Fig. 6

Methane production at different wall-shear stresses, COD = 400 mg/L. The methane production was shown. At seven wall-shear stresses, the average methane production were 0.93, 1.32, 1.63, 1.80, 2.04, 1.93 and 1.48 mg/(L wastewater day), respectively. Methane production increased with the increase of wall-shear stress until the wall-shear stress reached 1.45 Pa. The maximum methane production was 2.04 mg/(L wastewater day) and the minimum methane production was 0.93 mg/(L wastewater day)