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A sewage digester at the St Bernard Parish WWTP, Louisiana

Reduced energy cost, increased capacity - St Bernard, Louisiana

The problem: a damaged, underperforming plant

Meraux, Louisiana is located near New Orleans in St Bernard Parish, an area hard hit by hurricane Katrina in 2005. Excessive damage to the Parish's plants during the hurricane afforded the opportunity to consolidate flows from three small plants into the process at the Munster Wastewater Treatment Plant (WWTP). A complete headworks upgrade and expansion of the existing biological process was needed for the consolidation.

Prior to Katrina the Parish operated four treatment plants - Munster, Dravo, Violet, and Fazendville - with a combined capacity that was having trouble accommodating their peak wet weather flows. Two of the three plants being consolidated into Munster had energy-hungry aerated grit basins that were undersized for their wet weather flows and allowed the heavy grit load seen during storm events to enter into the treatment plant's processes.

The four existing plants had well over 100 hp (74.6 kW) in continuous energy requirements, yet they routinely bypassed grit, which deposited throughout the plant and accelerated wear. Their system had difficulties handling peak flows as high as 29 MGD (1,271 L/s) as the four plants combined were designed for peak flows of just 13 MGD (570 L/s).

Solution

Following the hurricane, engineering and construction firm CDM Smith was hired to design a plant upgrade for the Munster WWTP that would repair the damage and expand capacity to treat a majority of the Parish's wastewater. The new Munster plant would have over 65% more capacity than the combined peak wet weather flows of the four old plants. The new headworks would be located well above flood stage, extending 39' (12 m) above grade, to protect the plant from future hurricanes. It is believed to be the tallest elevated headworks in the country.

As Meraux is located in a coastal area, fine grit removal was a big concern. A new high efficiency Advanced Grit Management system consisting of three HeadCell® grit removal units, three SlurryCup™ grit washing and classifcation units, and three Grit Snail® dewatering units was installed to handle a peak wet weather flow of 50 MGD (2,191 L/s) with 95% removal of all grit 106 µm (micron) and larger.

Project parameters 

  • 30 MGD (1,314 L/s) Peak Capacity before upgrade 
  • 50 MGD (2,191 L/s) Peak Capacity after upgrade
  • Guaranteed removal of 95% of all grit 106 µm (micron) and larger

The outcome: better grit removal at reduced cost

Hurricane Katrina devastated the sewage treatment capacity of St Bernard Parish, necessitating significant repair. Even before the storm, the existing four-­plant treatment system was undersized, underperforming, and consuming significant energy. The four treatment plants' flows were consolidated into the largest existing plant, which required a complete headworks upgrade.

The new plant with the Advanced Grit Management system can handle significantly more flow, while using less than a quarter of the energy. The old system was costing between $71,000 and $74,000 each year to operate, while the new system only costs from $3,450 to $15,000 per annum, with the new system treating more flow and providing better performance.

The result was an annual savings between $59,000 and $67,550 every year for a system that used to ineffectively treat just 29 MGD (1,271 L/s).

In addition to the energy savings, the disposal cost of grit collected at the headworks is much less expensive than disposing of it in sludge, with sludge costing $34 per ton to dispose of while sending grit to the Parish landfill costs only $50 per 2.0-2.5 ton load. The improved grit removal is also expected to increase the life span of the plant's sludge pumps.

Plant Manager Steve Lombardo said: "I have never seen a system that removes so much grit. Our biggest problem now is if we have a rain event over the weekend we bury our grit dumpsters."

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