This study examined the effects of nickel on solid waste decomposition as well as its soluble concentrations during different times of addition. Three landfill reactors, loaded with 20 kg of waste, were used. Leachate recirculation was applied to all reactors, starting from Day 148. Nickel in the form of NiCl2 was added to the acid and methane reactors on Day 152 and 181, respectively. Leachate and gas parameters from all reactors exhibited similar trends during the first 151 days. Cumulative biogas production was356, 269, and 305 L for the control, acid, and methane reactors, respectively, indicating inhibition in the last two. Residence time of nickel in the acid reactor was more than two times that in the methane reactor (179 vs. 71 hours). Shorter residence time of soluble nickel during the methane phase addition may be responsible for better waste decomposition and could be beneficial for field application.
