NOVELTY - The brick biogas system comprises an elongated tank forming an elongated internal digester chamber, and an expansion chamber above a top tank half that is separated from the digestion chamber and is in fluid connection with the digestion chamber via an outlet channel (4). The tank comprises a front end section, multiple intermediate sections and a back section in its longitudinal direction. The front end section, the multiple intermediate sections and the back section: bound the digestion chamber; and comprises flanges that are coupled against each other.    USE - Used as a brick biogas system.    ADVANTAGE - The brick biogas system can be easily and economically produced in an efficient manner.    DETAILED DESCRIPTION - The brick biogas system comprises an elongated tank forming an elongated internal digester chamber, and an expansion chamber above a top tank half that is separated from the digestion chamber and that is in fluid connection with the digestion chamber via an outlet channel (4). The tank comprises a front end section, multiple intermediate sections and a back section in its longitudinal direction. The front end section, the multiple intermediate sections and the back section: bound the digestion chamber; and comprises flanges that are coupled against each other. The intermediate sections comprise multiple intermediate segments, which are positioned in series around the longitudinal axis of the tank. The intermediate segments comprise flanges at the meeting ends, and a deformable seal strip. The deformable seal strip: is formed as unity with the flangel; and extends oblique from the flange with its distal end towards the digestion chamber. The expansion chamber is open at the upper side. The open upper side is larger than the outlet channel in horizontal direction. The expansion chamber is bounded by a circumferential wall that extends upright from the tank. The circumferential wall comprises a free extending upper edge that bounds the open upper side of the expansion chamber, and wall segments that are coupled against each other. Transitions between the wall segments coincide with the transitions between the intermediate sections. The tank comprises an upper wall that bounds the upper side of the digestion chamber and the lower side of the expansion chamber. The outlet channel extends downwards from the upper wall into the digestion chamber. The flanges at the meeting ends of the intermediate sections extend below the lowest end of the outlet channel in vertical direction. The tank comprises an inlet channel (5) that extends downwards from the upper wall into the digestion chamber. The inlet channel is spaced apart from the outlet channel in the longitudinal direction of the tank. The outlet channel is: separated from the expansion chamber; and upwardly extended by the circumferential wall that is located inside the expansion chamber. The inlet channel extends deeper inside the digestion chamber than the outlet channel in downward direction. The intermediate tank sections form a cylindrical circumferential wall of the tank, which comprises a top tank half and a bottom tank half having horizontally extending flanges that are coupled against each other. The top tank half comprises a front top segment, multiple intermediate top segments and a back top segment having vertically extending flanges that are coupled against each other. The bottom tank half comprises a front bottom segment (20), multiple intermediate bottom segments and a back bottom segment (30) having vertically extending flanges that are coupled against each other. The intermediate top segments and the intermediate bottom segments are identically formed. The sections comprise a continuous insertion chamber along the flanges. The insertion chambers of the coupled flanges are positioned straight opposite each other. A common resilient sealing is inserted in the opposite insertion chambers. The sections comprise a wall section between the flanges, and an U-shaped insertion profile for the sealing between the wall section and its flange. The wall section connects to the back of the U-shaped insertion profile, and the flange forms a continuation of legs of the U-shaped insertion profile. The resilient sealing comprises an elongated base strip having sealing flaps along the length of the base strip that extend sideways from the base strip. The base strip and the sealing flaps are in cross section configured as arrow heads that point outside. The flanges are coupled by multiple couplings that are evenly distributed along the flanges. The couplings comprise a coupling pin having a coupling head and a coupling shaft extending from the coupling head. The flanges comprise sets of aligned holes. The coupling shaft is inserted. The couplings comprise a wedge having two wedge legs to accommodate the coupling shaft in between the two wedge legs. The wedge legs and the coupling shaft comprise locking edges that incline with respect to the longitudinal axis of the shaft. The locking edges are barbed shaped to enable the accommodation of the shaft between the wedge legs and to counteract disengagement. The coupling head has a convex shape and is configured to be biased towards a flatter shape, when the wedge is tightened.    DESCRIPTION OF DRAWING(S) - The figure shows a schematic view of a modular biogas tank.    Open expansion chamber (3)    Outlet channel (4)    Inlet channel (5)    Front bottom segment (20)    Back bottom segment. (30)