Cleaning Reagent Research Articles

Protonated polyethyleneimine enables synchronous crosslinking of polyimide nanofiltration membranes for dye desalination

Dye recovery and desalination are of great significance in the treatment of printing and dyeing wastewater. Nanofiltration (NF) has been proved an effective method for dye desalination. As organic solvents are usually coexisted, there is a great demand for organic solvent nanofiltration (OSN) membranes. Compared to thin film composite (TFC) membranes prepared by interfacial polymerized (IP), integrally skinned asymmetric (ISA) membranes with relatively thicker selective layer may present better separation stability in harsh solvent and cleaning reagent. In this work, polyethyleneimine-b-polyethersulfone (PEI-PES) is synthesized and added to PI solution directly, the crosslinking reaction proceeds along with phase conversion process. The PEI chains endow the membrane with good hydrophilicity and high positive charge. PEI-PES/PI membranes show stable permeability in organic solvents such as N, N-dimethylformamide (DMF), ethanol (EtOH) and toluene, etc. The rejections of dyes such as Congo Red (CR), Janus Green B, and Sunset Yellow are over 95 % in EtOH, while the rejections of salts like MgSO4 and Na2SO4 are around 20 %. After 200 h separation test, the rejection for CR remains around 92 % in DMF and 96 % in EtOH with a stable flux. The simple and cost-effective preparation process can accelerate the progress of the positively charged OSN membranes.

Sustainable control of organic-inorganic combined fouling of electroactive ultrafiltration membrane during electrocatalytic-driven self-cleaning process: Mechanism and implications

Organic-inorganic combined fouling of membrane is a tough problem that restrained its application in water treatment, which was insufficient and non-sustainable to be alleviated by conventional chemical cleaning. Herein, a facile and sustainable control strategy was developed to mitigate biopolymer-Ca2+ combined fouling for an electroactive metal-organic framework ultrafiltration membrane. Bovine serum albumin (BSA) and sodium alginate (SA) were selected as model biopolymer. The results showed BSA and SA fouling both accelerated with increasing Ca2+ concentration (0–1.0 mM) via calcium bridging action and hydraulic cleaning was insufficient to restore flux (flux recovery < 7 %). By comparison, flux can be fully recovered by applying electricity to all combined fouling, suggesting membrane presented outstanding self-cleaning performance. According to the free radical quenching test and physicochemical property of biopolymer, fouling control mechanism was revealed because in-situ electro-generated OH and O2− free radicals caused decomplexation of biopolymer and Ca2+, and then degraded biopolymer into smaller and less hydrophobic fragments that repulsed membrane. Extended Derjaguin–Landau–Verwey–Overbeek theory further unveiled the foulants-membrane interaction shifted from attraction to repulsion after self-cleaning. This strategy has the advantages of low chemical cleaning reagents and energy consumption, which may provide the guidance for sustainable control of organic-inorganic combined membrane fouling.

Removal, Adsorption, and Cleaning of Pharmaceutical on Polyamide RO and NF Membranes.

Pharmaceuticals are present in various waters and can be almost completely rejected by membrane separation processes, i.e., nanofiltration (NF) and reverse osmosis (RO). Nevertheless, the adsorption of pharmaceuticals can decrease their rejection, so adsorption can be considered a very important removal mechanism. In order to increase the lifetime of the membranes, the adsorbed pharmaceuticals must be cleaned from the membrane. The used pharmaceutical (albendazole), the most common anthelmintic for threatening worms, has been shown to adsorb to the membrane (solute-membrane adsorption). In this paper, which is a novelty, commercially available cleaning reagents, NaOH/EDTA solution, and methanol (20%, 50%, and ≥99.6%) were used for pharmaceutical cleaning (desorption) of the NF/RO membranes used. The effectiveness of the cleaning was verified by Fourier-transform infrared spectra of the membranes. Of all the chemical cleaning reagents used, pure methanol was the only cleaning reagent that removed albendazole from the membranes.

