Treatment Of Acid Mine Drainage Research Articles

Alkaline Chemical Neutralization to Treat Acid Mine Drainage with High Concentrations of Iron and Manganese

Due to its high acidity and toxic metal content, acid mine drainage (AMD) needs to be properly treated before being discharged into the environment. This study took the AMD collected from one specific mine in China as a sample and investigated the treatment methodology for AMD. The water quality of the AMD was measured, and the sample was treated with caustic soda (NaOH) and shell powder (one kind of conventional neutralizer, mainly composed of CaCO3) by the neutralization method. The results show that the AMD has a relatively low pH (2.16) and contains high concentrations of Fe (77.54 g/L), Mn (621.29 mg/L), Cu (6.54 mg/L), Ca (12.39 mg/L), and Mg (55.04 mg/L). NaOH was an effective neutralizer to treat the AMD and performed much better than shell powder. Various metals were precipitated, in the order of Fe(III), Cu, Fe(II), Mn, Ca, and Mg. The metal removal mechanisms included precipitation, adsorption, and co-precipitation. The optimal reaction conditions were the reaction duration was selected as 5 min and the mass ratio of NaOH to AMD was 0.16:1 (w:v). By this stage, the pH rapidly increased from 2.16 to 8.53 during AMD-NaOH interactions and various metals were efficiently removed (from 86.71% to 99.99%) by NaOH. The residual mass concentrations of Fe, Mn, Cu, Ca, and Mg after the treatment were 1.52, 1.77, 0.10, 1.65, and 2.17 mg/L, respectively. These data revealed that NaOH was a good treatment regent for this kind of AMD, based on the discharge criteria of China (GB28661 2012). Also, the shell powder was a helpful neutralizer for pH adjustment and copper removal. This neutralization method has the advantages of convenient operation, high speed, good effect, simple equipment, and low infrastructure cost. In addition, the resulting neutralized residue is a valuable and high-quality raw material, which can be used in metal smelting and separation.

Acid mine drainage treatment and metals recovery by means of selective precipitation using magnesium oxide (MgO): An experimental study

The treatment of acid mine drainage (AMD) by metals precipitation and neutralization releases a huge volume of highly polluted toxic sludge which can be valorized by the recovering of chemical species. In this study, the treatment of AMD and chemical species recovery by means of selective precipitation using magnesium oxide (MgO) was explored. One litre and half (1500 mL) of AMD from coal mine was used for the experiment. The pH of AMD water was gradually increased using an overhead stirrer and chemical species recovered at different pH gradients via a sequential precipitation technique. The results revealed that Fe(III) was recovered at pH 2.9–4 interval, Al at pH ≥ 4, Cu at pH ≥ 6.5, gypsum at pH 2.9–9.5 interval, Fe(II) at pH ≥ 7.5, Mn, Ni and Zn pH ≥ 8. The results further revealed significant removal of inorganic pollutants in the following order: Cu (100%) = Ni (100%) ≥ Fe (99.9%) ≥ Al (99%) ≥ Mn (98.6%) ≥ Zn (97.2%) ≥ SO42─ (76%). Reduction of electrical conductivity (EC) and total dissolved solid (TDS) were also observed in the order of 82% and 85% respectively. Characterization studies were used to underpin and succinct the fate of chemical species of pure MgO and sludge recovered at different pH gradients. The product water obtained at pH 9.5 conformed to the prescribed standard for effluent discharge as prescribed by regulatory bodies.

