A review on the forward osmosis applications and fouling control strategies for wastewater treatment

During the last decades,the utilization of osmotic pressure-driven forward osmosis technology for wastewater treatment has drawn great interest,due to its high separation efficiency,low membrane fouling propensity,high water recovery and relatively low energy consumption.This review paper summarizes the implementation of forward osmosis technology for various wastewater treatment including municipal sewage,landfill leachate,oil/gas exploitation wastewater,textile wastewater,mine wastewater,and radioactive wastewater.However,membrane fouling is still a critical issue,which affects water flux stability,membrane life and operating cost.Different membrane fouling types and corresponding fouling mechanisms,including organic fouling,inorganic fouling,biofouling and combined fouling are therefore further discussed.The fouling control strategies including feed pre-treatment,operation condition optimization,membrane selection and modification,membrane cleaning and tailoring the chemistry of draw solution are also reviewed comprehensively.At the end of paper,some recommendations are proposed.

Membrane fouling control by ultrasound in an anaerobic membrane bioreactor

fouling online in an anaerobic membrane bioreac-tor(AMBR).Short-term running experiments were carried out under different operating conditions to explore feasible ultrasonic parameters.The experimental results indicated that when the crossflow velocity was more than 1.0 m/s,mem-brane fouling could be controlled effectively only by hydro-dynamic methods without ultrasound.When ultrasound was applied,an ultrasonic power range of 60-150 W was suitable for the membrane fouling control in the experimental system.The experimental results showed that the membrane fouling was controlled so well that membrane filtration resistance(ΣR)could stay at 5×10^(11)m^(−1) for more than a week with the crossflow velocity of 0.75 m/s,which equaled the effect of crossflow velocity of more than 1.0 m/s without ultrasound.

Ceramic membrane fouling mechanisms and control for water treatment

Membrane separation, as an important drinking water treatment technology, has wide applications. The remarkable advantages of ceramic membranes, such as chemical stability, thermal stability, and high mechanical strength, endow them with broader prospects for development. Despite the importance and advantages of membrane separation in water treatment, the technique has a limitation: membrane fouling, which greatly lowers its effectiveness. This is caused by organics, inorganic substances, and microorganisms clogging the pore and polluting the membrane surface. The increase in membrane pollution greatly lowers purification effectiveness. Controlling membrane fouling is critical in ensuring the efficient and stable operation of ceramic membranes for water treatment. This review analyzes four mechanisms of ceramic membrane fouling, namely complete blocking, standard blocking, intermediate blocking, and cake filtration blocking. It evaluates the mechanisms underlying ceramic membrane fouling and summarizes the progress in approaches aimed at controlling it. These include ceramic membrane pretreatment, ceramic membrane surface modification, membrane cleaning, magnetization, ultrasonics, and nanobubbles. This review highlights the importance of optimizing ceramic membrane preparation through further research on membrane fouling and pre-membrane pretreatment mechanisms. In addition, combining process regulations with ceramic membranes as the core is an important research direction for ceramic membrane-based water treatment.

Control of membrane fouling during hyperhaline municipal wastewater treatment using a pilot-scale anoxic/aerobic-membrane bioreactor system

Membrane fouling limits the effects of long-term stable operation of membrane bioreactor （MBR）. Control of membrane fouling can extend the membrane life and reduce water treatment cost effectively. A pilot scale anoxic/aerobic-membrane bioreactor （A/O- MBR, 40 L/hr） was used to treat the hyperhaline municipal sewage from a processing zone of Tianjin, China. Impact factors including mixed liquid sludge suspension （MLSS）, sludge viscosity （Ix）, microorganisms, extracellular polymeric substances （EPS）, aeration intensity and suction/suspended time on membrane fouling and pollution control were studied. The relationships among various factors associated with membrane fouling were analyzed. Results showed that there was a positive correlation among MLSS, sludge viscosity and trans-membrane pressure （TMP）. Considering water treatment efficiency and stable operation of the membrane module, MLSS of 5 g/L was suggested for the process. There was a same trend among EPS, sludge viscosity and TMP. Numbers and species of microorganisms affected membrane fouling. Either too high or too low aeration intensity was not conducive to membrane fouling control. Aeration intensity of 1.0 m3/hr （gas/water ratio of 25：1） is suggested for the process. A long suction time caused a rapid increase in membrane resistance. However, long suspended time cannot prevent the increase of membrane resistance effectively even though a suspended time was necessary for scale off particles from the membrane surface. The suction/suspended time of 12 min/3 rain was selected for the process. The interaction of various environmental factors and operation conditions must be considered synthetically.

Recent Progress in Electrospun Nanofibers for the Membrane Distillation of Hypersaline Wastewaters

Membrane distillation(MD)utilizing low-grade thermal energy can be used to effectively desalinate hypersaline brines with a high freshwater recovery for water reuse.Membrane flux and durability are the two main indices used to evaluate MD membrane performance.In the past decade,electrospun nanofibrous distillation membranes(EFDMs)with a low mass transfer resistance have garnered increasing attention in MD research,owing to their high porosity and interconnected-pore structure.However,on the one hand,the pores of EFDMs compared to those of phase-inversion membranes are easily deformed and impacted by water flow,reducing membrane flux;on the other hand,the general hydrophobic interface is susceptible to being wetted,fouled and scaled during the desalination/concentration process,resulting in MD failure.This review will present a comprehensive discussion of the recent progress in electrospun nanofibers for the MD of hypersaline wastewaters with a focus on designing specially wettable membrane interfaces and welding-pore structured membranes to enhance MD distillation efficiency and durability simultaneously.Besides,the challenges and perspectives of MD in treating hypersaline wastewaters are also provided as a guide for future research on sustainable and clean freshwater recovery.