Occurrence and fate of chlorinated methylsiloxanes in surrounding aqueous systems of Shengli oilfield, China.

Mono-chlorinated products of cyclic volatile methylsiloxanes (cVMS), i.e., Monochlormet-hylheptamethylcyclotetrasiloxane [D3D(CH2Cl)], monochlormethylnonamethylcyclopenta-siloxane [D4D(CH2Cl)], and monochlormethylundemethylcyclohexasiloxane [D5D(CH2Cl)], were detected in water [

A review on the landfill leachate treatment technologies and application prospects of three-dimensional electrode technology.

With the expansion of urbanisation, the total amount of solid waste produced by urban residents has been increasing, and the problem of municipal solid waste disposal has also been aggravated. Landfill leachate treatment technologies could be divided into three categories: biological, physical and advanced oxidation treatment technology. Among them, advanced oxidation treatment technology has a good effect on the treatment of landfill leachate with little secondary pollution and has excellent application potential. Three-dimensional (3D) electrode technology, as a new type of advanced oxidation technology, could remove refractory pollutants in water and has attracted considerable attention. This article aims to (1) compare existing landfill leachate treatment technologies, (2) summarise 3D electrode technology application scenarios, (3) discuss the advantages of 3D electrode technology in landfill leachate treatment and (4) look ahead the future directions of 3D electrode technology in landfill leachate treatment. We hope that this article will be helpful to researchers who are interested in the field of landfill leachate treatment.

Distribution of methylsiloxanes in benthic mollusks from the Chinese Bohai Sea.

Methylsiloxanes are a class of silicone compounds that have been widely used in various industrial processes and personal care products for several decades. This study investigated the spatial distribution of three cyclic methylsiloxanes (D4-D6) and twelve linear methylsiloxanes (L5-L16) in mollusks collected from seven cities along the Bohai Sea. D4-D6 (df = 71%-81%) and L8-L16 (df = 32%-40%) were frequently detectable in the mollusk samples, while L5-L7 were not found in any mollusk samples. Cyclic methylsiloxanes (D4-D6) were found in mollusks with the mean concentrations of 15.7 ±â€¯12.3 ng/g ww for D4, 24.6 ±â€¯15.8 ng/g ww for D5 and 34.0 ±â€¯23.0 ng/g ww for D6. Among the seven sampling cities, the cyclic methylsiloxanes were predominant in mollusks, with the total cyclic methylsiloxanes (sum of D4-D6, ∑CMS) accounting for 74.2%-80.7% of the total methylsiloxanes. ∑CMS along the coastline demonstrated a clear gradient, with the highest concentrations in mollusks at the sampling sites located in the western part of the Bohai Sea and the lowest concentrations in mollusks from cities located in the eastern part of the Bohai Sea. The biota-sediment accumulation factors for cyclic methylsiloxanes (D4-D6) and linear methylsiloxanes (L8-L16) were estimated as 0.42 ±â€¯0.06-0.53 ±â€¯0.06 and 0.13 ±â€¯0.03-0.19 ±â€¯0.05, respectively.

Occurrence and profiles of methylsiloxanes and their hydrolysis product in aqueous matrices from the Daqing oilfield in China.

In the present study, the occurrence and distribution of methylsiloxanes (D4-D6, L5-L16) in the surface water and sediment collected from the Daqing oilfield were explored. For wastewater samples from an oilfield combination station, the concentrations of total cyclic methylsiloxanes (∑CMS, D4-D6) and total linear methylsiloxanes (∑LMS, L5-L16) ranged from 137-1911ng/L to 49.4-190ng/L, respectively. Cyclic methylsiloxanes were the predominant methylsiloxanes in the analyzed wastewater samples from the oilfield combination station. In addition, methylsiloxanes were detected in the surface water from three sampling areas, and the total concentrations varied from

Methylsiloxanes Release from One Landfill through Yearly Cycle and Their Removal Mechanisms (Especially Hydroxylation) In Leachates.

In one yearly cycle (2016), D4 and D5 were detected in biogas samples (n = 36, 0.105-2.33 mg/m3) from a Chinese municipal landfill, while D4-D6 were detected in influents/effluents of leachate storage pond (n = 72, < LOQ-30.5 µg/L). Mass loads of cVMS in both biogas (591-6575 mg/d) and leachate influents (659-5760 mg/d) increased from January to July (summer), and then decreased from July to December (winter). Removal experiments indicated that 1) hydrolysis and volatilization were predominant removal mechanism for D4 and D5, respectively, in leachate storage pond, responsible for their more significant removal (94.5-100%) in August; 2) indirect phototransformation (t1/2 = 25.5-87.0 days), such as hydroxylation by OH radical generated in leachates, was the predominant (50.0-75.5%) removal pathway for D6, which led to the largest removal efficiencies (65.2-73.7%) in June, the month with the largest sun light intensity and highest photosensitizer (e.g., Fe2+ and NO3-) concentrations. Monohydroxylated products of D5 and D6, D4TOH and D5TOH, were detected in leachate effluents (39.6-187 ng/L) during May-July. Compared to D5 and D6, volatilization half-lives of D4TOH (86.3 days) and D5TOH (177 days) in leachates were 2.9 and 1.4 times longer, while their hydrolysis half-lives (7.50 days for D4TOH and 21.5 days for D5TOH) were 7.1 and 10 times shorter, respectively.

Chlorinated Methylsiloxanes Generated in the Papermaking Process and Their Fate in Wastewater Treatment Processes.

Simulated experiments indicated that chlorinated volatile methylsiloxanes, detected by Q-TOF GC/MS, could be generated in a pulp-bleaching process, where poly(dimethylsiloxane)s fluids with volatile methylsiloxanes as impurities and molecular chlorine were used as a defoamer and bleaching agent, respectively. In the producing processes of one papermaking factory, the mean total concentrations of monochlorinated D4, D5, and D6, i.e., D3D(CH2Cl), D4D(CH2Cl), and D5D(CH2Cl), were 0.0430-287 µg/L in aqueous samples, while they were 0.0329-270 µg/g in solid samples. In the coupled papermaking-wastewater treatment processes, D3D(CH2Cl), D4D(CH2Cl), and D5D(CH2Cl) were detected in all water (0.113-8.68 µg/L) and solid samples (0.888-26.2 µg/g), with solid-water partition values (468-3982 L/kg) 1.08-4.82 times higher than those of their corresponding nonchlorinated analogs. The removing efficiencies of D3D(CH2Cl)-D5D(CH2Cl) in the whole wastewater treatment processes were 77.1-81.6%, and sorption to sludge (35.7-74.1%) and removal in the primary clarifier (7.19-32.5%) had major contributions to their total removal. Elimination experiments showed that 1) hydrolysis half-lives of D3D(CH2Cl)-D5D(CH2Cl) (0.9-346 h) in the primary clarifier (pH = 7.8-9.2) were 2.16-3.60 times shorter than those of their nonchlorinated analogs; 2) D3D(CH2Cl)-D5D(CH2Cl) were hardly degraded in oxic sludge treatment process, and their volatilization half-lives (7.38-21.1 h) in oxic sludge were 1.21-1.50 times longer than those of their nonchlorinated analogs.