Variation of Molecular Weight, Color, Biodegradability, Activated Carbon Adsorbability, and Toxicity by Ozonolysis of Ligninsulfonic Acid Sodium Salt

Abstract

Ligninsulfonic acid sodium salt (LS), which was a color-causing material typically found in wastewater from pulp and paper mills, was selected as a target compound for this study. Ozonolysis of LS was carried out in order to study its effect on molecular weight, decoloration, biodegradability, activated carbon adsorbability, and decrease in toxicity.
The structural change in molecule of LS w as surely expected through the variation of overall water quality parameters, though the degree of mineralization of LS was small. Degradation to lower molecular weight fragments was confirmed by ultrafiltration, and on an initial TOC basis, about 1∼2 % of glyoxylic and oxalic acids were detected as low molecular weight organic compounds. Decoloration, which was effectively caused by fragmentation, was represented as follows:
dC/dt= -kC= -k'RC
where C is color (Pt-Co unit) or the sum of absorbances in the wavelength interval of 50 nm from 350 to 700 nm, k and k' are the rate constants, and R is ozone dosage rate. Biodegradability represented in terms of the ratio of BOD₅ to TOC increased in the first stage, and after a temporary decrease in the mid stage, gradually increased. Activated carbon adsorbability varied with the amounts of ozone consumption and activated carbon addition. Formation potentials of total organic halides and trihalomethanes temporally increased in the initial stage, and then gradually decreased. They were further decreased by activated carbon adsorption following ozonization.