Skvortsova P. Ecological safety of biosorption technology of soil remediation

In connection with the strengthening of the problem of soil contamination by chemical substances, the number of studies related to the development and improvement of environmentally safe and economically beneficial soil restoration technologies is increasing. The use of traditional physical and chemical methods of soil restoration have certain disadvantages, which are characterized by high cost, energy consumption and the possibility of repeated pollution of ecosystems. Given this, biochemical methods of environmental protection, especially biosorption technology, are gaining popularity. That is why the thesis is aimed at substantiation, development and implementation of the optimal biosorption technology to eliminate environmental risks associated with chemical soil pollution. The purpose of the study is to substantiate the ecological safety of the biosorption technology for the remediation of soils contaminated with chemical substances, using the developed biocomposite based on digestate and phosphogypsum. For the first time, the synergistic effect of using phosphogypsum and anaerobic digestate as part of a biocomposite with biosorption properties for heavy metal ions and radionuclides has been theoretically substantiated. In order to increase the level of ecological safety of soils when using biosorption technology, the mechanisms of complexation of heavy metals with fluorescent components of dissolved organic matter of digestate were theoretically substantiated and the low degree of phytotoxicity of the biocomposite was experimentally confirmed based on the results of phytotesting. Methodological principles for assessing the ecological safety of soils as a result of the application of biosorption technology based on a biocomposite of anaerobic digestate and phosphogypsum through the Bayesian approach to the analysis of the ecological risk of soils contaminated with heavy metals have been developed. The scientific and methodological principles for evaluating the ecological and economic efficiency of biosorption technology have gained further development, which makes it possible to justify the feasibility of using the technology in a complex system of restoring soils disturbed as a result of military actions. The scientific approach to the development and implementation of a technological solution for biosorption technology using a biocomposite based on phosphogypsum and anaerobic digestate has been improved. The mechanisms of complex formation of heavy metals with dissolved organic matter of the digestate were analyzed and it was established that humic substances bind best to Cu2+ and Zn2+ ions, and fulvic substances – to Cr3+ and Pb2+ ions; the combination of fulvic-like and protein-like substances reduces the binding stability of all heavy metal ions; stable complexes of dissolved organic matter with Fe3+ ions are formed independently of the dominant organic components; the conditional stability constant of proteinaceous and humic components is higher at pH close to neutral than at acidic pH. Theoretical modeling and analysis of fluorescent components and organic functional groups that bind heavy metals suggested that chicken manure would be a better raw material for anaerobic digestion than sewage sludge if the goal is to obtain a digestate with a high content of humic substances and good binding properties. heavy metal leaching. Based on the phytotesting results, it was established that both types of digestate (based on chicken droppings and sewage sludge), both treated with phosphogypsum and untreated, are ecologically safe, since the germination index of pepper seeds was higher than 50%. The possibility of using these types of substrates as part of a biocomposite without toxic effects on the soil and directly on plant products is substantiated. The level of environmental risk was assessed for three scenarios of the development of events: for scenario 1 (soil contaminated by five heavy metals (Zn, Ni, Cd, Cu and Pb) in the places where military equipment is burned) the potential ecological risk index is 155.64±23.17, which corresponds to a moderate risk level; for scenarios 2 and 3 (in the case of using a biocomposite based on chicken manure and sewage sludge, respectively) the potential ecological risk index is 50.55±7.99 and the potential ecological risk index is 58.33±9.14, which corresponds to a low level of risk. As a result of the application of the Bayesian approach to environmental risk assessment, considering the developed system of qualitative indicators, a reduction in the level of risk from high to medium has been established. Thus, it was established that the proposed biosorption technology has a significant potential for soil purification from heavy metals due to the binding properties of the organic matter of the digestate and the sorption capacity of phosphogypsum and the nutrient medium to increase microbial activity.