Concentrating process of liquid digestate by disk tube-reverse osmosis system

The utilization of liquid digestates from centralized biogas plants commonly used in the agricultural sector of China is limited by the high transportation and storage costs resulting from their extremely large volumes. A pilot-scale disk tube-reverse osmosis (DT-RO) system was set up in the biogas plant of a poultry farm to test the efficiency of the concentrating process. This set up was operated for 1 year to optimize the system and evaluate membrane fouling. The liquid digestate volume remarkably decreased by about 25%, with a concentration factor of 4 under an operation pressure of 45 bar to 55 bar. Nutrients and mineral elements were simultaneously accumulated and total nitrogen and total phosphorus increased by 4.2 and 4.4 times, respectively. The total amino acid in the concentrated digestate reached 4.93 g/L. SEM-EDS analysis showed that membrane fouling was an integrated result of inorganic and organic fouling.