Acidogenesis of dairy wastewater produced volatile fatty acids, mainly acetate and propionate, plus hydrogen as by- product. Zinc (Zn) inhibited acidogenesis at concentrations over 10 mg l~-1; but at 10 mg l~-1, or less, it enhanced acidogenesis slightly. On the other hand, copper(Cu)inhibited acidogenesis at all tested concentrations ranging 5-400 mg l~-1. Production of acetate was inhibited by both metals at all concentrations; but production of propionate and hydrogen was favored at low concentrations of Zn(up to 80 mg l~-1) and Cu(up to 40 mg l~-1). Production of hydrogen corresponded with the degradation of carbohydrate and the production of propionate. Overall, Cu was 1.4-4.3 folds more toxic than Zn, according to the overall production patterns of fatty acids and hydrogen as well as degradation patterns of carbohydrate and protein.
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