Modeling biological drinking water treatment processes

A steady-state biofilm model was applied for modeling the removal of easily assimilable organic carbon (AOC) in biological drinking water treatment. It was found that there is an approximately linear relationship between substrate removal and influent concentration. The slope of the linear relationship, representing the approximate percentage removal of the substrate, is mainly determined by the dimensionless detention time (X{dollar}sp*{dollar}), a quantity developed in this research. Percentage removal increases convexly with increasing X{dollar}sp*{dollar}. Beyond a certain value of X{dollar}sp*{dollar}, further increases achieve little improvement.; Four model parameters, kX{dollar}sb{lcub}rm f{rcub}{dollar} (the product of the maximum specific rate of substrate biodegradation and biofilm density), K{dollar}sb{lcub}rm s{rcub}{dollar} (the half velocity constant), S{dollar}sb{lcub}rm min{rcub}{dollar} (the minimum substrate concentration for sustaining a steady-state biofilm) and D (average AOC diffusivity) were estimated using pilot and bench scale AOC data through data-fitting. The estimates for kX{dollar}sb{lcub}rm f{rcub}{dollar}, S{dollar}sb{lcub}rm min{rcub}{dollar} and D fell in the expected range of values. Both pilot and bench scale K{dollar}sb{lcub}rm s{rcub}{dollar} estimates, although still considered reasonable, were higher than expected from the literature. Probably because of this intrinsically high K{dollar}sb{lcub}rm s{rcub}{dollar}, kX{dollar}sb{lcub}rm f{rcub}{dollar} and K{dollar}sb{lcub}rm s{rcub}{dollar} estimates varied widely. A high K{dollar}sb{lcub}rm s{rcub}{dollar} implies that AOC biodegradation kinetics can be approximated as first order.; The pseudoanalytical solution to the steady-state biofilm model used for the parameter estimation was originally derived by assuming a first-order dependence of biofilm detachment rate on biomass. In this research, the first-order relationship was found to unrealistically overestimate biofilm thickness from S{dollar}sb{lcub}rm min{rcub}{dollar} estimates. This is attributed to the fact that biofilm detachment is often a complex process. A generalized definition of S{dollar}sb{lcub}rm min{rcub}{dollar} was therefore proposed to accommodate many possible detachment mechanisms, whose relationship with S{dollar}sb{lcub}rm min{rcub}{dollar} could be difficult to quantify. Such an S{dollar}sb{lcub}rm min{rcub}{dollar} should be regarded as a distinct biofilm kinetic parameter and determined independently.; With the generalized S{dollar}sb{lcub}rm min{rcub}{dollar} concept, a new solution requiring no assumption concerning biofilm detachment kinetics was devised for the steady-state biofilm model. However, the current pseudoanalytical solution should still be reasonable for describing substrate removal so long as S{dollar}sb{lcub}rm min{rcub}{dollar} is independently measured in-situ or estimated through data-fitting.