How sulfate-rich mine drainage affected aquatic ecosystem degradation in northeastern China, and potential ecological risk

Understanding seasonal variations in As and Pb river fluxes and their regulatory mechanisms through monitoring data

The Doce River Basin (DRB) suffers with the adverse impacts of mining activities, due to its high level of urbanization and numerous industrial operations. In this study, we present novel insights into contaminant flow dynamics, seasonal variations, and the primary factors driving concentration levels within the region. We conducted an extensive analysis using a database sourced from the literature, which contained data on the contamination of arsenic (As) and lead (Pb) in the Doce River. Our primary aim was to investigate the patterns of As and Pb flow throughout the entire basin, their response to seasonal fluctuations, and the key parameters influencing their concentration levels. The results showed significant seasonal fluctuations in As and Pb fluxes, peaking during the rainy season. The 2015 Fundão dam breach in the DRB led to notable changes, elevating elemental concentrations, particularly As and Pb, which were subsequently transported to the Atlantic Ocean. These increased concentrations were primarily associated with iron and manganese oxides, hydroxides, and sulfates, rather than precipitation, as evidenced by regressions with low R2 values for both As (R2 = 0.07) and Pb (R2 < 0.001), concerning precipitation. The PCA analysis further supports the connection between these elements and the oxides and hydroxides of Fe and Mn. The approach employed in this study has proven to be highly effective in comprehending biogeochemical phenomena by leveraging data from the literature and could be a model for optimizing resources by capitalizing on existing information to provide valuable insights for drainage basin management, particularly during crises.

eDNA-based diversity and multitrophic network reveal the effects of land use and pollutants on the subtropical Dongjiang River systems

Biodiversity and its constituted multitrophic network in rivers are accelerating change under human land use and pollutants. However, due to the lack of complete datasets across taxa limited by traditional morphological biomonitoring, the change patterns of biodiversity and multitrophic networks are still unclear. Here, we used the eDNA approach to capture multitrophic communities (including fish, aquatic insects, protozoa, diatom and bacteria) in the Dongjiang River, a typical subtropical river in southeast China, and analyzed the changing patterns of biodiversity and multitrophic networks in relation to land use and water pollution. First, our data showed that the eDNA approach provided a snapshot of the multitrophic communities in the Dongjiang River, and the monitored 5833 OTUs were annotated to 55 phyla, 144 classes, 329 orders, 521 families, 945 genera and 406 species. Second, the multitrophic diversity index had similar patterns on the longitudinal scale of rivers, with significant decreases from the upstream to the downstream, while individual taxonomic groups exhibited variable spatial patterns. While there were similar spatial patterns between network metrics and diversity index, the former had stronger relationships with the spatial distance. Third, the multitrophic diversity and networks were significantly negatively correlated with land use and water pollution (e.g., CODMn), and network structures often had stronger and non-linear responses. Overall, this study highlights that eDNA biomonitoring of multitrophic communities and networks can provide deeper insights into ecosystem changes and help develop more targeted management strategies.

Environmental DNA metabarcoding reveals the impact of different land use on multitrophic biodiversity in riverine systems

Human-induced changes in land use drive an alarming decline in river biodiversity and related ecosystem services worldwide. However, how different land use shapes aquatic multitrophic communities is still not well understood. Here, we used the biodiversity dataset from bacteria to fish captured by the environmental DNA (eDNA) approach in the four riverine systems with spatially different land use (i.e., Slightly disturbed group, Upstream disturbed group, Downstream disturbed group, and Strongly disturbed group) to reveal the changes in multitrophic biodiversity in relation to human land use. Firstly, our data showed that spatially different land use determined the pollutant loads of the riverine systems, most pollutants (e.g., TN and NH₃-N) had significant differences among the four riverine systems. Secondly, taxonomic α diversity across multitrophic levels did not necessarily change significantly, yet the change in community structure can be considered as a more sensitive indicator to reflect different land use, because different land use shaped the unique structure of multitrophic communities, and the dissimilarity of community structure was closely associated with land use gradient (e.g., positive relationships in the Slightly disturbed group, negative relationships in the Strongly disturbed group). Thirdly, different land use induced the shifts of key taxa, resulting in the variation of community structure and the change of co-occurrence network. Overall, these findings suggest that spatially different land use plays a critical role in shaping aquatic multitrophic communities, and an in-depth understanding of the interdependences between biodiversity and land use is a critical prerequisite for formulating river management strategies.

