The study of the cloging process of stormwater infiltration systems with various filter nozzles

The process of siltation on multilayer infiltration devices during filtration of stormwater runoff has been studied. Silting of devices determines their operational capacity, nevertheless the quantitative understanding of the silting process is quite limited, especially on devices with different filtering noozles. Therefore, a laboratory study of the effluent infiltration process has been conducted to better understand the physical processes of siltation. The silting process has been studied under conditions of a constant water level, with a concentration of suspended solids of 80 300 mg/dm3 using four filtering nozzles: basalt, sawdust, limestone and polyurethane foam. It has been discovered that the largest layer of silting is formed at the boundary between the filter and the soil due to the formation of a sludge plug, which "protects" the filter/soil boundary. The composition of the sludge plug of the upper layer filtering the volume of the column has been analyzed and it was determined that the physical siltation is mainly caused by migration of sediment particles with a diameter of less than 0.05–0.071 mm (the fraction of which is the main one in the formation of the sludge plug). The issue of distribution of suspended solids according to size throughout the volume of the filtering device has been studied. The main fractions that most adhesion and affect the process of silting devices have been established. Relationships between the rate of infiltration of stormwater runoff and the accumulation of suspended solids in the filter layer has been determined. The lowest rates of decrease in filtration rate have been observed when using limestone (40 %), polyurethane foam and basalt showed similar results (51 % and 55 %), the largest decrease in filtration rate was in sawdust – 74 %. The practical significance of the results of the study lies in understanding the processes of pollution (siltation) of surface runoff treatment devices, which in turn makes it possible to modernize cleaning systems (design, filter nozzles, etc.) and minimize the accumulation of certain fractions of suspended solids on the surface of the watershed.