A novel sulfidogenic process via sulfur reduction to remove arsenate in acid mine drainage: Insights into the performance and microbial mechanisms

Biological sulfidogenic processes based on sulfate-reducing bacteria (SRB) are not suitable for arsenic (As)-containing acid mine drainage (AMD) treatment because of the formation of the mobile thioarsenite during sulfate reduction. In contrast, biological sulfidogenic processes based on sulfur-reducing bacteria (S0RB) produce sulfide without pH increase, which could achieve more effective As removal than the SRB-based process. However, the reduction ability and toxicity tolerance of S0RB to As remains mysterious, which may substantially affect the practical applicability of this process when treating arsenate (As(V))-containing AMD. Thus, this study aims to develop a biological sulfur reduction process driven by S0RB, and explore its long-term performance on As(V) removal and microbial community evolution. Operating under moderately acidic conditions (pH=4.0), the presence of 10 mg/L As(V) significantly suppressed the activity of S0RB, leading to the failure of As(V) removal. Surprisingly, a drop in pH to 3.0 enhanced the tolerance of S0RB to As toxicity, allowing for efficient sulfide production (396±102 mg S/L) through sulfur reduction. Consequently, effective and stable removal of As(V) (99.9 %) was achieved, even though the sulfidogenic bacteria were exposed to high levels of As(V) (42 mg/L) in long-term trials. Spectral and spectroscopic analysis showed that As-bearing sulfide minerals were present in the bioreactor. Remarkably, the presence of As(V) induced notable changes in the microbial community composition, with Desulfurella and Clostridium identified as predominate sulfur reducers. The qPCR result further revealed an increase in the concentration of functional genes related to As transport (asrA and arsB) in the bioreactor sludge as the pH decreased from 4.0 to 3.0. This suggests the involvement of microorganisms carrying asrA and arsB in an As transport process. Furthermore, metagenomic binning demonstrated that Desulfurella contained essential genes associated with sulfur reduction and As transportation, indicating its genetic potential for sulfide production and As tolerance. In summary, this study underscores the effectiveness of the biological sulfur reduction process driven by S0RB in treating As(V)-contaminated AMD. It offers insights into the role of S0RB in remediating As contamination and provides valuable knowledge for practical applications.

Comparison of individual and ensemble machine learning models for prediction of sulphate levels in untreated and treated Acid Mine Drainage

Machine learning was used to provide data for further evaluation of potential extraction of octathiocane (S8), a commercially useful by-product, from Acid Mine Drainage (AMD) by predicting sulphate levels in an AMD water quality dataset. Individual ML regressor models, namely: Linear Regression (LR), Least Absolute Shrinkage and Selection Operator (LASSO), Ridge (RD), Elastic Net (EN), K-Nearest Neighbours (KNN), Support Vector Regression (SVR), Decision Tree (DT), Extreme Gradient Boosting (XGBoost), Random Forest (RF), Multi-Layer Perceptron Artificial Neural Network (MLP) and Stacking Ensemble (SE-ML) combinations of these models were successfully used to predict sulphate levels. A SE-ML regressor trained on untreated AMD which stacked seven of the best-performing individual models and fed them to a LR meta-learner model was found to be the best-performing model with a Mean Squared Error (MSE) of 0.000011, Mean Absolute Error (MAE) of 0.002617 and R2 of 0.9997. Temperature (°C), Total Dissolved Solids (mg/L) and, importantly, iron (mg/L) were highly correlated to sulphate (mg/L) with iron showing a strong positive linear correlation that indicated dissolved products from pyrite oxidation. Ensemble learning (bagging, boosting and stacking) outperformed individual methods due to their combined predictive accuracies. Surprisingly, when comparing SE-ML that combined all models with SE-ML that combined only the best-performing models, there was only a slight difference in model accuracies which indicated that including bad-performing models in the stack had no adverse effect on its predictive performance.

Unlocking water potential in drylands: Quicklime and fly ash enhance soil microbiome structure, ecological networks and function in acid mine drainage water-irrigated agriculture

