Abstract: Contaminated covered plastic waste material in the form of used Petri dishes, so-called agar plates, is rendered harmless and cleaned by placing the agar plates in a bacterium-tight heating chamber maintained substantially at atmospheric pressure and contacting them with water at an elevated temperature, preferably 90.degree.-98.degree. C. for a predetermined period of time. After the predetermined period the agar plates are rinsed with water which is then drained off through an outlet in the bottom of the heating chamber. The agar plates to be treated are loaded into the heating chamber in batches contained in bags wholly or partly consisting of a plastic material which is solid and substantially insoluble in water at room temperature but soluble in water at the elevated temperature.

Abstract: Contaminated plastic waste material in the form of used Petri dishes, so-called agar plates, is rendered harmless and cleaned by placing the agar plates in a bacterium-tight heating chamber maintained substantially at atmospheric pressure and contacting them with water at an elevated temperature, preferably 90.degree.-98.degree. C. for a predetermined period of time. After the predetermined period the agar plates are rinsed with water which is then drained off through an outlet in the bottom of the heating chamber. The agar plates to be treated are loaded into the heating chamber in batches contained in bags wholly or partly consisting of a plastic sheet material which is solid and substantially insoluble in water at room temperature but soluble in water at the elevated temperature.