ENVIRONMENTALREMEDIATIONBY COMPOSTINGWith close to 300,000 sites nationwide inneed of clean-up over the next 30 years,composting is among the remediationtechnologies being put to use.

ONTAMINATION of soils withtoxic and/or hazardous materialscan be traced back to industrial,military, municipal and agricul-tural activities. The extent of thiscontamination is significant. In2004, the U.S. Environmental

Protection Agency estimated that 294,000sites will need to be cleaned up over the next30 years. This includes 77,000 known sitesand an estimated 217,000 sites yet to be dis-covered. Total clean up costs are estimatedto be $209 billion.

These estimates include the seven majorclean-up programs: National Priorities List(NPL, or Superfund); Resource Conserva-tion and Recovery Act (RCRA) CorrectiveAction; Underground Storage Tanks (UST);Department of Defense (DOD); Departmentof Energy (DOE); Other (Civilian) FederalAgencies; and States and Private Parties(including brownfields).

If the risk of human or ecological healthdamage is deemed high enough, remedia-tion is required. Remediation is the processof taking action to reduce, isolate, or removecontamination from an environment withthe goal of preventing exposure to people oranimals. Remediation can be done by phys-ical (air stripping), chemical (reagent addi-tion), thermal (thermal desorption), or by bi-ological means. Biological remediationtechniques include composting, phytoreme-diation and landfarming, and lesser knownmethods such as bioaugmentation, biostim-ulation and bioslurping. Composting is con-sidered to be an ex-situ (meaning "out ofplace") treatment technology.

Part 1 ofthis article series discusses howcomposting technologies normally used fornonhazardous organic materials can be ap-plied to contaminated site remediation.Part 2 will examine how the addition of fin-ished compost to contaminated soils willhelp reduce toxic levels of pollution.

ENVIRONMENTAL CONTAMINANTSThere are over 330 listed environmental

contaminants with known human and/orecological health affects. They are segregat-ed into six groups of organic chemicals andtwo groups of inorganic chemicals:Organic Chemicals: Nonhalogenated

volatile organics (i.e. methanol, carbondisulfide); Halogenated volatile organics(i.e. carbon tetrachloride, perchloroethy-lene); Nonhalogenated semivolatile organ-ics (i.e. malathion, dimethyl phthalate);Halogenated semivolatile organics (i.e. pen-tachlorophenol (PCPs), polychlorinatedbiphenyls (PCBs)); Fuels (i.e. gasoline,diesel, fuel oil); Explosives (i.e. TNT, RDX,nitroglycerine) .Inorganic Chemicals: Metals (i.e. arsenic,

cadmium, lead, zinc); Radionuclides (i.e.cobalt-60, uranium, radium).

Not all organic chemicals are amenable tobiodegradation by composting. Radionu-clides and metals cannot be remediated(broken down) by compo sting; however,

metals can be adsorbed into less bioavail-~ble forms. The rate at which microorgan-Isms degrade contaminants is influenced bythe following factors: specific contaminantspresent; oxygen supply; moisture; nutrientsupply; pH; temperature; availability ofthecontaminant to the microorganism (claysoils can adsorb contaminants making themunavailable to the microorganisms); concen-tration of the contaminants (high concen-trations may be toxic to the microorganism);presence of substances toxic to the microor-ganism, e.g., mercury; or inhibitors to themetabolism of the contaminant.

The main advantage of ex situ treatment(removal of soils) is that it generally requiresshorter time periods than in situ treatment(in the ground), and there is more certaintyabout the uniformity oftreatment because ofthe ability to homogenize, screen, and con-tinuously mix the soil. However, ex situ treat-ment requires excavation of soils, leading toincreased costs and engineering for equip-ment, possible permitting, and material han-dling/worker exposure considerations.

BIOLOGICAL MECHANISMSComposting can change organic chemi-

cals and bind metals through several differ-ent mechanisms:Biological degradation is the process

where microorganisms break down water-soluble chemicals with enzymes in solution

Brown Environmental Servicesformed a treatment pile about3-feet deep covering an areaof 7.5 acres. Two windrowturners (one shown above)were used for continuousagitation of the pile and to addan inoculum and nutrients.

