41    BIODEGRADABILITY ENHANCEMENT OF
NON-IONIC SURFACTANTS USING OXIDATIVE
PRETREATMENT: LABORATORY STUDIES AND
ECONOMIC ANALYSIS
Mehmet Kitis, Graduate Research Assistant
Department of Environmental Systems Engineering
Clemson University
Clemson, South Carolina 29634
Craig D. Adams, Mathes Professor/Associate Professor
Department of Civil Engineering
University of Missouri-Rolla
Rolla, Missouri 65409
Glen T. Daigger, Professor and Head
Department of Environmental Systems Engineering
Clemson University
Clemson, South Carolina 29634
INTRODUCTION
Surface active agents (surfactants) consist of a hydrophilic and a hydrophobic portion, and are
used for a wide range of industrial and domestic purposes. Non-ionic surfactants typically use an
ethylene oxide (EO) chain as their hydrophilic portion. These "ethoxylated surfactants" may
have a variety of hydrophobic functionalities such as polypropylene oxide (PO), alkylphenols, or
linear primary- or secondary-alcohols. Non-ionic surfactants have several advantages over anionic and cationic surfactants including their stability over a wide pH range and their ability to
maintain their surfactant properties in soft or hard waters. In the 1980s, ethoxylated (non-ionic)
surfactants comprised more than 30% of the total worldwide surfactant use.1
Two major classes of non-ionic surfactants used by industry include the ethylene oxide/propy-
lene oxide (EO/PO) block copolymers and the alkylphenol ethoxylates (APEs) (Figure 1). Both
EO/PO block copolymers and (to a lesser degree) APEs are known to be biorecalcitrant, that is,
resistant to biomineralization.2-6 In the EO/PO block copolymers, the polypropylene glycol
(PPG) portion of the molecule imparts both the requisite hydrophobic portion of the surfactant,
as well as the biorecalcitrance to the molecule.6
Biodegradation studies of APEs have shown that initial biodegradation proceeds via EO-chain
shortening, thereby decreasing the aqueous solubility and increasing the APEs biorecalcitrance.7-8 This phenomena results in the characteristic partial biodegradability often observed for
APEs.9 Elimination of APEs during wastewater treatment is incomplete, resulting in release of
metabolites that may be toxic to aquatic organisms, have enhanced resistance to biodegradation,
and have the ability to bioaccumulate in microorganisms.10 Due to their biorefractory nature,
these surfactants are not treatable in conventional aerobic biological treatment processes and can,
in fact, inhibit the operation of these processes if their toxicity is sufficient.
Because it may not always be feasible to use biologically labile surfactants, there is a need to
identify and develop economical integrated treatment technologies that provide significant mineralization and detoxification of these industrial surfactants. In this research, the use of an integrated chemical/biological treatment process was investigated for the removal of selected EO/PO
block copolymers, PPG, and APEs. Chemical oxidation was accomplished using Fenton's
reagent (hydrogen peroxide/ferrous iron; H,02/[Fe(II)]) to enhance the biodegradability of surfactants (and PPG).
51st Purdue Industrial Waste Conference Proceedings, 1996. Ann Arbor Press, Inc., Chelsea. Michigan 48118.
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