Organic Removal Rate Research Articles

Improved Buffering Capacity and Methane Production by Anaerobic Co-Digestion of Corn Stalk and Straw Depolymerization Wastewater

A new method has been developed to improve the buffer capacity and methane production of the anaerobic digestion of Corn Stalk (CS), in which both an anaerobic co-digestion of CS with Straw Depolymerization Wastewater (SDW) and a mono-digestion of CS at different substrate concentrations (25.9, 36.2 and 45.3 mg/L) were investigated. Batch assays were conducted under thermophilic conditions for 70 days, which showed that an anaerobic co-digestion significantly increased the buffering capacity and methane production of the digestion process. The lag time for methane generation resulting from an anaerobic co-digestion of CS with SDW was 10 days, while the lag time for a mono-digestion of CS was 23 days. A maximum methane production of 214.81 mL/g-VS was obtained for the anaerobic co-digestion of CS with SDW when the substrate concentration was 36.2 g/L, which was around 13.54% higher than for mono-digestion of CS of 189.20 mL/g-VS. The removal rate for sulfate increased from 10.43% to 58.40% when the substrate concentration was increased from 25.9 to 45.3 mg/L for the anaerobic co-digestion of CS with SDW. Microbial communities were analyzed using 16S rDNA sequencing technology which showed that anaerobic co-digestion of CS and SDW promotes the growth of methanogens. The relative abundance of these methanogens (Euryarchaeota) for the anaerobic co-digestion of CS with SDW was increased significantly, being approximately 8.25% higher than that of a mono-digestion of CS, which was at a substrate concentration of 36.2 g/L. This means that the anaerobic co-digestion of CS and SDW is beneficial for improving buffer capacity and methane production from the digestion of CS, with higher organic matter and sulfate removal rates also being obtained.

Investigation of the interaction between intermediates from gasification of biomass in supercritical water: Formaldehyde/formic acid mixtures

Supercritical water gasification (SCWG) is a promising technology for converting wet biomass and waste into renewable energy. While the fundamental mechanism involved in SCWG of biomass is not completely understood, especially hydrogen (H2) production produced from the interaction among key intermediates. In the present study, formaldehyde mixed with formic acid as model intermediates were tested in a batch reactor at 400 °C and 25 MPa for 30 min. The gas and liquid phases were collected and analyzed to determine a possible mechanism for H2 production. Results clearly showed that both gasification efficiency (GE) and hydrogen efficiency (HE) increased with addition of formic acid, and the maximum H2 yield reached 17.92 mol/kg with a relative formic acid content of 66.67% in the mixtures. The total organic carbon removal rate and formaldehyde conversion rate also increased to 67.33% and 89.81% respectively. The reaction pathways for H2 formation form mixtures was proposed and evaluated, formic acid promoted self-decomposition of formaldehyde to generate H2, and induced a radical reaction of generated methanol to produce more H2.

Hydrothermal dewatering of low-rank coals: Influence on the properties and combustion characteristics of the solid products

The presence of increased moisture content, low energy density and maximum spontaneous combustion tendency has raised serious environmental issues, which are obstacles to large scale utilization of coals. Hydrothermal dewatering (HTD) is a promising method for upgrading low rank coals (LRCs). The influences of HTD, executed at different temperatures on solid product yield, removal rate of elements, organics and inorganics, and combustion characteristics in LRCs were studied. HTD treatment of LRCs was carried out in 2 L cylindrical autoclave at 200–300 °C for 1 h. For upgraded coals, the inherent moisture and oxygen content decreased significantly while fixed carbon content and calorific value increased. FTIR results indicate the conversion of LRCs near to high-rank coals (HRCs). The organic matter was removed due to loss of Methylene, Methyl groups and O-containing functional groups, whereas inorganic matter was removed mainly in the forms of Fe and Ca-containing minerals. The upgraded coals had higher ignition and burnout temperatures, while their combustion was shifted and delayed toward higher temperature zone. Activation energy of treated coals increased in ignition stage while decreased in combustion segment. Prominent changes were found in coal structure, composition, rank, and combustion characteristics at HTD temperature of 300 °C.