In water-stressed regions, treated acid mine drainage (AMD) water for irrigated agriculture is a potential solution to address freshwater scarcity. However, a significant knowledge gap exists on the short and long-term effects of treated AMD water on soil health. This study used high-throughput Illumina sequencing and predictive metagenomic profiling to investigate the impact of untreated AMD (AMD), quicklime- (A1Q and A2Q) and quicklime and fly ash-treated AMD water (AFQ) irrigation on soil bacterial diversity, co-occurrence networks and function. Results showed that untreated AMD water significantly increased soil acidity, electrical conductivity (EC), sulfate (SO42−), and heavy metals (HM), including reduced microbial diversity, disrupted interaction networks, and functional capacity. pH, EC, Cu, and Pb were identified as key environmental factors shaping soil microbial diversity and structure. Predominantly, Pseudomonas, Ralstonia picketti, Methylotenera KB913035, Brevundimonas vesicularis, and Methylobacteriumoryzae, known for their adaptability to acidic conditions and metal resistance, were abundant in AMD soils. However, soils irrigated with treated AMD water exhibited significantly reduced acidity (pH > 6.5), HM and SO42− levels, with an enrichment of a balanced bacterial taxa associated with diverse functions related to soil health and agricultural productivity. These taxa included Sphingomonas, Pseudoxanthomonas, Achromobacter, Microbacterium, Rhodobacter, Clostridium, Massillia, Rhizobium, Paenibacillus, and Hyphomicrobium. Moreover, treated AMD water contributed to higher connectivity and balance within soil bacterial co-occurrence networks compared to untreated AMD water. These results show that quicklime/fly ash treatments can help lessen impacts of AMD water on soil microbiome and health, suggesting its potential for irrigated agriculture in water-scarce regions.

Investigation of the migration of natural organic matter-iron-antimony nano-colloids in acid mine drainage

Colloids can potentially affect the efficacy of traditional acid mine drainage (AMD) treatment methods such as precipitation and filtration. However, it is unclear how colloids affect antimony (Sb) migration in AMD, especially when natural organic matter (NOM) is present. To conduct an in-depth investigation on the formation and migration behavior of NOM, iron (Fe), Sb and NOM-Fe-Sb colloids in AMD, experiments were performed under simulated AMD conditions. The results demonstrate significant variations in the formation of NOM-Fe-Sb colloids (1–3–450 nm) as the molar ratio of carbon to iron (C/Fe) increases within acidic conditions (pH = 3). Increasing the C/Fe molar ratio from 0.1 to 1.2 resulted in a decrease in colloid formation but an increase in particulate fraction. The distribution of colloidal Sb, Sb(III), and Fe(III) within the NOM-Fe-Sb colloids decreased from 68 % to 55 %, 72 % to 57 %, and 68 % to 55 %, respectively. Their distribution in the particulate fraction increased from 28 % to 42 %, 21 % to 34 %, and 8 % to 27 %. XRD, FTIR, and SEM-EDS analyses demonstrated that NOM facilitates the formation and crystallization of Fe3O4 and FeSbO4 crystalline phases. The formation of the colloids depended on pH. Our results indicate that NOM-Fe-Sb colloids can form when the pH ≤ 4, and the proportion of colloidal Sb fraction within the NOM-Fe-Sb colloids increased from 9 % to a maximum of 73 %. Column experiments show that the concentration of NOM-Fe-Sb colloids reaches its peak and remains stable at approximately 3.5 pore volumes (PVs), facilitating the migration of Sb in the porous media. At pH ≥ 5, stable NOM-Fe-Sb colloids do not form, and the proportion of colloidal Sb fraction decreases from 7 % to 0 %. This implies that as pH increases, the electrostatic repulsion between colloidal particles weakens, resulting in a reduction in the colloidal fraction and an increase in the particulate fraction. At higher pH values (pH ≥ 5), the repulsive forces between colloidal particles nearly disappear, promoting particle aggregation. The findings of this study provide important scientific evidence for understanding the migration behavior of NOM-Fe-Sb colloids in AMD. As the pH gradually shifts from acidic to near-neutral pH during the remediation process of AMD, these results could be applied to develop new strategies for this purpose.

