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The removal of cellular material from fermentation broths is of importance in many fermentation processes. The present work compares the performance of recently developed polyelectrolyte flocculating additives with traditionally available additives. Objectives are to establish criteria for the choice of a flocculating additive and establish optimum conditions for the formation of stable, fast settling floc, and for quantitative separation of cellular material from the medium. Fermentation broths of actively growing Candida intermedia were used to evaluate the effectiveness of fifty commercial flocculating additives at different dosages and pH values. Certain strong anionic and strong cationic polyelectrolytes and mineral hydrocolloids were found to be most effective in their enhancement of settling rates. Some differences in behavior exist between glucose grown cells, hydrocarbon grown cells, and washed cells in buffer suspension. Flocculation of cells from fermentation broths is concluded to be highly dependent upon adsorbed material. A high charge density to interact or compete with adsorbed material and a solubility in the adsorbed material are important facton in choosing an additive for a given application. The fluid mechanics of a flocculating suspension is an important variable since low shear does not provide adequate contacting between cells for floc formation and high shear leads to floc breakup. An apparatus was constructed to grow floc under constant fluid mechanical conditions both in laminar and turbulent flow regimes. Turbulent shear was found to be very important in forming large, compact floc in cases where irreversible ionic bridging is the mechanism as for the strong anionic polyelectrolyte, polystyrene sulfonate. Adequate mixing is required to disperse the flocculating additive, but the level of turbulence is relatively unimportant in cases where reversible colloidal bridging is the mechanism as for the mineral hydrocolloid, bentonite.

Odor control has been an important component of the operation of the Montgomery County Regional Composting Facility. After several facility improvements, which greatly reduced off-site odors, the discharge of compost process air remained the greatest source of odor impacts on the surrounding community. Thus, the WSSC assembled a research team to investigate methods of improving odor control treatment for the process air. The research team developed bench-scale tests and gas chromatographic methods that provided a better understanding of the chemical basis for odor control. Organic sulfur-containing compounds, especially dimethyl disulfide, were identified as the primary odorants in the process air. Effective removal of the reduced organic sulfides requires oxidation by sodium hypochlorite at a neutral pH. Ammonia interferes with this oxidation process and must be removed to allow effective and reliable oxidation. Hydrogen peroxide has also been used to improve oxidation and reduce chlorine odors. The removal of organic compounds has been enhanced by the use of surfactants. These findings have resulted in further full-scale improvements to the existing compost process air scrubbing system. Water Environ. Res., 64, 13 (1992).

SummaryThe consideration of fermentation principles in the treatment of industrial atid sanitary waste waters leads to substantial process improvements. In perticular, the rate of reaction can be improved by several fold by establishing the proper environmental conditions for microbial growth in a fermentation system. Recent work on the concentric cylinder air lift has shown it to be an economical fermentor with many advantages over conventional fermentors. An attempt to improve the economical performance of this system led to the development of the thin channel rectangular air lift fermentor. This was based upon a theoretical analgsis of performance parameters. The analysis indicates decreased bubble coalescence, increased bubble entrainment, decreased power costs, increased mass transfer coefficients, and decreased capital costs. Experience using a prototype thin channel rectangular air lift system with sanitary and industrial waste-water treatment systems has demonstrated exceptionally high rates of BOD removal at low operating and capital costs.

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