A hybrid constructed wetland for organic-material and nutrient removal from sewage: Process performance and multi-kinetic models

A pilot-scale hybrid constructed wetland with vertical flow and horizontal flow in series was constructed and used to investigate organic material and nutrient removal rate constants for wastewater treatment and establish a practical predictive model for use. For this purpose, the performance of multiple parameters was statistically evaluated during the process and predictive models were suggested. The measurement of the kinetic rate constant was based on the use of the first-order derivation and Monod kinetic derivation (Monod) paired with a plug flow reactor (PFR) and a continuously stirred tank reactor (CSTR). Both the Lindeman, Merenda, and Gold (LMG) analysis and Bayesian model averaging (BMA) method were employed for identifying the relative importance of variables and their optimal multiple regression (MR). The results showed that the first-order–PFR (M2) model did not fit the data (P > 0.05, and R2 < 0.5), whereas the first-order–CSTR (M1) model for the chemical oxygen demand (CODCr) and Monod–CSTR (M3) model for the CODCr and ammonium nitrogen (NH4−N) showed a high correlation with the experimental data (R2 > 0.5). The pollutant removal rates in the case of M1 were 0.19 m/d (CODCr) and those for M3 were 25.2 g/m2∙d for CODCr and 2.63 g/m2∙d for NH4-N. By applying a multi-variable linear regression method, the optimal empirical models were established for predicting the final effluent concentration of five days' biochemical oxygen demand (BOD5) and NH4-N. In general, the hydraulic loading rate was considered an important variable having a high value of relative importance, which appeared in all the optimal predictive models.

Enhanced Photocatalytic Activity toward Organic Pollutants Degradation and Mechanism Insight of Novel CQDs/Bi₂O₂CO₃ Composite.

Novel carbon quantum dots (CQDs) modified with Bi2O2CO3 (CQDs/Bi2O2CO3) were prepared using a simple dynamic-adsorption precipitation method. X-ray diffractometry (XRD), transmission electron microscopy (TEM), energy dispersive X-ray spectroscopy (EDX), and scanning electron microscopy (SEM) were used to test the material composition, structure, and band structures of the as-prepared samples. Methylene blue (MB) and colorless phenol, as target organic pollutants, were used to evaluate the photocatalytic performance of the CQDs/Bi2O2CO3 hybrid materials under visible light irradiation. Experimental investigation shows that 2–5 nm CQDs were uniformly decorated on the surface of Bi2O2CO3; CQDs/Bi2O2CO3 possess an efficient photocatalytic performance, and the organic matter removal rate of methylene blue and phenol can reach up to 94.45% and 61.46% respectively, within 2 h. In addition, the degradation analysis of phenol by high performance liquid chromatography (HPLC) proved that there are no other impurities in the degradation process. Photoelectrochemical testing proved that the introduction of CQDs (electron acceptor) effectively suppresses the recombination of e−-h+, and promotes charge transfer. Quenching experiments and electron spin resonance (ESR) suggested that ·OH, h+, and ·O2− were involved in the photocatalytic degradation process. These results suggested that the up-conversion function of CQDs could improve the electron transfer and light absorption ability of photocatalysts and ·O2− formation. Furthermore, the up-conversion function of CQDs would help maintain photocatalytic stability. Finally, the photocatalytic degradation mechanism was proposed according to the above experimental result.

Understanding Electrochemically Activated Persulfate and Its Application to Ciprofloxacin Abatement.

This study offers insight into the roles anodic and cathodic processes play in electrochemically activated persulfate (EAP) and screens EAP as a viable technique for ciprofloxacin degradation in wastewater. Sulfate radical formation at a boron-doped diamond (BDD) anode and persulfate activation at a graphite cathode were experimentally elucidated using different electrolytes and electrochemical setups. Rapid ciprofloxacin transformation occurred via pseudo-first-order mechanisms with respect to ciprofloxacin in persulfate electrolyte, reaching 84% removal in 120 min using EAP. Transformation pathways were compared to those in nitrate and sulfate electrolytes. Ciprofloxacin removal rates in the electrochemical system were 88% and 33% faster in persulfate than nitrate and sulfate electrolytes, respectively. Total organic carbon removal rates were 93% and 48% faster in persulfate than nitrate and sulfate, respectively. Use of sulfate electrolyte resulted in removal rates 6-7 times faster than those in nitrate solution. Accelerated removal in sulfate was attributed to anodic sulfate radical formation, while enhanced removal in persulfate was associated with cathodic persulfate activation and nonradical persulfate activation at the BDD anode. Quenching experiments indicated both sulfate radicals and hydroxyl radicals contributed to degradation. Comparisons between platinum and graphite cathodes showed similar cathodic persulfate activation and ciprofloxacin degradation.

