Performance of two differently designed permeable reactive barriers with sulfate and zinc solutions

Evaluation of Dispersed Alkaline Substrate and Diffusive Exchange System Technologies for the Passive Treatment of Copper Mining Acid Drainage

“…The redox potential (ORP) is a measure of how reducing or oxidizing an environment is. Free sulfide in SDES prototypes A and B, during phases 1 and 2, reduced the ORP to < −200 mV (Figure 2f), optimal for biological sulfate reduction [6]. However, the reaction of sulfide with metals (Cu, Zn, and Fe) during AMD feeding resulted in positive ORP values and an oxidizing environment.…”

“…The fourth isolate belongs to the phylum Bacteroidetes encompassing a large number of Gram-negative and anaerobic bacteria with a wide distribution in the environment, including soil, sediments, seawater and the digestive tract of animals. This phylum includes species of the genus Bacteroides [48] that have been identified in other sulfidogenic reactors for the treatment of AMD [6,24,45,49]. Additionally, species of the genus Bacteroides have been reported with the ability to degrade the cellulolytic material [50] and to act as intermediaries in the hydrolysis stage, in anaerobic digestion [47].…”

“…Also, the existing microbial diversity is favored by the configuration of the bioreactors that prevents the microorganisms from coming into direct contact with the AMD. This protection favors a greater bacterial diversity and, consequently, a higher production of sulfide [6,9] increasing the resilience of the reactor to toxic metal stress, temperature, acidity and exposure to oxygen present in AMD [51]. Table 3.…”

“…In the case of Chile, the most significant sources of AMD are the cordilleran copper deposits during snowmelt, which are located in the central zone of the country. Recently, research on its treatment has increased [5][6][7][8][9]. A particularity of this AMD is that it presents high concentrations of copper, which can be recovered economically [8].…”

“…Environmental factors (HRT, organic source, pH, metals, sulfates, and sulfides) have a significant impact on the composition of microbial communities, and the study of reactor microorganisms is critical for the selection of phylogenetic groups as inoculum [24]. Despite this, passive bioreactors are considered less robust than chemical systems because the characteristics of AMD are variable, and microbial communities can be particularly affected by low pH and temperatures, and toxic concentrations of metals [25], which has stimulated the development of sulfidogenic diffusion exchange systems (SDES) [6,9,26]. A distinctive characteristic of DES systems are exclusive zones for the flow of water through the bed (e.g., screen tubes or layers of sand), in order to favor the permeability of the bed and the protection of microbial communities within reactive, less permeable layers, from direct contact with the toxic components of the contaminated water.…”