Arkansas wastewater treatment plant pilots path to fledgling technology

Jon Hetzel
Proposal Coordinator
Garver Engineers
Little Rock, Arkansas

Phosphorus—algae's best friend—recently received an eviction notice that its days overrunning the Illinois River's headwaters soon will be limited.

An aerial view of the wastewater treatment plant in Siloam Springs, Ark., in 2006

The wastewater treatment plant at Siloam Springs, Ark., is looking to implement a young technology that will drastically limit the amount of phosphorus flowing from its discharge into Sager Creek, an Illinois River water source. Once the plant's upgrade is operational in 2009, it will be the only municipal wastewater infrastructure in Oklahoma and Arkansas to utilize Membrane Bioreactor technology.

Although a building block of nature, excess phosphorus can spur unwanted algae growth and hinder water quality. That is an issue facing the scenic Illinois River, as its tributaries have witnessed an increase of phosphorus in recent years. An excessive amount of the nonmetallic element has promoted the growth of algae, ultimately hindering the oxygen supply in the water and having the potential to harm fish and other aquatic life.

Phosphorus pollution often is linked to agricultural practices and ensuing runoff. However, the pollution cannot be pinpointed to only one source, and reducing the amount of phosphorus in the waters around northwest Arkansas and northeast Oklahoma is one place officials decided to start.

In 2002, the Environmental Protection Agency set in motion a mandate requiring wastewater treatment plants to reduce their phosphorus output to less than 0.037 milligrams per liter of water by 2012. The mandate is intended to reduce the amount of phosphorus pollution emanating from the plants and disturbing the Illinois River water quality.

At 0.037 mg/L, Oklahoma and Arkansas municipal officials feared the rigorous standard set by the EPA could not be met because the technology was not available to reduce phosphorus levels that low. The EPA found common ground with area officials, declaring a 1.0 mg/L phosphorus discharge limit must be met by 2009. However, in 2012, the EPA will reconsider the 0.037 mg/L limit for adoption and require wastewater treatment plants to meet the original effluent level.

Having witnessed a tremendous population growth, Siloam Springs is scheduled to expand its wastewater treatment plant. As part of the upgrade, the plant will reduce its phosphorus discharge into Sager Creek, a tributary of Flint Creek, a body of water that flows into the Illinois River.

Rather than design the plant simply to meet the interim compromise and face the possibility of a second upgrade in 2012, Siloam Springs officials decided to aim for the more stringent phosphorus level.

Garver Engineers has been working with Siloam Springs to research a fledgling technology that will drop the discharged phosphorus level below 0.037 mg/L. The technology utilizes two methods—Biological Nutrient Removal and a Membrane Operating System.

The technology uses membrane, a man-made material with microscopic pores that blocks desired agents but allows water to pass through the system. In essence, the wastewater is forced through filters that work like a screen window. Permitable substances pass through the material while the phosphorus is hindered in its passage.

This filtering and scrubbing process reduces the levels of phosphorus before the discharge and also helps remove nitrates, ammonia, turbidity, copper and Chlorophyll-A. The Membrane Operating System is often used to generate drinking water.

The pilot plant designed by Zenon/General Electric near the Siloam Springs Wastewater Treatment Plant

A recent pilot study was conducted at the plant by two membrane manufacturing companies, Zenon/General Electric and Memcor/Siemens Products. The two manufacturers created two pilot-sized secondary plants at the wastewater site to test the technology.

The four-phase, six-month pilot study verified the process. Data collected from the study concluded that by marrying the technologies, the phosphorus level both met and exceeded the 0.037 mg/L level. The average low fell well below 0.037 mg/L for both pilot plants, coming in around 0.02 mg/L of phosphorus.

The purer water will offer Siloam Springs a great deal of non-potable potential, including irrigation and industrial, commercial and municipal uses.

The implementation of Biological Nutrient Removal and a Membrane Operating System at the Siloam Springs Wastewater Plant is allowing the City and Garver Engineers to use technology that is ahead of the curve. The process is the first of its kind in the area, leading the way for other treatment plants across the nation to follow its technological path.

For clarification or verification purposes, contact Jon Hetzel at (501) 376-3633 or jdhetzel@garverengineers.com, or Garver Engineers Vice President Steve Jones at (405) 329-2555 or smjones@garverengineers.com. Garver Engineers offers a full range of engineering and related services including transportation, general civil, airport, water, wastewater, surveying, and construction management.