Technologies and Costs for Removal of Arsenic From Drinking Water

The maximum run length is 18,500 bed volumes. The amount of arsenic adsorbed onto the firstcolumn is:As ads = (22.8 Fg/L)(18,500 BV)(16,032 L/BV)(g/10 6 Fg) - 1474 gramsAs ads = 5288 gramsThus, the capacity of the roughing column before it needs to be regenerated is 5288 grams.This assumes that there is no arsenic already adsorbed onto the column. Under steady-stateoperation, the polishing column will become the roughing column and the redundant columnwith virgin media column becomes the polishing column. The media in the old roughingcolumn is replaced with virgin media and becomes the new redundant column. The adsorbedarsenic on the former polishing column will decrease run length whereas arsenic leakagethrough the second column will increase run length.D. The adsorptive capacity of the roughing column was 5288 grams based on the maximum runlength of 18,500 bed volumes. When the “old” polishing column is shifted and becomes the“new” roughing column, it already has a maximum of 1474 grams adsorbed onto it. Therefore,the remaining capacity is considerably lower than 5288 grams. The absorptive capacity of the“new” roughing column was first estimated by subtracting the arsenic that passed through thefirst column. This estimate was called the minimum capacity of column 2, since the polishingcolumn does not adsorb all of the arsenic that passed through the first column.Min Adsorptive Capacity - Column 2 = 5288 - 1474 grams = 3814 grams.E. As noted in the previous step, the minimum adsorptive capacity was estimated by assumingthat all of the arsenic that passed through the first column was adsorbed onto the secondcolumn. This would not be the case. The second column would have leakage effects as wellas increasing arsenic concentrations until the effluent concentration reached 2 Fg/L. Becausethe arsenic passing through the first column and reaching the second column is not constant,it is not possible to estimate a breakthrough curve. Therefore, a different approach was takento better estimate the adsorptive capacity. Arsenic leakage from the single column studysummarized in the Phase 3 Report (12) was examined to estimate leakage for the secondD-17