Anoxic-aerobic Membrane Bioreactor Research Articles

Dissolved organic nitrogen is a key to improving the biological treatment potential of landfill leachate

Biological treatment is one of the most promising efficient, low-carbon and affordable approaches for the treatment of recalcitrantly degradable wastewater, such as landfill leachate. However, even the macroscopic molecular level analysis of dissolved organic matter (DOM) is limiting to the enhancement of biological treatment efficacy, and there is an urgent need for deeper exploration of DOM to gain insights into the key constraining substances. In the present study targeting at piercing leachate organic at molecular level, nitrogen-containing dissolved organic matter (DOMN) was identified to be the bottleneck that govern the biotreatment potential. The conclusion was made based on two series of experiments that compared the same anoxic-aerobic membrane bioreactor process (A process) operated stably at different regions, and compared with C process that coupling A process with a circulation aeration membrane bioreactor to improve aeration efficiency. The results confirmed that the relative abundance of DOMN was absolutely dominant among the three categories of DOM in all biologically treated samples, contributing to 60.36 %–65.81 % in removed-DOM, 60.33 %–70.95 % in refractory-DOM and 63.14 %–71.36 % in derived-DOM. Specifically, the high latitude A process had much lower DOMN removal rate than the low latitude A process (p < 0.05) and much higher refractory and derivatization rates than the low latitude A process (p < 0.05). DOM had similar results. No statistically significant differences were observed in the proportion of the three categories of DOM (DOMN), the elements composition, and the subcategory composition of the C process compared to the A process, in which the DOM (DOMN) derivation rate of NEC1-C (31.92 % and 33.41 %) was much higher than that of NEC1-A (20.88 % and 22.19 %). However, the AIwa and AImodwa of the derived-DOM (DOMN) were significantly higher in the C process than in the A process, which implied that excessive aeration did not enhance the biological treatment potential of the A process, but instead led to the proliferation of microorganisms and the secretion of extracellular polymer substances, which resulted in the derivation of more complex compounds. The results of the correlation analysis indicated that there were some regional differences in the molecular information of DOMN driven by climate temperature. In addition, it was worth mentioning that the nominal oxidation state of carbon (NOSCwa) of derived-DOMN in different regions of A process was noticeably higher than the corresponding DOM (p < 0.0001), implying that the derived-DOMN were still highly biodegradable, in other words, there was still great room for improving the biological treatment potential of landfill leachate. The present study provided a deeper insight and analysis of landfill leachate at the molecular level (DOMN) through multiple practical engineering cases, with a view to providing a theoretical basis for efficient optimization of biological treatment.

Effect of Self-Made TiO2 Nanoparticle Size on the Performance of the PVDF Composite Membrane in MBR for Landfill Leachate Treatment.

The pollutant composition of landfill leachate is complex, and pollutant concentrations change greatly. Moreover, landfill leachates can easily penetrate into the soil and eventually pollute the ground water, which can cause environmental pollution and threaten human health. At present, landfill leachate treatment technology is still not mature. In this paper, the A/O-MBR (Anoxic–Aerobic Membrane Bioreactor) process is proposed to treat landfill leachate. To increase the hydrophilicity of the membranes and reduce the pollution of the membranes, the self-made TiO2 nanoparticles were used to modify the ultrafiltration membranes (PVDF-2). Meanwhile, PVDF-2 composite membranes showed the best separation performance. The optimum operating parameters were determined by changing the concentration of the pollutants in the reactor and selecting the dissolved oxygen, pH, and hydraulic residence time. The results show that the optimum operating conditions of MBR are mixed liquor suspended solids (MLSS) = 3200 mg/L, DO = 1.5–2.5 mg/L in a nitrifying tank, DO = 0–0.5 mg/L in a denitrifying tank, pH = 7–8, and a hydraulic retention time (HRT) = 5 h. To reach the “Discharge Standard of Pollutants for Municipal Wastewater Treatment Plants” (GB18918-2002), the effluent of the MBR system further enters into the RO system. This work presents an environmentally friendly synthesis of TiO2 nanoparticles and added into PVDF. The addition of self-made TiO2 in PVDF membrane has improved the antifouling performance significantly, which has the potential for the treatment of landfill leachate.

