Thermally modified fish scale as potential adsorbents for the remediation of nitrite, nitrate and ammonium ions in wastewater

The discharge of solid waste from various industrial units and its associated release of nutrient-rich wastewater affects aquatic ecosystem. Therefore the current study was undertaken to provide a first report about the adsorption potential of thermally modified fish scale adsorbents such as Dehydrated Fish scales (DFS), Fish Scale Biochar (FSB) and Activated Fish Scales (AFS) in reducing the concentration of nitrites, nitrates and ammonium ions in drain water. Prepared adsorbents were characterized with different analytical techniques such as FTIR, TGA, SEM, EDX and XRD. Adsorption capacities of adsorbents were examined as batch work by altering adsorbent dose, contact time and pH levels. Among the adsorbents, DFS exhibited significant (P < 0.05) and maximum removal percentage of nitrite (24.46%) and nitrate (26.18%) ions at 60 min contact time with 0.06 g dose level. About 33% reduction of ammonia was recorded in pH 10 using 0.12 g FSB at 60 min contact time. The experimental data fitted well with Langmuir isotherm and pseudo-second order models with maximum coefficient of determination (R-2) values (> 0.95). Influence of intra-particle diffusion resistance on adsorption of pollutants showed lower R-2 values (0.600-0.806) than other kinetic parameters. The thickness of boundary layer was determined (0.5-2.6 mg/g) for the prepared adsorbents. The economic feasibility of adsorbents used in this study (0.012 - 1.72 USD) was also calculated and compared with commercial activated carbon (1.82 USD). This study confirms that waste fish scales can be effectively employed as cost effective and eco-friendly adsorbents in the treatment of nitrogenous pollutants in wastewater.