Assess the learner's ability to apply mass-balance principles and reaction-kinetics models to analyze and optimize wastewater treatment systems; tasks include formulating steady-state and dynamic mass balances for common reactor types (CSTR, PFR, batch), incorporating first-order, Monod, or Michaelis–Menten kinetics, solving for effluent concentrations, hydraulic/solids retention times, reactor sizing and reaction rates, estimating or using given rate constants, and evaluating trade-offs (e.g., effluent quality vs. energy/sludge production) and sensitivity to key parameters in activated sludge and biofilm processes.