Biological reduction of sulphates has gradually replaced unit chemical processes for the treatment of acid mine drainage (AMD), which exerts a significant environmental impact due to its elevated acidity and high concentrations of heavy metals. Bioremediation is optimally suited for the treatment of AMD because it is cost-effective and efficient. Anaerobic bioremediation employing sulphate-reducing bacteria (SRB) presents a promising solution by facilitating the reduction of sulphate to sulphide. The formed can precipitate and immobilise heavy metals, assisting them in their removal from contaminated wastewater. This paper examines the current status of SRB-based bioremediation, with an emphasis on recent advances in microbial processes, reactor design, and AMD treatment efficiencies. Reviewed studies showed that SRB-based bioreactors can achieve up to 93.97% of sulphate reduction, with metal recovery rates of 95% for nickel, 98% for iron and copper, and 99% for zinc under optimised conditions. Furthermore, bioreactors that used glycerol and ethanol as a carbon source improved the efficiency of sulphate reduction, achieving a pH neutralisation from 2.8 to 7.5 within 14 days of hydraulic retention time. Despite the promising results achieved so far, several challenges remain. These include the need for optimal environmental conditions, the management of toxic hydrogen sulphide production, and the economic feasibility of large-scale applications. Future directions are proposed to address these challenges, focusing on the genetic engineering of SRB, integration with other treatment technologies, and the development of cost-effective and sustainable bioremediation strategies. Ultimately, this review provides valuable information to improve the efficiency and scalability of SRB-based remediation methods, contributing to more sustainable mining practices and environmental conservation. To ensure relevance and credibility, relevance and regency were used as criteria for the literature search. The literature sourced is directly related to the subject of the review, and the latest research, typically from the last 5 to 10 years, was prioritised.

The focus of this study was to improve the Reverse Osmosis Cooling (ROC) process by using CaCO₃ for neutralization and selective recovery of Fe(OH)₃ at pH 3.5. By using a specific inhibitor, ferric hydroxide was recovered separately from gypsum and other metals present in mine water. Ferric hydroxide was processed to pigment, a product that is imported and used as colorant in paints and tiles. In addition to pigment recovery, aluminum hydroxide and calcium carbonate can also be recovered from mine water. The following conclusions were made: (i) the rate of gypsum crystallization, in the absence of Fe³⁺, is influenced by the over saturation concentration in solution, the seed crystal concentration and temperature; (ii) gypsum crystallization from an over-saturated solution, in the presence of Fe(OH)₃ sludge, required an inhibitor dosage of 100 mg/L to keep gypsum in solution for a period of 30 min; (iii) gypsum crystallization from an over-saturated solution, in the presence of both Fe(OH)₃ sludge and CaCO₃ reactant, required a higher inhibitor dosage than 100 mg/L to keep gypsum in solution for a period of 30 min. A dosage of 200 mg/L kept gypsum in solution for the total reaction period; (iv) when only Fe(OH)₃ is present in the slurry, gypsum inhibition is more effective when Fe(OH)₃ sludge is allowed to settle after the initial mixing; (v) when both Fe(OH)₃ and CaCO₃ are present in the slurry, gypsum inhibition is more effective when the inhibitor is added over a period of time (10 min) rather than applying the total dosage at time zero; (vi) Fe(OH)₃ can be changed to yellow pigment (Goethite) by heating to 150 °C and to red pigment (Hematite) by heating to 800 °C. Pigment of nano particle size was produced; (vii) in the case of Na₂CO₃, the TDS increased from 12,660 mg/L in the feed to 13,684 mg/L due to the replacement of metal ions (Fe³⁺, Al³⁺, Fe²⁺, Mn²⁺ and Ca²⁺) with Na⁺ in solution. In the case where CaCO₃ was used for the removal of Fe³⁺ and Al³⁺, Ca(OH)₂ for the removal of Fe²⁺, Mn²⁺, and Na₂CO₃ for the removal of Ca²⁺, the TDS dropped from 12,661 mg/L to 2288 mg/L, due to gypsum precipitation. The alkali cost in the case of calcium alkalis amounted to ZAR29.43/m³ versus ZAR48.46/m³ in the case of Na₂CO₃.

The dynamic growth in green organic synthetic methodologies for diverse heterocyclic scaffolds has substantially contributed to the field of medicinal chemistry over the last few decades. The use of hybrid metal nanocatalysts (NCs) is one such benign strategy for ensuring the advancement of modern synthetic chemistry by adhering to the principles of green chemistry, which call for a sustainable catalytic system that converts reacting species into profitable chemicals at a faster rate and tends to reduce waste generation. The metal nanoparticles (NPs) enhance the exposed surface area of the catalytic active sites, thereby making it easier for reactants and metal NCs to have an effective interaction. Several review articles have been published on the preparation of metal NCs and their uses for various catalytic heterocyclic transformations. This review will summarize different metal NCs for the efficient green synthesis of various O-heterocycles. Furthermore, the review will provide a concise overview of the role of metal NCs in the synthesis of O-heterocycles and will be extremely useful to researchers working on developing novel green and simple synthetic pathways to various O-heterocyclic-derived molecules.

The water unavailability crisis in South Africa significantly contributes to socio-economic challenges affecting some of its underdeveloped former homeland areas. Limpopo province, which is predominantly rural, is nuanced by these challenges. The province is characterised by limited surface and groundwater resources, unevenly distributed, already overallocated and overused with limited scope for further development. At the same time, the province desperately needs high impact development to improve the socio-economic conditions of its communities. Water is the key resource required for those development initiatives to materialize. This study evaluates the water resources yield across the Limpopo District Municipalities. The mapping of the province’s water yield patterns across the five districts provides an insight into the extent of its water challenges and the cascading effects of this on developmental potentials of the province. The Pitman and Water Resources Yield Models were employed to achieve this. The total historical firm yield was estimated at 160.20, 39.84, 72.24, 125.79 and 120.96 Mm³/a for Vhembe, Capricorn, Waterberg, Mopani and Sekhukhune districts respectively. This study provides an insight into approaches that could be deployed by the districts to determine local water resources availability to support planned developmental projects while ensuring sustainable provision of water services to their communities.