TECHNOLOGY FOCUS - INSTRUMENTATION AND TESTING - Preferred Method: The fresh water led in the circuit exhibits a temperature of up to 65 degrees C. The stripping gas (exhaust gas) removed in the first cleaning stage from the first stripping column is either recycled to the fermenter of a biogas plant or conducted to the methane gas stream separated from the first washing stage or used as fuel gas. In the second purification stage, the methane is separated in two stages, where in the first stage, oxygen and in the second stage, stripping air or in reverse order, is fed, and two different fuel gases are obtained with different oxygen concentrations. The oxygen-rich fuel gas is used as a source of oxygen for biological desulfurization of biogas. The methane gas removed in the washing column either individually or together with the stripping gas removed from the first stripping column is fed to a further processing to increase the methane content. The supplied raw or biogas is adjusted to a sulfur content of less than 5 ppm before the discharge into the washing. After a certain operational duration, above 50 ppm of contaminated wash water removed during a concentration of the sulfur content in the washing step is replaced completely or partially by fresh water. A partial amount of the wash water removed at the bottom of the second stripping column is separated out, to which a hydrogen sulfide-binding reagent is added, and after the precipitation of sulfur sulfide, the wash water is recirculated. The separation efficiency for carbon dioxide dissolved in the wash water can be adjusted by means of the parameters of washing water amount and washing water temperature in the wash column, where a higher wash water amount and a deeper wash-water temperature lead to higher separation efficiency. The purified raw or biogas removed from the wash column is fed directly into the fermenter of a biogas plant to increase the methane concentration and the storage capacity of the biogas in the fermenter. False air is supplied for adjusting the vacuum in the third purification stage of the vacuum pump of the second stripping column. The false air supplied to the vacuum pump is preheated. The carbon dioxide gas separated from the stripping column is conducted to a condensation stage, in which water contained in the carbon dioxide gas is condensed at a partial pressure of less than 100 mbar. Preferred Components: A heat exchanger for cooling of the wash water is attached in the circuit line. The washing column and the two stripping columns exhibit same column diameter and different packing bulk height. The ratio of the bulk height of the washing step, first stripping column and second stripping column amounts to 3:0.5:1. The ratio of the packing surface of the first stripping column and second stripping column amounts to 1:0.2 to 1:0.8, preferably 1:0.5. The first stripping column is subdivided into two column sections, where each column section is equipped with a packed bed or packing and the upper column section is connected with oxygen feeding pipe and the lower column section is connected with an air feeding line. The washing column and the two stripping columns are arranged in a tower. The trays of the washing column and the stripping columns with respect to gas loading are technically dense and with respect to fluid loading are fully permeable. EXAMPLE - No suitable example given.