highest TN removal (76-87%) when subjected to 24-h flood period. TN removal performances of waste material-based wetlands were comparable to organic media-based systems. Tidal flow-based MFC wetlands achieved better TN removal than tidal flow wetlands because of supplementary electron production through fuel cell-based organics degradation kinetics. Maximum power production rates across the tidal flow-based MFC wetlands ranged between 53 and 57 mW/m2. Monod kinetics-based continuous stirred tank reactor (CSTR) models predicted NH3-N, TN, and COD removals (in wetland systems) more accurately. Kinetic models confirmed the influence of substrate (i.e., pollutant) and environmental parameters on pollutant removal routes.

Effect of calcinated pyrite on simultaneous ammonia, nitrate and phosphorus removal in the BAF system and the Fe2+ regulatory mechanisms: Electron transfer and biofilm properties

To efficiently remove nitrogen and phosphorus from secondary effluent with low values of COD/TN, a novel biological aerated filter (BAF) utilizing calcined pyrite with a large specific surface area (SSA) and pore diameter (PD) was designed to address this challenge. From the perspective of nutrients removal performance, and the corresponding effluent total nitrogen (TN) and PO43--P in the calcined pyrite autotrophic denitrification (CPAD) process decreased from 40.21 to 1.07 mg/L to 1.22 and 0.14 mg/L, respectively. Furthermore, the nutrients removal kinetics analysis showed that the CPAD and pyrite autotrophic denitrification (PAD) processes could be fitted with Half-order and Zero-order reactions via kinetics analysis, respectively, indicating that the TN removal performance of CPAD processes was better than that of the PAD process. Moreover, CPAD combined with sulfur autotrophic denitrification (SAD) processes was fitted by First-order reaction, and the TN removal performance was further enhanced over the CPAD process. From the perspective of microregulation, Fe2+ production in the PAD and CPAD processes could accelerate the electron transfer rate by increasing electron transport system activity (ETSA) and reducing electrochemical impedance spectroscopy (EIS). Moreover, Fe2+ stimulated microbes to produce more proteins (PN) and C10-HSL, which improved biofilm stability and interspecific communication processes. Notably, nitrifiers and autotrophic denitrifiers were simultaneously enriched via detection of high-throughput sequencing of 16 S rRNA genes, which verified the feasibility of simultaneous nitrification and autotrophic denitrification. Therefore, BAF with calcined pyrite and sulfur as composite fillers have a considerable advantage in nutrients removal.

Nitrogen removal and abundances of associated functional genes in rhizosphere and non-rhizosphere of a vertical flow constructed wetland in response to salinity

It investigated the nitrogen removal performance and the abundances of nitrogen functional genes in the rhizosphere and non-rhizosphere when vertical flow constructed wetland (VFCW) was used to treat brackish eutrophic water. The results demonstrated that both total nitrogen (TN) and ammonia nitrogen (NH4-N) removal efficiencies decreased with the salinity increasing from 0.05% to 1.0%. However, the removal efficiency of nitrate nitrogen (NO3-N) remained more than 93%. It was found by quantitative real-time polymerase chain reaction (qPCR) that abundances of amoA, nosZ, napA, nirK and nirS were greater in the rhizosphere than in the non-rhizosphere at the salinities of 0.05%, 0.5% and 1.0%. As the salinity increased, the abundance of amoA reduced. It indicated that the salinity inhibited the growth of ammonia oxidizing bacteria (AOB) and further hindered the nitrification, which resulted in the deterioration of TN removal performance. The abundances of nosZ, napA, nirK and nirS in the rhizosphere and non-rhizosphere were the highest at 1.0% salinity. The denitrifying bacteria might adapt to the salinity stress, which guaranteed high NO3-N removal efficiency.

Simultaneous nitrogen and carbon removal in a packed A/O reactor: effect of C/N ratio on microbial community structure.

