TECHNOLOGY FOCUS - ORGANIC CHEMISTRY - Preferred Process: The biogas slurry outlet of the stock solution tank is higher than the sewage outlet height, after depositing, the biogas residue is left in liquid stock solution storage tank bottom, after depositing, the clear biogas passes through liquid outlet and is transmitted to the biogas mechanical filtering device and methane multi-medium filtering device to filter with biogas stock solution conveying pump, biogas deposited on the liquid stock solution bottom part is cleaned by raw liquid tank cleaning device while cleaning the inner part of whole liquid stock solution storage tank; and the cleaning sewage is discharged out of the raw liquid storage tank and enters into sewage processing factory for concentrated processing. The biogas slurry filter device is set on the biogas multi-medium filtering device and cross-flow ultrafiltration device, where the biogas multi-medium filtering device filters out molecular weight greater than 25 Dalton of substance, the liquid cross-flow ultrafiltration permeates liquid and then condenses and separates. The ultrafiltration device adopts cross-flow method to concentrate and separating. The concentrated and separated element has a molecular weight of greater than 15 Dalton and is used as raw material for liquid fertilizer. The aromatic polyamide membrane element filtering device adopts three sections of separating method, where the slurry enters a first separating section, concentrated solution enters a second section of further concentrating and separating, the generated concentrated solution enters a third section of the concentrating and separating, the generated concentrated solution of the concentrated biogas liquid is stored in the storage tank, and the solution produced in the first section, second section and third section by the water purifying tank is used as washing. Water for cleaning all the device and pipeline is produced from the concentration and separation device consisting of aromatic polyamide membrane components. A certain amount of water pressure is provided inside the connecting pipeline for cleaning. ACTIVITY - Fertilizer.