Effects of SMP on Biofilm-Reactor Performance

The extended steady state biofilm model is utilized to predict the performance of a completely mixed biofilm reactor in terms of substrate removal, biofilm accumulation, soluble microbial products (SMP) formation, and total soluble organic carbon (SOC) removal. Three important aspects of how SMP formation affects the effluent quality from biofilm reactors for the concentration range of practical interest are relevant to advanced wastewater treatment, groundwater recharge, and drinking water treatment. First, for intermediate surface loadings, the concentrations of the effluent SMP and SOC are directly proportional to the influent substrate concentration, and SMP comprises the majority of effluent SOC. However, for high and very low loading, residual substrate is most of the effluent SOC. Second, SMP formation and SOC removal by the steady state biofilms are affected by both substrate utilization kinetics and reactor conditions. Changing reactor conditions, such as hydraulic detention time, affect the actual surface loading, while kinetic parameters, such as biofilm loss rate and cell yield, control the minimum achievable substrate concentration (Smin) and the minimum flux to give a deep biofilm (Jdeep). Third, in order to achieve the best treatment efficiency in terms of organic carbon (C), the biofilm reactor must maintain an optimum biofilm thickness that gives the lowest SOC concentration. At least in concept, biofilm thickness can be controlled by manipulating the shear loss component of the biofilm loss rate.