In this research, a novel packed anoxic/oxic moving bed biofilm reactor (MBBR) was established to achieve high-organic matter removal rates, despite the carbon/nitrogen (C/N) ratio of 2.7-5.1 in the influent. Simultaneous nitrification-denitrification (SND) was investigated under a long sludge retention time of 104days. The system exhibited excellent performance in pollutant removal, with chemical oxygen demand and total nitrogen (TN) enhanced to 93.6-97.4% and 34.4-60%, respectively. Under low C/N conditions, the nitrogen removal process of A/O MBBR system was mainly achieved by anaerobic denitrification. The increase of C/N ratio enhanced SND rate of the aerobic section, where dissolved oxygen was maintained at the range of 4-6mg/L, and resulted in higher TN removal efficiency. The microbial composition and structures were analyzed utilizing the MiSeq Illumina sequencing technique. High-throughput pyrosequencing results indicated that the dominant microorganisms were Proteobacteria and Bacteroidetes at the phylum level, which contributes to the removal of organics matters. In the aerobic section, abundances of Nitrospirae (1.12-29.33%), Burkholderiales (2.15-21.38%), and Sphingobacteriales (2.92-11.67%) rose with increasing C/N ratio in the influent, this proved that SND did occur in the aerobic zone. As the C/N ratio of influent increased, the SND phenomenon in the aerobic zone of the system is the main mechanism for greatly improving the removal rate of TN in the aerobic section. The C/N ratio in the aerobic zone is not required to be high to exhibit good TN removal performance. When C/NH4+ and C/TN in the aerobic zone were higher than 2.29 and 1.77, respectively, TN removal efficiency was higher than 60%, which means that carbon sources added to the reactor could be saved. This study would be vital for a better understanding of microbial structures within a packed A/O MBBR and the development of cost-efficient strategies for the treatment of low C/N wastewater.

Enhancement of organic matter and total nitrogen removal in a membrane aerated biofilm reactor using PVA-Gel bio-carriers

The Membrane Aerated Biofilm Reactor (MABR) is an attractive alternative for the removal of nitrogen from wastewater because of its ability to overcome the inherent limitations of conventional systems. But in MABR, the denitrification performance is low at low Hydraulic Retention Times (HRT). Therefore, a modified MABR which uses Polyvinyl Alcohol (PVA) gel beads as bio-carriers was used in this study to enhance the Total Nitrogen (TN) removal efficiency when treating domestic wastewater.By adding PVA-Gel in the MABR, the nitrification and TN removal performances increased by 14% and 13.4% respectively. At 12 h HRT and COD/N = 6, it had a maximum TN removal efficiency of 68.63%. The COD removal performance was always above 90.2%. Moreover, in contrast to a conventional MABR, the nitrification rate had an upward trend when the COD/N ratio was increased and/or when the HRT was reduced. Above results concluded that PVA-Gel addition enhanced the MABR performance.

Pilot study of nitrogen removal from landfill leachate by stable nitritation-denitrification based on zeolite biological aerated filter

A pilot (about 1 m3/d) process consisting of pre-denitrification and zeolite biological aerated filter (ZBAF) was established and run for nitrogen removal of landfill leachate. The results showed that stable nitritation and denitrification was achieved for landfill leachate with removal efficiency of Chemical Oxygen Demand (CODCr), ammonium and total nitrogen (TN) of 53.2 ± 3.0%, 93.5 ± 2.4% and 74.7 ± 9.4%, respectively. Based on the ammonium adsorption equilibrium by zeolite, stable free ammonia could be maintained for inhibition of nitrite oxidizing bacteria (NOB) and dominance of ammonia oxidizing bacteria (AOB) in ZBAF, resulting in efficient nitritation with a nitrite accumulation ratio higher than 90.0% and an average nitrite production rate of 1.387 kg NO2−-N m−3 day−1. High-throughput sequencing analysis further revealed enrichment of AOB and elimination of NOB in ZBAF. Compared to two-stage anoxic-oxic process, the pilot-scale process could save approximate 5000 mg/L glucose (about 3.10 US dollar/m3) with almost similar TN removal performance. All results obtained demonstrated the feasibility of the pilot process, which might be highly promising for the nitritation and denitrification of low C/N landfill leachate in the future.

