A combined treatment of sewage and/or waste water, sludges and shredded domestic biodegradable waste comprises, after physical pre-treatment, e.g. grease removal: (i) a first waste water and/or sewage liq.-solid sepn.; (ii) a prim. biological treatment; (iii) a second waste water liq.-solid sepn.; (iv) a sec. biological treatment; (v) anaerobic hydrological treatment of the sludges produced and the waste, after removal of wooden components and (vi) anaerobic methane fermenting treatment of the sludges and the waste. Also claimed is a device for carrying out the above method which provides changing sludge levels, due to the accumulation and release of the biogas in the anaerobic fermentation reactor, to transport the floating sludge to a blow-off device.    The device is pref. a fixed dome plant with a funnel as bottom to avoid the accumulation of solids. The device is pref. built around and/or under a liq.-solid separator but separated by a tank in between. The tank pref. functions as an hydrolysis and/or inlet device. The liq.-solid separator is pref. a Dortmund Tank. Prim. sewage sludge and sec. bacterial sludge are pref. sedimented in one Dortmund Tank, divided vertically by a wall. The prim. waste water treatment device is pref. on the separator. The device may be in the form of a closed tower with pref. only one air inlet. The device pref. has combined denitrification and phosphorous retention with an anaerobic fixed bed or soil filter made of Goethite, Hematite or other minerals iron-active surfaces. The device is pref. and area covered with a transparent cover with a slope upwards towards the direction of the intended airflow.    USE -   The method is used for treating the organic waste of domestic settlements, both liq. and solid.    ADVANTAGE -   The treatment of domestic sewage and anaerobic treatment of domestic biodegradable waste are combined in one device. There is maximised use of solar thermal energy and the gassing pressure energy of the biogas. There is low space requirement, and low construction and running costs.