SAND AND ACTIVATED CARBON AS BIOFILM CARRIERS FOR MICROBIAL-DEGRADATION OF PHENOLS AND NITROGEN-CONTAINING AROMATIC-COMPOUNDS

The aerobic biogradation of a mixture of 22 phenols, N-heterocycles and aromatic amines was studied in a model wastewater containing these components as sole carbon source. A mixed culture was isolated from soil, adapted to continuous flow conditions and immobilized on fluidized particles of sand or activated carbon. During long-term experiments in an airlift-loop reactor, dissolved organic carbon concentrations (DOC) of the medium were varied between 125 and 1000 mg/l and the dilution rate between 0.25 and 0.78 h-1. DOC removal in the sand system was constant with values fluctuating between 59 and 69%. Biomass concentration first increased in proportion to the volumetric DOC loading rate, but reached a plateau at loading rates above 200 mg/l.h with values fluctuating around 4.4 g/l. With activated carbon the biomass concentration was higher under the same conditions, but DOC removal decreased during operation down to a final value of 39%. It was assumed that biodegradation is superimposed by adsorption of organic matter up to the saturation of the carbon. Only a minor part of the biomas was immobilized on the coal particles, while the major part was aggregated as flocs and pellets. The low metabolic activity of the activated carbon system is ascribed to inhibitory effects of by-products. Gas chromatographic analysis of individual components revealed that the feed components were nearly completely degraded in both systems, but evidence was found for the formation of dead-end products.