The performance of hybrid MBRs and the improvement of denitrification with the addition of alkali-treated cellulose as microbial carrier and carbon source were investigated in this study.Three kinds of natural celluloses were evaluated by batch experiments.Straw was selected to construct a hybrid MBR(Fig.1).Results showed that the effect of alkali treatment on the accessibility of carbon source was obvious,the COD release capacity of the three carriers increased from 136-178 mg g-1 to 250-323 mg g-1,and the denitrification potential increased from 112.04-157.94 mg g-1 to 233.82-250.69 mg g-1 as compared with the untreated groups.