PLASMA ARCS FOR WATER TREATMENT

underwater plasma arc creating bubbles around particles in the water

A plasma arc water treatment system is a chemical-free means of disinfecting water, derived from a recurring problem encountered in sonoluminescence fusion research. The goal of sonoluminescence is to create a tiny ball of plasma under water, focused on a tiny bubble of air. The bubble is stabilized and excited by creating controlled cavitation; constant pulses of acoustic energy, which create a cycle of collapse and rebound; each time heating up the gas in the bubble enough to form plasma which is visible to the naked eye as a tiny point of blue light. The problem is any impurities in the water would also cavitate, taking energy away from the target air bubble. While unwanted in sonofusion research, it would be an effective way to destroy other impurities in water.
The process works by repeatedly discharging a high voltage high current electrical arc under water between 2 electrodes for a fraction of a second, which has the same effect as a lightning bolt. A strong acoustic shock wave is produced (thunder), which in water causes the effect known as cavitation to occur. Cavitation is seeded by particulates in the water column, i.e. microorganisms, created by the differential density of the organism and the surrounding water. This is akin to smaller ripples being formed in the wake of larger ripples where they intersect with branches or rocks in the water. Bubbles can also occur inside the cellular structure of the microorganisms, and because the bubbles are formed by an infusion of acoustic energy once the energy is removed the bubbles collapse. As each bubble collapses, it sends out shockwaves which rupture cell walls of the microorganisms, effectively killing them without chemicals. In a controlled sonoluminesence experiment, the target bubble glows with a faint blue light. This is caused by the bubble continually expanding and collapsing, emitting a small pulse of ultraviolet light during each collapse.
A plasma arc water treatment system would use this effect to destroy microorganisms within a radius of the plasma arc, and would reduce or eliminate the need for chlorination prior to filtration and could prevent biological fouling on screens and intake pipes. Excessive use of chlorine in the natural environment results in the formation of chlorination byproducts such as tri-halo methane, but this heavy chlorination is often required to keep water system intakes clear from such organisms as zebra mussels and algae colonies.
Of interest to industrial wastewater, a plasma arc system could also destroy many toxic chemicals by breaking down the molecular chains into simpler more harmless ones. The system would use only a pair of electrodes submerged in the water and a power source. Maintenance would be minimal as well. A plasma arc system would leave no byproducts or emissions in the water, making it a much more environmentally friendly solution than chlorination.

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About

Steve holds a degree in Environmental Engineering Technology from Humber College in Toronto, is a LEED Accredited Professional and a Certified Sustainable Building Advisor. He currently lives in Victoria BC and works as a green building consultant specializing in residential projects.

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