BIOREMEDIATION TECHNOLOGY

Projects demonstrate the effectiveness of composting as a bioremediation tool.

T HE ABILITY of the composting process to degrade soil contami- nants has been demonstrated in projects and research trials for a number of years. Recently, the U.S. Environmental Protection Agency's Office of Solid Waste and

Emergency Response released a report, "Use of Bioremediation At Superfund Sites." The inclusion of composting as one of four "ex situ" bioremediation technologies further validates its role as an acceptable treatment process.

The report cites eight composting projects a t Superfund sites (between FY 1982 and FY 1999). Contaminants treated include PAHs (polyaromatic hydrocarbons), other nonchlorinated and chlorinated semi- volatile and volatile organic compounds, BTEX (benzene, toluene, ethylbenzene and xylenes), pesticides and herbicides, and ex- plosives and propellants.

One of the largest composting-based bioremediation projects in the United States got underway in May 1999 at the Joliet Army Ammunition Plant in Illinois,

where there were 200,000 dry tons of soil contaminated by TNT, DNT, Tetryl and a small amount of RDX.

: The contaminated soil is composted in windrows. Cornposting amendments include corn processing by-products, wood chips and stable bedding.

Sevenson Environmental Services of Niagara Falls, New York oversees the composting project as a subcon- tractor to Montgomery Watson. Three steel buildings were constructed at the

Three steel buildings - 80 feet wide by 400 feet long - were constructed at the Joliet site (right). Contaminated soil is mixed with amendments and put into windrows inside the buildings (above). Each batch consists of 1,500 to 1,600 tons of contaminated soil.

months depending on when the thermophilic cycle ends. "The yard trimmings we're getting are rather woody so it takes seven to nine months to make finished compost," says Obern.

When he first began composting, the C:N ratio was 55 to 1.Obern ini- tially hoped to use the Class AA biosolids from Homestead, which are 5.5 percent nitrogen, to lower t h e ratio. "The problem with biosolids is that they are only avail- able during Florida's dry season be- cause they are air-dried outdoors and i t rains every day during the summer. We needed an alternative source of nitrogen when biosolids are not available."

Obern built a drip irrigxtion sys- tem and adds nitrogen in the form of ammonium nitrate, a commercial liquid fertilizer, during composting. The irrigation system is composed of one-inch-diameter poly tubing with drip emitters installed on five-foot centers. When a windrow is built, the tubing is placed on top of it and water and ammonium nitrate are pumped through the tubing with a 12-volt pump.

When a windrow is turned, the hose is moved over to one side of the windrow and the other half i s turned. The next day, the hose is moved to the other side and the re- maining half is turned. "The latest lab reports show that the C:N ratio is now 26 to 1," says Obern.

Boosting Organic Matter And Soil Quality

"We started with organic matter of 0.9 percent and now have it up to 2.3 or 2.4 percent," notes Obern. "Our goal is to try to get it up to around seven percent. This will i - crease the cation exchange and +" ter holding capacities of the soil, 6d

er crop quality."

J hopefully get some microbial en- hancement of root growth which will lead to higher crop yields and high-

The compost is applied once per crop prior to planting, a t a rate of 50 tonslacre. Obern is already noticing improvements in his crops. "At this high rate of compost application, it seems like the soil is retaining a lot ofnutrients. The crop has a beautiful color. In early October, we had more than four inches of rain within a few days and the crops are still green."

Composting a t C&B Farms has been hampered by two problems that Obern hasn't been able to find solutions for: heavy rainfall and small spreaders. "We get a total rainfall in excess of 70 inches yearly and can get 40 to 60 inches of rain on a three-month crop," he says. Be-

tween September 1 and October 1, 20 inches of rain had fallen on the farm, leaving the compost site under two to four inches of water. "We can't do composting the way we should under these conditions, but we can't afford to put down 20 acres of as- phal t and concrete," he notes. "We've already invested over $150/acre on composting, which is

The second problem, he says, is that even large manure spreaders are not large enough for spreading compost. "We have an H&S Model 3300, which is a 30-yard machine and the biggest manure spreader made, but it can only spread com- post on six acres a day," explains Obern. "If you plant 30 acres a week and it takes five ten-hour days to put out compost, then it's taking one guy working full time to put the compost down. We need to get a re- ally big spreader to put out the large amounts of compost needed for oup'operation." H

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site (each about 80 feet wide by 400 feet long) to house the composting operation. "We treat 1,500 to 1,600 tons on a dry weight basis, per batch," says Pat Faessler, Sevenson's site treatment manager. "Con- taminant concentration varies with each batch. The remediation standard we must reach is 190 mgkg for TNT and 8.4 mgkg for each isomer of DNT."

The composting cycle time - from when the feedstocks are mixed and the windrows built through collecting analytical samples and waiting for confirmation data is 36 to 40 days. "Approximately 20 days of that time period is what we consider active treatment with fairly regular turning and monitoring:-adds-FaFmlerCompostfngp takes place year round.

Feedstocks are mixed outside the build- ing with an Allu AS38 turner; the mix then is brought inside with a front-end loader and the windrows are constructed. The same turner is used to agitate the piles, typ- ically every one to three days during the ac- tive composting time.