Fate of aromatic amines through decolorization of real textile wastewater under anoxic-aerobic membrane bioreactor

Abstract The presence of residual dyes and their biotransformation products in textile wastewater is considered the main challenge of wastewater treatment plants. Many biological treatment methods have been used for treatment of textile wastewater. However, incomplete dye mineralization produces colorless Aromatic Amines (AAs) which are considered carcinogenic and highly toxic to aquatic organisms. This study assessed the removal efficiency and the fate of AAs in the treatment of real textile wastewater by anoxic-aerobic MBR. The fate of 22 AAs in both aqueous and sludge phases was investigated under different Internal Recycle ratio (IR). Most AAs possessing one aromatic ring and an Electron Donating Group (EDG) such as (-NH2) and (-CH3) are highly biodegradable under aerobic condition (above 80%), whereas AAs with 2 aromatic rings and strong Electron Withdrawal Group (EWG), such as azo bond and (-Cl) exhibited low to moderate removal efficiency (below 75%). The ∑AAs increased by 91% (from 205.1 to 393.7 ng/L) in the anoxic tank (IR=2.0), owing to the unique bacterial diversity under high IR operation scheme. On the other hand, ∑AAs in the anaerobic tank (IR=0.0) increased by 6.1% (from 489.26 to 519.1 ng/L), whereas, the ∑AAs in the aerobic tank remained constant at 50 ng/L in both cases. Most of AAs accumulated in sludge under reducing condition due to the refractory behavior of AAs in this environment, whereas hydrophobic AAs were slightly accumulated in aerobic sludge.

Integration of an anaerobic fluidized-bed membrane bioreactor (MBR) with zeolite adsorption and reverse osmosis (RO) for municipal wastewater reclamation: Comparison with an anoxic-aerobic MBR coupled with RO.

This study compared the performance of an anaerobic fluidized bed membrane bioreactor (AFMBR)-zeolite adsorption-reverse osmosis (RO) system and an anoxic-aerobic MBR-RO system for municipal wastewater reclamation. Both MBR-RO systems were operated in parallel with the same operating conditions. The results showed that the MBR systems achieved excellent organic removals (>95%) and the anoxic-aerobic MBR could also remove ∼57% of soluble total nitrogen. Compared to the aerobic MBR, the AFMBR displayed better membrane performance with less energy consumption, attributed to effective membrane scouring by liquid-fluidized GAC particles. Furthermore, a zeolite column was employed to remove ammonia in the AFMBR permeate, which ensured comparable organic and nitrogen levels in the feeds to RO units in the two processes. Although less organic substances and microbial cells were accumulated on the RO membrane fed with AFMBR-zeolite column effluent, its fouling rate (∼6.5±2.2bar/day) was significantly greater than that fed with anoxic-aerobic MBR permeate (∼1.1±1.5bar/day). This may be associated with more severe inorganic colloidal fouling on the RO membrane, illustrated by an electrical impedance spectroscopy fouling monitoring system.

Performances of Anoxic- Aerobic Membrane Bioreactors for The Treatment of Real Textile Wastewater

&lt;p&gt;Wastewater from textile industry is considered one of the major environmental challenges due to the large volume of highly colored, polluted and toxic effluent. This study investigated the treatability of real textile wastewater by pilot-scale anoxic-aerobic Membrane Bioreactor (MBR) system without sludge wasting for operation period of 100 days. The proposed system was investigated under different Internal Recycle (IR) ratios and the impact of IR ratio on Total Organic Carbon (TOC), Total Nitrogen (TN) and Color removals were examined. Under IR ratios between anoxic and aerobic tanks of 0.0, 0.5 and 2.0, the respective average removal efficiency of TN was 20.9%,53.4% and 71.7%, whereas average color removal of 81%, 85% and 88%, respectively was noted. The results indicated that increase of recycle ratio from 0.5 to 2.0 enhanced TN removal to about 71% and color removal to above 85%. The IR between anoxic and aerobic tanks has a significant role in TN and color removal due its effect on the development of bacterial communities. On the other hand, the results indicate over 93% TOC removal, which was independent of IR ratio.&lt;/p&gt;&#x0D;

