Removal of Acidity and Metals from Acid Mine Drainage-Impacted Water using Industrial Byproducts

Comparison of Adsorption Performance of Biochar Derived from Urban Biowaste Materials for Removal of Heavy Metals

This study investigated the adsorption performance of biochar produced from different types of urban biowaste material viz., sugarcane bagasse (SB), brinjal stem (BS), and citrus peel (CP) for removal of heavy metal ions (Pb, Cu, Cr, and Cd) from aqueous solution. The effects of biowaste material, dosage of biochar, solution pH, and initial concentration of heavy metal ions and isotherm models were performed to understand the possible adsorption mechanisms. The results showed that the biochar derived from BS and SB removes Cu (99.94%), Cr (99.57%), and Cd (99.77%) whereas biochar derived from CP removes Pb (99.59%) and Cu (99.90%) more efficiently from the aqueous solution. Biochar derived from BS showed maximum adsorption capacity for Cu (246.31 mg g-1), Pb (183.15 mg g-1), and Cr (71.89 mg g-1) while the biochar derived from CP showed highest for Cd (15.46 mg g-1). Moreover, biochar derived from BS and SB has more polar functional groups and less hydrophobicity than the biochar derived from CP. This study reveals that solution pH and biochar doses play a major role in removal of heavy metal ions from aqueous solution. The results of Langmuir model fitted well for Pb and Cu while the Freundlich model for Cr and Cd. Our study concludes that the biochar derived from different biowaste materials adsorbs heavy metal ions majorly through surface complexation and precipitation processes. The results of this study will be very useful in selecting the effective urban biowaste material for making biochar for heavy metal removal from the aqueous environment.

Green engineered mulch for phosphorus and metal removal from stormwater runoff in bioretention systems

Phosphorus and metals in stormwater runoff are major causes of water quality degradation. Bioretention systems are increasingly implemented to improve stormwater quality and to better manage stormwater quantity. Many studies have focused on modifying the composition of the soil bed to improve pollutant removal. However, the pollutant removal performance of bioretention systems can diminish over time, such as when clogging of the media occurs. Sediment accumulation on the soil surface may inhibit infiltration into the soil bed, thus limiting pollutant removal. Soil replacement may be eventually required as pollutants accumulate in the soil. In this study, a green retrofit material, called green engineered mulch (GEM), was generated by coating regular wood mulch with aluminum-based water treatment residuals (WTR) via a simple and low-energy process (patent pending). The GEM was developed to serve as a green retrofit for bioretention systems to enhance the removal of phosphorus and metals from stormwater runoff. The GEM was placed in a rain garden in Secaucus, NJ, USA for 15 months, during which 12 storm events (ranging from 6.0 mm to 89.6 mm) were monitored. Runoff and infiltrate samples were analyzed for dissolved and total concentrations of phosphorus and metals, along with other key water quality parameters. The GEM significantly reduced (p < 0.05) the total concentrations of phosphorus and metals in stormwater infiltrate compared to the inlet, unlike the regular mulch. Minimal or no contact with the GEM resulted in no significant pollutant removal from surface runoff. No significant pollutant export from the GEM was observed. The spent GEM can be disposed of as non-hazardous waste in municipal landfills. This study demonstrates that the GEM is a safe and effective retrofit. Moreover, the GEM is a simple and economical retrofit solution that can be used in place of regular mulch in bioretention systems.

Remediation technologies for acid mine drainage: Recent trends and future perspectives

Acid mine drainage (AMD) is a highly acidic solution rich in heavy metals and produced by mining activities. It can severely inhibit the growth of plants, and microbial communities and disturb the surrounding ecosystem. In recent years, the use of different bioremediation technologies to treat AMD pollution has received widespread attention due to its environment-friendly and low-cost nature. Various active and passive remediation technologies have been developed for the treatment of AMD. The active treatment involves the use of different chemical compounds while passive treatments utilize natural and biological processes like constructed wetlands, anaerobic sulfate-reducing bioreactors, anoxic limestone drains, vertical flow wetlands, limestone leach beds, open limestone channels, and various organic materials. Moreover, different nanomaterials have also been successfully employed in AMD treatment. There are also reports on certain plant growth-promoting rhizobacteria (PGPR) which have the potential to enhance the growth and productivity of plants under AMD-contaminated soil conditions. PGPR applied to plants with phytoremediation potential called PGPR-assisted phytoremediation has emerged as an economical and environment-friendly approach. Nevertheless, various approaches have been tested and employed, all the approaches have certain limitations in terms of efficiency, secondary pollution of chemicals used for the remediation of AMD, and disposal of materials used as sorbents or as phytoextractants as in the case of PGPR-assisted phytoremediation. In the future, more research work is needed to enhance the efficiency of various approaches employed with special attention to alleviating secondary pollutants production and safe disposal of materials used or biomass produced during PGPR-assisted phytoremediation.

