G-CNTs/PVDF mixed matrix membranes with improved antifouling properties and filtration performance

A novel nanocomposite OMWCNT-A-GO was synthesized by conjugating OMWCNT and GO. The P-OMWCNT-A-GO membrane was fabricated by non-solvent induced phase inversion. The P-OMWCNT-A-GO exhibits the best water flux, BSA rejection and flux recovery. It should be due to the enhanced membrane pore size, porosity and hydrophilicity. Although carbon nanomaterials have been widely used as effective nanofillers for fabrication of mixed matrix membranes (MMMs) with outstanding performances, the reproducibility of the fabricated MMMs is still hindered by the non-homogenous dispersion of these carbon nanofillers in membrane substrate. Herein, we report an effective way to improve the compatibility of carbon-based nanomaterials with membrane matrixes. By chemically conjugating the oxidized CNTs (o-CNTs) and GO using hexanediamine as cross-linker, a novel carbon nanohybrid material (G-CNTs) was synthesized, which inherited both the advanced properties of multi-walled carbon nanotubes (CNTs) and graphene oxide (GO). The G-CNTs incorporated polyvinylidene fluoride (PVDF) MMMs (G-CNTs/PVDF) were fabricated via a non-solvent induced phase separation (NIPS) method. The filtration and antifouling performances of G-CNTs/PVDF were evaluated using distillate water and a 1 g/L bovine serum albumin (BSA) aqueous solution under 0.10 MPa. Compared to the MMMs prepared with o-CNTs, GO, the physical mixture of o-CNTs and GO and pure PVDF membrane, the G-CNTs/PVDF membrane exhibited the highest water flux up to 220 L/m²/h and a flux recovery ratio as high as 90%, as well as the best BSA rejection rate. The excellent performances should be attributed to the increased membrane pore size, porosity and hydrophilicity of the resulted membrane. The successful synthesis of the novel nanohybrid G-CNTs provides a new type of nanofillers for MMMs fabrication.     

Aggravation of membrane fouling and methane leakage by a three-phase separator in an external anaerobic ceramic membrane bioreactor

The existence of three-phase separator did not affect COD removal in the EAnCMBR. The existence of three-phase separator aggravated methane leakage of EAnCMBR. The existence of three-phase separator aggravated membrane fouling rate of EAnCMBR. Start-up of EAnCMBR equipped three-phase separator was slightly delayed. The three-phase separator is a critical component of high-rate anaerobic bioreactors due to its significant contribution in separation of biomass, wastewater, and biogas. However, its role in an anaerobic membrane bioreactor is still not clear. In this study, the distinction between an external anaerobic ceramic membrane bioreactor (EAnCMBR) unequipped (R1) and equipped (R2) with a three-phase separator was investigated in terms of treatment performance, membrane fouling, extracellular polymers of sludge, and microbial community structure. The results indicate that the COD removal efficiencies of R1 and R2 were 98.2%±0.4% and 98.1%±0.4%, respectively, but the start-up period of R2 was slightly delayed. Moreover, the membrane fouling rate of R2 (0.4 kPa/d) was higher than that of R1 (0.2 kPa/d). Interestingly, the methane leakage from R2 (0.1 L/d) was 20 times higher than that from R1 (0.005 L/d). The results demonstrate that the three-phase separator aggravated the membrane fouling rate and methane leakage in the EAnCMBR. Therefore, this study provides a novel perspective on the effects of a three-phase separator in an EAnCMBR.     

An antifouling catechol/chitosan-modified polyvinylidene fluoride membrane for sustainable oil-in-water emulsions separation

