The adsorption of heavy metals in an acidogenic thermophilic anaerobic reactor

A two-phase, thermophilic anaerobic reactor was operated with a starch-based feed. Copper, zinc, nickel and lead (3 mM) were individually added to the feed each for a period of 30 h. The results were analysed to determine the extent of metal binding in the acidogenic, first-stage reactor and the degree of protection that this afforded to the traditionally more sensitive methanogenic phase. The results showed that zinc and nickel were not bound particularly well, that lead was bound very strongly and that copper had binding characteristics that were between these two extremes. When these findings were compared with an earlier study with a mesophilic sludge, zinc was shown to have a very different behaviour. A possible reason for this is given. An examination of the gas production by the methanogenic stage, in relation to the amount of metal reaching this stage, suggested that the phase separation did not offer any real protection from the toxic effects of heavy metals.