Anaerobic digestion of cattail with rumen culture in the presence of heavy metals.

The anaerobic digestion of cattail by rumen cultures in the presence of Cu(II), Cd(II) or Cr(VI) was investigated in this study. Three cases were respectively observed for the different metal dosages: promoted cattail degradation and methane production at a low heavy metal concentration, e.g., Cu(II) 2.4 mg/l, Cd(II) 1.6 mg/l, Cr(VI) 4.0 mg/l; reduced cattail degradation efficiency and methane production at a middle metal level; a severe inhibition to the cattail degradation at a high heavy metal dosage. The inhibition kinetics of Cu(II) on the digestion of cattail by rumen cultures was also analyzed and a simplified Andrews equation was used to describe such an inhibition. The inhibition constants for Cu(II) on the degradation of cattail, production of volatile fatty acids and formation of methane were estimated as 7.4, 9.5 and 6.4 mg/l, respectively. Comparative experimental results suggest that the order of toxicity degree of the tested metals on the rumen cultures was: Cd(II) > Cu(II) > Cr(VI).