Plant History

The 1930’s witnessed new Public Works projects from the rapidly growing city of Hammond, Indiana. The Hammond Sanitary District was formed, by legislation, in 1938. Its sewage disposal plant, located at 5143 Columbia Avenue, was completed in 1941. In 1948, the town of Munster was added to the district’s jurisdiction.

In addition to treating wastewater form homes, the Hammond plant treats wastewater from businesses and industrial users in Hammond and Munster. It serves 150,000 people over a 50-mile geographic area, and is responsible for nearly 400 miles of Hammond sewers, including the contract communities of Whiting, Highland, and Griffith. District operations are financed by a user-fee charged to all residents, businesses, and industries.

Go with the Flow

More than 40 pumping stations, or lift stations, along the Hammond Sanitary District’s sewer system facilitate the flow of sanitary sewage to the plant, and remove excess storm water. All wastewater entering the district’s Columbia Avenue pumping station flows by gravity through large interceptor sewers. All of the influent pumped to the plant flows to two grit tanks for preliminary treatment to remove and mechanically screen out largely inorganic material. This residue is washed and landfilled.

From the grit chambers, the wastewater enters pre-aeration tanks that oxidize odors and improve the settleability of suspended solids. After pre-aeration, the flow enters and open channel for distribution to 12 primary settling tanks that provide the retention time for settling the primary biosolids. These biosolids are transferred to digesters for anaerobic treatment, while the clarified water or primary effluent goes on to a biological process, or secondary treatment.

Secondary treatment speeds up the biological decomposition of wastes by forcing oxygen into the wastewater, which promotes the growth of microorganisms that feed on the organic material. This process, called aeration, uses air blown through diffuser assemblies located along the length of each tank. A mixture of wastewater and activated biosolids is agitated and aerated during this biological wastewater treatment process. The activated biosolids are subsequently separated from the treated wastewater (MIXED LIQUOR) by sedimentation, and wasted or returned to the process as needed. There are literally millions of bubbles in the chocolate-colored water.

The effluent is then distributed to the final tanks where the biomass is settled. The collected biosolids are sent to thickening facilities where it is prepared for further treatment. Clarified effluent from the secondary settling tanks is now relatively free of small particles called suspended solids.

This liquid is pumped to sand filters for tertiary treatment, a step that produces clear water. Chlorination disinfects the clear water, killing bacteria, before the flow is de-chlorinated and discharged to the Grand Calumet River.