Pollution poses a real threat, not only to the environment but to our very existence as well. Aside from poisoning our soil, waterways, and the air we breathe, pollution also causes considerable damage to plant, animal, and human lives and imperils the sustainability of our planet.
According to the World Health Organization (WHO), long-term exposure to ambient or outdoor air pollution accounts for about 4.2 million deaths, while indoor air pollution causes 3.8 million deaths, every year. Additionally, about 842,000 people die every year from diarrheal diseases. This is extremely unfortunate, since these deaths can easily be prevented with proper sanitation and access to clean water.
Moreover, regular exposure to some common soil pollutants causes headaches, nausea, skin rash, eye irritation, kidney and liver damage, neuromuscular blockage, and depression of the central nervous system. Worse, they are also known to increase the risk of certain cancers (e.g., leukemia, liver cancer, etc.) and may likely cause irreversible developmental damage in children.
Thankfully, there is a viable and effective solution to the problem: bioremediation.
What is Bioremediation and How Can It Help Solve the Problem?
Bioremediation is a process used to treat or restore contaminated media (e.g., soil, water, and subsurface material) by stimulating the growth of microorganisms that are capable of breaking down the target pollutants into non-toxic substances (e.g., water, carbon dioxide, and ethylene).
Bioremediation processes usually involve oxidation-reduction (redox) reactions wherein an electron donor (organic substrate) or electron acceptor (oxygen) is added to achieve the desired results. In the case of reduced pollutants such as hydrocarbons, oxygen is commonly added to enhance oxidation while an electron donor is added to stimulate the reduction of oxidized pollutants like chlorinated solvents, nitrate, oxidized metals, perchlorate, explosives, and propellants.
Some of the most common applications include removing or reducing harmful compounds in oil spills, underground pipe leaks, wastewater, and soils used for industrial and agricultural purposes.
Bioremediation techniques can be classified as in-situ (contaminants are treated on the same site) or ex-situ (treatment takes place in a different site).
In-situ bioremediation involves the addition of oxygen, nutrients, or microbes into the contaminated media to convert toxic compounds into water and carbon dioxide. Below are some of the most common in-situ techniques used in bioremediation.
- Bioventing – a process wherein oxygen is supplied to the unsaturated zone of the soil to stimulate microbial growth and activity, which will then accelerate the degradation of the target pollutant (usually a reduced contaminant such as petroleum, phenols, or polyaromatic hydrocarbons). Additional nutrients (i.e., vitamins, minerals), pH buffers, and special microbial cultures may also be added to further enhance the effectiveness of the process.
- Biostimulation – the process of making the environment more suitable for bioremediation through the addition of certain nutrients such as nitrogen, phosphorus, carbon, and oxygen.
- Biosparging – the process of injecting air and other nutrients under pressure to stimulate the action of indigenous bacteria and increase the rate of degradation of contaminants present in groundwater.
Ex-situ techniques may be considered when the necessary conditions for in-situ bioremediation cannot be achieved. For example, the soil may be dug up and treated inside a special tank or building to improve its condition, while contaminated groundwater may be pumped into a bioreactor and discharged to the ground or to a municipal wastewater system following treatment. Some of the most common ex-situ techniques include biopiles, windrows, and landfarming.
Advantages and Disadvantages
Evidently, bioremediation is less expensive and requires less energy compared to other traditional techniques such as soil washing, air stripping, bioleaching, thermal desorption, rhizofiltration, and vitrification. Moreover, it doesn’t produce any hazardous residues and can be designed to meet specific needs and combined with other technologies to increase its efficiency.
However, there are also certain limitations to this technology.
- It is only applicable to biodegradable compounds.
- It requires more time to complete the process.
- The effectiveness of the technology is highly dependent on microbial growth and the general environment.
- While the resulting by-products are generally harmless, certain bioremediation intermediates may be more toxic than the parent compounds.