3.2 Quantify the cost and effectiveness of biosolids disposition

Key Message: Because most biosolids are generated by municipal wastewater treatment facilities, emerging markets for biosolids products may offer economic and environmental benefits to communities. Understanding the costs and benefits of various technologies for processing biosolids can inform their sustainable use.

Importance

Because biosolids represent a significant source of nutrients, and a majority of biosolids are generated by government wastewater treatment facilities (WWTF), their disposition poses both challenges and opportunities for nutrient budgeting and management. Biosolids can be disposed in landfills, incinerated, spread on permitted land sites such as agricultural lands, golf courses, parks, or forests, or processed into fertilizer. In Sarasota County, biosolids from the six major WWTFs in Sarasota County are all transferred for a fee to the Charlotte County Bio-recycling Facility (CCBF) for processing. The facility, operated by Synagro, is permitted to process 10,000 tons per year of biosolids into Class AA compost, which it then sells. Quantifying the economic and environmental cost-benefit of biosolids disposition is an important element of holistic nutrient management. Emerging technologies and markets for biosolids disposition offer communities sustainable options with economic and environmental co-benefits.

Overview

Alternatives for Biosolids Disposition

As an alternative to landfilling, several standard options currently exist for processing and marketing biosolids. These generally include creation of compost and thermally dried (TD) fertilizer, or a thermal hydrolysis process (THP) for soil blending or cake production. In Florida, both compost and TD biosolids have been extensively marketed, but currently there are no THP processing facilities in Florida.

The composting process blends dewatered biosolids with a carbon source, such as wood chips or sawdust, to provide a suitable environment and food source for microbes. The process can be successful in transforming Class B biosolids into a Class AA product. Biosolids compost has been used extensively by the Florida citrus industry as well as in landscaping and nursery production (MDWSD 2016).

To produce TD fertilizer, biosolids are dried and granulated to produce a marketable fertilizer or fertilizer component. Operational costs, particularly energy costs, for TD facilities are substantial but are recovered through lower handling costs and revenues from the sale of dried biosolids (MDWSD, 2016). This end product can also be landfilled, used for land application, and/or burned as fuel. Use of TD dried biosolids combusted at cement kilns as an energy source may be feasible. However, this market has not yet been developed because, to date, fertilizer has been a more marketable commodity.

In the THP process with soil blending, dewatered Class AA biosolids can be used in the production of blended landscaping soils. This is an emerging management technique that has been gaining momentum nationally in horticultural markets (MDWSD, 2016). Tacoma Grow (TAGRO) in Washington is a well-known soil blending program. 

The THP process can also generate energy. This process heats the biosolids under pressure prior to anaerobic digestion. Raleigh, N.C. recently broke ground on its Neuse River Resource Recovery Facility that includes a THP component that will reduce their biosolids output by half, as well as a methane gas byproduct that can fuel up to 50 city buses a day (Stradling 2019). Although the primary goal is reducing the volume of biosolids, the project also will reduce greenhouse gas (GHG) emissions equivalent to 4,000 cars per day. At even greater scale, DC Water’s Blue Plains Advanced Wastewater Treatment (AWT) plant used THP to reduce its biosolids by 50%, generate 30% of the energy needed for the plant, and cut greenhouse gas emissions by 41%.

Challenges of Biosolids Disposition

Reusing nutrients captured in biosolids presents a sustainable disposal opportunity, but existing and emerging challenges impact the cost, effectiveness, and safety of disposal. Challenges include contaminants of emerging concern (CEC), which may be present in domestic and/or industrial wastewater biosolids applied to soils. These CECs include (EPA, 2009):

• Pharmaceuticals and Personal Care Products (PPCPs)
• Steroids and Hormones (S/H)
• Alkylphenols and Alkylphenol Ethoxylates (APEs) used in some detergents and cleaning products
• Bisphenol A (BPA) used primarily to make polycarbonate plastic and epoxy resins
• Polybrominated Diphenyl Ethers (PBDEs) used as flame retardants in furniture foam, back coatings for draperies and upholstery, and plastics in small appliances and consumer electronics
• Microplastics
• Pesticides

Issues currently impacting the use of biosolids in Florida include (MDWSD, 2016):

• 2010 Food Safety Modernization Act (November 2015). This Act places lengthy “days to harvest” restrictions on fresh fruits and vegetables grown using biosolids that have not been treated for pathogens. Although the regulation does not prohibit the use of biosolids, it allows growers cooperatives and purchasers to implement restrictions.
• Declines in Citrus Production due to Asian Citrus Psyllid infestation (Citrus Greening). This disease has led to dramatic declines of 40 to 50 % in Florida citrus yields, causing many citrus farmers to cease operation and jeopardizing the use of biosolids in citrus production.
• Nutrient Limits from the Lake Okeechobee and Estuary Recovery Plan. The Florida Department of Agriculture and Consumer Services (FDACS) revised its fertilizer content standards within this geographical area to require that all fertilizer products labeled for use on urban and sports turf be limited to the amount of nitrogen and phosphorus necessary to support healthy turf.

Finally, rule revisions currently being considered by the Florida Department of Environmental Protection (FDEP) for nutrient management on land have added uncertainty to the biosolids marketplace. FDEP has indicated that the revised rule may reduce the land available for spreading Class B biosolids by 75% due to stricter site criteria as well as surface and groundwater monitoring requirements (FDEP 2019b). Approximately 125 site permits, 125 agricultural landowners, 127 domestic wastewater treatment facilities (WWTF), 9 biosolids treatment facilities, and 46 septage management facilities will be required to comply with the proposed rule. The revisions may be especially burdensome for the 40 domestic wastewater facilities in small, rural counties and cities lacking cost-effective economies of scale.

Approach

Evaluation of sustainable alternatives for biosolids disposition should evaluate cost and market return, along with environmental and social impacts.

Based upon an evaluation of biosolids management alternatives for the Miami-Dade Water and Sewer Department (MDWSD 2018), annualized costs for the various processing options generally compare as follows:

Base Case                                                            $500-$700/Ton

Class B  Composting                                          $700-$800/Ton

Class AA Thermal Drying (TD)                           $550-$700/Ton

Class AA Thermal Hydrolysis Process (THP)   $550-$650/Ton

These costs reflect the benefit of scale associated with a large urban area such as Miami-Dade and are expected to be significantly higher for WWTFs serving small, rural areas.

The Miami-Dade evaluation also considered environmental, social, and economic costs — the “Triple Bottom Line” (MDWSD 2018). Each of these cost components included the following:

1. Economic – capital and operating cost
2. Environmental – carbon footprint considerations, impacts to soil and water quality, impacts and risks to air quality, and impacts and risks to regulation and permitting
3. Social – traffic, roads, and public safety; facility and product odors; beneficial uses of biosolids products/marketability; other community impacts (aesthetics and noise)

Wholesale market values for biosolids products vary substantially with high quality processed granules values 30 times more than agricultural compost (Table 3.2.1). While these market values consider the Florida-specific issues referenced previously, they do not necessarily reflect the potential impacts of the state’s proposed rule revisions for biosolids (see Chapter 3.3). The THP cake is assigned a low speculative value because markets have not been developed for it in South Florida and because it is generally considered a “less finished” product.

It may be advantageous for Sarasota County to co-locate a similar bio-recycling and energy facility at its Central County Landfill. This could take advantage of the available carbon/ligneous waste delivered to the landfill and provide a sufficient buffer from residences and businesses for such operations.