Effect of activated carbon on the biological treatment of oil‐water emulsions

Abstract

AbstractWaste water, derived from the reprocessing of used emulsions or suspensions, contains high concentrations of emulsified mineral oil and stabilizers, as well as different additives that are needed during the treatment process.Two stirred‐tank reactors and two fixed‐bed reactors were used to study the biodegradation of these waste‐water compounds during two‐stage biological treatment. The waste water was first proceesed in an activated sludge reactor to remove easily biodegradable substances. The effluent from the first stage was treated in three parallel operating reactors: an activated sludge tank containing different amounts of powdered activated carbon (PAC, between 0 and 2%), an upflow anaerobic fixed‐bed reactor and an aerobic fixed‐bed reactor (trickling filter). The results from the continuous treatment were compared with laboratory batch experiments.About 60% of the influent TOC was reduced by the first activated sludge treatment. The removal efficiency increased to about 70% by using a second activated sludge stage. This degradation was comparable to the maximum degree of degradation measured in laboratory batch experiments. PAC addition to the second activated sludge tank resulted in increased degradation rates. The removal efficiency increased to about 76% when 0.1% PAC was added and to 96% with 1% PAC. The removal efficiency decreased to 84% when the proportion of PAC was further increased to 2%. Variations in the amount of PAC addition per unit influent volume in the range of 50 and 200 mg/l had no significant effect on the TOC removal.Degradation models based on the MONOD‐type equation were found to be in close correlation with the results obtained from batch experiments. However, the biological removal rates measured in batch experiments did not reflect the removal capacity determined in continuous operating treatment systems.