Supercritical carbon dioxide fluid cleaning of extracellular polymeric substance surrogates on seawater reverse osmosis membranes

Fouling of seawater reverse osmosis (SWRO) membranes cause of reduced water flux and increased energy usage, which requires frequent cleaning to maintain performance. We demonstrate Supercritical carbon dioxide (sCO2) fluid, as an alternative membrane cleaning reagent, can effectively remove extracellular polymeric substances (EPS) that form on SWRO membranes. Carbon dioxide (CO2) gas was turned into sCO2 fluid by elevating the pressure (to 7.5 MPa) and temperature (to 35 °C). The SWRO membrane coupons were fouled by EPS surrogate materials (sodium alginate or bovine serum albumin), and the sCO2 cleaning was conducted to recover the deteriorated water permeation flux. We present that the sCO2 cleaning can effectively eliminate the EPS surrogate materials from the membrane surface with a great cleaning efficiency (75–90 %). In addition, it was observed that sCO2 cleaning does not alter the properties (i.e., surface functional groups and salt-rejecting performance) of polyamide-based SWRO. Our findings suggest that sCO2 is applicable to remove EPS surrogate materials from the membrane.

Cleaning mechanism of gypsum scaling in hydrophobic porous membranes

Mineral scaling is one of the major challenges for membrane distillation in concentrating high-salinity brine. This work first investigated the characteristic of CaSO4 scaling, then explored different cleaning reagents to evaluate their efficiencies and mechanisms. By analyzing the SEM and EDX mapping images, the CaSO4 scaling process could be divided into surface and pore scaling stages. Three cleaning solutions, i.e., commercial detergent (20 %), EDTA-4Na (0.05 M), and MgCl2 (0.8 M), were chosen for their high CaSO4 solubility (0.7 g CaSO4 per 100 g H2O). At the surface scaling stage, three cleaning solutions exhibited excellent removal of CaSO4 scaling with approximately similar 96 % cleaning efficiencies. However, at the pore scaling stage, only the commercial detergent showed high efficiency (89 %). Such high cleaning efficiency was mainly attributed to the detergent's high total dissolved solids (salinity), low pH, and high diffusion rate (5.46 μm cm−1 min−1) across the membrane. Moreover, periodic cleaning at the surface scaling stage with the commercial detergent followed by drying throughout a 43.5 h continuous concentration test on an actual RO brine could restore the PTFE membrane performance completely, giving 90 % of the total water recovery. This work provides new insights into the cleaning mechanism for gypsum scaling in a hydrophobic porous membrane.

Effect of chemical cleaning on nanofiltration process in treating surface water

Nanofiltration (NF) has been increasingly used in drinking water treatment plants; however, the severe membrane fouling caused by organic matter poses great challenges to the application of NF technology. This study investigated the mitigation of NF membrane fouling by different chemical cleaning reagents (e.g., citric acid, NaOH, Na4-EDTA, and Na-SDS), Na4-EDTA and Na-SDS performed better to achieve NF permeability recovery of up to 90.5–94.2 % just in a single chemical cleaning cycle. The hydraulic irreversible membrane fouling could be reduced by 44.9–53.8 % in the multi-cycle operation of chemical cleaning. Na4-EDTA-based cleaning was beneficial to the removal performance of sulfamethazine (SM2) and conferred higher removal efficiency than Na-SDS-based cleaning efficiency. The impact of chemical cleaning on energy consumption was evaluated and indicated that Na4-EDTA-based cleaning could reduce the proportion of unfavorable energy consumption by 4.54 %. The operation stability of the NF process could be effectively improved by chemical cleaning, and the organic pollutants accumulated on the membrane surface can be removed, especially the chemical cleaning using Na4-EDTA and Na-SDS. These findings could improve the operational efficiency of the NF process with low energy consumption, low chemical consumption, and less adverse environmental impact.

A green, hybrid cleaning strategy for the mitigation of biofouling deposition in the elevated salinity forward osmosis membrane bioreactor (FOMBR) operation

Forward osmosis membrane bioreactors (FOMBRs) are currently gaining attention from the wastewater treatment industry, for their potential to produce high effluent quality and a relatively better flux stability against fouling. However, only using physical cleaning methods is not sufficient to recover the water flux performance satisfactorily under a long-term operation. This study comprehensively investigated the efficiency of a hybrid, environmentally-friendly cleaning strategy involving a combination of physical and free nitrous acid (FNA) cleanings under a long-term FOMBR operation. During 92 days of FOMBR operation, physical cleaning recovered the water flux by 85%, whilst FNA cleaning contributed to an additional 5% of the recovery. In addition, FNA cleaning also offered a retardation of fouling deposition by maintaining the water flux 18–30% more than that obtained by only the physical cleaning. A possible mechanism for FNA's role as the cleaning reagent was proposed for the first time in this study based on the water flux performance and membrane autopsy analysis. The results showed FNA cleaning broke down the residual fouling layer, preferencing protein-based substances. A lower ratio of protein to polysaccharides of the residual fouling layer contributed to a more negatively charged membrane surface (- 42.34 ± 0.30 mV) compared to the virgin one (- 17.54 ± 0.81 mV). This resulted in a stronger electrostatic repulsion between the foulants and the membrane surface, and thus slowed down the biofouling deposition process. This study suggested FNA solution has the great potential not only to recover the membrane performance, also as a strategy to slow down fouling deposition.

