Average Removal Rate Research Articles

Existent state and removal rate of silver in lead-silver slag during the melt-vaporization process

In this paper, Ag containing in lead-silver slag was recovered during the melt-vaporization process, the existent state of Ag in soot was analyzed, the influence of reaction temperature, the carbon ratio, and reaction time on the removal rate of silver was explored, and process conditions were optimized by using the response surface methodology. Silver chloride, silver metal, silver sulfide, silver oxide, and silver sulfate are the main silver phases in the lead-silver slag, among which silver chloride and silver sulfide are major phases. The silver oxide (Ag2O) and silver chloride (AgCl) in the lead-silver slag volatilize into soot, the silver sulfide (Ag2S) is oxidized by oxygen to form silver sulfate (Ag2SO4), and elemental silver volatilizes with Pb and Zn to form alloys. The silver in the final exists as Ag, AgCl, Ag2O and Ag2SO4 in the soot. The removal rate of silver increases gradually with increasing reaction temperature and tends to remain stable at 1300?C. With a gradual increase in the carbon ratio, the removal rate of silver first increases and then decreases, and the highest value is 80.12 wt% when the carbon ratio is 16.30 wt%. With increasing holding time, the removal rate of silver increases gradually and then stabilizes about 79.97 wt% even at the holding time of 150 min. The optimum process conditions for silver removal are a reaction temperature of 1340?C, a carbon ratio of 16.10 wt%, and a holding time of 165 min, and the average removal rate of silver under these conditions is 80.42 wt%. The research in this paper lays a theoretical foundation for the removal and utilization of silver from lead and silver residue.

Degradation of Dye Wastewater by a Novel mBT-MPR Visible Light Photocatalytic System

The high efficiency and low consumption green wastewater treatment technology has important practical significance for the recycling of printing and dyeing wastewater. The efficiency of visible light catalytic degradation of organics is greatly affected by the performance of the catalyst and the photo reactor. Therefore, Bi2WO6/TiO2/Fe3O4 (mBT) visible light photocatalyst was accurately prepared by the ammonia iron double drop method. In order to improve the photodegradation efficiency, a tubular magnetic field-controlled photocatalytic reactor (MPR) was developed. The novel mBT-MPR visible light photocatalytic system was proposed to treat RhB simulated wastewater. The experimental results showed that when the dosage of mBT catalyst was 1 g/L and visible light was irradiated for 60 min, the average removal rate of rhodamine B (RhB) with initial an concentration of 10 mg/L in the simulated wastewater for four times was 91.7%. The mBT-MPR visible light photocatalysis system is a green and efficient treatment technology for organic pollutants in water with simple operation, low energy consumption, and no need for catalyst separation.

The control efficiency and mechanism of heavy metals by permeable pavement system in runoff based on enhanced infiltration materials

As one of the commonly used stormwater management measures, permeable pavement system (PPS) played a prominent role in controlling runoff pollution and alleviating urban waterlogging. In this study, new enhanced infiltration materials (construction waste brick, coal gangue, activated carbon, multi-walled carbon nanotube, multi-layer graphene) were applied in PPS and the control efficiency and mechanism of typical heavy metals (HMs, Mn2+, Pb2+, Zn2+, Cu2+, Cd2+, Ni2+) was investigated in runoff. Furthermore, the influences of different rainfall intensities and antecedent dry periods on HMs removal by PPS were evaluated. The results showed that all PPS with enhanced infiltration materials have little leaching effect on HMs (＜3 μg/L). All the selected enhanced infiltration materials meet the requirements of PPS. The concentration of HMs in the effluent of PPS dropped sharply first, followed rebounded and then maintained at a stable range. Activated carbon PPS (AC), Multi-walled carbon nanotube PPS (MCN), and Multi-layer graphene PPS (MG) could significantly improve the control effect of PPS on nearly all selected HMs. The average removal rates of AC, MCN and MG for six HMs were 75.48%–99.35%, 81.30%–97.59%, and 73.03%–99.33%, respectively. Compared with Traditional PPS (TR), the effluent concentrations of HMs in construction waste brick PPS (CW) and coal gangue PPS (CG) were relatively higher and unstable. AC, CN and MG could adapt to different rainfall conditions and the maximum removal rates of most HMs exceed to 99%. With antecedent dry periods increased, the control effect of HMs was significantly improved. The influences of the antecedent drying period on HMs removal followed as: CW＞CG＞TR＞MG＞CN＞AC. This study provided novel methods to eliminating HMs in runoff and provides implications for the design of PPS.

