2016-2017 Funded Proposal
Proposed Research Area: Waste to Energy Conversion in Oil and Gas Industry.
Over the last decade, significant increase in oil and gas production has resulted via unconventional oil and gas production methods. This includes hydraulic fracturing and shale-derived oil and gas extraction. These methods result in production of significant amounts of wastewater, which contains salt and organic contaminants. Energy efficient methods are required for removal of these contaminants and for safe disposal of the wastewater into the environment. The proposed research investigates use of microbial fuel cells and electrolysis cells (MFC/MEC) for production of electricity and hydrogen from waste streams in the upstream oil and gas industry. The renewable energy generated can then be used to power devices to remove salt from the wastewater, resulting in synergistic removal of salt and organic contaminants.
Production of natural gas via hydraulic fracturing generates wastewater causing environmental pollution threatening the health of our drinking water supplies, rivers, streams and groundwater. The process called hydrofracking or fracking generates massive amounts of polluted water, which has two components:
- Flowback water, which is the fracturing fluid returning to surface when drilling pressure is released, and
- Produced water, which is all the water that emerges from the well after production begins.
The produced water often contains large amounts of salts, which come from the formation containing the fossil resources. It also contains organic hydrocarbons (sometimes referred to as oil and grease) and organic additives, added during the fracking process. The organics can damage ecosystem health if released into environment by depleting oxygen or causing algal blooms.
Management of fracking wastewater is typically done via five basic operations during production of oil and natural gas from shale and other formations:
- Minimization of produced water generation,
- Recycling and reuse within gas drilling operations,
- Disposal, and
- Beneficial use outside of operations.
On-site options primarily include the first two options, which are practiced during the flowback period. Off-site options, which include the latter three, dominate produced water
management practices. The on-site options are advantageous since they can minimize fresh water usage, however, they accumulate by-products and can be energy-intensive if removal of the by-products is
practiced. Treatment is the most complex management option and is often energy-intensive and costly.
Proposed work will focus on development of MECs for production ofrenewable hydrogen from organic components present in waste streams and understanding the effect of various contaminants in fracking wastewater on the production ofrenewable energy. The work will include two tasks as follows:
- (a) Enrichment of electroactive consortium to treat salt-contaminated wastewater in MEC.
- (b) Determination of hydrogen production potential and understanding the effect of salts and other contaminants on productivity.
Task a: Enrichment
Initial work will focus on enrichment of a microbial consortium for treatment of produced or fracking water stream. Inoculum for this work will be obtained from an existing MFC operating in Dr. Borole's laboratory using acetate as the carbon source. Dr. Hazen's laboratory will provide the produced and fracking water samples obtained from various oil and gas fields for enrichment and testing in MFC.
The effect of salt has been examined in Dr. Borole's laboratory previously using model wastewater streams with acetate as the organic contaminant. The proposed work will focus on using real oil and gas field streams to demonstrate the feasibility of this approach for practical waste streams. A schematic of a microbial electrolysis cell is shown in Figure I.
Higher concentration of salt ions up to 35 g/L has been shown to improve current production due to improved charge transfer between anode and cathode. A few studies have investigated the effect of salt on performance ofMFC/MECs; however, their application for oil and gas field samples has been limited. The proposed work lays the groundwork for a proposal to NSF in the area of environmental sustainability and engineering related to oil and gas industry.
Task b. Hydrogen Production and Testing
Presence of salt in water can prove advantageous or detrimental for hydrogen production in MECs. While salt can enhance conductivity, which improves hydrogen productivity; it can also be toxic to the microbes at higher concentrations. Based on results from Task a, we will test hydrogen production for samples which have salt concentration under the toxic levels. A study by Carmona-Martinez et al. reported operation of a bioanode at 35 g/L NaCl for several days. A current density of 2 A/m2 was sustained for over 50 days. This shows that microbial communities can maintain electroactivity at salt concentrations up to 35 g/L for at least several months. A hydrogen productivity of 0.9 LIL-day has reported at an acetate concentration of 6.4 g/L. We have demonstrated current densities up to 35 A/m and hydrogeproductivities up to four-times higher for treatment of inhibitory compounds in biorefinery wastewater. We will investigate hydrogen production using oil and gas field waste streams to wastewater We will investigate hydrogen production using oil and gas field waste streams to demonstrate the potential of this method for renewable hydrogen production and safe disposal of wastewater. To our knowledge, there are no studies investigating long term electroactivity using produced or fracking water. We will use flow-back water to determine maximum hydrogen productivity and test the MEC up to 4 months to determine the stability of hydrogen production.
Different salts and contaminants can have different effects on the electroactivity and hydrogen productivity. We will investigate the effect of specific salt ions and organic components known to be present in fracking waters. These include chloride, sodium, calcium, magnesium, barium, strontium, etc., which are present at relatively high concentrations. The organic contaminants include polycyclic aromatic hydrocarbons (PAHs), heterocyclic compounds, alkyl phenols, aromatic amines, alkyl aromatics (alkyl benzenes, alkyl biphenyls), long-chain fatty acids, and aliphatic hydrocarbons Synthetic wastewaters will be generated and tested using groups of these compounds/ions. Microbial activity has been tested in subsurface and laboratory in the presence of these contaminants, however, activity of exoelectrogenic organisms has not been tested. Preliminary data will be obtained to support a full proposal on this topic to NSF.