A geometry based optimal control approach for low pressure filtration processes: a secondary effluent upgrading case study*

Abstract The current paper presents a geometrically inspired approach for the optimization and control of low pressure filtration units for (waste)water treatment. The optimization aims at minimizing the operational costs, encompassing both energy and chemical cleaning costs (and, hence, accounting for reversible as well as irreversible fouling), while ensuring a minimum required nett water flux. Advantage has been taken of the process’ cyclic nature. In each cycle the transmembrane pressure increases during the forward flow phase due to fouling and decreases again due to backflushing. Assuming linear increases/decreases allows the use of simple geometric approaches for computing analytical cost and constraint expressions. Relating both slopes to operational parameters as forward flux and filtration time, provides the handles for the actual control and optimization. However, due to the discrete nature of the number of cycles in one operation run, a relaxation strategy is employed for solving the optimization problem. Simulation results are presented for a preliminary filtration model inferred from a microfiltration plant for secondary effluent upgrading in the context of a research project with the Keppel Seghers company.