Simultaneous removal of carbamazepine and Cd(II) in groundwater by integration of peroxydisulfate oxidation and sulfidogenic process: The bridging role of SO42

Heat-activated PDS oxidation (HAPO) has been widely used for in-situ chemical oxidation (ISCO) of micropollutants in groundwater, whereas the aesthetic demerit of additional SO₄^2- production is largely overlooked. In this study, the sulfidogenic process is used to offset the aesthetic demerit, and the production of SO₄^2- is then employed to recycle heavy metals. The innovative integration technology with PDS oxidation and sulfidogenic process via the bridging role of SO₄^2- was reported to remove micropollutants and heavy metals in groundwater simultaneously. HAPO could completely degrade CBZ, producing 400 mg/L SO₄^2- with the addition of 0.50 g/L PDS. Sulfate-reducing bacteria (SRB) utilize SO₄^2- generated from HAPO as the electron acceptor in the sulfidogenic process, removing and recycling Cd(II) via the precipitation of CdS. The SRB tolerance experiment revealed the viability of PDS oxidation coupled with the sulfidogenic process via the bridging role of SO₄^2-. Overall, the integration technology is a green and promising technology for simultaneous micropollutants removal and heavy metals recycling in groundwater.

Prediction and Potential Treatment of Underground Contaminated Water Based on Monitoring of pH and Salinity in a Coal Mine Waste Heap, Southern Poland

This study presents a potential treatment method for contaminated groundwater from a waste heap in southern Poland. The method is based on the continuous monitoring of two parameters: pH and electrical conductivity (EC). Four years of historical monitoring data (2007–2010) were modeled using a Visual MODFLOW based numerical model of groundwater flow and migration of pollutants for low and high precipitation periods. Mapping the natural conditions in the numerical model allowed for the direction of contaminant migration in the aquifer to be identified. Groundwater treatment via injection of a nano zerovalent iron (nZVI) suspension into the aquifer was then designed; the target contaminant was Zn(II) because of its high concentrations and relatively high toxicity. Online monitoring for mining waste heaps is proposed to record sudden outflows of contaminants into the groundwater related to climate change and to take remedial action via nZVI injection. EC is the variable to be introduced into the contaminant migration model, which allows to determine the nZVI injection locations. As a result, the aquatic environment would be effectively and economically protected. The optimal use of nZVI, without intensively interfering with the environment, is ensured. This method is a convenient tool when making decisions to treat mining-impacted groundwater.

Assessment of benthic invertebrate diversity and river ecological status along an urbanized gradient using environmental DNA metabarcoding and a traditional survey method

