The use of natural montmorillonite clays in the process of coagulation purification of laundry wastewater

Abstract

A variety of methods, for example, electroflocculation and the same method, complemented by nan-ofiltration are used for the treatment of wastewater from surface-active substances (surfactants). The authors proposed to use a combination of adsorption and coagulation with a small amount of flocculant to ensure a good cleaning effect from surfactants and suspended substances and reduce costs.
Natural montmorillonite clay from the Askan Deposit (Georgia) was used for the experiments. The model solution of laundry wastewater contained 1 g/dm³ of both anionic and nonionic surfactants. White kaolin (0.2 g/dm³) was added to the model solution as a turbidity simulator. Organic impurities were modelled by the addition of sugar (100 mg/dm³). It was shown that a long period of phase contact and a high amount of adsor-bent are required in order to achieve a high degree of purification of the studied drains using clay. In the next series of experiments, a coagulant, a solution of FeCl₂, flocculant, and clay in the amount of 2 g/dm³ were added to the model solution. The clay additive not only played the role of an effective adsorbent, but also acted as the weighting agent for the coagulant sediment.
The effectiveness of coagulation in combination with clay was evaluated by the residual concentration of total organic carbon (TOC) of the purified solution, the COD of the purified model solution, dried and calcined residue, suspended solids and residual concentration of total iron and the pH value of the original and purified solutions.
The optimal conditions were: clay=2 g/dm³, Fe²⁺=100 mg/dm³, flocculant=1.5 mg/dm³, and a settling time of 5 minutes. When stirring for 45 minutes, the degree of purification was 41 Rel. %. When comparing the use of dry bentonite clay and its 10% suspension in water, it was found that when adding dry clay, the sediment enlargement and clarification of the liquid phase occured at a higher rate, and the purification from organic impurities reached 56 Rel.% and suspended substances reached 90 Rel. %.
Based on the conducted research, we can conclude that coagulation with additives of Askan bentonite clay is successful for pre-treatment of laundry drains with the possibility of recycling the resulting sludge without intermediate drying by the carbon-mineral adsorbents-catalysts technology.