Abstract
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.
Highlights
IntroductionThe main cause of acid mine drainage (AMD) is the oxidation of sulphide minerals (mainly pyrite) due to their exposure to oxygen, water, and microorganisms
Acid mine drainage (AMD), known as acid rock drainage, can contain high concentrations of sulphate, metals, and metalloids that can contaminate groundwater and watercourses and damage the health of aquatic species, plants, wildlife, and humans (Johnson 2003; Simate and NdlovuElectronic supplementary material The online version of this article contains supplementary material, which is available to authorized users.Centre of Marine Sciences (CCMAR), University of Algarve, Gambelas Campus, bldg 7, 8005‐139 Faro, PortugalFaculty of Sciences and Technology, University of Algarve, Gambelas Campus, bldg 8, 8005‐139 Faro, PortugalPresent Address: Department of Geosciences, GeoBioTec, Geobiosciences, Geotechnologies and Geoengineering Research Center, University of Aveiro, Campus de Santiago, 3810‐193 Aveiro, Portugal2014)
The sulphate concentration of the neutralized winter AMD (nwAMD) remained as high (1803 mg/L) as in winter AMD (wAMD) before pH neutralization (Table 1). These results are similar to those obtained by Vitor et al (2015), who used marble powder to neutralize acid mine drainage (AMD) collected at the São Domingos Mine: the pH was raised to ≈ 7, and Fe was almost totally removed, while Zn, Cu, and sulphate concentrations were respectively ≈ 10, 1, and 2000 mg/L
Summary
The main cause of AMD is the oxidation of sulphide minerals (mainly pyrite) due to their exposure to oxygen, water, and microorganisms It may occur naturally but is accelerated by mining activities that increase the exposure of Fe sulphide minerals to such conditions (Egiebor and Oni 2007; Johnson 2003; Johnson and Hallberg 2005). Active treatment requires significant ongoing costs for operation, including labour, chemicals, and electricity, and are generally more appropriate for use at operating mines or for high flow rates, while passive and semi-passive treatment are more cost-effective solutions for inactive or abandoned mines sites where the remote location or other factors require the use of low-maintenance, low-cost treatment options (Johnson and Hallberg 2005; Simate and Ndlovu 2014; Skousen et al 2017). Passive systems can operate for a long time (typically at least a decade) without any supplemental chemicals or energy, while semi-passive systems require a low dose of
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