Thesis Details

Thesis Title: Impact of alkylphenol ethoxylate surfactants on wastewater toxicity
Thesis Author: Julianna Michna
Abstract: Numerous studies have been conducted to evaluate the biodegradation of alkylphenol ethoxylate (APE) surfactants and the toxicity oftheir degradation byproducts; however, conflicting results have been reported. Alkylphenol ethoxylate biodegradation is a multi-phase reaction that gradually breaks the chemical structure of the surfactant into smaller by-products. The ultimate goal of biodegradation is the breakdown of the long-chain APE molecule into carbon dioxide and water. Intermediate by-products of biodegradation can include lower molecular weight oligomers of APEs, ether carboxylates, dicarboxylates, and alkylphenols. As the size of APE compounds decreases, the toxicity increases. Therefore, the toxicity of the effluent depends on the degree of biodegradation of the surfactant. For this research, nonylphenol ethoxylate (NPE) surfactants, the largest type of APEs consumed in textile manufacturing, were used as a representative of the family. The purpose of this study was to determine whether specific by-products of APE biodegradation cause effluent toxicity. To achieve this purpose, residual oligomers of NPE surfactants were evaluated using high performance liquid chromatography and gas chromatography/mass spectrophotometry. The chronic toxicity of the by-products was assessed using USEPA standard 7-day chronic testing procedures for Ceriodaphnia dubia. At levels typically used in textile operations, NPEs showed good biodegradability, but were determined to be toxic. Nonylphenol ethoxylates were found to contribute to toxicity at 75 mg/L, where primary biodegradation of the surfactant was incomplete.