Then Z08 biodegradation products of soybean wastewater were investigated. After 10 d biodegradation, COD in final effluent was 298 mg/L and major products of soybean wastewater biodegradation were acetic acid (30.9 mg/L), propionic acid (43.4 mg/L), butyric acid (85.3 mg/L) and valeric acid (2.2 mg/ L), and no alcohol or C1 acid was identified. The four short-chain organic acids counted 60% of COD, and the remaining 40% might come from complex macromolecules which were not identified. These short-chain organic acids were easily biodegradable, so the
reduction limit might be caused by the disproportion of nutrition or lack of trace elements.