New composite biocarriers engineered to contain adsorptive and ion-exchange properties improve immobilized-cell bioreactor process dependability.

Novel biocarriers that combine the adsorptive properties of activated carbon with the ion-exchange properties of zeolite-based type Z inorganic oxide biocarriers (D. R. Durham, L. C. Marshall, J. G. Miller, and A. B. Chmurny, Appl. Environ, Microbiol. 60:3329-3335, 1994.) were developed. These biocarriers, designated Type CZ, possess fundamental properties that heretofore have not been described for available microbial immobilization matrices. Type CZ biocarriers provide an environment that promotes dense microbial colonization and maintains bioreactor productivity by buffering immobilized microorganisms from unfavorable operating conditions. Data demonstrating protection of immobilized bacteria from organic shock loads and extended pH shocks are presented. In addition, bioreactors containing the composite Type CZ biocarriers continue to remove waste stream contaminants during periods of oxygen deprivation and nutrient limitation.

Characterization of Inorganic Biocarriers That Moderate System Upsets during Fixed-Film Biotreatment Processes.

Inorganic matrices were developed for fixed-film bioreactors affording protection to microorganisms and preventing loss of bioreactor productivity during system upsets. These biocarriers, designated Type-Z, contain ion-exchange properties and possess high porosity and a high level of surface area, which provide a suitable medium for microbial colonization. Viable cell populations of 10/g were attainable, and scanning electron micrographs revealed extensive external colonization and moderate internal colonization with aerobic microorganisms. Laboratory-scale bioreactors were established with various biocarriers and colonized with Pseudomonas aeruginosa, and comparative studies were performed. The data indicated that bioreactors containing the Type-Z biocarriers were more proficient at removing phenol (1,000 ppm) than bioreactors established with Flexirings (plastic) and Celite R635 (diatomaceous earth) biocarriers. More significantly, these biocarriers were shown to moderate system upsets that affect operation of full-scale biotreatment processes. For example, subjecting the Type-Z bioreactor to an influent phenol feed at pH 2 for periods of 24 h did not decrease the effluent pH or reactor performance. In contrast, bioreactors containing either Celite or Flexirings demonstrated an effluent pH drop to approximately 2.5 and a reduction in reactor performance by 75 to 82%. The Celite reactor recovered after 5 days, whereas the bioreactors containing Flexirings did not recover. Similar advantages were noted during either nutrient or oxygen deprivation experiments as well as alkali and organic system shocks. The available data suggest that Type-Z biocarriers represent an immobilization medium that provides an amenable environment for microbial growth and has the potential for improving the reliability of fixed-film biotreatment processes.