to utilize them for metabolism. Two pro-cesses that can modify an organic chemicalsstructure to make it more water-soluble arehydrolysis (adding water to break chemicalbonds) and oxidation.Extracellular decomposition is the process

where microorganisms secrete enzymes tobreak down large organic molecules into asmaller form for edsier absorption into themicroorganism. This is how cellulose, hemi-cellulose and lignin are degraded in com-posting. Fungi are the source of most extra-cellular enzymes.Intracellular decomposition takes place

once the chemical has been absorbed bythe microorganism. Mineralization, theprocess of converting an organic materialto carbon dioxide and water, is the pre-dominant process at work inside the mi-croorganism.Adsorption is an electrochemical pro-

cess where positively- or negatively-charged organic molecules bind withtheir charge-opposite counterparts in or-ganic matter and clays. This is the mech-anism by which metals can be bound andbecome less bioavailable.Volatilization is a physical process that

changes a material from one physicalstate to another (i.e. from liquid phase togas phase). Mixing of contaminated soilsis a major source ofvolatilization (up to 30percent of an organic chemical can be lostthis way). Volatilization of hazardouschemicals is both a public health and airquality concern (EPA regulates 188 haz-ardous air pollutants under the Clean AirAct).Volatilization is highly temperature-dependent (higher temperatures producemore volatilization). Moisture can eitherblock volatilization by clogging air chan-nels with water or can increase it by liber-ating weakly-adsorbed chemicals. Bybreaking weak adsorption bonds, liberat-ed hazardous chemicals can volatilize dueto the agitation of excavation.

COMPOSTING CONSIDERATIONSTraditional composting of nontoxic or-

ganic materials is based on proper recipeformulation, thorough mixing, aerobiccomposting and curing to produce a sta-ble and mature compost for product mar-kets in the shortest possible time at theleast possible cost. Composting of con-taminated soils has a different endpoint(the degradation of the contaminant), andproduct marketability is not an issue, sotemperatures, time, C:N ratios, moisturecontent and porosity are somewhat lessimportant considerations. Thennophilictemperatures have been shown to greatlyaccelerate the degradation of some con-taminants (like polycyclic aromatic hy-drocarbons (PAHs», but at a greater riskof gaseous volatilization. (The Occupa-tional Safety and Health Administration(OSHA) has set a limit of 0.2 milligramsofPAHs per cubic meter of air.)

In some cases, anaerobic conditionsmay be needed to degrade highly chlori-nated compounds, a step which is thenfollowed with aerobic treatment to de-grade the partially dechlorinated com-pounds as well as the other constituents.Anaerobic microbial processes that are ofsignificance in environmental remedia-tion include denitrification, iron/man-ganese reduction, sulfidogenesis andmethanogenesis. Sulfidogenic and iron-reducing microbial populations can de-halogenate and mineralize chlorinatedand brominated aromatic compounds.

Moisture levels in the range of20 to 80

percent are considered sUitablle for thebioremediation of soils, but the microbesin composting thrive best be~ween 40and 60 percent moisture. Nutrient pro-cess design is focused on C:N:P ratios, inwhich ratios of 120:10:2 are not uncom-mon. Each remediation project!is differ-ent, due to variations in the nature of thecontaminant, initial concentration ofthat contaminant, desired endpoint (of-ten influenced by risk assessments),degradation rate (dependent on both thenature ofthe contaminant and the ener-gy level of the compostable feedstocks),concerns over volatilization and leach-ing, and available space.

Composting can be done with aeratedstatic piles, in-vessel systems, or withwindrows. Windrow composting is con-sidered to be the most cost-effect'ivealter-native, but it may also have the highestlevels offugitive emissions ofVolatile Or-ganic Compounds (VOCs). Compostingwith aerated static piles, also known asbiopiles, is an effective means of remedi-ating petroleum contamination.

MIXING CONTAMINATED SOILSRemediation via composting can be ac-

complished by mixing contaminated soilswith fresh, high-energy feedstocks or bysimply adding a mature, finished compostto contaminated soils. A mix ratio of 30percent soil and 70 percent feedstocks hasbeen observed to reach thermophilic tem-peratures. A mix of 18 percent soil and 82percent yard trimmings remediated 40percent of the PCBs in a contaminatedsoil over a period of370 days. Compostinghas been shown to be an effective ap-proach to the remediation of explosives-contaminated soils, with degradation of99.7 percent ofTNT, 99.8 percent ofRDX,and 96.8 percent ofHMX at the UmatillaArmy Depot. A mature, six-month oldcompost mixed with petroleum contami-nated soils was observed to degradepetroleum at a rate eight times fasterthan with in-situ bioremediation (naturalattenuation).

