Ponchatoula wastewater has a fascinating journey
PONCHATOULA–Traffic and greenery at the junction of I-55 and U.S. Highway 51 hide one of Ponchatoula’s great feats of modern technology – its Wastewater Treatment Plant.
A recent private tour of the facility was a real eye-opener as to how advanced the city is in yet another area of caring for its people.
Sewerage and Water Department Director Dave Opdenhoff proudly pointed out the treatment is accomplished by biological rather than chemical means.
In the city itself, wastewater drains southward by gravity. With the highest elevation about 26 feet, to get enough “fall”, the original sewer lines in some places are 20 feet underground, making repairs to the 80-plus-year-old system extremely difficult.
Thus, the grants Mayor Bob Zabbia and his administration have secured mean work will begin soon on the Sewer Rehabilitation Project, aiding tremendously in a smoother transfer from across town to its 31-acre site in the southeast corner at the edge of the swamp.
The plant has 23 lift or “pumping” stations, pumping electronically at all times with a back-up generator on a major lift station so during an outage, the wastewater can keep moving.
Looking across the “aerated lagoon” (official name for what’s called the “Pond”), one can see the 3 cells that make it up.
Treatment begins as the wastewater enters Cell One on the northwest section where 4 electric floating aerators mix and discharge the wastewater into the air adding oxygen to the water to begin the biological breakdown of the wastewater using aerobic bacteria. This process began in 1992 with the first upgrade to the facility since its installation in the early ’60s, changing it from an oxidation pond to an aerated lagoon.
Wastewater then moves into Cell 2 via a 36” conduit on the far side from where it entered the facility. Air in this cell is provided by underwater diffusers. Three 50-horsepower compressors are configured to run only one at a time. They can be run concurrently but they are alternated every thirty days. As the oxygenated wastewater enters Cell Two, it meets a combination of aeration and Duckweed to shade the water, helping with the growth of anaerobic bacteria. Using a grid system keeps the Duckweed covering from floating into another area. Wastewater then exits Cell 2 on the western side of the lagoon via an opening in a curtain used to divide the lagoon into separate cells. The back-and-forth of the flow creates a serpentine flow pattern and a theoretical 30-day detention time in the lagoon.
The current multi-million-dollar upgrade over the past 18 months is nearly complete. The upgrade included raising the levies 18” and added an automated “weir”. An ultrasonic depth chamber registers the depth of the outflow and sends a signal back to the weir gate to regulate the rising and falling of the wastewater in the lagoon.
Upon leaving Cell Three, final treatment uses ultraviolet disinfection. Four groups of 6-feet long lights are in a trough through which the water passes. These are sequentially turned on and off based on the flow and are capable of disinfecting 2.5 million gallons of wastewater a day. (An average Ponchatoula day is 1.4 million gallons.) This device sends data to a control panel, monitoring flow and level and giving daily, monthly and annual reports.
Also new is a dissolved oxygen probe for continuous monitoring of oxygen as well as pH numbers. The Department of Environmental Quality establishes the outfall quality for the city and data is collected and sent in monthly.
A sampler calibrated to flow grabs hourly samples and creates a composite sample which is transported daily to Curtis Environmental in La Place for analysis. Results from the testing lab are compiled and reported to DEQ.
The permit is for 200 parts per million fecal matter bacteria per day, as well as dissolved oxygen, pH, total suspended solids, and biological oxygen demand. The upgrades have allowed the city to meet the permit requirements and only a few minor adjustments to the system are still needed.
At one-time nutria rats were undermining the levees but alligators moved in as watch-dogs, solving that problem. In fact, they work so well Opdenhoff says, “Crew members just have to be cautious when working around the lagoon that we don’t encounter a mama gator in the tall grass on the sides of the levees!”
At the end of its to-and-fro journey through the three cells, treated wastewater exits the plant to enter the swamp on the southeast through what the DEQ’s map shows simply as “Drainage Ditch”.
Ponchatoula Wastewater Treatment – a successful combination of man, science, and nature.
By Kathryn J. Martin