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In this work, the adsorption of polycyclic aromatic hydrocarbons (PAHs) from aqueous solution by rice husk activated carbon (RHAC) was compared with adsorption using conventional, powdered activated carbon as the adsorbent. The adsorbent capacity of RHAC was found to be higher than all other agricultural and industrial adsorbents evaluated. The kinetics of PAHs was similar even after 24 hours. The removal of PAH occurred in the following order: naphthalene < phenanthrene < pyrene. Our study results show that molecular weight and solubility play vital roles in the adsorption of PAH on RHAC. The study results pointed to the occurrence of an intra-particle mechanism in all cases. The isotherm models that best represented the data obtained were Freundlich for naphthalene, Redlich-Peterson for phenanthrene, and Langmuir for pyrene. The results of this study were compared with previous studies.

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Biochar derived from agricultural biomass waste is increasingly recognized as multifunctional material for various applications according its characteristics. It is therefore essential to investigate biochar properties before large-scale application. In this study, rice straw-derived biochars produced at different temperature (550, 650, 750 o C). The resulting biochars were subjected to liquidphase oxidation by different agents including KOH, HNO 3 , H 2 SO 4 , H 2 O 2 and KMnO 4 to obtain biochar with different properties. Pore structure characteristics including surface area, micro and meso pore volume, and pore size distribution were studied. Biochar surface is sensitive to the type of modifying reagent. Biochars treated by KOH, KMnO 4 and H 2 O 2 give higher nitrogen uptake in the range of micropores and mesopores. The rice straw-derived biochars especially produced at 650 o C and treated by KOH have the highest surface area (179.7 m 2 /g) and micropore volume (0.081 cc/g) than the rest of biochars. In contrast, biochars treated by H 2 SO 4 and HNO 3 give lower nitrogen uptake and lead to loss of the biochars porosity. Loss of micropore volume is as low as 10-40% of pore volume in H 2 SO 4 and HNO 3 treated biochars. Biochars exhibit wide pore size distribution, from narrow micropores to wide mesopores. One modal distribution was obtained with peak oscillate in region of 1.0 to 1.3 nm in the case of micropore region. However, for mesopore region, two minima at about 3.0 nm and 5.0 nm were observed. More homogonous micropore distribution was produced from KOH and H 2 O 2 treatment in contrast to that of HNO 3 and H 2 SO 4 treatment, which give heterogeneous micropore distribution.

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