The responses of activated sludge to membrane cleaning reagent H2O2 and protection of extracellular polymeric substances

Hydrogen peroxide (H2O2) is evaluated as a potential replacement for chlorine to control biofouling in membrane bioreactors (MBRs). However, H2O2 might diffuse into the mixed liquor and damage microorganisms during membrane cleaning. This study comprehensively analyzed the impacts of H2O2 on microbes. Key enzymes involved in phenol biodegradation were inhibited with H2O2 concentration increased, and thus phenol degradation efficiency was decreased. Increase of lactic dehydrogenase (LDH) and intracellular reactive oxygen species (ROS) indicated more severe cell rupture with H2O2 concentration increased. At the same H2O2 concentration, Extracellular polymeric substances (EPS) extraction further led to inhibiting the activity of key enzymes, decreasing phenol degradation efficiency, and enhancing LDH release and ROS production, demonstrating that the existence of EPS moderated the adverse impacts on microbes. Spectroscopic characterization revealed the increase of H2O2 decreased tryptophan protein-like substances, protein-associated bonds and polysaccharide-associated bonds. Hydroxyl and amide groups in EPS were attacked, which might lead to the consumption of H2O2, indicated EPS protect the microorganism through sacrificial reaction with H2O2.

Fabrication of pervaporation desalination membranes with excellent chemical resistance for chemical washing

Pervaporation membranes have exhibited great potential for desalinating brine solutions. However, the flux recovery after membrane washing and the membrane's resistance to chemical cleaning reagents were barely studied. Our group has reported excellent desalination properties of PVA based pervaporation membranes. Nevertheless, the membranes were damaged during chemical cleaning due to the poor chlorine resistance of PVA. In this study, the more active 1, 2-diol units of PVA were removed by sodium periodate treatment. And then, the modified PVA was crosslinked by FS-3100, a fluorocarbon based crosslinker, to improve its hydrostability and chlorine resistance. The FS-3100 crosslinked composite (PVA-FS/PVDF) showed a water flux of 34 ± 1 kg m−2 h−1 with a NaCl rejection of 99.93% when desalinated a 35000 ppm NaCl solution at 70 °C. Salt rejections were maintained after soaking in 2000 ppm NaClO, acid (pH = 2), and alkali (pH = 12) solutions for 168, 180, and 180 h, respectively. A long term desalination experiment was carried out using Tween 20 and HA as foulants. The water fluxes could be recovered to 100% after chemical washing without losing salt rejections, indicating an excellent long term operation stability of the FS-3100 crosslinked PV membranes.

Characterization of triclosan and triclocarban in indoor dust from home micro-environments in Vietnam and relevance of non-dietary exposure

Contamination status, spatial variability, and exposure risk of triclosan (TCS) and triclocarban (TCC) in indoor dusts from different micro-environments were evaluated for the first time in Vietnam as well as in Southeast Asian region. TCS and TCC were measured in 89 dust samples collected from bedrooms, living rooms, and kitchens of private houses in four northern cities including Hanoi, Bac Ninh, Hung Yen, and Nam Dinh, by means of liquid chromatography–tandem mass spectrometry. Concentrations of TCS and TCC ranged from <5 to 1090 (median 33.2) and from <3 to 531 (median 19.3) ng g−1, respectively. Concentrations of TCS and TCC in the kitchen and bedroom dusts were markedly higher than levels found in the living room samples, probably due to their applications in kitchen utensils, household cleaning reagents, and personal care products. A strong positive correlation between TCS and TCC concentrations was detected in the whole dataset (R2 = 0.810, p < 0.001). For samples in which both TCS and TCC were quantified, TCS/TCC ratios ranged from 0.3 to 12 with a median value of 1.8, and did not show big differences between micro-environments. Human exposures to TCS and TCC through dust ingestion were estimated for various age groups with 95% CI daily intake doses ranging from (0.032–0.070) to (0.340–0.740) and from (0.017–0.033) to (0.175–0.345) ng kg-bw−1 d−1 for adults and infants respectively. Although our derived values were much lower than reference doses, more comprehensive risk assessment considering multiple exposure pathways of TCS and TCC is needed.

