Hybrid aerobic and anaerobic wastewater and sludge treatment systems and methods

A method of increasing the capacity of a wastewater treatment system having a biological treatment train with at least one biological reactor selected from the group consisting of an anaerobic reactor, an anoxic reactor, a contact tank, a sequencing batch reactor, and an aerobic reactor, a solids-rich outlet of the biological treatment train fluidly connected upstream of an inlet of an anaerobic digester distinct from the at least one biological reactor, the method comprising:

• directing a first fraction of a solids-rich sludge produced in the biological treatment train into an inlet of the anaerobic digester in an amount resulting in a concentration of methanogenic bacteria present in the solids-rich sludge produced in the biological treatment train being at least 10% of a concentration of methanogenic bacteria present in mixed liquor in the anaerobic digester;
• directing anaerobically digested sludge from an outlet of the anaerobic digester into an aerobic stabilization tank through a conduit fluidly connecting the outlet of the anaerobic digester to a first inlet of the aerobic stabilization tank;
• and
• directing sludge from an outlet of the aerobic stabilization tank to an inlet of the at least one biological reactor through a conduit fluidly connecting the outlet of the aerobic stabilization tank to the inlet of the at least one biological reactor.