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

Abstract 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.