Enormous water-logging in ancient abandoned mining shafts of Kolar Gold Fields (KGFs), has largely induced the leaching of sulfide-rich gold minerals contaminating the aquifer system with hazardous elements. Transport of these contaminant has posed threat to the health of the urban population of Kolar township. A detailed survey of borewells, covering radius of 10 km of the KGF was carried out during pre and post-monsoon seasons and various parameters were assessed. Almost 80% of the water samples exceeded the regulatory limits of potable water criteria with excess arsenic (As; 12–127 μg/L), fluoride (F; <0.005 μg/L), dissolved salts (>500 mg/L). Water Quality Index (WQI) was used to understand the overall urban groundwater quality. At the centre of sampling circle core, mineral dissolution was found to be the function of pH, induced by acidophilic sulfur oxidizing bacteria. Modelling of predicted microbial metabolic pathways in metagenomics libraries using PICRUSt, indicated complex functional networks. High expression of siderophore proteins (> 2 cm halo in the chrome azurol test) caused Fe-sequestration, secondary Fe-mineral formation and subsequent release of As. Sulfide bearing Au-rich minerals (Arsenopyrite, Scorodite, Jarosite) were bio-weathered leading to release of H3AsO3+ at low pH, resulted in groundwater composition of Ca–HCO3 type and Ca–Na–HCO3 or Ca–Mg–Cl type.@en

Comparative analysis of hybridized microbial fuel cell (MFC) with constructed wetland systems (CW) as continuous and batch flow in with/without plant setups has been done. The sewage-generated WW was spiked with reverse osmosis (RO) concentrate [1:1] and was used as the substrate. The effects of RO-induced salinity and efficiency of wastewater (WW) biomass conversion to energy have been analyzed. The analysis was based on the removal of chemical oxygen demand (COD), total suspended solids (TSS), total dissolved solids(TDS), voltage generation, and energy recovery (NERs) to find out the performance efficiency of the four systems. Systems consisted of two batch setups with the downflow regime, batch setup with plant (BWP) and batch setup without plant (BWOP) and two continuous setups with the upflow regime, continuous setup with plant (CWP) and continuous setup without plant (CWOP). The maximum COD removal and energy recoveries in BWP, BWOP, CWP, and CWOP were 91.66%, 86.45%, 90.62%, and 83.33% and 6.20, 1.98, 0.98, and 0.72 W·h/kgCOD, respectively. The incorporation of RO concentrate positively influenced the performance of CW-MFCs by its induced salinity specifically in presence of Canna indica, thus increasing the energy output as indicated by the voltage generation and energy recoveries.@en