Biological nutrient removal in the anaerobic side-stream reactor coupled membrane bioreactors for sludge reduction

An anoxic-aerobic membrane bioreactor (AO-MBR), an anaerobic side-stream reactor (ASSR) coupled MBR (A-MBR), and an MBR with ASSR packed with carriers (AP-MBR) were operated parallelly to investigate biological nutrient removal, microbial community structure and mass balance of nutrients in sludge reduction systems. Compared to AO-MBR, A-MBR and AP-MBR were both efficient in COD and NH4+-N removal, had significantly higher nitrogen removal, reduced sludge production by 35.0% and 45.9%, but deteriorated biological phosphorus removal. Nitrosomonadaceae and Nitrospira were major bacteria responsible for ammonium and nitrite oxidation in the three systems. Inserting ASSR and packing carriers both favored denitrifying bacteria enrichment and organic substances release, and thus resulted in higher nitrate uptake rate (NUR) in the anoxic tank. Higher endogenous NUR in ASSR than in anoxic tank also indicated that ASSR and carriers both accelerated sludge decay. Denitrification and sludge reduction occurred in ASSR played important roles in biological nutrient removal.

Research on the processing technology of upgrading and reconstruction projects of the wastewater treatment plant in Jianfeng city

The upgrading and reconstruction projects of the wastewater treatment plant(WWTP)in Leshan city are introduced,through investigation and analysis of the current situation of WWTP, while considering to meet water quality demands of effluent. The article presents the programs of Anoxic-Aerobic Membrane Bioreactor(A/O-MBR). Following an investigation and multiple upgrading of the plant, water quality reaches first grade A standard of Discharge Standard of Pollutants for Municipal Wastewater Treatment Plant (GB 18918-2002).

Influence of high doses of antibiotics on anoxic-aerobic membrane bioreactor in treating solid waste leachate

This study aims to investigate the influence of high antibiotics doses on the efficiency of an anoxic-aerobic membrane bioreactor (ANX-AMBR) in treating solid waste leachate for one-year operation without sludge withdrawal. Two doses of a mixture of norfloxacin (NOR), trimethoprim (TRM), sulfamethoxazole (SMX) and tetracycline (TC), a total of 4 mg L−1 (1 mg L−1 each) and a total of 20 mg L−1 (5 mg L−1 each), had been fed into the ANX-AMBR operated at HRTs of 12 h and 24 h. A high efficiency of organic matter removal could be achieved >90% in all conditions. The highest elimination of NOR, 77%; TRM/SMX/TC, 50–57%, was found under a 12 h-HRT with the antibiotic dose of 4 mg L−1. However, high antibiotic doses gave adverse effects on nitrite reduction-oxidation including antibiotic removal efficiency in the ANX-AMBR. Additionally, the extracellular polymeric substances were produced remarkably in the system after the antibiotic dose of 20 mg L−1. Mass balance analysis suggests that biodegradation was a major role in antibiotics removal in this system. Batch studies showed that the first order kinetics rate constants (k) of antibiotics biodegradation were 0.509–1.573 d−1 of ANX and 0.128–0.516 d−1 of AMBR.

Development of artificial neural networks to predict membrane fouling in an anoxic-aerobic membrane bioreactor treating domestic wastewater

An artificial neural network (ANN) was first developed to predict the transmembrane pressure in an anoxic-aerobic membrane bioreactor (AO-MBR) treating domestic wastewater. A few studies about prediction of membrane fouling in MBRs using ANNs have been published so far, even though our recent work indicates that ANNs show a great potential for this application. In this study, 10 parameters linked to wastewater treatment and measured in the different parts of the AO-MBR system were used as the input variables of the ANN. The goal was to select the most relevant input parameters to predict the evolution of the transmembrane pressure based on the performances of the ANN. An ANN model was selected for its satisfying performances (R2 = 0.850). In conclusion, ANNs could be a valid method to predict membrane fouling in AO-MBR systems treating domestic wastewater.