Optimized aeration strategies for nitrogen removal efficiency: application of end gas recirculation aeration in the fixed bed biofilm reactor.

Aeration strategy played an important role in reactor performance. In this study, when superficial upflow air velocity (SAV) decreased from 0.16 to 0.08cms-1, low dissolved oxygen concentration (DO) of 2.0mgL-1 occurred in reactor. The required depth for anoxic microenvironment in biofilm decreased from 902.3 to 525.9μm, which enhanced the growth of denitrifying bacteria and total nitrogen (TN) removal efficiency. However, decreasing aeration intensity resulted in insufficient hydraulic shear stress, which led to weak biofilm matrix structure. Mass biofilm detachment and reactor deterioration then occurred after 87days of operation. An end gas recirculation aeration strategy was proposed to separately manipulate DO and aeration intensity. Low DO and high aeration intensity were simultaneously achieved, which enhanced the metabolism of denitrifying bacteria (such as Flavobacterium sp., Pseudorhodobacter sp., and Dok59 sp.) and EPS-producing bacteria (such as Zoogloea sp. and Rhodobacter sp.). Consequently, high TN removal performance (82.1 ± 2.7%) and stable biofilm structure were achieved.

Nutrient removal from urban stormwater runoff by an up-flow and mixed-flow bioretention system.

Bioretention is one of the most popular technical practices for urban runoff pollution control. However, the efficiency of nutrient removal from urban stormwater runoff by bioretention systems varies significantly. To improve the nutrient removal performance, innovative up-flow and mixed-flow bioretention systems were proposed in this study, and a laboratory study was conducted to investigate the runoff retention and nutrient removal performance. During the leaching experiment using tap water as the inflow, turbidity, chemical oxygen demand (COD), total nitrogen (TN), and total phosphorus (TP) leaching phenomenon was obvious. COD and TN leaching controls were obviously improved when the up-flow and mixed-flow bioretention systems were adopted comparing with the conventional bioretention. During the semi-synthetic runoff experiments, after the leaching experiments' performance (accumulated 2.78 times of empty bed volume), there were no significant differences in COD mass removal efficiencies of conventional and up-flow bioretention processes (p > 0.05); however, the COD mass removal efficiencies of the mixed-flow bioretention processes increased by 10% when compared with conventional bioretention. The TN mass removal efficiencies of the up-flow and mixed-flow bioretention increased obviously from 17% ± 13% (conventional) to 41% ± 23% (up-flow) and 31% ± 16% (mixed-flow). However, there were no significant differences in TP mass removal or runoff reduction among the three bioretention columns (p > 0.05). Both up-flow and mixed-flow bioretention can effectively improve TN mass removal, and the mixed-flow bioretention did not show a better TN removal performance than the up-flow bioretention because these two bioretention had almost the same volume of the saturated zone. Overall, the results indicate the mixed-flow bioretention proposed in this study can effectively improve TN mass removal and slightly improve COD mass removal relative to conventional methods via increases in hydraulic retention time and in-flow paths, respectively.

Evaluation of Pilot-Scale Constructed Wetlands with Phragmites karka for Phytoremediation of Municipal Wastewater and Biomass Production in Ethiopia

