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McGill University

Department of Civil Engineering and Applied Mechanics

CIVE 225 Environmental Engineering

Winter 2015

Laboratory Session #2

Disinfection wit !V Ligt

Starting on "an 2$ 2015

All of the Montreal-area wastewater treatment plants release their effluents into rivers

(the St !awrence or "iviere des #rairies$ that in turn supply the sourcewater fordownstream drin%ing water supplies &one of the plants currently disinfect their effluent

Chlorine' the disinfectant commonly used for drin%ing water' is not an option for

wastewater ecause it is fatal to fish and other a)uatic life Also' organic matter inwastewater reacts with chlorine to produce trihalomethanes' which are considered

carcinogenic Ultraviolet light and o*onation are alternate disinfectants that can e used

to disinfect wastewater+n this laoratory' you will attempt to determine the disinfection efficiency of U, light on

a treated' ut not disinfected' wastewater sample ecal coliforms will e the targeted

organism

Each laoratory session will e provided with effluent from the !aprairie wastewatertreatment plant in Ste Catherine' .ueec /his is a Montreal-area plant that uses

iological treatment methods and releases effluent into the St !awrence "iver Each

group will test the raw effluent for fecal coliforms and will also attempt to disinfectindividual 01 ml susamples with different doses of ultraviolet (U,$ light U, light will

e applied using a collimated eam apparatus that allows the dose of light to e easily

measured Disinfected samples will then e tested for fecal coliforms A relationship

etween the U, dose and achieved disinfection can e determined /he data from allgroups within a session will e comined

%art &' Disinfection with ultraviolet light (UV): Collimated beam method

(eory

Around 2341' !amert found that the intensity of monochromatic light decreasede5ponentially with the path length of a cell containing a dilute solution in which thecompounds were radiation-asoring and the solvent was nonasoring Mathematically'his findings can e e5pressed as follows

where %lis a wavelength-dependent proportionality constant' called the asorptioncoefficient (cm-2$6 lis the path length6 +ois the incident intensity' and + is the transmittedintensity /he dimensionless fraction +7+ois called the transmittance' /

Morowit* (2801$ derived an e)uation to calculate the average radiation intensity' + 9avg'inside an irradiated volume of a stirred wastewater medium /he e)uation is

lnI

I = - k l

o

(2$

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/he incident intensity' +9o' can e measured with a radiometer' with units of m:attscm-;

/he depth of the wastewater medium' d' in cm' can e measured with a ruler /heasorption coefficient' %' is otained from E)uation 2 y measuring the transmittance of

the wastewater at a wavelength of ;0< nm :hen the length of the cell path is e)ual to 21cm' the value of simply ecomes e)ual to the natural logarithm of +7+o E)uation ; canthen e written as follows (&ote that ln(27/$ must then ta%e on units of reciprocal length=cm-2$

where +avg9 = average intensity (m:attscm-;$

+o9 = incident intensity (m:attscm-;$

d = depth of wastewater sample under U, irradiation (cm$/ = transmittance (when cell path length > 21 cm$ (as decimal fraction of 2$

Instr)mentation an* materials Spectrophotometer with U, lamp' ? ;0< nm

"adiometer to measure incident intensity

U, lamp ? ;0< nm (mercury low vapour pressure$' mounted over a collimating

tue /he platform has to e level and the collimating tue perpendicular to the

platform /he ottom of the collimating tue has a shutter that is activated with a

timer

Safety glasses for U, e5posure and late5 gloves

+rradiation dishes

Magnetic stirrer and ar

/imer6 ruler6 ;0 m! pipette

Effluent sample from wastewater treatment plant6 refrigerated

%roce*)re

It is mandatory to wear uv protective eye glasses and gloves when working with the UVlamp Measure the transmittance'T' of the sample with the spectrophotometer ? ;0< nm

+n duplicate' pour 01 m! of sample into an irradiation dish' measure depth (d$ in

cm Add stirar Cover dishes with tinfoil and set aside /urn on the radiometer' @*ero@ the instrument

:ith the radiometer' measure the incident intensity &ote= the radiometer displays

:cm-;

Using T, d,andIo' calculate the average intensity with E)uation

dk

e-1I=I

dk-*o

*avg

(;$

T

1d

e-1I=I

T

1d-

*o

*avg

ln

ln

($

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Effective*ose + average intensity , e-.os)re time /sec> mW , cm2, s

Each group is assigned ; effective disinfection doses Calculate the time for which

each sample must e e5posed

Set the timer for the re)uired time (in seconds$ #lace the sample on the stirrer

under the collimating eam /urn on stirrer /urn on timer (this opens the shutter$

+mmediately after irradiation' shield each dish from light

Carry out the assay of the fecal coliforms according to the instructions

%resentation of res)lts

&ote that a result of 1 colonies on your filter cannot e scaled up to show 1 colonies per211 ml (or any larger volume$ 1 colonies on a filter signifies B2cfu7(volume filtered$

