Performance of a membrane bioreactor used for the treatment of wastewater contaminated with heavy metals

Anaerobic dynamic membrane bioreactor treating swine wastewater: Fate of sulfonamide antibiotics and heavy metals with their effect on filtration performance

Sulfonamide antibiotics (SMs) and heavy metals, simultaneously existing in swine wastewater, threat ecological security and public health. Anaerobic dynamic membrane bioreactor (AnDMBR) technology has shown great potential for excellent and cost-effective treatment of various types of industrial wastewaters. Herein, it was for the first time applied for treating the swine wastewater containing both SMs and heavy metals, with particular efforts devoted to understanding the fate of SMs and heavy metals with their effect on dynamic membrane (DM) fouling. The AnDMBR exhibited effective removal efficiency of COD (91.2 %), sulfamethoxazole (SMX) (94.2 %), sulfadiazine (SDZ) (51.2 %), sulfamethazine (SMZ) (52.8 %), Cu2 + (88.5 %) and Zn2+ (73.3 %). Biodegradation and bioadsorption was found to be the major mechanism for the removal of SMs and heavy metals, respectively, with DM playing considerable roles. Furthermore, EPS adsorption turned out to be another key mechanism for removing SMs and heavy metals, particularly in DM. The exposure to SMs and heavy metals significantly increased the specific resistance of DM, and consequently expedited DM fouling. This was mainly due to the increased content of small particles, EPS content (mainly hydrophobic proteins) and relative abundance of biofouling-related bacteria (i.e., Firmicutes, Chloroflexi and Clostridia), resulting in a denser DM structure with lower porosity.

Relationships Between Physicochemical and Structural Properties of Commercial Vermiculites

This study examines the effects of thermal (1000 °C), hydrothermal (100 °C), mechanochemical (ambient T), and microwave (~100 °C) treatments on three types of Chinese vermiculites, one with lower potassium content than the others. The goal was to obtain materials with enhanced properties related to specific surface areas. The response of the vermiculites to treatments and their physicochemical properties were analyzed using X-ray diffraction (XRD), thermal analysis (TG and DTG), and textural characterization via the BET method. XRD analyses showed similar mineral composition in treated and untreated samples, but the treatments affected the intensity and width of phase reflections, altering crystallinity and structural order, as well as the proportions of vermiculite, hydrobiotite, and phlogopite. Thermogravimetric analysis revealed two mass loss stages: water desorption (from 25 °C to about 250 °C) and recrystallization or dehydroxylation (above 800 °C). The isotherms indicated mesoporous characteristics, with hydrothermally CO2-treated samples having the highest specific surface area and adsorption capacity. The samples with vermiculite, hydrobiotite, and phlogopite generally showed moderate to high specific surface area (SBET) values, and mechanochemical treatments significantly increase SBET and pore volume (Vp) in the vermiculite and hydrobiotite samples. Crystallinity affects SBET, average Vp, and average pore size, and its monitoring is crucial to achieve the desired material characteristics, as higher crystallinity can reduce SBET but improve mechanical strength and thermal stability. This study highlights the influence of different treatments on vermiculite properties, providing valuable insights into their potential applications in various fields (such as thermal insulation in vehicles and aircraft, and the selective adsorption of gases and liquids in industrial processes, improving the strength and durability of building materials like cement and bricks).

Investigation of the performance of the combined moving bed bioreactor-membrane bioreactor (MBBR-MBR) for textile wastewater treatment

The present study focused on the investigation of the performance of a Moving Bed Bioreactor coupled with a Membrane Bioreactor (MBBR-MBR) on a small scale for textile wastewater treatment. The parameters examined in this study included the removal efficiency of chemical oxygen demand (COD), biochemical oxygen demand (BOD), total suspended solids (TSS), turbidity, color, and heavy metals (HM). The two reactors were operated consecutively and maintained aerobic conditions. The idea is to reduce the pollutant load significantly through the activity of microorganism attached to the biofilm covered carriers in MBBR and successive membrane filtration. The system demonstrated a favorable outcome even in a smaller hydraulic retention time (HRT) of 1 day, which presents a significant advantage in terms of cost and space saving. The removal effectiveness of COD attained a maximum of 92 %, BOD reached a maximum of 95 %, and the color removal performance obtained a removal efficiency of 87 %. Furthermore, the treatment showed remarkable efficiency in removing up to 100 % of TSS and 96 % of turbidity. Additionally, an evaluation was conducted on the elimination of heavy metals, including Zinc (Zn), Lead (Pb), Chromium (Cr), and Iron (Fe). The efficacy of removing these HMs was found to exceed 85 %. All these favorable outcomes contribute to the improvement of effluent quality, mitigation of contamination hazards, and fouling reduction.

