Fig. 1: Unit operations in benchmark configurations and their prominence in the U.S.

a, b Distinguishing features of benchmark WRRF configurations and c their distribution in the Contiguous United States. A WRRF configuration is referred to as a unique combination of a liquid code (a) and a solid code (b) as defined in Tarallo et al.¹³. Plot c is adapted based on publicly available survey data on US POTWs¹⁸, among which plant-wide process simulation models are available for the highlighted configurations. The full range of liquid treatment trains span a variety of treatment targets (i.e., rBOD, NIT, BNR, ENR) defined by the effluent concentrations of key contaminants¹³. “-P” for “prime” in the liquid code is a suffix indicating a variation on the mainstream process, unrelated to the standalone “P” liquid treatment train.