Question

Crater Lake water analysis Constituent Concentration Raw Water TOC Bromide Turbidity Giardia cysts Virus Cryptosporidium oocysts <1.0 mg/L Not detected <5 NTU <l/100 L <1/100 L <0.075/L Treated Water Turbidity pH Temperature <0.3 NTU 7.5 5°C 13-25. A 76.000 m'/d direct filtration plant is applying free chlorine as a disinfectant a a dose of 2.0 mg/L. Their low flow is 19,000 m3/d. Their water analysis is the same as that for Crater Lake (Problem 13-24). To save money, they would like to reduce the chlorine dose at low flow. The t1o of their contact chamber is 27.5 minutes under peak flow conditions (pH = 7.0 and 5°C). Check the plant operation to confirm that they are meeting the LT2ESWTR disinfection requirements, and determine whatl dose they should use at low flow.

Answer 1

To meet the LT2ESWTR disinfectant need UV systems for drinking water target cryptosporidium and other virues..UV disinfectant is effective for inactivate cryptosporidium and giardia financially but it has less effective against viruses..so there is atleast two disinfectants used in unfiltered system surface water treatment rule (SWTR) needed of 3log for inactivate giardia lamblia, cryptosporidium and 4logs for removal of viruses should be achieved..

To meet disinfectant requirement with two disinfectant (ozone, UV light, and chloride dioxide)..2log inactivate of giardia and 4log inactivation of virues with chlorine..each disinfectant must be active by inactivate atleast one of this three pathogens( viruses, cryptosporidium, giardia). To achieve this residual requirements it using UV light disinfectant it must be continuously monitoring needed in the LT2ESWTR and it must recorded with periods any reactor operates outside of validated conditions..

Be sure at least 99% inactivation of pathogens with 99% water delivered to the public each month..Dose for LT2ESWTR rules using dose response data from bench scale by LPmercury vaporizer lamps..LP lamp data allow UV dose should be quantified due to LP lamps can produce initially in a single wavelength around (254um)..but MP lamps different from LP lamp, MP lamps different from LP lamp it provides polychromatic wavelengths that different in intensity and effectiveness.. The various UV doses from LP lamps.it will be reactor validation testing the doses should meet the filteration plant criteria..it has different log credits for various pathogens..operating conditions UVdose include the flowrate..unfiltered systems using UVdisinfectant that is needed to achieve 2log inactivation of pathogens by UVreaction for validated conditions..

Low flow rate include 0.5 log for cryptosporidium UVdose is 1.6mj/cm2 and giardia UV dose 1.5 MJ/cm2 and viruses UV dose 39mj/cm2..The disinfectant residual concentration point of entry can't be less than 0.2mg/dl ( measured as free chlorine residual) for more than 4hours ..It must be equal or greater than 0.2mg/dl ..in this case they are using 2.0mg/ dl , so they are meeting the LT2ESWTR disinfectant requirement...