Characterization of ash generated by sewage sludge incineration and tested as a substrate for revegetation

Abstract

The present communication presents the results of studies of the composition and physical properties of ash generated by incineration of sewage sludge at the Northern Sewage Water Treatment Plant in Saint Petersburg. The suitability of ash for biological reclamation has been determined. The composition of ash is heterogeneous, which is due to the diversity of wastewater entering the treatment facilities. In terms of its granulometric composition, ash corresponds to dusty loam or dusty clay sand according to Kachinskiy classification. The gross composition of ash is close, in terms of the content of prevalent oxides, to the zonal soils. Silica, aluminum and iron oxides prevail. Organic matter content is very low (up to 1-3%), whereas the contents of potassium and phosphorus compounds is excessive for plant vegetation. Because of the high-temperature treatment of raw sediment, there is no nitrogen, which is an essential nutrient for plants. Ash suspension is alkaline. The hydrolytic acidity of ash is low. Ash porosity is high. Elevated in the ash are the contents of some heavy metals and their labile forms. Among them, cadmium is referred to hazard Сlass 1. Despite numerous studies of the utility of ash for different applications, it is still not used in industry. The large amounts of ash disposed at landfills, the problem of its utilization being still suspended, necessitates further studies of the composition and properties of ash as a possible substrate suitable for reclamation purposes. To this end, ash was applied to a test plot, and several perennial grasses were sowed there. The observation that wild growing plants vigorously penetrate the test plot suggests the possibility of reclamation of ash dumps for sanitary and hygienic purposes.