Preparation of electrically enhanced forward osmosis(FO)membrane by two-dimensional MXenes for organic fouling mitigation

In this work,a conductive thin film composite forward osmosis(TFC-FO)membrane was firstly prepared via vacuum filtering MXenes nanolayer on the outer surface of polyethersulfone membrane followed by interfacial polymerization in the other side.Moreover,its feasibility of mitigating organic fouling under electric field was evaluated.Results indicated that the addition of MXenes greatly reduced the electric resistance of membrane from 2.1×10^(12)Ωto 46.8Ω,enhanced the membrane porosity and promoted the membrane performance in terms of the ratio of water flux to reverse salt flux.The modified TFC-FO membrane presented the optimal performance with 0.47 g/m^(2)loading amount of MXenes.Organic fouling experiments using sodium alginate(SA)and bovine serum albumin(BSA)as representative demonstrated that the introduction of MXenes could effectively enhance the anti-fouling ability of TFC-FO membrane under the electric field of 2 V.The interelectron repulsion hindered organic foulants attaching into membrane surface and thus effectively alleviated the membrane fouling.More importantly,the modified TFC-FO membrane showed good stability during the fouling experiment of 10 h.In all,our work proved that introducing MXenes into the porous layer of support is feasible to alleviate organic fouling of FO membrane.

Roles of membrane and organic fouling layers on the removal of endocrine disrupting chemicals in microfiltration

To understand the adsorption behavior of endocrine disrupting chemicals（EDCs） is important for enhancing the treatment performance and preventing potential secondary pollution caused by EDCs desorption in a microfiltration system. The dynamic adsorption of four representative EDCs, namely estriol（E3）, 17β-estradiol（E2）, 17α-ethynylestradiol（EE2）, and 4-nonylphenol（4-NP） in a microfiltration system was investigated using the Thomas＇ model.The product of the equilibrium constant and the total adsorption capacity of the membrane,Ka, for E3, E2, EE2, and 4-NP were 4.91, 9.78, 15.6, and 826, respectively, strongly correlating with the compound octanol–water partition coefficient（KOW）. Adsorption appeared to be enhanced when organic fouling formed on the surface of membrane, indicating the role of an additional adsorption column for EDCs acted by a fouling layer in microfiltration. Results of a comparison between the Ka values for clean membrane and fouled membrane illustrated that the significant contribution made by fouling layers may be attributed to the foulant layer＇s hydrophobicity（in the case of calcium humate layer） and thickness（in the case of calcium alginate layer）. This study provided a novel perspective to quantitatively analyze the dynamic adsorption behavior of trace pollutants in membrane process.

An ecological study on the fouling organisms in Yantai Harbour

Yantai Harbour (37°33′15″N , 121°23′42″E) is situated at the north coast of Shandong Peninsula and is a large fishing and commercial port of North China. From June 1983 to May 1984, a yearly panel test on fouling organisms was carried out at the non-fixed jetties in the inner and outer harbour. The test method was according to "the Marine Survey

Study of fouling organisms at Tuoji Island in the Bohai Channel

From June 1984 to May 1985, monthly and seasonal panel tests of fouling organisms were carried out on rafts at Tuoji Island. Seventy - three species were obtained. The occurring frequencies of the following species are all at least 30%: Ectocarpus confervoides, Polysiphonia urceolata, Tubularia mesembryanthmum, Cfytia edwardsi, Tubulipora pulchra, Celleporella hyalina, Mytilus edulis, Hiatella arctica, Caprella acanthogaster, Corophium crassicome, Jassa cf.falcata and Podocerus cf . inconspicuus. Large or calcareous species are not dominant ones. The wet weight is comparatively light, the yearly wet weight being 9.12 kg m-2. Attaching seasons of major species are from June to October and no bio - attachment occurs between January and April. Fouling organisms at Tuoji Island differ rather greatly from those in the harbours along the continental coast, showing the charcteristics of fouling organisms in the northern island harbours of China.

Distribution of fouling bryozoans in the northern South China Sea

This paper reports the species composition and distribution of fouling bryozoans in the northern SouthChina Sea. 34 species identified belong to 23 genera, 22 families of fouling bryozoa, of which most of 24 species on thebuoys attached to concrete sinkers. The 13 species on platforms mainly included Schizoporella errata and Membranipora savartii. Depth distribution of species, larval settlement behaviour and larvae type of fouling bryozoa are discussed.

An electrochemical study on the effects of marine fouling organisms on steel used in the sea

-Study on the effects of microorganism secretive membrane and covering layer of macrofouling organisms-Balanus reticulatus, Ostrea plicatula, Membranipora, Corophium and Algae on the corrosion of carbon steel and low-alloy steel by the determination of natural corrosive potentials, linear polarization and the polarization curver of dynamic potential scanning through an electrochemical equipment.The results show that the microorganism secretion membrane formed on sample surface has some protective role, during the initial period of exposure (about ten days). Then protective role decreases and corrosive rate increases with the lapse of immersion time. The protective role of some macrofouling organisms is shown in order as follows: Corophium> Balanus reticulatus>Algae>Membranipora>Ostrea plicatula.