Replacing rice bran with low-molecular-weight substrates affected the performance and metabolic feature of sulfate-reducing bioreactors treating acid mine drainage

The sulfate-reducing bioreactor presents an auspicious approach for eradicating toxic metals from acid mine drainage (AMD). In earlier studies, the incorporation of rice bran as a substrate in bioreactors was observed to foster the proliferation of a diverse range of microorganisms, consequently leading to the undesirable development of biofilms atop the bioreactor. To selectively stimulate sulfate-reducing bacteria (SRB) within the bioreactor, we examined the consequences of introducing three low-molecular-weight substrates in lieu of rice bran under 12 varying conditions. The sulfate reduction performance was marginally impacted by the incorporation of lactate with corn steep liquor (CSL) compared to ethanol or glucose with CSL, and the microbial composition in the presence of lactate differed significantly from those containing ethanol or glucose. The integration of ethanol and glucose with/without CSL efficiently lowered oxidation-reduction potential and promoted the proliferation of Desulfosporosinus-related SRB (relative abundance: ∼26.6%). Given that the employment of glucose initially activated fermentative bacteria such as Clostridium spp., ethanol emerged as an efficacious alternative substrate to rice bran, which directly fosters the accumulation of Desulfosporosinus sp. without encouraging the growth of other microorganisms that contribute to the unwanted formation of biofilms within the sulfate-reducing bioreactors employed in AMD treatment.

Potato (Solanum tuberosum L.) cultivars physiological, biochemical performance and yield parameters response to acid mine water irrigation and soil physiochemical properties

This paper aimed to analyse the potato cultivar’s response to physiological, biochemical performance, yield parameters and soil physiochemical properties when subjected to quicklime (un)treated acid mine drainage (AMD) irrigation. A randomized design experiment was conducted with five water treatment levels: TW1; TW2; TW3; TW4 to TW5 replicated four times. The results showed that the quicklime treatment increased the pH of the AMD water, reduced the concentration of EC, NO3−, SO42− and ameliorated heavy metals. However, unsafe levels of heavy metals above the maximum permissible (WHO/FAO) levels were found in Pb, Mg and Mo for water (TW4 and TW5), while As, Cd and Cr for soils (ST4 and ST5) respectively. For potato tubers (TT4 and TT5) concentrations of As, Cd, Cr, and Pb were above the maximum levels. Stomatal conductance, chlorophyll content and yield parameters responded positively by increasing significantly on TW4 and TW5 treatments, but negatively (reduced) towards TW2 and TW3 treatments. A higher bioaccumulation factor was obtained for Zn ˃ Cu ˃ Mg ˃ Pb ˃ Mn, which was an indication of the contamination status of soil, with Zn being more concentrated than other metals. The findings indicate that quicklime-treated AMD is usable for potato irrigation with regular monitoring of heavy metal levels and strict observation of water reuse protocols. The use of this large source of ameliorated (AMD) water will go a long way in improving food security in South Africa and/or in countries where agriculture production is around mining areas.

Needs and Options for Improving Gold Mining Waste Management Practices for Sustainable Development in Tanzania

The main objective of this study was to evaluate current mining waste management practices and their challenges. This study aimed to identify existing technologies and practices, and to present improvement needs and options for environmentally sustainable practices for mining operations. Other researchers have reported many practices and technologies for managing mining waste, but the efficiency, applicability, and need for customization were not specifically addressed for developing countries. This study used field observations, measurement methods, and laboratory analysis to collect data. This study showed a large amount of mine waste rock compared to the tailings wastewater from gold processing plant produced annually. This comprises approximately 5.2 million m3 of mine contaminated water generated by leaching from the waste rock dump (WRD) and 2.3 million m3 from the tailings storage facility (TSF). The study also identified the use of TSF cut-off trenches for seepage collection, the use of lime to treat acid mine drainage (AMD), the discharge of AMD into the TSF, and the recycling of TSF water as the best practices for managing mining waste. Furthermore, the study also found that the most common environmental problems were caused by TSF water and AMD water. However, mining waste management can be improved by modifying existing practices and adopting cost-effective technologies and practices to control and treat excess mining water.

