The process of "self-purification" had to be studied experimentally. A commission presumably led by Frankland obtained the order to investigate the problem. Waste-water from the channel was mixed with river water and filled automatically from
1.5 Mineralization of Organics in Rivers, Soils or by Experiment 113
one vessel to another after short interruptions. In the course of this filling process, oxygen must be transferred from air if it was necessary for the reaction. But the concentration of the organics was not considerably reduced, even after several weeks. Therefore, the "self-purification" observed was no simple chemical process. Alexander Müller was probably the first who suspected, in 1869, that the degradation of organics must be a microbiological process (Roechling 1899).1
An initial answer resulted from experiments by J. König. A wire mesh was sprayed with wastewater for some weeks and it was observed that a biofilm had formed and that dissolved organics had been removed (König 1883). In this light, the experiments of Wolffhügel and Thiemann are also important, being the first to study the growth of bacteria on culture medium after adding drinking and process water. In these experiments, they were advised by Robert Koch (Wolffhügel and Thiemann 1883).
Between 1885 and 1890, several further studies were published proving that microbiological processes must be responsible for the production of H2CO3 and HNO3 by the oxidation of organic compounds and NH4+ (Emich 1885; König 1886; Knauff 1887; Weigmann 1888; Winogradsky 1890).
Nevertheless, another group of chemists could not be convinced by the results of these experiments. Dunbar, the famous director of the Staatliche Hygiene Institut in Hamburg cited Travis in his paper in 1912 (Dunbar 1912), who strongly denied the microbial degradation of organics. Travis presented experimental results on the occasion of the seventh International Congress of Chemists in London in 1907, which should have proved pure chemical oxidation instead of biodegradation by microorganisms. However, Dunbar criticized Travis's methods in his last paper (Dunbar 1912), and obviously the idea of the pure chemical mechanisms was no longer supported in scientific meetings and journals.
We should not conclude this brief description of the birth of environmental microbiology without emphasizing the work of Winogradsky (1890), who carried out fundamental and most important studies on nitrification. In contrast to all the bacteria which use organic compounds as a source of energy and/or carbon, nitrifying bacteria are chemolitho-autotrophs, obtaining energy by the oxidation of NH+ and NO- and obtaining carbon from the reduction of CO2 (Chapter 10). He discovered all these facts and much more about this kind of bacteria, catabolism and anabo-lism during the years prior to 1890; and it is astonishing that the dispute about the oxidation of organic and inorganic compounds as a result of chemical or biological processes was not concluded for several further years.
In 1891, the first textbook on hygiene, "Grundriss der Hygiene" by C. Flügge, was published in its second edition (Flügge 1891). Rightfully, the reader could expect that the very important dictions of the past decade would have been mentioned. But the book, with its 560 pages, did not give any references to the topic. Should we conclude that the papers published in the journal "Gesundheits-Ingenieur", for example, were not noticed by doctors working in the field of hygiene?
1) A. Müller is mentioned in several other papers. But until now, the original publication has not been found.
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