The role of ozone pretreatment on optimization of membrane bioreactor for treatment of oil sands process-affected water

Previously, anoxic-aerobic membrane bioreactor (MBR) coupled with mild ozonation pretreatment has been applied to remove toxic naphthenic acids (NAs) in oil sands process-affected water (OSPW). To further improve MBR performance, the optimal operation conditions including hydraulic retention time (HRT) and initial ammonia nitrogen (NH4+-N) need to be explored. In this study, the role of ozone pretreatment on MBR optimization was investigated. Compared with MBR treating raw OSPW, MBR treating ozonated OSPW had the same optimal operation conditions (HRT of 12 h and NH4+-N concentration of 25 mg/L). Nevertheless, MBR performance benefited from HRT adjustment more after ozone pretreatment. HRT adjustment resulted in NA removal in the range of 33–50% for the treatment of ozonated OSPW whereas NA removal for raw OSPW only fluctuated between 27% and 38%. Compared with the removal of classical NAs, the degradation of oxidized NAs was more sensitive to the adjustment of operation conditions. Adjusting HRT increased the removal of oxidized NAs in ozonated OSPW substantially (from 6% to 35%). It was also noticed that microbial communities in MBR treating ozonated OSPW were more responsive to the adjustment of operation conditions as indicated by the noticeable increase of Shannon index and extended genetic distances.

Beer and soft drinks industry wastewater treatment using an anoxic-aerobic membrane bioreactor (MBR) coupling with nanofiltration in Sahelian context

The beverage industries release large amounts of wastewater containing organic and mineral pollutants (sodium). The conditions of biomass acclimation as well as the influence of environmental factors pertaining to the Sahelian context are not well documented in previous studies with regards to industrial wastewater treatment by membrane bioreactor (MBR). This work shows the biomass behavior during the acclimation period and the effluent treatment effectiveness. The experimental system consists of an association of anoxic and aerobic reactors with a ceramic ultrafiltration membrane followed by a nanofiltration unit as post-treatment for treated water reclamation. The hydraulic retention time ranged from 16 to 57 h and a solid retention time of 30 d was defined. The volume loads increased from 0.3 to 15.9 kg(COD) m(-3) d(-1). The results reveal the need for pH, temperature and feed flow control during start-up phase. COD removal rate up to 95% was reached at the end of the treatment step with a turbidity reduction of 92%. The nanofiltration allowed retention of more than 90% of the concentrations of principal ions contained in the treated wastewater with a COD and sodium concentration less than 175 and 186 mg/L, respectively.

Fate and behavior of dissolved organic matter in a submerged anoxic-aerobic membrane bioreactor (MBR).

In this study, the production, composition, and characteristics of dissolved organic matter (DOM) in an anoxic-aerobic submerged membrane bioreactor (MBR) were investigated. The average concentrations of proteins and carbohydrates in the MBR aerobic stage were 3.96±0.28 and 8.36±0.89mg/L, respectively. After membrane filtration, these values decreased to 2.9±0.2 and 2.8±0.2mg/L, respectively. High performance size exclusion chromatograph (HP-SEC) analysis indicated a bimodal molecular weight (MW) distribution of DOMs, and that the intensities of all the peaks were reduced in the MBR effluent compared to the influent. Three-dimensional fluorescence excitation emission matrix (FEEM) indicated that fulvic and humic acid-like substances were the predominant DOMs in biological treatment processes. Precise identification and characterization of low-MW DOMs was carried out using gas chromatography-mass spectrometry (GC-MS). The GC-MS analysis indicated that the highest peak numbers (170) were found in the anoxic stage, and 54 (32%) compounds were identified with a similarity greater than 80%. Alkanes (28), esters (11), and aromatics (7) were the main compounds detected. DOMs exhibited both biodegradable and recalcitrant characteristics. There were noticeable differences in the low-MW DOMs present down the treatment process train in terms of numbers, concentrations, molecular weight, biodegradability, and recalcitrance.

