July 14, 2010 | General

Oil And Compost Could Prove A Good Mix In The Gulf

petroleum contaminated soil remediationBioCycle July 2010, Vol. 51, No. 7, p. 20
EPA bioremediation expert says providing an “organic matrix” could allow microbes to clean up hydrocarbon pollutants in the water and along the coast.
Dan Sullivan

AS A VETERAN member of the U.S. EPA’s Environmental Response Team, Harry L. Allen III, PhD, has helped manage the Exxon Valdez oil spill, cyanide spills in Latvia and Guyana, toxic waste dumps in Haiti and the continuing toxic legacy of Agent Orange in Vietnam.
He’s wringing his hands on the sidelines, though, as one of the worst manmade environmental disasters in history makes its way to U.S. shores from deep within the Gulf of Mexico. “The EPA has no jurisdiction [over the Deepwater Horizon oil spill],” he says. “EPA is a member of an advisory committee, that’s it.” Currently the Coast Guard and National Oceanic and Atmospheric Administration have jurisdictional oversight, he adds. “The EPA is on the sidelines here — I am making a personal effort to see if that can be changed through public acclamation.”
The oil gushing out of a pipe 5 miles below the ocean’s surface in the Gulf of Mexico is light crude, Allen explains, which in chemical terms means it is made up more of alkanes (saturated hydrocarbons) than of polyaromatic (ringed) hydrocarbons found more in asphaltic or heavy crude. The good news, he says, is that light hydrocarbons are both more biodegradable and less likely to sink and smother sensitive ecosystems, such as coral reefs. The bad news is that the overuse of both surface and subsurface dispersants inhibits both of these properties. Dispersing the oil also makes it much harder to recover by conventional means. “Over-application of dispersants to suspend the oil in the water column means that the oil may eventually sink as the oily mass gathers particulate matter,” says Allen. “Dispersion also makes the oil more available to bacteria, which require a lot of dissolved oxygen to degrade both the oil and the dispersant; this can cause dangerously low oxygen concentrations in the water column.” While dispersing the oil somewhat reduces its inherent toxicity, Allen explains, the overall toxic effect may actually be increased because the dispersed plume is spread through a much greater volume of water. In short, he says, using dispersants simply to keep the oil from forming a surface slick can actually limit the cleanup and threaten ecosystems on the ocean’s floor that may have not been in danger without the added chemicals.
“I personally told them to stop, that the surface dispersant wasn’t effective,” Allen told BioCycle from his Edison, New Jersey headquarters. “It’s not enough to affect a change in the 100,000 barrels a day that we’re now talking about. It’s so much bigger now than we had anticipated that dispersants may be doing more harm than good. My recommendation now would be to stop, but I do not think they have.”
petroleum tolerant grasses
Allen specializes in the cleanup of oil spills, hazardous waste and contaminated soils through bioremediation – the use of microscopic organisms to break down toxic chemicals. He suggests that compost could play a pivotal role in mitigating the Deepwater Horizon spill both on shore and in shallow waters. The only limitation would be that the mixture should not sink.
Compost is a rich source of bacteria and actinomyces, microscopic organisms that fall somewhere between bacteria and plants. These are equipped with complex metabolic systems that breakdown complex hydrocarbons like those found in oil, pesticides and other common petroleum-based pollutants.
“Microorganisms need some kind of growth medium,” Allen says. “The key is that you have to have suitable environmental conditions for bacterial growth and the organic matrix. Compost is the secret ingredient that allows the bacteria to work.”
The sensitivity of the affected coastal areas impedes traditional cleanup methods. “The issue here is that certain ecosystems are intolerant of mechanical or chemical activity,” he says. “The mops-and-brooms cleaning method would do more damage to salt marshes and wetlands than if you left them alone.”
Adding straight nutrients to contaminated soils to jumpstart the microbiology and allow the oil to degrade in place offers another possible scenario. But overloading of nutrients such as nitrogen and phosphorous from agricultural runoff has historically been a problem for coastal areas, particularly in the Gulf of Mexico.
“In nature there are not a lot of available nutrients; they are bound up in organic matter and only release slowly as it degrades,” Allen explains. “From plant material to duck poop,” he says, what gradually gets released into the ecosystem is quickly and efficiently taken back up by plants and other organisms in a relatively tight cycle. Oil and dispersants present an additional load on the system. In order for bioremediation to work, the microorganisms need both a hospitable environment and food. That’s where compost comes in. “You not only have to have a matrix for bacterial growth, you have to add nutrients,” Allen says.
The addition of clean soil and compost bulked up with a high percentage of sawdust, bagasse (cane residue from sugar production) or other absorptive materials could act as an oil sponge while delivering enough slow-release, relatively stable nutrients for the microorganisms to break down the offending hydrocarbons, suggests Allen. Once the microbes begin doing their job, he says, the added and amended soils could be left in place or relocated.
Harry Allen, EPAA slight twist of the same solution may be possible in the ocean. “EPA is against any sinking agents because they tend to smother, and they degrade very slowly on the bottom,” Allen explains. “We’ve prevailed in making a policy that sinkers are not good.” But floating material such as compost made up of enough ground woody vegetation so as to not sink could provide a suspended “biodegradation mat” and the necessary combination of organic matrix and nutrition to begin breaking down the oil, he says. The suspended mat could eventually be skimmed up and removed to land to fully compost on a “biopad,” with assurances in place that the polluting hydrocarbons did not find their way back to surface or ground water.
“We’ve been decommissioning oil wells and oily waste generated by that process for years,” he says. “We take the oil and debris into a passive treatment system [biopad] and allow it to degrade on its own with some help by mixing in compost and nutrients. Then we apply it to land treatments – oil-tolerant grasses – where we can be assured that it won’t erode away back into the water. We’ve found that if you supply a rich source of [compost] material to a system that as soon as it is exposed to the substance you want to have degraded, it gets working right away.”

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