PURPOSE: To improve purification efficiency of crude liquid due to microorganism and to enhance the effect for separating and removing microorganism by charging 1W 15vol% basing on the volume of a reaction tank of small piece chaped material having ≤10mm size and a specifeid specific gravity to crude liquid contg. org. substances contained in a batch type microbiological reaction tank.

CONSTITUTION: After filling a reacting tank with crude liquid to a normal high liquid level through a crude feeding pipe 6, dispersion of air or dispersion of air in combination with stirring is performed to disperse small piece shaped material in the tank uniformly. When ≥50% of soluble org. hydrocarbon compds. contained in the crude liquid in the tank is decreased by oxidation and assimilation by the effect of aerobic microorganisms sticking to the surface of the small piece shaped material, dispersion of air and stirring of the liquid are cased and lumps of microorganisms stripped off the small piece shaped material are settled to the bottom of the tank. Then, about 50W80% of the liquid in the tank is drawn as purified liquid through a discharge pipe 7, and 0.1W 1% of the liquid in the tank is drawn together with excess sludge through a sludge discharge pipe 10.