Xiaoxiang Cheng

Application of Fe(II)/peroxymonosulfate for improving ultrafiltration membrane performance in surface water treatment: Comparison with coagulation and ozonation

Coagulation and ozonation have been widely used as pretreatments for ultrafiltration (UF) membrane in drinking water treatment. While beneficial, coagulation or ozonation alone is unable to both efficiently control membrane fouling and product water quality in many cases. Thus, in this study an emerging alternative of ferrous iron/peroxymonosulfate (Fe(II)/PMS), which can act as both an oxidant and a coagulant was employed prior to UF for treatment of natural surface water, and compared with conventional coagulation and ozonation. The results showed that the Fe(II)/PMS-UF system exhibited the best performance for dissolved organic carbon removal, likely due to the dual functions of coagulation and oxidation in the single process. The fluorescent and UV-absorbing organic components were more susceptible to ozonation than Fe(II)/PMS treatment. Fe(II)/PMS and ozonation pretreatments significantly increased the removal efficiency of atrazine, p-chloronitrobenzene and sulfamethazine by 12-76% and 50-94%, respectively, whereas coagulation exerted a minor influence. The Fe(II)/PMS pretreatment also showed the best performance for the reduction of both reversible and irreversible membrane fouling, and the performance was hardly affected by membrane pore size and surface hydrophobicity. In addition, the characterization of hydraulic irreversible organic foulants confirmed its effectiveness. These results demonstrate the potential advantages of applying Fe(II)/PMS as a pretreatment for UF to simultaneously control membrane fouling and improve the permeate quality.

Microcystis aeruginosa-laden water treatment using enhanced coagulation by persulfate/Fe(II), ozone and permanganate: Comparison of the simultaneous and successive oxidant dosing strategy

In this study, the application of enhanced coagulation with persulfate/Fe(II), permanganate and ozone for Microcystis-laden water treatment was investigated. Two oxidant dosage strategies were compared in terms of the organic removal performance: a simultaneous dosing strategy (SiDS) and a successive dosing strategy (SuDS). To optimize the oxidant species, oxidant doses and oxidant dosage strategy, the zeta potential, floc size and dimension fraction, potassium release and organic removal efficiency during the coagulation of algae-laden water were systematically investigated and comprehensively discussed. Ozonation causes most severe cell lysis and reduces organic removal efficiency because it releases intracellular organics. Moreover, ozonation can cause the release of odor compounds such as 2-methylisoborneol (2-MIB) and geosmin (GSM). With increasing doses, the performance of pollutant removal by coagulation enhanced by persulfate/Fe(II) or permanganate did not noticeably improve, which suggests that a low dosage of persulfate/Fe(II) and permanganate is the optimal strategy to enhance coagulation of Microcystis-laden water. The SiDS performs better than the SuDS because more Microcystis cell lysis occurs and less DOC is removed when oxidants are added before the coagulants.

Free-standing hierarchical α-MnO 2 @CuO membrane for catalytic filtration degradation of organic pollutants

Catalytic membrane, due to its compact reactor assembling, high catalytic performance as well as low energy consumption, has proved to be more attractive for wastewater treatment. In this work, a free-standing α-MnO2@CuO membrane with hierarchical nanostructures was prepared and evaluated as the catalytic membrane to generate radicals from peroxymonosulfate (PMS) for the oxidative degradation of organic dyes in aqueous solution. Benefiting from the high mass transport efficiency and the hierarchical nanostructures, a superior catalytic activity of the membrane was observed for organic dyes degradation. As a typical organic dye, more than 99% of methylene blue (MB) was degraded within 0.23 s using dead-end filtration cell. The effects of flow rate, PMS concentration and buffer solution on MB degradation were further investigated. Besides MB, the catalytic membrane also showed excellent performance for the removal of other dyes, such as congo red, methyl orange, rhodamine B, acid chrome blue K and malachite green. Moreover, the mechanism study indicated that OH and SO4- generated from the interaction between PMS and Mn/Cu species with different oxidation states mainly accounted for the dyes degradation. The catalytic filtration process using α-MnO2@CuO catalytic membrane could provide a novel method for wastewater purification with high efficiency and low energy consumption.

Effect of PAC particle layer on the performance of gravity-driven membrane filtration (GDM) system during rainwater treatment

The gravity-driven membrane filtration (GDM) process is very suitable for decentralized drinking water or rainwater treatment due to low maintenance (no backwashing, physical flushing and chemical cleaning) and low energy consumption. However, the ultrafiltration process alone seldom satisfies the standard of organics removal. To meet the purpose of water reuse, we applied a powdered activate carbon (PAC) layer and sand layer on the membrane surface of a GDM system to improve the quality of the effluent in this study. In addition, the flux development and fouling layer properties were also systematically investigated. Results show that the presence of a PAC layer enhanced the organics removal by nearly 20%, including the fluorescent organics (such as aromatic proteins, tryptophan proteins and humics) removal. However, the sand layer assisted system did not show any improvement, as observed when compared with the control. With regard to the permeate flux development tendency, the flux could be kept stable in the PAC/GDM system (3.0 L m−2 h−1) and control system (4.5 L m−1 h−1), whereas the flux of the sand/GDM system did not stabilize with the final value of 2.3 L m−2 h−1 on day 55. The reason for the lower stable flux in PAC/GDM system was that PAC acted as a bio-carrier and that a large amount of biomass with higher EPS contents (proteins and polysaccharides) developed on the membrane. The main explanation for the unstable flux in the sand/GDM system was the low porosity of the bio-fouling layer, which significantly increased the hydraulically reversible and cake layer resistances. However, the permeate flux could be restored easily in these systems by simple flushing because hydraulically reversible resistance accounted for large proportions (>90%) of the total filtration resistance.