Untersuchungen über die rolle der niederen fettsäuren beim anaeroben faulprozess und einblicke in seine biozönose

Abstract

1. (1) The reaction of volatile organic acids on the digestion of sewage sludge was observed with the help of subsequent chromatographic tests. 2. (2) The volatile acids, which accumulated as the metabolic products at the end of the acidic phase, were composed of acetic acid, propionic acid and butyric acid. In normal domestic sewage sludge, their proportions were in the region 2:1:1. 3. (3) In unseeded batch experiments these acids decomposed in the acetic acid-butyric acid-propionic acid sequence. The two even numbered C-chains were decomposed by the same type of bacteria. The odd numbered C-chains were, however, decomposed by a different type. This was consistent with the Knoop's β-oxydation ( Fig. 1). 4. (4) In a continuous process, where the charging took place once a day, two basically different states were evident. Firstly, the equilibrium between the populations and the daily supply of nutrition, whereby the populations remained constant. Secondly, the state of unbalance, where the supply of nutrition caused an increase in the populations. This increase constrained it into the phase of logarithmic growth, causing a change in their characteristics, and brought forth an antagonism. In the state of equilibrium, all acids are uniformly decomposed. The antagonism to the propionic acid decomposing bacteria is distinct in the unbalanced state, causing an accumulation of this acid ( Fig. 2). 5. (5) In order to estimate the decomposing properties of specific substrates and to discover the source of any possible accumulation of propionic acid, fat and glucose were subjected to seeded batch experiments. A test with protein was unnecessary as it is clearly dependent on the subtrate. 6. (6) For the decomposition of fat, maize oil was chosen. Since, after the saponification of the glycerides, the higher fatty acids were immediately attacked by the methane bacteria, the acetic acid and the butyric acid were seldom released from their enzymatic linkage. The decomposition occurred very slowly. Only a large overloading lead to the lowering of the pH index. This was due to the presence of acetic acid, and slight amounts of butyric and propionic acid ( Fig. 3). 7. (7) The anaerobic decay of glucose occured very rapidly. The sequence of the participating bacteria populations were recognised by their respective metabolism products. They were, consecutively, lactic acid, acetic acid, and gaseous methane plus carbon dioxide. A short and very deep sinking of the pH index was noticed. This was probably caused by the accumulation of intracellular pyrovic acid which had absorbed the neighbouring kations. In parallel reactions, butyric acid and small amounts of propionic acid were produced ( Figs. 4 and 5). 8. (8) Under shock loading with fats and carbohydrates, the decomposition process was hardly influenced by the fatty substances. The carbohydrates disturbed a balanced decomposition process the most because of their great decomposition speed caused by their high intramolecular oxygen content.