195
The most common biocide in use is called glutaraldehyde (Kahrilas et al. 2016).
It is a member of the aldehyde chemical family, of which formaldehyde is possibly
better known. Both have pungent odors, with glutaraldehyde reportedly smelling
like rotten apples. Formaldehyde was classified by the EPA in 2010 as a carcinogen
(USEPA 2010), whereas glutaraldehyde is not. However, glutaraldehyde is still not
“safe,” as exposure may result in throat and lung irritation, asthma, breathing difficulties, dermatitis, nasal irritation, sneezing, wheezing, burning eyes, and conjunctivitis (https://www.cdc.gov/niosh/topics/glutaraldehyde/default.html; accessed
3/9/2020). Glutaraldehyde was found to polymerize into dimers and trimers (two
monomers or three monomers bonded together) at downhole pressures and temperatures. It precipitates out of solution under alkaline pH conditions or high temperatures, seemingly limiting its usefulness for controlling downhole microbes
(Kahrilas et al. 2016).
Other common biocides added to frack fluid include tongue-twisting chemicals
like alkyl dimethyl benzyl ammonium chloride, Bronopol, chlorine dioxide,
chloromethylisothiazolinone, Dazomet, dibromonitrilopropionamide, didectyl
dimethyl ammonium chloride, dimethyloxazolidine, methylisothiazolione,
N-bromosuccinimide, peracetic acid, sodium hypochlorite, tetrakis hydroxymethyl
phosphonium sulfate, tributyl tetradecyl phosphonium chloride, and trimethyloxazolidine (Kahrilas et al. 2015, Table S-1). These have been used on various frack
jobs with varying degrees of success.
Biocides are hazardous chemicals to have on-site, and must be handled carefully
by the frack crews. If the containers leak and the chemicals escape, they pose a
hazard to anything in the environment that encounters them (refer back to Fig. 8.1).
People have been investigating less toxic biocides for frack water disinfection along
with other options that don’t involve chemicals additives at all. However, attempts
to disinfect frack water using ozone, ultraviolet radiation, chlorination, or milder
biocides either did not work very well, cost too much, or both. Some biocides like
sodium hypochlorite, better known as chlorine laundry bleach, would seem to be
cheap, effective, and environmentally benign. Sodium hypochlorite is a relatively
simple chemical compound (NaOCl) that destroys organic material through oxidation, leaving Na and Cl (salt) behind as waste products. These are environmentally
benign compared to the breakdown products of some other biocides. If chlorine
bleach can be made to work consistently as a preferred biocide, and is cheaper and
safer than the alternatives, it will get more use.
Another additive of concern is polyacrylamide, used as a friction reducer to create “slickwater.” Polyacrylamide itself is not particularly toxic, but as it naturally
degrades one of the intermediate byproducts is acrylamide, a reproductive toxin and
carcinogen (Exon 2006). This environmental breakdown process is called natural
attenuation or NA, and understanding the paths taken by various chemical additives
as they degrade is critical for determining the point at which a compound is rendered truly harmless.
Competition is intense for developing additives that will improve the performance of fracks on specific shale plays. New chemicals are constantly being tested.
Many of the formulations are proprietary, and tightly held as secrets by
10.2 Can Fracking Be Greener?
The most common biocide in use is called glutaraldehyde (Kahrilas et al. 2016).
It is a member of the aldehyde chemical family, of which formaldehyde is possibly
better known. Both have pungent odors, with glutaraldehyde reportedly smelling
like rotten apples. Formaldehyde was classified by the EPA in 2010 as a carcinogen
(USEPA 2010), whereas glutaraldehyde is not. However, glutaraldehyde is still not
“safe,” as exposure may result in throat and lung irritation, asthma, breathing difficulties, dermatitis, nasal irritation, sneezing, wheezing, burning eyes, and conjunctivitis (https://www.cdc.gov/niosh/topics/glutaraldehyde/default.html; accessed
3/9/2020). Glutaraldehyde was found to polymerize into dimers and trimers (two
monomers or three monomers bonded together) at downhole pressures and temperatures. It precipitates out of solution under alkaline pH conditions or high temperatures, seemingly limiting its usefulness for controlling downhole microbes
(Kahrilas et al. 2016).
Other common biocides added to frack fluid include tongue-twisting chemicals
like alkyl dimethyl benzyl ammonium chloride, Bronopol, chlorine dioxide,
chloromethylisothiazolinone, Dazomet, dibromonitrilopropionamide, didectyl
dimethyl ammonium chloride, dimethyloxazolidine, methylisothiazolione,
N-bromosuccinimide, peracetic acid, sodium hypochlorite, tetrakis hydroxymethyl
phosphonium sulfate, tributyl tetradecyl phosphonium chloride, and trimethyloxazolidine (Kahrilas et al. 2015, Table S-1). These have been used on various frack
jobs with varying degrees of success.
Biocides are hazardous chemicals to have on-site, and must be handled carefully
by the frack crews. If the containers leak and the chemicals escape, they pose a
hazard to anything in the environment that encounters them (refer back to Fig. 8.1).
People have been investigating less toxic biocides for frack water disinfection along
with other options that don’t involve chemicals additives at all. However, attempts
to disinfect frack water using ozone, ultraviolet radiation, chlorination, or milder
biocides either did not work very well, cost too much, or both. Some biocides like
sodium hypochlorite, better known as chlorine laundry bleach, would seem to be
cheap, effective, and environmentally benign. Sodium hypochlorite is a relatively
simple chemical compound (NaOCl) that destroys organic material through oxidation, leaving Na and Cl (salt) behind as waste products. These are environmentally
benign compared to the breakdown products of some other biocides. If chlorine
bleach can be made to work consistently as a preferred biocide, and is cheaper and
safer than the alternatives, it will get more use.
Another additive of concern is polyacrylamide, used as a friction reducer to create “slickwater.” Polyacrylamide itself is not particularly toxic, but as it naturally
degrades one of the intermediate byproducts is acrylamide, a reproductive toxin and
carcinogen (Exon 2006). This environmental breakdown process is called natural
attenuation or NA, and understanding the paths taken by various chemical additives
as they degrade is critical for determining the point at which a compound is rendered truly harmless.
Competition is intense for developing additives that will improve the performance of fracks on specific shale plays. New chemicals are constantly being tested.
Many of the formulations are proprietary, and tightly held as secrets by
10.2 Can Fracking Be Greener?