oxygen demand biological and chemical

8/15/2019 Oxygen Demand Biological and Chemical

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Oxygen Demand: Biochemicaland Chemical

ENV20 Introduction to Environmental Engineering

ADNieva


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Biological Oxygen Demand (BOD) 5

- amount of dissolved oxygen used-up bymicroorganism to break up organic materials inwater at 20 oC over a period of 5 days (standard)

unit of measurement: mg 2!"

- clean waters # $ mg!"- polluted rivers %5 mg!"


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Biological Oxygen Demand (BOD)

- amount of oxygen utili&ed by microorganisms in performing oxidation

- 'easure of t e strengt of a water or awastewater

- e greater t e concentration of ammonia-nitrogen or degradable organic carbon* t e

ig er t e + ,


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Biological Oxygen Demand (BOD)drinking water:

-. mg!" minimum treatment of c lorination -5 mg!" coagulation* flocculation*

sedimentation* filtration

-/ mg!" special treatment

$0- 20 days for stabili&ation + ,u 5 days + , 5 (standard)

+ , u twice t e + ,5 + ,u is t e ultimate + ,


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Sources of BOD1imple carbo ydrates from p otosynt esisw en used by plants and animals to synt esi&emore complex carbon-based c emicals suc as

sugars and fats are utili&ed by organisms asenergy source w ic t en exert carbonaceousoxygen demand (CBOD)


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Sources of BOD

lants utili&e ammonia to produce proteinsw!c are complex and carbon-based w! aminogroups (-34 2) as part of t eir structure

roteins are broken down into peptides andt en to amino acids and t en converted intoammonia w ic t en exert nitrogenousoxygen demand (NBOD)


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When a water sample containingdegradable organic matter is placed in aclosed container & inoculated w/ bacteriathe o!"gen consumption t"picall" #ollowsthe pattern$


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Lo

BODt

BOD exerted

L remaining

OxygenConsumption& Equi alentOrganic!emo al

Time, Days

"BOD approac#esasymptotically as tapproac#es infinity


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During the first few days the rate of oxygen depletionis rapid because of the high concentration of organic

matter present.

As the concentration of organic matter decreases, sodoes the rate of the oxygen consumption.

The rate of w/c oxygen is consumed is directly proportional to the concentration of degradableorganic matter remaining at any time t.


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dLt = -rA where Lt = oxygendt e ui!alent of the organics

remaining at time t, mg/L-rA = -"Lt where " = reaction rate

constant, d-#

dLt = -"Lt dt

dLt = -"dt Lt


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$rom the figure.

%&Dt = Lo-Lt = Lo- Loe-"t= Lo '#-e-"t(

where Lo is the ultimate %&D, the maximumoxygen consumption possible when the wastehas been completely degraded


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TEMPE !T" EThe %&D rate constant should beexperimentally determined for thetemperature of the recei!ing water.

Laboratory testing is done at standard

temperature of )*o

+ the %&D rateconstant is ad usted to the recei!ing watertemperature using the e uation

T = " )* ' (T-)*


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TEMPE !T" EwhereT = temperature

" T = %&D rate constant at thetemperature of interest,day #‑

" )* = %&D rate constantdetermined at )* o +, day -#

= temperature coefficient

T = 0 o + 1 )* o + = #.#23T = )* o + 1 2* o + = #.*34


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$#eoretical Oxygen Demand6iven in mg 2!" is calculated from t estoic iometry of t e oxidation reactionsinvolved

#!MP$E P OB$EM

7 waste contains .00 mg!" of C(4 2 ) and 50mg!" of 34 . -3 Calculate t ecarbonaceous ,* t e nitrogenous

,* and t e total , of t e waste


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Laboratory 5easurement of %iological&xygen demand '%&D(

6ample 6i7e = !ol. of undiluted sample x #**

!ol. of diluted sample

Dilution factor = !ol. of diluted sample8!ol. of undiluted sample

= #** / sample si7e '9(


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%&& ml BOD bottle diluted inoculated ' microorganismssto ered to exclude air

%et#ods used in t#e la&oratory

bubbles

dilution O 2 9 mg/L BOD to 2-6 mg/L in dilution bottle(Blanks)

incubated in a dark room 2 o! "or t#days

com$utation o" BOD t determination o" ultimate BOD %BOD rate constant


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*hat is COD+C , is a measure of t e oxygen e uivalent of t eorganic matter content of a sample t at is susceptible

to oxidation by a strong c emical oxidant

%tandard ethods #or the E!amination o# Water andWastewater


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' $! E'$SP,O#P,O O"#

sources: rain-all. distilleries (/&&& mg P $)0

standard: not to exceed %& 1g P $ -or la2es 3 ri4ers tore4ent E"T, OP,5C!T5ON

Other sources: -ertili6ers. chemicals. soa s. detergents.esticides. alloys. animal -eed su lements. catalysts.

lubricants. corrosion inhibitors

7rom rocesses such as: soil erosion. se'age run8o--.industrial 'aste'ater e--luent. atmos heric reci itation.agricultural run8o--


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' $! E'$SN5T O9EN

5n ri4er 'ater. it re-lects the age o- the ollutant;

sources: N,


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' $! E'$S&!ersupply of :utrients : ;

Abundant Algae &xygen Demand?

