ABSTRACT
The removal of perchlorate and nitrate from contaminated drinking water using regenerable ion-exchange processes produces a high salt brine (3-10% NaCl) laden with high concentrations of perchlorate and nitrate. This bench-scale research describes the operation of acetate-fed granular activated carbon (GAC) based fluidized bed reactors (FBR) for perchlorate-only, and combined nitrate and perchlorate removal from synthetic brine (6% NaCl). The GAC was inoculated with a salt-tolerant culture developed by the authors and used previously in batch systems. An FBR was an effective design for perchlorate reduction and exhibited first-order degradation kinetics with respect to perchlorate concentrations. Nitrate was also removed by the organisms in the column and had no negative effects on the removal of perchlorate using the FBR design. However, at higher concentrations of nitrate the FBR was more difficult to operate due to loss of carbon and biomass from the formation of nitrogen bubbles and the high recycle flow rates needed.
Subject(s)
Bioreactors , Nitrates/chemistry , Perchlorates/chemistry , Salts/chemistry , Water Pollutants, Chemical/chemistry , Biodegradation, Environmental , Chromatography, Ion Exchange , Kinetics , Water/chemistry , Water PurificationABSTRACT
An ion exchange process with biological perchlorate and nitrate destruction and reuse of spent regenerant brine has been proposed as an efficient and environmentally sound method to treat perchlorate-contaminated groundwater. A culture capable of reducing perchlorate and nitrate in spent ion exchange regenerant brine containing at least 30 g/L NaCl is needed for this to be feasible. A batch culture inoculated from activated sludge failed to acclimate to more than 15 g/L NaCl whether nitrate was present or not. A mixed culture inoculated from marine sediment was capable of simultaneously reducing 100mg/L perchlorate and denitrifying 500 mg/L nitrate within 5 h in a synthetic medium in the presence of 30 g/L NaCl. The growth conditions to maintain this culture in a healthy state required the addition of trace metals, Na2S, and phosphate. A second culture capable of removing 100 mg/L perchlorate from synthetic medium containing 60 g/L NaCl within 24 h was also developed.
Subject(s)
Nitrates/metabolism , Perchlorates/metabolism , Salts/chemistry , Waste Disposal, Fluid/methods , Biodegradation, Environmental , Bioreactors , Ion Exchange , Phosphates/chemistry , Seawater/chemistry , Sewage/chemistry , Sulfides/chemistry , Time FactorsABSTRACT
A rugged resin concentration method followed by gamma counting was developed for measuring 226Ra and 228Ra in drinking water. Using typical distribution system pressure, 310 kPa (45 psig), radium in a 20-L sample was concentrated 100-fold onto 200 mL of ion-exchange resin beads that were then sealed in a glass jar for gamma activity measurement. Parameters and materials affecting the concentration step were studied with the objective of maximizing radium recovery in a short time. Empty bed contact times were varied from 0.1-3.0 min (2.0-0.67 mL min-1) and input concentrations of radium were varied from 370-3700 Bq m-3 (10-100 pCi L-1). Varying these parameters did not affect the percentage recovery of radium by the resin. At each empty bed contact time after all adsorbent media were tested, more than 99% of the influent radium was adsorbed. In these experiments, activities were counted for 100 min using a gamma-ray spectrometer equipped with a 3 x 3-inch sodium iodide (thalium-activated) [NaI(Tl)] crystal detector. Activity calculations were based on resin loaded with traceable standard solutions of 226Ra and 286Ra from the National Institute of Standards and Technology. Analyzing entire spectra with a least-squares analysis program resulted in limits of detection for 226Ra and 228Ra of 7.4 Bq m-3 (0.2 pCi L-1) and 33.3 Bq m-3 (0.9 pCi L-1), respectively.
Subject(s)
Radium/analysis , Water Pollutants, Radioactive/analysis , Ion Exchange Resins , Spectrometry, Gamma/methodsABSTRACT
Panhandling was used to study sharing of resources. Male panhandlers were more successful in spring than in autumn. Female panhandlers were more successful than males in autumn. Panhandlers were generally successful only when submissively approaching individuals who were eating. Families and male-female pairs were resistant to panhandling. The results are discussed in terms of reciprocal altruism and kinship selection.