A pilot horizontal subsurface flow constructed wetland (HSSFCW) was constructed, covered with geomembrane, and packed with gravel as substrate. Phragmites karka was planted in one cell and the other cell was left unplanted. The experiment was carried out over a 3-year period at two hydraulic loading rates (HLRs): 0.025 m/d and 0.05 m/d. The aim of the study was to evaluate the phytoremediation and biomass production potential of Phragmites karka for municipal wastewater treatment to remove chemical oxygen demand (COD), total nitrogen (TN), and total phosphorus (TP). The highest average COD, TN, and TP removal performances attained were 94.1%, 97.3%, and 89.9%, respectively, at HLR of 0.025 m/d, and 90.4%, 86.8%, and 88.5%, respectively, at HLR of 0.05 m/d. COD, TN, and TP removal performances were considerably higher in the planted HSSFCW than in the unplanted (p < 0.05). The study found: a progressive increase in plant density, from 3 ± 1 to 113 ± 43 shoots per m2; an increase in plant height (erect), from 8 to 365 cm; and growth of the running stem of P. karka (stolon) to 16 m after 16 months. The maximum nutrient content and nutrient accumulation of the above-ground biomass of P. karka recorded were 78.7 gN/kg DW and 21.6 gP/kg DW, and 2014.7 gN/m2 and 550.4 gP/m2 throughout the experimental period. The findings from the experiments showed the successful performance of the HSSFCW cell planted with P. karka for the treatment of municipal wastewater. P. karka demonstrated high biomass production and high nutrient removal performance. We conclude that scaling up this pilot HSSFCW has great potential for treating municipal wastewater in Ethiopia and other low-income countries with similar climatic conditions.

Fe(II)-dosed ceramic membrane bioreactor for wastewater treatment: Nutrient removal, microbial community and membrane fouling analysis

Ferrous dosing is used to reduce phosphorus concentration and alleviate polymeric membrane fouling in membrane bioreactor (MBR). However, limited studies have been conducted to investigate the impacts of ferrous dosing on ceramic membrane fouling, nutrient removal efficiency and microbial community. Accordingly, the aim of this study was to investigate the effect of intermittent ferrous dosing with Fe/P molar ratios of 2 and 1 (with a dosing frequency of every two days) on the overall nutrient removal, functional microbial changes and membrane fouling in ceramic membrane bioreactors (CMBR) in treatment of wastewater. TP concentration of 10 mg/L in influent decreased to 1.94 ± 0.62 mg/L (control), 0.38 ± 0.22 mg/L (Fe/P = 1) and 0.31 ± 0.18 mg/L (Fe/P = 2) in the effluent, respectively. Meanwhile, the effluent total nitrogen (TN) concentrations with Fe/P = 1 treatment (6.80 ± 2.02 mg/L) and Fe/P = 2 treatment (5.12 ± 2.28 mg/L) were lower than that of the control (7.72 ± 2.36 mg/L). Compared to Fe/P = 1, the TN removal performance was better for Fe/P = 2 mainly due to the increased abundance of denitrifying bacteria (Zoogloea and Acinetobacter). In addition, excess iron dose might have toxic effects on bacterial physiology, however the Fe concentrations that cause cell damage vary for different bacteria. The relative abundance of Zoogloea (aerobic denitrifying bacteria) continuously increased with ferrous addition (Fe/P = 2), while other bacteria including Dechloromonas, Hyphomicrobium and Thauera (anoxic denitrifying bacteria), Nitrospira (nitrifying bacteria) and Candidatus Accumulibacter (phosphorus accumulating organism) decreased sharply. Furthermore, membrane fouling was effectively moderated by ferrous dosing and Fe/P = 1 treatment showed improved membrane fouling mitigation than Fe/P = 2. Overall, intermittent ferrous addition in CMBR with Fe/P molar ratio of 1 was beneficial to the removal of nutrients (TP, TN and organics), enhanced succession of microbial community and membrane fouling mitigation.

Investigation of rapid granulation in SBRs treating aniline-rich wastewater with different aniline loading rates

