In spite of the recent oil price declines the shale oil production is recovering at a rapid rate. With it, the amount of water used in hydraulic fracturing grows as well, including the water used both at the front end of this process, in fracking liquid, and at the back end, the flowback and produced water. The front-end water has to meet specific environmental standards before it can be pumped into the well, especially with regard to microorganism and mineral contents. Similarly, flowback and produced water must meet certain standards before it can be re-used or discarded. These water purification requirements increase the cost of oil and natural gas product, thus creating an increasing need for more cost-effective methods water disinfection and demineralization.

To address this need, Drexel engineers have developed a new system and method for fracking and produced water treatment using high-voltage high-current plasma spark discharge. It is a challenge to produce a short-duration spark discharge in this type of liquid, especially in produced water because of its high electrolytic conductivity, which exceeds that of sea water by about 10-fold. To produce a spark discharge in such water a gas bubble is created between two electrodes, and reliable generation of gas bubbles at precise location and rate in high water flow and volume conditions is the problem solved by this invention.

Such high performance precision and electrode durability have been achieved by the specially designed electrode. In such electrode, both anode and cathode form a co-axial arrangement and are positioned in the same side, not facing or opposing each other.  The anode is located at the center of the co-axial arrangement, whereas the cathode (ground electrode) forms the outer cylindrical casing. Gas is introduced to the confined space between the two electrodes through a hole at the side wall of the cylindrical casing. Alternatively, the anode electrode has a cylindrical shape, which has a hollow channel. Gas can be introduced into the confined space between the two electrodes through the hollow channel inside the center electrode (i.e., used as anode). The coaxial design of the electrodes simplifies their installation and reduced maintenance costs. More importantly, it enables using multiple electrodes in the same reactor allowing for larger water treatment throughput.