PEMODELAN KUALITAS AIR PERMUKAANINTRODUCTION(Week #1)

DR. ENG. WIDYANINGTIAS

SA-5023

An Urban Water-wastewater System

❖ Chapra, p. 5

FUNDAMENTAL QUANTITYMass and Concentration

❖ Mass is extensive property

❖ Concentration is intensive property

c = m/V [1.1]

(mg/L ~ g/m3)

(ppm)

Example 1

If 2x10-6 lb of salt is introduced into 1 m3 of distilled water, what is the resulting concentration in ppb.

Solution:

❖ Using Eq. [1.1]

❖ Convert pound to gram

❖ Convert unit obtained to ppb

Rates (Chapra, p.8)

❖ Mass loading rate

W = m/t = Q.c [1.2]

❖ Volumetric flow rate

Q = U.Ac [1.3]

❖ Mass flux rate

J = m/(t.Ac) = W/Ac = U.c [1.4]

FUNDAMENTAL QUANTITY

❖ A pond having constant volume and no outlet has a surface area As of 104 m2 and a mean depth H of 2 m. it initially has a concentration of 0.8 ppm.

Two days later a measurement indicates that the concentration has risen to 1.5 ppm.

(a) What was the mass loading rate during this time?

(b) If assumed that the atmosphere is he only one point source of pollutant, estimate the flux occurred!

Example 2

Solution

❖ Calculate system volume

❖ Calculate mass of pollutant at the initial time

❖ Calculate the mass loading rate

❖ Calculate the flux of pollutant

MATHEMATICAL MODELS

❖ Model representation

c = f(W; physics, chemistry, biology)

c = (1/a).W [1.5]

a = assimilation factor

Model Implementation

❖ Simulation mode: simulate system response (c) as a function of a stimulus (W) and system characteristic (a)

❖ Design mode I (assimilative capacity):

W = a.c

❖ Design mode II (environmental modification)

a = W/c

MATHEMATICAL MODELS

Example 3❖ Lake Ontario in the early 1970s had a total phosphorus loading of

approximately 10,500 mta (metric ton per annum, metric ton = 1000kg) and an in lake concentration of 21µg/L.

❖ In 1973 the state of NY and the province of Ontario ordered a reduction of detergent phosphate content. this action reduced loading to 8000 mta.

(a) Compute the assimilation factor of Lake Ontario!

(b) What in-lake concentration would result from the detergent reduction action?

(c) If the water-quality objective is to bring in-lake levels down to 10µg/L, how much additional load reduction is needed?

Solution

❖ Calculate assimilation factor

❖ Calculate in-lake concentration level

❖ Calculate loading reduction

Conservation of Mass and the Mass Balance

❖ Empirical models: an inductive or data based approach (eq. regression techniques)

❖ Mechanistic models: a deductive or theoretical approach (eq. Newton’s law, conservation law)

MATHEMATICAL MODELS

Conservation of Mass and the Mass Balance

❖ Mechanistic water-quality models are based on the conservation of mass (mass is neither created nor destroyed!)

Accumulation = loading + transport + reaction

❖ Chapra, p. 13

MATHEMATICAL MODELS

Assignment 1.