Water Softening by Means of Crystallization in a Small Scale Fluidized Bed Reactor

The potential for water softening by means of crystallization in a small scale fluidized bed reactor for residential use was investigated in two stages. During the first stage, the pellet crystallization softening process was used to treat a moderately hard water (132 mg/L as CaCO3) with a low magnesium hardness of 44 mg/L as CaC03 The parameters investigated included pH, upflow rate, media bed height, media bed material, and time. The second stage of the investigation involved treating a very hard water (449 mg/L as CaCO3 with the pellet crystallization softening process. This alternate water supply had approximately four times the magnesium hardness (178 mg/L as CaCO3). The parameters investigated during Stage 2 were pH, temperature and iron concentration. Results of the first stage revealed that a softened water with a total hardness of 70-80 mg/L of CaC03 could be achieved at a pH of approximately 9.4 and there was no significant change in softening capacity of the pellet crystallization process over an average period of 68 hours of continuous operation. No significant reduction in magnesium hardness was observed. A reduction in media height from 40 inches to 20 inches and a reduction in upflow rate from 4 gpm to 2.6 gpm did not result in any significant reduction in the softening ability of the process. Quartz filter sand, after a conditioning period, proved to be just as effective as the initial calcite crystals were as a seed material for crystallization. The results of the second stage of the investigation indicated that removal of hardness at a specified pH will be greater with an elevated water temperature. The presence of iron appeared to inhibit the removal of hardness. Elevated water temperature and pH levels produced a microfloc which did not adhere to the media Further research is recommended to reduce the amount of microfloc produced