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Technologies and Costs for Removal of Arsenic From Drinking Water

Technologies and Costs for Removal of Arsenic From Drinking Water

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23. The disposal cost <strong>for</strong> the spent activated alumina media is $60/ton.Basis. The disposal rate <strong>of</strong> $60/ton was used to estimate costs <strong>for</strong> the White Rock <strong>Water</strong>Company (2). The two water system byproducts documents (14, 15) contain the same costequation <strong>for</strong> <strong>of</strong>f-site nonhazardous l<strong>and</strong>fill cost <strong>for</strong> various system sizes. The cost equation<strong>for</strong> disposal in a nonhazardous l<strong>and</strong>fill from these two documents was also examined toestimate disposal costs. That cost equation had two variables: tons <strong>of</strong> sludge requiringdisposal <strong>and</strong> transportation distance. The transportation distance could range from 5 to 50miles. Using the upper bound <strong>of</strong> 50 miles, the equation simplified to a multiplier <strong>of</strong>$45.58/ton. The Phoenix case study used a disposal rate <strong>of</strong> $120/wet ton (4). The basis <strong>for</strong>this rate is not discussed. The $60/ton rate was selected <strong>for</strong> the cost analysis because it wasbased on a full-scale system that was disposing spent alumina. The volume <strong>of</strong> waste beinggenerated is not significant, so even using $120/wet ton would not appreciably affect the wastedisposal costs.24. The only other potential waste stream is backwash water. Due to the infrequent need <strong>for</strong>backwashing <strong>and</strong> the low volume <strong>of</strong> waste, no costs were assigned <strong>for</strong> backwashing.Basis. Both the Very Small Systems Document (10) <strong>and</strong> the <strong>Water</strong> Model (6) provided abackwash rate <strong>of</strong> 8 - 9 gpm/sq ft <strong>and</strong> a backwash duration <strong>of</strong> 10 minutes. The backwash rate<strong>and</strong> duration are based on a design where the activated alumina media is being regenerated.Backwashing was not per<strong>for</strong>med at the White Rock <strong>Water</strong> Company probably due to thefrequent media replacement. Backwashing is not per<strong>for</strong>med on a routine basis at the other tw<strong>of</strong>ull-scale systems (3). At Plant C, backwashing was per<strong>for</strong>med twice over a period fromAugust 1997 to September 1999. When backwashing was per<strong>for</strong>med on August 5, 1998, thebackwash rate was 3 gpm <strong>and</strong> the duration was 5 minutes. At Plant D, backwashing wasoriginally scheduled every four months, but this was discontinued after it was found to beunnecessary. Backwashing was not per<strong>for</strong>med between May 1998 <strong>and</strong> September 1999.Backwashing costs are not included in the Phoenix case study, which is the only case study toevaluate disposable activated alumina (4). Routine backwashing is not essential to operation<strong>of</strong> these plants <strong>and</strong> if per<strong>for</strong>med, would produces a very small waste stream. Backwash waterD-24

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