Removal of Microcystis aeruginosa by manganese activated sodium percarbonate: Performance and role of the in-situ formed MnO2.

Previous studies have found that pre-oxidation of manganese salts such as potassium permanganate and potassium manganate can remove algae in water, while existing problems such as excessive oxidation and appearance of chromaticity. In this study, our objective was to induce a Fenton-like reaction by activating sodium percarbonate (SPC) with divalent manganese (Mn(II)) to pre-oxidize algae-contaminated water. The optimal dosage of Mn(II)/SPC was determined by assessing the zeta potential of the algae and the residual Mn(II) in the solution. Moreover, we conducted a characterization of the cells post-reaction and assessed the levels of dissolved organic carbon (DOC). The disinfection by-products (DBPs) (sodium hypochlorite disinfection)of the algae-containing water subsequent to Mn(II)/SPC treatment were measured. Experiments show that Mn(II)/SPC pre-oxidation at optimal dosage acquired 88% removal of algae and less damage to the cell membrane. Moreover, the Mn(II) acted not only as a catalyst but also formed MnO2 which adsorbed onto the cell surface and facilitated sedimentation. Furthermore, this technology exhibits the capability to effectively manage algal organic matters present in water, thereby mitigating the formation of nitrogen-containing DBPs. These results highlight the potential of Mn(II)/SPC treatment for treating water contaminated with algae, thus ensuring the safety and quality of water resources.

In situ oxidized TiO2/MXene ultrafiltration membrane with photocatalytic self-cleaning and antibacterial properties.

Self-cleaning, antimicrobial ultrafiltration membranes are urgently needed to alleviate the low flux problems caused by membrane fouling in water treatment processes. In this study, in situ generated nano-TiO2 MXene lamellar materials were synthesized and then 2D membranes were fabricated using vacuum filtration. The presence of nano TiO2 particles as an interlayer support layer widened the interlayer channels, and also improved the membrane permeability. The TiO2/MXene composite on the surface also showed an excellent photocatalytic property, resulting in enhanced self-cleaning properties and improved long-term membrane operational stability. The best overall performance of the TiO2/MXene membrane at 0.24 mg cm-2 loading was optimal, with 87.9% retention and 211.5 L m-2 h-1 bar-1 flux at a filtration of 1.0 g L-1 bovine serum albumin solution. Noticeably, the TiO2/MXene membranes showed a very high flux recovery under UV irradiation with a flux recovery ratio (FRR) of 80% as compared to the non-photocatalytic MXene membranes. Moreover, the TiO2/MXene membranes demonstrated over 95% resistance against E. coli. And the XDLVO theory also showed that the loading of TiO2/MXene slowed down the fouling of the membrane surface by protein-based contaminants.

Molecular insights towards changing behaviors of organic matter in a full-scale water treatment plant using FTICR-MS.

The changing behavior of organic matter in a full-scale water treatment process was characterized based on the three-dimensional excitation-emission matrix (3D-EEM) and Fourier transform ion cyclotron resonance mass spectrometry (FTICR-MS). Polyaluminum chloride (PAC) as a coagulant can help to effectively remove soluble microbial by-products-like and aromatic protein-like substances during coagulation and sedimentation, corresponding to tannin and coagulated aromatic regions. The leakage of soluble microbial products during sand filtration resulted in an increase in the intensity of biomass-like regions. Nitrogen-containing compounds have higher weighted average value of double bond equivalents (DBEw) and the modified aromaticity index (AImod-w) than nitrogen-free compounds. Water treatment can preferentially remove unsaturated nitrogen-containing compounds with more O atoms and higher-oxidation-state carbon. The dissolved organic carbon (DOC) and UV254 were not correlated well with changes in nitrogen-containing compounds due to the preferential removal of nitrogen-containing compounds. This study revealed the specificity of organic matter removal during water treatment, and it was helpful in optimizing treatment processes for various raw water to ensure water quality.

[Study on photocatalytic degradation of 1, 2, 3-trichlorobenzene using the microwaved MWNTs/TiO2 composite].

Composite photocatalyst, MWNTs/TiO2, is prepared using sol-gel method and dried through microwave irradiation. Characterization of the composite shows that, with the increase of microwave power till 400 W, the average diameter of MWNTs/TiO2 composite reduces gradually, and better dispersion of the composites is also acquired at the microwave power of 400 W. However, a further increase of the power results in the average diameter of the composite enlarged, and more aggregative composites are obtained. Furthermore, photodegradation of 1,2,3-trichlorobenzene (1,2,3-TCB) with the composite photocatalysts of MWNTs/TiO2 induced under different microwave conditions is studied. It is found that the photodegradation of 1,2,3-TCB follows the first-order kinetics. The microwaving conditions for producing the composite photocatalysts with the highest photocatalytic activity are further determined as 5 min irradiation at 400 W. Under such conditions, the rate constant of 1,2,3-TCB photodegradation is 0.023 7 min(-1) which is elevated by 52% comparing to those obtained using non-microwaved composites.

[Photocatalytic degradation of 1,2, 4-trichlorobenzene with TiO2 coated on carbon nanotubes].

Effects and kinetics of photocatalytic degradation of 1,2,4-trichlorobenzene with composite photocatalysts of TiO2 coated on carbon nanotubes and nano-TiO2 photocatalysts were studied, respectively. It was found that the composite photocatalysts was better than the nano-TiO2 for photocatalytic degradation of 1,2,4-trichlorobenzene. After 60 min UV irradiation at 254 nm, there was 70% of the initial 1,2,4-trichlorobenzene degraded with the composite photocatalyst while only 51% of the initial 1,2,4-trichlorobenzene degraded with the nano-TiO2. Results of photocatalytic degradation kinetics also proved that the 1,2,4-trichlorobenzene degradation rate constant with the composite photocatalyst was 0.019 6 h(-1), which was increased by 63.3% compared to that with nano-TiO2. According to molecular structure theory, analysis of dissociation energy of C--Cl bond of chlorobenzenes predicated that main pathway of photocatalytic degradation of 1,2,4-trichlorobenzene followed that its ortho-Cl could be took off first to form 1, 4-dichlorobenzene, and it might be further dechlorized and finally be mineralized. The first step of photodechlorination for 1,2,4-trichlorobenzene was also experimentally confirmed through identified 1,4-dichlorobenzene as its product.