Cellulose-based eco-friendly wafer-cleaning reagent

As the semiconductor industry has advanced, precisely patterned wafers of the sub-nanometer scale have been produced; hence, the development of cleaning reagents to remove contaminants from such wafers has received increasing attention. However, conventional cleaning solutions have significant drawbacks, including high cost and toxicity to both humans and the environment. In this work, we developed an eco-friendly cleaning reagent containing cellulose nanocrystals (CNCs) and a biodegradable amphoteric surfactant, cocamidopropyl betaine (CAPB), at optimal concentrations. The proposed system was applicable to both bare and patterned wafers, achieving a contaminant removal efficiency of ca. 100% without wafer damage. After investigating the cleaning mechanism utilizing different analytical techniques, we determined that the synergistic effect of the CNC/CAPB and free CAPB that includes the physical bombardment, electrostatic repulsion, and the adsorption inhibition of contaminants, contribute to the effective cleaning process. We expect this eco-friendly and cost-effective cleaning reagent to be readily adopted in the production of semiconductor products, as it could reduce the overall cost of producing electronics.

Fouling control in ceramic nanofiltration membranes during municipal sewage treatment

Using ceramic nanofiltration membranes for treatment of municipal sewage is upcoming. However, the knowledge on fouling control methods for this application are very limited. The most commonly used fouling control method, chemical cleaning, has disadvantages. Chemical cleaning negatively impacts (i) the glass seal layer of tubular ceramic nanofiltration membranes and (ii) the environment, especially when using sodium hypochlorite for removal of organic fouling. Therefore, the use of chemical cleaning should be limited as much as possible. In this research, first, the well-known fouling control methods for polymeric micro- and ultrafiltration membranes, were studied on ceramic nanofiltration membranes: hydraulic backwash and forward flush. Second, a precoat method was combined with a chemical reaction to aid the detachment of the formed cake layer. In this method, a precoat layer was filtered atop of the membrane surface before the start of filtration. The precoat layer then acts as a barrier between the foulants and the membrane surface. After filtration, the precoat layer reacts with the cleaning reagent underneath the fouling layer to enable fast removal of fouling. Results showed that hydraulic backwash was not effective to be used for this type of membranes. Forward flush was able to maintain a higher flux but the relative production downtime was high. Reaction based precoat was most effective in maintaining a high flux and resulted in the highest net water production. Two reaction based precoat methods were tested of which the reaction of calcium carbonate with citric acid was more effective than a Fenton reaction.

Enhancement of COD Removal from Oilfield Produced Wastewater by Combination of Advanced Oxidation, Adsorption and Ultrafiltration.

The wastewater produced from the oilfield is chemically corrosive due to high salinity in combination with high temperatures. It is also rich in contaminants, such as oil, polyacrylamide, emulsions, suspended solid, etc. The density difference between the oil and water in the wastewater is low, which makes separation via gravity difficult. In this study, a combined pilot treatment is studied, which includes Fenton oxidation, settlement, activated carbon adsorption, and ultrafiltration (UF). The operational conditions of Fenton oxidation are optimized based on alleviating the fouling of the UF membrane. When the Fenton oxidation was operated at the molar ratio of H2O2 to FeSO4 3:1 and pH 2.2–2.5, the UF membrane could operate continuously for 20 h without cleaning. The membrane was fouled by the organics (oil/grease) and polymer, which can be effectively removed by composite cleaning reagent consisting of 0.1% NaOH and 0.1% sodium dodecylbenzenesulfonate (SDBS). With the UF treatment, the chemical oxygen demand (COD) of the effluent was less than 50 mg/L, which could meet the upgraded standard.

