User:Debra Tabron/sandbox

Emulsified Vegetable Oil (EVO) is commonly added as a slowly fermentable substrate to stimulate in situ anaerobic bioremediation. This article summarizes information about EVO transport in the subsurface, consumption during anaerobic bioremediation, and methods for effectively distributing EVO throughout the target treatment zone.

Related Article(s):

• Anaerobic Bioremediation
• Anaerobic Bioremediation Design Considerations
• Chlorinated Solvents

CONTRIBUTOR(S): Dr. Robert Borden, P.E.

Key Resource(s):

• Post-Remediation Evaluation of EVO Treatment – How Can We Improve Performance?
• Protocol for Enhanced In Situ Bioremediation Using Emulsified Edible Oil (Solutions-IES, 2006)

Introduction

- rapid flocculation	0 mV	<	zeta potential	<	-5 mV
- incipient instability	-10 mV	<	zeta potential	<	-30 mV
- moderate stability	-30 mV	<	zeta potential	<	-40 mV
- good stability	-40 mV	<	zeta potential	<	-61 mV
- excellent stability			zeta potential	<	-61 mV

Table 1. Effect of solution composition on zeta potential

Colloid	Average Zeta Potential (mV) (standard deviation)
	DI Water	200 mg/L CaCl2
SA17 Soil 15-23’	-29.4 (0.8)	-8.5 (0.5)
SA17 Soil 30-40’	-22.3 (0.9)	-7.5 (0.9)
OU2 Soil 37-40’	-19.9 (0.5)	-12.2 (0.9)
EOS 598B42	-43.0 (0.7)	-10.3 (0.4)

Table 2. Oil retention in laboratory columns flushed with EOS598B42 and either DI water or 200 mg/L CaCl₂

Aquifer Material	Average Oil Retention (g oil/g sediment) (standard deviation)
	DI Water	200 mg/L CaCl2
SA17 Zone B	0.0027 (0.0027)	0.0133 (0.0060)
OU2	0.0144 (0.0018)	0.0381 (0.0114)

Summary

Emulsified Vegetable Oil (EVO) is commonly added as a slowly fermentable substrate to stimulate in situ anaerobic bioremediation. Commercially available EVO typically contains a mixture of 45 to 60% vegetable oil present in small (0.5 to 2.0 µm) droplets, more readily fermentable soluble substrates (e.g. fatty acids or alcohols), surfactants, nutrients and water. Oil droplets are retained by aquifer material when they collide with sediment surfaces and stick (referred to as interception). The tendency of oil droplets to stick to aquifer material varies due to a number of factors including pH, droplet and matrix grain surface coatings, ionic strength, surface roughness, sediment surface charge heterogeneity, and blocking of the sediment surface with previously retained droplets. Following injection, the vegetable oil is hydrolyzed to glycerol and long-chain fatty acids (LCFAs), which are subsequently fermented to hydrogen (H₂) and acetate. The rate of LCFA fermentation and resulting H₂ production is limited by sorption to sediment surfaces and/or precipitation with divalent cations (Ca⁺², Mg⁺², Mn⁺², Fe⁺²). Since H₂ is rapidly consumed near where it is produced, the oil droplets should be distributed as uniformly as possible throughout the target treatment zone. This involves injecting sufficient EVO and sufficient water to distribute the EVO throughout the treatment zone.

See Also

• Development of Permeable Reactive Barriers Using Edible Oils
• Edible Oil Barriers for Treatment of Chlorinated Solvent- and Perchlorate-Contaminated Groundwater
• Protocol for Enhanced In Situ Bioremediation Using Emulsified Edible Oil
• Emulsion Design Tool Kit