Application of Active and Passive Treatment of Acid Mine Drainage to Comply with the Threshold Parameter of Coal Mining Wastewater

Most of the coal mining in Indonesia that uses the open pit mining method faces serious problems, namely the treatment of acid mine drainage. This constitutes a relatively large volume of wastewater, especially in areas that have rainfall in the range of 2000–4000 mm yearly. Acid mine drainage as acidic wastewater formed during excavation cannot be avoided due to the oxidation process during overburden removal. The acidic wastewater that has formed must be managed strictly and appropriately prior to being released into public waters. There are two methods of treating acid mine wastewater, namely active and passive treatments. Active treatment is generally used more frequently during operations, considering the time, effort, and costs; however, when entering the mine closure period, natural processes must be used at lower costs. Undertaking passive treatment in this area has shown a reduction in the chemical materials used and has enabled a greater amount of wastewater to be managed. The purpose of this research is to describe the active and passive treatment processes in the management of acid mine drainage and to analyze the results of passive treatment in preparation for the mine closure stage. Development of passive treatment by swampy forest system can reduce cost of treatment, naturally process and more environment friendlier by reducing the quicklime materials.

Comparison of Artificial Neural Fuzzy Inference System (ANFIS) and Response Surface Methodology (RSM) Model in Predicting the Outlet Flow Rate of Passive Treatment System Column

Acid mine drainage (AMD) is one of the major environmental problems the mining and mineral processing industries face. Treatment of AMD involves active and passive treatment. In the long term, passive treatment is the most effective way to treat acid mine drainage, but it can be expensive. if handled properly. Therefore, the study of flow rate in a passive treatment system is one of the important ways to identify optimum hydraulic retention time to ensure the maximum percentage of heavy metal removal can be achieved while keeping the cost to a minimum level. This study focused on developing and comparing the Response Surface Methodology (RSM) model and Artificial Neural Fuzzy Inference System (ANFIS) model to predict the outlet flow rate of the passive treatment system column based on three parameters inlet flow time, thickness of peat soil bed, and inlet flow rate. The RSM model was created by Design-Expert software whereas MATLAB created the ANFIS model with 80% of data used for the model training and 20% of the data for model testing. The models' performances were compared in terms of statistical errors (AAPE, RMSE, R2, STD, minimum error, and maximum error). It was found the ANFIS model has performed better in predicting the outlet flowrate with R2 value of 0.99 RSM model with the value of 0.97. The inlet flow rate was an insignificant parameter affecting the outlet flow rate of the passive treatment column. From the 3-D surface response plot, the highest outlet flow rate is predicted to be 524 mL/min.

Source reduction and end treatment of acid mine drainage in closed coal mines of the Yudong River Basin.

After the closure of the Yudong coal mine, the pH value was approximately 3.0, and the Fe and Mn concentrations reached 380 and 69 mg/L, respectively, in the acid mine drainage (AMD), causing serious pollution to the water bodies in the nearby watershed. Combined with the formation conditions of AMD, the comprehensive treatment technology of source reduction-end treatment is adopted to treat the AMD. The treatment area of the goaf is 0.3 km3, the filling and grouting volume is about 6.7 m3, and the curtain grouting volume is 4,000 m3. Through the grouting and sealing treatment in the goaf, the water volume is reduced to less than 85% of the initial volume (100 m3/h). After the end treatment, the pH value of the effluent is around 7.0, the content of Fe and Mn is less than 0.1 mg/L, and the removal rate is above 99%. The project was subsequently operated at RMB 0.85 yuan/t. This project is aimed at the treatment of AMD from small coal mines in complex terrain conditions. It has the characteristics of low cost and high efficiency and can provide an effective treatment technology for AMD in southwestern China and areas with the same geological conditions.

Implementation of swampy forest system for acid mine drainage treatment to meet threshold value

Coal mining with the area of the potential acid-forming category can generate acid mine drainage. Acid mine drainage (AMD) that has been formed must be appropriately managed. There are two techniques to treat AMD by the challenge specificity, including the prohibitive cost of the conventional active treatment with an uncertain process and the passive treatment, which faces time constraints and a wider area for preparation. A novel swampy forest system is a development to overcome the weaknesses of conventional processing by naturally responsive mitigation, reducing cost and speed, which results in greater capacity in AMD treatment. The swampy forest system implemented in coal mining relies on three main components: empty fruit bunches as organic matter, grass, and selected tree species planted in the treatment pond. The system effectively changes the non-compliance parameters of wastewater when entered at the system’s inlet to meet the threshold value after processing. It allows for flowing to the public bodies references with the applicable regulation.

