DISINFECTION CE326 PRINCIPLES OF ENVIRONMENTAL ENGINEERING Iowa State University Department of Civil, Construction, and Environmental Engineering Tim Ellis, Associate Professor March 22, 2010

Announcements  Wednesday lab in Town classroom –Finish water treatment plant lab –Exam review  2 nd exam scheduled for this Friday, March 26 th

HISTORY  J_____ S____ and the Broad Street pump in 1854  he was able to show that 59 of the 77 c________ victims used the pump on Broad Street  There was a w___________ in the vicinity where cholera was endemic but nobody at this workhouse got cholera.  This particular workhouse had its own w___.  The cause of contamination turned out to be the d_____ of an infected person that was within three feet of the well. ohnnow holera orkhouse ell rain

Broad Street Pump

Chlorination  Disinfection of water supplies by c____________ began in Chicago and New Jersey in 1908,  within 2 years chlorination of w_____ s________ was practiced in N.Y., Montreal, Milwaukee, Cleveland, Nashville, Baltimore, and Cincinnati.  By 1918, over 1000 c_____ treating more than __ bgd were chlorinating their water supplies.  By 1923 the typhoid death rate had dropped more than 90%  By the beginning of WWII, typhoid, cholera, dysentery were practically eliminated in U.S. hlorination aterupllies ities 3

Theory  Chick’s Law: rate, k, is a function of c___________ and t______ (i.e., CT) and type of organism  Typical disinfectants: –Chlorine:Cl 2 + H 2 O → HOCl + Cl - –Chloramines NH 3 + HOCl → NH 2 Cl + H 2 0 NH 2 Cl + HOCl → NHCl 2 + H 2 0 NHCl 2 + HOCl → NCl 3 + H 2 0 oncentrationime monochloramine dichloramine trichloramine

Pellet dropper Tablet feeder Chlorinators

Gas – 2,000 pound Courtesy Smith Group Consulting, LLC Chlorinators

+- battery Electrolytic Cell NaCl + H e - NaOCl + H 2 anodecathode Na + + e -  Na 2Cl -  Cl 2 + 2e - +-

Hand held chlorine producing unit (CPU)

If the products are mixed, the result is household bleach. 2 NaOH(aq) + Cl 2 (g) = NaCl(aq) + NaOCl(aq) + H 2 O

Chlorine Contact Tank

Ozonation  strong o______, but no residual  no THM f_________ but other (non- chlorinated) DBPs possible  often used as a p__________ disinfectant xidant ormed rimary

Chlorine Dioxide  strong oxidant, but not a powerful as o_____  dose limited to 1.0 mg/L due to health concerns of chlorite and c_______  residual is not long l______ zone hlorate asting

Ultraviolet (UV) Light  uses thin layer of water and mercury vapor arc l_____ emitting UV in the range of 0.2 to 0.29 micron  depth of light p_________ limited to mm  powerful, but no residual amp enetration

ADSORPTION  takes advantage of physical/chemical bond of pollutant with adsorbent (typically g_______ activated carbon or p_________ activated carbon)  one ounce of GAC has a surface area of ____ acres  good process for removal of –THMs –DBPs –SOCs –VOCs ranular owdered 5-10

ADSORPTION  PAC dose is typically _____ mg/L can be as high as ___mg/L  GAC can be used instead of a_______ in dual media filters, –called filter adsorbers –must replace GAC every ____ years  separate stage adsorption unit (contactor unit) –GAC must be replaced or regenerated every __ to __ months nthracite

Particle Size vs. Treatment Alternatives

Macromolecules Smaller Particles Large Suspended Particles MFUFNFRO Divalent salts Monovalent salts Water Micro filtration (MF) - bacteria, algae, clay, large MW humic acids Ultra filtration (UF) - humic acids, viruses, protein Nanofiltration (NF) – viruses, divalent salts Reverse Osmosis (RO) – monovalent salts Membrane Treatment

Reverse Osmosis