2.5. Effect of heavy metals on digestion
The effects of some selected trace elements on biogas production were evaluated by adding varying concentrations (50–200 ppm) of ZnSO4, CuSO4 and NiCl2 to digesters containing 50 g of rice husk. 200 mL of these solutions were added to the digesters while the same volume of ordinary water was added to the control digester. Digesters were then inoculated with 50 mL of cow rumen liquor to initiate fermentation.