Low-concentration methanol effect on the microorganisms, nitrogen removal, and recovery of the completely autotrophic nitrogen removal over nitrite.

Methanol has a significant effect on the performance of the completely autotrophic nitrogen removal over the nitrite (CANON) process. In this research, the effect of low-concentration methanol on the functional microorganisms and nitrogen removal and recovery in the CANON system is investigated. The result shows that the anaerobic ammonium-oxidizing bacteria (AnAOB) was suppressed with low-concentration methanol addition, and the phylum Planctomycetes was hidden. The genus Candidatus Brocadia was restrained, and the relative abundances reduced from 25.5 to 15.0% in the upper biofilm and from 20.3 to 14.3% in the bottom biofilm, respectively. However, low-concentration methanol promoted the nitrifying oxidizing bacteria (NOB) activity. This phenomenon reduced the average ammonium nitrogen removal rate from 95.0 to 70.7%, and the average total nitrogen removal rate decreased from 81.3 to 43.6%, respectively. The results demonstrated that the low-concentration methanol as an organic carbon matter harmed the CANON process. Fortunately, the CANON system had an excellent self-healing ability when the methanol was stopped, with the average ammonium nitrogen removal rate and total nitrogen removal rate returning to 95.5 and 80.9%, respectively. This research supplies a reference for practical engineering design and application by improving the understanding of the effects of low-concentration methanol on CANON process performance.

The Effect of Up-Flow Rate on the Nitrogen Treatment Efficiency and Sludge Characteristics of ANAMMOX Process with Up-Flow Anaerobic Sludge Bed Reactor

Anaerobic ammonia oxidation (ANAMMOX) technology is a novel biological nitrogen removal technology with potential applications for the treatment of nitrogenous wastewater treatment prospects. Most of the literature explores the growth environment of anaerobic ammonia-oxidizing bacteria and total nitrogen removal efficiency but the influence of reactor operating conditions (such as up-flow rate) on the treatment efficiency and sludge growth property of anaerobic ammonia-oxidizing bacteria is rarely discussed. Therefore, the purpose of this study is to discuss the effect of up-flow rate on the treatment efficiency and sludge property of the anaerobic ammonia oxidation treatment procedure adopting up-flow anaerobic sludge bed (UASB) as a reactor. The results show that up-flow rate has a significant effect on sludge concentration and sludge growth rate. The highest sludge concentration and maximum sludge growth rate could be obtained at the up-flow rate of 3.21 m/h. According to the analysis results of the sludge concentration, we speculate that when the flow rate was lower than 3.21 m/h, the sludge particles did not easily collide with each other to produce a larger sludge floc. On the contrary, when the up-flow rate was higher than 3.21 m/h, the larger sludge floc could be decomposed by the shear force. The sludge concentration was reduced by these two reasons. On the other hand, the average total nitrogen volume removal rates in test runs 1 through to 4 were 0.18 g-N/m3/d, 0.19 g-N/m3/d, 0.20 g-N/m3/d and 0.20 g-N/m3/d at up-flow rates from 1.95 m/h to 3.70 m/h, respectively. Therefore, the treatment efficiency was not affected by the up-flow rate in these operating conditions.

Nanostructured Gallium Nitride Membrane at Wafer Scale for Photo(Electro)catalytic Polluted Water Remediation.

Photo(electro)catalysis methods have drawn significant attention for efficient, energy-saving, and environmental-friendly organic contaminant degradation in wastewater. However, conventional oxide-based powder photocatalysts are limited to UV-light absorption and are unfavorable in the subsequent postseparation process. In this paper, a large-area crystalline-semiconductor nitride membrane with a distinct nanoporous surface is fabricated, which can be scaled up to a full wafer and easily retrieved after photodegradation. The unique nanoporous surface enhances broadband light absorption, provides abundant reactive sites, and promotes the dye-molecule reaction with adsorbed hydroxyl radicals on the surface. The superior electric contact between the nickel bottom layer and nitride membrane facilitates swift charge carrier transportation. In laboratory tests, the nanostructure membrane can degrade 93% of the dye in 6 h under illumination with a small applied bias (0.5V vs Ag/AgCl). Furthermore, a 2 inch diameter wafer-scale membrane is deployed in a rooftop test under natural sunlight. The membrane operates stably for seven cycles (over 50 h) with an outstanding dye degradation efficiency (>92%) and satisfied average total organic carbon removal rate (≈50%) in each cycle. This demonstration thus opens the pathway toward the production of nanostructured semiconductor layers for large-scale and practical wastewater treatment using natural sunlight.