• Underwater superoleophobic membrane was fabricated by deposition of catechol/chitosan. • The membrane had ultrahigh pure water flux and was stable under harsh pH conditions. • The membrane exhibited remarkable antifouling property in O/W emulsion separation. • The hydration layer on the membrane surface prevented oil droplets adhesion. Low-pressure membrane filtrations are considered as effective technologies for sustainable oil/water separation. However, conventional membranes usually suffer from severe pore clogging and surface fouling, and thus, novel membranes with superior wettability and antifouling features are urgently required. Herein, we report a facile green approach for the development of an underwater superoleophobic microfiltration membrane via one-step oxidant-induced ultrafast co-deposition of naturally available catechol/chitosan on a porous polyvinylidene fluoride (PVDF) substrate. Membrane morphology and surface chemistry were studied using a series of characterization techniques. The as-prepared membrane retained the original pore structure due to the ultrathin and uniform catechol/chitosan coating. It exhibited ultrahigh pure water permeability and robust chemical stability under harsh pH conditions. Moreover, the catechol/chitosan hydrophilic coating on the membrane surface acting as an energetic barrier for oil droplets could minimize oil adhesion on the surface, which endowed the membrane with remarkable antifouling property and reusability in a cyclic oil-in-water (O/W) emulsion separation. The modified membrane exhibited a competitive flux of ~428 L/(m²·h·bar) after three filtration cycles, which was 70% higher than that of the pristine PVDF membrane. These results suggest that the novel underwater superoleophobic membrane can potentially be used for sustainable O/W emulsions separation, and the proposed green facile modification approach can also be applied to other water-remediation materials considering its low cost and simplicity.     

Comparison of membrane fouling in ultrafiltration of down-flow and up-flow biological activated carbon effluents

The UF membrane fouling by down- and up-flow BAC effluents were compared. Up-flow BAC effluent fouled the membrane faster than down-flow BAC effluent. The combined effects dominated irreversible fouling. The extent of fouling exacerbated by inorganic particles was higher. The TMP, permeate flux, and normalized membrane flux during 21 days of UF of DBAC and UBAC effluents. Fouling during ultrafiltration of down- and up-flow biological activated carbon effluents was investigated to determine the roles of polysaccharides, proteins, and inorganic particles in ultrafiltration membrane fouling. During ultrafiltration of down- flow biological activated carbon effluent, the trans-membrane pressure was≤26 kPa and the permeate flux was steady at 46.7 L?m⁻²?h⁻¹. However, during ultrafiltration of up-flow biological activated carbon effluent, the highest trans-membrane pressure was almost 40 kPa and the permeate flux continuously decreased to 30 L?m⁻²?h⁻¹. At the end of the filtration period, the normalized membrane fluxes were 0.88 and 0.62 for down- and up-flow biological activated carbon effluents, respectively. The membrane removed the turbidity and polysaccharides content by 47.4% and 30.2% in down- flow biological activated effluent and 82.5% and 22.4% in up-flow biological activated carbon effluent, respectively, but retained few proteins. The retention of polysaccharides was higher on the membrane that filtered the down- flow biological activated effluent compared with that on the membrane that filtered the up-flow biological activated carbon effluent. The polysaccharides on the membranes fouled by up-flow biological activated carbon and down- flow biological activated effluents were spread continuously and clustered, respectively. These demonstrated that the up-flow biological activated carbon effluent fouled the membrane faster. Membrane fouling was associated with a portion of the polysaccharides (not the proteins) and inorganic particles in the feed water. When there was little difference in the polysaccharide concentrations between the feed waters, the fouling extent was exacerbated more by inorganic particles than by polysaccharides.     

Hydrophilic/underwater superoleophobic graphene oxide membrane intercalated by TiO2 nanotubes for oil/water separation

GO/TiO₂ membrane was prepared by assembling GO nanosheets and TiO₂ nanotubes. The intercalation of TiO₂ nanotubes enlarged the space of GO interlayers and modified the surface morphology. Hydrophilic/underwater superoleophobic property of GO/TiO₂ membrane was obtained. Water permeability, hydrophilicity, oleophobicity and antifouling ability of GO-based membrane were all enhanced by intercalating TiO₂ nontubes. Membrane technology for oil/water separation has received increasing attention in recent years. In this study, the hydrophilic/underwater superoleophobic membrane with enhanced water permeability and antifouling ability were fabricated by synergistically assembling graphene oxide(GO) nanosheets and titanium dioxide (TiO₂) nanotubes for oil/water separation. GO/TiO₂ membrane exhibits hydrophilic and underwater superoleophobic properties with water contact angle of 62° and under water oil contact angle of 162.8°. GO/TiO₂ membrane shows greater water permeability with the water flux up to 531 L/(m²·h·bar), which was more than 5 times that of the pristine GO membrane. Moreover, GO/TiO₂membrane had excellent oil/water separation efficiency and anti-oil-fouling capability, as oil residual in filtrate after separation was below 5 mg/L and flux recovery ratios were over 80%.The results indicate that the intercalation of TiO₂ nanotubes into adjacent GO nanosheets enlarged the channel structure and modified surface topography of the obtained GO/TiO₂ membranes, which improved the hydrophilicity, permeability and anti-oil-fouling ability of the membranes, enlightening the great prospects of GO/TiO₂ membrane in oil-water treatment.     