A 22-Site Comparison of Land-Use Practices, E-coli and Enterococci Concentrations

Land-use practices can greatly impact water quality. Escherichia (E.) coli and Enterococcus are accepted water quality indicators. However, surprisingly little research has been conducted comparing both organisms' population density relationships to land use practices and water quality. Stream water grab samples were collected monthly (n = 9 months) from 22 stream monitoring sites draining varying land use practice types in a representative mixed-land-use watershed of the northeastern United States. E. coli and enterococci colony forming units (CFU per 100 mL) were estimated (n = 396) and statistically analyzed relative to land use practices, hydroclimate, and pH, using a suite of methods, including correlation analysis, Principal Components Analysis (PCA), and Canonical Correspondence Analysis (CCA). Correlation analyses indicated significant (p < 0.05) relationships between fecal indicator bacteria concentrations, water quality metrics and land use practices but emphasized significant (p < 0.05) negative correlations between pH and instream enterococci concentrations. PCA and CCA results indicated consistent spatial differences between fecal indicator bacteria concentrations, pH, and land use/land cover characteristics. The study showed that pH could be considered an integrated proxy variable for past (legacy) and present land use practice influences. Results also bring to question the comparability of E-coli and enterococci relative to dominant land use practices and variations in pH and provide useful information that will help guide land use practice and water pollutant mitigation decision making.

Environmental Assessment Impact of Acid Mine Drainage from Kizel Coal Basin on the Kosva Bay of the Kama Reservoir (Perm Krai, Russia)

The Kosva Bay is permanently affected by acid mine drainage (AMD) from Kizel Coal Basin in the Perm Krai of Russia. This discharge is released in the middle part of the Kosva River from the abandoned mines. This study investigates the current trace element (TE) concentrations for Zn, Cu, Pb, Ni, Cr, Cd, As, and Hg and the mineral composition, major oxides, grain size of sediments, and acute toxicity using two test organisms within the site of AMD downstream from the Kosva River and up to the Kosva Bay of Kama Reservoir. The objectives of this study were to analyze the quality of sediment and level pollution of Kosva Bay using pollution and ecotoxicological indices. The environmental indices, namely the contamination factor (CF), the geoaccumulation index (Igeo), and the potential ecological risk factor (Eri), indicate contamination by Cr and Pb in sediments at the site of AMD, with the highest values for Cr, Cu, and As in the Kosva Bay sediments downstream of abandoned coal mines. The results of Igeo and CF average values in bay of sediments showed different degrees of contamination, from moderate contamination to considerable contamination, respectively. According to the potential ecological risk index (RI) values, the Kosva Bay sediments exhibited low to moderate risk, and As and Cd have the highest contribution rate. According to LAWA and the Polish geochemical classification of sediments, sediments of the bay correspond to the highest levels (IV–III classes) for Cr, Ni, and Hg. Based on the SQGC, Hg, Cd, Cr, and Ni are the most probable for resulting in adverse effects on aquatic organisms in this study. The results of this study indicate that complex pollution and ecotoxicological indices must be supported by ecotoxicologal tests. High precipitation totals, low evaporation rates, and flow regulation stream by the Shirokovsky Reservoir located upstream from abandoned coal mines provide significant fluctuations in streamflow, which is probably the most important factor controlling the distribution and mobility of TE in the studied sediments.

Enhanced removal of heavy metals and phosphate in stormwater filtration systems amended with drinking water treatment residual-based granules

To address the clogging issues in stormwater filtration systems, a drinking water treatment residual (DWTR)-based granule (DBG) substrate was developed herein by pyrolyzing and granulating the DWTR with bentonite and corncob. Toxicity characteristic leaching procedure studies indicated that fabricating into DBG stabilized the Al and heavy metals in DWTR and restrained the leaching risk. Then the removal performance of phosphate (PO₄-P) and heavy metal ions by the DWTR and DBG was evaluated in batch and laboratory-scale column experiments. Results from batch tests showed that the amount of Pb(Ⅱ) adsorbed by DBG (18.47 ± 0.56 mg g⁻¹) was approximately 2.3 times of that adsorbed by DWTR (8.05 ± 0.19 mg g⁻¹), whereas the PO₄-P adsorption capacity of DBG (8.63 ± 0.24 mg g⁻¹) was much lower than that of DWTR (25.33 ± 0.81 mg g⁻¹). This could be ascribed to the addition of corncob and bentonite (at a mass ratio of 20% and 40% in DBG, respectively), which provided extremely high cation exchange capacity for the Pb(Ⅱ) adsorption, while no effective PO₄-P adsorption component was involved. Moreover, the pyrolysis process could improve the Pb(Ⅱ) and PO₄-P adsorption capacity of the raw-mixture by 42% and 7%, whereas granulation process decreased those of the pyrolysis-mixture by 15% and 20%, respectively, owing to the reduction of accessible surface area in the DBG. Under various stormwater runoff conditions, the involvement of DBG in stormwater filtration systems exerted consistently fancy performance of Cu(Ⅱ), Pb(Ⅱ), Cd(Ⅱ) and PO₄-P removal, with average removal rates of over 86.20% and desorption rates of less than 3.50%, indicating irreversible and strong complexion between the contaminants and DBG. The DBG column manifested good permeability and stable hydraulic conductivity (2.74-2.52 m d⁻¹) over a 54-day rainfall period, which was beneficial to address the clogging issue of DWTR. Overall, this study provides an alternative pathway to enhance the hydraulic condition and treatment performance of the stormwater filtration systems for urban runoff management.