Performance evaluation of duplex constructed wetlands for the treatment of diesel contaminated wastewater

A duplex constructed wetland (duplex-CW) is a hybrid system that combines a vertical flow (VF) CW as a first stage with a horizontal flow filter (HFF) as a second stage for a more efficient wastewater treatment as compared to traditional constructed wetlands. This study evaluated the potential of the hybrid CW system to treat influent wastewater containing diesel range organic compounds varying from C7 – C40 using a series of 12-week practical and numerical experiments under controlled conditions in a greenhouse (pH was kept at 7.0 ± 0.2, temperature between 20 and 23° C and light intensity between 85 and 100-μmol photons m−2 sec−1 for 16 h d−1). The VF CWs were planted with Phragmites australis and were spiked with different concentrations of NH4+-N (10, 30 and 60 mg/L) and PO43--P (3, 6 and 12 mg/L) to analyse their effects on the degradation of the supplied petroleum hydrocarbons. The removal rate of the diesel range organics considering the different NH4+-N and PO43--P concentrations were simulated using Monod degradation kinetics. The simulated results compared well with the observed database. The results showed that the model can effectively be used to predict biochemical transformation and degradation of diesel range organic compounds along with nutrient amendment in duplex constructed wetlands.

The structure optimization of gas-phase surface discharge and its application for dye degradation

A gas-phase surface discharge (GSD) was employed to optimize the discharge reactor structure and investigate the dye degradation. A dye mixture of methylene blue, acid orange and methyl orange was used as a model pollutant. The results indicated that the reactor structure of the GSD system with the ratio of tube inner surface area and volume of 2.48, screw pitch between a high-voltage electrode of 9.7 mm, high-voltage electrode wire diameter of 0.8 mm, dielectric tube thickness of 2.0 mm and tube inner diameter of 16.13 mm presented a better ozone (O3) generation efficiency. Furthermore, a larger screw pitch and smaller wire diameter enhanced the O3 generation. After the dye mixture degradation by the optimized GSD system, 73.21% and 50.74% of the chemical oxygen demand (COD) and total organic carbon removal rate were achieved within 20 min, respectively, and the biochemical oxygen demand (BOD) and biodegradability (BOD/COD) improved.

Comparison of filtration and treatment performance between polymeric and ceramic membranes in anaerobic membrane bioreactor treatment of domestic wastewater

Abstract The feasibility of an anaerobic ceramic membrane bioreactor (AnCMBR) was investigated by comparison with a conventional anaerobic membrane bioreactor (AnMBR). With regard to treatment performance, the AnCMBR achieved higher organic removal rates than the AnMBR because the ceramic membranes retained a high concentration of biomass in the reactor. Despite a high mixed liquor suspended solid (MLSS) concentration, the AnCMBR exhibited lower membrane fouling. To elucidate effects of sludge properties on membrane fouling in the AnCMBR and AnMBR, soluble microbial products (SMPs) and extracellular polymeric substances (EPSs) were analyzed. The SMP and EPS concentrations in the AnCMBR were higher than in the AnMBR. This may be because some suspended solids bio-degraded and likely released protein-like SMPs in the AnCMBR. Hydrophobicity and surface charges were analyzed; the sludge in the AnCMBR was found to be more hydrophobic and less negative than in the AnMBR because protein was abundant in the AnCMBR. Despite the adverse properties of the sludge in the AnCMBR, it showed more stable filtration performance than the AnMBR. This is because the alumina-based ceramic membrane had a superhydrophilic surface and could thus mitigate membrane fouling by hydrophilic-hydrophobic repulsion. The findings from this study have significant implications for extending the application of AnCMBRs to, for example, treatment of high-strength organic waste such as food waste or livestock manure.

Electron donation characteristics and interplays of major volatile fatty acids from anaerobically fermented organic matters in bioelectrochemical systems

ABSTRACTAnaerobic fermentation liquid of waste organic matters (WOMs) is rich in volatile fatty acids (VFAs), which can be treated with bioelectrochemical systems for both electrical energy recovery and organics removal. In this work, four major VFAs in the fermented WOMs supernatant were selected to examine their electron donation characteristics for power output and their complicated interplays in microbial fuel cells (MFCs). Results indicated a priority sequence of acetate, propionate, n-butyrate and i-valerate when served as the sole electron donor for electricity generation. The MFC solely fed with acetate showed the highest coulombic efficiency and power density, and the longest period for electricity production. When two of the VFAs were added with equal proportion, both acids contributed positively to electricity generation, while the selective or competitive use of substrates by diverse microorganisms behaved as an antagonism effect to prolong the degradation time of each VFA. When acetate and propionate, the preferable substrates for electricity generation, were mixed in various proportions, their large concentration difference led to improved electrical performance but decreased organic removal rate.