PVDF ultrafiltration membranes of controlled performance via blending PVDF-g-PEGMA copolymer synthesized under different reaction times

PVDF blended different graft ratio of PVDF-g-PEGMA were systematically studied. Tuning the amphiphilic copolymer synthesis time to control membrane performance. The PVDF membrane with PVDF-g-PEGMA at 19 h possesses most surface oxygen content. The synthesis time of PVDF-g-PEGMA at 9 h is good for high flux UF membrane. Polyvinylidene fluoride grafted with poly(ethylene glycol) methyl ether methacrylate (PVDF-g-PEGMA) was synthesized using atomic transfer radical polymerization (ATRP) at different reaction times (9 h, 19 h, and 29 h). The corresponding conversion rates were 10%, 20% and 30%, respectively. PVDF was blended with the copolymer mixture containing PVDF-g-PEGMA, solvent and residual PEGMA under different reaction times. In this study, we explored the effect of the copolymer mixture additives with different synthesis times on cast membrane performance. Increasing the reaction time of PVDF-g-PEGMA causes more PVDF-g-PEGMA and less residual PEGMA to be found in the casting solution. Incremental PVDF-g-PEGMA can dramatically increase the viscosity of the casting solution. An overly high viscosity led to a delayed phase inversion, thus hindering PEGMA segments in PVDF-g-PEGMA from migrating to the membrane surface. However, more residual PEGMA contributed to helping more PEGMA segments migrate to the membrane surface. The pure water fluxes of the blended membrane with reaction times of 9 h, 19 h, and 29 h are 5445 L·m⁻²·h⁻¹, 1068 L·m⁻²·h⁻¹and 1179 L·m⁻²·h⁻¹, respectively, at 0.07 MPa. Delayed phase inversion can form smaller surface pore size distributions, thus decreasing the water flux for the membranes with PVDF-g-PEGMA at 19 h and 29 h. Therefore, we can control the membrane pore size distribution by decreasing the reaction time of PVDF-g-PEGMA to obtain a better flux performance. The membrane with PVDF-g-PEGMA at 19 h exhibits the best foulant rejection and cleaning recovery due to its narrow pore size distribution and high surface oxygen content.     

Electro-assisted CNTs/ceramic flat sheet ultrafiltration membrane for enhanced antifouling and separation performance

• A stable and electroconductive CNTs/ceramic membrane was fabricated. • The membrane with the electro-assistance exhibited optimal fouling mitigation. • The removal efficiency was improved by the -2.0 V electro-assistance. • Electro-assisted filtration is energy-saving than that of commercial membrane. Ultrafiltration is employed as an important process for water treatment and reuse, which is of great significance to alleviate the shortage of water resources. However, it suffers from severe membrane fouling and the trade-off between selectivity and permeability. In this work, a CNTs/ceramic flat sheet ultrafiltration membrane coupled with electro-assistance was developed for improving the antifouling and separation performance. The CNTs/ceramic flat sheet membrane was fabricated by coating cross-linked CNTs on ceramic membrane, featuring a good electroconductivity of 764.75 S/m. In the filtration of natural water, the permeate flux of the membrane with the cell voltage of -2.0 V was 1.8 times higher than that of the membrane without electro-assistance and 5.7-fold greater than that of the PVDF commercial membrane. Benefiting from the electro-assistance, the removal efficiency of the typical antibiotics was improved by 50%. Furthermore, the electro-assisted membrane filtration process showed 70% reduction in energy consumption compared with the filtration process of the commercial membrane. This work offers a feasible approach for membrane fouling mitigation and effluent quality improvement and suggests that the electro-assisted CNTs/ceramic membrane filtration process has great potential in the application of water treatment.     

