After reading this article you will learn about:- 1. Concept of Bioremediation 2. Key Features of Bioremediation 3. Kinds 4. Solid Phase.
Concept of Bioremediation:
Bioremediation is a treatment technology that uses biodegradation of organic and metallic contaminants through stimulation of indigenous microbial populations by providing certain amendments, such as adding oxygen, limiting nutrients, or adding exotic microbial species.
It uses naturally occurring or externally-applied microorganisms to degrade and transform hazardous organic constituents into compounds of reduced toxicity and/or availability.
Specific technologies fall into two broad categories:
(1) Ex situ technologies (e.g. slurry phase, land treatment, solid phase, composting), and
(2) In situ technologies.
Active remediation can include addition of amendments such as nutrients or oxygen while passive remediation utilizes natural attenuation to adequately characterize, model and monitor the site to evidence natural attenuation and protection of potential receptors.
Key Features of Bioremediation:
1. Most bioremediation treatment technologies destroy the contaminants in the soil matrix.
2. These treatment technologies are generally designed to reduce toxicity either by destruction or by transforming toxic organic compounds into less toxic compounds.
3. Indigenous microorganisms, including bacteria and fungi, are most commonly used. In some cases, wastes may be inoculated with specific bacteria or fungi known to biodegrade the contaminants in question. Plants may also be used to enhance biodegradation and stabilize the soil.
4. The addition of nutrients or electron acceptors (such as hydrogen peroxide or ozone) to enhance growth and reproduction of indigenous organisms may be required.
5. Field application of bioremediation may involve:
b. Soil handling
c. Storage of contaminated soil piles
d. Mixing of contaminated soils
e. Aeration of contaminated soils
f. Injection of fluid
g. Extraction of fluid
h. Introduction of nutrients and substrates
Kinds of Bioremediation:
There are several kinds of bioremediation processes, some of them are listed:
1. Natural Attenuation
2. Aerobic/Anaerobic biodegradation
3. Bio piles
4. Land Treatment
5. Bio scrubbers
6. Methanotrophic Process (in situ)
7. Plant Root Uptake (Phytoremediation)
8. Solid Phase Bioremediation
9. Bio Wall for Plume Decontamination (in situ)
14. Binding of Metals
15. Fungi Inoculation Process
16. Slurry Phase Bioremediation
18. Bioremediation of Metals (Changing the Valence)
Solid Phase of Bioremediation:
The solid phase bioremediation treatment can be conducted in lined land treatment units or in composting piles. A lined land treatment unit consists of a prepared bed reactor with a leachate collection system and irrigation and nutrient delivery systems. The unit may also contain air emission control equipment.
Bioventing uses relatively low-flow soil aeration techniques to enhance the biodegradation of soils contaminated with organic contaminants. Although bioventing is predominantly used to treat unsaturated soils, applications involving the remediation of saturated soils and groundwater (augmented by air sparging) are becoming more common.
Generally, a vacuum extraction, an air injection, or a combination of both systems is employed. An air pump, one or more air injections or vacuum extraction probes and emissions monitors at the ground surface level are commonly used (Fig. 29.10(b)).
ii. Land farming:
Ex situ processes also include land farming, which involves spreading contaminated soils over a large area. Bioremediation may also be conducted in a bioreactor, in which the contaminated soil or sludge is slurred with water in a mixing tank or a lagoon. Bioremediation systems require that the contaminated soil or sludge be sufficiently and homogeneously mixed to ensure optimum contact with the seed organisms
Bioreactors function in a manner that is similar to sewage treatment plants. There are many ways in which a bioreactor can be designed; but most are a modification of one of two systems. In the first system which is often referred to as a trickling filter or fixed media system, the aqueous waste stream is allowed to trickle over a solid support, such as rocks, that have been colonized extensively by microorganisms.
As the liquid waste stream passes over the solids, the microorganisms break down the contaminants. Before the treated waste stream can be discharged, it must be clarified so that the number of microorganisms present in the discharge is in compliance with the regulations.
This system can also be referred to as a bio filter which is also used to treat contaminated gas streams. For this form of treatment to be effective the contaminant must be volatile.
The process of bioremediation enhances the rate of the natural microbial degradation of contaminants by supplementing these microorganisms with nutrients, carbon sources or electron donors. This can be done by using indigenous microorganisms or by adding an enriched culture of microorganisms that have specific characteristic that allow them to degrade the desired contaminant at a quicker rate.
Ideally bioremediation results in the complete mineralization of contaminants to H2O and CO2 without the build up of intermediates.
Bioremediation processes can be broadly categorized into two groups:
a. In situ and
b. Ex situ.
Ex situ bioremediation technologies include bioreactors, bio filters, land farming and some composting methods. In situ bioremediation technologies include bioventing, bio sparging, bio stimulation ,liquid delivery systems and some composting methods.
The newly introduced phytoremediation treatment, involving plant uptake/degradation of contaminants, can be used either as an in situ or ex situ method. In situ treatments tend to be more attractive to vendors and responsible parties because they require less equipment, generally are more cost effective and cause less disturbance to the environment.
However, the difficulties associated with implementing the in situ processes have limited their application in the field. Bioremediation using white-rot fungi to innoculate contaminated media is a promising technology that is currently being researched.
This technology can be used for both ex situ or in situ treatment. Generally, this fungi is used to innoculate a composting process, but it does have other bioremediation applications.
a. In situ Biodegradation:
The in situ biodegradation process is generally used in conjunction with the groundwater pumping and soil flushing systems to circulate nutrients and oxygen through a contaminated aquifer and the associated soil.
The process usually involves introducing aerated nutrient-enriched water into the contaminated zone through a series of infiltration galleries and injection wells and recovering the water down gradient.
The recovered water can then be treated, if necessary, and reintroduced into the soil on site (where allowed by the applicable regulations). The in situ biodegradation system may also include aboveground treatment and conditioning of the infiltration water with nutrients and an oxygen source or another electron acceptor (Fig. 29.10a).
b. Ex situ Bioremediation:
Ex situ processes also include land farming, which involves spreading contaminated soils over a large area Bioremediation may also be conducted in a bioreactor, in which contaminated soil or sludge is slurred with water in a mixing tank or a lagoon.
Bioremediation systems require that the contaminated soil or sludge be sufficiently and homogeneously mixed to ensure optimum contact with the seed organisms. There are many variation of the basic bio-reacter designs that have been applied for the treatment of pesticides and other hazardous wastes.