Active acoustic piping that allows treatment of material flowing in a piping system is disclosed. Treatment of waste water and other fluids is enabled, where acoustic radiation operates on the flow material. An inner pipe has a plurality of transducer elements disposed on its external perimeter. A buffer zone around the transducer elements provides an acoustic impedance mismatch, which concentrates the acoustic energy into the flow material traveling in the inner pipe. Processes such as decontamination, flow unclogging, fluid and particulate mixing, particulate size reduction, and particulate separation are enabled. No pressure compensation scheme is required.