Solid-waste management is a major challenge in urban areas throughout the world. Without an effective and efficient solid-waste management program, the waste generated from various human activities, can result in health hazards and have a negative impact on the environment. Continuously and uncontrolled discharge of industrial and urban wastes into the environmental sink has become an issue of major global concern. The industrial and anthropogenic activities had also led to the contamination of agricultural lands which results the loss of biodiversity. Although the use of pesticides, herbicides increases the productivity of crop but also increase the contamination in the soil, water and air.
Bioremediation is not only a process of removing the pollutant from the environment but also it an eco-friendly and more effective process. The pollutants can be removes or detoxify from the soil and water by the use of microorganism, known as bioremediation.
In the presence of aerobic conditions and appropriate nutrients, microorganisms can convert many organic contaminants to carbon dioxide, water, and microbial cell mass. Aerobic bioremediation uses oxygen as the electron acceptor. Aerobic metabolism is more commonly exploited and can be effective for hydrocarbons and other organic compounds, such as petroleum hydrocarbons and some fuel oxygenates (e.g., methyl tertiary-butyl ether [MTBE]). Many organisms are capable of degrading hydrocarbons using oxygen as the electron acceptor and the hydrocarbons as carbon and energy sources.
Aerobic bioremediation is most often used at sites with mid-weight petroleum products (e.g., diesel fuel and jet fuel), because lighter products such as gasoline tend to volatilize readily and can be removed more rapidly using other technologies (e.g., air sparging or soil vapor extraction). Heavier petroleum products such as lubricating oils generally take longer to biodegrade than the lighter products, but enhanced aerobic bioremediation technologies may still be effective.
Technologies to accelerate naturally-occurring in situ bioremediation include biosparging, bioventing, and the use of oxygen-releasing substances such as pure oxygen, hydrogen peroxide, ozone, and commercial oxygen-releasing compounds. These technologies work by providing an additional supply of oxygen to the subsurface, which then becomes available to aerobic bacteria.
Bioventing involves supplying air or oxygen, and nutrients if needed, into the unsaturated zone. Oxygen is delivered to the unsaturated zone by forced air movement either through extraction or injection of air to increase oxygen concentrations. Direct air injection is used more commonly to control air flow rates and provide only enough oxygen to sustain microbial activity. Bioventing is designed primarily to treat contaminants in the vadose zone or capillary fringe.
Bioventing has a strong record of treating aerobically degradable contaminants such as fuels, but also has been used to treat a variety of other contaminants, including nonhalogenated solvents (e.g., benzene, acetone, toluene, and phenol). While bioventing is relatively inexpensive, this method can take a few years to clean up a site, depending on contaminant concentrations and site-specific removal rates.
Biosparging is an in-situ remediation technology that uses indigenous microorganisms to biodegrade organic constituents in the saturated zone. In biosparging, air (or oxygen) and nutrients (if needed) are injected into the saturated zone to increase the biological activity of the indigenous microorganisms. Biosparging can be used to reduce concentrations of petroleum constituents that are dissolved in groundwater, adsorbed to soil below the water table, and within the capillary fringe. Although constituents adsorbed to soils in the unsaturated zone can also be treated by biosparging, bioventing is typically more effective for this situation.
The biosparging process is similar to air sparging. However, while air sparging removes constituents primarily through volatilization, biosparging promotes biodegradation of constituents rather than volatilization.
Advantages Of Biosparging
Readily available equipment; easy to install.
Creates minimal disturbance to site operations.
Short treatment times, 6 months to 2 years under favorable conditions.
Is cost competitive.
Enhances the effectiveness of air sparging for treating a wider range of petroleum hydrocarbons.
Requires no removal, treatment, storage, or discharge of groundwater.
Disadvantages Of Biosparging
Can only be used in environments where air sparging is suitable (e.g., uniform and permeable soils, unconfined aquifer, no free-phase hydrocarbons, no nearby subsurface confined spaces).
Some interactions among complex chemical, physical, and biological processes are not well understood.
Lack of field and laboratory data to support design considerations.
Potential for inducing migration of constituents.