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Bioremediation of Organochlorine Solvents in Groundwater Institute of Technology, Sligo Department of Environmental Science and Technology By: Leif Barry Edel Kilgallon Breda King Subject: Waste Management Lecturer: Dr. Michael Broaders
INTRODUCTIONOrganochlorine Compounds • Toxaphene • Endrin • Dieldrin • Aldrin • Endosulfan • Chlordane • Heptachlor • Dichlodiphenyltrichloroethane (DDT) All have been manufactured since the 1940s for use as pesticides. They are not safe for household application. They persist in the environment long after initial use.
What are Chlorinated Solvents Chlorinated solvents and their natural transformation products are the most prevalent organic groundwater contaminants. Consisting of chlorinated alphatic hydrocarbons (CAHs) have been used for: Degreasing aircraft engines Automoible parts Electronic components Dry cleaning clothes
Examples of Organochlorine Solvents • trichloroethylene (TCE) • 1,1,1 trichloroethane (TCA) • Perchloroethylene (PERC) tetrachloroethane is a manufactured chemical that is widely used in the dry cleaning of fabrics,including clothes. tetrachloroethane is found in consumer products including some paints and spot removers, water repellents, brake and wood cleaners, glues and suede protectors.
Other names for tetrachloroethane include perchloroethylene (PERC) and tetrachloroethylene. In the USA, EPA studies showed that people who wear freshly dry cleaned clothes, such as a jacket and shirt, every week over a 40 year period could inhale enough PERC to measurably increase their risk of cancer by as much as 150 times.
The major sources of pollution by organochlorine solvents to groundwater • Landfills • Leaking tanks/pipes • Spillages • Soakaway drainage • Lagoons • Well injection • Sewage landspreading/infiltration and leakage from other aquifers
Minor sources of pollution by organochlorine solvent to groundwater • Surface water • Irrigation • rainfall
Organochlorine solvents discharged in sufficient quantities may form an immiscible layer separate from the main body of water. This is because of the Low solubility of the solvents And their different characteristics they are: Denser and Less viscous Than water An aquifer may remain contaminated for hundreds or thousands of years. Due to low guideline values it may only take a few litres of solvent to contaminat millions of gallons of groundwater.
WHO Guidelines for chlorinated solvents in drinking water Contaminant Guideline value (mg/l) 1,2- dichloroethane 10 1,1- dichloroethane 0.3 Chloroform 30
Goundwater Supply of Drinking Water Ireland 11% Germany 25% USA 50%
Limits for Drinking Water • WHO guidelines for chlorinated solvents in drinking waterContaminant. Guideline value (ug/l)1,2- • dichloroethane 101,1- • dichloroethene 0.3 • chloroform 30 Tentative guideline values: • Carbon tetrachloride 3.0 • tetrachlorethene 10.0 • trichlorethene 30.0
Pathway of Exposure • Inhalation • Swallowing • through the skin.
Health Effects • Acute • Generally last only minutes, hours or days • Are reversible once the exposure is over. • They are more easily identified. Common acute effects from solvent exposure include:
Respiratory Irritation • Eye Irritation. • Dermatitis. • CNS Depression. • Heart Arrhythmia
Chronic Effects • occur after repeated exposures • are often long-lasting • irreversible. • Symptoms may appear gradually, so they may be initially ignored. This can make it hard to identify the chronic health problems related to solvent exposure.
Chronic health effects include: • Respiratory Effects. • Dermatitis • Nervous System. • Liver Damage • Blood • Reproductive Effects • Cancer
Effects depends on serval factor • how easily the solvent evaporates at the ambient temperature? • what are the characteristics of that solvent; is it water soluble or able to dissolve fats? • what is the concentration of the solvent in the air at the place of work? • what type of work is involved, light or heavy? (Panting increases the amount inhaled.) • how long does the exposure last?
Prevention & Control • SOLVENT SELECTION • TRAINING • CONTAINERS • GLOVES, GOGGLES • AIR CONTAMINATION • DOCUMENTATION
What is Bioremediation? • The term bioremediation is applied to any system or process in which biological methods are used to transform or immobilize contaminants in soil or groundwater.
How does it work? The right temperature, nutrients, and amount of oxygen must be present in the soil and groundwater. • These conditions allow the microbes to grow and multiply and eat more chemicals. • Drill wells and pump some of the groundwater into tanks. Here, the water is mixed with nutrients and air before it is pumped back. • Groundwater can also be mixed underground by pumping nutrients and air into the wells.
There are two types of Bioremediation. • Ex-Situ Bioremediation • In-Situ Bioremediation
Ex-situ Bioremediation • Pump and Treat • This is the most commonly used technology for contaminated groundwater. • Now used to contain contaminated material rather than to remediate it.
In-situ Bioremediation • Percolation • Pump, treat and reinject • Injection wells • Hydrogen peroxide injection • Air sparging
Cometabolism • Most studies on biodegradation of chlorinated solvents have focused on using aerobic microbial metabolism • An exception • Cometabolism with another substance
Synergism • Many biodegradations require the cooperation of more than a single species of microbe • Two or more species of microbes carry out a transformation that one alone could not • Some reactions take place in mixtures of species but not in pure culture or take place more readily in multi-species associations • Pseudomonas spp.
Treatment Walls • Involves installing a permeable wall • It consists of an excavated ditch
Disadvantages of In-Situ treatment • Ineffective at contaminated sites where conditions are unfavourable • Longer treatment times • Nature of contaminant distribution
Advantages of In-Situ Treatment • More cost effective • Little disruption to site processes • No need for large treatment areas • It minimises exposure to humans and the environment to contaminants
Conclusion • Bioremediation is by far one of the most innovative technologies to be employed by man/woman for remediation of contaminated groundwater • There is a lot yet to be learned and understood about bioremediation of contaminated groundwater • This is a remarkable and true story of a David and Goliath battle