Enhanced treatment effect and universality of novel ARAO coupling process on municipal sewage: A pilot study

Under the impending demand of wastewater treatment plants (WWTPs) upgrading and reconstruction, it is feasible to propose a new process with low cost and high efficiency based on traditional process. Novel anaerobic-RBC-anoxic-oxic (ARAO) process was obtained after coupling traditional anaerobic-anoxic-oxic (A2/O) process with rotating biological contactor (RBC). Compared to traditional A2/O process, ARAO process has more efficient municipal wastewater treatment effect. Within 40 days of continuous operation, the average removal rates of COD, NH4+-N, TN and TP of sewage by ARAO process are 87%, 87%, 75% and 87%, respectively. The optimal operating conditions of ARAO process are the mixed liquor reflux ratio (MLRR) of 200%, the mixed liquor suspended solids (MLSS) of 3500–4500 mg/L, the dissolved oxygen (DO) concentration of 2–3 mg/L and the hydraulic retention time (HRT) of 6 h. The enhanced enzyme activity of ARAO process compared with A2O was determined through extracellular enzyme activity (EEA) and extracellular polymeric substances (EPS), and the microbial abundance and dominant species were further analyzed through high-throughput sequencing. The three-dimensional fluorescence measurement results showed a significant improvement in wastewater treatment efficiency. In addition, ARAO process has good adaptability to low temperature wastewater, low concentration wastewater and high concentration wastewater, which provides a good reference for the upgrading and reconstruction of WWTPs in the future.

Mechanism of HMBR in Reducing Membrane Fouling under Different SRT: Effect of Sludge Load on Microbial Properties.

Extracellular polymeric substances (EPS) are the main causative agents of membrane fouling, and the use of a hybrid membrane bioreactor (HMBR) can mitigate this by reducing the EPS content. Four bench scale sets of HMBRs were used simultaneously to treat domestic wastewater. The effect of sludge retention times (SRT) on membrane fouling in HMBRs and the underlying mechanism were investigated by comparing and analyzing the changes in sludge load, microbial characteristics, EPS distribution characteristics, and transmembrane pressure under different SRTs. Results revealed that, among the four SRTs (10 d, 20 d, 30 d, and 60 d), the best removal rates of chemical oxygen demand and total nitrogen were observed for an SRT of 30 d, with average removal rates of 95.0% and 57.1%, respectively. The best results for ammonia nitrogen and total phosphorus removal were observed at an SRT of 20 d, with average removal rates of 84.3% and 99.5%, respectively. SRT can affect sludge load by altering the biomass, which significantly impacts the microbial communities. The highest microbial diversity was observed at an SRT of 30 d (with a BOD sludge load of 0.0310 kg/kg∙d), with Sphingobacteriales exhibiting the highest relative abundance at 19.6%. At this SRT setting, the microorganisms produced the least amount of soluble EPS and loosely bond EPS by metabolism, 3.41 mg/g and 4.52 mg/g, respectively. Owing to the reduced EPS content, membrane fouling was effectively controlled and the membrane module working cycle was effectively enhanced up to 99 d, the longest duration among the four SRTs.

Iron-containing carriers stimulate nitrogen conversions in one-stage reactors treating N-rich digester supernatant

Iron incorporation in biomass carriers (0%, 1%, 5%, and 10% of carrier weight) at nitrogen loading rates (NLR) from 0.08 to 0.30 g/(g MLVSS·d) was tested during the treatment of nitrogen-rich digester supernatant in one-stage reactors, in which hybrid biomass (suspended/attached) was inhabited by ammonia-oxidizing bacteria, Anammox bacteria, and denitrifiers. The Anammox process dominated at the highest NLR and increased the volumetric nitrogen removal rate to about 500 g/(m3·d). Total microbial composition was most strongly affected by NLR, however, Anammox bacteria abundance was also affected by the iron content. These bacteria predominated in reactors with 5%-iron carriers, which ensured the highest nitrogen removal efficiency (up to 75%) and kinetics: the average ammonium removal rate was at least 40% higher than in the reactor without iron. The presence of 10%-iron carriers in the reactor inhibited the ammonium oxidation rate; an increase in ammonium removal rate with increasing initial ammonium concentration was the lowest. The contribution of Anammox to nitrogen removal was demonstrated by the simultaneous increase in biomass heme c content to about 0.1 µmol/mg protein along with increasing iron content to 5% and NLR. The incorporation of iron into the carrier structure allowed for a long-term release of mostly ferrous iron to the supernatant, thus accelerating its treatment.

