Roles of Microbial Extracellular Polymeric Substances in Corrosion and Scale Inhibition of Circulating Cooling Water

Circulating cooling water plays a major role in petrochemical electric power, steel, metallurgical, and other industries. Corrosion and scale inhibitors in circulating cooling water systems face the challenges of high cost, low efficiency, and heavy pollution. Extracellular polymeric substances (EPS) were considered as novel, efficient, and environmentally friendly corrosion and scale inhibitors in circulating cooling water systems due to their availability, high efficiency, and lack of benefit from secondary pollution. However, roles of EPS in corrosion and scale inhibition remain unknown yet. Herein, Gram-negative (Pseudo -monas putida) and Gram-positive (Bacillus megaterium) bacteria were selected to explore the corrosion and scale performance and mechanisms of soluble EPS (s-EPS). Performances of s-EPS from P. putida (s-EPS-P. putida) in corrosion and scale inhibition were obviously superior to those of s-EPS from B. megaterium (s-EPS-B. megaterium). The previously undiscovered roles of s-EPS in corrosion and scale were uncovered: (1) the chelating ability of s-EPS (mainly humic substances) prevented the formation and growth of CaCO3 crystals; (2) s-EPS (mainly carbohydrates) formed a dense protective film by integrating with metal ions on a carbon steel surface to prevent the corrosion of A3 carbon steel. Our work provides a deeper mechanistic understanding of corrosion and scale inhibitory performances, allowing advanced development and optimization of s-EPS as a corrosion and scale inhibitor.