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ABSTRACT Composition of the biomixture is crucial for the success of a bio-purification system. The rice straw-compost biomixture （BM） was mixed with the rice husk ash （RHA, 5 and 10%）, sugarcane bagasse ash （SBA, 5 and 10%） and wheat straw biochar （WBC, 1, 5 and 10%） and adsorption of atrazine and fipronil was studied. Fipronil was more sorbed than atrazine in all biomixtures. Both ashes and biochar increased sorption of atrazine, but the effect varied with the level of the amendment. The adsorption coefficient （Kd） values for atrazine in biomixtures were 6.82 （BM）, 8.64 （RHA5%）, 8.80 （RHA10%）, 7.26 （SBA5%）, 7.66 （SBA10%）, 8.26 （WBC1%）, 26.79 （WBC5%） and 46.68 （WBC10%）. Ashes did not have much effect of fipronil sorption [48.92 （BM）, 49.68 （RHA5%）, 54.04 （RHA10%）, 45.35 （SBA5%）, 46.11 （SBA10%）]; however, WBC1% biomixture showed 100% fipronil sorption. The adsorption data were subjected to the Freundlich, the Langmuir and the Temkin isotherms. Among the three isotherms used for adsorption data modelling, the Freundlich isotherm best explained the pesticide sorption. This study suggested that ashes/biochar mixed rice straw-compost biomixtures can be exploited in bio-purification systems.
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