Development of combined coagulation-hydrolysis acidification-dynamic membrane bioreactor system for treatment of oilfield polymer-flooding wastewater

• We created a combined system for treating oilfield polymer-flooding wastewater. • The system was composed of coagulation, hydrolysis acidification and DMBR. • Coagulant integrated with demulsifier dominated the removal of crude oil. • The DMBR proceed efficiently without serious membrane fouling. A combined system composed of coagulation, hydrolysis acidification and dynamic membrane bioreactor (DMBR) was developed for treating the wastewater produced from polymer flooding. Performance and mechanism of the combined system as well as its respective units were also evaluated. The combined system has shown high-capacity to remove all contaminants in the influent. In this work, the coagulant, polyacrylamide-dimethyldiallyammonium chloride-butylacrylate terpolymer (P(DMDAAC-AM-BA)), integrated with demulsifier (SD-46) could remove 91.8% of crude oil and 70.8% of COD. Hydrolysis acidification unit improved the biodegradability of the influent and the experimental results showed that the highest acidification efficiency in hydrolysis acidification reactor was 20.36% under hydraulic retention time of 7 h. The DMBR proceeded efficiently without serious blockage process of membrane fouling, and the concentration of ammonia nitrogen (NH₃-N), oil, chemical oxygen demand and biological oxygen demand in effluent were determined to be 3.4±2.1, 0.3±0.6, 89.7±21.3 and 13±4.7 mg/L.     

Enhanced cross-flow filtration with flat-sheet ceramic membranes by titanium-based coagulation for membrane fouling control

• Ceramic membrane filtration showed high performance for surface water treatment. • PTC pre-coagulation could enhance ceramic membrane filtration performance. • Ceramic membrane fouling was investigated by four varied mathematical models. • PTC pre-coagulation was high-effective for ceramic membrane fouling control. Application of ceramic membrane (CM) with outstanding characteristics, such as high flux and chemical-resistance, is inevitably restricted by membrane fouling. Coagulation was an economical and effective technology for membrane fouling control. This study investigated the filtration performance of ceramic membrane enhanced by the emerging titanium-based coagulant (polytitanium chloride, PTC). Particular attention was paid to the simulation of ceramic membrane fouling using four widely used mathematical models. Results show that filtration of the PTC-coagulated effluent using flat-sheet ceramic membrane achieved the removal of organic matter up to 78.0%. Permeate flux of ceramic membrane filtration reached 600 L/(m²·h), which was 10-fold higher than that observed with conventional polyaluminum chloride (PAC) case. For PTC, fouling of the ceramic membrane was attributed to the formation of cake layer, whereas for PAC, standard filtration/intermediate filtration (blocking of membrane pores) was also a key fouling mechanism. To sum up, cross-flow filtration with flat-sheet ceramic membranes could be significantly enhanced by titanium-based coagulation to produce both high-quality filtrate and high-permeation flux.     

Transparent exopolymer particles (TEPs)-associated protobiofilm: A neglected contributor to biofouling during membrane filtration

• Bacteria could easily and quickly attached onto TEP to form protobiofilms. • TEP-protobiofilm facilitate the transport of bacteria to membrane surface. • More significant flux decline was observed in the presence of TEP-protobiofilms. • Membrane fouling shows higher sensitivity to protobiofilm not to bacteria level. Transparent exopolymer particles (TEPs) are a class of transparent gel-like polysaccharides, which have been widely detected in almost every kind of feed water to membrane systems, including freshwater, seawater and wastewater. Although TEP have been thought to be related to the membrane fouling, little information is currently available for their influential mechanisms and the pertinence to biofouling development. The present study, thus, aims to explore the impact of TEPs on biofouling development during ultrafiltration. TEP samples were inoculated with bacteria for several hours before filtration and the formation of “protobiofilm” (pre-colonized TEP by bacteria) was examined and its influence on biofouling was determined. It was observed that the bacteria can easily and quickly attach onto TEPs and form protobiofilms. Ultrafiltration experiments further revealed that TEP-protobiofilms served as carriers which facilitated and accelerated transport of bacteria to membrane surface, leading to rapid development of biofouling on the ultrafiltration membrane surfaces. Moreover, compared to the feed water containing independent bacteria and TEPs, more flux decline was observed with TEP-protobiofilms. Consequently, it appeared from this study that TEP-protobiofilms play a vital role in the development of membrane biofouling, but unfortunately, this phenomenon has been often overlooked in the literature. Obviously, these findings in turn may also challenge the current understanding of organic fouling and biofouling as membrane fouling caused by TEP-protobiofilm is a combination of both. It is expected that this study might promote further research in general membrane fouling mechanisms and the development of an effective mitigation strategy.     

