Natural gas serves as a major energy supply in United States. Hydraulic fracturing is the process of extraction of unconventional natural gas from the tight sandstones, and shale's bed. Hydraulic fracturing uses fracking fluid which consists of large volumes of fresh water, proppants (e.g. Sand), slicking agents, and antimicrobial solutions. These flow back water carries a large amount of bacteria which are responsible for the biofilm formation that can eventually clog the fissures (source) and inhibit gas extraction during down-hole production. Numerous toxic chemicals are used as biocides to eliminate the biofilm. These biocides are toxic and can deteriorate the subsurface environment. There has been exploration of alternative products for viable bacterial control but none are without any human health and/or environmental impacts. To replace these biocides, the potential use of copper solution was examined as a safer alternative to traditional biocides. Copper ions or copper compounds have been used to inhibit bacteria in many forms like solid and, liquids for centuries. Copper solutions can impede the bacterial growth while reducing the harm to the environment. This research was mainly focused on two objectives: i) to test the effectiveness of copper solution against gram positive and gram negative bacteria and ii) to explore the efficacy of copper ion solution as comparison to flow back biocide solutions.
The bacteria Escherichia coli and Staphylococcus aureus were used to represent gram negative and gram positive cells. The Staphylococcus epidermis is an aerobic bacteria present in some fracking wells which can also be experimented on in the culture. The experiment was performed using 30mL copper ion solution (250ppm Cu+2) and equivalent volume of flow back water, which were added to bacteria cultured vials at 4-6 hours to investigate the ability to inhibit bacterial strains. The growth with copper treatment was impeded for approximately 12 hours for gram negative bacteria and approximately 8-10 hours for gram positive bacteria. However, flow back water was found to inhibit all bacteria growth for up to 48-56 hours as concluded using both turbidity and viable cells count test results. To mimic the flow back water antimicrobial properties, copper ion solution may need to be added at 10-12 hours interval to replace the toxic chemicals used in fracturing fluids. It is not clear what chemicals, concentrations of the chemicals or the cost of the chemical are used in flow back water. Future studies should investigate and optimize the cost and economic viability of the copper solution. Copper and its compound are considered to be benign to the environment and they can also be toxic to deleterious bacteria, this property of copper would not only help fracking industries to remove biofilm problem but also help to preserve the subsurface environment.