Subcritical water oxidation of propham by H2O2 using response surface methodology (RSM)

ABSTRACTThis study was conducted to investigate the degradation of propham, which is a compound that pollutes water and seriously threatens human health, by subcritical water oxidation and using H2O2 as an oxidising agent. The maximum total organic carbon removal rate of propham was obtained as 73.65% at 40 min of treatment time and 60 mM of H2O2 concentration and 373 K of temperature. In addition, response surface method based on the Box-Behnken design was applied to design the degradation experiments of propham for determination of the combined effects of process variables, namely temperature, concentration of oxidising agent and treatment time. The proposed quadratic model of propham degradation, which was examined with the analysis of variance, was used for navigating the design space. The R2 and adjusted R2 values of the model were determined as 0.9921 and 0.9819 respectively. It was shown that propham was effectively degraded, thus could be removed from the water by using an environmentally friendly method.

Facilitated extracellular electron transfer of Geobacter sulfurreducens biofilm with in situ formed gold nanoparticles

The conductivity of a biofilm is the key factor for the high current density of a bioelectrochemical system (BES). Most previous works have focused on electrode modification, but, this only benefits the microorganisms that directly contact the electrode. The low conductivity of biofilm limits the current density of the BES. In this work, gold nanoparticles (Au-NPs) were successfully fabricated in situ into a Geobacter sulfurreducens biofilm to increase the conductivity. 20 ppm NaAuCl4 (the precursor) was slowly dropped into the anode chamber at a rate of 1.3 mL/h in a continuous-flow three-electrode BES. The Au(III) was transformed to Au-NPs, which then precipitated in the biofilm via biological mineralization. The current density of the anode increased by 40%. Meanwhile, the removal percentage of the organic substrate (acetate) was enhanced 2.2 times, from 24.7% to 53.3%, after the in situ fabrication of Au-NPs. This method greatly lowered the charge transfer resistance of the anode and enhanced the anodic limiting current. Our results proved that the current density and organic removal rate of the G. sulfurreducens biofilm in the anode were effectively enhanced by in situ Au-NP fabrication. This work not only provides a simple and effective strategy for enhancing the electricity generation of BES with conductive NP fabrication, but also improves the understanding of the extracellular electron transfer (EET) of exoelectrogens.

Magnéli phases Ti O2−1 as novel ozonation catalysts for effective mineralization of phenol

Magnéli phases TinO2n−1 have been demonstrated as promising environmentally friendly materials in advanced oxidation processes. In this study, Magnéli phases TinO2n−1 have been used as catalysts for the ozonation of phenol in aqueous solution for the first time. The materials exhibited excellent catalytic ozonation activities both in phenol degradation and mineralization. When Ti4O7 was added, the reaction rate was six-fold higher than that of with ozone alone, while the total organic carbon removal rate was substantially elevated from around 19.2% to 92%. By virtue of the good chemical stability of the materials, a low metal leaching of less than 0.15 mg·L− 1 could effectively avoid the secondary pollution by metal ions. Radical quenching tests revealed O2− and 1O2 to be active oxygen species for phenol degradation at pH 5. As semiconductor catalysts, TinO2n−1 materials show electronic transfer capability. Ozone adsorbed at B-acid sites of the catalyst surface can capture an electron from the conversion of Ti(III) to Ti(IV), and is thereby broken into the active oxygen species. It was interesting to observe that TinO2n−1 exhibit better catalytic activity for phenol degradation and mineralization with lower n value. The difference in electrical conductivity can be considered as a major factor for the catalytic performances. More highly conductive catalysts show a faster electron-transfer rate and better catalytic activity. Thus, significant evidences have been obtained for a single-electron-transfer mechanism of catalytic ozonation with Magnéli phases TinO2n−1.

