Biodegradation and secondary effluent toxicity of ethoxylated surfactants

Abstract Several aromatic- and aliphatic-based, ethoxylated surfactants were tested for their biodegradability and aquatic toxicity reduction. For all the tested surfactants, almost complete primary biodegradation by the activated sludge process was achieved, as measured by the CTAS test. Aliphatic-based products demonstrated better biodegradability in terms of TOC and COD reduction efficiency than aromatic-based products. Toxicities of individual surfactants, their mixtures and effluents from biological reactors treating surfactant mixtures were determined using Mysidopsis bahia . For aromatic-based (i.e. nonlyphenol-based) surfactants with the same ethylene oxide molar ratio, the toxicity of the non-biodegraded product was highest for the non-ionic (unsubstituted) surfactant. Toxicities of the non-biodegraded, aliphatic-based surfactants were in the same range as those of the non-biodegraded aromatic-based products. Increasing ethylene oxide molar ratios resulted in an exponential decrease in surfactant toxicities. Biological treatment of the aliphatic-based surfactants resulted in non-toxic effluents even at high (600 mg/l) influent concentrations. Effluents from reactors treating aromatic-based surfactants demonstrated markedly higher toxicities than those from treatment of aliphatic-based products. The presence of an active group appeared to have less effect on biological effluent toxicity than did the product base structure (i.e. aromatic or aliphatic).