TECHNOLOGY FOCUS - ORGANIC CHEMISTRY - Preferred Materials: The organic material is of animal origin. It is fish or fish waste, or fowl or fowl waste. It is a material of plant origin including a cultivated plant or cultivated plant waste, e.g. cabbage, potato, or potato peel. It is a material of microbial origin, e.g. yeast or yeast waste.Preferred Method: The bioconversion is a pressurized process. It is carried out at pressure which is over the atmospheric pressure, or at a pressure of 1.2-6 bar, preferably over 2 bar. The bioconversion is an unpressurized process. The second reactor is pressurized. The pressure in the second reactor is over 1.8 bar. The organic material is stored in acidic or basic conditions prior to carrying out the bioconversion. The bioconversion is mesophilic or thermophilic. The bioconversion is carried out by microorganisms existing in the organic material or by added microorganisms. It is carried out in anaerobic conditions. At least two reactors are employed, one of which is used for the bioconversion and the other is used for biogas cleaning. The reactor in which the biogas is cleaned contains ammonia or a mixture of organic material and ammonia. The ammonia was produced in the hydrolysis of the organic material.Preferred Components: To the first reactor, where the bioconversion takes place, is added buffer solution and optionally organic partly hydrolyzed material from the second reactor. The formed buffer solution contains ammonium bicarbonate or ammonium carbonate and free ammonia and/or carbonic acid at the ratio of 1:10.    TECHNOLOGY FOCUS - MECHANICAL ENGINEERING - Preferred Apparatus: The equipment further includes a pipe for introducing the organic material into the first reactor, a pipe for discharging the biogas from the first reactor, and a pipe for removing the partly or completely hydrolyzed product from the first reactor. The reactors can be vats, containers, or pipes. EXAMPLE - To a reactor having a capacity of 300 l was introduced organic material that contained 18.8 kg bone flour, 28.9 kg fish, and 3.8 kg genetically manipulated yeast and 20 l inoculum which contained own microbes of different fishes and yeast. The pressure in the reactor was 2 bar. The pH in the reactor was 8.2. The total ammonium content was 9200 mg/l. The ammonium ion content was calculated to be 8700 mg/l and the content of carbonates was 46300 mg/l. The alkalinity and phosphate content were determined to be 3200 and 1200 mg/l, respectively. The amount of composition of the biogas obtained from the reactor was measured. On the following day the reactor yielded 109.4 l/day of biogas containing 74.6% methane and 20% carbon dioxide.