Comparison of the removal of COD by a hybrid bioreactor at low and room temperature and the associated microbial characteristics

► The hybrid bioreactor (HB) can cultivate and foster cryophil microorganisms. ► The HB can efficiently remove organic matters at low- and room-temperature. ► The dehydrogenase activity in low temperature HB is high. ► The functional diversities of microorganisms in low temperature HB are high.