Application of direct contact membrane distillation process to treat anaerobic digestate

In this study, a membrane distillation process was applied to treat the digestate produced from the anaerobic digestion of livestock wastewater with a high concentration of suspended solids, chemical oxygen demand (COD), total nitrogen (TN), and phosphorus (TP). Laboratory scale direct contact membrane distillation was performed to observe the variation of flux and rejection rate of each component according to the transmembrane temperature, cross flow velocity, and pH of the feed solution. In 90-min distillation, almost no fouling occurred and the permeate flux increased from 4.2 to 38.8 LMH by increasing the transmembrane temperature from 20 to 60 degrees C and cross flow velocity from 0.09 to 0.27 m/s. In long term distillation, a constant flux of 17.5 LMH was maintained for the initial 24 h but then decreased gradually to reach 5 LMH in 72 h. The flux decline occurred more rapidly as the pH of feed solution increased from 7 to 8.5. More than 99% rejection of COD and TP were achieved regardless of the distillation condition and processing time. The rejection rate of TN was affected dominantly by the extent of cake layer formed on the membrane surface rather than the pH and temperature of the feed solution. (C) 2016 Elsevier B.V. All rights reserved.