Abstract: The discharge of wastewater containing heavy metals is one of the major security risks for drinking water. The heavy-metal polluted waste water treatment has long been a focus for environmental protection researchers. The new Standard for Drinking Water Quality (GB5749-2006) reduces arsenic concentration from 0.05 mg/L to 0.01 mg/L. This paper studies the treatment of low concentration arsenic (Ⅲ) water, arsenic being a representative anion in industrial wastewater by applying spent grains modified by microwave as biosorbent. The optimal modified conditions of spent grains were low-fire microwave for 7 min. Arsenic removal rate reaches 99.4 % in the waste water (pH=9, modified spent grains 10 g/L, initial arsenic concentration 0.5 mg/L, biosorption reaction 30 min). The arsenic adsorption kinetics of microwave modified spent grains conforms to quasi-second kinetics equation.