Effects of Ferric Salts on Sludge Anaerobic Digestion and Desulphurization

The treatment and disposal of excess sludge is a great challenge. Anaerobic digestion can achieve sludge reduction and harmless. However, its application is largely limited due to the low biogas production, low organic matters removal rate, odor gas production, corrosive gas destroying equipment. Sulfur is a key element resulting in these problems. In this research, potassium ferrate and ferric chloride were added to enhance anaerobic digestion. The research investigated the effects on biogas production, H2S content, microbial diversity with the addition of potassium ferrate and ferric chloride. We found that with 2.5 mg/g TS potassium ferrate, the enhancement was the highest, the total biogas production improved 18% compared with control group and organic removal rate reached 30.66%. Considering the effect of sulfur removal, 5 mg/g TS potassium ferrate resulted in the best effect, the content of H2S gas decreased 139.4%. With 2.5 mg/g TS ferric chloride, total biogas production improved 8% comparing with the control group, the content of H2S gas decreased 46%, no remarkable effect was found on the content of nitrogen and phosphorus in slurry.

Models for organics removal from vinasse from ethanol production

Global ethanol production generates almost 100 billion liters per year of a high-strength liquid waste called vinasse. One sustainable method of treating vinasse using environmental biotechnology is anaerobic digestion, which generates biogas that can be used as a renewable energy resource. Although a number of models have been developed for predicting biogas generation rates, no previous study has modeled liquid organic removal rates for vinasse treatment. The goal of this research was thus to develop models for predicting liquid-phase organic removal rates for anaerobic treatment of vinasse. 6-L laboratory-scale batch reactors were filled with vinasse of six different compositions and operated at three different mesophilic temperatures (30, 35, 40 °C). Biochemical and chemical oxygen demand (BOD and COD) were measured over time using Standard Methods 5210B and 5220C. Based on data collected, multiple linear regression equations (R2 = 0.79 and 0.94) were developed to predict first-order rate constants kBOD and kCOD as functions of temperature and vinasse composition (initial values of nitrogen, potassium, phosphorous, and sulfur). The first-order models developed require a small number of readily available input parameters. They apply to treatment of vinasse from ethanol produced from corn and milo; future work can test their applicability to ethanol produced from other feedstocks. The models can be used for sizing/design of reactors for anaerobic treatment of vinasse.

Performance of direct anaerobic digestion of dewatered sludge in long-term operation

Direct anaerobic digestion of dewatered sludge with total solids (TS) content of 15–20% was tested in a horizontal digester for one and half years. The system kept stable with pH 7–8. The concentration of volatile fatty acids was lower than 800 mg/L, free ammonia nitrogen was lower than 200 mg/L, and total alkalinity kept higher than 6000 mg/L. The performance was influenced by organic load rate (OLR) and organic content in feed sludge. When volatile solids (VS) in TS of feed sludge reached 60–65% at OLR 3.50–3.70 g/(L·d), the process exhibited the best performance with organic removal rate of 32.19 ± 7.73% and methane production of 156.86 ± 13.05 ml/g VS added. Microbial analyses indicated that Methanosarcina became predominant and Methanosaeta almost disappeared. Moreover, hydrogenotrophic and methylotrophic methanogens accounted for 18.13–29.40% and 11.58–29.56% of the total, respectively. These provide a new guideline for small-scale or centralized sludge treatment.

Optimization of organic matter degradation kinetics and nutrient removal on artificial wetlands using Eichhornia crassipes and Typha domingensis

ABSTRACTThis study describes the optimization of the wastewater treatment process through the use of a free water surface flow constructed wetland with floating macrophytes at the laboratory level (20 L). A factorial design 23 was used in order to find the best operation conditions of the wastewater treatment process. The performance of macrophytes Eichhornia crassipes and Typha domingensis was investigated by operating the wetland system at hydraulic retention times of 2 and 4 days. The results showed an optimum operational condition that removed 92.39% of initial organic load (measured as COD). The nutrient removal efficiency of the constructed wetland was 99.28% for total nitrogen and 87.78% for phosphorus. The best operating condition includes the use of E. crassipes, with 4 days of hydraulic retention and the use of gravel as a filter. According to this, organic matter degradation kinetics was studied by the comparison of three kinetic models: first-order model, Stover–Kincannon model and Grau-second-order model. Stover–Kincannon and Grau kinetics models were more appropriate to represent the organic matter degradation kinetics in constructed wetland, with a determination coefficient of 0.9997. Based on the kinetic removal results, the process showed a maximum rate of organic load removal of 2500 mg/L d.

