Bentonite hydrochar composite for removal of ammonium from Koi fish tank

• High adsorption capacity bentonite hydrochar composite was developed.
• Bentonite hydrochar composite was prepared under CO2 atmosphere.
• The composite could completely remove the ammonia from the Koi fish tank.
• Adsorption mechanism of NH3 onto composite was dominated by ion exchange process.

The work is concerned with a bentonite hydrochar composite made from bentonite and cassava peel. Bentonite was obtained from a Ponorogo deposite, Indonesia, and cassava peel was agricultural waste. The preparation of the composite was carried out at 500 °C under a flow of carbon dioxide. The sample was characterized by argon adsorption at 87 K, X-ray diffraction, scanning electron microscope, and Fourier transform infrared spectroscopy methods. The adsorption of ammonium from the solution was conducted in a batch condition at 30 °C. The dynamic condition was employed in the removal of ammonium from Koi fish tank. Biochar and bentonite hydrochar composite samples had microporous structure whereas the bentonite in the composite possessed mesoporous structure. Langmuir and Freundlich adsorption isotherms were used to correlate the experimental data of adsorption of ammonium from Koi fish tank. The results indicated that the Langmuir equation described the adsorption experimental data well. Combination between van der Waals force and ion exchange increased the adsorption of ammonia onto the bentonite hydrochar composite. Adsorption of ammonia in a real aquaculture system indicated that the composite could completely remove the ammonia from the Koi fish tank within 60 min.

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