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Credit: Siemens Water Technologies Corp.

Airflow to the moving bed biological reactor is controlled by the Smart AGAR control system by using luminescent dissolved oxygen probes and a programmable logic controller-based control panel. The probes send signals to the PLC that is used to control the positive displacement blower motor speed via variable-frequency drives. The operator sets the desired dissolved oxygen concentration at the operator interface, depending on the season and effluent requirements.

The system began meeting the effluent ammonia limit less than two weeks after start-up. Influent and effluent samples were analyzed regularly for the first four months.

Samples taken from each stage of the treatment train indicated that the majority of the nitrification was occurring in the first stage where the media sees the highest ammonia concentration. Stages two and three had lower removal rates as the ammonia concentration was diminished, making these stages polishing reactors.

After leaving the system, the wastewater flows to the newly installed effluent pump station, where the water is pumped to the existing constructed wetlands before being sent through an ultraviolet disinfection process and finally discharged to Spanish Creek, which feeds St. Marys River, which serves as the border between Georgia and Florida and is a popular fishing waterway.

— Todd Schwingle is a product engineer for the biological nutrient removal group at Siemens Water Technologies Corp. in Waukesha, Wis. Marcus Sack is a project manager for P.C. Simonton & Associates Inc. for municipal water and sewer system expansions in Hinesville, Ga.