Due to the increase in volumes of mate-rials to be handled by mixing contaminat-ed soils with traditional compostable feed-stocks, many ex-situ bioremediationprojects will use inoculums of cultured in-digenous bacteria and nutrient broths tocreate the proper conditions for biologicaldegradation. In many cases, this inoculumofindigenous microbes has the same effectas recycling overs from compost screeningback into the feedstock mixing system ata composting facility. Typically, indige-nous microbes are capable of effecting re-mediation because they are acclimated tothe contaminant as well as their mi-croniche; however, research is currentlyunderway at a number of facilities usingexogenous, specialized microbes or genet-ically engineered microbes (GEMs) to op-timize bioremediation. Several companies

Costs forremediation withcomposting varywith amount of soilto be treated, mixratio of soil tocompostables,availability and costof amendments,type of contaminantand process design.

now make and market proprietary formula-tions of biodegradable surfactants, solvents,emulsifiers, degassing agents, nutrients,biostimulants and specialty strain, non-pathogenic bacteria. These liquid solutionsare easily introduced into and mixedwith thecontaminated soil.

Costs for remediation with compostingvary with the amount of soil to be treated,mix ratio of soil to compostables, availabili-ty and cost of amendments, type ofcontam-inant and process design. Reported costs in-clude: $84 to $190/ton for explosives-contaminated soil and $266/ton for soil con-taminated with PAHs, PCPs and VOCs.Costs forbiopilesare reported to be as lowas$30 to $60/ton.

There are limitations to the use of com-posting for remediation. These include:Challenges in scaling up from bench (or lab-oratory) to pilot to full-scale operations;Need for very large available space to com-post many thousands of cubic yards of con-taminated soils; Increase in the total volumeofmaterials to be handled (due to addition ofbulking agents), which can affect final dis-posal costs; Possible generation of interme-diate decomposition products with even

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Untreated -soil stockpilearea

higher levels oftoxicity during the biodegra-dation process; Volatilization of gases, withthe attendant air pollution considerations;Possible increase in metal concentrationsdue to the loss of carbon in composting; andPotential for hazardous constituents that donot degrade to become nonextractable andbound to the soil matrix.

REMEDIATING FUEL Oil CONTAMINATIONBrown Environmental Services in New-

town, Pennsylvania recently completed asuccessful remediation of a two-acre fuel-oilcontaminated site in Baltimore, Marylandunder a Brownfield Agreement with theMaryland Department of the Environment,Oil Control Program. The 60-acre parcelnear Baltimore Harbor used to house a heat-ing oil company that offloadedfuel oil into aone million gallon above-ground storagetank. The new land owner, Obrecht-RiehlProperties, plans to convert the site to resi-dential use.

Steven F. Coe, President of Brown Envi-ronmental Services, said his firm was hiredas the prime contractor for the remediationwork. Initial soil contamination levels were50,000 to 75,000 milligrams per kilogram

(mglkgl of Total Petroleum Hydrocarbons(TPH).The remediation target was to reduceTPH levels to 230 mglkg.

It was decided to use a carefully-screenedform of bioaugmentation; Brown Environ-mental developed proprietary solutions ofcultured bacteria to carry out the biodegra-dation. Approximately 30,000 cubic yards ofsoil were excavated, digging down two feetbelowthe groundwater table. The excavatedsoil was formed into a treatment pile ap-proximately 3-feet deep covering an area of7.5 acres. Using two Brown Bear auger-typewindrow turners, the pile was turned con-tinuously, adding inoculum and nutrients.Nutrients were added to keep Carbon:Nitro-gen:Phosphorus ratios at optimum levels.The same mix of inoculants and nutrientswere used to simultaneously treat almost 20million gallons ofgroundwater. The ground-water was cleaned to the point where it couldbe discharged without a permit from theState ofMaryland.

Coe noted that the pile's temperaturesrarely exceededmesophilic levels (30°-35°C).Brown Environmental's approach to bioaug-mentation does not require frequent temper-ature monitoring, and the project scheduleallowed remediation to take place duringsummer months. It was able to meet the TPHtarget level of 230 mglkg in over 80 percentofthe pile within fivemonths, and the Mary-land Department of the Environment issuedan approval letter in early August. Coe saidcosts for the project averaged $25/ton, whichhe attributed to the extensive laboratory andpilot scalework completedto ensure they hadthe right bacterial inoculant. "We see ourfront-end investment in research and devel-opment as an insurance policyto ensure thecertainty of success,"he noted.

