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New Life as Fertilizer
Louisville, Kentucky’s sewer district revamped its wastewater treatment system to turn solids from trash to marketable pellets, reducing costs and saving landfill space in the process
By Jonna Lilly
Amid
a sprawling industrial area in north-central Kentucky sits a formidable
complex bustling with activity. On a beautiful autumn afternoon, I set
out for the building known to produce a unique product. Not knowing what
to expect, I was greeted by enthusiastic engineers of the Louisville and
Jefferson County Metropolitan Sewer District (MSD). They were eager to
discuss their product known as Louisville Green, a premium quality fertilizer
produced at the recently-upgraded Morris Forman Wastewater Treatment Plant
(MFWTP). This comes as a byproduct of a project that reduces landfill
disposal volume and saves an estimated $4 million in operation and maintenance
costs annually.
MSD owns and operates the Morris Foreman facility, which treats over 100 million gallons of wastewater a day. From the mid-1970s to late 2001, solids from surrounding Jefferson County were dewatered and heat treated by a process known as Zimpro at the 45-year-old MFWTP and then disposed of in a landfill. The drawbacks to this system included not only the high volume of solids that required disposal but also high labor and maintenance costs, not to mention the offensive odor generated.
Under the direction of then-executive-director Gordon Garner, a licensed engineer, MSD initiated a design-build project in 1999 to replace the entire solids handling system. A $65 million contract was awarded to a joint venture formed by Black & Veatch, one of the country’s largest engineering firms, and J.S. Alberici Construction Company to design and construct a new solids handling system. It would include oxygen-free anaerobic digesters to handle primary solids, centrifuge dewatering to separate liquids and solids, and solids drying in rotary drum dryers.
Replacing
the solids handling system in a plant with space limitations while maintaining
uninterrupted service proved quite a challenge. "It was an interesting
time, when the old equipment was down, and the new equipment wasn’t
fully operational yet," says MSD’s West Region Operations Manager
David Carty. One reason for the project’s success was MSD’s
decision to involve operators and maintenance staff from design through
construction and startup. "This is the first time we used a startup
team through all aspects of the project, and it was very helpful for everyone
to be involved."
Three individual teams formed to facilitate the project. As an extension of the construction management team overseeing the design-build contract, the Start-Up team visited other dryer installations to help them develop the startup and operating plan. They also produced standard operating procedures and assisted in training of MSD operators. The Biosolids Quality Team collected and monitored biosolids data to prepare MSD to apply for land application permits from Kentucky and Indiana and fertilizer licenses from various states. Finally, the Biosolids Management Team, composed of members of various departments and a marketing expert, focused on marketing the product.
In addition, MSD Executive Director Bud Schardein, Biosolids Administrator Robert Bates, and a consultant visited five other public wastewater management agencies for guidance and direction. These trips enabled MSD representatives to interact directly with their counterparts to discuss startup issues, operational problems they encountered, marketing strategies, and management approaches. They told MSD that in almost every case, initial problems occurred in their biosolids pellet production.
Consequently,
MSD learned it would be best to market its pellets in bulk to fertilizer
or agricultural markets and that it was economically advantageous to produce
and market so-called Green Grade pellets. They also heard that successful
marketing would positively impact public perception about wastewater management
agencies.
Squeezing in New Equipment
Since no new buildings were to be erected, all new equipment had to be
carefully squeezed into existing plant space. It proved especially challenging
to install the four 14-foot diameter rotary drum dryers, actually the
largest capacity dryers in North America. Engineering Director Derek Guthrie
managed the engineering effort from MSD’s end, working with Black
and Veatch engineers.
According to Robert Bates, water and solids from other MSD plants are passed through bar screens to remove larger debris and then through a grit removal process. From that point, four anaerobic digesters break down the solids, called primary sludge. The MFWTP reaps a cost-saving benefit from this process, as methane gas discharged by the digesters fuel the dryers used later. After digestion, the material moves to the dewatering phase, where five centrifuges separate more water from solid matter.
Next comes drying. More water is removed from the solids, and they are heated to temperatures above 195 degrees F. to kill bacteria, viruses, and mold. Pellets are formed by taking a smaller dried product and mixing it with dewatered cake to form a pellet with a dry core and wet outer layer. The pellet then passes through a triple rotary drum dryer. If the pellet is too small, it returns to the process via a recycle bin. Storage facilities house about five days worth of production. Dried pellets range from one to four millimeters in size, the smaller sizes costing more to produce.
This
new solids handling process has proved successful for several reasons.
First, the new system replaces the former Zimpro system, which generated
off-site odors and concerned plant neighbors. Second, the volume of solids
for disposal has been reduced by more than two-thirds. MSD’s Biosolids
Marketing Project Manager Sharon Worley, who has a degree in civil environmental
engineering, explains, "Beyond saving MSD money by reducing annual
landfill costs, the process also generates a pelletized biosolids product
which can be beneficially reused in a wide variety of applications."
A Better Fertilizer
Known as Louisville Green, the product is an environmentally safe fertilizer
and a slow-release organic product, meaning it requires fewer applications
because it breaks down slowly. Nutrients and moisture are held in longer,
and healthier root growth results.
In mid-2004, MSD allowed the distribution of over 500 tons of Louisville Green biosolids pellets to a variety of users, including fertilizer blenders, golf courses, sod farms, and Kentucky state government agencies, to gauge reactions to the product. While some people expressed concerns about the safety of such a product, the Louisville Green team emphasizes that on a daily basis, they test it to ensure safety for people, animals, and plants. In addition, it meets "Class A, Exceptional Quality" guidelines of the federal government.
Initial impressions of the pellets have also included concerns about dust, size, and odor, so the Louisville Green team has actively sought a product more in line with consumer demand. Bates reports, "We have made several operational changes to achieve a more marketable product." MSD now sprays pellets with a fine mist of oil to reduce dust, makes them in smaller sizes, and adds ferric chloride to reduce odor. "As a result of these changes, we have taken what historically had been a costly wastestream and turned it into a potential revenue stream," Bates adds.
Worley
explains that it has required a cultural change for MSD to transition
from a waste disposal mentality to one of product marketing. "We
realized we wanted to learn to walk before we ran, so we felt taking a
few months to investigate the marketability of the product would be beneficial."
To give employees a sense of ownership in the project, MSD held a contest
to name the new product. Several interesting options emerged, including
"BI-AGRA," "Deja-Du," "Metro Magic," and
"Superdoo!" "Louisville Green" prevailed as the winning
entry, however, emphasizing the plant-friendly aspect of the product.
In its continuing quest to make Louisville Green a viable product, MSD plans to hire a full-time Marketing Manager, Worley says. In addition, by the spring of 2005, they plan to place the pellets on hardware store shelves in 40-pound bags for sale to the general public.
Although Carty concludes that the Louisville Green project has been challenging, he thinks MSD has blazed a path for others to follow. Many other wastewater treatment facilities nationwide will probably adopt similar processes as landfill space becomes more scarce and the lure of additional revenue spurs them to action. "We have such a sense of pride in our product," he says. "It truly is a win-win for everybody."
As an English major and writer in New Albany, Indiana, Jonna Lilly has taught at several colleges and universities and written for numerous national publications and websites.
For more information on the Louisville Green project to convert biosolids to fertilizer, visit www.louisvillegreen.com
For more information on the Louisville and Jefferson County Metropolitan Sewer District, visit www.msdlouky.org
Progressive
Engineer
Editor: Tom Gibson
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©2004 Progressive Engineer