Degradation of nonylphenolic surfactants in activated sludge batch tests

The fate of nonylphenol polyethoxylate surfactants in the activated sludge wastewater treatment process is a concern due to the formation of estrogenic nonlyphenols on degradation and due to the large amounts discharged to the aquatic environment through sewage treatment works. Batch tests using activated sludge from a Husmann apparatus were used to determine the effects of these compounds physico-chemical properties and biological sludge characteristics on biodegradation. Degradation of nonylphenol polyethoxylates with up to 12 ethoxy groups was observed in unacclimated sludge with a concomitant production of nonylphenol and short chain nonylphenol polyethoxylate compounds. Degradation was determined to be a biotic process involving intracellular enzyme activity, which resulted in sludge age being an influential parameter. With increasing sludge age there is an increase in mixed liquor solids concentration in activated sludge which results in greater bacterial numbers and the potential for greater species diversity which therefore increases compound degradation. However, increased degradation of long chain compounds resulted in an accumulation of shorter chain compounds and nonylphenol, which are more resistant to degradation.