REMEDIATINGEXPLOSIVES·CONTAMINATED SOil

Tooele Army Depot (TEAD) was estab-lished by the U.S. Army in Tooele, Utah in1942 to provide a storage depot for WorldWar II supplies, ammunition and combat ve-hicles. Consisting of 23,610 acres, TEAD isnow an ammunition storage and manufac-turing facility for the Army. The TNTWashout Facility at TEAD was used for de-commissioning explosive munitions, whichincluded steam cleaning and rinsing muni-tions casings. The rinsewater flowedthrough a series of settling tanks and filtersto a series of unlined, bermed washoutponds. Elevated levels (up to 20,000 mglkg)of 2,4,6,-trinitrotoluene (2,4,6-TNT) and cy-clotrimethlylene trinitramine (RDX) havebeen detected in the surface and subsurfacesoils at this facility.

The Army has decided to undertake Cor-rective Action at the TNT Washout facilityin 2007.The remediation will include the ex-cavation of approximately 10,000 cubicyards of 2,4,6-TNT and RDX contaminatedsoils, construction of a temporary treatmentfacility, bioremediation/composting of thecontaminated soil, and backfilling areas

with the treated soil. The majority of the ex-plosives-contaminated soils are present at adepth of 7-feet below ground surface or less.

Composting was chosen by the Army asthe remediation technology for TEAD basedon successful similar remediation projectsat Umatilla Army Depot in Oregon and Joli-et Army Ammunition Plant in Missouri.(Reports on those remediation projects canbe found in the following BioCycle articles:"Clean Up At Munitions Sites," March1996; "Bioremediating Explosives Contam-inated Soil," May 1999; "Military WinsWith Bioremediation Through Compost-ing," March 2001; and "Advances In Com-posting Contaminated Soils," November2001.) Excavating explosives-contaminatedsoil does not raise the same issues aboutvolatilization that can occur with chemical-ly-contmmnated soils. "These types of con-taminants don't tend to volatilize," saidApril Fontaine, the project manager at theU.s. Army Corps of Engineers. "They tendto stick to soil particles."

The composting process selected for use atTEAD will be the turned windrow method,with 30 percent of the compostable mix con-sisting of excavated contaminated soil. Theremainder of the compost recipe consists ofwood chips (10%), alfalfa (15%), lettuce(10%), barley (10%), cow manure (20%) andpoultry litter (5%). The lettuce, barley andanimal manures are the nitrogenousamendments and alfalfa and wood chips arethe bulking agents.

The composting amendments will be load-ed into 12-14 cubic yard end dump mixingtrucks until the truck is 70 percent full. Thetrucks will then drive to the soil stockpilearea, where they will be filled to capacitywith screened, untreated explosives-con-taminated soil. The trucks will mix the in-gredients together as they travel to the Com-post Treatment Facility (Figure 1) wherethey will unload the mix to be formed intowindrows. The Compost Treatment Facilityis sized to treat three windrows, each 26-feetwide by 300-feet long. Approximately 18,000gallons of water will be applied daily by awater truck to maintain soil moisture levelsbetween 40 and 60 percent of the soil's wa-ter holding capacity. Windrows will beturned with a Frontier pull-behind windrowturner. Treatability studies conducted sev-eral years ago concluded that each batch ofcontaminated soil could be composted tomeet the Corrective Action Goals (31 mglkgfor RDX and 86 mglkg for 2,4,6-TNT) within20 days and that thermophilic temperatureswould be reached within three days andwould stay at thermophilic elevated levelsfor more than 20 days.

The Compost Treatment Facility will be al30-foot by 450-foot temporary SprungStructure erected over a 4-inch thick asphaltconcrete pad. The pad consists of a compact-ed layer of road-base m.aterial, 4-inches ofasphalt concrete and a 4-inch asphalt curbaround the edges.

While composting has been shown to be a

viable remediation technique for many typesof environmental contaminants, advances inbiological engineering of formulated micro-bial solutions now appears to offer both costand logistical advantages over compostingas a remediation technology. •

Nutrient processdesign is focused onC:N:P, in whichratios of 120:10:2 arenot uncommon.

Craig Coker is a Principal in the firm of CokerComposting & Consulting in Roanoke, Vir-ginia, who specializes in providing technicalsupport to the composting industry in the areasof planning, permitting, design, construction.,operations and compost sales and marketing.

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