A mix that includes soil is significantly more dense than one consisting primarily of leaves, for example, which means that the volume capacity of the turner decreases. "If specifications say a machine can turn five cubic yardsflinear foot, it will not have that same capacity with this material," says Faessler. "Equipment capacity can be limit- ed by density." In addition, a turner with lower RPMs may be more suitable to soil re- mediation projects because there tends to be debris in the soil, such as rocks, and a lower RPM machine helps to minimize pro- jectiles created by the turner.

Sevenson expects the project will last an- other four to five years. So far, about 50,000 dry tons of soil have been remediated. At this point, the treated soil is being stock- piled until an end use is determined.

Faessler, who worked on one of the origi- nal composting bioremediation projects a t the Umatilla Army Depot in Oregon, be- lieves composting is becoming more popular for soil remediation. "You need to have a contaminant that is a little more difficult to degrade, as you do end up with more treat- ed product than you start out with. But composting is seen as an approach that can be applied to a few different types of con- taminants." He adds that cost comparisons with other technologies is difficult because it is rare to find an "apples to apples" reme- diation situation. "However, all things be- ing equal, composting is probably less than $80/ton, depending on the size of the project and the specific requirements."

TACKLING HYDROCARBONS Before getting into soil remediation via

composting, Glen Brown of Brown's Com- post Company, Inc , in Lloydminster, Saskatchewan worked for a company that used a thermal degradation technolo- gy to treat hydrocarbon contaminated soil. "The process heats up contaminated soil until contaminants evaporate and then the

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"However, all things being equal, composting is probably less than $801 ton, depending on the size of the project and the specific -

requirements," says Pat Faessler.

vapors are drawn off and put through an afterburner a t 1850 degrees," recalls Brown. "That would result in zero emis- sions, but the only problem is, you end up with a soil that was sterilized and nothing would grow in it."

As a soil technician, Brown always had an interest in composting, but it wasn't until 1999 that he decided to pursue it full-time, including its application to remediating soils contaminated with hydrocarbons. "I found that at the right temperature, the mi- crobes degrade the hydrocarbons," he says. "Success depends in part on how fine the contaminated particle is divided to expose it to microbes. For example, it is hard for mi- crobes to get t 5 T t h ~ c ~ t e r O f a l u m p ~ f dirt - that is six inches in diameter. But if that is broken into one-quarter inch pieces, and compost and/or compost tea is added, there is a lot better chance to get right to the source of the contamination."

While Brown has experience using the composting process to remediate soil, he cur- rently works with a finished compost prod- uct. His company composts agricultural residuals, including alfalfa, liquid pig ma- nure, straw and leaves, at four sites it man- ages. He follows the composting methodolo- gy developed by Midwest Bio-Systems and utilizes the Aeromaster composter turners. Over 20,000 cubic yards of material are pro- duced. A variety of compost teas are brewed using the compost produced.

Brown's Compost Company works with oil contaminated sites in Alberta and Saskatchewan. Typically, the sites are at oil wells (versus soil contaminated with re- fined petroleum products). Brown uses a recipe of about 25 percent finished compost and 75 percent contaminated soil, but that varies depending on the degree of contami- nation. The soil and compost are mixed to- gether and built into a windrow, and then compost tea is applied. The piles are turned, oftentimes with equipment already located at the oil well. "The first project in central Saskatchewan started at 140,000 ppm con- tamination and was brought down to about 4,000 ppm in three turnings," notes Brown. "The ~ecoiid project-was in-Albertaywhere the level of contamination was 55,000 ppm and it was reduced to Alberta's Tier 1 crite- ria in 20 days."

Combining feedstocks such as raw ma- nure with contaminated soil is effective as a bioremediation method, but lengthens degradation time and costs, he adds. "Bac- terial microbes in the manure are benefi- cial. Using finished compost plus compost tea as an inoculant, however, increases the microbial activity as much as 100 times that of raw manure and in return, yields a much more cost and time effective solution. Using fresh manure requires additional structuring agents, leading to higher pro- cessing costs."

Brown's Compost Company performs bioassays with compost and contaminated

oculant that can be introduced into the re- I mediation oroiect," says Brown. "The bacte- ria are familiar with "the contaminant and this in turn speeds up the degradation rate."

RESEARCH WITH DRILLING MUD An upcoming article will review recent

and current research on composting and bioremediation. Among the new research initiatives is work with invert drilling mud from oil well sites, being done by Donna Chaw of Olds College in Alberta. Drilling holes create a lot of silty mud that is con- taminated with salt and diesel, explains Chaw. "It's lighter in hydrocarbons - the contamination in the soil gets up to about 13 to 14 percent."

The research project will involve combin- ing the mud with fresh manures and blend- ing in a bulking agent like wood chips or sawdust, then building static piles. The goal is to get the level of contamination down to 2.5 percent. "We will be experimenting with different aeration methods," adds Chaw, "and will be trying to limit labor as much as possible, because access to these sites is dif- ficult." The project is scheduled to get un- derway by the end of 2001. - N.G.

The U.S. EPA report mentioned in this article, "Use of Bioremediation At Superfund Sites," is available at EPA's web site: http:l 1www.epa. gou 1 tio 1 or http: 1 1 clu-in.org.