On march 24th, 1989 the oil tanker Exxon Valdez struck Bligh Reef in the Prince William Sound region of Alaska to begin one of the biggest maritime fatalities at that time. The tanker slammed into the reef around 12am local time releasing 10.8 million gallons of oil into waters of Prince William Sound as the hull of the vessel was torn open in the accident. Around the same time, Bioremediation was gaining traction as an effective method for oil clean-ups. The United States Environmental Protection Agency (EPA) and Exxon Corporation, both began testing different compounds regarding bioremediation and these tests looked quite promising. The technique involved adding fertilizers to enhance the growth of naturally occurring bacteria which have the ability to degrade certain toxic hydrocarbons present in the oil. From 1989 to 1990, more than 100,000 pounds of fertilizer was applied with more than 2000 applications in the affected areas. The result being that fertilizer degraded nearly all oil compounds by mid-1992 thus cleaning the water body.
Bioremediation and Biodegradation are often interchangeable terms. Our Biosphere has an enormous distribution of microorganisms that can grow in a wide range of environmental conditions. The versatility of such organisms can be exploited to remove or degrade contaminants, pollutants and toxins from soil and water. Certain microorganism have the ability to digest, convert, utilise or modify toxic pollutants and obtain energy or produce biomass in return. This process of using live organisms for degradation of toxicants from environment is called Bioremediation. Human activities produces an enormous variety of toxic by-products which if left untreated can cause destruction to ecosystems. The technique of Bioremediation can help us retrieve polluted soil and water. The living organisms used in this technique are actually natural decomposers. Since the beginning of time, nature has been correcting itself. But the intensity of pollution caused by human activities has overpowered nature’s ability to self-heal. Thankfully, advancements in Science and technology has resulted in the discovery of an environmental friendly technique to remediate ecosystems that have been destroyed. There has been cases like the one mentioned above where highly contaminated sites have become toxin free using bioremediation.
How does Bioremediation works? The process stimulates microbes to use toxic contaminants as their source of food and energy. These microbes are already present in the contaminated environment but it usually takes many years for the area to remediate naturally. Through human intervention the activity of these microorganisms can be enhanced. In cases where the microbes are low in number or nearly absent, Bioremediation can be introduced by adding fungi or bacteria that can be mixed with soil or water. This process is called Bio-augmentation, which works in highly effective manner to clean up the toxicants. For Bioremediation to work effectively following conditions are required-
1. Optimum temperature for microbes to flourish
2. A pH ration from 6.5 to 7.5
3. Microbial contaminants that provide fuel for food and energy
4. Water in form of soil moisture content or in liquid form
5. Nutrients like nitrogen, sulphur, potassium and phosphorus for microbial growth.
6. Oxygen and carbon for degradation and energy source.
When all the conditions are in balance, microbes can grow at an enormous rate. However, if optimum conditions are lacking, microbes can die altogether and the contaminants remain in the environment till they are naturally rectified. Oxygen plays a highly important role in Bioremediation as it is required for biological degradation. Microbes are mainly of two types- ones that thrive on air (Aerobic) and others which don’t (Anaerobic). Aerobic conditions are very commonly used in bioremediation. Anaerobic are rarely used, especially in highly contaminated sites like mining areas. This technique also requires precise monitoring.
Bioremediation can be done either in-situ, or ex-situ. In-situ means that bioremediation is done right where the site has been contaminated. In ex-situ, contaminants are taken to remote or isolated treatment location. Ex-situ treatment requires a lot of physical work from removing the contaminants and displacing them to treatment sites. Further there is a chance of contaminating another site during transportation. In-situ is therefore preferred bioremediation method with a less amount of physical work and prevents the spreading or spilling of contaminants through trucking or pumping. Thanks technological advancements today that we can treat polluted sites without any ex-situ measures.
The process of biological remediation starts with analysis of polluted sites. The site is then isolated and residential microbes are characterized like what kind of microbes exist in the site and what are needed for decontamination. The activity of these microbes and their interactions with contaminants are observed by scientists in labs to develop a field plan. After the research is done properly, bioremediation is implemented and constantly monitored while making any adjustments if required.
In America today, Bioremediation is the main choice for contaminated site recovery. From accidental chemical spills to petroleum stations, industrial sites, landfills and farms are all excellent candidates for biological remediation. In India, we still have research going on for bioremediation techniques though many polluted sites have also been biologically remediated. One of the biggest advantage of Bioremediation is reduced impact on ecosystems. It works for organic pathogens, arsenic, fluoride, nitrate, volatile organic compounds, metals and many other pollutants like ammonia and phosphates. It’s effective for cleaning insecticides and herbicides, as well as saltwater intrusion into aquifers. As long as human activities continue to threaten our natural environment, this invaluable technique will help us reclaim our polluted soil and water.
