BACKGROUNDOil palm shell (OPS) is a biomass widely available from palm oil mills. Self-purging microwave pyrolysis (SPMP) was performed to produce carbon-rich biochar from OPS for the adsorption of methylene blue dye. The effect of feedstock amount on the pyrolysis temperature, yield and characteristics of the biochar were investigated. RESULTThe amount of feedstock was directly proportional to the final pyrolysis temperature. The pyrolysis reached a maximum final temperature of 760 degrees C when 300g of OPS was loaded into the reactor without microwave absorbent. A heating rate of up to 105 degrees C min(-1) was recorded, producing a yield of 40wt% of biochar at a short processing time of 20min. The biochar obtained at 700 degrees C showed relatively low volatile matter (24wt%), higher fixed carbon content (66wt%), carbon (78.5wt%), oxygen (17.7wt%), a highly porous structure with high BET surface area of 410m(2) g(-1) and pore volume of 0.16cm(3) g(-1), and recorded a methylene blue dye adsorption efficiency of 20mg g(-1). CONCLUSIONThe SPMP approach showed exceptional promise to produce biochar with low H/C ratio (0.5) and O/C ratio (0.2), which indicated a high degree of carbonization and stability of the biochar to act as a durable agent in wastewater treatment. (c) 2018 Society of Chemical Industry