Mechanistic insights and targeted mitigation of calcium scaling and biofouling in recirculating wet scrubber

This study addresses the mechanistic coupling between calcium-driven inorganic scaling and biologically associated fouling in a laboratory-scale recirculating wet scrubber operated under controlled alkaline chemistry relevant to acid-gas scrubbing. The system was designed as a controlled fouling analogue rather than a full physicochemical replica of industrial acid-gas absorption. Increasing Ca 2+ concentration shifted the water chemistry toward greater thermodynamic favorability for calcium-bearing mineral precipitation, particularly CaCO 3 , CaMg(CO 3 ) 2 , and CaF 2 . The resulting deposits became progressively denser and more crystal-rich, while elemental analysis showed a concentration-dependent increase in deposit Ca content. At the same time, loss on ignition, Fourier-transform infrared spectroscopy (FT-IR), extracellular polymeric substance (EPS) measurements, and bacterial community analysis indicated that the deposits contained substantial organic and microbial components, suggesting that inorganic scaling and biofilm-associated accumulation occurred concurrently. Biocide treatment substantially reduced viable microbial abundance, deposit mass, and pressure-drop development under Ca-rich conditions, although residual deposition persisted when Ca 2+ remained present. These results support a coupled physicochemical–biological fouling mechanism in which calcium availability enhances inorganic scaling tendency and may also stabilize EPS-rich mixed deposits under recirculating alkaline conditions. However, direct calcium-removal strategies, pathogen-specific detection, and microbial functional assays were not performed; therefore, the findings should be interpreted within the scope of a controlled laboratory fouling analogue.