In this study, mechanisms of membrane fouling caused by polysaccharides with different molecular structures in polyaluminum chloride (PACl) coagulation-ultrafiltration (C-UF) process were explored. Carrageenan and xanthan gum were chosen for model foulants of straight chain and branched chain polysaccharides, respectively. Filtration experiments showed that, with PACl dosage of 0-5 mM, specific filtration resistance (SFR) of carrageenan and xanthan solution showed a unimodal pattern and a continuous decrease pattern, respectively. A series of experimental characterizations indicated that the different SFR pattern was closely related to structure of foulants layer. Density functional theory (DFT) calculation suggested that Al3+ preferentially coordinating with the terminal sulfonyl groups of carrageenan chains to promote gel layer formation at low PACl concentration (0.15 mM). There existed a chemical potential gap between bound water in gel layer and free water in the permeate, so that, filtration through gel layer corresponded to rather high SFR for overcoming this gap. In contrast, Al3+ coordinating with the non-terminal sulfonyl groups of carrageenan at high PACl concentration caused transition from gel layer to cake layer, leading to SFR decrease. However, xanthan gum itself can form a dense gel layer with a complex polymer network by virtue of the interlacing of main chains and branches. Al3+ coordinating with the carboxyl groups on branched chains of xanthan gum resulted in clusters of polymer chains and flocculation, corresponding to the reduced SFR. This proposed molecular-level mechanism well explained membrane fouling behaviors of polysaccharides with different molecular structure, and also facilitated to optimize C-UF process for water treatment.

Molecular insights into membrane fouling caused by polysaccharides with different structures in polyaluminum chloride coagulation-ultrafiltration process.

Pretreatment for alleviation of RO membrane fouling in dyeing wastewater reclamation

Mitigation of reverse osmosis membrane fouling by electrochemical-microfiltration- activated carbon pretreatment

Molecular insights into membrane fouling caused by polysaccharides with different structures in polyaluminum chloride coagulation-ultrafiltration process

The development of novel reverse osmosis (RO) membranes resistant to multiple types of fouling is a need to secure clean water production and meet rising water demands. In this paper, the RO membrane surface-functionalized with antibacterial graphene oxide (GO) and antiscalant maleic acid was prepared and tested. The polymerization of maleic acid on the GO functionalized RO membrane was achieved using microwave radiation. The membrane surface characterization showed a decrease in membrane surface roughness from 74.7 nm to 69.0 nm and an increase in membrane hydrophilicity as the contact angle decreased from 41.7 ± 4.50 to 22.0 ± 1.10. The modified membrane was tested against inorganic scaling and biofouling, and the results demonstrated that the modified membrane has improved resistance to multiple fouling types as compared to the unmodified RO membrane. When tested in the presence of calcium sulfate scaling solution (inorganic fouling), the normalized permeate flux was found to be stable at 0.91 and 0.95 for 0.01 and 0.02 wt% maleic acid-modified RO membranes, respectively. Moreover, the modified membranes also demonstrated bacteriostasis rates of 96.1 %–97.1 % showing their anti-bacterial characteristics. Both types of membrane fouling (inorganic and biofouling) were also studied simultaneously, and the results showed that the RO membranes with dual capabilities can inhibit both mineral formation and biofilm growth concurrently. 

Investigating the effect of polymer-modified graphene oxide coating on RO membrane fouling

Performance of different pretreatment methods on alleviating reverse osmosis membrane fouling caused by soluble microbial products

The invention discloses an organic pollution and blocking control method of a reverse osmosis membrane. The method comprises the steps of preliminarily determining a feeding proportion of active carbon and ferric chloride through determination results of molecular weight of organic matter in an influent water sample and a three-dimensional fluorescence spectrogram of the sample, determining feeding concentration intervals of the active carbon and ferric chloride according to a DOC (dissolved organic carbon) concentration, obtaining corresponding DOC removal rates, determining the best active carbon feeding concentration A and the best ferric chloride feeding concentration B by stabilizing a minimum dose required for removing DOC, feeding the active carbon of the concentration A into reverse osmosis influent for absorption for 0.5-1h, and feeding ferric chloride of the concentration B for coagulation to remove the active carbon and the residual organic matter. The method has the characteristics of low cost, low energy consumption, simplicity in operation and the like, and achieves the purposes of stabilizing the quality of the RO (reverse osmosis) system influent, reducing a pollution and blocking speed of an RO system, improving operating stability of the RO system, and prolonging operating time of the RO system, thereby lowering operating cost of the RO system by removing organic pollutants from the RO system influent.

Pin-Sheng Fang

Papers

Performance of different pretreatment methods on alleviating reverse osmosis membrane fouling caused by soluble microbial products

Organic pollution and blocking control method of reverse osmosis membrane