Carl E. Camp

Reduction of Cr(6+) to Cr(3+) in a Packed-Bed Bioreactor

Hexavalent chromium, Cr(6+), is a common and toxic pollutant in soils and waters. Reduction of the mobile Cr(6+) to the less mobile and less toxic trivalent chromium, Cr(3+), can be achieved with conventional chemical reduction technologies. Alternatively, Cr(6+) can be biochemically reduced to Cr(3+) by anaerobic microbial consortia which appear to use Cr(6+) as a terminal electron acceptor. A bioprocess for Cr(6+) reduction has been demonstrated using a packed-bed bioreactor containing ceramic packing, and then compared to a similar bioreactor containing DuPont Bio-Sep beads. An increase in volumetric productivity (from 4 mg Cr(6+)/L/h to 260 mg Cr(6+)/L/h, probably due to an increase in biomass density, was obtained using Bio-Sep beads. The beads contain internal macropores which were shown by scanning electron microscopy to house dense concentrations of bacteria. Comparisons to conventional Cr(6+) treatment technologies indicate that a bioprocess has several economic and operational advantages.

Calcium alginate bead immobilization of cells containing tyrosine ammonia lyase activity for use in the production of p-hydroxycinnamic acid.

An Escherichia coli catalyst with tyrosine ammonia lyase activity (TAL) has been stabilized for repeated use in batch conversions of high tyrosine solids to p‐hydroxycinnamic acid (pHCA). The TAL biocatalyst was stabilized by controlling the reaction pH to 9.8 ± 0.1 and immobilizing the cells within a calcium alginate matrix that was cross‐linked with glutaraldehyde and polyethyleneimine (GA/PEI). We found a GA range where the bead‐encapsulated TAL was not inactivated, and the resulting cross‐linking provided the beads with the mechanical stability necessary for repeated use in consecutive batch reactions with catalyst recycle. The GA/PEI calcium alginate TAL catalyst was used in 41 1‐L batch reactions where 50 g L−1 tyrosine was converted to 39 ± 4 g L−1 pHCA in each batch. The practical usefulness and ease of this process was demonstrated by scaling up the TAL bead immobilization and using the immobilized TAL catalyst in four 125‐L bioconversion reactions to produce over 12 kg of purified pHCA.

Immobilization of a Sulfide-Oxidizing Bacterium in a Novel Adsorbent Biocatalyst Support

Preliminary experiments have shown thatT. denitrificans strain F can be immobilized in DuPont BIO-SEP beads and used to treat refinery spent sulfidic caustic in a packed-bed reactor. Sulfides were oxidized to sulfate with very little off-gassing of sulfide as H2S. The volumetric productivity of the packed-bed reactor was shown to be almost an order of magnitude greater than the maximum observed in a stirredtank reactor treating the same caustic and using the same organism. This is especially significant since the packed-bed reactor had not been optimized and was not operating at its maximum rate.

Biotreatment of produced water for removal of sulfides, organics, and toxicity

Water coproduced with petroleum may contain sulfides and organic constituents that give the water an aquatic toxicity preventing surface discharge. A simulated sour produced water and actual field samples of produced water were successfully biotreated with mixed cultures ofThiobacillus denitrificans and floc-forming heterotrophs. Complete removal of benzene, toluene, phenol, acetic acid, sulfides, and Microtox toxicity was achieved. These results indicate that a reactor system as simple in concept as a specialized activated sludge system can be used to treat produced water with these mixed contaminants, allowing surface discharge of the water for reuse.