Research on an eco-safe filtration plant for wastewater treatment made of natural raw materials

Purpose. To develop a new eco-safe filtration plant for wastewater treatment based on natural and secondary raw materials, which will allow rational use of natural resources with further mathematical modeling of hydrodynamics of mixing treated wastewater in bioponds to predict removal of residual concentrations from the filter. Methodology. A complex of modern methods of theoretical and experimental research was used to solve the tasks. Concentration of pollutants was determined using methods of atomic adsorption spectroscopy, titrimetry and gravimetric methods, as well as pyrometric analysis. A laboratory installation was created, which included a receiving tank, a filter column, and a tank for collecting purified wastewater. Prediction of distribution and mixing of treated effluent in bioponds was carried out using mathematical and computer software. Findings. An environmentally safe filtration plant (containing sand, fallen leaves of linden, poplar, and plastic residues separated by a polymer mesh) was created to purify wastewater from suspended substances and nitrates. Kinetics of changes in concentration of suspended solids and nitrates in urban wastewater were studied. When using the filtration plant, concentration of suspended solids decreased by 85–92 %. Concentration of nitrates in purified water processed with such a plant is reduced from 12 to 0.25–0.05 mg/dm3. A mathematical model concerning distribution of purified water in a biopond was obtained, which allows predicting possible migration distributions of residual concentrations in purified water during its natural movement downstream. Originality. For the first time, influence of the species origin of fallen leaves on the performance indicators of wastewater filtration plant of urban sewage treatment constructions was investigated, which made it possible to substantiate a new way of disposal of this type of waste. For the first time, it was established that wastewater treatment using an eco-safe filtration plant based on natural and secondary raw materials, containing layers of sand, fallen oak, linden, and poplar leaves, gives an opportunity to reduce contents of suspended solids in wastewater by 1.5 times of the maximum permissible concentration; and such treatment also reduces concentration of nitrates by 4 times from the initial level. Pollutants from wastewater are mechanically fixed in pockets (microcracks, cracks) of fallen leaves, formed during drying of leaves, which is explained by hardening of intercellular spaces with formation of a specific geometry of holes. For the first time, mathematical modeling of purified wastewater movement in a biological pond with a complex geometry was performed, which allows estimating the concentration of the pollutant at its outlet from the pond. Practical value. The created environmentally safe wastewater filtration plant gives an opportunity to perform not only filtering, but also an effective biological purification of wastewater from nitrates on the surface of layers of fallen leaves. The wide use of the proposed installation will allow attracting plastic of polyethylene bottles used in everyday life as a secondary raw material. Based on the proposed mathematical model of movement of purified liquid containing residual concentrations of pollutants, it is possible to carry out qualitative forecasting and optimization of the process of cascade wastewater treatment at industrial and economic enterprises.