Benthic invertebrate diversity is one of the most commonly used bioindicators for assessing aquatic ecosystem health in river systems. Although an increasing number of studies have focused on assessing benthic invertebrate diversity using environmental DNA metabarcoding and traditional survey methods, benthic invertebrate diversity and ecological status assessments performed across different landscapes within river systems have not been well documented. Here, the diversity and ecological status of benthic invertebrates and the influence of water quality on the invertebrate assemblage distribution along an urbanization gradient in rivers from the Jingjinji (JJJ) region, China, were investigated using eDNA metabarcoding and the traditional method. With the combination of the two methods, 395 benthic invertebrates from 6 phyla, 27 orders, 94 families, and 222 genera were identified. The species richness of the benthic invertebrate community in the mountain area was significantly higher than that in the urban and agricultural areas. Compared to the traditional results, eDNA metabarcoding obtained a significantly greater number of species from every sampling site (P = 0.000) and detected a notably higher abundance in Annelida (P = 0.000). Furthermore, the nonmetric multidimensional scaling (NMDS) and permutational multivariate analysis of variance (PERMANOVA) based on the Bray-Curtis dissimilarity index indicated that the benthic invertebrate communities from the different habitats were discriminated more accurately and easily using eDNA metabarcoding (P = 0.038) than with the traditional method (P = 0.829). Additionally, the assemblages identified by eDNA metabarcoding were more closely linked to water quality and could be realistically used to assess the ecological status of rivers. Our findings highlight that eDNA metabarcoding could represent a rapid and reliable method for estimating benthic invertebrate diversity and ecological status in river systems.

Increasing anthropogenic salinisation leads to declines in community diversity, functional diversity and trophic links in mountain streams

Anthropogenic salinisation is becoming an increasing global issue for freshwater ecosystems, leading to serious biodiversity loss and ecosystem degradation. While the effect of anthropogenic salinisation on freshwater ecosystems has been intensively studied in recent years, most studies focus on salinisation effects on the individual or single groups of organisms without considering the effect on the ecosystem levels, such as diversity and trophic links. Therefore, we conducted a long-term field survey from May 2009 to August 2016 at 405 sites in northeast China to investigate the effect of a gradient of salinisation on community diversity, functional diversity and trophic links in mountain streams. Samples of water chemistry, periphyton, macroinvertebrates and fish were collected. Our results showed that as anthropogenic salinisation increased, Ca²⁺, Mg²⁺, HCO₃^- and SO₄^2- exhibited significant increases (p < 0.05). These increased ions caused decreases in taxonomic evenness and biotic integrity, but an increase in the beta diversity for periphyton and macroinvertebrates, and a slight increase in the evenness of fish. The increased salinisation resulted in the extirpation of salt-sensitive taxa and declines in macroinvertebrate functional richness and functional redundancy, which consequently led to simplified trophic links. Our results implied that if salt-tolerant taxa in high salinisation sites were not functionally redundant with less tolerant taxa, alterations of their functional composition probably decrease the stability of ecosystem functions. Overall, our study suggests that the ongoing anthropogenic salinisation is posing serious threats to biodiversity and trophic links in river ecosystems, and should be considered in future river restoration and biodiversity conservation.

Enhanced biotreatability of petroleum hydrocarbon-contaminated mining waste coupled with the attenuation of acid drainage production

A biostimulation study was conducted on mining waste residue with nutrient (nitrogen and phosphorus) and/or liming agent (ash or CaCO₃ ) amendment to assess petroleum hydrocarbon (PHC) biodegradation efficiency by indigenous microorganisms. Compounds accumulated and/or released by treated samples were also monitored to determine the potential for acid mine drainage production during biostimulation. The potential for natural attenuation (i.e., the biodegradation of PHC contamination) was initially low but increased significantly upon nutrient addition. The best results were obtained when nutrient addition was coupled with the addition of a liming agent, notably CaCO₃ , which contributed to maintaining near-neutral pH values. In fact, during treatment without a liming agent, pH decreased due to the oxidation of sulfide minerals, resulting in acid mine drainage production with increased metals released into sample leachates. Sulfur- and iron-oxidizing bacteria were detected primarily in samples not amended with liming agents, and the predominant organisms were affiliated with Acidithiobacillus spp. and Acidiphilium spp. Overall, the results of the present study demonstrated that amendment with a liming agent when treating PHC-contaminated mining waste residue contributes to maintaining a pH close to neutrality, mitigates sulfate release, and reduces the release of metals without negatively affecting the activity of PHC degraders.

