In Business, Creating Sustainable Enterprises & Communities

CLEAN-UP METHODS WITHOUT CHEMICALS

In Business, January-February, Vol. 29, No. 1, p. 28

With close to 300,000 sites nationwide in need of remediation over the next 30 years, companies are finding ways to improve results with latest technologies.

Craig Coker

CONTAMINATION of soils with toxic and/or hazardous materials can be traced back to industrial, military, municipal and agricultural activities. The extent of this contamination is significant. The U.S. Environmental Protection Agency estimates that 294,000 sites will need to be cleaned up over the next 30 years. This includes 77,000 known sites and an estimated 217,000 sites yet to be discovered. Total clean-up costs are estimated to be $209 billion.
If the risk of human or ecological health damage is deemed high enough, remediation is required. Remediation is the process of taking action to reduce, isolate, or remove contamination from an environment with the goal of preventing exposure to people or animals. Remediation can be done by physical (air stripping), chemical (reagent addition), thermal (thermal desorption), or by biological means. Biological remediation techniques include composting, phytoremediation and landfarming, and lesser known methods such as bioaugmentation, biostimulation and bioslurping.

ENVIRONMENTAL CONTAMINANTS
There are over 330 listed environmental contaminants with known human and/or ecological health affects. They are segregated into six groups of organic chemicals and two groups of inorganic chemicals:
Organic Chemicals: Nonhalogenated volatile organics (i.e. methanol, carbon disulfide); Halogenated volatile organics (i.e. carbon tetrachloride, perchloroethylene); Nonhalogenated semivolatile organics (i.e. malathion, dimethyl phthalate); Halogenated semivolatile organics (i.e. pentachlorophenol (PCPs), polychlorinated biphenyls (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 to biodegradation by composting. Radionuclides and metals cannot be remediated (broken down) by composting; however, metals can be adsorbed into less bioavailable forms. The rate at which microorganisms degrade contaminants is influenced by the following factors: specific contaminants present; oxygen supply; moisture; nutrient supply; pH; temperature; availability of the contaminant to the microorganism (clay soils can adsorb contaminants making them unavailable to the microorganisms); concentration of the contaminants (high concentrations may be toxic to the microorganism); presence of substances toxic to the microorganism, e.g., mercury; or inhibitors to the metabolism of the contaminant.
The main advantage of ex situ treatment (removal of soils) is that it generally requires shorter time periods than in situ treatment (in the ground), and there is more certainty about the uniformity of treatment because of the ability to homogenize, screen, and continuously mix the soil. However, ex situ treatment requires excavation of soils, leading to increased costs and engineering for equipment, possible permitting, and material handling/worker exposure considerations.

BIOLOGICAL MECHANISMS
Composting can change organic chemicals and bind metals through several different mechanisms:
Biological degradation is the process where microorganisms break down water-soluble chemicals with enzymes in solution to utilize them for metabolism. Two processes that can modify an organic chemicals structure to make it more water-soluble are hydrolysis (adding water to break chemical bonds) and oxidation.
Extracellular decomposition is the process where microorganisms secrete enzymes to break down large organic molecules into a smaller form for easier absorption into the microorganism. This is how cellulose, hemicellulose and lignin are degraded in composting. Fungi are the source of most extracellular enzymes.
Intracellular decomposition takes place once the chemical has been absorbed by the microorganism. Mineralization, the process of converting an organic material to carbon dioxide and water, is the predominant process at work inside the microorganism.
Adsorption is an electrochemical process where positively- or negatively-charged organic molecules bind with their charge-opposite counterparts in organic matter and clays. This is the mechanism by which metals can be bound and become less bioavailable.
Volatilization is a physical process that changes a material from one physical state to another (i.e. from liquid phase to gas phase). Mixing of contaminated soils is a major source of volatilization (up to 30 percent of an organic chemical can be lost this way). Volatilization of hazardous chemicals is both a public health and air quality concern (EPA regulates 188 hazardous air pollutants under the Clean Air Act). Volatilization is highly temperature-dependent (higher temperatures produce more volatilization). Moisture can either block volatilization by clogging air channels with water or can increase it by liberating weakly-adsorbed chemicals. By breaking weak adsorption bonds, liberated hazardous chemicals can volatilize due to the agitation of excavation.

NEW FIRMS IN THE FIELD
Brown Environmental Services in Newtown, Pennsylvania recently completed a successful remediation of a two-acre fuel-oil contaminated site in Baltimore, Maryland under a Brownfield Agreement with the Maryland Department of the Environment, Oil Control Program. The 60-acre parcel near Baltimore Harbor used to house a heating oil company that offloaded fuel oil into a one million gallon above-ground storage tank. The new land owner, Obrecht-Riehl Properties, plans to convert the site to residential use.
Steven F. Coe, president of Brown Environmental Services, said his firm was hired as the prime contractor for the remediation work. Initial soil contamination levels were 50,000 to 75,000 milligrams per kilogram (mg/kg) of Total Petroleum Hydrocarbons (TPH). The remediation target was to reduce TPH levels to 230 mg/kg.
It was decided to use a carefully-screened form of bioaugmentation; Brown Environmental developed proprietary solutions of cultured bacteria to carry out the biodegradation. Approximately 30,000 cubic yards of soil were excavated, digging down two feet below the groundwater table. The excavated soil was formed into a treatment pile approximately 3-feet deep covering an area of 7.5 acres. Using two auger-type windrow turners, the pile was turned continuously, adding inoculum and nutrients. Nutrients were added to keep Carbon:Nitrogen:Phosphorus ratios at optimum levels. The same mix of inoculants and nutrients were used to simultaneously treat almost 20 million gallons of groundwater. The groundwater was cleaned to the point where it could be discharged without a permit from the state of Maryland.
Coe noted that the pile's temperatures rarely exceeded mesophilic levels (30°-35°C). Brown Environmental's approach to bioaugmentation does not require frequent temperature monitoring, and the project schedule allowed remediation to take place during summer months. It was able to meet the TPH target level of 230 mg/kg in over 80 percent of the pile within five months, and the Maryland Department of the Environment issued an approval letter in early August. Coe said costs for the project averaged $25/ton, which he attributed to the extensive laboratory and pilot scale work completed to ensure they had the right bacterial inoculant. “We see our front-end investment in research and development as an insurance policy to ensure the certainty of success,” he noted.
While composting has been shown to be a viable remediation technique for many types of environmental contaminants, advances in biological engineering of formulated microbial solutions now appears to offer both cost and logistical advantages over composting as a remediation technology.

Craig Coker is a Principal in the firm of Coker Composting & Consulting in Roanoke, Virginia, who specializes in providing technical support to the composting industry in the areas of planning, permitting, design, construction, operations and compost sales and marketing.