Study of biogas slurry concentrated by reverse osmosis system: characteristics, optimization, and mechanism

Biogas slurry, also called liquid digestate, refers to the liquid part of the anaerobic digestate produced from the anaerobic digestion process, which is an environmental pollution source if it is discharged without proper treatment. To recover the nutrients in the biogas slurry, a membrane system was designed to concentrate in the work. The effects of pretreatment technology including gravity settling and ultrafiltration process were studied via analyzing the chemical oxygen demand (COD), ammonia nitrogen (NH₃-N), total nitrogen (TN), and conductivity. Reverse osmosis was applied in the biogas slurry concentration. The performance of reverse osmosis membrane used in the concentration process was studied by analyzing the permeate and concentrate (retentate), the volume reduction factor, and the concentration factor. The suitable parameters were selected as 20.0-25.0°C for influent temperature, 0.8-1.0Mpa for operating pressure, and 6.0-8.0 for influent pH. Furthermore, the feasible concentration factor was evaluated as 4. The economic, environmental, and social benefits could be gained if (concentrated) biogas slurry was used as a substitute for chemical fertilizers.