UTILIZATION OF CALCINED SORBENT FROM ASH-AND-SLAG WASTE FROM THERMAL POWER ENGINEERING PLANTS FOR WASTEWATER TREATMENT

Abstract

The discharge of untreated or insufficiently treated sewage into water bodies leads to their pollution, contributing to the emergence and spread of viruses and bacteria that have a negative impact on the ecosystem. One of the indicators of water contamination by pathogenic microorganisms is ammonium ions. The sorption method based on industrial waste as sorbent precursors has become widespread for treating wastewater from ammonium ions. The article presents the results of studies of a calcined sorbent based on ash-and-slag wastes from thermal power engineering plants for the treatment of real wastewater, discharged into the Kuban river within the city of Krasnodar, to remove ammonium ions (NH4+ concentration 21 mg/dm3). The effect of sorption time (10, 30, 60, 90, 150, and 180 min) and sorbent dose (0.5, 1, 2, 3, and 5 g) on treatment efficiency is investigated. The experimental data are processed on the basis of kinetic equations. It is shown that the equation of the pseudo-first-order (Lagergren) provides the best description of experimental data on sorption in comparison with the pseudo-second-order equation (Ho and McKay) and the Elovich equation. It has been established that internal diffusion adsorption is the limiting stage. Treatment efficiency was 72.8 % at a sorbent dose of 5 g for solution volume 50 cm3 and sorption time 180 min. It is shown that the sorbent dose affects the time within which the phase equilibrium between the solution and calcined sorbent is established. The larger is sorbent dose, the larger number of adsorption centres are occupied by ammonium ions per unit time, so, for the fixed ammonium ion concentration in initial solution, shorter sorption time will be necessary to achieve equilibrium. For real wastewater, the time necessary for equilibrium to be achieved exceeds the value determined experimentally with the model mixtures using small sorbent doses. Reasonability of the application of calcined sorbent for treatment of real wastewater is confirmed.