Transcript Filtration
Filtration • A “polishing” solid/liquid separation step • Intended to remove particles • Other impacts – biodegradation – organics adsorption (especially to GAC) – Mn and Fe adsorption Water Treatment Processes • • • • • • Sedimentation Coagulation/Flocculation Filtration Disinfection Softening Aeration Filter Operation Deposition in a Filter Disinfection • Kill or inactivate pathogens – Bacteria, viruses protozoa • Disinfectants – – – – – Chlorine (Cl2, HOCl or OCl-) Chloramines (NH2Cl or NHCl2) Ozone (O3) Chlorine Dioxide (ClO2) Others: Bromine, UV light • Primary purpose for drinking water treatment Chick’s Law cont. N ln = - kt No where, No = initial concentration of microorganisms, no./mL N = concentration of microorganisms at time t, no./mL t = time of disinfection, [hr] k = an empirical constant descriptive of the particular microorganisms and disinfectant in use, [hr-1] Or: N = No e-kt Softening • Addition of: – Lime (Ca(OH)2) – Soda Ash (Na2CO3) • Removes calcium and magnesium • Removes particles • Can also remove some DOC (Dissolved organic carbon), but not as much as coagulation • Uses high pH Hardness Classification Description of Hardness Soft Medium Hard Extremely hard Hardness, as mg CaCO3/L < 50 50 to 150 150 to 300 > 300 Softening Chemistry Ca(OH)2 + HCO3- + Ca+2 2CaCO3 + 2H2O Mg+2 + Ca(OH)2 Mg(OH)2 + Ca+2