Pilot-plant Study of Anoxic-aerobic Membrane Bioreactor （AO-MBR） on the Changes of Membrane Flux under Constant Pressure

Under a constant pressure, a pilot-plant test was conducted through the use of anoxic-aerobic membrane bioreactor （AO-MBR）, and this test operated steadily for 251 days. During the experiment, there were a total of four membrane cleaning processes, for the 90th day, the 150th day, the 210th day and the 240th day, respectively （The cleaning cycle was 90 days, 60 days, 60 days and 30 days, respectively）. From the initial 33.26 L/m^2.b dropped to 20.03 L/m^2.h after the fourth membrane cleaning, membrane flux reduced to 60.22% of the initial flux. During the 180 thd-210 thd of the experiment, the powdered activated carbon （PAC）, the segment size of which is 80-100, was put into anoxic reactor. Membrane flux decreased from 16.02 L/m^2·h to 15.29 L/m^2·h, and then rose to 15.65L/m^2·h. The dosing of PAC had a significant effect on the maintenance of a high membrane flux and extending running time. Before several membrane cleanings, a wire of membrane was intercepted from membrane module. It was found that the membrane surface sediments seemed to the inorganic colloid formed by Fe^2＋, Ca^2＋ and biofilm formed by some micro-organisms after the membrane surface pollutants were analyzed preliminarily with scanning electron microscopy （SEM）.

Membrane flux dynamics in the submerged ultrafiltration hybrid treatment process during particle and natural organic matter removal

Particles and natural organic matter （NOM） are two major concerns in surface water, which greatly influence the membrane filtration process. The objective of this article is to investigate the efiect of particles, NOM and their interaction on the submerged ultrafiltration （UF） membrane flux under conditions of solo UF and coagulation and PAC adsorption as the pretreatment of UF. Particles, NOM and their mixture were spiked in tap water to simulate raw water. Exponential relationship, （JP/JP0 = a×exp{-k[t-（n-1）T]}）, was developed to quantify the normalized membrane flux dynamics during the filtration period and fitted the results well. In this equation, coefficient a was determined by the value of JP/JP0 at the beginning of a filtration cycle, refiecting the flux recovery after backwashing, that is, the irreversible fouling. The coefficient k refiected the trend of flux dynamics. Integrated total permeability （ΣJP） in one filtration period could be used as a quantified indicator for comparison of different hybrid membrane processes or under different scenarios. According to the results, there was an additive effect on membrane flux by NOM and particles during solo UF process. This additive fouling could be alleviated by coagulation pretreatment since particles helped the formation of flocs with coagulant, which further delayed the decrease of membrane flux and benefited flux recovery by backwashing. The addition of PAC also increased membrane flux by adsorbing NOM and improved flux recovery through backwashing.

Study on the Effect of Operating Parameters on Water Yield of Hollow Fibre Vacuum Membrane Distillation Using CFD Simulation and Response Surface Methodology

Coal chemical bases in Northwest China are suffering from geographical water scarcity and a large amount of highly saline wastewater that needs to be treated during the production process, resulting in water and energy consumption becoming a key issue in the process of confined zero discharge. Membrane distillation is a thermally driven water treatment technology that can achieve higher water production efficiency and lower energy consumption by using hollow fibre membrane distillation in combination with a vacuum permeation side. In this study, CFD simulation calculations and response surface method analysis of hollow fibre membrane modules were carried out to further reveal the effects of different process operating parameters on water yield and the interactions between the operating parameters. It was found that the influence of the parameters on the membrane flux was as follows: feed inlet temperature > vacuum pressure ≈ feed inlet flow rate > feed inlet sanility, and the optimal operating parameters were predicted to be vacuum pressure of 38.88 kPa, feed solution temperature of 353.15 K, feed solution concentration of 4.13%, and inlet velocity of 0.60 m/s, which achieve membrane flux of 38.90 kg∙m−2∙h−1 according to the response surface method. This study provides more in-depth theoretical guidance for the application of hollow fibre vacuum membrane distillation technology in the treatment of coal chemical high salt wastewater.

Analysis of Temperature and Concentration Polarizations to Improve the Performance of Vacuum Membrane Distillation

Vacuum membrane distillation technology shows considerable promise for the treatment of mine water. Nevertheless, the current vacuum membrane distillation technology’s significant reliance on a heat source presents a challenging equilibrium between its energy consumption and thermal efficiency. Consequently, the present study employed computational fluid dynamics (CFD) calculations and analyses to examine the phenomena of temperature-differential polarisation and concentration-differential polarisation generated during the membrane distillation process, and to ascertain the extent to which the operating parameters affect them. Furthermore, it was observed that CPC and TPC exhibited a notable decline with the elevation of feed inlet temperature, while the polarisation phenomenon was diminished with the augmentation of feed inlet flow rate. The optimal equilibrium between membrane flux and thermal efficiency is intimately associated with the operating parameters. Additionally, this study offers a theoretical rationale for the enhancement of vacuum membrane distillation performance.