Experimental investigation of effective parameters on productivity improvement of the EDM process for corrosion-resistant metals

Inconel 625 superalloy and stainless steel 304 are known for their significant corrosion resistance along with their high hardness and strength. Therefore, they are used in a wide range of industries, including oil and gas and nuclear. Electrical discharge machining is among the most widely used processes for machining of these metals. However, this process has limitations, such as low material removal efficiency, high surface roughness, and the formation of a recast layer. Therefore, in this study, the effective parameters on increasing the material removal efficiency and reducing recast layer thickness are investigated. These parameters include the dielectric fluid, electrode material, discharge current, and pulse duration. After performing the test matrix, the effect of each of the input parameters on the material removal rate, surface roughness, and thickness of the recast layer is evaluated using the ANOVA method. The results of this analysis showed that the type of dielectric fluid and the presence of silver oxide nanoparticles have a significant effect on output variables. When using sunflower oil fluid containing nanoparticles and the silver electrode, the recast layer and surface roughness are reduced, while the average material removal rate increases by 40% compared to the traditional mode. Also, due to the biodegradability of deionized water and sunflower oil fluids, the environmental sustainability of the process in this study is increased and while increasing productivity, it leads to the sustainable development of the EDM process.

Optimization of EDM Machinability of Hastelloy C22 Super Alloys

In this study, machinability tests were carried out on a corrosion-resistant superalloy subjected to shallow (SCT) and deep cryogenic treatment (DCT) via electrical discharge machining (EDM), and the effect of the cryogenic treatment types applied to the material on the EDM processing performance was investigated. Experimental parameters, including pulse-on time (300, 400 and 500 μs), peak current (A) (6 and 10 A) and material types (untreated and treated with SCT and DCT), were used to construct the full factorial experimental design. The resulting average surface roughness (Ra) and material removal rate (MRR) results were optimized using the Taguchi L18 method. According to the Taguchi-based gray relational analysis, the optimal parameters for both Ra and MRR were determined as cryogenic treatment, pulse-on time and peak current, respectively. The response table obtained using the Taguchi method showed the most effective factors as A1BlC3 for Ra and A2B2C1 for MRR values. According to the ANOVA results for determining parameters affecting performance, peak current was the most effective factor for average surface roughness and MRR, at 74.79% and 86.43%, respectively. When examined in terms of Taguchi-gray relational degrees, the optimal parameters for both Ra and MRR were observed in the experiment performed with the SCT sample at a peak current of 6 A and 300 μs pulse-on time.

Long-term assessment of the nutrient recovery capacity and biomass productivity of Scenedesmus almeriensis in raceway reactors using unprocessed urban wastewater

The present work aims to assess the treatment of unprocessed urban wastewater using the microalga Scenedesmus almeriensis. Two 12 m3 raceway reactors, one supplemented by wastewater and the second by chemical fertilizer, operating outdoors in a semi-continuous mode, were used for eight months. Results suggested that S. almeriensis can be produced in wastewater without affecting the photosynthetic apparatus reaching a productivity of 13 g·m−2·day−1 on average in both the systems. Furthermore, the nutrient content in terms of nitrogen, phosphorous and chemical oxygen demand of the wastewater was reduced under the European limitations during most of the period, with an average removal rate of 2.2, 0.2 and 3.0 g·m−2·day−1 respectively. Therefore, raceways demonstrated a high potential for microalgal production and successful biotreatment, proving robust and reliable. Finally, the effect of environmental conditions on biomass productivity of the clean system was evaluated in a model with high accuracy (R2 = 0.9, p = 0.0002).