Reductive transformation of hexavalent chromium by ferrous ions in a frozen environment: Mechanism, kinetics, and environmental implications

The transformation between hexavalent chromium (Cr⁶⁺) and trivalent chromium (Cr³⁺) has a significant impact on ecosystems, as Cr⁶⁺ has higher levels of toxicity than Cr³⁺. In this regard, a variety of Cr⁶⁺ reduction processes occurring in natural environments have been studied extensively. In this work, we investigate the reductive transformation of Cr⁶⁺ by ferrous ions (Fe²⁺) in ice at -20 °C, and compare the same process in water at 25 °C. The Fe²⁺-mediated reduction of Cr⁶⁺ occurred much faster in ice than it did in water. The accelerated reduction of Cr⁶⁺ in ice is primarily ascribed to the accumulation of Cr⁶⁺, Fe²⁺, and protons in the grain boundaries formed during freezing, which constitutes favorable conditions for redox reactions between Cr⁶⁺ and Fe²⁺. This freeze concentration phenomenon was verified using UV-visible spectroscopy with o-cresolsulfonephthalein (as a pH indicator) and confocal Raman spectroscopy. The reductive transformation of Cr⁶⁺ (20 µM) by Fe²⁺ in ice proceeded rapidly under various Fe²⁺ concentrations (20-140 µM), pH values (2.0-5.0), and freezing temperatures (-10 to -30 °C) with a constant molar ratio of oxidized Fe²⁺ to reduced Cr⁶⁺ (3:1). This result implies that the proposed mechanism (i.e., the redox reaction between Cr⁶⁺ and Fe²⁺ in ice) can significantly contribute to the natural conversion of Cr⁶⁺ in cold regions. The Fe²⁺-mediated Cr⁶⁺ reduction kinetics in frozen Cr⁶⁺-contaminated wastewater was similar to that in frozen Cr⁶⁺ solution. This indicates that the variety of substrates typically present in electroplating wastewater have a negligible effect on the redox reaction between Cr⁶⁺ and Fe²⁺ in ice; it also proposes that the Fe²⁺/freezing process can be used for the treatment of Cr⁶⁺-contaminated wastewater.

Mine drainage: Remediation technology and resource recovery

Drainage from current and historic mining operations remains a persistent environmental problem. Numerous research and development efforts were made in 2019 with a goal to minimize the impact of mine drainage on the environment, while other research endeavors addressed the mine drainage issue from a different perspective, where mine drainage was considered a resource for water and valuable products, such as metals, sulfuric acid, and rare earth elements. Thus, this review has two main sections: (a) focusing on research efforts in mine drainage remediation technology, and (b) emphasizing advances in resource recovery from mine drainage. The first section covers traditional and emerging passive and active treatment technologies. The second section summarizes resource recovery efforts using various technologies, such as selective precipitation, membrane process, and biological systems. PRACTITIONER POINTS: Significant progress continued to be made in the management of mine drainage and related issues. Recent remediation technology advances in mine drainage were presented. Technologies focusing on resource recovery from mine drainage were reviewed.

A combined chemical and phytoremediation method for reclamation of acid mine drainage-impacted soils

Production of acid mine drainage (AMD) and acid sulfate soils is one of the most concerning environmental consequences associated with mining activities. Implementation of appropriate post-mining AMD management practices is very important to minimize environmental impacts such as high soil acidity, soil erosion, and metal leachability. The objective of this study was to develop a cost-effective and environment-friendly "green" technology for the treatment of AMD-impacted soils. This study utilized the metal-binding and acid-neutralizing capacity of an industrial by-product, namely drinking water treatment residuals (WTRs), and the extensive root system of a metal hyper-accumulating, fast-growing, non-invasive, high-biomass perennial grass, vetiver (Chrysopogon zizanioides L.) to prevent soil erosion. Aluminum (Al)-based and calcium (Ca)-based WTRs were used to treat AMD-impacted soil collected from the Tab-Simco coal mine in Carbondale, IL. Tab-Simco is an abandoned coal mine, with very acidic soil containing a number of metals and metalloids such as Fe, Ni, Zn, Pb, and As at high concentrations. A 4-month-long greenhouse column study was performed using 5% and 10% w/w WTR application rates. Vetiver grass was grown on the soil-WTR mixed media. Turbidity and total suspended solid (TSS) analysis of leachates showed that soil erosion decreased in the soil-WTR-vetiver treatments. Difference in pH of leachate samples collected from control (3.06) and treatment (6.71) columns at day 120 indicated acidity removal potential of this technology. A scaled-up simulated field study was performed using 5% WTR application rate and vetiver. Soil pH increased from 2.69 to 7.2, and soil erosion indicators such as turbidity (99%) and TSS (95%) in leachates were significantly reduced. Results from the study showed that this "green" reclamation technique has the potential to effectively treat AMD-impacted soils.