Development of a Calculation Method for a Combined Filter

Introduction. If wastewater treatment becomes less effective, the intensity of treatment facilities should be increased. Several approaches to solving this issue have been described in the literature. For example, to intensify the coagulation process, researchers have used controlled mechanical mixing of coagulants with effluents, mixing with air, and injecting the coagulant using jet or chamber mixers. The authors of this paper propose integrating a vertical clarifying filter (VCF) and a mixing chamber into one housing. This is a novel approach that eliminates the disadvantages of operating separate devices, such as the need for additional space, the possibility of forming aggregates close to the area where they are removed on filters, and avoiding breakage of flakes in connecting pipelines. Experimental evidence has previously demonstrated the effectiveness of this installation. The aim of this study is to develop a scientific methodology for calculating the combined filter, which is essential for widespread adoption. Materials and Methods. The mixing efficiency of the fluidized bed was determined using the Camp criterion, which characterized the energy spent on mixing. Relevant publications on the subject were also taken into account. Special attention was paid to the description of coagulation. Before developing the calculation method, the authors conducted experiments and created a mathematical model of the installation. The operation of a combined filter with a mixing chamber consisting of a rapid mixing tank with a floating load and a settling tank was considered. The main initial data for the calculation method included: maximum wastewater flow rate, water viscosity, filter diameter, distance from load to housing, backwash intensity, and the volume of expansion of load during backwashing. Results. The paper shows that the Camp criterion depends on various factors, including mass, area, contact time, and viscosity of particles in a fluidized bed. The calculation of the mixing chamber of the filter was based on this dependence. The regeneration of filters related to the efficiency of backwashing was taken into account. The method for calculating the mixing chamber was presented, and factors that could reduce the effectiveness of backwashing were discussed. As compensation, it was proposed to increase the intensity of backwashing or reduce the height of the filter layer. It was shown how to calculate the dimensions of the mixing chamber elements — the diameter and height of the tanks. A self-check was included in the calculation to avoid errors. Discussion and Conclusion. For the first time, an improved combined filter design and a method for calculating it are described. The proposed approach makes it possible to determine the dimensions of the mixing chamber and ensure the necessary backwash efficiency. The new solution is of practical interest for enterprises that operate wastewater treatment plants with VCF.