| The biosolids are applied to farmland using manure spreaders pulled by tractors. Application areas are marked with flags to protect adjacent property, streams and roadways. |
As municipal budgets continue to tighten, cities across the United States are seeking cost-effective ways to best manage their infrastructure and identify savings. With this in mind, more cities are looking to expand from a traditional treatmentand-disposal approach to one that centers on resource recovery and fnding value in waste.
Oklahoma City has experienced signifcant success with its 18,000-acre permitted cropland biosolids reuse program. Developed and implemented by Veolia Water North America as part of a 25-year public-private partnership with the city, the program has reduced sludge disposal costs and provides local farmers with a soil amendment at zero cost to the landowner. The program currently produces a combined total of 25,000 dry tons of Class B biosolids per year.
BACKGROUND
Before the partnership, Oklahoma City had already experimented with several biosolids land application methods. The goal was to fnd a sustainable way to reuse biosolids generated by its wastewater facilities. Its frst experiments were in liquid land application, but the city found that hauling the heavy, wet biosolids was expensive and unsustainable.
In 1988, Oklahoma City and Veolia Water determined that belt press technology could be integrated into the facilities to remove liquid from the biosolid stream. This process accelerated the program. By taking dewatered solids to the feld instead of liquid sludge, the city found that its hauling costs were reduced. This made the process more effcient and fnancially sustainable.
HOW IT WORKS
All four of the city's wastewater facilities participate in the biosolids reuse program, and up to 100,000 wet tons of biosolids are treated and processed each year. Veolia Water monitors and treats the waste stream at each facility, minimizing contaminants that would make the biosolids unft for use in the land application program.
"Our product goes through testing to ensure that contaminants don't come in at levels that are above regulatory levels," said Wade Braxton, Veolia Water biosolids supervisor. "Because we monitor the waste stream from the start, we are able to treat the biosolids in a manner that minimizes contaminants in order to produce Class B quality sludge for the program."
As Class B biosolids, the product can only be applied to land designated for non-human consumption crops.
Belt presses remove water from the treated biosolids, making it lighter and easier to transport. Currently, three of Oklahoma City's wastewater treatment facilities — Deer Creek, South Canadian and North Canadian — use a belt press. The other facility, Chisholm Creek, transports liquid waste to Deer Creek to be belt-pressed.
Lime is added to the biosolids to stabilize the mixture by increasing the pH above 12. The lime destroys any remaining pathogens, making the biosolids safe for land application. Additionally, the lime serves as a benefcial soil amendment.
While the city continuously produces biosolids, weather and the needs of farmers vary. The treated biosolids are transported to the North Canadian facility for storage until needed, since it is located in a more rural area. Approximately 30 loads of biosolids are picked up from the facilities each day.
