WASTEWATER TREATMENT DEVICE AND WASTEWATER TREATMENT METHOD

摘要

Provided is a wastewater treatment device of which the denitrification ability can be kept high regardless of the load of inflowing wastewater. The disclosed wastewater treatment device includes, in the following order from the upstream side: a sedimentation-type solid-liquid separation tank (1) into which wastewater flows and in which the inflowed wastewater is separated into solid and liquid; an anaerobic treatment tank in which the treated water from the solid-liquid separation tank (1) is subjected to anaerobic treatment; an aerobic treatment tank (3) in which the treated water from the anaerobic treatment tank is subjected to aerobic treatment; and a circulation return path (17) that returns the treated water from the aerobic treatment tank (3) to the anaerobic treatment tank; wherein the wastewater treatment device carries out nitrification-denitrification treatment by circulating activated sludge between the anaerobic treatment tank and the aerobic treatment tank (3). The wastewater treatment device includes a sludge-concentration adjustment means that adjusts the concentration of sludge in the treated water transferred from the solid-liquid separation tank (1) to the anaerobic treatment tank in a manner such that the concentration becomes suitable for the nitrification-denitrification treatment, regardless of the load of the wastewater that flows into the solid-liquid separation tank (1).