Novel eco-friendly polylactic acid nanocomposite integrated membrane system for sustainable wastewater treatment: Performance evaluation and antifouling analysis

Water contamination caused by heavy metals, nutrients, and organic pollutants of varying particle sizes originating from domestic and industrial processes poses a significant global challenge. There is a growing concern, particularly regarding the presence of heavy metals in freshwater sources, as they can be toxic even at low concentrations, posing risks to human health and the environment. Currently, membrane technologies are recognized as effective and practical for treating domestic and industrial wastewater. However, these technologies are hindered by fouling issues. Furthermore, the utilization of conventional membranes leads to the accumulation of non-recyclable synthetic polymers, commonly used in their production, resulting in adverse environmental consequences. In light of our previously published studies on environmentally friendly, biodegradable polylactic acid (PLA) nanocomposite mixed matrix membranes (MMMs), we selected two top-performing PLA-based ultrafiltration nanocomposite membranes: one negatively charged (PLA-M-) and one positively charged (PLA-M+). We integrated these membranes into systems with varying arrangements to control fouling and eliminate heavy metals, organic pollutants, and nutrients from raw municipal wastewater collected by the local wastewater treatment plant in Abu Dhabi (UAE). The performance of two integrated systems (i.e., PLA-M+/PLA-M- and PLA-M-/PLA-M+) was compared in terms of permeate flux, contaminant removal efficiencies, and fouling mitigation. The PLA-M+/PLA-M- system achieved removal efficiencies of 79.6 %, 92.6 %, 88.7 %, 85.2 %, 98.9 %, 94 %, 83.3 %, and 98.3 % for chemical oxygen demand (COD), nitrate (NO3--N), phosphate (PO43--P), ammonium (NH4+-N), iron (Fe), zinc (Zn), nickel (Ni), and copper (Cu), respectively. On the other hand, the PLA-M-/PLA-M+ system recorded removal efficiencies of 85.8 %, 95.9 %, 100 %, 81.9 %, 99.3 %, 91.9 %, 72.9 %, and 98.9 % for COD, NO3--N, PO43--P, NH4+-N, Fe, Zn, Ni, and Cu, respectively. Notably, the PLA-M-/PLA-M+ system demonstrated superior antifouling resistance, making it the preferred integrated system. These findings demonstrate the potential of eco-friendly PLA nanocomposite UF-MMMs as a promising alternative to petroleum-based polymeric membranes for efficient and sustainable wastewater treatment.

Beyond Energy Balance: Environmental Trade-Offs of Organics Capture and Low Carbon-to-Nitrogen Ratio Sewage Treatment Systems

Several life-cycle assessments (LCAs) have evaluated the environmental impacts (EIs) of different wastewater treatment (WWT) configurations, attempting resource recovery and energy efficiency. However, a plant-wide LCA considering up-concentration primary treatment and low carbon-to-nitrogen (C/N) ratio sewage at the secondary biological treatment (SBT) has not yet been conducted. This study identifies the environmental trade-offs and hotspots for the chemically enhanced primary treatment (CEPT) and low C/N ratio SBT emerging processes compared to conventional WWT. The life-cycle inventories were calculated using a stoichiometric life-cycle inventory framework that couples stoichiometry and kinetics to obtain site-specific water, air, and soil emissions. The midpoint results of LCA show that CEPT with anaerobic digestion (AD) for sludge treatment achieves energy self-sufficiency, but increases marine eutrophication (MEu) by 1 order of magnitude compared to conventional WWT. A mainstream anaerobic fluidized-bed bioreactor and a partial nitritation-anammox fluidized-bed membrane bioreactor which can reduce all environmental impacts by 17-47%, including MEu, are proposed as the SBT of the low-carbon CEPT settled sewage. Integrating the standardized S-LCI framework resulted in a site-specific LCA that aids decision-makers on choosing between higher reductions in most EIs at the expense of high MEu or less but consistent reductions in all EI categories.