Effects of Backfilling Excavated Underground Space on Reducing Acid Mine Drainage in an Abandoned Mine

Three-dimensional groundwater flow around an abandoned mine was simulated to evaluate the effects of backfilling the excavated underground space of the mine on reducing the acid mine drainage (AMD). The conceptual model of the groundwater flow consists of not only variable geological formations but also vertical shafts, horizontal drifts, and the other excavated underground space. The steady-state groundwater flow in both days with high and little rainfall was calculated to calibrate the model. The calculated groundwater levels and flow rate of the AMD agreed with the measured ones by calibrating the hydraulic conductivity of the host rock, which was sensitive to groundwater flow in the mine. This validated model was applied to predict the flow rate of the AMD when backfilling the excavated underground space. The results showed that the flow rate of the AMD decreased by 5% to 30%. This indicates that backfilling the excavated space is one of the effective methods to reduce AMD of abandoned mines.

Sulfate and metals removal from acid mine drainage in a horizontal anaerobic immobilized biomass (HAIB) reactor

The acid mine drainage (AMD) can causes negative impacts to the environment. Physico-chemical methods to treat AMD can have high operational costs. Through passive biological methods, such as anaerobic reactors, sulfate reduction, and recovery of metals are promoted. This study evaluated the performance of a horizontal anaerobic immobilized biomass (HAIB) reactor for the treatment of synthetic AMD using polyurethane foam as support material, and anaerobic sludge as inoculum. Ethanol was used as an electron donor for sulfate reduction, resulting in an influent chemical oxygen demand (COD) in the range of 500-1,500 mg/L and COD/sulfate ratio at 1. A gradual increase of sulfate and COD concentration was applied that resulted in COD removal efficiencies higher than 78%, and sulfate removal efficiencies of 80%. Higher sulfate and COD concentrations associated with higher hydraulic retention times (36 h) proved to be a better strategy for sulfate removal. The HAIB reactor was able to accommodate an increase in the SLR up to 2.25 g SO₄^2-/L d^-1 which achieved the greatest performance on the entire process. Moreover, the reactor proved a suitable alternative for reaching high levels of metal removal (86.95 for Zn, 98.79% for Fe, and 99.59% for Cu).

Modeling of the groundwater flow system in excavated areas of an abandoned mine

This study evaluated the assumption that back-filled excavated areas of old mine workings can be modeled as porous media, where groundwater flow is governed by Darcy's law. The Yatani mine, located in Yamagata Prefecture, Japan, was selected for this study because several mining methods were used during its operation and detailed drawings of the excavated areas of the mine are available. The model was calibrated using combinations of hydraulic conductivities (k), with the best-matched case being selected by comparing calculated and measured AMD fluxes. Modeled AMD fluxes along the drainage tunnel (-2 L level) were consistent with measured data when the excavated areas were considered to be porous media with a specific hydraulic conductivity, and the presence of faults and permeability were taken into account. The model also successfully predicted the increasing trend of AMD flux from the shaft to adit mouth. In the numerical model, the back-filled excavated areas were assumed to behave as porous media, which was shown to be a valid assumption in this mine. The model demonstrated that back-filling the excavated areas and drainage tunnel with low permeability materials could reduce the flux of Zn in AMD by up to 61%.

