NOVELTY - Treating concentrated biogas slurry and discharging clear liquid comprises: (i) pre-treating biogas slurry discharged from an anaerobic reactor, utilizing the large particles and solid suspension in farmland as slag and treating the upper clear liquid; (ii) aerobically nitrifying the slurry and converting ammonium nitrogen to nitride nitrogen; (iii) carrying out membrane concentration for the nitrified water to obtain concentrated liquid, and discharging the liquid or recycling; (iv) regulating nutrients of the concentrated liquid to obtain an organic biogas nutrient liquid; (v) sterilizing.    USE - The method is useful for treating concentrated biogas slurry and discharging clear liquid.    ADVANTAGE - The method: converts ammonia nitrogen in the biogas slurry to nitrate nitrogen by nitrification, thus reducing the nitrogen content in water; improves nutrients in the concentrate liquid more than two times; and has high recovering rate of fresh water (80%), which can be recycled after sterilization. The device is economical, has high utilization rate of biogas slurry and standard discharge of liquid and is environmental friendly.    DETAILED DESCRIPTION - Treating concentrated biogas slurry and discharging clear liquid comprises: (i) pre-treating biogas slurry discharged from an anaerobic reactor, utilizing the large particles and most of solid suspension of the biogas slurry in farmland as slag, and treating the upper clear liquid; (ii) aerobically nitrifying the treated biogas slurry, converting the ammonium nitrogen to nitride nitrogen, and degrading the organic substance; (iii) carrying out membrane concentration for the nitrified water to obtain concentrated liquid, subsequently treating the concentrated liquid, and discharging the liquid after meeting the standard or recycling the liquid; (iv) regulating nutrients of the concentrated liquid to obtain an organic biogas nutrient liquid; (v) sterilizing, and flushing the poultry livestock with the sterilized liquid or discharging the liquid after meeting the standard. An INDEPENDENT CLAIM is also included for a device for treating the concentrated biogas slurry and discharging clear liquid, comprising: a biogas liquid depositing tank (1), a nitrifying tank (3), a membrane concentration tank (4), a concentrated liquid storage tank (13) and a fresh water storage tank (14). The upper clear liquid in the biogas liquid depositing tank is transferred to the nitrifying tank. The ammonium nitrogen in the biogas slurry in the nitrifying tank is converted to nitride nitrogen. The organic substance is removed partially. The biogas slurry enters to the membrane concentrated tank from the bottom after the biogas slurry is nitrified and converts the nitrogen in the nitrifying tank. The clear liquid is pumped by the membrane component and suction pump in the membrane concentrated tank and then enters to the clear liquid storage tank which is to be sterilized, is discharged or reused as flushing water. A concentrated liquid reflux and a drain hole is installed at the bottom of the membrane concentration tank and part of the concentrated liquid reflux to the nitrifying tank by the reflux pump is nitrified and part of the concentrated liquid is discharged to the concentrated liquid storage tank to regulate nutrients, thus the organic nutrient liquid is obtained.    DESCRIPTION OF DRAWING(S) - The drawing shows a schematic representation of the device for treating concentrated biogas slurry and discharging clear liquid.    Biogas liquid depositing tank (1)    Nitrifying tank (3)    Membrane concentration tank (4)    Concentrated liquid storage tank (13)    Fresh water storage tank (14)