Surface modification of mesoporous silica nanoparticle with 4-triethoxysilylaniline to enhance seawater desalination properties of thin-film nanocomposite reverse osmosis membranes

• Mesoporous silica nanoparticle was modified with 4-triethoxysilylaniline. • AMSN-based TFN-RO membranes were prepared for seawater desalination. • Water transport capability of the AMSN was limited by polyamide. • Polyamide still plays a key role in permeability of the TFN RO membranes. Mesoporous silica nanoparticles (MSN), with higher water permeability than NaA zeolite, were used to fabricate thin-film nanocomposite (TFN) reverse osmosis (RO) membranes. However, only aminoalkyl-modified MSN and low-pressure (less than 2.1 MPa) RO membrane were investigated. In this study, aminophenyl-modified MSN (AMSN) were synthesized and used to fabricate high-pressure (5.52 MPa) RO membranes. With the increasing of AMSN dosage, the crosslinking degree of the aromatic polyamide decreased, while the hydrophilicity of the membranes increased. The membrane morphology was maintained to show a ridge-and-valley structure, with only a slight increase in membrane surface roughness. At the optimum conditions (AMSN dosage of 0.25 g/L), when compared with the pure polyamide RO membrane, the water flux of the TFN RO membrane (55.67 L/m²/h) was increased by about 21.6%, while NaCl rejection (98.97%) was slightly decreased by only 0.29%. However, the water flux of the membranes was much lower than expected. We considered that the enhancement of RO membrane permeability is attributed to the reduction of the effective thickness of the PA layer.     

Using loose nanofiltration membrane for lake water treatment: A pilot study

• A pilot study was conducted for drinking water treatment using loose NF membranes. • The membranes had very high rejection of NOM and medium rejection of Ca²⁺/Mg²⁺. • Organic fouling was dominant and contribution of inorganic fouling was substantial. • Both organic and inorganic fouling had spatial non-uniformity on membrane surface. • Applying EDTA at basic conditions was effective in removing membrane fouling. Nanofiltration (NF) using loose membranes has a high application potential for advanced treatment of drinking water by selectively removing contaminants from the water, while membrane fouling remains one of the biggest problems of the process. This paper reported a seven-month pilot study of using a loose NF membrane to treat a sand filtration effluent which had a relatively high turbidity (~0.4 NTU) and high concentrations of organic matter (up to 5 mg/L as TOC), hardness and sulfate. Results showed that the membrane demonstrated a high rejection of TOC (by>90%) and a moderately high rejection of two pesticides (54%–82%) while a moderate rejection of both calcium and magnesium (~45%) and a low rejection of total dissolved solids (~27%). The membrane elements suffered from severe membrane fouling, with the membrane permeance decreased by 70% after 85 days operation. The membrane fouling was dominated by organic fouling, while biological fouling was moderate. Inorganic fouling was mainly caused by deposition of aluminum-bearing substances. Though inorganic foulants were minor contents on membrane, their contribution to overall membrane fouling was substantial. Membrane fouling was not uniform on membrane. While contents of organic and inorganic foulants were the highest at the inlet and outlet region, respectively, the severity of membrane fouling increased from the inlet to the outlet region of membrane element with a difference higher than 30%. While alkaline cleaning was not effective in removing the membrane foulants, the use of ethylenediamine tetraacetate (EDTA) at alkaline conditions could effectively restore the membrane permeance.     

