Activated carbon and wood chips were applied respectively as packing material of bio-trickling filter and bio-filter which composed the compound bio-filter and the effect of different operating parameters on NOx removal efficiency were studied. The results show that the best operating conditions of the compound bio-filter are: NO inlet concentration 604.5 mg/m(3), spray volume 1.2 L/h, gas flow 0.6 m(3)/h(empty bed residence time 103.7 s).In such cases,NOx removal efficiency is over 96% and NOx removal load of the packing material is 29.66 g/(m(3).h). The remove of NOx is mainly completed by the packing layer of 0 similar to 50 cm height both in the bio-trickling filter and in the bio-filter, that is to say,when the total packing layer height of the compound bio-filter is 100 cm, the purification effect is ideal and economical; The system can return to normal in about 7 hr when the dynamic load changes largely and suddenly, showing that it has strong anti shock load capacity.