The evaluation of corrosion rate of steel during chemical cleaning of steam boilers

Traditional and new washing acid reagents are used for chemical cleaning of internal surfaces of steam-water pipes of boilers. In previous studies, the rate of removal of lumpy and uniform deposits in the evaporative pipes of high-pressure steam boilers depending on the type of cleaning solution and the duration of cleaning was obtained. However, during chemical cleaning, removing deposits is accompanied by corrosion processes of the metal pipes, which leads to their loss. In the scientific and technical literature there are practically no data characterizing this process when using new detergent reagents. The aim of the study is to obtain experimental data on the corrosion rate of steels during the acid stage of chemical cleaning with the use of new cleaning reagents such as Antirzhavin, Deskam and Auge Pro AC 60. The gravimetric method of determination of metal corrosion rate of evaporative pipes is used. The samples of corrosion in cold and heated washing solutions during chemical cleaning from deposits by etching are employed. The laboratory testing has revealed the dependences of corrosion rate of carbon steel of boiler evaporative pipes and corrosion indicating plates in heated and not heated washing solutions of the inhibited hydrochloric acid and acid reagents on cleaning duration. It has been found that the corrosion rates of carbon steel are reduced during the cleaning process and at the end of the acid stage in solutions of inhibited hydrochloric acid and reagent solutions have values exceeding the maximum permissible corrosion rate in a cold inhibited technical solution of hydrochloric acid. However, they are less than those for pure metal and metal with scale. The experimental data obtained can be used in the selection of a chemical reagent for acid cleaning and its optimal duration, as well as in the selection of the method of steel corrosion control during cleaning.

Metabolism and Biodegradation of Spacecraft Cleaning Reagents by Strains of Spacecraft-Associated Acinetobacter.

Spacecraft assembly facilities are oligotrophic and low-humidity environments, which are routinely cleaned using alcohol wipes for benchtops and spacecraft materials, and alkaline detergents for floors. Despite these cleaning protocols, spacecraft assembly facilities possess a persistent, diverse, dynamic, and low abundant core microbiome, where the Acinetobacter are among the dominant members of the community. In this report, we show that several spacecraft-associated Acinetobacter metabolize or biodegrade the spacecraft cleaning reagents of ethanol (ethyl alcohol), 2-propanol (isopropyl alcohol), and Kleenol 30 (floor detergent) under ultraminimal conditions. Using cultivation and stable isotope labeling studies, we show that ethanol is a sole carbon source when cultivating in 0.2 × M9 minimal medium containing 26 μM Fe(NH4)2(SO4)2. Although cultures expectedly did not grow solely on 2-propanol, cultivations on mixtures of ethanol and 2-propanol exhibited enhanced plate counts at mole ratios of ≤0.50. In support, enzymology experiments on cellular extracts were consistent with oxidation of ethanol and 2-propanol by a membrane-bound alcohol dehydrogenase. In the presence of Kleenol 30, untargeted metabolite profiling on ultraminimal cultures of Acinetobacter radioresistens 50v1 indicated (1) biodegradation of Kleenol 30 into products including ethylene glycols, (2) the potential metabolism of decanoate (formed during incubation of Kleenol 30 in 0.2 × M9), and (3) decreases in the abundances of several hydroxy- and ketoacids in the extracellular metabolome. In ultraminimal medium (when using ethanol as a sole carbon source), A. radioresistens 50v1 also exhibits a remarkable survival against hydrogen peroxide (∼1.5-log loss, ∼108 colony forming units (cfu)/mL, 10 mM H2O2), indicating a considerable tolerance toward oxidative stress under nutrient-restricted conditions. Together, these results suggest that the spacecraft cleaning reagents may (1) serve as nutrient sources under oligotrophic conditions and (2) sustain extremotolerances against the oxidative stresses associated with low-humidity environments. In perspective, this study provides a plausible biochemical rationale to the observed microbial ecology dynamics of spacecraft-associated environments.

Iron fouling prevention and membrane cleaning during reverse osmosis process

Fouling inhibition is one of the most important challenges in membrane processes. Manifesting under several forms and origins, fouling significantly reduces the performance of membranes during water desalination process. Despite its low concentration, iron is considered as one of the most common inorganic pollutants that generate oxides and hydroxides causing membrane fouling. In the current work, reverse osmosis (RO) membrane fouling caused by iron precipitation was investigated. Herein, the mechanism of iron salt crystallization by oxidation technique was experimentally studied. In addition, the regeneration of a fouled RO membrane by iron precipitation was carried out. Analysis with scanning electron microscopy, infrared (IR) and X-ray diffraction (DRX) spectroscopy has been performed to identify deposits. It was shown that the collected deposit is essentially the lepidocrocite (γ-FeOOH). RO membrane regeneration was carried out using citric acid as a cleaning reagent with a concentration of 0.01%. The efficiency of the treatment was tested through the assessment of the recovery ratio, pressure drop and iron accumulation. In addition, complexation–filtration using citric acid was tested to remove iron during pretreatment step to inhibit membrane fouling. IR and DRX data showed the complex iron citrate (Fe–citrate) was found in the RO retentate, which proves that the complexation–filtration process was clearly efficient.

