| Four mathematical models--SSABM, DSABM, SMABM, and DMABM were developed to describe acetate degradation, acetate degradation with sulfate reduction, phenol degradation, and phenol degradation with sulfate reduction in an anaerobic biofilm process, respectively. The models incorporate mechanisms of diffusive mass transport and Monod kinetics. The model--DMABM has three features: the phenol and sulfate substrates diffuse in the growing biofilm simultaneously, the acetate and sulfate are dual-limiting substrates, and the biological reaction term is nonlinear. An advanced numerical technique, a combination of orthogonal collocation method and Gear's method, was employed to solve these four mathematical models. Four pilot-scale tests were conducted to verify the models. The reactor volume is 42.65 L which yields a hydraulic retention time of 2.5 days. The reactor temperature was controlled at 35{dollar}spcirc{dollar}C by using an automatic moisture-proof heater.; The models-generated substrates concentration curves agreed well with those obtained in all pilot-scale tests, which indicated that the models correctly simulated the phenomena which occurred in the reactor if the reasonable shear loss term was determined. In the first test, the removal efficiency of acetate is 98.0%. In the second test, the removal efficiencies of acetate and sulfate are 99.0% and 91.7%, respectively. In the third test, the removal efficiency of phenol is 97.6%. In the fourth test, the removal efficiencies of phenol and sulfate are 98.2% and 88.0%, respectively. The pilot-scale studies show the process can remove organics and sulfate to very low levels. The sensitivity analysis in DMABM shows that the change in one of the biokinetic coefficients (k{dollar}sb{lcub}rm p{rcub}{dollar}, Y{dollar}sb{lcub}rm p{rcub}{dollar}, K{dollar}sb{lcub}rm sp{rcub}{dollar}, b{dollar}sb{lcub}rm p{rcub}{dollar}) significantly affects the biodegradation of the substrate effluent curves. The change in operational parameters (S{dollar}sb{lcub}rm bp0{rcub}{dollar}, S{dollar}sb{lcub}rm bu0{rcub}{dollar}, Q) affects the entire course of the substrate effluent curves. However, the mass-transfer coefficient (k{dollar}sb{lcub}rm fp{rcub}{dollar}) did not affect the substrate effluent curves due to the dominance of diffusional resistance in the biofilm. The procedures presented in this study could be employed for the design of anaerobic biofilm treatment processes to remove multiple contaminants in industrial wastewater. |
