The Use of Nitrate Injections to Stimulate Biodegradation - Ppt

7/29/2019 The Use of Nitrate Injections to Stimulate Biodegradation - Ppt

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The use of nitrate injections to

stimulate biodegradation of BTEXcompounds and ethanol

San Diego State University

ENV E 637 Industrial and Hazardous Waste

Treatment

Professor Melissa M. Valdovinos

Karina L. Sertich Arruda


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Introduction

This method uses nitrate in order toaccelerate the recovery of

groundwater contaminated with BTEX

compounds and ethanol, which areusually among the components of

gasoline.


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Nature of BTEX

BTEX stands for Benzene, Toluene,Ethylbenzene and Xylenes.

Benzene Toluene Ethylbenze

ne
http://en.wikipedia.org/wiki/File:IUPAC-cyclic.svghttp://en.wikipedia.org/wiki/File:Structural_formulas_ethylbenzene.svghttp://en.wikipedia.org/wiki/File:Toluol.svg


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Nature of BTEX

BTEX compounds may affect humanbeings, either by being ingested (e.g.drinking contaminated water), by

inhalation or by touching them (skinabsorption).

Harm the central nervous system;

Skin burning;

Respiratory problems;

May cause cancer (benzene).


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Nature of BTEX

According to the USEPA (United StatesEnvironmental Protection Agency), the

Maximum Contaminant Levels (MCLs)

for drinking water are:

Chemical Compound Maximum Contaminant Level

(MCL)

Benzene 0.005 mg/l

Toluene 1.000 mg/l

Ethylbenzene 0.700 mg/l

Total Xylenes 10.000 mg/l


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Treatment Process

Biostimulation with nitrate acceleratesbiodegradation of the BTEX compoundsin anaerobic conditions.

Denitrification will happen, because O2is not the main electrons receptor.

Nitrate will, then, act as a receptor ofelectrons, enhancing the biodegradation

of the ethanol, and therefore, of theBTEX compounds.

Nitrate will be converted to N2, which isvolatile and non-toxic.


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Treatment Process

Example: Reaction of Toluene:

6123 + 7.2+ + 7.23

= 72 +

7.62O + 3.62


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Treatment Process

BTEX compounds are successfullybiodegraded in anaerobic conditions

with nitrate, with the exception of

benzene, which is better degraded inaerobic conditions.


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Treatment Process

Advantages Disadvantages

Nitrate has a great mobility Nitrate is also a contaminant

Great solubility MCL of 10 mg/l

Produces less biomass than

aerobic reactions

Nitrate in excess may cause

illnesses (blue baby syndrome)

Less expensive than aerobic

treatments

Needs careful dosages


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Case Study

An experiment of anaerobic biostimulation with nitrate injection wasdone in real scale in the city ofFlorianpolis-SC, in Brazil.

Fifty monitoring wells were constructedin order to keep track of the plume of

contaminants and six wells were built toinject nitrate into the groundwater, at adistance of 1 meter of the contaminantsource, 3 upstream and 3 downstream.


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Case Study

Area of experiment, showing the monitoring andinjection wells. Source: COSTA, 2008.


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Case Study

The water table : depth of 1.8 meter

Monitoring and injection wells - 5

depths: 2.3m, 2.8m, 3.8m, 4.8m and5.8m.


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Case Study

Monitoring well and the different sampling levels.

Source: COSTA, 2008.


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Case Study

100 liters of gasoline (which containsabout 25% of ethanol in Brazil) were

spilt on the groundwater on the

experiment area (along with somenutrients).

Approximately 2 months later thenitrate injections were done, 3 times a

week for almost 10 months.


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Case Study

After the spill, 9 samplings were taken,approximately with a period of 3

months between the samplings.

A peak in the BTEX compounds was

observed after 17 months of the spill,

due to the insolubility of thesechemicals in water, so they took a long

time to dissolve.


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Case Study

After the 17 months, the concentration ofBTEX compounds decreased due to thebiodegradation reaction.

Nitrate concentration was really low inthe period of the injections, due to itsconsumption in the biodegradation

process. When injections ceased, nitrateconcentration decreased gradually, notonly by its consumption in thebiodegradation but also because of

natural spatial distribution.


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Case Study

Comparison to a similar case with onlyMNA: without nitrate, the decrease inthe BTEX compounds concentration

was only observed after 33 monthsafter the spill of gasoline.

Ethanol was also biodegraded before

with the aid of nitrate, with a differenceof about 5 months compared to theMNA case study.


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Conclusion

Biodegradation was anticipated for theBTEX compounds and ethanol with

nitrate injections.

Effective remediation technique and

less costly than injecting O2.

Needs careful dosage in order not to

exceed the MCL.


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References

Costa, Ana Hilda Romero. Biostimulationwith nitrate injection into groundwaterimpacted by gasoline and ethanolrelease. Florianpolis, 2008. xvii. 248

p. PhD Thesis. Universidade Federal deSanta Catarina. Departamento deEngenharia Sanitria e Ambiental.Programa de Ps-graduao emEngenharia Ambiental.

United States Environmental Protection

Agency USEPA. Can be found at:

The Use of Nitrate Injections to Stimulate Biodegradation - Ppt

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