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Polyvinyl chloride (PVC) plastic wastes can bring a series of problems during pyrolysis or incineration such as the emission of dioxins, corrosion, slagging in the reactors, etc. Hydrothermal treatment of PVC plastics has been intensively studied as it can efficiently remove chlorine from PVC plastics under relatively mild reaction conditions (220-300 °C) to provide value-added products. Meanwhile, the research progress, knowledge gaps, and challenges in this field have not been well addressed yet. This paper gives a comprehensive review of hydrothermal dechlorination of PVC plastics regarding reactors, process variables and fundamentals, possible applications, and challenges. The main pathways of hydrothermal dechlorination of PVC plastics are elimination and -OH nucleophilic substitution. Catalytic hydrothermal and co-hydrothermal optimize the chemical reactions and transportation, boosting the dechlorination of PVC plastics. Hydrochar derived from PVC plastics, on the one hand, is coalified close to sub-bituminous and bituminous coal and can be used as low-chlorine solid fuel. On the other hand, it is also a porous material with aromatic structure and oxygen-containing functional groups, with good potential as adsorbent or energy storage materials. Further studies are expected to focus on waste liquid treatment, revealing the energy and economic balance, reducing the dechlorination temperature and pressure, expanding the application of products, etc. for promoting the implementing the hydrothermal treatment of PVC plastic wastes.

Ranitidine is widely concerned due to it is mainly related to the transformation into highly toxic carcinogenic products and non-readily biodegradable characteristics in aquatic environment. In this study, biodegradation of ranitidine during rural human feces (HF) aerobic composting was investigated. Results show that both levels of ranitidine are quickly removed in the first-3-day composting. The microorganisms play a vital role in the ranitidine degradation, especially for Firmicutes at the thermophilic period. The effect of ranitidine on the aerobic composting was further analyzed under the normal content (10 mg/kg) and high content (100 mg/kg). The 10 mg/kg ranitidine quickens temperature rise and organic matter degradation of the composting, while the 100 mg/kg ranitidine produces inhibiting effects. However, the effects only occur in the early stage of composting, and then tend to disappear with the removal of ranitidine. Fluorescence spectra confirm that humification and aromatization of dissolved organic matters (DOMs) in the substrates are fastened in 10 mg/kg group, while delayed in 100 mg/kg group. Metagenomic analysis reveals that relative abundances of Firmicutes and sequences related to carbohydrates metabolism increase in the groups mixed with the ranitidine at the early period. The findings provide the first new and systematical insights into degradation characteristics and potential effect of ranitidine during the rural HF composting.

The complex seawater matrix has significantly influenced the determination of estuarine dissolved Hg(II), hindering its monitoring and risk assessment in maricultural areas. In this work, SiO

Street dust is a vital pertinent indicator to urban environmental quality, while only limited information is available on Hg from street dust in a subtropical city, as well as the bonding reactions...

Much attention has been focused on the synthesis of TiO2 based materials as photocatalysts for water pollutant treatment, it still needs overcome difficulties of separation of TiO2 photocatalyst from the treated water and the recombination of photo-induced carriers to improve catalytic activities. In this paper, a magnetical core-shell Fe3O4@SiO2@Sn-TiO2 (FST-S) composite photocatalyst was designed and prepared via prepared via Stober and sol-gel methods. The effect of Sn2+ coating TiO2 on the surface of Fe3O4@SiO2 nanoparticles was principally investigated. The photocatalytic performance and recyclability of FST-S were evaluated by photodegradation of tetracycline hydrochloride (TC). Experimental results show that Sn2+ doping increased the content of TiO2 in composite photocatalyst. Because some Sn2+ ions lead to the decrease in the stability of Sn2+-TiO2 nanoparticles and then low-stable Sn2+-TiO2 nanoparticles enter into the composite photocatalyst by condensation with the Sn2+-TiO2 outer shells of FST-S. The photodegradation results show that FST-S sample exhibits an outstanding photocatalytic capacity with a superior degradation rate of 98.2% within 40 min and a good reusability without significant decrease of activity after reused for six cycles. The reaction rate constant (k) of the FST-S was 3.86 times compared with that of without Sn doping Fe3O4@SiO2@Sn (FST). Reactive species scavenging experiments revealed that O2-• it plays a dominant role in photodegradation process. The distinct enhancement of photocatalytic activity of Fe3O4@SiO2@Sn-TiO2 is mainly ascribed to the high amount of TiO2 and low recombination rate of photogenerated electron-holes. This work initiates a novel strategy to prepare magnetical core-shell photocatalysts with excellent activity.

In the traditional Fenton process, the efficient generation of hydroxyl radical (HO ) strongly relies on an acidic circumstance and the iron ions would precipitate and form large amounts of hazardous iron-containing sludge at alkaline pH. To realize stable heterogeneous Fenton-like catalytic degradation at alkaline condition, Fe3O4 submicrospheres with SiO2 coating were successfully synthesized by using water glass as the silica sources via a facile ultrasound assisted method. The as-obtained Fe3O4@SiO2 spheres were further used as catalysts for the Fenton-like degradation of tetracycline hydrochloride (TC). The Fe3O4@SiO2 submicrospheres exhibited superior catalytic activity in higher pH environment (pH value = 11), and the degradation efficiency toward TC was ca. 80% after ten successive runs. The kinetics for the catalytic degradation of TC were agreed well with the second-order kinetic model. The reaction rate constant (k) over the Fe3O4@SiO2 submicrospheres at a pH value of 11 was 7.69 times greater than that at a pH value of 3. Reactive species scavenging experiments revealed that HO and superoxide radical (O2− / HO2− ) played a dominant role during the Fenton-like degradation of TC at pH 3 and pH 11, respectively. Possible Fenton-like degradation pathways of TC were proposed through the identification of intermediates using the high performance liquid chromatography coupled with mass spectrometry (HPLC-MS), which involved cleavage of methyl groups, N-dimethyl group, and hydroxy groups, ring-opening reaction, etc. The degradation efficiency of TC was close to 91.5% and total organic carbon (TOC) in solution was eliminated by about 41.4% at the optimized conditions. In a word, with the unique acidic surface properties and abundant Si-OH bonds, the Fe3O4@SiO2 submicrospheres exhibited well dispersion, good catalytic activity, strong alkali resistance and excellent recyclability in an ultrasonic-Fenton-like system.

In order to reveal the chlorine behavior during hydrothermal carbonization (HTC) of medical waste, polyvinyl chloride and medical waste model (MW) were respectively treated by HTC at temperature ranging from 220 °C to 300 °C for 30 min. HTC products were characterized by Fourier Transform Infrared Spectrometer, X-ray Photoelectron Spectroscopy, etc. It is found that HTC can efficiently remove chlorine from both polyvinyl chloride and MW. The most dramatical dechlorination can be induced by HTC at around 240 °C. With HTC temperature increased, organic chlorine in HT-MW and solid product from polyvinyl chloride HTC (HT-PVC) is decreased. Interestingly, with 240 °C HTC, the organic chlorine of HT-MW was 15.30%, much lower than that of HT-PVC of 86.84%, indicating the cellulosic materials in MW can significantly boost the conversion of organic chlorine into inorganic form in HTC at 240 °C. While spherical particles assigned to HTC of cellulosic materials aggregate at the pores of polyvinyl chloride particle, trapping the release of chlorine into the liquid, consequently to lower dechlorination efficiency compared to that of polyvinyl chloride. Since the chlorine retain in the solid product was mainly in form of inorganic, further dechlorination is potential for MW by combining HTC with leaching/extracting.