Factors affecting the degradation of ballast substances from citric acid production by sulphate-reducing bacteria

Abstract

The purification of effluents from citric acid production is quite a difficult technical problem. This is due to the concentration and character of ballast substances present there, including betaine, proteins, amines, volatile and non-volatile acids, dyes, mineral salts (especially sulphate) etc. In Czechoslovakia from the year 1935 to 1953 some of the sewage waters originating during citric acid production were decontaminated with the aid of the so-called methane fermentation carried out according to a patent of the Dansk Gaerungs Industrie (1933, 1935). In this process, however, not all types of sewage water could be dealt with directly and some of them had to be pretreated prior to the process, at a considerable cost. In addition to this, the time required for destruction of the ballast substances was not adequate to the fermentation period and to the effect obtained. Using this method, it was possible within 15 to 20 days of fermentation to decrease the oxidizability (expressed by a 4-hour permanganate test) from 12,000--15,800 to 4200--5800 mg. O8/1. which corresponds to a purification effect of 63.5--65%. In the newly described method of decontamination of these waters the sulphate-reducing bacteria of the genus Desulfovibrio were made use of. I t is well-known that these bacteria possess the ability to utilize a wide spectrum of organic substances as hydrogen donators and oxygenous compounds of sulphur as the source of growth energy. In this way, the above bacteria can oxidize organic substances down to carbon dioxide. The rate of the process can be increased by the presence of some symbiotic bacteria such as Pseudomonas fluorescens, Bacillus mycoides, Aerobacter (Ktipsiz, 1928; Rubenchik, 1947; Barta & Gr@gr 1953, 1958. I t is for this reason that in the decontamination process various accompanying bacterial types are employed according to the type of the water. The purification process is carried out anaerobically, continuously and by multi-stage procedures. Butlin (1958) prefers to use sulphate-reducing bacteria in combination with methane bacteria for fermenting sludge of municipal filter stations and enriches the environment by waste sulphate. In the process a gas rich in hydrogen sulphide is produced. Bar ta and Gr@gr (1953) introduced the application of sulphate-reducing bacteria m combination with bacteria splitting betaine for purification of yeast-producttion sewage waters. The solution of the purification of yeast-production wastes with the aid of sulphate reducers resulted then in the application of this method to sewage waters from citric acid production. By using this method the fermentation period is reduced to 5--6 days giving a permanganate purification value of 78% (calculated from annual averages), an improvement expressed by the BOC 5 value amounting to 81.3% and a reduction of sulphate of 70~o. The present communication deals with factors contributing to a better understand-