Page 7 - OSMERT-2 Module 6 (inside pages) final
P. 7

conditions such as the infiltration of water-containing nutrients and oxygen or other electron
               acceptors for groundwater treatment.

               Biosparging.Biosparging involves the injection of air under pressure below the water table to
               increase groundwater oxygen concentrations and enhance the rate of biological degradation of
               contaminants by naturally occurring bacteria. Biosparging increases the mixing in the saturated
               zone and thereby increases the contact between soil and groundwater. The ease and low cost
               of installing small-diameter air injection points allows considerable flexibility in the design and
               construction of the system.

               Bioaugmentation. Bioremediation frequently involves the addition of microorganisms indigenous
               or exogenous to the contaminated sites. Two factors limit the use of added microbial cultures
               in a land treatment unit: 1) nonindigenous cultures rarely compete  well enough with an
               indigenous population to develop and sustain useful population levels and 2) most soils with
               long-term exposure to biodegradable waste have indigenous microorganisms that are effective
               degrades if the land treatment unit is well managed.

               Ex situ bioremediation
               These techniques involve the excavation or removal of contaminated soil from ground.

               Land farming is a simple technique in which contaminated soil is excavated and spread over a
               prepared bed and periodically tilled until pollutants are degraded. The goal is to stimulate
               indigenous biodegradative microorganisms and facilitate their aerobic degradation of
               contaminants. In general, the practice is limited to the treatment of superficial 10–35 cm of soil.
               Since land farming has the potential to reduce monitoring and maintenance costs, as well as
               clean-up liabilities, it has received much attention as a disposal alternative.

               Composting is a technique that involves combining contaminated soil with nonhazardous organic
               amendants such as manure or agricultural wastes. The presence of these organic materials
               supports the development of a rich microbial population and elevated temperature
               characteristic of composting.

               Biopiles  are  a hybrid of land farming and composting. Essentially,  engineered cells  are
               constructed as aerated composted piles typically used for treatment of surface contamination
               with petroleum hydrocarbons. They are a refined version of landfarming that tends to control
               physical losses of the contaminants by leaching and volatilization. Biopiles provide a favorable
               environment for indigenous aerobic and anaerobic microorganisms.

               Bioreactors.Slurry reactors or aqueous reactors are used for ex situ treatment of contaminated
               soil and water pumped up from a contaminated plume. Bioremediation in reactors involves the
               processing of contaminated solid material (soil, sediment, sludge) or water  through an
               engineered containment system. A slurry bioreactor may be defined as a containment vessel
               and apparatus used to create a three-phase (solid, liquid, and gas) mixing condition to increase
               the bioremediation rate of soil-bound and water-soluble pollutants as a water slurry of the
               contaminated soil and biomass (usually indigenous microorganisms) capable of degrading target
               contaminants. In general, the rate and extent of biodegradation are greater in a bioreactor

   2   3   4   5   6   7   8   9   10   11   12