Pollution of water by organic and inorganic contaminants is a serious environmental issue. The primary emphasis of this present investigation was to reduce wastewater pollution and environmental burden related to fish waste disposal. Prime pollutant parameters such as biological oxygen demand (BOD) and chemical oxygen demand (COD) in fish processing effluent were treated by adsorbents produced from waste fish scales viz., dried fish scale adsorbent and fish scale biochar. A control was used and the entire study was carried out in batch mode to assess the influence of adsorbent dosage levels, contact time, and pH conditions. The experiments revealed that prepared fish scale biochar was as effective as control in achieving a significant (p < 0.05) reduction of BOD (87%) and COD (84%) at 150 min treatment time with 0.24 and 0.48 g dosage level. The optimum pH range was found to be 6–8. The experimental data fitted well with pseudo‐second‐order and Langmuir isotherm models (R2 > 0.911). The influence of intraparticle diffusion in adsorption treatment was tested with Weber–Morris plot. The experiments were done in triplicate and all data were statistically tested using MS Excel, IBM SPSS (version 26), and OriginPro software packages.