The pH value influence on biodegradability of organic substances
Prof. Ing. Pavel Pitter, DrSc.
The dissertation thesis deals with studies of the pH value influence on biodegradability of selected chlorinated organic substances by mixed culture of microorganisms in activated sludge.
Biodegradability characteristics of studied compounds were obtained by use of respirometric tests, batch kinetic tests, and static test according to Zahn and Wellens. Above mentioned biodegradation tests were performed under different pH values and results were formulated on the basis of obtained data.
The work also studied the influence of pH value on the activity of inoculum used for the tests. The activity was observed by means of a standard readily biodegradable substrate – sodium benzoate, and also by means of 3-chloropropionic acid. Also the influence of inoculum adaptation was studied during these tests, either adaptation to different pH value, or to specific substrate.
In order to maintain a stable pH value in duration of biodegradability tests, buffer solutions had to be added. In the course of presented thesis, also composition and concentration of these buffer solutions was evaluated.
The pH value exhibits major effect on biodegradation of dichloroacetic acid, when with higher pH value, higher extent and rate of biodegradation was observed. In case of monochloroacetic acid the dependence was very similar, but the sensitivity was lower. On the contrary, 3-chloropropionic acid, exhibited higher biodegradation rate and extent in lower pH values. Other substances in this study were not very sensitive to pH value changes, in respect to their biodegradability.
The results also approved theoretical considerations concerning the influence of chemical structure on biodegradability of a given compound. The chlorinated derivatives of acetic acids were more easily degaradable, when they obtained less chlorine atoms in their molecule, similar difference was found between mono- and di- chloropropionic acids. 3-chloropropionic acid was the most easily biodegradable substance of all tested compounds. In case of dichlorinated propionic acids, the number of chlorine atoms bonded to one carbon atom plays an important role, and so 2,2-dichloropropionic acid was found to be easier biodegradable than 2,3-dichloropropionic acid.