In this work, aerobic granules were cultivated in two reactors which were denoted as RL and RH under 0.6 and 1.8 kg m−3 d−1 of aniline loading rates, respectively. The aerobic granular sludge (AGS) in the two sequential batch reactors for treating aniline-rich wastewater was compared. The results showed that the AGS could be rapidly formed with sludge volume index below 30 mL g−1. The AGS in RL had more filamentous bacteria than that in RH by microstructural observations while the secretion of protein in extracellular polymeric substances was improved in RH and in turn increased relative hydrophobicity of AGS. Within 4-h cycle, the excellent removal of aniline and chemical oxygen demand (COD) were achieved in the two reactors. The removal efficiencies of aniline and COD were consistently over 99.7%, 89.6%, respectively in RL and 98.6%, 86.6%, respectively in RH. As for nitrogen removal, NH4+-N released from aniline biodegradation could also be reduced efficiently via nitrification and no nitrite accumulation occurred in both the reactors. Total nitrogen removal performance in RH was better, due to a more compact structure of AGS. The investigation of microbial community succession by pyrosequencing showed that the diversity of microorganisms decreased when AGS was developed. Proteobacteria especially Gammaproteobacteria significantly increased during aerobic granulation in both reactors. It was also found that the relative abundance of Actinobacteria was higher in RH than that in RL. Furthermore, the strains responsible for aniline biodegradation, nitrification, denitrification, and phosphorous accumulation were detected in the systems.

Nitrogen removal performance and microbial community of an enhanced multistage A/O biofilm reactor treating low-strength domestic wastewater.

The low-strength domestic wastewater (LSDW) treatment with low chemical oxygen demand (COD) has drawn extensive attention for the poor total nitrogen (TN) removal performance. In the present study, an enhanced multistage anoxic/oxic (A/O) biofilm reactor was designed to improve the TN removal performance of the LSDW treatment. Efficient nitrifying and denitrifying biofilm carriers were cultivated and then filled into the enhanced biofilm reactor as the sole microbial source. Step-feed strategy and internal recycle were adopted to optimize the substrate distribution and the organics utilization. Key operational parameters were optimized to obtain the best nitrogen and organics removal efficiencies. A hydraulic retention time of 8h, an influent distribution ratio of 2:1 and an internal recycle ratio of 200% were tested as the optimum parameters. The ammonium, TN and COD removal efficiencies under the optimal operational parameters separately achieved 99.75 ± 0.21, 59.51 ± 1.95 and 85.06 ± 0.79% with an organic loading rate at around 0.36kg COD/m3d. The high-throughput sequencing technology confirmed that nitrifying and denitrifying biofilm could maintain functional bacteria in the system during long-period operation. Proteobacteria and Bacteroidetes were the dominant phyla in all the nitrifying and denitrifying biofilm samples. Nitrosomonadaceae_uncultured and Nitrospira sp. stably existed in nitrifying biofilm as the main nitrifiers, while several heterotrophic genera, such as Thauera sp. and Flavobacterium sp., acted as potential genera responsible for TN removal in denitrifying biofilm. These findings suggested that the enhanced biofilm reactor could be a promising route for the treatment of LSDW with a low COD level.

Sustainable operation of submerged Anammox membrane bioreactor with recycling biogas sparging for alleviating membrane fouling

A submerged anaerobic ammonium oxidizing (Anammox) membrane bioreactor with recycling biogas sparging for alleviating membrane fouling has been successfully operated for 100d. Based on the batch tests, a recycling biogas sparging rate at 0.2m3h−1 was fixed as an ultimate value for the sustainable operation. The mixed liquor volatile suspended solid (VSS) of the inoculum for the long operation was around 3000mgL−1. With recycling biogas sparging rate increasing stepwise from 0 to 0.2m3h−1, the reactor reached an influent total nitrogen (TN) up to 1.7gL−1, a stable TN removal efficiency of 83% and a maximum specific Anammox activity (SAA) of 0.56kg TNkg−1 VSSd−1. With recycling biogas sparging rate at 0.2 m3 h−1 (corresponding to an aeration intensity of 118m3m−2h−1), the membrane operation circle could prolong by around 20 times compared to that without gas sparging. Furthermore, mechanism of membrane fouling was proposed. And with recycling biogas sparging, the VSS and EPS content increasing rate in cake layer were far less than the ones without biogas sparging. The TN removal performance and sustainable membrane operation of this system showed the appealing potential of the submerged Anammox MBR with recycling biogas sparging in treating high-strength nitrogen-containing wastewaters.