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IV. Wastewater Treatment

Topic IV. 4. Pollution Loads on the Receiving Water. Wastewater Quality Parameters - BOD,

COD, TOC, PE. Oxygen Balance in the Receiving Water

Pollution Load

Definition: Mass of a definite pollutant, released in definite period (day,

month, year) into the receiving water with the wastewater emissions.

Kinds of pollution loads: Suspended solids - SS Organic substances containing carbon - BOD, COD, TOC Substances containing nitrogen - Ntot, Norg, NH4-N, NO3-N

Substances, containing phosphorus - Ptot, Porg , PO4-P, P2O5-P

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Wastewater Quality Parameters - BOD, COD, PE

Biochemical Oxygen Demand - BOD, g/m3

Definition: Mass of dissolved oxygen utilised in definite time by the aerobic

micro-organisms during processes of dissimilation of organic substances,

containing carbon.

Particularities: BOD is a complex measure, indicating indirectly availability of

biodegradable pollutants mass concentration BOD reflects only biodegradable part of carbonaceous organic

substances BOD reflects only such a part of carbonaceous organic substances,

which is utilised in processes of dissimilation (breathing) Biodegradable organic substances utilised by the aerobic micro-

organisms in the processes of assimilation (cell mass building) is not reflected by BOD

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Biochemical Oxygen Demand - BOD

Fazes of aerobic oxidation of organic substances

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Biochemical Oxygen Demand - BOD

BOD Kinetics

; ;tkat LL .110.

)101.( .1 tkatatt LLLLY

)(11121

21).()( TTTkTk

tt LkdtdL ./ '1 3,2/'

11 kk

048,11

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Chemical Oxygen Demand - COD, g/m3

Definition: Mass of the oxidiser utilised in oxidation of (almost) all the organic substances in water.

Particularities: COD is associated with potassium dichromate -

K2Cr2O7 as an oxidiser in presence of silver sulphate - AgSO4 as a catalyzer

Similar parameter, called oxidability is associated with potassium permanganate - KMnO4 as an oxidiser

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Total Organic Carbon - TOC, g/m3

Definition: Carbon mass of the organic substances in water/wastewater

Analytical determination: Procedure as for COD determination

Procedure for C-fixing in BaCO3

Particularities: TOC is a general measure for organic pollutants mass in

water/wastewater (similar to COD function, but more precise) TOC reflects both biodegradable and biorefractory organic substances

in water/wastewater

....2722 COHClOCrKCorg

322 )( BaCOOHBaCO

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People Equivalent - PE

Definition: Number of population releasing the same pollution load as the one released with definite industrial wastewater emission

Qind - industrial water quantity, m3/d

Qdom - domestic water quantity, m3/d

Cind - pollutant concentration in industrial wastewater, g/m3

a - pollutant daily mass per citizen (pollutant norm), g/d.ca

Particularities: PE differ according to the kind and norm of the pollutant PE is a general and common measure of industrial pollution load

dom

indind

Qa

CQPE

.

.

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People Equivalent - PE

Pollutants norms

Suspended solids Non-settled wastewater- a = 65 g/d.ca Settled wastewater - a = 40 g/d.ca

BOD5 Non-settled wastewater- a = 60 g/d.ca Settled wastewater - a = 40 g/d.ca

Nitrogen - a = 8 - 12 g/d.ca

Phosphorus (as PO4+) - a = 4,4 g/d.ca

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Oxygen Balance in the Receiving Water

Rate of dissolved oxygen consumption for biodegradable organic pollutants dissimilation in the receiving water (BOD kinetics)

Rate of dissolved oxygen recovering in the receiving water (reaeration)

Net rate of dissolved oxygen concentration change in the receiving water

tt LkdtdL ./ '1 tk

t LL .0

110.

tmtsmt DkOOkdtdO .).(/ '' tk

t DD .0

210. 3,2/'2 mkk )(

2122222).()( TTTkTk 018,12

ttmttnet LkDkdtdLdtdOdtdO ..// '1

'

tmtt DkLkdtdD ../ ''1

tsnet DOO constOs

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Oxygen Balance in the Receiving Water

Streeter - Phelps Equation(integral of the last differential equation)

tktktkt D

kk

LkD .

0..

12

01 221 10.)1010.(.

00 ,0 DLt

max,tcrit Dt

01

)120

1

2

12 .

.(1.lg.

1

Lk

kkD

k

k

kktcrit

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Oxygen Balance in the Receiving Water

Graphical Interpretation of the Streeter-Phelps Equation