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.