This study demonstrates the feasibility of sequentially producing both hydrogen and methane from wastewater sludge using a clostridium. strain, as was isolated by Wang et al. (2003a). Three commonly used pre-treatments were applied to wastewater sludge to increase the hydrogen yield. Then, the waste liquor was externally dosed with methanogenic bacteria to produce methane. The waste liquor after fermentation of hydrogen produced more methane than was directly derived without fermentation of hydrogen. The reduction of nitrogen-containing organic matter is shown to compete with the formation of hydrogen, yielding ammonium nitrogen (NH3-N) in the fermented liquor.