Assessment of organic removal in series- and parallel-connected microbial fuel cell stacks

Microbial fuel cells (MFCs) degrade organic contaminants in wastewater while simultaneously producing electricity, but must be stacked to yield adequate voltage and current. This study examined the evolution of the chemical oxygen demand (COD) removal rate and efficiency in two identical individual MFCs (i-MFCs) in series- and parallel-connected stacks (sc- and pc-MFCs, respectively) under batch and continuous operation. The stack voltage and current increased in the respective series and parallel connections of the two i-MFCs (MFC unit 1 and MFC unit 2). Voltage reversal was observed in the sc- MFC below an external load of 100 Ω. Regardless of occurrence of the voltage reversal, organic reduction between i-MFCs and sc-MFCs showed no significant difference (gap of < 9% and < 6% in COD removal rate and efficiency, respectively); additionally, organic removals between the two individual MFCs in series indicated differences less than 9% of COD removal rate and 5% of COD removal efficiency in batch mode. Continuous operation also yielded similar organic removals as the MFCs in individual and series connection (voltage reversal occurred) mode, even over 8 days operation. Parallel connection yielded identical organic removals and currents in the two individual MFCs of the pc-MFC, even though the two separate i-MFCs showed different organic removal rates and current productions. This study provides the guide for the application of stacked MFCs for power source and efficient organic pollutant removal in wastewater treatment process.

Metagenomic characterization of biofilter microbial communities in a full-scale drinking water treatment plant

Microorganisms inhabiting filtration media of a drinking water treatment plant can be beneficial, because they metabolize biodegradable organic matter from source waters and those formed during disinfection processes, leading to the production of biologically stable drinking water. However, which microbial consortia colonize filters and what metabolic capacity they possess remain to be investigated. To gain insights into these issues, we performed metagenome sequencing and analysis of microbial communities in three different filters of a full-scale drinking water treatment plant (DWTP). Filter communities were sampled from a rapid sand filter (RSF), granular activated carbon filter (GAC), and slow sand filter (SSF), and from the Schmutzdecke (SCM, a biologically active scum layer accumulated on top of SSF), respectively. Analysis of community phylogenetic structure revealed that the filter bacterial communities significantly differed from those in the source water and final effluent communities, respectively. Network analysis identified a filter-specific colonization pattern of bacterial groups. Bradyrhizobiaceae were abundant in GAC, whereas Nitrospira were enriched in the sand-associated filters (RSF, SCM, and SSF). The GAC community was enriched with functions associated with aromatics degradation, many of which were encoded by Rhizobiales (∼30% of the total GAC community). Predicting minimum generation time (MGT) of prokaryotic communities suggested that the GAC community potentially select fast-growers (<15 h of MGT) among the four filter communities, consistent with the highest dissolved organic matter removal rate by GAC. Our findings provide new insights into the community phylogenetic structure, colonization pattern, and metabolic capacity that potentially contributes to organic matter removal achieved in the biofiltration stages of the full-scale DWTP.

Coking Wastewater Treatment Efficiency and Comparison of Acute Toxicity Characteristics of the AnMBR-A-MBR and A2-MBR Processes

Coking wastewater contains high-strength refractory organic pollutants and is commonly treated by biological treatment processes. To improve the efficiency of biological treatment, two laboratory scale processes, anaerobic membrane bioreactor/anoxic/aerobic membrane bioreactor (AnMBR-A-MBR) and anaerobic/anoxic/aerobic membrane bioreactor (A2-MBR), were developed for coking wastewater treatment. The removal of main pollutants and the stability of different pollutant loadings were compared under the optimum operating conditions. Acute toxicity distribution, variations, and toxic matter characteristics of the two processes were investigated by solid-phase extraction, components separation, the luminous bacteria Q67 test, and three-dimensional fluorescence spectrometry. The results showed that the organic pollutant removal rate of AnMBR was 15.3%, which was significantly higher than the anaerobic stage of the A2-MBR system (3.4%), and the AnMBR-A-MBR system had greater resistance to pollutant loading. Acute toxicity of AnMBR-A-MBR system in each stage effluent was lower than the A2-MBR system and the total toxic unit removal rate of both were 85.2% and 79.2%, respectively. The acute toxicity of the polar component in each stage effluent was the highest, and the polar and mid-polar components contributed to the majority of the toxicity. The toxicity of each stage effluent mainly originated from Region Ⅱ aromatic protein analogues, which could be the main acute toxicity substances of the polar component.