In contrast to the conventional UASB reactor ANUBIX™ – CES system, with a built-in three-phase separator at the top of the reactor which diverts the biogas and retains solids, in this reactor, sludge separation is performed externally in a special lamella type separator, the GWE SUPERSEP™ – CF. The effluent of the sludge separator flows by gravity into any post-treatment that might be required.