Effects of ozonation and coagulation on effluent organic matter characteristics and ultrafiltration membrane fouling

Effluent organic matter （EfOM） is the major cause of fouling in the low pressure membranes process for wastewater reuse. Coagulation and oxidation of biological wastewater treatment effluent have been applied for the fouling control of microfiltration membranes. However, the change in EfOM structure by pre-treatments has not been clearly identified. The changes of EfOM characteristics induced by coagulation and ozonation were investigated through size exclusion chromatography, UV/Vis spectrophotometry, fluorescence spectrophotometry and titrimetric analysis to identify the mechanisms in the reduction of ultrafiltration （UF） membrane fouling. The results indicated that reduction of flux decline by coagulation was due to modified characteristics of dissolved organic carbon （DOC） content. Total concentration of DOC was not reduced by ozonation. However, the mass fraction of the molecules with molecular weight larger than 5 kDa, fluorescence intensity, aromaticity, highly condensed chromophores, average molecular weight and soluble microbial byproducts decreased greatly after ozonation. These results indicated that EfOM was partially oxidized by ozonation to low molecular weight, highly charged compounds with abundant electron- withdrawing functional groups, which are favourable for alleviating UF membrane flux decline.

Fouling distribution in forward osmosis membrane process

Fouling behavior along the length of membrane module was systematically investigated by performing simple modeling and lab-scale experiments of forward osmosis （FO） membrane process. The flux distribution model developed in this study showed a good agreement with experimental results, validating the robustness of the model. This model demonstrated, as expected, that the permeate flux decreased along the membrane channel due to decreasing osmotic pressure differential across the FO membrane. A series of fouling experiments were conducted under the draw and feed solutions at various recoveries simulated by the model. The simulated fouling experiments revealed that higher organic （alginate） fouling and thus more flux decline were observed at the last section of a membrane channel, as foulants in feed solution became more concentrated. Furthermore, the water flux in FO process declined more severely as the recovery increased due to more foulants transported to membrane surface with elevated solute concentrations at higher recovery, which created favorable solution environments for organic adsorption. The fouling reversibility also decreased at the last section of the membrane channel, suggesting that fouling distribution on FO membrane along the module should be carefully examined to improve overall cleaning efficiency. Lastly, it was found that such fouling distribution observed with co-current flow operation became less pronounced in counter- current flow operation of FO membrane process.

Implications of membrane fouling toward the removal of the pharmaceutical sulfamethoxazole by nanofiltration processes

The influence of membrane fouling on the retention of the trace organic contaminant sulfamethoxazole by a nanofiltration(NF) process was investigated.Organic fouling caused a severe flux decline possibly due to pore blocking and adsorption directly after the commencement of the fouling layer development.Such membrane-foulant interactions were absent for colloidal fouling,which resulted in a more gradual flux decline.Membrane charge played a significant role in the separation process of inorganic salts,where the retention was the highest in a caustic environment(high pH) due to more swollen membrane material caused by the higher negative charge on the membrane.Organic fouling and a combination of colloidal and organic fouling led to a significant increase in the membrane negative charge.The influence of membrane fouling on solute retention was dependent on the fouling behaviour and the physicochemical properties of the model foulants,where the model foulants probably contributed to an increase in the retention of charged solutes due to enhanced electrostatic interactions.Organic fouling caused an increase in the retention of inorganic salts and sulfamethoxazole due to pore blocking.In contrast,colloidal fouling caused a decrease in the retention of inorganic salts due to cake-enhanced concentration polarisation.However,the presence of a colloidal fouling layer did not reduce the retention of sulfamethoxazole.A mixture of colloidal and organic matter improved the retention of inorganic salts.A similar conclusion can be inferred for sulfamethoxazole at pH 4 when the compound exists in a neutral form.

Identifying the major fluorescent components responsible for ultrafiltration membrane fouling in different water sources

Three-dimensional fluorescence excitation–emission matrix（EEM） coupled with parallel factor analysis（PARAFAC） was performed for a total of 18 water samples taken from three water sources（two lakes and one wastewater treatment plant（WWTP） secondary effluent）,with the purpose of identifying the major ultrafiltration（UF） membrane foulants in different water sources. Three fluorescent components（C1, C2 and C3） were identified,which represented terrestrially derived humic-like substances（C1）, microbially derived humic-like substances（C2）, and protein-like substances（C3）. The correlations between the different fluorescent components and UF membrane fouling were analyzed. It was shown that for the WWTP secondary effluent, all three components（C1, C2 and C3） made a considerable contribution to the irreversible and total fouling of the UF membrane.However, for the two lakes, only the C3 exhibited a strong correlation with membrane fouling, indicating that the protein-like substances were the major membrane foulants in the lake waters. Significant attachment of C1, C2 and C3 to the UF membrane was also confirmed by mass balance analyses for the WWTP secondary effluent; while the attachment of C1 and C2 was shown to be negligible for the two lakes. The results may provide basic formation for developing suitable fouling control strategies for sustainable UF processes.