Crowley Facility Ranks
Among Largest Systems of Its Kind

By Charles East, Jr.
Photos by David Humphreys

ASK A SOUTH LOUISIANIAN what the city of Crowley is famous for, and you'll probably be told it's the "Rice Capital of America." But Crowley has also earned its own identity in environmental circles: the city's innovative wastewater treatment facility is one of the largest combined "artificial marshrock/reed filter" systems in the world.

This emerging technology, also known by the terms "microbial rock filter" system and "constructed wetlands," features a large pond for municipal wastewater and storm-water storage and preliminary treatment, as well as a natural filter.

The filter consists of a shallow basin filled with rock, on which plants --- in Crowley's case, southern giant bulrush are grown. The plant roots are presumed to provide additional treatment by taking some nutrients from the wastewater and by introducing oxygen into the wastewater flow.

The Crowley facility was built at a cost of $3.76 million and funded by a construction grant through DEQ using U.S. Environmental Protection Agency (EPA) funds, as well as local monies.

The system began operation in June 1992. It is classified as innovative because it relies on technology that has not been proven fully and because it is designed for low energy consumption, utilizing natural treatment processes and wind-driven aeration.

The cost savings on electricity and other utilities are noteworthy. Crowley's previous plant, a mechanical operation, experienced total utility costs of about $2,500 or more per month. The average monthly utility bills for the new wastewater treatment facility have totaled only about $130.

Because the artificial marshrock/reed process practically eliminates the need for chemical or mechanical means of treatment and usually incorporates gravity flow throughout most of the system the operation and maintenance costs are substantially less than those experienced with conventional treatment processes.

Including the price of land, Crowley's new facility cost less than a new mechanical plant would have. Mayor Robert Istre and the Crowley City Council solved several problems by going to the artificial marsh-rock/reed system: (1) They closed an old treatment plant, located in a residential area, that emitted bad odors and attracted gnats, flies, and mosquitoes. (2) They now meet more stringent discharge permit requirements for less than the cost of typical plant construction. (3) They reduced maintenance costs for wastewater treatment. (4) The city doesn't have to process and dispose of sludge off-site; instead, solids form in a thin layer at the bottom of the treatment system pond and don't need to be removed for many years: perhaps as long as a century, according to project engineers. (5) And Crowley has an environmentally friendly facility that is being studied for use in establishing uniform design criteria for future treatment systems.

It should be noted that artificial marsh-rock/reed filter systems of this size are relatively new technologies and are not fully accepted by some experts in the wastewater industry. Strong opinions on both sides of the issue have demonstrated the need for further study. Nevertheless, some wastewater treatment system designers are convinced of the merits of the process and continue to design and build more systems of this kind. Crowley's treatment system includes the following components:

An aerator in the facultative pond

• FACULTATIVE POND The oxidation pond covers 78 acres and contains 10 aerators, which help pump dissolved oxygen into the water and also maintain an even mix of solids suspended in the water within the pond. These aerators are wind-driven, with an electric motor backup for periods when there is not enough wind. The pond provides primary treatment and includes capacity for storm-water storage during wet weather (25 million gallons per foot of storage in the pond above the normal operating level). Organic and inorganic matter, otherwise part of a sludge disposal problem, will settle on the bottom of this pond and remain there for an estimated 100 years before requiring removal.

  Helpful marsh vegetation.

  
  

• OPEN MARSH AREA The open marsh, which spans more than 22 acres is planted with southern giant bulrush and covered with duckweed floating on the surface.

  The combination of windscreen from the bulrush and shade from the duckweed is intended to reduce the algae in the wastewater -- after the water migrates from the

  Bulrush is prominent at the acility.

  pond -- and to provide additional treatment. Algae is reduced because the duckweed prevents sunlight from reaching the water, partially cutting off photosynthesis and major oxygen production. Algae will otherwise cause high concentrations of total suspended solids in the discharge.

• TORPEDO GRASS BUFFER AREA This buffer area is about

  The microbial rock filter, made of limestone.

  seven-tenths of an acre and is intended to filter any duckweed that may spill out of the open marsh area. It also includes two aerators to ensure adequate dissolved oxygen in the wastewater that enters the microbial rock filter.
• MICROBIAL ROCK FILTER The filter, covering 18 acres planted with southern giant bulrush, is designed to provide final "polishing" of the wastewater. About 18 inches thick, the filter consists of individual pieces of large limestone rock. This layer is separated from the ground by a liner made of polypropylene mesh.

  Changing an ultraviolet bulb.

• ULTRAVIOLET DISINFECTION This method of disinfection was selected to meet the permit fecal coliform bacteria limit because it was more cost effective than chlorination and dechlorination.
• RECIRCULATION SYSTEM A single pump capable of delivering approximately one million gallons per day was recently added at the post-aeration basin, the treatment unit that receives water after it is disinfected. One purpose of this pumping system is to recirculate the treated water to the facultative pond in periods of low flow. This provides a means of constantly delivering adequate amounts of water to the artificial marsh and rock-reed plants, even during periods of relatively dry weather. The recirculation system also allows the operator to break up stagnant zones in the facultative pond that could otherwise cause odor problems.

Click for full-size photo (242K).

The artificial marsh-rock/reed filter system is essentially a controlled natural process for the secondary and tertiary treatment of wastewater following primary treatment in the oxidation pond, according to project engineering consultant Tim Mader of Mader-Miers Engineering, Inc. in Lafayette.

Fred Trahan, project engineer with the firm, says the system treats water in much the same way as a natural stream, in which the action of the water flowing over the rocks in the stream bed -- combined with the aquatic plants' absorption of dissolved nutrients gives the water a purity and clarity.

In fact, Crowley Wastewater Superintendent Jean Simon says the wastewater that has been treated and filtered through the local system is actually cleaner than the natural bayou water it ultimately flows into.

To arrive at that clean, filtered stage, the Crowley wastewater goes through a treatment process lasting about 60 days, Simon explains. (See diagram) Wastewater enters the system at the inflect area and is forced hydraulically and encouraged -- through the action of aerator/mixers to move out and around a fingerlike peninsula before traveling back down toward the effluent exit. This phase lasts a minimum of 52 days, Simon says.

After leaving the main pond, the water travels by gravity into four shallow marshes, where it remains for a minimum of three days. It then travels to the rock/reed filter area, taking about two days (under present flows) before passing through to the ultraviolet contact chamber for disinfection. Finally, the water proceeds to the post aeration basin -- equipped with its own aerator -- before discharge into Bayou Placeman Brule. The bayou empties into the Mermentau River.

During periods of hot and dry weather, Mader says, it is possible with the recirculation system for the Crowley treatment facility to function for days without any discharge into the receiving bayou.

"DEQ is highly appreciative of the leadership and cooperation shown by Mayor Istre, the City Council, and their staff in bringing about this new system," says Dale Givens, Assistant Secretary for DEQ's Office of Water Resources. "We applaud the steps they are taking to improve Crowley's wastewater collection and treatment."

Local officials are justifiably proud of the innovative system. In fact, tours of the facility can be arranged by contacting the City of Crowley.