Improving Acid Mine Drainage Treatment through Electrocoagulation: Effect of Time, Electrode Distance, and Electrode Types

This study explores the feasibility of employing electrocoagulation technology to manage Acid Mine Drainage (AMD) wastewater, focusing on reducing heavy metal concentrations, particularly iron (Fe) and manganese (Mn). Samples of AMD liquid waste from PT Lhoong Setia Mining in Aceh Province, Indonesia, underwent electrocoagulation using Al-Zn and Al-Fe electrodes with Direct Current (DC). The investigation considered various parameters, including contact time (ranging from 0 to 45 minutes), electrode distance (2, 2.5, and 3 cm), and electrode type (Al-Fe and Al-Zn). The study revealed that prolonged electrocoagulation increased the reduction of Fe and Mn metals due to enhanced Al(OH)3 formation. While Al-Zn electrodes exhibited rapid coagulant formation initially, Al-Fe electrodes sustained effectiveness throughout the process. Optimal reduction of Fe and Mn concentrations occurred at different electrode distances, emphasizing the critical role of spacing in electrocoagulation efficiency. Furthermore, the electrocoagulation process successfully elevated pH levels within acceptable limits and effectively reduced Total Suspended Solids (TSS) in AMD waste, aligning with regulatory standards. This research underscores the potential for electrocoagulation as a viable technology for mitigating the environmental impact of AMD and addresses knowledge gaps related to efficient pollutant removal in mining wastewater treatment. Future studies should explore parameter optimization and consider transitioning to continuous operation for increased effectiveness, particularly in remote mining locations.

Recovery of Cu2+ from acid mine drainage by bentonite-carbide slag composite particle through spontaneous film formation-crystal self-growth-fixed mineralization

In this study, a novel bentonite-carbide slag composite particle (BCS) with endogenetic crystal ion of OH− was prepared by using bentonite and carbide slag as raw materials to treat acid mine drainage containing Cu2+. Macroexperiment, microtest, and theoretical analysis were adopted to reveal the characteristics and mechanism of BCS for the recovery of heavy metal ions from acid mine drainage (AMD). The results showed that the solution around the BCS can spontaneously form a spherical colloid film interface layer, and Cu2+ can be recovered by self-growth film formation and fixed mineralization through the synergistic effect of adsorption, precipitation, induced crystallization, and self-growth mineralization. Two stages, including liquid film formation and self-growth mineralization, existed in the formation and mineralization of mineralized films. This study provided a new treatment perspective for the removal and fixed mineralization recovery of heavy metal ions in AMD. It also provides a scientific theoretical basis for the spontaneous film formation, crystallization, self-growth, and fixed mineralization recovery of heavy metal ions in AMD by the endogenetic crystal ion of OH− in BCS.

Effect of comparison ratio of additives on changes in pH levels, TSS, Fe, and Mn metals in the acid mine water treatment process at KPL BB 13 PT bukit asam, tbk.

Mining activities with an open system at PT Bukit Asam Tbk. have the potential to produce acid mine drainage due to contamination by rocks with sulfur content. Acid mine drainage treatment is carried out by the active method in the Mud Settling Pond (KPL). Addition of alum (Al2(SO4)3) and quicklime (CaO) to increase pH levels and reduce water turbidity. Management is carried out to meet environmental quality standards, namely with a pH value of 6-9, a maximum TSS value of 400, and for Mn and Fe a maximum of 4 and 7 mg/L, respectively. Jar Tests were conducted on samples from KPL BB-13 with mixed doses of alum and quicklime used were 0.02 and 0.10 grams; 0.03 and 0.12 grams; 0.04 and 0.14 grams; 0.05 and 0.16; 0.06 and 0.18; and 0.7 and 0.20. The best test results are at a mixed dose of 0.02 grams of alum and 0.10 grams of quicklime to obtain a pH value of 7 (neutral), besides that TSS and Fe metal levels have decreased. Mn metal also decreased, but did not meet environmental quality standards. Increased doses for field scale under actual conditions of observation required alum as much as 1.00 g/s and quicklime as much as 5.0052 g/s. The evaluation results show that the acid mine drainage treatment carried out by the company is more effective and efficient than the dose of laboratory test results.

