Sustainable treatment of the dye wastewater generated from unorganized small-scale units using an economical ceramic clay-bimetallic MOF filter

The discharges of unused and waste dyes generated from scattered and unorganized small-scale units in surface water bodies have been adversely affecting aquatic and human life from time immemorial. Collecting and treating dye-laden wastewater (50–100 L/unit/day) from such installations is a formidable challenge for municipal wastewater treatment plants, as they are mostly dispersed in near and far away surroundings. This study reports the development of a cheap decentralized two-step technique comprising coagulation-flocculation and filtration by adsorption (FeAl(BDC) MOF) to treat such wastewater at the point of generation for possible reuse or direct discharge. Progressively, the limitations of the FeAl(BDC) with application in a continuous flow, recovery, and reuse led to the development of a hollow clay-based ceramic filter. The hollow cavity of the ceramic filter was filled with a FeAl(BDC): Sand (1:9) mixture weighing 11.9 ± 0.5 g. The first stage reduced turbidity (<5 NTU) and Chemical Oxygen Demand (COD) by 75 % but did not meet reuse or direct discharge specifications. The second stage experimental setup was run in two filtration modes: gravity and pressure. Both the filtration modes reduced the turbidity, colour, and COD by 96–98 %. However, gravity mode was found to be more economical. Further, the sludge and spent-FeAl(BDC) were safely disposed of in a cement-flyash brick with prospects of minimal leaching. Overall, the study presents a cradle-to-grave approach for economically and effectively treating dye-laden wastewater from small-scale industries with a safe and sequestrated disposal strategy.