Development of a fabricated first-flush rainwater harvested technology to meet up the freshwater scarcity in a South Asian megacity, Dhaka, Bangladesh.

The scarcity of freshwater in most of the megacities in the world is an important concern. In this regard, scientifically harvested rainwater could provide an effective measure to this crisis. In this attempt, we developed a cost-effective sensor-based automated first-flush rainwater harvesting system (RHS) to improve the freshwater scarcity and economic development of megacities like Dhaka, Bangladesh. To investigate the performance of the developed system, a suit of representative rainwater samples was systematically collected, preserved, and assessed between the months of July-December 2021 for water quality parameters such as physicochemical (pH, EC, TDS, DO, hardness, and alkalinity), anions (F-, Cl-, NO2 -, NO3 -, Br-, and SO4 2-), elemental (Ca, Mg, Cr, As, Cd, Hg, Pb, Be, Ni, Se, and Fe), and microbial contamination analysis. A Multiparameter digital meter and a titrimetric method were employed for measuring the physicochemical properties whereas elemental concentration was detected using an inductively coupled plasma-mass spectrometer and atomic absorption spectrometer. The changes in microbial contamination in the preserved rainwater were investigated from time to time during the whole experimental period. The findings showed that the mean pH (6.90) and concentrations (mg/L) of other concerning parameters such as TDS (15.5), DO (7.26), hardness (14.9), Cl- (3.59), NO3 - (4.84), SO4 2- (4.62), Fe (<0.2), Cr (0.086 µg/L), As (0.224 µg/L), Cd (0.260 µg/L), Hg (0.270 µg/L), and Pb (5.530 µg/L) in the harvested rainwater samples were below the WHO drinking water guidelines and literature data implying that the harvested rainwater derived from the developed RHS is completely safe for drinking and other uses even in respect to the microbial contamination (total bacterial counts: 0-15 CFU/mL, and total and fecal coliform less than 1.8 MPN/100 mL) for long storage. Hence, this technology has a huge opportunity to mitigate safe freshwater scarcity and groundwater depletion issues, especially in megacities such as Dhaka, Bangladesh.

Corrigendum to "Development of a fabricated first-flush rainwater harvested technology to meet up the freshwater scarcity in a South Asian megacity, Dhaka, Bangladesh" [Heliyon 9 (1) (January 2023) Article e13027].

[This corrects the article DOI: 10.1016/j.heliyon.2023.e13027.].

Wrinkled Flower-Like rGO intercalated with Ni(OH)2 and MnO2 as High-Performing Supercapacitor Electrode.

This study reports a simple one-step hydrothermal method for the preparation of a Ni(OH)2 and MnO2 intercalated rGO nanostructure as a potential supercapacitor electrode material. Having highly amorphous rGO layers with turbostratic and integrated wrinkled flower-like morphology, the as-prepared electrode material showed a high specific capacitance of 420 F g-1 and an energy density of 14.58 Wh kg-1 with 0.5 M Na2SO4 as the electrolyte in a symmetric two-electrode. With the successful intercalation of the γ-MnO2 and α-Ni(OH)2 in between the surface of the as-prepared rGO layers, the interlayer distance of the rGO nanosheets expanded to 0.87 nm. The synergistic effect of γ-MnO2, α-Ni(OH)2, and rGO exhibited the satisfying high cyclic stability with a capacitance retention of 82% even after 10 000 cycles. Thus, the as-prepared Ni(OH)2 and MnO2 intercalated rGO ternary hybrid is expected to contribute to the fabrication of a real-time high-performing supercapacitor device.