Performance evaluation of A2O MBR system with graphene oxide (GO) blended polysulfone (PSf) composite membrane for treatment of high strength synthetic wastewater containing lead

High strength synthetic wastewater containing 5 mg L^-1 of lead was studied for treatment using an A2O MBR system. The system showed 99% removal of ammonia and COD, a maximum removal of 52% of total phosphorus and an average minimum removal of 72% of total nitrogen. A maximum lead removal of 98% was achieved for hydraulic retention time (HRT) of 144 h, which decreased to 85% when the influent COD concentration was decreased. Mass balance for lead revealed that much of its removal was through accumulation by the biomass present in the anaerobic and anoxic tanks. Comparative study on virgin PSf and GO blended PSf membrane showed that the GO blended membrane lasted 1.4 times longer than the other. SEM-EDS of membranes showed lead peaks on the fouled and un-fouled sections of the membranes indicating the association of lead with the foulant and the role of membrane in lead separation. Good separation efficiency was achieved irrespective of the membranes used.

Sustainable removal of pernicious arsenic and cadmium by a novel composite of MnO2 impregnated alginate beads: A cost-effective approach for wastewater treatment

There is a dire necessity of developing low cost waste water treatment systems, for the efficient removal of noxious heavy metals (and metalloids) such as Arsenic (As) and Cadmium (Cd). Magnetic biopolymer (CABs-MO) was synthesized by the entrapment of nanocrystalline MnO₂ in the polymeric microcapsules of calcium alginate (CABs). Batch experiments were conducted under constant pH (6.5), temperature (25^OC), different initial concentrations (30-300 mg L^-1) and contact times (0-48 h) to study the adsorption isotherms and removal kinetics of pristine (CABs) and hybrid biopolymer (CABs-MO) for the removal of As and Cd. The pseudo-equilibrium process was mathematically well explained by the pseudo-second-order kinetic (R² ≥ 0.99) and Langmuir isotherm model (R² ≥ 0.99) with the highest monolayer sorption capacity of 63.6 mg g^-1 for Cd on CABs-MO. The As removal rate was maximum up to 6.5 mg g^-1 after 12 h of contact period in a single contaminant system than in the mixed contaminant (As + Cd) system (0.8 mg g^-1), though the effect was non-significant for Cd (p < 0.05; t-test). The performance of the 10 mM HCl as a regenerating agent was superior (for As in comparison to Cd, p < 0.05; t-test) compared to distilled water (DW) through three to five regeneration cycles. Therefore, the obtained results clearly validate the feasibility of CABs-MO as a potential promising adsorbent for removing metal contaminants from the wastewater. Further research is required to study the decontamination of emerging contaminants with such novel composite beads characterized by varied physico-chemical properties.

Comparative study on treatment performance, membrane fouling, and microbial community profile between conventional and hybrid sequencing batch membrane bioreactors for municipal wastewater treatment

A sequencing batch conventional membrane bioreactor (SB-CMBR) and sequencing batch hybrid membrane bioreactor (SB-HMBR) were operated in parallel under two different hydraulic retention times (HRTs) (namely 12 h and 6 h), and their chemical oxygen demand (COD) and nutrient removal performance, membrane fouling behavior, and microbial community characteristics were compared. Both systems exhibited high organic matter (> 95%) and ammonium (> 98%) removal performance regardless of the HRT applied. As the HRT was reduced from 12 to 6 h, total nitrogen removal slightly increased in both reactors, being higher in the carrier-based MBR, where anoxic zones may have been established within the biofilm. Conversely, total phosphorus removal improved only in the SB-CMBR at the shorter HRT. Moreover, activity batch assays have shown a faster P uptake rate in the SB-CMBR than in the SB-HMBR, a result likely associated with the lower relative abundance of phosphate-accumulating organisms in both adhered and suspended biomass fractions in the hybrid MBR. The results also revealed that more pronounced increases in the transmembrane pressure and, consequently, in the membrane fouling rate at higher COD loading rates were observed in the SB-CMBR, where the soluble microbial products (proteins, polysaccharides, and especially, transparent exopolymer particles), supernatant turbidity, and filamentous bacteria were more significant. Overall, as compared to the conventional MBR, the plastic media-based SB-HMBR showed a lower fouling propensity at all hydraulic conditions tested.

