TY JOUR TI IMPROVEMENT OF BIOGAS PLANT OPERATION MODES KW energy supply KW organic waste KW biogas KW fermentation KW biofertilizers KW ecology JO Vestnik of Kazan State Agrarian University AU Gayfullin, I.. AU Ziganshin, B.G. AU Haliullin, D.T. PY 2025 IS 20 PB Kazan state agrarian University