A system and method integrating treatment of waste, polar Fats/Oils/Greases (FOG) with conventional anaerobic wastewater treatment facilities for biologically fueling digestion of solids in, and steady state production of methane from treated wastewater streams that includes a slipstream loop circulating warmed, actively digesting sludge from the base to the head of the anaerobic wastewater treatment facility, a conditioning tank with input screened by a rock trap, actively digesting sludge pumped from the slipstream loop into the tank via the rock trap, before and after FOG wastes are pumped from a hauler tank via a hose connecting to the rock trap into the conditioning tank and mixed with actively digesting sludge in the tank to produce a feedstock slurry rich in volatile fatty acids for injection at a metered rate back into the actively digesting sludge slipstream loop for introduction at the head of the anaerobic wastewater treatment facility.