Preloading the flocs on the membrane surface is beneficial to enhance the removal of contaminants and alleviate membrane fouling in the membrane-filtration process, but the appropriate flocs and its mechanism of action need to be further clarified. The present study first focused on the flocs generated by titanium xerogel coagulant (TXC) with PFS and PACl as comparation. Three flocs were separately pre-loaded on the ultrafiltration membrane to explore their performance of removing four toxic heavy metals (As(III), As(V), Sb(III) and Sb(V)) and alleviating membrane fouling. Results showed that the flocs produced by TXC and PFS could adsorb toxic oxygenates continuously, and the removal performance of TXC flocs is better than that of PFS, while the removal performance of PACl flocs is limited. After long-term operation, the membrane fouling of pre-loaded TXC floc was minimal, and the irreversible fouling was 1/3 and 1/6 of that of PFS and PACl, respectively. Meanwhile, the backwash time was 2.0 and 2.2 times longer than PFS and PACl, respectively. The mechanism of membrane fouling alleviation by floc preloading was clarified by floc characterization and model calculations. According to the n value in the model after fitting, an intermediate blocking mechanism dominated with the larger and more loose flocs in TXC system (n = 1.54), while a complete pore blocking mechanism dominated in the PFS (n = 1.98) and PACl (n = 2.11) systems. The results demonstrated that preloading the TXC flocs were superior to that of PFS and PACl in the membrane-filtration process.
Yan Zhang,Jianjing Liu,Yutong Fu,Ke Tan,Zhaoyang Ye,Meidong Lang
A novel polyion complex (PIC) drug carrier was developed via electrostatic self-assembly in aqueous media based on our previous copolymer methoxy poly(ethylene glycol)-b-poly(γ-amino-ε-caprolactone) (mPEG-b-PACL) and anti-hepatotoxic drug ammonium glycyrrhizinate (AMG). The formation and the physicochemical properties of the polyion complex nanoparticles in aqueous solution were investigated by various methods. The results demonstrated that AMG was encapsulated successfully and the nanoparticles had a core–shell or tri-layer spherical structure based on the length of the PACL. The AMG/PACL PIC also displayed a high loading capacity and encapsulation efficiency of up to 41.8% and 91.7%, respectively. Furthermore, the nanoparticles enabled a continuous and sustained in vitro AMG release and the release half time was about 3 times that of the free AMG's. Results obtained by 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyl tetrazolium bromide (MTT) assay, flow cytometry and fluorescence microscopy revealed that AMG loaded nanoparticles demonstrated greater prevention of liver cell apoptosis induced by lipopolysaccharide (LPS). These findings indicated that methoxy poly(ethylene glycol) (mPEG)-b-poly(γ-amino-ε-caprolactone) could be an efficient AMG carrier and could even be used as a delivery template for some other negatively charged water-soluble drugs or gene delivery systems.
Understanding membrane fouling mechanisms, particularly the pretreatment-mediated fouling mitigation mechanism, is critical for controlling algal fouling. This study examined the fouling control mechanism of extracellular organic matter (EOM) by combined heat-activated potassium peroxymonosulfate (PMS) and polyaluminum chloride (PACl) treatment using extended Derjaguin-Landau-Verwey-Overbeek (XDLVO)-based interaction energy analysis. Results showed that combined PMS and PACl treatment effectively mitigated membrane fouling, with the fouling control performance being highly dependent on PACl dosage. PACl 5 mg/L under combined PMS treatment worsened membrane fouling, while PACl dosages 10 – 40 mg/L alleviated it, with the best performance achieved at 40 mg/L. XDLVO theory analysis revealed that PMS-PACl (10 – 40 mg/L) treatment enhanced repulsive membrane-foulant interactions and transformed membrane-foulants and foulants-foulants interactions from attractive to repulsive. Moreover, both membrane-foulant and foulant-foulant repulsive interactions increased with increasing PACl dosage. In contrast, although integrated PMS and PACl 5 mg/L weakened foulant-foulant attractive interaction than control EOM, serious membrane fouling was still observed, likely due to stronger attractive membrane-foulant interactions during the initial filtration stage. This research offers new mechanistic insights into fouling control and provides a theoretical basis for algal-laden water treatment. Download: Download high-res image (209KB) Download: Download full-size image
The applications of natural polymeric flocculants due to their green feature has been recently received much more attention. In this work, the combined usages of a cationic starch-based coagulant and polyaluminum chloride (PACl) were extensively evaluated for various addition sequences in the coagulation of both raw (surface water from the Jiuxiang River) and synthetic turbid water (two kaolin suspensions with different initial turbidities). Two typical cationic starch-based coagulants with different structures (St-G and St-E) were tried. In comparison to St-G, St-E and PACl used individually as well as St-G and St-E dosed after PACl, the combination of the starch-based coagulants fed before PACl showed higher turbidity removal efficiency, which featured not only less optimal doses of both inorganic and organic coagulants but also lower residual turbidity. On the basis of a detailed analysis of the particle size and its distribution in solution supernatants before and after coagulation by two starch-based coagulants and PACl, polymeric coagulants preferentially coagulate the small-sized colloids due to their distinct long-chain structures, but PACl preferentially coagulates the medium-sized ones. Thus, the medium-sized particles that were previously formed by the starch-based coagulants would be collectively and effectively removed by the subsequent addition of PACl. The addition sequence of the inorganic and organic coagulants in their combined usage is an important factor for improvement of the turbidity removal efficiency in practice.
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