Technologies and Costs for Removal of Arsenic From Drinking Water

3.7 ADSORPTION PROCESSES3.7.1 Activated AluminaActivated alumina (AA) is a physical/chemical process by which ions in the feed water aresorbed to the oxidized AA surface. Feed water is continuously passed through the bed to removecontaminants. The contaminant ions are exchanged with the surface hydroxides on the alumina.Disposable activated alumina (no regeneration) costs were developed using the following approach.Four sets of costs were developed - two for unadjusted pH and two where the pH has been adjustedto the optimal pH of 6. The costs for pH adjustment to optimal pH 6.0 are included as a separatemodule in these cost estimates since it is only used for two of the options.The three models routinely used to estimate unit costs are all based on regeneration of themedia, operation at optimal pH, and use of single columns. Most of the costs are based on fluorideremoval rather than arsenic removal. It was determined that the existing cost models could not be usedto estimate costs for disposable activated alumina. To estimate costs, it was assumed that the aluminawould be arrayed in small columns operated in series rather than in one larger column. This willprovide greater utilization of the media before disposal and is more consistent with the other designsusing disposable activated alumina.Design Assumptions: Capital Costs with Natural pHThe following assumptions were made to estimate the capital cost of activated alumina whenthe water is not adjusted for pH. The basis for these assumptions are provided in Appendix D.1. The pH will not be adjusted to operate the process at the optimal pH between 5.5 and 6.0.The activated alumina process will be operated at the natural pH of the system to simplify theprocess and avoid potential problems with lowering the pH. Two pH ranges will beevaluated 7.0 #pH < pH 8.0 and 8.0 # pH #8.3.2. The pH will not need to be adjusted after the activated alumina process. The activatedalumina process should not adversely affect the finished water pH. Those systems with highnatural water pH will not need a new pH adjustment process. Those systems with lowernatural water pH values will continue to rely on the existing corrosion control process.3-36