Effects of ZnO nanoparticle exposure on wastewater treatment and soluble microbial products (SMPs) in an anoxic-aerobic membrane bioreactor

The effect of zinc oxide nanoparticles (ZnO NPs) on the performance of an anoxic-aerobic submerged membrane bioreactor (MBR), and the characterization of the soluble microbial products (SMPs) produced in the presence of ZnO NPs was evaluated. Continuous operation over 144 days showed that ZnO NPs at concentrations of 10 and 50 mg/L exerted a negative impact on chemical oxygen demand (COD) and nitrogen removal, although ZnO NPs were efficiently removed in the MBR (>92%). 10 and 50 mg/L ZnO NPs decreased COD removal substantially from 93.1± 0.6% to 90.1± 0.8% (<0.05) and 86.3± 2.3% (<0.05), respectively. Similarly, with 10 and 50 mg L ZnO NPs, the decreased in NH4N removal was 8.1% and 21.1%, respectively. Exposure to 1, 10 and 50 mg/L ZnO NPs increased SMP concentrations by 12.8%, 42.4% and 51.5%, respecti. High performance size exclusion chromatograph (HP-SEC) analysis revealed that the presence of ZnO NPs caused a significant increase in high-molecular weight (MW) (583 kDa) SMPs at 1 and 10 mg/L ZnO NP concentration. A substantial decrease in the concentration of high-MW compounds in the MBR effluent was observed at the end of the experiment. Excitation emission matrix (EEM) fluorescence contours revealed that SMPs were dominated by amino acid-, tryptophan protein-, polyaromatic-, and polycarboxylate-type substances. The presence of ZnO NPs enhanced the production of amino acid-like (7.5–25.1%) and tryptophan protein-like compounds (31.7–38.1%), compared to the control (6.0–20.2% for amino acid-like compounds; and 28.5–36.7% for tryptophan protein-like compounds). In contrast, the fulvic and humic acid-like compounds decreased with exposure to ZnO NPs. This work may help better understanding the effect of nanoparticle exposure on wastewater treatment performance and SMP characteristics.

Effects of ozone pretreatment and operating conditions on membrane fouling behaviors of an anoxic-aerobic membrane bioreactor for oil sands process-affected water (OSPW) treatment

Two identical anoxic-aerobic membrane bioreactors (MBRs) were operated in parallel for 742 consecutive days for raw and ozonated oil sands process-affected water (OSPW) treatment. The MBRs not only substantially degraded OSPW classical and oxidized NAs, but also demonstrated outstanding membrane fouling control performance (the MBR receiving raw OSPW experienced its first severe fouling with a transmembrane pressure (TMP) of −35 kPa on Day 433). The mild ozonation (30 mg O3/L) pretreatment of OSPW remarkably enhanced OSPW NA degradation, and improved the MBR's fouling control in terms of prolonged long-term slow TMP growth phase and reduced TMP jump frequency. Ozonation substantially altered the feed water organic composition, reshaped the microbial community (e.g., reduced growth of extracellular polymeric substances (EPS) producers and biofilm formation facilitators), and lowered EPS production and EPS protein/polysaccharides (PN/PS) ratio, consequently leading to the better fouling control. Examination on fouling behaviors at different HRTs of the raw OSPW MBR indicates that HRT also played a role in determining the dominating fouling mechanism during the sharp TMP rise phase. Therefore, the results of this study suggest that the low-dose ozone pretreatment is a good option to enhance organic contaminant degradation and alleviate membrane fouling in the MBR for OSPW treatment.

