Sustainable reduction of sulfate contained in gypsum waste: perspectives and applications for agroforestry waste and sanitary sewage

Abstract

This review article explores sustainable biotechnological strategies for converting sulfate compounds and lignocellulosic waste, focusing on using sulfate-reducing bacteria (SRB) and the valorization of agroforestry residues and sanitary sewage. SRB show potential in effluent treatment, mine drainage, and the removal of sulfate and heavy metals from wastewater, with their metabolic activity being influenced by factors such as pH, temperature, and chemical oxygen demand/sulfate (COD/SO4=) ratio. In the context of a sustainable bioeconomy, the challenge of converting lignocellulosic waste into value-added products is addressed through physical pretreatment techniques such as milling, extrusion, microwave irradiation, and ultrasound, which are efficient in valorizing waste from urban tree pruning. The article highlights the importance of bioreactors in transforming raw materials into desirable biochemical products, discussing different types of bioreactors, such as batch, continuous stirred tank, airlift, fluidized bed, upflow anaerobic sludge blanket (UASB), and bubble column, and their specific advantages and disadvantages. Sustainable sulfate reduction is the central focus, integrating the application of SRB and the conversion of lignocellulosic waste in a way that complements the objectives of the work and promotes a more cohesive flow in the summary. Thus, the interrelationship between effluent treatment strategies and waste valorization is emphasized from an environmental sustainability perspective, highlighting the relevance of this study in the broader context of a sustainable bioeconomy.