Soil modification in a chronosequence of postagricultural ecosystems of the intrazonal lithogenic matrix (Arkhangelsk region, Russia)

Processes of soil self-restoration and soil modification in the chronosequence of postagricultural ecosystems located within the intrazonal (floodplain) soils of boreal forests were studied. Successional changes in ecological features of the floodplain meadow soil properties in the postagricultural period were considered. We used arable land plots (22 model fields) in the Northern Dvina River delta (Primorsky District, Arkhangelsk region, Northwestern Russia) that have been removed from agricultural practice for the past 50 years and are currently at the self-overgrowing stage. Primary/secondary floodplain meadows with natural floodplain soils were used as reference plots. Changes in soil profiles and chemical properties in an old-arable horizon were observed during the restoration of abandoned fields. Floodplain soils of the Northern Dvina River basin occupied 4.8% of the area. These soils were characterized by high fertility and were actively used in agricultural production in the past. Postagricultural ecosystems of the Northern Dvina River floodplain tended to form natural waterlogged soils to varying extents. Ecosystems were characterized by a short period of soil restoration. The soil restoration process was slower than the vegetation cover restoration process. Soil fertility of the arable horizon persisted for 20 years. A cost-effective return of floodplain meadow lands to agricultural production is feasible over a period of 40 years. Then, soils return to natural floodplain soils, whereby they become waterlogged and lose their fertility.

Classification and Disposal Strategy of Excess Sludge in the Petrochemical Industry

The excess sludge in the petrochemical industry is large in quantity, complex in composition, and highly harmful, and its rational disposal is of great significance for environmental protection and sustainable development. In the present study, a classification and disposal strategy for the excess sludge in the petrochemical industry is proposed. The strategy first analyzes the dioxin, flammability, corrosivity, reactivity, and leaching properties of the sludge, from which the waste type of the sludge (general waste or hazardous waste) can be determined. Then, methods of disposal can be selected depending on the type of waste and the corresponding risk analysis, enabling rationalized disposal of the sludge. To verify the effectiveness and practicability of the proposed sludge classification and disposal strategy, research on petrochemical excess sludge samples (i.e., Ah, Bl, and Cq) originated from three different regions in China is carried out as a case study. The component analysis of the above three sludge samples revealed that they are all general wastes. In addition, the possibility of employing Cq sludge for landfill, soil modification, and greening mud, as well as the risk of landfill and incineration disposal in solid waste landfills are investigated. Furthermore, natural radioactive elements uranium and thorium in Cq sludge sample are studied. The results show that Cq sludge cannot be used for landfill, soil modification, and greening mud due to excessive arsenic content. The proposed strategy provides a basis for the selection of reasonable petrochemical excess sludge disposal methods.