Bioinspired cellulose-based membranes in oily wastewater treatment

• Cellulose-based membrane separates oily wastewater mimicking the living things. • The three central surface mechanisms were reviewed. • Preparation, performance, and mechanism are critically evaluated. • First review of wettability based cellulose membrane as major material. • The current and future importance of the research are discussed. It is challenging to purify oily wastewater, which affects water-energy-food production. One promising method is membrane-based separation. This paper reviews the current research trend of applying cellulose as a membrane material that mimics one of three typical biostructures: superhydrophobic, underwater superoleophobic, and Janus surfaces. Nature has provided efficient and effective structures through the evolutionary process. This has inspired many researchers to create technologies that mimic nature’s structures or the fabrication process. Lotus leaves, fish scales, and Namib beetles are three representative structures with distinct functional and surface properties: superhydrophobic, underwater superoleophobic, and Janus surfaces. The characteristics of these structures have been widely studied and applied to membrane materials to improve their performance. One attractive membrane material is cellulose, which has been studied from the perspective of its biodegradability and sustainability. In this review, the principles, mechanisms, fabrication processes, and membrane performances are summarized and compared. The theory of wettability is also described to build a comprehensive understanding of the concept. Finally, future outlook is discussed to challenge the gap between laboratory and industrial applications.     

Influence of pore size and membrane surface properties on arsenic removal by nanofiltration membranes

Four NF membranes were compared regarding arsenate rejection and their properties. Rejection of arsenate had no relationship with membrane pore size. A more negative surface charge was favorable for arsenate rejection at neutral pH. A severe membrane fouling could lead to a great reduction of arsenic rejection. Nanofiltration (NF) has a great potential in removing arsenate from contaminated water. The performance including arsenate rejection, water permeability and resistance to fouling could however differ substantially among NF membranes. This study was conducted to investigate the influence of membrane pore size and surface properties on these aspects of membrane performance. Four fully-aromatic NF membranes with different physicochemical properties were adopted for this study. The results showed that surface charge, hydrophobicity, roughness and pore size could affect water permeability and/or arsenate rejection considerably. A more negative surface charge was desirable to enhance arsenate rejection rates. NF90 and a non-commercialized membrane (M#1) demonstrated the best performance in terms of arsenate rejection and water permeability. The M#1 membrane showed less membrane fouling than NF90 when used for filtration of real arsenic-containing groundwater. This was mainly due to its distinct chemical composition and surface properties. A severe membrane fouling could lead to a substantial reduction of arsenic rejection. The M#1 membrane showed the best performance, which indicated that membrane modification could indeed enhance the overall membrane performance for water treatment.     

Design of nanofibre interlayer supported forward osmosis composite membranes and its evaluation in fouling study with cleaning

• A fine fibre (40–60 nm diameter) interlayer (~1 µm thickness) was electrospun. • Fine fibre interlayer promoted formation of defect-free dense polyamide layer. • FO membrane with dual-layer substrate had less organic fouling potential. • High reverse salt flux accelerated organic fouling on FO membrane. Nanofibre-supported forward osmosis (FO) membranes have gained popularity owing to their low structural parameters and high water flux. However, the nanofibrous membranes are less stable in long-term use, and their fouling behaviours with foulants in both feed solution (FS) and draw solution (DS) is less studied. This study developed a nanofibrous thin-film composite (TFC) FO membrane by designing a tiered dual-layer nanofibrous substrate to enhance membrane stability during long-term usage and cleaning. Various characterisation methods were used to study the effect of the electrospun nanofibre interlayer and drying time, which is the interval after removing the M-phenylenediamine (MPD) solution and before reacting with trimesoyl chloride (TMC) solution, on the intrinsic separation FO performance. The separation performance of the dual-layer nanofibrous FO membranes was examined using model foulants (sodium alginate and bovine serum albumin) in both the FS and DS. The dual-layer nanofibrous substrate was superior to the single-layer nanofibrous substrate and showed a flux of 30.2 L/m²/h (LMH) when using 1.5 mol/L NaCl against deionised (DI) water in the active layer facing draw solution (AL-DS) mode. In the fouling test, the water flux was effectively improved without sacrificing the water/solute selectivity under the condition that foulants existed in both the FS and DS. In addition, the dual-layer nanofibrous TFC FO membrane was more robust during the fouling test and cleaning.     

