The best yields and productivities of 0.38 g . g-' and 0.35 g . I-' h-I, respectively, for the propionic acid production in a batch system using sugar-cane final molasses as carbon source were obtained when an initial TRS concentration of 50 g . I-' was used.It was obvious that this process is severely inhibited by the acids produced and the most drastic effect (p = 0) was at a TVA concentration near to 250 mmol . I-', independently of the initial TRS concentration employed. A generalizated equation of noncompetitive inhibition was adjusted:and kinetic inhibition constants for each initial TRS concentration studied were estimated.

Five 4.02-1 UASB (Upflow Anaerobic Sludge Blanket) reactors were continuously operated at 30 "C under different hydrodynamic regimes for more than 120 days. The effect of the upflow liquid velocity (ULV) over the range of 0.25 to 2.0 m/h on the biological characteristics of the granules formed by treating vinasses (waste water of alcohol distilleries) from sugar cane molasses was investigated constantly maintaining the volumetric loading rate (VLR) (8 g COD1 . d). Granular sludge was found at all the ULV tested. The size, shape, etc., of the granules indicated that the ULV had a considerable effect on the sludge cultivated in this type of system, thereby acting as a selection process for the biomass. The best results in relation to the time of appearance, size, shape, consistence, stability, composition, and the accumulation were observed in the ULV range between 0.25 and 0.5 m/h. Microscopic studies of the granules using optical and epifluorescence microscopes and the scanning electron micrograph (SEM) showed a heterogeneous biomass and revealed the cell characteristics.

The batch propionic acid fermentation of sugar cane molasses by Propionibacterium acid propionici PP-I was studied at various pH values ranging from 5 to 7. The optimum pH range for cell growth was between 6 and 7, whereas the specific growth rate decreased with the pH in the acidic range down to 0.197 h-' at pH 5. The propionic acid yield increased with decreasing pH; it changed from 22% (wt/wt) at pH 7 to 38% at pH 5. It has been obvious that this process is inhibited by the products of the fermentation and more severely in the acidic range where the acids are in an unionized state. A generalized equation of the non-competetive inhibition was adjusted for each pH value, and kinetic inhibition constants were estimated.

The behaviour of thermophilic anaerobic sludge from the UASB process was investigated under suboptimal conditions. Stability studies, carried out during the normal operation of the reactors, showed that a short-term decrease in temperature had no influence on the behaviour of the process. Nevertheless, interruptions in feeding and a long-term decrease in temperatures can produce very drastic effects on the stability of the system.