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Appendix 1 List of Participants CHARLES E. HESS, CO-CHAIRMAN Dean, College of Agricultural and Environmental Sciences University of California, Davis LANDA, CO-CHAIRMAN Director, South Bohemian Biological Center Czechoslovak Academy of Sciences (CSAV) Ceske Budejovice NAS Participants SUSAN S . BROWN Microbial Genetics Division Pioneer Hi-Bred International DUANE CHAPMAN Department of Agricultural Economics Cornell University C . VERNON COLE Agricultural Research Service U.S. Department of Agriculture JOHN E. COWELL Environmental Sciences Department Monsanto Agricultural Company BENJAMIN F . GEORGE Agricultural Research Division Heinz, USA JOHN R. LAMPE (Observer) East European Program Woodrow Wilson Center for Scholars Smithsonian Institution 213
212 BOD5 and COD values of sludge liquor which is commonly sent back for biological treatment are substantially decreased. In other thickening processes this effect cannot be achieved because all other processes utilize physical methods which cannot influence these val- ues. Even more promising results were obtained when the bioflotation unit was operated batch-wise. In this case the thickened sludge had a total suspended solids concentration of more than 80 g/L. This is particularly important when the bioflotation process is utilized at small wastewater treatment plants which serve communities with a few residents. In this case, only small volumes of waste-activated sludge have to be thickened and the batch process is very suitable. Longer hydraulic retention time helps attain a higher total suspended solids concentration in thickened sludges. In this case investment costs are much lower. The bioflotation process is suitable for nearly all plants which treat wastewater biologically. According to our experience it cannot be used in plants which treat wastewater with very low concentrations of nitrogen, e.g., wastewater from the pulp and paper industry. Biological flotation and thickening has the following advantages over other alternatives: ⢠Polyelectrolyte is not required. ⢠Energy consumption is very low. ⢠Space requirements are small. ⢠During bioflotation, the BODS and COD are substantially re- duced. Because of very low energy consumption, technical simplicity, and low investment and operation costs, bioflotation is a very promis- ing process for waste-activated sludge thickening. REFERENCES Barta, J., S. Ciiinska, V. HavUn, V. Mateju, J. Maixner. 1984a. Proc. d. Jahrestreffen 1984, Verein Deutscher Ingenieure, Miinchen, p. 763-772. Barta, J., M. Verner, I. Pardus, D. Vesely, G. Aronson. 1984b. Czechoslovak Patent No. 228 403 du Toit, P.J., T.R. Davies. 1973. Water Res. 7:489-500. McCarty, P.L., R.T. Haug. 1971. Microbiol. Asp. of Poll., Academic Press, London. Muller, V. 1971. Gewasserschutz, Wasser, Abwasser. Aachen 6:325-357.