Draw the disinfection efficiency curve y plotting /log scale vs Effective *ose

& > count of surviving fecal coliforms' measured as colony forming units (CUs$

&ote that for this graph' the y a5is is log-scale' ut the numers are real numers

or the linear portion of the (log-linear$ curve' determine the disinfection rate

constant (%$

U, disinfection efficiency curves fre)uently have a non-linear tail that persists

despite high disinfection doses Comment on possile reasons for this

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%art 3' esting for fecal coliforms

(eory/he coliform group of acterial organisms originates most often - ut not always -

in the intestinal tract of warm-looded animals and humans /he presence of coliformsin drin%ing or recreational water therefore indicates a potential health ha*ard ecause of

the possile presence of other enteric organisms that are pathogens (causing dysentery'typhoid fever' cholera etc$ Coliforms do not represent a health ha*ard per se' ut they

are used as indicators for pollution monitoring' since they share haitat and growingconditions with the pathogens /he ease and speed of testing for coliforms over that for

most pathogens are definite advantages

ecal coliforms are those coliforms that are fecal in origin ecal coliforms arereadily distinguished when grown on M-C medium (a culture roth of specified

composition$' at an incuation temperature of

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2 ml> (21- ml effluent$

2 ml

(>21-2 ml effluent$

2 ml

(>21-; ml effluent$

8 ml dilution water

2 ml effluent

sterili*e them y pulling them through the flame #lace memrane filter (grid side up$ with sterile

forceps on the filter holder and assemle unit

+f less than 21 m! of sample is to e filtered' add K21 m! of dilution water to the funnel #ipet

re)uired amount of sample into the dilution water at the ottom of the funnel +f 21 ml (or more$ of

sample is eing filtered' dilution water is not necessary /urn on vacuum to filter (diluted$ sample

"inse funnel with sterile dilution water

Ma%e sure all li)uid has passed through efore turning vacuum off

"emove funnel' remove filter memrane with sterile forceps to a petri dish Gently roll filter (grid

side up$ onto the culture medium Gently pat down the filter along edges with the flat twee*ers toavoid trapped air and to ensure close contact

+nvert and stac% petri dishes' incuate at

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6ig 18 Serial *il)tionsFORMAT OF LABORATORY REPORT 2

Cover Page (2)Title: Enumeration of Fecal Coliforms and Disinfection by UVCourse name and numberames of !rou" members: (in al"#abetical order)$D numbers of !rou" members in brac%ets ne&t to t#e corres"onding name

Date of 'ubmission

bstract () brief descri"tion of t#e tec#ni*ues used and t#e e&"eriment conductedalong +it# t#e ma,or conclusions (results) from t#e e&"eriment- Fore&am"le. if t#e aim of youre&"eriment +as to determine t#e disinfection rate constant. state t#eresult in t#eabstract-

$ntroduction (/)0 !ive an overvie+ of t#eory (in your o+n +ords) of coliform tests and UV

disinfection1 comment on t#eir signicance ("ur"ose or usefulness)-0 'tate t#e ob,ective(s)-

3aterials and 3et#ods (42)0 Descri"tion of "rocedures (t#e descri"tion s#ould be t#oroug# enoug#t#at anot#er"erson can re"eat t#e same e&"eriment)-0 3aterials and e*ui"ment used- T#e 5sam"le6 is also a material- 7#at isit8 7#ere.+#en. #o+. +as it collected80 E&"lain and clarify t#e reason for certain ste"s t#at +ere follo+ed-

9esults (4/)0 Presentation of ra+ data-0 Calculation of UV doses and t#e coliform counts at dierent doses-0 !ra"# t#e Dose;9res"onse curve0 Presentation of t#e a""roac# to estimate t#e disinfection rate constant

Discussion of results (42)0 E&"lain any data "oints t#at +ere not usable in calculations-0 'tatistical analysis (mean and variance) of t#e data-0 Discuss any e*ui"ment "roblems and its bearing on t#e results-0 Comment on t#e validity of t#e results-

$n addition to your general discussion. discuss your results in terms of t#e

follo+ing 2guidelines-4-Ontario Ministry of the Environment euent guidelines reuire !2"" !"coli#F$%&""ml'(Environmental Commissioner of 4>? Sewage Treatment: Not GoodEnough. Redefning Conservation- EC< nnual 9e"ort. Toronto- T#e @ueenAs Printerfor

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Esta,lishments reuire !-"" fe.al .oliforms #F$%&"" ml'(9egulations. Codes and Protocols. 9e"ort EP';4;EC;;. Federal ctivitiesEnvironmental ranc#. Environmental Conservation Directorate. "ril. 4G

"eferences ($