Potential Use of Waste-to-Bioenergy By-Products in Bioremediation of Total Petroleum Hydrocarbons (TPH)-Contaminated Soils

Detoxification of soils contaminated with petroleum hydrocarbons constitutes a worldwide challenge. Bioremediation is an efficient strategy for soil cleanup, but low nutrients level and microbial density in contaminated soils are limiting the process. Reasonable practice of waste management encourages soil application of organic wastes, and thus, reduction of the amount of wastes deposited on landfills. Land application of organic matter is likewise a resource-saving alternative to chemical fertilizers and moreover supports carbon sequestration in soil organic matter (SOM) reducing the emission of greenhouse gasses such as CO2. Addition of mature organic matter to soil represents a sustainable and cost-effective bioremediation strategy. Here, we have reviewed (1) the use of organic matter and mineral nutrients in bioremediation during composting treatments at laboratory and full scale; (2) properties of digestate including biological stability, nutrients, pathogens, and organic contaminants; (3) monitoring approaches in bioremediation of soil amended with digestate including chemical and biological assays as well as the use of molecular markers. Organic matter is an efficient nutrient source during composting of polluted soils. Remediation efficiency of total petroleum hydrocarbons (TPH)-contaminated soils during composting with organic amendments at laboratory scale was reported to be high with 99% alkanes removal after 60 days. For full-scale biopiles treatment, 38–57% of TPH could be removed after 53 days. Addition of organic matter to soils also improves soil characteristics like pH and structure as well as elevates bacterial density and diversity. Studies on organic matter have indicated that anaerobic digestion and post-treatment of digestate, (e.g., composting), decrease pathogen content. Digestate has also elevated nutrient status and biological stability in comparison with raw feedstock which may be further improved by composting. Organic contaminants present in feedstock are decreasing during anaerobic digestion and composting while trace elements accumulate. As toxicity of soils after bioremediation is not always directly associated with contaminant concentration decrease, in remediation monitoring field, a battery of ecotoxicological tests are applied including ecotoxicological markers and bioassays. This chapter is focused on the valorization of digestate as a nutrient source for bioremediation of TPH-contaminated soils by composting.