Modeling and optimization of the flocculation process of polydisperse travertine suspension employing an eco-friendly hybrid flocculant

Abstract

One of the major problems in the stone processing industry is the creation of wastewater with a high degree of residual turbidity and the use of high water volume. Therefore, the treatment of waste water and its reuse is very important in terms of economic and environmental considerations. In the present study, the flocculation performance of hybrid flocculant naturally derived from chitosan and plant was statistically investigated for the clarification of travertine processing wastewater, in terms of the residual turbidity/turbidity removal efficiency and settled sludge volume, containing micron and sub-micron particles with median particle sizes of 9.32 μm and negative surface charges dominating at all pHs that produced a high degree of stability. TOPSIS (technique for order preference by similarity to ideal solution) method by using the Taguchi factorial design is used to optimize the operating variables such as hybrid flocculant dosage, suspension pH, and mixing time to find out the optimum operating conditions optimizing selected quality criteria such as turbidity removal and settled sludge volume. The flocculant dosage affected significant residual turbidity of the suspension as well as the turbidity removal efficiency and the settleable solid volume. A total of 87.90% in the residual turbidity value and 1.67% in the turbidity removal efficiency improvement rate was obtained with the use of TOPSIS-based Taguchi optimization methodology. Another important factor was determined as the suspension pH. The amount of settleable solid increased with the increasing of suspension pH. The residual turbidity value indicated a tendency to increase at first and then decrease with the increasing of suspension pH. A total of 8.15% improvement rate in the residual turbidity value was achieved compared with the values in the literature using hybrid flocculant and multi-response optimization techniques.