Unified Basis for Biological Treatment Design and Operation

A unified basis for design and operation of biological waste treatment systems employing suspensions of microorganisms is developed from microbial kinetic concepts and continuous culture of microorganisms theory. Biological solids retention time, θ_c, average time period a unit of biological mass is retained in the system, is suggested as an independent parameter for process design and control. Steady-state kinetic models are presented for three process configurations, i.e., completely mixed reactor without solids recycle, completely mixed reactor with solids recycle, and plug flow reactor with solids recycle. Reported values of kinetic coefficients are tabularized for: (1) aerobic treatment of carbonaceous wastes; (2) aerobic biological nitrification; (3) anaerobic methanogenic fermentation of carbonaceous wastes. These coefficient values are substituted into the models to determine lower limits, i.e., minimum values of θ_c, for each process. Minimum values of θ_c of models are compared with θ_c values for actual treatment systems.