Comparison of different chemical cleaning reagents on fouling recovery in a Self-Forming dynamic membrane bioreactor (SFDMBR)

Abstract Self-forming dynamic membrane bioreactor (SFDMBR) using large pore size (>5 μm) membrane material is regarded as a cost-effective technology with less fouling and high permeate flux. However, no successful long-term operation without chemical cleaning is achieved. Therefore, an optimum chemical cleaning reagent needs to be explored with the understanding of foulants structure. This study compared the cleaning effects of three typical chemical cleaning reagents, i.e. sodium hydroxide (NaOH), sodium hypochlorite (NaClO), and sodium dodecyl sulfate (SDS), using a lab-scale SFDMBR. NaClO is identified as the most effective cleaning reagent in view of its trans-membrane pressure (TMP) reduction and permeability recovery efficiency. NaClO could achieve 99.0% of permeability recovery and full TMP reduction, while NaOH and SDS could only recover 87.7% and 76.5% of initial permeability and showed limited efficiency in TMP reduction, although all three reagents can achieve over 70% of extracellular polymeric substances (EPSs). The major foulant of the SFDMBR was a complex mixture of sludge flocs with EPS. NaClO cleaning can largely remove the flocs and EPS by oxidization effects while NaOH and SDS were only effective in EPS removal, which explained why NaClO cleaning showed the best performance. β-polysaccharide attached on the mesh fibers and acted as the binding substance between the foulants and mesh fibers is the main reason for irremovable inner pore fouling, which only could be significantly removed with NaClO cleaning. These results well explain the difference of filtration performance after three types of chemical cleaning.

Evaluating the membrane fouling formation and chemical cleaning strategy in forward osmosis membrane filtration treating domestic sewage

Free nitrous acid (FNA) shows strong potential as an effective cleaning reagent in fouling control in a forward osmosis filtration system, with a relatively longer time required.

変敗コーンペーストから分離された&lt;i&gt;Paenibacillus&lt;/i&gt;属の生育性状解明

Spore-forming bacteria Paenibacillus spp. were isolated from spoiled corn paste stored below 10℃. Spoilage associated with pH decrease was reproduced by inoculating isolated strains to normal corn paste. To obtain insights to prevent recurrence of Paenibacillus-mediated spoilage, we further characterized the growth temperature, drug sensitivity, and heat resistance of the isolated strains. The isolated Paenibacillus strains could grow at as low as 2.5℃, suggesting that contamination by these strains can cause spoilage during cold chain transport and storage. We also report that these strains can be controlled by heat treatment such as 140℃ for 8 sec, and by treatment with cleaning reagent containing sodium dichloroisocyanurate.

Microalgae (Scenedesmus obliquus) dewatering using forward osmosis membrane: Influence of draw solution chemistry

Forward osmosis (FO) is gaining increasing interests for its potential applications in biofuel generation. In this study, bench-scale experiments were conducted to investigate the FO performance for microalgae dewatering which is one of the technical challenges in algal biofuel production. The filtration performance was assessed by analyzing permeate water flux and algal biomass concentration in the feed solution. Compared to the active layer facing draw solution (AL-DS) orientation (>45% flux reduction), active layer facing feed solution (AL-FS) was more efficient (<15% flux reduction) due to the lower membrane fouling and higher cleaning efficiency (>90% water flux recovery after deionized water flushing). In the AL-FS orientation, FO performance strongly depended on the draw solution chemistry with NaCl exhibiting the best results. When Ca2+-containing solution was used as draw solution, microalgae responded to the back diffusion of calcium ions by an extensive excretion of carbohydrates, accelerating the formation of algal flocs, thus enhancing the rate and extent of flux decline and reducing the algae dewatering efficiency. However, most of the flux decline was reversible by simple hydraulic flushing without any chemical cleaning reagents and air scouring. In addition, substantial adsorption of algal biomass was observed on feed spacer. This study has the implication for Scenedesmus obliquus dewatering using FO technology. Selection of AL-FS orientation, Ca2+-free draw solutions and prevention of microalgae adhesion onto feed spacer may significantly improve the efficiency and productivity of the dewatering process.