Adsorption of heavy metal tolerance strains to Pb2+ and Cd2+ in wastewater

The functional strains with high tolerance to heavy metal Pb²⁺ and Cd²⁺ were screened from soil obtained in a heavy metal waste accumulation area. The immobilized biological adsorbent was made by embedding method and used for treatment of wastewater containing heavy metals. The effects of initial concentration of heavy metals, adsorption time, pH value of wastewater, and dosage of adsorbent on adsorption performance were investigated. The study showed (1) the strains tested were Brevibacterium and their maximum tolerable concentrations for Pb²⁺ and Cd²⁺ were 2200 and 700 mg/L, respectively; (2) the maximum adsorption rate for Pb²⁺ and Cd²⁺ was 87.77% and 57.50% respectively when the dosage of adsorbent was 10 g/L and the pH value of wastewater was 6; (3) Pb²⁺ and Cd²⁺ could be adsorbed in the equilibrium solution for 40 min and the maximum adsorption capacity reached 114.36 mg/g and 82.12 mg/g, respectively; and (4) when the initial pH value of the wastewater was 5-7, the adsorption rate decreased with the increase of the concentration, and the initial concentration of Pb²⁺ had a greater effect on the adsorption rate than Cd²⁺. Langmuir and Freundlich equation showed that the adsorption of Pb²⁺ and Cd²⁺ was mainly on the surface of monolayer. And the pseudo-second-order kinetic equation indicates that Cd²⁺ has a relatively greater adsorption rate than Pb²⁺ does.

Mechanisms of microbial community structure and biofouling shifts under multivalent cations stress in membrane bioreactors

Five lab-scale membrane bioreactors (MBRs) were continuously operated to investigate the mechanisms and linkages of the microbial community and membrane fouling with trivalent metal cations (Fe(III) and Al(III)) and bivalent metal cations (Ca(II) and Mg(II)) shock loads. COD and NH₄⁺-N removals showed recovery trends along with treatment process in the presence of metals. Trivalent metal cations reduced trans-membrane pressure (TMP) as well as fouling rate (dTMP/dt) and extended membrane module replacement period by binding activated sludge extracellular polymeric substance (EPS) and effluent soluble microbial product (SMP) productions. Illunima sequencing of 16S rRNA gene showed that metal stress stimulated specific metal-tolerance bacteria in the MBRs. Canonical correspondence analysis indicated that EPS and SMP made different contributions to the distribution of microbial community structure in Fe(III) and Al (III) systems, respectively. Under bivalent metal conditions, microbial community shifts and Ca(II) binding bridge worked together to inhibit EPS and SMP, while filamentous bacteria stimulated by Mg(II) that mainly controlled membrane fouling. This study has shown that the comparison of tri- and bivalent metals for membrane fouling control with binding bridge and functional microorganisms can provide a strategy for practical membrane bioreactor applications.

Assessing membrane fouling and the performance of pilot-scale membrane bioreactor (MBR) to treat real municipal wastewater during winter season in Nordic regions

In this study, the performance of a pilot-scale membrane bioreactor (MBR) to treat real municipal wastewater was assessed at low temperatures (7 to 20°C) in Nordic regions. First, the effect of low temperatures on membrane fouling was evaluated by monitoring trans-membrane pressure. A significant membrane fouling was observed when the sludge temperature inside the MBR unit was below 10°C with a 75% permeability drop, thus indicating high deterioration of the membrane performance at low temperatures. Moreover, increasing values of sludge volume index (SVI) during low temperatures showed high deterioration of sludge settleability. As for the pollution removal, MBR achieved high performances primarily for pathogens and emerging micropollutants. The average log reductions of 1.82, 3.02, and 1.94 log units were achieved for norovirus GI, norovirus GII, and adenoviruses, respectively. Among the four trace organic compounds (TrOCs), the average removal efficiencies of bisoprolol, diclofenac and bisphenol A were 65%, 38%, and >97%, respectively. However, carbamazepine was not efficiently removed (-89% to 28%). Regarding trace metals, an average removal of >80% was achieved for Cd, Pb, and V. For the rest of the metals, the removal capacities were between 30 and 60%.