Constant carbon dosing of a pilot-scale denitrifying bioreactor to improve nitrate removal from agricultural tile drainage

Denitrifying bioreactors are effective tools for removing nitrate from agricultural drainage water. However, as woodchips age with time, a shortage of labile carbon supply limits nitrate removal by microbial denitrification when high nitrate pulses occur in drainage waters. In this study, we investigated the potential of methanol dosing at a constant rate to increase nitrate removal rates in a 58 m3 pilot-scale bioreactor (25 m3 saturated volume) installed on a dairy farm for two consecutive drainage seasons. The drainage water in the bioreactor had a mean hydraulic retention time (HRT) of 12.7 days and 13.5 days in the 2020 and 2021 drainage seasons. With 14.4 L of methanol solution (8% v/v) added per day, the seasonal nitrate removal rates were 8.6 g N m−3 d−1 in 2020 and 5.1 g N m−3 d−1 in 2021 when the methanol dosing rate was halved. Both rates (2020 and 2021) were enhanced as compared to seasonal rates of 0.67–1.60 g N m−3 d−1 in previous years (2017 and 2018) when the bioreactor was not dosed. When there were very large pulses of nitrate into the bioreactor, which exhausted added methanol, nitrate was observed at concentrations above limiting ranges (> 3 mg N L−1) at the outlet on several occasions in 2021. Cumulative nitrate load reductions of 1859 g N and 1620 g N occurred in 2020 and 2021, respectively, resulting in overall nitrate removal efficiencies of 85 and 73%, respectively.Methanol concentrations decreased by order of magnitude along the bioreactor length, from mean inlet concentrations of 327 mg CH3OH-C L−1 in 2020 (higher dosing rate) to concentrations of <50 mg CH3OH-C L−1 at the outlet. The mean methanol removal rates of 106 g CH3OH-C m−3 d−1 in 2020 and 109 g CH3OH-C m−3 d−1 in 2021. A 90% (2020) and 100% (2021) overall methanol removal efficiency was calculated. With methanol dosing, sulfate removal occurred in the bioreactor, with an average sulfate removal rate of 8.5 g SO42−-S m−3 d−1 in 2020 and 0.5 g SO42−-S m−3 d−1 in 2021. This work demonstrated that methanol additions to bioreactors could enhance denitrification rates even when nitrate was limiting without considerable losses of methanol being released to the receiving waters.

Revealing the behavior of perfluorooctane sulfonic acid in an aerobic granular sludge system: Fate and impact

The biogeochemistry (i.e., migration and transformation) and impacts of perfluorooctane sulfonic acid (PFOS) in an aerobic granular sludge (AGS) system have been studied. The results suggested that PFOS removal rates under 0.1, 0.5 and 5.0 mg/L PFOS treatment were 89.23 ± 0.92 %, 71.92 ± 1.45 % and 48.15 ± 1.90 %, respectively, which was mainly attributed to the adsorption mechanism involving electrostatic, hydrophobic and ionic bridging interactions. Meanwhile, the adsorbed PFOS deteriorated sludge flocculation. Compared with the control, 0.1 mg/L PFOS treatment increased the concentration of effluent suspended solids (ESS) from 70 ± 5 to 238 ± 15 mg/L. Interestingly, the denitrification performance of the AGS improved (i.e., total nitrogen (TN) average removal rate increased from 87.05 ± 0.21 % to 96.56 ± 0.05 %), which was contrary to the outcomes for activated sludge. Further analysis showed that PFOS reduced the percentage of norank_f_norank_o_Ardenticatenales, norank_f_Sphingomonadaceae and Candidatus_Competibacter maintaining the particle stability, which led to the decrease in AGS flocculation. In addition, the relative abundance of nitrite-oxidizing bacteria Nitrospira decreased under PFOS exposure, while the total abundance of denitrifying bacteria (mainly Dechloromonas) increased. This might enhance the short-cut nitrification and denitrification capacity of the AGS system and promote the removal of TN. However, PFOS had no obvious impact on the settleability of AGS and the transformation of chemical oxygen demand (COD) and soluble phosphorus (SOP). Our findings will provide theoretical insights and practical support for risk control in the process of treating fluoride-containing wastewater.

