Effects of Potassium, Magnesium, Zinc, and Manganese Addition on the Anaerobic Digestion of De-oiled Grease Trap Waste

Dosage of nutrients for anaerobic digestion is essential to maintain their treatment performance. Kitchen waste generally contains low concentrations of nutrients, especially metals. However, for de-oiled grease trap waste (GTW), such a kitchenwaste, little data are available in terms of nutrient supplementation to enhance anaerobic digestion. In order to determine the effects of different concentrations of metals on anaerobic digestion of de-oiled GTW and the optimal metal dosages, a step-wise batch experiment for four metals, potassium (K), magnesium (Mg), zinc (Zn), and manganese (Mn), with a blank test as control, was conducted to gradually lower the concentrations of metals. The supplementation of individual K, Mg, Zn, and Mn did have effects on enhancing the process to different extents. The appropriate concentrations of investigated metals for accelerating anaerobic digestion of de-oiled GTW were as follows: K 720.2 mg/g COD, Mg 47.3 mg/g COD, Zn 1.1 mg/g COD, and Mn 11.6 mg/g COD, respectively. The requirements of four metals obtained in the experiment agreed with the results of theoretical calculations.