Selective copper extraction by multi-modified mesoporous silica material, SBA-15

Selective copper (Cu) recovery from wastewater mitigates environmental pollution and is economically valuable. Mesoporous silica adsorbents, SBA-15, with amine-grafting (SBA-15-NH₂) and manganese loading along with amine-grafting (Mn-SBA-15-NH₂) were fabricated using KMnO₄ and 3-aminopropyltriethoxysilane. The characteristics of the synthesized adsorbents were evaluated in detail in terms of its crystal structure peaks, surface area and pore size distribution, transmission electron microscope and X-ray photoelectron spectroscopy. The results established the 2.08mmol/g of Cu adsorption capacity on Mn-SBA-15-NH₂. Furthermore, in a mixed heavy metal solution, high selective Cu adsorption capacity on Mn-SBA-15-NH₂ (2.01mmol/g) was achieved while maintaining 96% adsorption amount as that of a single Cu solution. Comparatively, Cu adsorption on SBA-15-NH₂ decreased by half due to high competition with other heavy metals. Optimal Cu adsorption occurred at pH5. This pH condition enabled grafted amine group in Mn-SBA-15-NH₂ to form strong chelating bonds with Cu, avoiding protonation of amine group (below pH5) as well as precipitation (above pH5). The adsorption equilibrium well fitted to Langmuir and Freundlich isotherm models, while kinetic results were represented by models of linear driving force approximation (LDFA) and pore diffusion model (PDM). High regeneration and reuse capacity of Mn-SBA-15-NH₂ were well established by its capacity to maintain 90% adsorption capacity in a multiple adsorption-desorption cycle. Cu was selectively extracted from Mn-SBA-15-NH₂ with an acid solution.

Impacts of point-source Net Alkaline Mine Drainage (NAMD) on stream macroinvertebrate communities

Over 4000 km of Pennsylvania's flowing waters and attendant ecosystems have been degraded by mine drainage to the exclusion of multiple designated uses. Both Acid Mine Drainage (AMD) and Net Alkaline Mine Drainage (NAMD) may result from coal extraction depending on the underlying geology. Acid Mine Drainage is characterized as an acidic mixture of toxic heavy metals in solution, while NAMD is circumneutral in pH with metals forming oxidized precipitates. The ecological impacts of AMD have been well documented but NAMD-impacted streams have received considerably less attention. We selected 10 low-order tributaries of the Ohio and Youghiogheny rivers in southwestern Pennsylvania impacted by point-source inputs of NAMD for assessment of water quality and benthic macroinvertebrate communities. Levels of pH, total iron (Fe), and sulfate (SO₄) were significantly elevated in the impacted stream reaches when compared with upstream reference sites while total alkalinity and specific conductance were equivalent. Macroinvertebrate abundance declined by 92% in the impacted stream reaches, but community structure in terms of taxonomic composition and species richness was similar. Total iron, total sulfate, and specific conductance were significantly linked to macroinvertebrate community impairment. The presence of resident macroinvertebrate communities in the unimpacted reaches suggests that remediation would result in a rapid recolonization and establishment of viable downstream ecosystems.

Acid mine drainage sources and hydrogeochemistry at the Yatani mine, Yamagata, Japan: A geochemical and isotopic study

This paper describes the geochemistry of groundwater and its flow system in the closed Yatani mine in southern Yamagata Prefecture, Japan. The mine is located in a sulfide deposit containing pyrite and has been generating acid mine drainage (AMD). The study was intended to elucidate the formation of AMD and its flow patterns using geological, hydrological, geochemical, and isotopic techniques. The results indicate that AMD is formed by the interaction of groundwater with sulfide minerals, sand slime, and tailings back-filled into excavated mine areas. Groundwater recharge areas were identified on the mountain slope at an elevation of ~900 m. The formation of AMD in the drifts and shaft was more extensive than that in the deeper drainage levels. Principal component analysis was applied to the hydrogeochemical data to identify the causes of AMD formation. The first, second, and third principal components reveal that the increased ion concentrations in mine drainage are a result of water-mineral reactions in excavated mine areas, the contribution of groundwater in deep reductive environments, and isotopic fractionation during precipitation, respectively. A promising method of reducing AMD formation is to prevent contact between dissolved oxygen and sulfide minerals by increasing the drainage level or by filling the shallow underground excavated area with cementitious materials.