Long-term variation characteristics of nutrients in the water and sediments of a surface flow constructed wetland with micro-polluted water sources

This study aimed to evaluate the long-term effects of a large-scale constructed wetland purifying micro-polluted water and explore accumulation characteristics and influencing factors of nutrients in sediments. For this purpose, the water quality and nutrients in sediments of the long-running large-scale constructed wetland of Yanlong Lake were monitored for eight years since the wetland began operation. The results demonstrated that the average removal rates of permanganate index (CODMn), ammonia nitrogen (NH4+-N), total nitrogen (TN) and total phosphorus (TP) were 4.39 ± 12.64%, 41.57 ± 16.36%, 32.61 ± 23.36% and 47.05 ± 20.39% in the constructed wetland from 2013 to 2020, respectively. The CODMn removal effects were the lowest. Sediments of the constructed wetland were moderately polluted and the cumulative level of nutrients was mainly affected by the organic matter content, influent water quality, water depth and plant function. Firstly, TN and TP in sediments are significantly positively correlated with total organic carbon. Besides, the nutrient concentrations in sediments increased along the water flow direction. Furthermore, the nutrient concentrations in sediments increased with water depth, and the carbon was greatly affected. In addition, the overgrowth and lodging of wetland plants could promote the nutrients accumulation in sediments. This research results provide a scientific basis for improving the purification capacity of long-running surface flow constructed wetlands.

Purification effects of recycled aggregates from construction waste as constructed wetland filler

Three groups of constructed wetlands based on gravel (#1), asphalt concrete + red brick (#2), and red brick (#3) were constructed to explore their purification effects and the characteristics of microbial community structure. The results show that the construction waste recycled aggregates have little leaching risk of heavy metals; the adsorption of nitrogen and phosphorus by the three fillers could be well fitted by pseudo-first-order and pseudo-second-order kinetic models (R2 > 0.96); the adsorption of NH4+-N by the three fillers could be well fitted by the Freundlich model (R2 > 0.656); the adsorption of phosphorus could be well fitted by the Langmuir and Freundlich models, except for gravel (R2 > 0.875). The average removal rate of COD, NH4+-N, TN, and TP was 60.85 %, 94.69 %, 73.42 %, 39.12 % (#1); 67.32 %, 20.31 %, 22.26 %, 27.81 % (#2); 67.35 %, 17.7 %, 25.8 % and 46.98 % (#3). There was no significant difference in the purification effect of the three fillers on COD. The adsorption effect on NH4+-N was: gravel > red brick/asphalt concrete, and the adsorption effect on TP was: asphalt concrete > red brick > gravel. The microbial population richness of the upper filler was #2 > #1 > #3, the uniformity was #1 > #2 > #3, and the diversity was #1/#2 > #3. The microbial communities were dominated by Proteobacteria, Actinobacteriota, Bacteroidota and Chloroflexi.

Fabrication of micro-hole using novel Maglev EDM

In the current scenario, micro-manufacturing through the electro-discharge machining (EDM) process is a prominent technique for achieving desired complex micro/nano-features of any product. The precision and accuracy of producing features are the prerequisites of micro-machining. The current work aims to check the feasibility of the novel Maglev EDM for fabricating micro-holes on a thin nickel sheet (thickness = 500 μm). The study presents the viability of the newly developed system by comparing it with the conventional EDM process. A pure direct current power supply is assembled with a magnetic levitation-based gap monitoring mechanism to overcome the setbacks of conventional EDM. The novel setup utilizes the combined effect of the permanent electromagnet to diminish arcing and short-circuiting. The control parameters for the operation were 12 V open-circuit voltage and 2 A peak current while maintaining a duty factor of 95.564 percent. The measured discharge voltage and discharge current were 6.64 V and 900 mA, respectively. Tungsten rod (ø 650 μm) and deionized water were used as a tool and a dielectric medium, respectively, for the experiment. Further, the machined micro-hole and micro-tool analysis have been carried out using high-resolution microscopy, scanning electron microscopy and energy dispersive spectroscopy reports. The newly developed Maglev EDM’s feasibility to produce micro-holes on conductive materials has been confirmed in the present work with an average material removal rate of 40 μg/min.

Effects of sponge iron dosage on nitrogen removal performance and microbial community structure in sequencing batch reactors

The application of sponge iron (SI) carriers can improve the biochemical treatment performance of sequencing batch reactors (SBR) during wastewater treatment. This study used SBR reactors to explore the effects of SI dosage on the nitrogen removal performance and reactor stability and microbial community structure under low temperature and ultra-low load. In contrast to conventional SBR, the average removal rate of total nitrogen (TN) in the biological sponge iron system (BSIS) was increased by 5.38 % for 45 g/L, 18.93 % for 90 g/L, and 13.52 % for 135 g/L, respectively. The nitrogen removal performance and reactor stability showed the best performance under the SI dosage of 90 g/L. The addition of SI formed the anaerobic-anoxic-aerobic microenvironments, which facilitate the propagation of denitrifying bacteria (Saccharimonadales, Hydrogenophaga) and iron bacteria (Rhodoferax and Acinetobacter) in the BSIS. This study provides a new insight on the application of SI in the wastewater treatment.

