Saving Money in Mississippi through Decades-long Public-Private Partnership
In 1994, Severn Trent proposed, administered and constructed an upgrade to the aeration system by converting from the original coarse bubble diffuser system to a fine bubble system. This was accomplished with in-house and subcontracted labor, saving the city significant dollars over employing the services of an outside contractor. This upgrade generated an estimated annual savings of $550,000 in electrical costs and provided routine compliance within discharge permit parameters.
During the latest major plant upgrade, which was initiated by Severn Trent, the city solicited and received bids for the upgrade with the lowest quotation being in excess of $20 million. Our consultants provided the city with alternative treatment technology that reduced construction costs by more than $6 million.
Today, the project encompass three wastewater treatment plants totaling 125 mgd, 92 pumping stations and sludge disposal (dewatering and land application) of 11,000 dry tons of biosolids annually. The nearly 263,000 customers who receive sewer service from the city produce approximately 14.8 billion gal of treated wastewater per year.
The three treatment plants utilize the following processes:
- Savanna (46/120 mgd) – Activated sludge, single stage nitrification (contact stabilization by design) operated in the conventional mode for nitrogen removal. The treatment process involves the following steps: influent pumping, screening, grit removal, anoxic/diffused aeration, secondary clarification, reaeration, aerobic digestion, effluent disinfection, dechlorination and pH adjustment.
- Trahon (4.5 mgd) – Activated sludge by oxidation ditch. The treatment process involves the following steps: influent pumping, screening, grit/grease removal, aeration, disinfection and dechlorination.
- Presidential Hills (0.75 mgd) – Aerated lagoon operation. The treatment process involves the following steps: influent pumping, aeration, polishing pond, sand filtration, effluent disinfection and dechlorination.
Under normal operating conditions, effluent is discharged from all three plants by gravity flow. In wet weather conditions, effluent is pumped from the Savanna plant to the Pearl River. Sludge produced by the Trahon plant is transported as liquid to the Savanna plant where, together with the Savanna sludge, it is dewatered using belt filter presses and transported to land application sites for incorporation as fertilizer.
The city had contracted its sludge disposal since 1978. In 1999, Severn Trent was awarded this contract, saving the city nearly $3 million over the term of the last contract.
Severn Trent uses process control and standard operation procedures to minimize odor issues at these facilities. As part of this process, Severn Trent carefully reviews each site and makes the appropriate determination on what procedures are needed. For example, at the Savanna plant, a biological agent is used in the collection system, and chemical odor destruction methods (ferric sulfate) are applied at the plant.
Jackson is a prime example of the benefits of a private-public partnership. This is not only evidenced by the cost-saving alternatives and NPDES permit compliance provided by the private partner, but also the long-term relationship established between the city and Severn Trent Services.