Development of low-cost natural adsorbent for the abatement of pollution from tannery effluent – A green technology

Tanneries are known to be one of the most polluting industries due to the generation of harmful contaminants at various stages, from the beam house to finishing. Each day, significant quantities of tannery wastewater containing contaminants like chromium salts are released into open areas, farmlands, rivers and other corpses of water. This practice poses a severe threat to the environment health, leading to extensive soil and water pollution. In this study, a biological material (scales of fish Catla catla) is employed as an adsorbent for biosorption of contaminants from tannery effluent. Every day a considerable amount of fish scales is generated and thrown away from the local fish market, which burdens the environment and causes environmental pollution. The primary emphasis of this study is to reduce wastewater pollution and the environmental burden of fish waste disposal. Two adsorbents were prepared by treating the dried fish scales with NaOH and Orthophosphoric acid to enhance the adsorbent properties by creating pores and roughness of the surface. Then, it was characterized using FTIR, SEM, and TGA analyses. After characterization, adsorbents were subjected to the adsorption of a standard chromium solution to detect the ideal adsorbent dose, contact time, and pH conditions of adsorption. The study's findings showed that during adsorption, the maximum uptake capacity of acid-treated adsorbent is found at pH 4 with an adsorbent dose of 20 g/L for a 60-minute contact time. That base-treated adsorbent is obtained at pH 2.50 with an adsorbent amount of 20 g/L for 4 hours of contact time. Then, the adsorbents were used to treat tannery effluents, and it was discovered that they successfully removed pollutants like chromic oxide, total suspended solids (TSD), total dissolved solids (TDS), BOD, COD, and others. The results indicated that the acid-treated adsorbent achieved optimal removal percentages for chromic oxide, BOD₅, COD, TDS, and TSS at 72.82%, 42.85%, 56.12%, 13.37%, and 35%, respectively. Thus, the study concluded that acid and base-washed fish scale adsorbents are affordable and straightforward to use adsorbents for removing pollutants from tannery effluent.