Propionate is a key intermediate in the conversion of complex organic matter under methanogenic conditions. Oxidation of this compound requires obligate syntrophic consortia of acetogenic proton- and bicarbonate reducing bacteria and methanogenic archaea. Although H 2 acts as an electron-carrier in these consortia, evidence accumulates that formate plays an even more important role. To make energy yield from propionate oxidation energetically feasible for the bacteria and archaea involved, the concentrations of H 2 and formate have to be extremely low. On the other hand, the diffusion distance of these carriers has to be small to allow high propionate conversion rates. Accordingly, the high conversion rates observed in methanogenic bioreactors are due to the fact that the propionate-oxidizing bacteria and their methanogenic partners form micro-colonies within the densely packed granules.
Thioglycolic acid, a simple sulfur group- chained carboxylic acid, is a clear liquid; melts at -16. c, boils at 96 C; soluble in water. It is an useful chemical intermediate in the chemical reactions such as addition, elimination and cyclization. Sulfur group will react with bases, acids, ketoness and organic halogen compounds, whereas the carboxylic group will preferentially react In the presence of alcohols or amines. The applications of thioglycolic acid and its derivatives are wide in the fields of of PVC stabilizers, down-hole acidizing, corrosion inhibition in the oil field industry, manufacturing of pharmaceuticals, agrochemicals and dyes, hair care products (waving, hair removal and hair straightening), shrink-resistant treatment of wool, fabric dying, leather processing.
These experiments were performed to determine the degradation of VFA (acetate, propionate and butyrate) and the maximum methanogenic activity of granular sludge from the thermophilic anaerobic digestion of pure molasses. The compositions of acetate, propionate and butyrate used as substrate were 25:35:40. The tests were performed at constant temperature (55°C) and pH 7 on two duplicate batch reactors (I and II) running in parallel and were repeated to show the effect of acclimatization. During the first feeding, there was a significant lag phase and after about 23 h incubation the volumes of CH 4 gases produced from two reactors were only about 20 and 490 ml, respectively. In this experiment, propionate was converted to acetate only after the initial concentrations of butyrate and acetate had completely degraded. Acetate formed from propionate was immediately converted to methane and carbon dioxide. The maximum methanogenic activities of the first feeding were not high because the natural populations of the propionate-degrading bacteria were low and the sludge adapted itself to the VFAs' substrate very slowly. In a second experiment with the same sludge, the maximum methanogenic activities of the second feedings were about times higher than those of the first feedings because of the adaptation of the sludge and increase of populations of the propionate-degrading bacteria.