1. Sanitary Engineering Lecture 3

2. Population estimation
Many methods are used to forecast the population in the future. Each method has it’s own assumptions
1. Arithmetic increases method: Assumption: The rate of change is constant
(P = population t, = time)
Pt = population after time (t).
Po= present or initial population
Validity: valid only if the curve is close to the real growth of the population in previous years

3. Example 1:
The recent population of a city is inhabitant. What is the predicted population after 30 years if the population increases 4000 in 5 years.
Solution: The arithmetic increase method

4. 2. Uniform percentage of increase: ( Geometric Increase ): Assumption: Uniform rate of increase
By integration

5. Example 2:
The recent population of a city is inhabitant. What is the predicted population after 30 years if the growth rate k= 3.5% .
Solution: Uniform percentage of increase (Geometric Increase)

6. Application
a) use the predicted population method to estimate the Population number
Growth Rate = 4 [%]
Area = donuom
Year
Population
person
Population density
Person /donuom
2010
120000
2015
2020
2025
2030
2035

7. b) Find the Population density in [Person /donuom]
c) Find the waste water rate flow Q if the water demand is 70 l/person
d) Find the dimension for a WWTP if CBOD = 200 mg/l and the TS-Concentration is 4kg/m3

8. 3. Curvilinear method:
It is a method of comparison of the city under consideration with similar cities lager in size.
4. Saturation method:
In this method, the maximum possible density of population is estimated according to the number of apartments and stories per unit area and the
maximum family members.
5. Logistic method
6. Declining Growth method:
7. Ratio method