Influence of Coagulation Treatment on the Efficiency of Lignin Containing Wastewater Purification

Abstract

An effective way to remove lignin substances from the effluents of pulp and paper mills is the coagulants treatment. According to the local treatment scheme, lignin-containing waste water is treated separately, i.e. before mixing with the general flow of the enterprise. To study the efficiency of the process of coagulation of lignin by aluminum- and iron-containing reagents, it is proposed to apply the response surface methodology, namely - the rotatable central composition plan of the second order for three factors. The object of research was model water containing 400 mg/l sulfate lignin. The effect of coagulant dosage, pH and duration of wastewater treatment on the degree of lignin and chromaticity purification was studied. All the derived models were verified to be adequate. Response surfaces were constructed to demonstrate the effect of regime parameters on the output characteristics. It was found that pH and coagulant dosage have a significant effect on the efficiency of lignin removal. The optimal pH and dosage intervals for the studied reagents were determined: aluminum sulfate and oxychloride, aluminum alum and iron sulfate (III). The duration of coagulant treatment in the range from 1 to 4 minutes has no effect on the degree of purification. The best results were obtained using aluminum oxychloride: lignin and chromaticity purification efficiency exceeded 90 % under the following optimal conditions: pH 6,7...7,0, dosage - 50...55 mg Al2O3/l.