Fluidized bed reactor for the biological treatment of ion-exchange brine containing perchlorate and nitrate

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.

Development of cultures capable of reducing perchlorate and nitrate in high salt solutions

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.

Panhandling: Sharing of Resources

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.