Water Well Journal
Issue link: https://read.dmtmag.com/i/692787
In addition to ion exchange, another process is also used for the softening of water—lime softening or more commonly called lime-soda softening. As lime in the form of limewater is added to raw water, the pH of the water is raised and the equilibrium of the carbonate species in the water is shifted. Dissolved carbon dioxide (CO 2 ) is changed into a bicarbonate (HCO - 3 ) species and then into carbonate (CO 2- 3 ). This action causes calcium carbonate to precipitate due to exceeding the associated solubility product. Additionally, magnesium can be precipitated as magnesium hydroxide in a double displace- ment reaction. In this process both the calcium and, to an ex- tent, magnesium in the raw water as well as the calcium added with the lime are precipitated. This is in contrast to ion exchange softening where sodium is exchanged for calcium and magnesium ions. In lime soften- ing, there is also a substantial reduction in the level of total dissolved solids (TDS) whereas in ion exchange softening, there is no significant change in the level of TDS. Lime soft- ening can also be used to remove other harmful materials from water—including iron, manganese, radium, and ar- senic—although the process requires an intimate knowledge of water chemistry and the proper use and balance of chemi- cals. Lime-soda softening is not used as commonly as ion ex- change softening in today's water treatment environment due to the ability to now synthesize various types of resin and the complexity with the process of lime-soda. This concludes part three of our series on solids separation methods. I hope it has been informative for you so far. We will wrap up the series next month with a fourth installment providing more detail on microfiltration and ultrafiltration membrane methods. Until then, work safe and smart. WWJ Ed Butts, PE, CPI, is the chief engineer at 4B Engineering & Consulting, Salem, Oregon. He has more than 35 years experience in the water well business, specializing in engineering and business management. He can be reached at epbpe@juno.com. Learn How to Engineer Success for Your Business Engineering Your Business: A series of articles serving as a guide to the groundwater business is a compilation of works from long-time Water Well Journal columnist Ed Butts, PE, CPI. The hardback book features 37 complete "Engineering Your Business" columns and the figures and tables that originally ran with the articles. The columns cover the groundwater industry and are divided into six areas: contractor classroom, getting started, troubleshooting pumps, rehabilitation, business basics, and tricks of the trade. Visit NGWA's Online Bookstore at www.NGWA.org for more information. waterwelljournal.com 48 July 2016 WWJ ENGINEERING from page 47