Removal of Natural Organic Matter by Forward Osmosis Membrane： Flux Behaviour and Foulant Characterization

Fouling of cellulose triacetate（CTA） forward osmosis（FO） membranes by natural organic matter（NOM） was studied by means of a cross-flow fiat-sheet forward osmosis membrane system. The NOM solution was employed as the feed solution（FS）, and a sodium chloride solution（3 tool/L） was used for the draw solution（DS）. The process was conducted at various temperatures and cross-flow velocities. The flux decline was investigated with 3 h forward osmosis operation. The substances absorbed on the membranes were cleaned by ultrasonic oscillation of the fouled membranes and were characterized by methodologies including fluorescence excitation-emission matrices （EEMs） and liquid chromatography with an organic carbon detector（LC-OCD）, and the variations of membrane properties were also investigated by Fourier transform infrared spectrometer（FTIR） and a contact angle meter. It was noted that the rejection efficiency of NOM is remarkable and that ultrasonic oscillation is an effective method to extract the NOM fouled on the CTA membranes after FO process. A higher cross-flow velocity and lower temperature benefit the anti-fouling capacity of the membrane significantly. Although humic substances accounted for the majority of the NOM, aromatic proteins and amino acids were the main fouling components on the membranes, with symbolic FTIR peaks at 2355, 1408 and 873 cm^-1. The present surface foulant made the membranes becoming more hydrophilic, as demonstrated by a significant decrease in contact angle（ranging from 20% to 46%） under all the operation conditions.

Fatty acid fouling of forward osmosis membrane:Effects of pH,calcium,membrane orientation,initial permeate flux and foulant composition

Octanoic acid（OA） was selected to represent fatty acids in effluent organic matter（EOM）. The effects of feed solution（FS） properties, membrane orientation and initial permeate flux on OA fouling in forward osmosis（FO） were investigated. The undissociated OA formed a cake layer quickly and caused the water flux to decline significantly in the initial 0.5 hr at unadjusted p H 3.56; while the fully dissociated OA behaved as an anionic surfactant and promoted the water permeation at an elevated p H of 9.00. Moreover, except at the initial stage, the sudden decline of water flux（meaning the occurrence of severe membrane fouling） occurred in two conditions： 1.0.5 mmol/L Ca2＋, active layer facing draw solution（AL-DS） and 1.5 mol/L Na Cl（DS）; 2. No Ca2＋,active layer-facing FS（AL-FS） and 4 mol/L Na Cl（DS）. This demonstrated that cake layer compaction or pore blocking occurred only when enough foulants were absorbed into the membrane surface, and the water permeation was high enough to compact the deposit inside the porous substrate. Furthermore, bovine serum albumin（BSA） was selected as a co-foulant.The water flux of both co-foulants was between the fluxes obtained separately for the two foulants at p H 3.56, and larger than the two values at p H 9.00. This manifested that, at p H 3.56,BSA alleviated the effect of the cake layer caused by OA, and OA enhanced BSA fouling simultaneously; while at p H 9.00, the mutual effects of OA and BSA eased the membrane fouling.

A mussel-induced approach to secondary functional cross-linking 3-aminopropytriethoxysilane to modify the graphene oxide membrane for wastewater purification

Graphene oxide(GO)with one-atom-thick exhibit remarkable molecule sieving properties,but its low permeance flux renders it difficult to be applied in practice as a high-permeance separation membrane.In this study,we design complex membrane from covalently crosslinked GO,polydopamine(PDA),and 3-aminopropytriethoxysilane(APTES)as building blocks to fabricate the high-permeance GO-based membrane via the vacuum filtration method.A branched crosslinking product(PDA/APTES)working as a clamp grasped the hydrophilic functional groups(hydroxyl,epoxy,carboxyl)on GO for improving the GO membrane flux.The interlayer structure of the GO membrane was optimized according to the crosslinker concentration,reaction time,initial p H,and temperature for RGO/PDA/APTES(RGPA)in this study.At the optimized reaction conditions including the crosslinker concentration of 1.4 m L/L,the temperature of 80°C,the time of 16 h,and the initial p H of 8.5 for RGPA mixture,the interlayer gallery of RGPA membrane was effectively tunes,endowing high flux ranging from 11.98 L m^(-2)h^(-1)to 1823.97 L m^(-2)h^(-1).Besides,the RGPA membrane ensured the high rejections to dye solutions such as methylene blue(MB)(>99%)and congo red(CR)(>90%).Meanwhile,the superior reusable performance of the RGPA membrane was achieved,together with the rejections for MB and CR to 96.32%and 93.1%after 4 cycles,respectively.Also,the RGPA membrane possessed superior anti-fouling performances for bovine serum albumin(BSA)aqueous solution and excellent stabilities in harsh conditions(p H 3,7 and 11).Grafting the crosslinker onto GO nanosheets exhibits the distinct advantages of achieving the high flux,high rejections to dyes,and superior reusable performance of membranes,posing a great application potential for membrane separation technology in wastewater treatment.

Fabrication and performance of PET mesh enhanced cellulose acetate membranes for forward osmosis

Polyethylene terephthalate mesh（PET） enhanced cellulose acetate membranes were fabricated via a phase inversion process. The membrane fabrication parameters that may affect the membrane performance were systematically evaluated including the concentration and temperature of the casting polymer solution and the temperature and time of the evaporation, coagulation and annealing processes. The water permeability and reverse salt flux were measured in forward osmosis（FO） mode for determination of the optimal membrane fabrication conditions. The optimal FO membrane shows a typical asymmetric sandwich structure with a mean thickness of about 148.2 μm. The performance of the optimal FO membrane was tested using 0.2 mol/L Na Cl as the feed solution and 1.5 mol/L glucose as the draw solution. The membrane displayed a water flux of 3.47 L/（m2·hr） and salt rejection of95.48% in FO mode. While in pressure retarded osmosis（PRO） mode, the water flux was4.74 L/（m2·hr） and salt rejection 96.03%. The high ratio of water flux in FO mode to that in PRO mode indicates that the fabricated membrane has a lower degree of internal concentration polarization than comparable membranes.