Impact of nickel and zinc on degradation of organic waste

Abstract

The purpose of this research was to determine the impact of nickel and zinc on degradation of organic waste. This was accomplished by operating two laboratory-scale simulated landfill reactors with leachate recycle through both the acidogenic formation and methane fermentation phases of landfill stabilization. The batch anaerobic digesters were operated for 195 days. Initial conditions, such as quantities and compositions of organic waste as well as of anaerobic seeded, were kept the same for both reactors. Input organic waste consisted of vegetable and fruit wastes. After the onset of the acidogenic and methanogenic conditions in each reactor, nickel and zinc were added according to the amounts suggested for co-disposal under the directives of the Turkish Hazardous Waste Control Regulations. The leachate recirculation ratio of this experiment studied was divided into five stages (0%, 5%, 7%, 15%, and 25% of total moisture in system). The results of the experiments indicated that impact of nickel and zinc was seen on landfill stabilization process as indicated by leachate and gas production parameters, especially ORP, COD, methane percentage, and methane gas production. Moreover, the retention times of soluble nickel and zinc added during acidogenic phase and methanogenic phase were 179, 140 hours, and 71 and 57 hours, respectively. Heavy metal retention times and heavy metal effluent concentrations were compared. Nickel and zinc could stay in liquid phase for longer time and thus, remained toxic to microbial communities in the reactor that heavy metals were added during acidogenic phase. However, concentrations tended to decrease as a result of precipitation in either sulfide or carbonate form for both reactors.