Some practical aspects of the “biocarbon process”

In the presence of granular activated carbon the aerobic decomposition of organic compounds is facilitated (Koppe et al., 1974a,b). As could be shown by many laboratory tests several effects are given. First of all the faster adaptation of the bacteria has to be mentioned which is most important with substances which are difficult to be degraded like pentaerythrite. Additionally the degradation efficiency of the activated sludge process will be increased and equalized by granular activated carbon. Finally the effect of low temperatures can be compensated by the presence of granular activated carbon. With domestic wastewater for instance full nitrification could be obtained at a temperature of 4°C.Adsorption of organic compounds cannot be the explanation because the effect could be observed during several months whereas the calculated adsorption capacity had to be exhausted after two days. True causes are that specialized bacteria are retained in the pores and niches of the activated carbon in the lag-phase, that micro-organisms find area to grow in the log-phase (approximately 100 m²/m³ with 1 kg m⁻³ granular activated carbon) and that the enrichment of some exoenzymes at the activated carbon occurs (compare Figs. 1 and 2; and Müller & Sekoulov, 1975; Lue-Hing et al., 1976; Larsson et al., 1976; Rincke & Wolters, 1970). Since micro-organisms and activated carbon intimately react, this modification of the activated sludge process was called “biocarbon process” which has to be distinguished from the process with powdered activated carbon (de Walle & Chian, 1977).After completion of the laboratory tests, full-scale tests were started. In full-scale tests several difficulties had to be overcome. In some cases it was difficult to avoid the sedimentation of the granular activated carbon in the aeration tanks. Another task was the separation of the carbon from the surplus activated sludge. Finally it was of interest to determine how much carbon is lost by wet abrasion to be able to make a feasibility calculation. The full-scale tests have been performed in two wastewater treatment plants of the Ruhrverband: Nordenau and Günne.