Bacterial community dynamics in an anoxic-aerobic membrane bioreactor – Impact on nutrient and trace organic contaminant removal

The bacterial community in different redox regimes of an anoxic-aerobic MBR under different operating conditions was investigated using pyrosequencing. With internal recirculation (IR) between the anoxic and aerobic reactors, the bacterial communities in these reactors were highly similar in structure and phylogenetic relationship, indicating IR as a key driving force shaping the bacterial communities that are responsible for the core function in the system. Without IR, each redox condition sustained the growth of distinct bacterial communities according to their oxygen requirement, and the anoxic community presented a low capacity of nutrient and trace organic contaminant (TrOC) removal. Higher bacterial diversity under longer sludge retention time (SRT) was evident; however, except for a few TrOCs, removal efficiency of TOC, TN and TrOCs were the same irrespective of the SRT. The presence of TrOCs induced shifts in bacterial communities, and a correlation between bacterial communities and TrOC transformation was noted. The important candidates for TrOC biotransformation were the taxa within Proteobacteria, particularly Methylophilales and Myxococcales. Other bacterial groups potentially contributing to TrOC biotransformation were those related to nitrogen removal, such as Rhodocyclales and Plantomycetes. In contrast, the detected members of Cytophagaceae (Bacteroidetes) appeared not to contribute to TrOC biotransformation.

Simultaneous nitrification/denitrification and trace organic contaminant (TrOC) removal by an anoxic-aerobic membrane bioreactor (MBR).

Simultaneous nitrification/denitrification and trace organic contaminant (TrOC) removal during wastewater treatment by an integrated anoxic-aerobic MBR was examined. A set of 30 compounds was selected to represent TrOCs that occur ubiquitously in domestic wastewater. The system achieved over 95% total organic carbon (TOC) and over 80% total nitrogen (TN) removal. In addition, 21 of the 30 TrOCs investigated here were removed by over 90%. Low oxidation reduction potential (i.e., anoxic/anaerobic) regimes were conducive to moderate to high (50% to 90%) removal of nine TrOCs. These included four pharmaceuticals and personal care products (primidone, metronidazole, triclosan, and amitriptyline), one steroid hormone (17β-estradiol-17-acetate), one industrial chemical (4-tert-octylphenol) and all three selected UV filters (benzophenone, oxybenzone, and octocrylene). Internal recirculation between the anoxic and aerobic bioreactors was essential for anoxic removal of remaining TrOCs. A major role of the aerobic MBR for TOC, TN, and TrOC removal was observed.

Membrane fouling related to microbial community and extracellular polymeric substances at different temperatures

An anoxic-aerobic membrane bioreactor was established to investigate the role of microorganisms and microbial metabolites in membrane fouling at different temperatures. The results showed that the membrane fouling cycle at 303, 293, and 283 K were 30, 29, and 5.5 days, respectively. Polysaccharides dominated the extracellular polymeric substances (EPS) and soluble microbial products (SMP) at 303 and 293 K, instead, proteins was the predominant composition of metabolites at 283 K. The correlation coefficient (r(2)) was calculated to identify the relationship between temperature (T), filtration resistance (R) and compositions of EPS and SMP. In biocake, the EPS polysaccharides (EPSc) was the most correlative factor to temperature (T) and filtration resistance (R); in mixed liquor, the ratio of SMP polysaccharides to proteins (SMPc/p) was the most correlative factor. The microbial community structure and the dominant species was the major reason causing the change of EPS and SMP composition.

Textile wastewater treatment in a bench-scale anaerobic-biofilm anoxic-aerobic membrane bioreactor combined with nanofiltration

This study evaluated the treatability of textile wastewaters in a bench-scale experimental system, comprising an anaerobic biofilter, an anoxic reactor and an aerobic membrane bioreactor (MBR). The MBR effluent was thereafter treated by a nanofiltration (NF) membrane. The proposed system was demonstrated to be effective in the treatment of the textile wastewater under the operating conditions applied in the study. The MBR system achieved a good COD (90–95%) removal; due to the presence of the anaerobic biofilter, also effective color removal was obtained (70%). The addition of the NF membrane allowed the further improvement in COD (50–80%), color (70–90%) and salt removal (60–70% as conductivity). In particular the NF treatment allowed the almost complete removal of the residual color and a reduction of the conductivity such as to achieve water quality suitable for reuse.