Industrial by-products and wastes from Portugal and Spain were tested for the first time as carbon sources/electron donors for sulphate reducing bacteria. Cultures in mineral medium supplemented with the tested substrates were monitored and sulphate reduction efficiency is discussed in light of substrates compositions, dosages and corresponding chemical oxygen demand/[SO4 2-] ratios. The use of doses targeting a ratio of 1.5 was a good strategy to optimize sulphate reduction activity. As expected, this activity was faster for substrates that have in their composition simple compounds such as low chain alcohols and organic acids and/or compounds that can be rapidly degraded such as sugars, though it also occurred in a longer-term perspective with substrates composed mainly of slowly degradable compounds such as cellulose and lignin. Among eighteen tested substrates, six supported high sulphate reduction efficiency during incubation periods varying between two and four weeks (sugared water from a factory of candies, beetroot molasses, olive mill wastewaters not decanted and decanted, orange molasses without conservative and municipal wastewater from Mina de São Domingos, Portugal), while eight substrates sustained moderate sulphate reduction efficiency during periods from three to seven weeks (water from washing beetroots, Carbocal®, orange molasses with conservative, liquor extracted from orange peels, orange peel fragments, water from washing industrial equipments used to produce orange juice, pine nut shells and pine cone fragments). Nevertheless, after four months of incubation, total sulphate removal was observed with three of the solid substrates tested (orange peels, pine nut shells and pine nut cones).

Previous tests using a growth medium and olive mill wastewater (OMWW) have shown that it supplies carbon and electron donors suitable for sulphate reducing bacteria (SRB). We assessed the co-treatment of acid mine drainage (AMD) and OMWW using SRB-enriched bioreactors and identified the most abundant bacterial populations present under optimized conditions. The process requires a neutralizing agent to create optimal pH conditions for successful removal of the AMD’s main contaminants. Concentrations of SO42−, Al, Fe, Cu, Zn, and Mn decreased to below Portugal’s maximum admissible values for irrigation waters, and all but Mn were reduced to less than Portugal’s emission limit values (ELVs) for wastewater discharges. Phenol concentrations—the main pollutants in OMWW—dropped to values between 1/10 and 1/5 their initial concentrations in batch tests using mixtures of AMD and OMWW, and to 1/2 their initial concentrations in flow-through tests. The final total phenol concentrations were still above the ELV for wastewater discharges, but phenols are not regulated in irrigation waters, and OMWW is used by some producers to irrigate soils. Six main SRB groups were identified as likely having a fundamental role in the bioremediation process: the genera Desulfovibrio, Sulfurospirillum, and Acetobacter and the families Sphingomonadaceae, Prevotellaceae, and Deferribacteraceae.