COLOR REMOVAL FROM SULFITE WASTES
WITH CATIONIC SURFACTANTS
K. Larry Roberts Assistent Professor
Civil Engineering Department
Tennessee Technological University
Cookeville, Tennesee 38501
Jih-Gaw Lin, Assistant Professor
Department of Environmental Engineering
National Cheng Kung University
Tainan, Taiwan
Republic of China
INTRODUCTION
A two-year study was conducted jointly at the University of Tennessee and Tennessee Technological University to evaluate the use of cationic surfactants in treating water and wastewater. It was
found that surfactants are efficient disinfectants and that they coagulate and remove suspended solids
and large organic molecules such as humic acid.
Certain structural and reactive similarities between humic acid and sulfonated lignin were noted,
and it was postulated that surfactants could be used to remove color from pulp and paper mill wastes.
A preliminary evaluation of the feasibility of this idea was conducted; the results are presented in this
paper.
BACKGROUND
A surface active agent, or surfactant, has an amphipathic structure [1]. It contains both a
lyophobic and lyophilic component. The lyophobic component in water is a long hydrocarbon chain,
frequently straight but occasionally branched and sometimes halogenated and oxygenated. A ring
structure attached at the base of the chain imparts additional hydrophobicity.
The hydrophilic component of a surfactant is either a highly polar structure or an ionized structure. Most cationic surfactants are derived from amines. Tertiary amines combine with alkyl halides
to produce quaternary ammonium surfactants which are of special interest due to their strong
coagulant and disinfecting qualities [2].
In the treatment of pulp and paper mill wastes, the reactions of the quaternary ammonium compounds (quats) with color bodies are of particular interest. The color bodies produced as a by-product
of the neutral sulfite process are composed of sulfonated lignins [3]. The lignin is sulfonated at a
relatively low temperature and then the cellulose fiber is removed mechanically. The sulfonated lignin
bodies range in size from sub-colloidal to supracolloidal. There is some evidence of dissolution down
to the molecular level, but this would depend on the degree of sulfonation of the molecule and the pH
of the water.
Lignin, either soluble or colloidal, is classified as a hydrophobic substance [4]. Its solubility or
stability is dependent upon the ionized functional groups which are natural to the molecule or added
during the sulfonating process. Reducing the pH causes the reassociation of these groups and the
resultant coagulation of the lignin. Hydrophobic molecules or colloids in water have great attraction
for similar molecules or colloids.
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