Liquid samples were collected from the nutrient media sump for the volatile fatty acids (VFA) and nutrient analysis. The nutrient analysis included NH 4 + , total nitrogen (TN), PO 4 3-, K + , and trace metals Fe, Ni, Co, and Mn. The VFA concentration was measured using GC (7890B, Agilent Technologies, Santa Clara, CA, USA) equipped with a flame ionization detector (FID) and a polyethylene glycol column (HP-INNOWax, Agilent Technologies, Santa Clara, CA, USA; 30 m × 0.25 mm × 0.25 µm). Samples for the VFA analysis were pretreated before the analysis, where 0.10 mL of phosphoric acid (85 wt %) and 0.5 ml of DI water were added with 0.5 mL of the sample. After that, the samples were centrifuged for 15 min (Eppendorf mini Spin), filtered through a 0.5 µm cellulose filter into GC vials, and then injected into the GC. NH 4 + , TN, PO 4 3-, and K + were measured using a spectrophotometer and HACH Lange LCK cuvette test system (LCK-303 NH 4 + , LCK-338 TN, LCK-049 PO 4 3-, and LCK-228 K + ). Before the analysis samples were diluted 10-30 times to meet the measuring range of the LCK cuvette. Trace metals were measured by atomic absorption spectrometry equipped with a graphite tube atomizer (AAS, Agilent AA-200 series graphite furnace atomic absorption spectrometer, Agilent Technologies, Santa Clara, CA). AAS was calibrated using standard solutions from Agilent and hollow cathode lamp also from Agilent were used for each of the metals, Fe, Ni, Co, and Mn.