Transforming Food Waste Into Fuel

Insight

Recognized as large energy consumers, wastewater treatment plants (WWTPs) also have the potential to be efficient, energy-producing facilities.

Anaerobic digestion, which is commonly used to treat wastewater solids, naturally produces methane as it breaks down organic matter. Harnessing methane to produce heat, electric power or biofuel (also known as biomethane)—and offset facility power needs— is becoming an important energy management option.

Through a process called co-digestion, many treatment plants are enhancing anaerobic digestion with organic waste. Adding fat, oil and grease (FOG), as well as food waste, to anaerobic digestion accelerates this process, producing more methane gas for beneficial use and reducing the amount of solid waste conveyed to landfills.

The benefits of FOG are driving industry competition, according to CDM Smith's experts. Because the addition of food waste is so beneficial to digestion, demand for FOG is creating competition among WWTPs. Treatment plant owners receive fees from the waste haulers collecting FOG from restaurants and also benefit from increased energy production, which could have far-reaching effects in the industry.

Strategic Upgrades, Superior Results
The addition of FOG has been successful at the city of Riverside’s regional water quality control plant in Southern California. CDM Smith is helping with innovative plant upgrades, including a new 26-million-gallon-per-day (mgd) membrane bio- reactor, new primary clarifiers, a solids handling facility, two new digesters and a permanent FOG unloading station. The plant’s capacity will be initially expanded from 40 to 46 mgd and ultimately to 52 mgd during the project’s second phase.

Although the original digesters were performing well and producing energy to help run the facility, Riverside Public Works Department wanted a more effective system. Pilot testing proved that increasing the amount of FOG to 20 to 30 percent of overall volatile solids loading would improve volatile solids destruction by 5 to 10 percent while increasing gas production. As a result, FOG will be added to the new and upgraded digesters.

In addition, CDM Smith collaborated with Arizona State University to test a sludge disintegration technology that breaks down cell membranes in waste activated sludge (WAS) prior to anaerobic digestion to increase gas production. Studies at Riverside indicated a 30-percent increase in gas produced from WAS.

The plant’s existing clarifier will be augmented with additional clarifiers to meet increased capacity.

In this building, energy is recovered from methane gas to offset the regional water quality control plant’s energy needs.

A Hidden Source of Resources

Although anaerobic digestion is well established in wastewater treatment, the premise of food waste as fuel is being further examined as part of a demonstration project at the U.S. Air Force Academy—funded and managed by the U.S. Department of Defense (DoD) Environmental Security Technology Certification Program (ESTCP).

Military installations produce a significant amount of pre- and post-consumer food waste, as well as cooking oil and grease trap waste. This waste and the power of anaerobic bacteria will be used to produce energy-rich, renewable biomethane in an organic waste anaerobic digestion system.

“Digesting organic waste has enormous potential. Not only will it reduce the amount of waste going to landfills, but it produces a high-end energy product that will offset energy use, reduce greenhouse gas emissions, and help us reach our renewable energy goals,” says Dr. Andrea Leeson, ESTCP program manager for environmental restoration.

CDM Smith is designing and building the Air Force Academy’s demonstration plant in Colorado Springs, Colorado—the first to exclusively use food waste—to determine the effectiveness of converting high-energy wastes into biomethane. The demonstration will determine the types and compositions of waste that can be digested, as well as optimal conditions for operation and production.

Refining Technology to Meet Regulations

There has been a great degree of understanding about the benefits of anaerobic digestion for a while, but now the technology has been refined and the use of FOG and food waste is garnering attention and becoming increasingly popular. Successfully harnessing energy from organic waste will help the DoD and other agencies meet U.S. federal regulations that require renewable energy sources—7 percent by 2013, as mandated by the 2005 Energy Policy Act, and 25 percent by 2025, as mandated by the 2007 National Defense Authorization Act.

As beneficial reuse continues to take center stage and FOG and food waste systems have ongoing success, opportunities will increase for creating energy from waste and offsetting energy needs economically.

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