Technologies and Costs for Removal of Arsenic From Drinking Water

Basis. An old activated alumina design manual for fluoride removal recommends that the beddiameter be equal to or greater than the bed depth to prevent “wall effects” (5). This sourcealso states that good practice dictates that the bed depth be a minimum of three feet and amaximum of six feet. The Water Model assumed a bed depth of 5 feet for all conceptualdesigns (6). Many of the conceptual designs in the cost estimating manual had bed depths thatexceeded the diameter, so the recommendation in the design manual was not strictly appliedto all designs. For design flows less than 50,000 gallons per day, the bed depth is greater thanthe bed diameter. The data from the three case studies where activated alumina is beingoperated without regeneration, the bed depth is greater than the bed diameter (2, 3).7. The vessel cost has been sized based on 50% bed expansion during backwash even thoughbackwashing may not be necessary on a routine basis for smaller systems. The vessel volumewas calculated as (1.5)(media volume).Basis. The old design manual and the Water Model used 50% bed expansion to size the vessel(5, 6). Both of these designs are based on regeneration of the media rather than disposableoperation. The bed expansion for the one case study where it could be calculated was 30%(3). The design approach used as the basis for the case studies in the AwwaRF report used80% expansion (7). However, this design was also based on regeneration of the media ratherthan disposable media operation and was based on designs greater than 1 mgd. Since theexpansion is only necessary for backwashing, 50% expansion was assumed for all sizes.Backwashing is not performed on a routine basis at any of the three small systems operatingactivated alumina without regeneration.8. The vessel cost is based on the following equation:Cost = 63.288 * (Vessel Volume in gallons) ^ 0.679Basis. Quotes were obtained from two manufacturers for glass-lined carbon steel vessels withworking pressure rating between 75 and 150 psi and meeting American Society of MechanicalEngineers (ASME) Code Section VIII requirements. Sizes ranging from 140 gallons to 6764gallons were used to develop the equation. Vessel costs for sixteen different sizes wereD-4