Bioremediation of acid mine drainage using sulfate-reducing wetland bioreactor: Filling substrates influence, sulfide oxidation and microbial community

Two sulfate-reducing wetland bioreactors (SRB-1 filled with lignocellulosic wastes and SRB-2 with river sand) were applied for synthetic acid mine drainage treatment with bio-waste fermentation liquid as electron donor, and the influence of filling substrates on sulfate reduction, sulfur transformation and microbial community was studied. The presence of lignocellulosic wastes (mixture of cow manure, bark, sawdust, peanut shell and straw) in SRB-1 promoted sulfate reduction efficiency (68.9%), sulfate reduction rate (42.1 ± 11 mg S/(L·d)), dissolved sulfide production rate (27.4 ± 7 mg S/(L·d)), and particularly caused high conversion ratio of sulfate reduction into dissolved sulfide (66.4%). In comparison, the relatively low sulfate reduction efficiency (42.9%), sulfate reduction rate (27.0 ± 10 mg S/(L·d)), dissolved sulfide production rate (5.6 ± 3 mg S/(L·d)) and low dissolved sulfide conversion efficiency (21.2%) occurred in SRB-2. Mixed organic substrates including easily assimilated electron donors (in manure) and lignocellulosic matter were effective to promote quick start and long-term microbial sulfate reduction. More than 98% of produced dissolved sulfide was oxidized dominantly by photoautotrophic green sulfur bacteria (genera Chlorobium and Chlorobaculum), of which 64.6% and 54.5% was converted into elemental sulfur for SRB-1 and SRB-2. The oxidation of sulfide into elemental sulfur for potential recovery rather than sulfate is preferred. Diverse sulfate reducing bacteria and sulfide oxidizing bacteria co-existed in the treatment system, which led to a sustainable sulfur transformation. High metal removal efficiency for Fe (99.6%, 92.5%), Cd (99.9%, 99.9%), Zn (99.4%, 98.5%), Cu (94.5%, 94.6%) except for Mn (9.3%, 3.6%) was achieved, and effluent pH increased to 6.5–7.7 and 6.7–7.7 for SRB-1 and SRB-2, respectively. Microbial community was regulated by filling substrates. Synergism between lignocellulosic decomposing bacteria and sulfate reducing bacteria played a vital role in lignocellulosic bioreactor treating AMD, in addition to fermentation liquid serving as effective electron donor.

Pine cone derived polyethersulfone/biochar-Fe3O4 mixed matrix membranes for removal of arsenic from acid mine drainage

