Nutrient removal from binary aqueous phase by dolochar: Highlighting optimization, single and binary adsorption isotherms and nutrient release

• Binary adsorption of nutrients on dolochar was inferred by multi component models.
• Reported phosphate and nitrate uptakes were 327.7 and 6.51 mg g−1, respectively.
• Quadratic models were established to evaluate nutrient removal efficiency.
• Optimization was done by ANOVA to maximize efficiency.
• Thin layer funnel analytical test labels dolochar as a slow release nutrient supplier.

The viability of utilizing sponge iron industry based waste ‘dolochar’ as a proficient adsorbent for nutrient (phosphate and nitrate) removal and subsequent slow release of nutrient from the spent dolochar has been undertaken in this study. The efficacy of dolochar has been explored in both single and binary adsorption systems containing nutrients. The proposed experimentally obtained quadratic models for both the phosphate and nitrate removal were substantiated by analysis of variance (ANOVA) with high R2 values of 0.99 and 0.98, respectively. Response surface methodology (RSM) based optimization followed by experimental validation resulted in phosphate removal efficiency of 96.7% and nitrate removal efficiency of 57.1%. Single component adsorption equilibrium data fitted well to pseudo-second order kinetic and Langmuir isotherm models with Langmuir maximum adsorption capacity, qm of 327.7 and 6.51 mg g−1 for phosphate and nitrate, respectively. Out of non-modified Langmuir, modified Langmuir, extended Langmuir and extended Freundlich, multi component isotherm models, binary adsorption equilibrium data fitted well to the extended Freundlich model. Thin layer funnel analytical test results reveals the slow nutrient release nature of spent dolochar. The results suggest that the dolochar has the potential to serve as a sustainable adsorbent for nutrient removal from wastewater along with the scope of utilizing spent dolochar as a slow release nutrient supplier.

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