Structure and distribution of inorganic components in the cake layer of a membrane bioreactor treating municipal wastewater

A laboratory-scale submerged anoxic-oxic membrane bioreactor treating municipal wastewater was operated to investigate the structure and distribution of the inorganic cake layer buildup on the membrane. BCR (European Community Bureau of Reference) sequential extraction, X-ray photoelectron spectroscopy (XPS), and both map and line scan of energy-dispersive X-ray analysis (EDX) were performed for cake layer characterization. BCR results showed that Si, Al, Ca, Mg, Fe, and Ba were the predominant inorganic elements in the cake layer, and they occurred mostly as crystal particles. Crystal SiO2 was the dominant inorganic compound while Ca in the form of CaSO4 (dominant) and CaCO3 were also present, but exerted little effect on the cake layer structure because most of these compounds were deposited as precipitates on the reactor bottom. EDX results indicated that Si and Al accumulated together along the cross-sectional cake layer in the form of Si-Al (SiO2-Al2O3) crystal particles.

Performance evaluation and modeling of a submerged membrane bioreactor treating combined municipal and industrial wastewater using radial basis function artificial neural networks

Treatment process models are efficient tools to assure proper operation and better control of wastewater treatment systems. The current research was an effort to evaluate performance of a submerged membrane bioreactor (SMBR) treating combined municipal and industrial wastewater and to simulate effluent quality parameters of the SMBR using a radial basis function artificial neural network (RBFANN). The results showed that the treatment efficiencies increase and hydraulic retention time (HRT) decreases for combined wastewater compared with municipal and industrial wastewaters. The BOD, COD, [Formula: see text] and total phosphorous (TP) removal efficiencies for combined wastewater at HRT of 7 hours were 96.9%, 96%, 96.7% and 92%, respectively. As desirable criteria for treating wastewater, the TBOD/TP ratio increased, the BOD and COD concentrations decreased to 700 and 1000 mg/L, respectively and the BOD/COD ratio was about 0.5 for combined wastewater. The training procedures of the RBFANN models were successful for all predicted components. The train and test models showed an almost perfect match between the experimental and predicted values of effluent BOD, COD, [Formula: see text] and TP. The coefficient of determination (R(2)) values were higher than 0.98 and root mean squared error (RMSE) values did not exceed 7% for train and test models.

Potentially novel copper resistance genes in copper-enriched activated sludge revealed by metagenomic analysis

In this study, we utilized the Illumina high-throughput metagenomic approach to investigate diversity and abundance of both microbial community and copper resistance genes (CuRGs) in activated sludge (AS) which was enriched under copper selective stress up to 800 mg/L. The raw datasets (~3.5 Gb for each sample, i.e., the copper-enriched AS and the control AS) were merged and normalized for the BLAST analyses against the SILVA SSU rRNA gene database and self-constructed copper resistance protein database (CuRD). Also, the raw metagenomic sequences were assembled into contigs and analyzed based on Open Reading Frames (ORFs) to identify potentially novel copper resistance genes. Among the different resistance systems for copper detoxification under the high copper stress condition, the Cus system was the most enriched system. The results also indicated that genes encoding multi-copper oxidase played a more important role than those encoding efflux proteins. More significantly, several potentially novel copper resistance ORFs were identified by Pfam search and phylogenic analysis. This study demonstrated a new understanding of microbial-mediated copper resistance under high copper stress using high-throughput shotgun sequencing technique.

Fermentation of lignocellulosic hydrolyzate using a submerged membrane bioreactor at high dilution rates

A submerged membrane bioreactor (sMBR) was developed to ferment toxic lignocellulosic hydrolyzate to ethanol. The sMBR achieved high cell density of Saccharomyces cerevisiae during continuous cultivation of the hydrolyzate by completely retaining all yeast cells inside the sMBR. The performance of the sMBR was evaluated based on the ethanol yield and productivity at the dilution rates 0.2, 0.4, 0.6, and 0.8h(-1) with the increase of dilution rate. Results show that the yeast in the sMBR was able to ferment the wood hydrolyzate even at high dilution rates, attaining a maximum volumetric ethanol productivity of 7.94 ± 0.10 g L(-1)h(-1) at a dilution rate of 0.8h(-1). Ethanol yields were stable at 0.44 ± 0.02 g g(-1) during all the tested dilution rates, and the ethanol productivity increased from 2.16 ± 0.15 to 7.94 ± 0.10 g L(-1)h(-1). The developed sMBR systems running at high yeast density demonstrate a potential for a rapid and productive ethanol production from wood hydrolyzate.

