Search

Because waters contaminated with nutrients often have high levels of nitrates and phosphates, the removal of both from aqueous solution with hydrotalcite, a clay mineral ion exchange media, was investigated. Isotherms were developed for nitrate and phosphate removal in single ion solutions within the ranges typically found in eutrophic waters or contaminated wells. Residual concentrations were compared to Environmental Protection Agency recommended levels for drinking and surface waters. Next, experiments were performed to determine what effect the presence of one anion had on the removal of the other. First, removal of phosphates in high and low nitrate concentration solutions was compared to phosphate removal in the single ion solutions. Likewise, removal of nitrates in high and low phosphate solutions was compared to nitrate removals in the single ion solution. Statistical analyses were performed to delineate these results. Phosphates, at the concentrations considered, were almost completely removed by hydrotalcite. Nitrates, on the other hand, were removed to below the EPA limit for only initial nitrate levels up to 30 mg L−1. Removal was over 90% for 25 mg L−1 nitrate, but decreased significantly at higher concentrations. Phosphate removal remained over 95% and was not affected significantly by the presence of nitrates for nitrate levels up to 40 mg L−1. Nitrate removals, however, were significantly decreased by the presence of phosphates at phosphate levels as low as 0.31 mg L−1. However, a second batch contact of the residual solution with fresh hydrotalcite was sufficient to reduce both phosphates and nitrates to below EPA standards. For both nitrate and phosphate removal, however, the pH requirements necessitate a pump and treat system, which limits the applicability of the process. [ABSTRACT FROM AUTHOR]

On-site ion exchange studies investigated the combined removal of arsenic (V) [As(V)l and nitrate from drinking water in McFarland and Hanford, Calif., and Albuquerque, N.M. Whereas previous ion exchange workers had studied removal of high concentrations of As (> 50 mug/L As) without nitrate present, these studies focused on removing 10-15 mug/L As to achieve a product water with < 2 mug/L As while also maintaining nitrate below its maximum contaminant level. Results of 1-in.- (25-mm-) column experiments showed that conventional sulfate-selective resins were better than special nitrate-selective resins for combined As(V) and nitrate removal. The conventional resins yielded longer run lengths and leaked less As and nitrate into the product water. Decreasing empty bed contact time from 3.0 to 1.5 min did not greatly alter As leakage into the product water. Particulate iron in the ion exchange feed increased As leakage in the product water. Two commercially available computer programs were reasonably accurate in predicting both As and nitrate run lengths for various influent nitrate and sulfate concentrations. Generally, predicted As and nitrate run lengthswere within +/-35 percent of those observed experimentally. [ABSTRACT FROM AUTHOR]

While nurses may not routinely service the water treatment system or mix the dialysate, they are responsible for understanding all the clinical ramifications of water and dialysate for HD and helping to piece together the entire treatment picture. Although historically the water treatment system has been in the technicians' domain, knowing the technical aspects is important in order for the entire team to work together toward the patients' ultimate well being. This article describes the composition of water treatment systems for hemodialysis as well as the monitoring and testing necessary to assure that both water and dialysate are safe for patient use.

We estimated the number of transportation deaths that would be associated with water treatment in Albuquerque to meet the EPA's recently proposed revisions of the Maximum Contaminant Level (MCL) for arsenic. Vehicle mileage was estimated for ion exchange, activated alumina, and iron coagulation/microfiltration water treatment processes to meet an MCL of 0.020 mg/L, 0.010 mg/L, 0.005 mg/L, and 0.003 mg/L. Local crash, injury, and death rates per million vehicle miles were used to estimate the number of injuries and deaths. Depending on the water treatment options chosen, we estimate that meeting an arsenic MCL of 0.005 mg/L will result in 143 to 237 crashes, 58 to 98 injuries, and 0.6 to 2.6 deaths in Albuquerque over a 70-year period, resulting in 26 to 113 years of life lost. The anticipated health benefits for Albuquerque residents from a 0.005 mg/L arsenic MCL, estimated using either a multistage Weibull or Poisson model, ranged from 3 to 80 arsenic-related bladder and lung cancer deaths prevented over a 70-year period, adding between 43 and 1,123 years of life. Whether a revised arsenic MCL increases or reduces overall loss of life in Albuquerque depends on the accuracy of EPA's cancer risk assessment. If the multistage Weibull model accurately estimates the benefits, the years of life added is comparable or lower than the anticipated years lost due to transportation associated with the delivery of chemicals, disposal of treatment waste, and operation of the water treatment system. Coagulation/microfiltration treatment will result in substantially fewer transportation deaths than either ion exchange or activated alumina.

Perchlorate (ClO4-) has been detected in numerous ground and surface waters, and has recently been added to the drinking water Candidate Contaminant List in the United States. Perchlorate can be removed from drinking water using ion exchange, but this results in the production of highly saline (7-12%) perchlorate-contaminated brines. Perchlorate-degrading microbial enrichments capable of growth in highly saline water were obtained by screening six salt water environments including marine and lake surface waters, salt marshes, subtidal sediments, and a biofilm/sludge from a seawater filter. Perchlorate reduction was obtained in three of these samples (seawater, saline lake water, and biofilm/sludge) at a salinity of 3%. The salinity range of two of these cultures was extended through serial transfers into media having higher salt concentrations (3-7%). Growth rates were measured over a salinity range of 1-15%. The maximum growth rate measured for the saline lake-water enrichment was 0.060+/-0.003 d(-1) (doubling time of 11.6+/-0.8 d) at a salinity of 5%. Growth rates decreased to 0.037+/-0.002 d(-1) at a salinity of 11%, and no growth was observed at salinities of 13 or 15%. These results demonstrate for the first time that biological perchlorate reduction is possible in solutions having a salinity typical of ion exchange brines.