CHAFFEE RENOVATES WASTE TREATMENT WITH NEW TECHNOLOGY

CHAFFEE -- Although it cost $500,000 to renovate the final cell of Chaffee's triple-cell waste-water treatment system, the only active component used in the final treatment process - lemnacae plants - was literally free for the taking.

Lemnacae is the Latin word for the aquatic duckweed plant, a species of floating water plant that's found throughout the world. In this case, the duckweed plant for Chaffee's waste-water treatment system was harvested from a slough of the beheaded Castor River near the Diversion Channel west of Advance.

On Friday, the city will hold a ribbon-cutting ceremony and open house from 1-5 p.m. at the Chaffee waste-water treatment plant. The plant is west of the Columbia Sportswear plant in Chaffee Industrial Park.

Work on the project began a year ago and was completed this month.

Alan W. McSpadden, consulting engineer for Smith and Co. of Cape Girardeau, said the final, or tertiary cell of Chaffee's waste-water treatment plant, utilizes a new concept to reduce suspended solids in the effluent.

It is also the first such system of this type to be installed anywhere in Missouri. Smith & Co. was the consulting engineering firm for the waste-water improvement project.

Chaffee has been in trouble for many years with the Missouri Department of Natural Resources and the federal Environmental Protection Agency because the outflow of its waste-water treatment plant has had consistently high counts of suspended solids, mostly algae.

Like many other cities in the United States, Chaffee's waste-water treatment plant uses a lagoon system to treat sewage. The sewage lagoons -- usually three of them -- utilize algae as part of the microbiological process that breaks down and eliminates solid and liquid wastes.

Unfortunately, the rich nutrients the algae consumes in the treatment process also causes it to grow rapidly, especially during the summer months. When that happens, the amount of suspended solids in the effluent, or outflow from the plant, skyrockets. That's something the DNR and EPA frown on.

To get the suspended solids count back within mandated guidelines, Chaffee decided to use the lemna waste-water treatment process. McSpadden said the heart of the process is the tiny duckweed plant that floats and grows on the surface of the lagoons.

Said McSpadden: "The duckweed covers the surface of the lagoon, which reduces the amount of sunlight that can enter the water. This reduces and controls the growth of algae since algae needs sunlight to grow."

To illustrate, McSpadden said before the lemna process was installed in the tertiary cell, the effluent discharge from the cell often contained as much as 500 parts per million of suspended solids. Since the lemna process was installed, the level of suspended solids has dropped to 60 ppm, below the DNR limit of 80 ppm.

"We expect the count will drop even more," McSpadden said. "Right now the city is drawing down the water level in the primary cells, so there is an abnormally high discharge of effluent. After the desired water level is reached, we expect the ppm count will drop even more."

McSpadden said a matrix of floating barriers divides the tertiary cell into small sections, or grids, in which the duckweed floats and grows. The flexible barriers -- made of synthetic materials and anchored to the shore -- shield the duckweed from the wind and prevents wave action on the surface of the lagoon.

Floating hydraulic baffles extend to the bottom of the lagoon and 4-6 inches above the surface. This forces the treated waste-water coming from the secondary treatment cell to flow through a serpentine channel before it's finally discharged as effluent.

McSpadden said the baffles prolong the amount of detention time in the tertiary cell to allow for the removal of suspended solids and other pollutants.

"The nice thing about this process is that it uses no moving mechanical parts, said McSpadden. "The only piece of equipment we use is a harvester to harvest the duckweed plants."

Duckweed can grow in water temperatures as low as 42 degrees. Below that it survives by sinking to the bottom of the lagoon and going dormant until it warms up. Because duckweed plants grow, they must be harvested to thin out the plant population, said McSpadden. A small, motorized paddle-wheel boat travels over the surface of the water, pushing the excess duckweed to collectors near the shore.

McSpadden said the harvested duckweed has a high nutrient content and can be used for agricultural purposes as fertilizer or for composting. It can also be used as a mulch for landscaping or gardening when mixed with wood chips, leaves or shredded paper.

Cost of the tertiary cell renovation was paid for by a DNR revolving loan to Chaffee. Citizens approved a bond issue to guarantee the loan. The bonds will be paid off over a 20-year period from sewage fee revenues.