Pressurized line presents peculiar problem
The treated effluent from all wastewater treatment plants across the country must meet local dissolved oxygen standards before discharging into receiving waters. A municipal facility in southern Mississippi, designed by Carollo Engineers, features a pressurized effluent line that discharges into a local river. Since the line is pressurized, the standard method for increasing dissolved oxygen—a cascade—is not a valid option.
The plant’s engineer chose a Mazzei  Injector aeration system for the maximum transfer of oxygen with the lowest possible energy usage and minimal operator involvement. The system includes two air injection skids (duty/standby), each of which consists of a booster pump, an injector, pressure gauges, a control panel, and a 6–in.-by-24-in. Pipeline Flash Reactor (PFR) .
A sidestream is taken off the effluent pipeline and directed through a booster pump and then through a 2-in. Mazzei Injector  to aspirate atmospheric air. The aerated sidestream is mixed back into the effluent pipeline through four nozzles in the stainless steel PFR. The aeration system’s control panel is designed to run the injection skid pump (which drives the aeration system) when the effluent pumps are operating.
The plant was activated in August 2010, and it has been meeting discharge dissolved oxygen limits with no problems ever since. The facility’s operators, who are responsible for maintaining several plants in Hancock County, appreciate the minimal maintenance and low operator involvement the system requires.