TECHNOLOGY FOCUS - BIOTECHNOLOGY - Preferred Method: The nitrification process comprises nitrous acid type nitrification process for converting ammonia to nitrite using ammonium oxidizing bacteria, and denitrifying process for eliminating ammonia and nitrile using denitrifying microorganisms. The nitrate contained in the waste liquid is removed using heterotrophic denitrifying bacteria after the anaerobic ammonia oxidation process. The method further involves measuring concentration of ammonia contained in the produced liquid fertilizer and controlling the amount of waste liquid mixed with the liquid fertilizer after the methane fermentation based on the measured results such that the concentration of ammonia in the liquid fertilizer is within a predetermined range. The method further involves measuring concentration of nitrogen contained in the produced liquid fertilizer and controlling the amount of waste liquid processing amount in the nitrification and denitrification process based on the measured results such that the concentration of ammonia in the liquid fertilizer is within a predetermined range. The concentration of ammonia in the liquid fertilizer is 50-100 mg/l in winter season and 50 mg/l or less in summer season. The method further involves measuring the concentration of colloidal particulate suspended solid in the waste liquid in the nitrification process and/or denitrifying process, and controlling supply amount of the colloidal particulate suspended solid based on the measured result such that the colloidal particulate suspended solid concentration in the waste liquid is within a predetermined range. The nitrifying and denitrifying microorganisms are entrapped on immobilization support made of polymer gel. The concentration of colloidal particulate suspended solid is 1000-30000 mg/l. Preferred Apparatus: The apparatus comprises a flow path for connecting liquid fertilizer storage tank and nitrification tank and introducing the waste liquid in the storage tank into the nitrification tank, and another flow path for connecting oxidation tank and storage tank and introducing waste liquid processed in the oxidation tank into the storage tank. The apparatus further contains measurement unit for measuring the ammonia nitrogen concentration of the produced liquid fertilizer, and control units for controlling the amount of waste liquid mixed with the liquid fertilizer and controlling the waste liquid processing amount. The apparatus further has measurement unit to measures the colloidal particulate suspended matter concentration, and control unit for controlling the supply amount of the colloidal particulate suspended matter. ACTIVITY - Fertilizer. No biological data given.    MECHANISM OF ACTION - None given.