Precipitation of calcium ions in hard water by pulsed spark discharge

Summary form only given. Most natural or domestic water contains excessive calcium and carbonate ions which are considered to provoke problems for both drinking and industrial water systems. Various methods are used to soften hard water, including reverse osmosis, adding precipitation inhibitors and nanofiltration et. al, but most of them are generally deleterious for environment or human health and their use is forbidden in drinking water. In this work, it is shown the calcium ions can be precipitated and thus the hardness of water can be reduced by repeatedly application of pulsed spark discharge. The comparison of the softening effect for different hardness is made Water with hardness up to 900 was made by continuously circulation and evaporation of Philadelphia city tap water in a mini cooling tower. Possible mechanisms, including local heating, reactive species, Shockwaves produced by the discharge are discussed. The plasma assisted removal of water hardness has the advantage of posing no potential threat for environment by needing no chemical additives.