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In this study, palm oil mill sludge was used as a precursor to prepare biochar using conventional pyrolysis. Palm oil mill sludge biochar (POSB) was prepared at different preparation variables, i.e., heating temperature (300-800 °C), heating rate (10-20 °C/min) and holding time (60-120 min). The prepared biochars were tested for sulfur dioxide (SO) adsorption in a fixed bed reactor using 300 ppm of SO gas at 300 ml/min (with N gas as balance). Response surface central composite experimental design was used to optimize the production of biochar versus SO removal. A quadratic model was developed in order to correlate the effect of variable parameters on the optimum adsorption capacity of SO gas. The experimental values and the predicted results of the model were found to show satisfactory agreement. The optimum conditions for biochar preparation to yield the best SO removal was found to be at 405 °C of heating temperature, 20 °C/min of heating rate and 88 min of holding time. At these conditions, the average yield of biochar and adsorption capacity for SO gas was reported as 54.25 g and 9.75 mg/g, respectively. The structure of biochar and their roles in SO adsorption were investigated by surface area, morphology images, infrared spectra, and proximate analysis, respectively. The characterization findings suggested that POSB adsorbs SO mainly by the functional groups.

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Rice husk was utilized into biochar by pyrolysis and used as adsorbent for ammonium removal. Rice husk biochar (RHB) was produced at temperature of 350°C, 400°C, 450°C, 500°C, and 550°C. Characteristics of biochar were analyzed by moisture content, ash content, pH Zero Charge and Fourier Transform Infrared (FTIR) Spectroscopy. As the temperature for the pyrolysis increases, the moisture content of RHB decreases while the ash content of RHB increases. From the pH zero charge analysis, the value obtained from analysis is pH 7. The FTIR spectra showed the organic part of RHB with different functional groups such as alkene, alcohol, phenol, ether, ester etc. Based on the result of the characterization test, RHB500 was chosen as the best biochar for the adsorption of ammonium. The equilibrium contact time was 180 minutes and the optimum adsorbent dosage was 0.1g and the optimum concentration of ammonium was 1.2 ppm. For the adsorption-desorption of ammonium, RHB can run up to 5 cycles for biochar regeneration. Adsorption kinetic, pseudo-second-order model is more preferable than pseudo-first-order model because R2 value is 0.9995 which closer to 1.

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