Over-sulfated soils and sediments treatment: A brief discussion on performance disparities of biological and non-biological methods throughout the literature

Abstract

High sulfate concentrations in industrial effluents as well as solid materials (excavated soils, dredged sediments, etc.) are a major hindrance for circular economy outlooks. SO42- acceptability standards are indeed increasingly restrictive, given the potential outcomes for public health and ecosystems. This literature review deals with the treatment pathways relying on precipitation, adsorption and microbial redox principles. Although satisfactory removal performances can be achieved with each of them, significant yield differences are displayed throughout the bibliography. The challenge here was to identify the parameters leading to this variability and to assess their impact. The precipitation pathway is based on the formation of two main minerals (ettringite and barite). It can lead to total sulfate removal but can also be limited by aqueous wastes chemistry. Stabilizer kinetics of formation and equilibrium are highly constrained by background properties such as pH, Eh, SO42- saturation state and inhibiting metal occurrences. Regarding the adsorption route, sorbents’ intrinsic features such as the qmax parameter govern removal yields. Concerning the microbial pathway, the chemical oxygen demand/SO42- ratio and the hydraulic retention time, which are classically evoked as yield variation factors, appear here to be weakly influential. The effect of these parameters seems to be overridden by the influence of electron donors, which constitute a first order factor of variability. A second order variability can be read according to the nature of these electron donors. Approaches using simple monomers (ethanol lactates, etc.) perform better than those using predominantly ligneous organic matter.