The City of St. Petersburg, Fla., was looking to upgrade its biosolids management program to harvest more energy and to produce a Class A product that would be suitable for land application as regulations tighten.
With dozens of possible options involving capital costs, operational costs and revenue projections from potential resources, the choices were dizzying. Brown and Caldwell engineers helped the city and George Cassady, director of Water Resources, identify a dramatically streamlined plan, meeting their long term needs, saving millions of dollars and winning support from city leaders. Hereís how they did it.
Describe the scope of the project to upgrade St. Petersburg’s biosolids management.
George Cassady has more than 25 years of experience in the water and wastewater business in both the public and private sectors. He joined the city of St. Petersburg as Water Resources Director in 2008. He has a bachelor's degree in Chemical Engineering from Auburn University and a master's degree in Engineering from University of Southern Florida.
We’re planning to upgrade our biosolids management at four wastewater treatment plants that use anaerobic digestion. We serve approximately 317,000 customers and treat 35 mgd average flow through. All four plants are about 30 years old and we knew that with newer technology we could better leverage our biosolids as a resource, especially in the area of energy production, and better serve the community for the long term future.
What were the primary drivers for the project?
Our drivers were to improve the economic performance of our plants with more energy production and to move to a Class A biosolids product. We are currently producing a Class B biosolid and it is looking like that will be difficult to reuse for land application in Florida. We also have a significant yard waste collection program and we wanted to determine if we could process the yard waste in the same stream.
What options did you consider?
Everything. We had a very large, complex matrix of different solutions, their costs, their risks and their benefits. It became a little overwhelming — the variables, their impacts, new technologies. We finally acknowledged that we could use some help and guidance, both in terms of learning what is out there and working for other facilities, and what would work best for us.
How did you go about finding the right solution for your utility?
The folks at Brown and Caldwell led us through an analysis of about three dozen scenarios, and quantified all the factors — capital costs, operational costs, the potential savings of various energy production technologies, and the costs associated with the risks of each option. This analysis was incredibly helpful because it took us out of the realm of speculation and into the world of facts and numbers. Everything was expressed in terms of net present worth. Eventually the best choice became clear.
What solution did you select?
Our plan is to use thermophilic and mesophilic digestion in series to produce Class A biosolids and maximize gas production as well. We also found that we can pump all of our biosolids to a single plant for processing. With a relatively small investment in some additional force mains, we would avoid the cost of upgrading digestion at every plant. The numbers were extremely compelling, saving something on the order of $30 million over 20 years.
What are the primary benefits of this solution?
There are lots of benefits. The biggest is that we feel this positions our utility to be the best stewards of public funds we can be, by taking a long view and developing a plan that should last 5o years or more. The financial benefits are great, but the community comes first. One big benefit was that we didn’t want to have cavalcades of trucks hauling biosolids around our very dense urban environments. We avoid that with this approach.
What makes you confident that this is the best possible solution?
It’s pretty black and white. There were a few other options that were close in net present worth when everything was said and done, but each one involved risks or impacts that we found unacceptable.
What did BC contribute to the selection process?
The toolkit BC brought to the table allowed us to vet about 35 approaches very quickly and thoroughly. That was invaluable. Coming up with the idea of pumping all our biosolids to a single plant was something we never considered. It’s a simple, elegant solution — the answer was under our feet but we didn’t see it!
How has the solution played out with your stakeholders/public opinion?
The City Council unanimously endorsed the concept.
What’s next for the project?
We’re currently analyzing the hydraulics of the plan to double-check that the pumping option will work. Once that is complete, we’ll pull the trigger on the rest of the plant.
What do you enjoy about what you do?
I’ve been in this industry for 28 years. I enjoy providing a service that people really can’t live without. And I enjoy being on this team that is truly dedicated to serving the community. We’re delighted at the prospect of this upgrade being something that will pay dividends for our customers for decades to come.