A modern perspective on municipal fats, oils & grease management
Fats, oils and grease (FOG) are a dirty and difficult challenge for the wastewater industry. Annually, FOG costs municipalities millions of dollars to manage. When not properly intercepted, FOG can adhere to sewer pipes, cause blockages and damage lift stations. If left in wastewater, FOG can create hydrogen sulfide, a poisonous gas corrosive to sewer infrastructures.
According to the U.S. EPA, 23,000 to 75,000 sanitary sewer overflows (SSOs) occur each year, and the majority are caused by FOG. SSOs can cause water quality problems, environmental damage and can threaten public health. Even when accumulated, FOG does not escalate into blockages and sewer backups, but it can still disrupt wastewater treatment facilities by increasing operations and maintenance requirements.
The U.S. EPA developed the national pretreatment program to prevent harmful pollutants, such as FOG, from entering the sewer system and potentially causing damage to publicly owned treatment works (POTW) or passing through the POTW untreated, which ultimately pollutes the environment. Additionally, municipalities implement and enforce local pretreatment programs to regulate commercial, industrial, institutional, manufacturing and other non-residential establishments that introduce pollutants into POTWs.
Enforcement of more stringent regulations, availability of more efficient grease interceptor technology and greater awareness of the impact of FOG on communities and the environment is gradually improving grease trap waste collection. However, the rising problem for municipalities is FOG disposal. Preventing FOG from entering sewer lines is only part of the solution. What can municipalities do to manage the massive amounts of collected FOG? How can POTWs complete the cycle of FOG collection and disposal in a cost-effective and eco-friendly way?
Modernizing the Paradigm
Recognized as one of the most progressive wastewater treatment facility authorities in North America, Hampton Roads Sanitation District (HRSD) is dedicated to protecting “public health and the waters of Hampton Roads,” with the goal of providing clean waterways for future generations. HRSD provides service to 18 cities and counties of southeast Virginia, an area of over 3,087 square miles with a population of 1.7 million. HRSD operates nine major treatment plants and seven smaller plants in eastern Virginia, with a combined treatment capacity of 249 million gallons of wastewater from homes and businesses per day.
As part of its mission and dedication to improving the local ecosystem, HRSD is upgrading facilities and processes at its Nansemond Treatment Plant. Located in Suffolk, Virginia, the Nansemond Treatment Plant has already received national awards for outstanding compliance with its environmental permits.
Although the facility itself does not experience treatment challenges from FOG buildup, HRSD regularly pioneers projects to benefit the environment and water quality. The current project plans to include a FOG separation system that will convert waste into resources. Jacobs, the leading provider of technical, professional and construction services, will be responsible for placement of the major system components and oversee the facility, which will screen decant and process FOG from indirect haulers.
Following an industry-wide search for the most efficient and advanced system to separate FOG into its basic components, HRSD chose Downey Ridge Environmental Company’s hydronic thermal separation system, Greasezilla, for its process that reclaims high-energy resources from FOG.
The system maximizes the energy recovery potential within FOG by separating it into its basic components, sending the water back to the treatment center headworks while responsibly recovering an advance biofuel without the need for additives, additional processing, blending or fossil fuels.
By applying heat, the system generates three distinct layers:
- Brown Grease: The first layer is a very low moisture, high free fatty acid brown grease advanced biofuel (ABF) offtake that is a fuel grade drop-in substitute for No. 5 or No. 6 fuel oil. Approximately 10 to 15% of the separated material, the offtake is a marketable commodity, ready for boiler use without further processing. The quality of the ABF—with a moisture level of less than 1%—makes it an ideal reactor-ready feedstock for the growing number of emerging biodiesel conversion technologies. Also, the hydronic thermal separation system operates on only 5% of the ABF it produces.
- Batter: The second layer is the organic matter left over after the brown grease is separated. The batter, making up approximately 3 to 5% of the separated material, is a balanced, homogenized substrate input source for anaerobic digestion.
- Effluent Water: Once the brown grease and batter are removed, the remaining water, now pasteurized and nearly free of all suspended solids, is safe for discharge to the treatment center headworks.
The two-tank, two-boiler system will sit ahead of the wastewater treatment facility and process up to 40,000 gallons per day, which equates to more than 14 million gallons of FOG per year.
Greasezilla was designed specifically with the intent of handling greasy wastewater in a way that is not too operationally intensive or costly. The total operating expense of the system is less than $50,000 per year and energy costs are less than $3,000.
The inclusion of a process that is able to convert FOG waste into a useful product is a further benefit in that a nuisance waste is turned into a commodity grade product. The ABF can be sold to offset a portion of the operational cost associated with grease trap waste management and provide a carbon neutral fuel source that can help offset the environmental impact of the user of the resulting biofuel.
Best Practices Meet Sustainability
While the potential problems of FOG lead some POTWs to prohibit or place restrictions on its discharge both through the collection system and as hauled waste, others, like HRSD, look beyond traditional operational processes and implement emerging technologies that complement their mission of watershed stewardship.
With the HRSD project, we are starting to see a transformation in the way traditional wastewater utilities view themselves and manage their operations. Combining best practices with cutting-edge technologies that support resource recovery, efficiency and sustainability, wastewater treatment facilities are becoming utilities of the future. As resource recovery centers for water, energy and nutrients, a holistic approach to water management can deliver significant environmental, economic and social benefits to local communities and ecosystems.