Depletes Dissol!ed &xygen

Anaerobic +onditions

E"T OP,5C!T5ON is the enrichment o- 'aters by inorganic lantnutrients (N.P. ) resulting rimary roducti4ity 5t is the natural

rocess in the li-e history o- -resh'ater la2e systems ' c tend togradually change -rom oligotro hic to a eutro hic system


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$ f E #i i


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$ypes of Eutrop#ication

Oligotro hic term describing -resh'ater bodies ' c are

oor in lant nutrients 3 there-oreun roducti4e

Cultural Eutro hicatioon arti-icial enrichment

E l i l Eff f E #i i


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Ecological Effects of Eutrop#ication / massi4e algal blooms

increase in turbidity causing massi4e reduction in trans arencyto light

death o- macro hytes due to shading out

? aesthetically un leasantresulting in slimmy masses. smells 3 -lies% increase in organic detritus< ra id deoxygenation

massi4e reduction in in4ertebratese--ect on the -ood 'eb

E l i l Eff f E #i i


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Ecological Effects of Eutrop#ication high oxygen demand

reduction o- O ? in 'ater due to acti4ities o- the

aerobicbacteria is com ensated -or by di--usion o- O ? -rom the'atersur-ace 3 -rom surrounding areas o- higher O ? ' cha ensslo'ly

decrease in dissol4ed oxygen the anaerobic bacteria ' c oxidi6e organiccom ounds ' o the resence o- O ? start to thri4e

roducing end roducts such as , ?#. N, % 3 C, <toxic

E l i l Eff t f E t #i ti


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Ecological Effects of Eutrop#ication

Deoxygenation

de ends on tem erature8 dilution o- e--luent degree o- ri4er aeration8 BOD o- the discharge 3 recei4ing 'ater lus theamount o-

organics in the ri4er

eoxygenation dilution o- e--luent 3 reduction in the e--luent

through decom osition


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D& 6ag +ur!econcentration o# dissolved o!"gen in a river isan indicator o# the general health o# the river

'ivers have some capacit" #or sel#(puri#ication

As the amount o# wastes increases the D) leveldecreases* +he D) should not drop to ,(- mg/.

#or the e!istence and persistence o# these a uaticlives*


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D& 6ag +ur!e

I# the D) is completel" removed #ishand other higher animals are illed ordriven out the water becomes blac ish

and #oul smelling as the sewage anddead animal li#e decompose underanaerobic conditions*


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D& 6ag +ur!e

)ne o# the ma1or tools o# water ualit"management in rivers is the abilit" toaccess the capabilit" o# a stream to absorbwaste load*+his is done b" determining the pro#ile o#the D) concentration downstream #rom a

waste discharge*+his pro#ile is called the D) sag curve*


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%i l gi l t t t th d


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%iological treatment methods Aerobic Acti!ated 6ludge Treatment 5ethodsTric"ling $iltration&xidation ;onds

Lagoons Aerobic Digestion

Anaerobic Anaerobic Digestion 6eptic Tan"s Lagoons


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7n 7ctivated 1ludge 1ystem


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7n 7ctivated 1ludge 1ystem


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Aerobic Biological Treatment

Attached ell 3bio#ilm4 5rocesses Attached ell 3bio#ilm4 5rocesses

+ric ling #ilters+ric ling #ilters

+owers pac ed with solid media to support+owers pac ed with solid media to supportbio#ilm #ormation6 waste stream #lows downward bio#ilm #ormation6 waste stream #lows downward

'otating 7iological ontactor 3'7 4 'otating 7iological ontactor 3'7 4%olid dis s with attached bio#ilms rotate on a%olid dis s with attached bio#ilms rotate on a

hori8ontal a!is to alternatel" contact the wastehori8ontal a!is to alternatel" contact the waste stream and the atmosphere stream and the atmosphere


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7naerobic 1ludge ,igestion

) 2 9 , : 2 → +@ 0 9 2 : 2 )

: ; )): → +@ 0 9 ) 2


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oxygen demand biological and chemical

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