Effect of particle erosion on mining-induced water inrush hazard of karst collapse pillar

As a typical disaster-causing geological structure, karst collapse pillar (KCP) is widely distributed in coalfields of northern China. The interior of KCP is filled with loose and weakly cemented rock masses. Fine particles can be eroded under the hydraulic pressure and the disturbance of the coal mining operation. Then, water inrush pathway can be formed easily, resulting in water inrush hazard. The release of untreated coal mine water can pollute the environment and waste the limited water resource in China. To investigate the particle erosion effect on the water inrush mechanism of KCP, FLAC^3D numerical investigations were conducted to simulate the water flow process of KCP in the mining floor during the coal seam excavation, according to the stress-seepage coupling model with the consideration of the particle erosion. Besides, the evolution of shear stress field, seepage field, and plastic zone along was obtained as working plane advances. Meanwhile, the influence of the thickness of a waterproof rock floor and the hydraulic pressure of aquifer on the formation of water inrush pathway was analyzed. Numerical results indicated that: (1) Shear failure of the KCP near the side of the working plane occurs under the effect of mining excavation; then, the KCP connects with the damage area around the working plane; finally, the water inrush pathway is formed. (2) Water inrush disaster will not occur immediately when the KCP is connected with the damaged area around the working plane; it only occurs when the KCP is completely exposed in the mining. (3) With the mining advances, the thinner the waterproof rock floor and the greater the hydraulic pressure of the aquifer, the easier the groundwater can lead up, and the KCP tends to be damaged with the formation of water inrush pathway.

Effects of secondary salinisation on macroinvertebrate functional traits in surface mining-contaminated streams, and recovery potential

Secondary salinisation has become a hot spot internationally due to its adverse effects on freshwater ecosystems. Although its effects on ecosystem patterns has been broadly studied, its potential effect on ecosystem functions, in particular on the functional traits of freshwater organisms, and functional trait recovery are largely unknown. In this study, we conducted a field investigation at 405 sample sites from May 2009 to July 2016 in surface mining-contaminated streams, in order to evaluate the influence of secondary salinisation on macroinvertebrate functional traits and the recovery potential of dominant functional traits. Results of univariate models showed that sensitive, very tolerant, gill-breathers, cutaneous-breathers, shredders, predators and gatherers were the most responsive indicators to enhanced specific conductivity and sulfate loadings with sensitive, gill-breathers, shredders and predators demonstrating a reduction in abundance, whereas cutaneous-breathers and gatherers exhibiting an increase. Complicated relationships among different species indicated that co-exclusions would not occur because all macroinvertebrate taxa exhibited positive correlations. Results of relative recovery potential showed that omnivores and gatherers recovered quickly following improvements in water quality, whereas gill-breathers, pneumostome-breathers, filterers and scrapers would be expected to recover slowly due to their sensitivity to both specific conductivity and sulfate and low drift propensity. Overall, secondary salinisation has posed severely ecological risks to macroinvertebrate functional attributes in surface mining-contaminated streams, and their effects should be considered in future conservation plans.

Feeding strategies for the acquisition of high-quality food sources in stream macroinvertebrates: Collecting, integrating, and mixed feeding

Aquatic macroinvertebrates play an important functional role in energy transfer in food webs, linking basal food sources to upper trophic levels that include fish, birds, and humans. However, the trophic coupling of nutritional quality between macroinvertebrates and their food sources is still poorly understood. We conducted a field study in subalpine streams in Austria to investigate how the nutritional quality (measured by long-chain polyunsaturated fatty acids, LC-PUFAs) in macroinvertebrates changes relative to their basal food sources. Samples of macroinvertebrates, periphyton, and leaves were collected from 17 streams in July and October 2016 and their fatty acid (FA) composition was analyzed. Periphyton FA varied strongly with time and space, and their trophic effect on macroinvertebrate FA differed among functional feeding groups. The match between periphyton FA and macroinvertebrate FA decreased with increasing trophic levels, but LC-PUFA content increased with each trophic step from periphyton to grazers and finally predators. Macroinvertebrates fed selectively on, assimilated, and/or actively controlled their LC-PUFA, especially eicosapentaenoic acid (EPA, 20 : 5ω3) relative to their basal food sources in the face of spatial and temporal changes. Grazer FA profiles reflected periphyton FA with relatively good fidelity, and especially their EPA feeding strategy was primarily linked to periphyton FA variation across seasons. In contrast, shredders appeared to preferentially assimilate more EPA over other FA, which was determined by the availability of high-quality food over seasons. Predators may more actively control their LC-PUFA distribution with respect to different quality foods and showed less fidelity to the basal FA profiles in plants and prey. Overall, grazers and shredders showed relatively good fidelity to food FA profiles and performed as both "collectors" and "integrators" for LC-PUFA requirements across seasons, while predators at higher trophic levels were more "integrators" with added metabolic complexity leading to somewhat more divergent FA profiles. These results are potentially applicable for other aquatic consumers in freshwater and marine ecosystems.