Effect of 2-butenal manufacture wastewater to methanogenic activity and microbial community

The inhibition ratio sharply increased with the increasing COD. The absorbance of UV-vis at 420 nm showed a linear correlation with the SMA. The molecular structure of EPS has changed when COD was 9585 mg/L. Illumina Miseq sequencing was employed to reveal the microbial composition. The synthesis of 2-butenal, which is a vital raw material for the production of sorbic acid as a food preservative, generates some toxic by-products, so it is urgent to seek better detoxification strategies for the treatment of 2-butenal manufacture wastewater. In this study, batch experiments were carried out to investigate the inhibition effect of wastewater on the methanogenic activity. To understand the wastewater toxicity to anaerobic granular sludge, variations of the specific methanogenic activity (SMA) and extracellular polymeric substance (EPS) constituents at various wastewater CODs were investigated. Ultraviolet-visible (UV-vis) spectra and Fourier transform infrared (FT-IR) spectra were employed to analyze the structure of the EPS. The results showed that the inhibitory ratio of 2-butenal manufacture wastewater was less than 8.4% on the anaerobic granular sludge when the CODs were less than 959 mg/L. However, the inhibitory ratio increased from 36.4% to 93.6% when CODs increased from 2396 mg/L to 9585 mg/L, with the SMA decreasing from 39.1 mL CH₄/(gVSS·d) to 3.2 mL CH₄/(gVSS·d). The diversity of the microbial community under various CODs was researched by Illumina 16S rRNA Miseq sequencing and the results demonstrated that Proteiniphilum、Petrimonas and Syntrophobacter were the dominant bacteria genera in all sample. Regarding archaea, Methanobacterium was the most dominated archaea genera, followed by the Methanosaeta group in all samples. Moreover, the bacterial communities had changed obviously with increasing CODs, which indicated high CODs played a negative impact on the richness and diversity of bacterial community in the sludge samples.     

Feasibility assessment of up-flow anaerobic sludge blanket treatment of sulfamethoxazole pharmaceutical wastewater

The UASB system successfully treated sulfamethoxazole pharmaceutical wastewater. High concentration sulfate of this wastewater was the main refractory factor. UASB recovery performance after a few days of inflow arrest was studied. The optimal UASB operating conditions for practical application were determined. Treatment of sulfamethoxazole pharmaceutical wastewater is a big challenge. In this study, a series of anaerobic evaluation tests on pharmaceutical wastewater from different operating units was conducted to evaluate the feasibility of using anaerobic digestion, and the results indicated that the key refractory factor for anaerobic treatment of this wastewater was the high sulfate concentration. A laboratory-scale up-flow anaerobic sludge blanket (UASB) reactor was operated for 195 days to investigate the effects of the influent chemical oxygen demand (COD), organic loading rate (OLR), and COD/SO₄^2? ratio on the biodegradation of sulfamethoxazole in pharmaceutical wastewater and the process performance. The electron flow indicated that methanogenesis was still the dominant reaction although sulfidogenesis was enhanced with a stepwise decrease in the influent COD/SO₄^2? ratio. For the treated sulfamethoxazole pharmaceutical wastewater, a COD of 4983 mg/L (diluted by 50%), OLR of 2.5 kg COD/(m³·d), and COD/SO₄^2? ratio of more than 5 were suitable for practical applications. The recovery performance indicated that the system could resume operation quickly even if production was halted for a few days.     

Distribution and removal of antibiotic resistance genes during anaerobic sludge digestion with alkaline,thermal hydrolysis and ultrasonic pretreatments

Sludge digestion is critical to control the spread of ARGs from wastewater to soil. Fate of ARGs in three pretreatment-AD processes was investigated. UP was more efficient for ARGs removal than AP and THP in pretreatment-AD process. The total ARGs concentration showed significant correlation with 16S rRNA gene. The bacteria carrying ARGs could be mainly affiliated with Proteobacteria. Sewage sludge in the wastewater treatment plants contains considerable amount of antibiotic resistance genes (ARGs). A few studies have reported that anaerobic digestion (AD) could successfully remove some ARGs from sewage sludge, but information on the fate of ARGs in sludge pretreatment-AD process is still very limited. In this study, three sludge pretreatment methods, including alkaline, thermal hydrolysis and ultrasonic pretreatments, were compared to investigate the distribution and removal of ARGs in the sludge pretreatment-AD process. Results showed that the ARGs removal efficiency of AD itself was approximately 50.77%, and if these three sludge pretreatments were applied, the total ARGs removal efficiency of the whole pretreatment-AD process could be improved up to 52.50%–75.07%. The ultrasonic pretreatment was more efficient than alkaline and thermal hydrolysis pretreatments. Although thermal hydrolysis reduced ARGs obviously, the total ARGs rebounded considerably after inoculation and were only removed slightly in the subsequent AD process. Furthermore, it was found that the total ARGs concentration significantly correlated with the amount of 16S rRNA gene during the pretreatment and AD processes, and the bacteria carrying ARGs could be mainly affiliated with Proteobacteria.     