Efficacy of single-chamber microbial fuel cells for removal of cadmium and zinc with simultaneous electricity production

Simultaneous high power generation (3.6 W/m(2)) and high Cd (90%) and Zn (97%) removal efficiencies were demonstrated in a single chamber air-cathode microbial fuel cell (MFC). The maximum tolerable concentrations (MTCs) were estimated as 200 μM for Cd and 400 μM for Zn. Increasing the concentrations of Cd to 300 μM and Zn to 500 μM resulted in voltage drops by 71 and 74%, respectively. Feeding the MFCs with incrementally increased Cd and Zn concentrations resulted in much slower reduction in voltage output. Biosorption and sulfides precipitation are the major mechanisms for the heavy metal removal in the MFCs.

Co-treatment of acid mine drainage with municipal wastewater: performance evaluation

Co-treatment of acid mine drainage (AMD) with municipal wastewater (MWW) using the activated sludge process is a novel treatment technology offering potential savings over alternative systems in materials, proprietary chemicals and energy inputs. The impacts of AMD on laboratory-scale activated sludge units (plug-flow and sequencing batch reactors) treating synthetic MWW were investigated. Synthetic AMD containing Al, Cu, Fe, Mn, Pb, Zn and SO4 at a range of concentrations and pH values was formulated to simulate three possible co-treatment processes, i.e., (1) adding raw AMD to the activated sludge aeration tank, (2) pre-treating AMD prior to adding to the aeration tank by mixing with digested sludge and (3) pre-treating AMD by mixing with screened MWW. Continuous AMD loading to the activated sludge reactors during co-treatment did not cause a significant decrease in chemical oxygen demand (COD), 5-day biochemical oxygen demand, or total organic carbon removal; average COD removal rates ranged from 87-93%. Enhanced phosphate removal was observed in reactors loaded with Fe- and Al-rich AMD, with final effluent TP concentrations<2 mg/L. Removal rates for dissolved Al, Cu, Fe and Pb were 52-84%, 47-61%, 74-86% and 100%, respectively, in both systems. Manganese and Zn removal were strongly linked to acidity; removal from net-acidic AMD was <10% for both metals, whereas removal from circum-neutral AMD averaged 93-95% for Mn and 58-90% for Zn. Pre-mixing with screened MWW was the best process option in terms of AMD neutralization and metal removal. However, significant MWW alkalinity was consumed, suggesting an alkali supplement may be necessary.

Heavy metal speciation and acid treatment of activated sludge developed in a membrane bioreactor

The aim of this study was to identify the heavy metals forms (exchangeable and bound to carbonate, Fe/Mn oxides, bound to organic matter and sulphide, and residual) associated with different fractions of excess sludge produced by a membrane bioreactor (MBR). Furthermore, the release of metals from the sludge to the liquid was investigated by applying acid treatment using 10% (v/v) H2SO4 (T = 25 degrees C, solid-liquid ratio 1:5 w/v) for contact time ranging from 15 min to 4 h. Metal partitioning in sludge, as determined by the sequential chemical extraction showed that the dominant form of both Ni and Zn was bound to the exchangeable and carbonate fraction; the latter were very unstable and sensitive to environmental conditions. The dominant Cu fraction was bound to organic matter and sulphide, while Pb was found to be mainly in the residual fraction which is very stable. Metal speciation after acidification with H2SO4 indicates changes of metal content in sludge and an increase of the exchangeable and bound to carbonate fraction for all metals except Cu. Acidification resulted in removal of 82% for Ni, 78% for Zn, 47% for Cu and 45% for Pb.

Effects of heavy metal wastewater on the anoxic/aerobic-membrane bioreactor bioprocess and membrane fouling

Heavy metals have significant negative effects on anoxic/aerobic-membrane bioreactors (A/O-MBR). The changes in the performance of A/O-MBR fed with municipal wastewater containing 0.25-2.56 mg/L (low concentrations) and 3.7-32.3mg/L (high concentrations) of zinc, copper, lead, and cadmium were studied in this paper. The nitrification rate decreased to 27% and 46%, whereas the denitrification rate decreased to 20% and 34% under treatment with low/high concentrations of heavy metals, which indicate that heavy metals more significantly affect nitrification than denitrification. Heavy metals also resulted in the increase of carbohydrate of extracellular polymer substances and a smaller particle size distribution. Scanning electron microscope images, energy-dispersive X-ray spectroscopy and atomic absorption spectrometry analysis of fouled membranes showed solid inorganic scale deposits on the membrane. All these results suggest that heavy metals affect membrane fouling in two ways: (a) modification of sludge characteristics; and (b) contribution to inorganic fouling.

