Effects of De-icing Salts on the Respiration of the Microorganisms of Activated Sludge

Winter road maintenance is particularly ensured using the application of chemicals on roads. Especially in urbanised areas, the solution of water with de-icing salts is discharged into sewer system transporting this water to wastewater treatment plant, where it can cause lot of problems. Beside the corrosive effects of salt on the materials used for sewer system and technological equipment of wastewater treatment plant, salt concentration affects the efficiency of biological wastewater treatment. The analyses performed with activated sludge from wastewater treatment plant showed that commonly used de-icing salts (NaCl, MgCl2, CaCl2) profoundly affected the respiratory activity of its microorganisms. Increasing concentrations of chloride in the influent of the wastewater treatment plant caused a progressive decrease in respiratory activity and a progressive prolongation of the acclimation period of the microbial community. The extent of the increase in the acclimation period was dependent on the examined road salt.