In this study novel type of mixed matrix membranes (MMMs) were prepared through phase inversion. This fabricated MMMs were impregnated with biochar (BC) and biochar-Fe3O4 (FBC) composites for selective removal of As(V) ions from acid mine drainage through the adsorptive-filtration processes. Scanning electron microscopy (SEM) images revealed that the BC and FBC adsorbents had heterogeneous surface morphologies with varying particle diameters. Fourier transform infrared spectroscopy (FTIR) analysis confirmed the existence of polar functional groups, which aided the improvements in the adsorptive removal of As(V) ions. BET surface area increased from 8.32 m2/g of pristine BC adsorbent to 19.90 m2/g for the FBC adsorbents. Pure water flux increased from 239.9 L/m2.h (M0) to 359.4 L/m2.h (M6), and the water contact angle decreased from 70.7° (M0) to 51.4° (M6). The maximum adsorption capacity achieved was 34.92 mg/g and 49.54 mg/g for BC and FBC MMMs, respectively, at pH 10. The adsorption isotherms and kinetics were analyzed using the Freundlich model and Pseudo-first-order model, respectively, which provided the best-fit to the experimental data. Consequently, the adsorption isotherm data indicated that the removal of As(V) ions was influenced by electrostatic interaction, hydrogen bonding, diffusion (pore filling), and inner-sphere complexation mechanisms. Furthermore, the leaching rate of FBC from membrane labelled M6 was investigated at various pH levels, showing rates of 2.01 µg/m2.h, 0.09 µg/m2.h, and 0.08 µg/m2.h at pH 2, pH 7 and pH 10, respectively. The decrease in leaching rate observed under neutral (pH 7) and basic (pH 10) conditions is ascribed to the improved stability of Fe3O4 NPs within the membranes. The membrane containing 1.5 wt% of FBC demonstrated enhanced effectiveness in removing toxic metals not only for As (99.9 %) but also Cr (99.8 %). These findings indicate that the membrane has great potential towards the treatment of acid mine drainage.

The purification of acid mine drainage through the formation of schwertmannite with Fe(0) reduction and alkali-regulated biomineralization prior to lime neutralization

Acid mine drainage (AMD) contains abundant Fe (II), Fe(III), and SO42−, as well as a large amount of dissolved toxic metals and metalloids, posing a serious threat to the environment. In this study, an integrated technique for the treatment of AMD was proposed. The technique started with pre-oxidation followed by Fe(0) reduction and alkali-regulated biomineralization and then ended with lime neutralization. The technique removed toxic metal oxyanions in the pre-oxidation stage and recovered pure schwertmannite during the subsequent alkali-regulated biomineralization. Fe(III), which could not be directly biomineralized, was reduced to Fe(II) by Fe(0). A small amount of alkali was added to regulate the hydrolytic mineralization reaction after Fe(II) oxidation in AMD, which in a single biomineralization could remove in the form of schwertmannite >95 % of soluble Fe in the AMD. In the subsequent lime neutralization process, the amount of lime required and the sludge produced were reduced by 75.4 % and 84.9 %, respectively, compared to the raw AMD. Additionally, the content of non-ferrous metals in the sludge increased 5.6-fold. Compared with non-alkali-regulated biomineralization, the schwertmannite obtained by the alkali-regulated biomineralization had a higher adsorption capacity for oxyanions (e.g., arsenic, chromium, and antimony). The new approach should significantly reduce the treatment cost of AMD and recover Fe and S elements in the form of valuable secondary minerals, such that it is reasonable to expect that it will be widely adopted in practical applications.

Permeable Concrete Barriers to Control Water Pollution: A Review

Permeable concrete is a class of materials that has long been tested and implemented to control water pollution. Its application in low-impact development practices has proved its efficiency in mitigating some of the impacts of urbanization on the environment, including urban heat islands, attenuation of flashfloods, and reduction of transportation-related noise. Additionally, several research efforts have been directed at the dissemination of these materials for controlling pollution via their use as permeable reactive barriers, as well as their use in the treatment of waste water and water purification. This work is focused on the potential use of these materials as permeable reactive barriers to remediate ground water and treat acid mine drainage. In this respect, advances in material selection and their proportions in the mix design of conventional and innovative permeable concrete are presented. An overview of the available characterization techniques to evaluate the rheology of the paste, hydraulic, mechanical, durability, and pollutant removal performances of the hardened material are presented and their features are summarized. An overview of permeable reactive barrier technology is provided, recent research on the application of permeable concrete technology is analyzed, and gaps and recommendations for future research directions in this field are identified. The optimization of the mix design of permeable reactive concrete barriers is recommended to be directed in a way that balances the performance measures and the durability of the barrier over its service life. As these materials are proposed to control water pollution, there is a need to ensure that this practice has minimal environmental impacts on the affected environment. This can be achieved by considering the analysis of the alkaline plume attenuation in the downstream environment.