Bacterial Community Structure and Antibiotic Resistance Gene Changes in IFAS+Magnetic Coagulation Process Wastewater Treatment Plant in Cold Regions

The main objective of this study was to explore the changes in bacterial communities and antibiotic resistance genes (ARGs) in an integrated fixed-film activated sludge (IFAS)+magnetic coagulation process wastewater treatment plant (WWTP) in Xinjiang. The bacterial communities and ARGs in the influent, suspended activated sludge, attached biofilm, and effluent were studied using 16S rRNA gene sequencing and metagenomic sequencing. The results showed that the average relative abundances of Chloroflexi and Nitrospirae in activated sludge were 3.50% and 0.03%, respectively, and their relative abundances in biofilm reached 10.02% and 2.12%, respectively. The average removal rates of NH4+-N and TN increased from 91.89% and 66.76% to 97.71% and 91.90% after the reformation of this wastewater treatment plant, respectively, indicating that IFAS enhanced the biological nitrogen removal capacity of wastewater treatment plants in cold regions. The average relative abundances of Ferruginibacter and Rhodoferax related to iron redox in the biological treatment section were 5.24% and 3.72%, respectively, and the relative abundance of Rhodoferax in effluent reached 9.48%, indicating that the magnetic powder had an impact on the bacterial community. The IFAS wastewater treatment plant had an obvious removal effect on ARGs, and the relative abundance of ARGs decreased from 191.08×10-3‰ in the influent to 32.58×10-3‰ in the effluent. The relative abundance of ARGs in activated sludge was 63.25×10-3‰-72.38×10-3‰, which was significantly higher than 41.31×10-3‰ in biofilm. However, the relative abundances of dominant subtypes of ARGs such as sul2, floR, and rpoB2 in biofilm were 5.77×10-3‰, 2.52×10-3‰, and 2.03×10-3‰, respectively, which were higher than the 3.15×10-3‰-3.57×10-3‰, 1.73×10-3‰-2.24×10-3‰, and 1.28×10-3‰-1.76×10-3‰ in activated sludge. The network analysis indicated that Caldilineaceae_norank and Trichococcus were respectively positively correlated with sul2 and floR. These results can provide theoretical reference for the optimal operation and ARGs control of WWTPs in cold regions.

Enhanced nitrate removal and side effects of methanol dosing in denitrifying bioreactors

The nitrate removal efficiency of denitrifying bioreactors decreases when the carbon supply from woodchips is insufficient, particularly during large nitrate pulses. This study aimed to assess the effects of methanol dosing, as an external carbon source, on nitrate removal rates in mesocosm-scale bioreactors while monitoring the secondary effects of dosing that may occur. A secondary goal was to quantify sulfate reduction rates and methanol consumption in the presence and absence of nitrate to aid in determining the dosing load to minimize undesirable effects such as methanol entering receiving waters and minimizing sulfate reduction. We continuously dosed the bioreactors with nitrate (∼20 mg NO3−-N L−1), methanol (∼35 mg CH3OH-C L−1), and sulfate (∼9 mg SO42−-S L−1), which was already present in the tap water. In a long-term controlled mesocosm experiment, we established three bioreactor treatments to investigate nitrate, methanol, and sulfate removal rates with and without the presence of nitrate and methanol. Compared to the woodchip control treatment, methanol dosing resulted in an approximately fourfold increase in nitrate removal rates from 7 to 27 g N m−3 day−1. Methanol dosing increased sulfate removal rates, from average sulfate removal rates of 1.5 g SO42−-S m−3 day−1 under nitrate-prevailing conditions to 5.5 g SO42−-S m−3 day−1 removal rates under nitrate-limiting conditions compared to woodchip control removal of 0.3 g SO42−-S m−3 day−1. Mean methanol removal rates were 23 g CH3OH-C m−3 day−1 under nitrate-prevailing conditions compared to 18 g CH3OH-C m−3 day−1 in the woodchip control experiment. Improved nitrate removal rates, as well as methanol consumption and sulfate removal rates, might be leveraged to develop innovative low-footprint bioreactors.