Fate and effects of polydimethylsiloxanes on pilot and bench-top activated sludge reactors and anaerobic/aerobic digesters

Abstract

The effect of polydimethylsiloxanes (PDMS) on bench-scale activated sludge reactors and pilot-scale anaerobic and aerobic digesters was investigated, and a mass balance was performed using radiolabeled PDMS. Polydimethylsiloxane loadings of up to 10,000 mg kg −1 dry weight of MLVSS had no effect on the maximum specific substrate utilization rate, half-saturation constant, endogenous decay coefficient, and cell yield in model activated sludge units. In addition, the operating parameters pH, suspended solids, sludge volume index, and specific oxygen uptake rate showed no difference between PDMS-loaded and control systems. A mass balance, in which 14C-labeled PDMS was added to bench-scale activated sludge systems, showed that essentially all of the PDMS partitioned onto the microbial biomass. Pilot-scale aerobic and anaerobic digesters loaded with 100 mg kg −1 PDMS showed no difference in pH and solids concentrations compared to control systems. In addition, PDMS-loaded aerobic digesters exhibited oxygen uptake rates equal to control systems; PDMS-loaded anaerobic digesters produced the same amount of gas as control digesters. These results show that PDMS behaves as an inert material with no significant effect on wastewater treatment processes (other than the expected benefit of foam control).