Ozonation as an efficient pretreatment method to alleviate reverse osmosis membrane fouling caused by complexes of humic acid and calcium ion

Humic acids (HA) didn’t cause obvious reverse osmosis (RO) membrane fouling in 45 h. Osmotic pressure (NaCl) affected slightly the RO membrane fouling behavior of HA. Ca²⁺ promoted aggregation of HA molecules and thus aggravated RO membrane fouling. Ozonation eliminated the effect of Ca²⁺ on the RO membrane fouling behavior of HA. The change of the structure of HA was related to its membrane fouling behavior. Humic acid has been considered as one of the most significant sources in feed water causing organic fouling of reverse osmosis (RO) membranes, but the relationship between the fouling behavior of humic acid and the change of its molecular structure has not been well developed yet. In this study, the RO membrane fouling behavior of humic acid was studied systematically with ozonation as a pretreatment method to control RO membrane fouling. Furthermore, the effect of ozone on the structure of humic acid was also explored to reveal the mechanisms. Humic acid alone (10–90 mg/L, in deionized water) was found not to cause obvious RO membrane fouling in 45-h operation. However, the presence of Ca²⁺ aggravated significantly the RO membrane fouling caused by humic acid, with significant flux reduction and denser fouling layer on RO membrane, as it was observed by scanning electron microscope (SEM) and atomic force microscope (AFM). However, after the pretreatment by ozone, the influence of Ca²⁺ was almost eliminated. Further analysis revealed that the addition of Ca²⁺ increased the particle size of humic acid solution significantly, while ozonation reduced the SUVA₂₅₄, particle size and molecular weight of the complexes of humic acid and Ca²⁺ (HA-Ca²⁺ complexes). According to these results and literature, the bridge effect of Ca²⁺ aggregating humic acid molecules and the cleavage effect of ozone breaking HA-Ca²⁺ complexes were summarized. The change of the structure of humic acid under the effect of Ca²⁺ and ozone is closely related to the change of its membrane fouling behavior.     

Co-application of energy uncoupling and ultrafiltration in sludge treatment: Evaluations of sludge reduction,supernatant recovery and membrane fouling control

• Effects of metabolic uncouplers addition on sludge reduction were carried out. • TCS addition effectively inhibited ATP synthesis and reduced sludge yield. • The effluent quality such as TOC and ammonia deteriorated but not significantly. • Suitable dosage retarded biofouling during sludge water recovery by UF membrane. Energy uncoupling is often used for sludge reduction because it is easy to operate and does not require a significant amount of extra equipments (i.e. no additional tank required). However, over time the supernatant extracted using this method can deteriorate, ultimately requiring further treatment. The purpose of this study was to determine the effect of using a low-pressure ultrafiltration membrane process for sludge water recovery after the sludge had undergone an energy uncoupling treatment (using 3,3′,4′,5-tetrachlorosalicylanilide (TCS)). Energy uncoupling was found to break apart sludge floc by reducing extracellular polymeric substances (EPS) and adenosine triphosphate (ATP) content. Analysis of supernatant indicated that when energy uncoupling and membrane filtration were co-applied and the TCS dosage was below 30 mg/L, there was no significant deterioration in organic component removal. However, ammonia and phosphate concentrations were found to increase as the concentration of TCS added increased. Additionally, due to low sludge concentrations and EPS contents, addition of 30–60 mg/L TCS during sludge reduction increased the permeate flux (two times higher than the control) and decreased the hydraulic reversible and cake layer resistances. In contrast, high dosage of TCS aggravated membrane fouling by forming compact fouling layers. In general, this study found that the co-application of energy uncoupling and membrane filtration processes represents an effective alternative method for simultaneous sludge reduction and sludge supernatant recovery.