Organic chlorinated compounds are generated as intermediates or byproducts in solvents or pesticides manufacturing industries, and are generated as intermediates or by-products. In this study, 2,4-dichlorophenol(2,4-DCP) was selected because it is the precursor of dioxins which is very difficult to measure and has a high potential to contaminate soil and water. The objective of this study is to find out the characteristics and engineering design factors of biological activated carbon (BAC) process for the removal of 2,4-DCP.
Mixed culture developed from MLSS of wastewater treatment plants was acclimated in 2,4-DCP, and then biofilm was formed on activated carbon(AC) and glass beads. Through the continuous operation of the three reactors; (1) the adsorption(ADS) reactor with activated carbon only, (2) the BAC reactor with activated carbon covered with microorganism, and (3) the biofilm(BF) reactor with glass beads, the degradation of 2,4-DCP was compared.
The biodegradation of 2,4-DCP under either aerobic or anoxic conditions depending on the film thickness was investigated stoichiometrically in the BAC and the BF reactor. Total organic carbon(TOC) removal efficiency was 42% in the BF reactor, and 72% in the BAC reactor, respectively. And the biological activity of 2,4-DCP was higher in the BAC reactor than the BF reactor.
In anoxic condition of the BAC reactor, $ΔTOC_{anoxic}/ΔNO_3-N$ value was 0.95 when 2,4-DCP:$NO_3$-N ratio was 1:1, and 0.62 when the ratio was 1:2. It was showed that 2,4-DCP concentration was a limiting factor in films. Bioregeneration rate of BAC which calculated from $ΔTOC_{anoxic}/ΔNO_3-N$ in the biofilm reactor, was 0.89g TOC/㎥ AC-hr when 2,4-DCP:$NO_3$-N ratio was 1:1, but bioregeneration didn't occur when the ratio was 1:2. ΔTOC/ΔCl indicating 2,4-DCP degradation degree is the range of 0.9-1.1, and it correspond to stoichiometric value, 1.01.
Also, the effects of the variation of the loading rate were studied at steady state. The removal efficiencies of TOC of the BAC and the biofilm reactor in volumetric loading rate of 0.088~0.4 TOCkg/㎥. day were 70-90% and 38-70%, respectively. This means that the high loading operation in the biofilm reactor is possible and the BAC reactor has favorable buffer capacity for the variation of loading rate. The amount of microorganisms was constant due to the formation of the thick biofilm at steady state regardless of loading rate.
One of the most essential methods to design the processes using porous media such as activated carbon adsorber is the prediction through breakthrough curve. In this study, the breakthrough curve of the BAC process for the treatment of refractory pollutants was evaluated by the simplified engineering analysis. Through the experiments, the slope of the breakthrough curve can be determined by retardation factor, R and apparent dispersion coefficient, $D_{app}$ which is composed of hydrodynamic dispersion, mass transfer limit effect and nonlinear isotherm effect.
The estimated concentration of effluent was agreed well with the experimental values. Therefore, it is possible to make use of this simple hybrid method in the designing of BAC processes, remediation of soil & groundwater, and other porous media related projects.