Heavy metal and sulfate removal from sulfate-rich synthetic mine drainages using sulfate reducing bacteria

The removals of heavy metals and sulfate in the synthetic acid mine drainages (AMDs) by Desulfovibrio desulfuricans, sulfate-reducing bacteria (SRB), and the indigenous bacteria isolated from the mine area soil sample were studied to compare the AMD treatment efficiencies. The AMD treatment by the D. desulfuricans grown in the Desulfovibrio medium was used to represent bioaugmentation, while the AMD treatment by the indigenous bacteria grown in the Desulfovibrio medium was used to represent biostimulation. The consumption of lactate and sulfate suggested that the zinc (Zn) removal in the Zn-spiked Desulfovibrio medium by D. desulfuricans involved chemical precipitation and biosorption. The complete Zn removal by D. desulfuricans took 24 h, while the indigenous bacteria took 360 h. The significantly lower rate can probably be attributed to the composition of the culture. The removal of Zn in the sulfate-rich synthetic AMD-containing Desulfovibrio medium (i.e., AMD) was adversely affected by the presence of other heavy metals. Also, the sulfate reduction by D. desulfuricans and the indigenous bacteria was reduced from 47% to 20% and from 36% to 6%, respectively. The inhibitive effects on the removal of heavy metals and sulfate were greater with the Zn/Cu-spiked AMD than the Zn-spiked AMD. Overall, the indigenous bacteria showed potential for removing heavy metals and sulfate in AMDs, while the removal efficiency was lower than D. desulfuricans. The continuous supply of carbon sources with an adaptation period may be required to enhance the AMD treatment efficiency by the indigenous bacteria.

Assessing the sustainability of acid mine drainage (AMD) treatment in South Africa

The environmental sustainability of acid mine drainage (AMD) treatment at semi-industrial scale is examined by means of the life cycle assessment (LCA) methodology. An integrated process which includes magnesite, lime, soda ash and CO₂ bubbling treatment was employed to effectively treat, at semi-industrial scale, AMD originating from a coal mine in South Africa. Economic aspects are also discussed. AMD is a growing problem of emerging concern that cause detrimental effects to the environment and living organisms, including humans, and impose on development, health, access to clean water, thus also affect economic growth and cause social instability. Therefore, sustainable and cost effective treatment methods are required. A life cycle cost analysis (LCCA) revealed the viability of the system, since the levelized cost of AMD treatment can be as low as R112.78/m³ (€7.60/m³ or $9.35/m³). Moreover, due to its versatility, the system can be used both at remote locales, at stand-alone mode (e.g. using solar energy), or can treat AMD at industrial scale, thus substantially improving community resilience at local and national level. In terms of environmental sustainability, 29.6 kg CO_2eq are emitted per treated m³ AMD or its environmental footprint amount to 2.96 Pt/m³. South Africa's fossil-fuel depended energy mix and liquid CO₂ consumption were the main environmental hotspots. The total environmental footprint is reduced by 45% and 36% by using solar energy and gaseous CO₂, respectively. Finally, AMD sludge valorisation, i.e. mineral recovery, can reduce the total environmental footprint by up to 12%.