Removal of residual organic carbon in drinking water using immobilized-cell bioreactors

This research developed a laboratory-scale immobilized-cell bioreactor for biological drinking water treatment, particularly for removals of assimilable organic carbon (AOC), trihalomethane (THM) precursors, and selected ozonation by-products (OBPs) which were acetaldehyde and formaldehyde. A theoretical model was formulated to understand and predict the biodegradation of AOC in the bioreactor.; Two biocarriers with distinct immobilization techniques were employed. They were calcium alginate beads using cell entrapment and Type-Z carrier using cell binding. Type-Z carrier was found to be superior to Ca-alginate beads due to its inorganic origin and simplicity in cell immobilization. The functionality and applicability of the immobilized-cell bioreactors for removals of various residual organic carbons were demonstrated with the exploitation of ozonated natural water. Ozonation resulted in the increases in AOC and aldehydes which were effectively biodegraded through the immobilized-cell bioreactors at hydraulic retention times (HRTs) ranging from 6 to 30 minutes. In addition, ozonation caused a conversion of humic to nonhumic substances and enhanced the removal of THM precursors.; There were well-defined linear relationships between the pairs of removal rate and influent concentration for AOC, formaldehyde, and acetaldehyde. Thus at a specified influent concentration, the removal rate can be predicted. A transformed linear relationship between HRT and specific removal rate was also observed. The established linear relationships provide a simple yet useful tool to aid in operation and design of the bioreactors.; Scanning electron microscopic examinations revealed porous structure of Type-Z biocarrier and the discrete colonization of microorganisms on the carrier surface. Thus a model was formulated based on an effectiveness factor concept rather than on a conventional biofilm theory. The experimental results indicated that utilization of AOC followed first-order kinetics. Despite the simplicity of the proposed model, the predictions strongly agreed with the experimental data. Considering the complexity of the biological processes in general, the accuracy of the model can be judged satisfactorily.