Integration of aerobic granular sludge and mesh filter membrane bioreactor for cost-effective wastewater treatment

Conventional MBR has been mostly based on floc sludge and the use of costly microfiltration membranes. Here, a novel aerobic granule (AG)-mesh filter MBR (MMBR) process was developed for cost-effective wastewater treatment. During 32-day continuous operation, a predominance of granules was maintained in the system, and good filtration performance was achieved at a low trans-membrane pressure (TMP) of below 0.025 m. The granules showed a lower fouling propensity than sludge flocs, attributed to the formation of more porous biocake layer at mesh surface. A low-flux and low-TMP filtration favored a stable system operation. In addition, the reactor had high pollutant removal efficiencies, with a 91.4% chemical oxygen demand removal, 95.7% NH(4)(+) removal, and a low effluent turbidity of 4.1 NTU at the stable stage. This AG-MMBR process offers a promising technology for low-cost and efficient treatment of wastewaters.

Impact of herbicide Ametryn on microbial communities in mixed liquor of a membrane bioreactor (MBR)

Ametryn, which is a second generation herbicide, was introduced to a lab-scale MBR at a concentration of 1mg/L and a 20-40% removal was observed at HRT ranging from 7.8 to 15.6h for an average influent Ametryn concentration of 0.8 mg/L. Components of EPS (protein and carbohydrates) increased in the bioreactor and the observed biomass production reduced after the addition of Ametryn. In a batch study, GAC was added to MBR mixed liquor and removal of Ametryn via biodegradation and adsorption were measured. Five common bacterial colony types (Gram negative and positive bacilli and Gram negative cocci) were identified and three of these were resistant to Ametryn up to 5mg/L. GAC was found to be a very effective Ametryn adsorption medium and in some occasions Ametryn may have acted as a nutrient source for bacteria.

Model development and parameter estimation for a hybrid submerged membrane bioreactor treating Ametryn

A lab-scale membrane bioreactor (MBR) was used to remove Ametryn from synthetic wastewater. It was found that concentrations of MLSS and extra-cellular polymeric substances (EPS) in MBR mixed liquor fluctuated (production and decay) differently for about 40 days (transition period) after the introduction of Ametryn. During the subsequent operations with higher organic loading rates, it was also found that a low net biomass yield (higher death rate) and a higher rate of fouling of membrane (a very high rate during the first 48 h) due to increased levels of bound EPS (eEPS) in MBR mixed liquor. A mathematical model was developed to estimate the kinetic parameters before and after the introduction of Ametryn. This model will be useful in simulating the performance of a MBR treating Ametryn in terms of flux, rate of fouling (in terms of transmembrane pressure and membrane resistance) as well as treatment efficiency.

Assessment of metal removal, biomass activity and RO concentrate treatment in an MBR-RO system

This work investigated the removal of metals from wastewater using a combined Membrane Bioreactor-Reverse Osmosis (MBR-RO) system. The concentrate produced by the RO system was treated by a fixed bed column packed with zeolite. The average metal removal accomplished by the MBR treating municipal wastewater was Cu(90%), Fe(85%), Mn(82%), Cr(80%), Zn(75%), Pb(73%), Ni(67%), Mg(61%), Ca(57%), Na(30%) and K(21%), with trivalent and divalent metals being more effectively removed than monovalent ones. The metal removal achieved by the MBR system treating wastewater spiked with Cu, Pb, Ni and Zn (4-12 mg L(-1) of each metal) was Pb(96%)>Cu(85%)>Zn(78%)>Ni(48%). The combined MBR-RO system enhanced metal removal from municipal wastewater to the levels of >90.9->99.8%, while for wastewater spiked with heavy metals the removal efficiencies were >98.4%. Fixed bed column packed with zeolite was effective for the removal of Cu, Pb and Zn from the RO concentrate, while Ni removal was satisfactory only at the initial stages of column operation. The presence of heavy metals increased inorganic fouling.