Degradation of trichloronitromethane by iron water main corrosion products.

Halogenated disinfection byproducts (DBPs) may undergo reduction reactions at the corroded pipe wall in drinking water distribution systems consisting of cast or ductile iron pipe. Iron pipe corrosion products were obtained from several locations within two drinking water distribution systems. Crystalline-phase composition of freeze-dried corrosion solids was analyzed using X-ray diffraction, and ferrous and ferric iron contents were determined via multiple extraction methods. Batch experiments demonstrated that trichloronitromethane (TCNM), a non-regulated DBP, is rapidly reduced in the presence of pipe corrosion solids and that dissolved oxygen (DO) slows the reaction. The water-soluble iron content of the pipe solids is the best predictor of TCNM reaction rate constant. These results indicate that highly reactive DBPs that are able to compete with oxygen and residual disinfectant for ferrous iron may be attenuated via abiotic reduction in drinking water distribution systems.

Degradation of chloropicrin in the presence of zero-valent iron.

Halonitromethanes (HNMs) are a class of halogenated disinfection byproducts formed upon the addition of chlorine to water containing organic matter. Batch experiments were performed to investigate the reaction pathways and kinetics of three HNMs (chloropicrin or trichloronitromethane [TCNM], dichloronitromethane [DCNM], and chloronitromethane [CNM]) with zero-valent iron (Fe0). All three compounds reacted rapidly in the presence of Fe0 (1.8-4.4 g/L) with methylamine (MA) as the final product. The geometric surface area-normalized rate constants decreased with decreasing halogenation: TCNM (301 L/[h-m2]) > DCNM (153 L/(h-m2)) > CNM (45.9 L/[h-m2]). Nitromethane, an intermediate species, rapidly reacted to form MA (302 L/[h-m2]). These reactions all experienced some degree of mass transfer limitation (9-73%). The average carbon and chlorine mass balances for TCNM were >85%, indicating that the major reaction products were recovered. The degradation of TCNM and DCNM proceeded via the parallel reaction pathways of hydrogenolysis and alpha-elimination. For TCNM, 60.7 +/- 8.7% of reaction proceeded via hydrogenolysis and 39.3 +/- 6.4% via alpha-elimination. Knowledge of HNM reaction pathways and kinetics in the presence of Fe0 may be useful for predicting the fate of these compounds in drinking water distribution systems containing cast or ductile iron pipe and for developing treatment systems for HNM removal from water.

Zeta potential as a measure of polyelectrolyte flocculation and the effect of polymer dosing conditions on cell removal from fermentation broth.

Characterization of flocculation for cell removal from fermentation broth via polyelectrolyte addition is commonly based on qualitative methods such as physical appearance of the floc. The use of zeta potential as a quantitative measure of floc character was evaluated as an indicator of optimal polymer addition. Zeta potential was found to increase with increasing cationic polyelectrolyte dosage, but never reached zero regardless of the total amount of polymer added, indicating flocculation occurs at least partially through a bridging type mechanism. Experiments were conducted using various polymer concentrations (25-75 g/L) and dosing methods (batch, incremental and continuous addition) that resulted in variable overall polymer requirements to achieve optimum flocculation. Zeta potential was found to be constant at optimal floc character regardless of the total amount of polymer added, polymer concentration, or method of polymer addition. Experiments with two additional types of fermentation broth also showed characteristic zeta potentials at optimal flocculation. Polymer requirements to achieve a particular floc character can vary greatly, depending on polymer dosing conditions and fermentation batch. The effect of polymer dosing conditions on the polymer requirement to obtain optimal floc character was evaluated. Polymer dosing method and calcium concentration were both found to have a significant effect (P < 0.0001) with continuous polymer addition and high calcium concentration requiring less polymer than did batch polymer addition and low calcium concentration, respectively. Polymer dosing concentration did not significantly affect polymer requirement for optimal flocculation.

Extracellular enzyme loss during polyelectrolyte flocculation of cells from fermentation broth.

Association of extracellular protein product with flocculated cells reduces product yield. Here, partitioning of the enzyme subtilisin between the liquid and polyelectrolyte-flocculated and sedimented Bacillus increased as the polymer dosage was increased beyond that necessary to obtain optimum floc character (brain floc) for cell removal by centrifugation. Partitioning to the cell floc is partly physical entrapment at all polymer dosages; however, at higher levels there is also direct interaction between the polyelectrolyte and enzyme. Enzyme loss was not likely due to pH denaturation during the flocculation process because conditions were within the stable pH range of the enzyme. The direct interaction between polyelectrolyte and enzyme was characterized through turbidimetric titrations and partitioning studies. Neither changes in the polymer feed concentration nor the method of polymer addition reduced the enzyme loss at dosages optimal for cell removal.