Biosolids Program

The City of Fort Worth has always been dynamic and progressive in the area of beneficial reuse of biosolids. 

When the city’s first water reclamation facility opened in 1923, “air-dried” biosolids from lagoons and drying beds were beneficially reused on area highway easements and medians through agreements with the Texas Department of Transportation. City parks, golf courses and greenhouses beneficially reused biosolids, too.

In the 1980’s, the water utility began looking at other alternatives for dewatering and proper disposal because of population growth and new regulatory requirements. Since the area is surrounded by farm and ranch lands, beneficial reuse through land application was determined to be the most cost effective. 

The city initially privatized the dewatering transportation and land application through a contractual agreement in 1991. Belt-presses were used to dewater the material, resulting in a cake-like end product. Subsequent contracts were issued because of the program’s low cost and positive public acceptance. 

EPA Class A (Exceptional Quality) biosolids were applied to registered and noticed agricultural land in Tarrant and 11 surrounding counties for many years. The Class A EQ rating was the result of an excellent pretreatment program, full anaerobic digestion and post lime stabilization. 

The Texas Commission on Environmental Quality made rule changes to create a Class AB standard for biosolids that are processed using belt-filter presses. TCEQ issued a permit to the City of Fort Worth in 2018 with the new Class AB standard. As a result, Fort Worth’s biosolids were designated as Class AB with the permit renewal TCEQ issues in 2018. However, biosolids meeting the TCEQ Class AB criteria also meet EPA’s Class A (Exceptional Quality) standards. 

In response to rising program costs and an increase in odor complaints, Fort Worth decided in 2017 it was time to re-evaluate how it was processing and beneficially reusing its biosolids. A Biosolids Master Plan was commissioned and site visits were performed to evaluate alternative methods for biosolids processing and reuse. 

The proposed alternatives were evaluated against several criteria, including odor performance and projected program costs.  The Master Plan was completed in January 2019, and its evaluation determined that direct thermal drying was the best option for Fort Worth.

The utility subsequently issued a request for proposals on June 7, 2019 for qualified companies that could continue to operate the existing Class AB biosolids processing facility, while at the same time designing and constructing a new Class A thermal dryer facility.  Later that same year the City chose the winning bidder for the project (Synagro of Texas-CDR). On Dec. 10, 2019, Fort Worth City Council approved entering into a public-private partnership with Synagro to design, build and operate a new processing facility.

Synagro took over operations on April 1, 2020 using the existing Class AB processing equipment. By focusing on operating in a manner consistent with good neighbor practices, Synagro was able to effectively eliminate community odor concerns that had previously been associated with the biosolids program.

The drum dryer was placed into operation in July 2022 and is the preferred method for processing Fort Worth’s biosolids. The end product is a Class A dried pellet that is registered as a fertilizer in Texas. These pellets can be marketed and distributed to customers such as farmers, ranchers and golf courses.  The pellets also have the potential to be utilized as a renewable energy source. By contract, Synagro is responsible for determining end use of the product. 

The belt filter-presses are used only as a backup option when the dryer is offline for extended periods of time.

Since the mid-1990s, Fort Worth has used a third-party contractor to provide its biosolids services.  On April 1, 2020 Synagro took over these responsibilities, which include the following:

1. Operation and maintenance of the biosolids processing facility;

2. Transportation of Class AB biosolids to the land application sites;

3. For Class AB Biosolids, performing beneficial reuse of biosolids via land application; and

4. Marketing and distribution of Class A dried pellets as a registered fertilizer

Both Class A and Class AB biosolids must meet stringent environmental standards established by the EPA and the State of Texas. To ensure product quality, Synagro must use an independent certified laboratory to analyze the biosolids. Samples of biosolids are collected and analyzed for several parameters, including pathogens, metals, PCBs, and pH. Sampling frequency is established by contract, as well as by federal, state, and local regulatory requirements.

The water utility performs routine and unannounced visits and inspections to the dewatering facility and Class AB land application sites to ensure that best management practices and regulatory requirements are effectively and properly implemented.

Odor Monitoring

Ideally, biosolids will have an “earthy” aroma; however, sometimes the other types of odors, like ammonia or manure may be detected.  Biosolids odors usually dissipate from an application area within a few days, depending on wind and weather conditions.  Landowners may also assist in reducing odors by mixing or incorporating biosolids into the soil.

During land application of Class AB biosolids, City of Fort Worth personnel inspect the site and evaluate odor intensity.  In July 2013, Village Creek staff added a new technique to the biosolids program in order to assess odors more accurately and consistently at land application sites.  An instrument known as an olfactometer enables City inspectors to quantify the strength of odors using different filter cartridges (as pictured above).  Olfactometer and weather data collected in the field provides important information that is used to manage land application activities, investigate odor complaints and establish a consistent odor-monitoring history for each application site.

Stormwater Runoff and Buffer Zones

The biosolids contractor must apply Class AB biosolids uniformly and in accordance with Texas Commission on Environmental Quality (TCEQ) regulations on farm and ranch lands to help protect water quality and prevent runoff .  TCEQ Rule 312.44 specifies that Class AB biosolids may not be applied during rainstorms or during periods in which surface soils are water saturated, flooded, frozen or snow-covered.  To achieve this objective, biosolids are stored during inclement weather either at a dewatering facility or on wet weather pads.

Class AB buffer zones are used to provide spacing between the land application and surrounding areas such as occupied residential dwellings, property boundaries, roadways, groundwater wells and surface waters (ponds, lakes and streams), etc. to protect water quality and minimize the effect of odors.  For Class AB biosolids, the contractor maintains a 750-foot buffer zone from any occupied residential structure and a 50-foot buffer zone from property boundaries and public rights-of-way. 

Nutrients

Recycling biosolids through land application allows valuable nutrients to be returned to the soil. The nutrients in biosolids are not as soluble as those in chemical fertilizers and are therefore released more slowly. Conditions for vegetative growth are enhanced as a result. City of Fort Worth biosolids are about 18 percent to 20 percent solid after the addition of lime, the remainder is water content that is also returned to the soil, which is helpful during periods of drought.