1. Environmental Engineering
CIVL 241
Fundamentals

2. Environmental Engineering
What is your definition of Environmental Engineering? “ Take care of garbage “ “ keep the air and water clean so we can use it “ “ take care of pollution “

3. Environmental Engineering
Environmental Engineers protect the health by minimizing the release and impact of pollutants into the air, land, and water. They work each day to design control and treatment systems that reduce or limit the negative effects that human have on the many ecosystems of the world.

4. Environmental Engineering Dimensions and Units.

5. Fundamental Dimension : quantitative description for basic characteristics, such as force (F), mass (M), length (L), and time (T).
Derived Dimensions : calculated by an arethmatic manipulation of one or more fundamental dimensions. Velocity has dimensions of length per time (L/T) and volume is L3.
Dimensions are descriptive but not numerical. They cannot describe how much, they simply describe what. Length described in units as a meter or yard.

6. Engineering Dimensions and Units
Density : is mass divided by unit volume
Where :
ρ : density
M: mass
V: volume
In SI unit density is kg/m3 while in American system is Ib/ft3
Water density is 1000 kg/m3 or 62.4 Ib/ft3

7. Engineering Dimensions and Units
Concentration: is the mass of material A in a unit volume consisting of material A and some other material B.
The concentration of A in a mixture of A and B is:
Where:
CA: concentration of A
MA: mass of material A
VA : volume of material A
VB: volume of material B

8. In many environmental aqueous systems, its appropriate to assume that 1mg/l equal to ppm, provided that the fluid is primarily water so the density of the solution is 1g/ml

9. Engineering Dimensions and Units
Flow Rate: can be either mass or volumetric flow rate. Mass flow rate unit is kg/s or Ib/s, and volumetric flow rate is in m3/s or ft3/s.
So mass (M) of material passing a point in a flow line during a unit time is related to the volume (V) of that material.
Mass =Density x Volume
Volumetric flow rate can convert to mass flow rate :
QM = QV x ρ (1)

10. Engineering Dimensions and Units
The relationship between mass flow of some component A, concentration of A, and the total volume flow (A+B) is
QMA = CA x QV(A+B) (2)
The difference between Equ.1 and 2 is that at 1 applicable to only one material in a flow stream while at 2 relates to two different materials in a flow stream.

11. Retention Time: is the time required to fill the container, and the average time the fluid spends in a reactor or control volume. Retention time also called detention time, or residence time.
if the volume of container such as large tank is V (L3), and the flow rate into the tanks is Q (L3/t). Then the residence time is:
The average retention time can be increase by reducing the flow rate or increasing the volume.

12. Example 1
plastic beads with a volume of 0.04 m3 and a mass of 0.48 kg are placed into a container, and 100 liters of water poured into the container. What is the concentration of plastic beads, in mg/L?
Solution

13. Example 2
A wastewater sludge has a solids concentration of 10,000 ppm. Express this in percent solids (mass basis), assuming that the density of the solids is 1 kg/cm3.
solution

14. Example 3
A wastewater treatment plant discharge a flow of m3/s (water plus solids) at a solids concentration of 20 mg/L, how much solids is the plant discharge each day?
Solution

15. Quiz
A water treatment plant has 6 settling tanks that operate in parallel. And each tank has a volume of 40 m3. if the flow to the plant is 35 m3/s. what is the retention time in each of the settling tank? If the entire flow goes first through one tank then the second and so on, what would be the retention time in each tank?

16. Environmental Engineering
Material Balances

17. Outline
material balance around a "black box" unit operation is introduced first.
In all cases the flow is assumed to be at steady state, that is, not changing with time.
Initially, these black boxes have nothing going on inside them that affects the materials flow. Then it is presumed that material quantities are produced or consumed within the box.

18. 3.1 MATERIAL BALANCES WITH A SINGLE MATERIAL
Figure 3.1&3.2 shows a black box into which some material is flowing. All flows into the box are called influents and represented by the letter X.
If no processes are going on inside the box that will either make more of the material or destroy some of it and if the flow is assumed not to vary with time (that is, to be at steady, state).
[ mass per unit time] = [ mass per unit time]
IN OUT
[X0]= [ X1]+ [ X2 ]
generally convenient to use the volume balance for liquids and the mass balance for solids.

19. 3.1.1 Splitting Single-Material Flow Streams
Previous figure illustrates that under steady state conditions and no material being produced or destroyed then the material balance :
[ X0]= [ X1]+ [ X2 ]
The material X can, of course, be separated into more than two fractions, so the material balance can be:
where there are n exit streams, or effluents.

20. Splitting Single-Material Flow Streams
EX.3.1 A city generates 102 tons/day of refuse, all of which goes to a transfer station. At the transfer station the refuse is split into four flow streams headed for three incinerators and one landfill. If the capacity of the incinerators is 20, 50, and 22 tons/day, how much refuse must go to the landfill? Solution The input stream is the solid waste delivered to the transfer station. Four output stream , three for incinerators and one for landfills.

21. Splitting Single-Material Flow Streams

22. 3.1.2 Combining Single-Material Flow Streams
A black box can also receive numerous influents and discharge one effluent. as shown in Figure 3.4. If the influents are labeled X1, X2, , X„„ the material balance would yield steady state condition is remaining for combining single material flow streams .

23. Combining Single-Material Flow Streams
EX.4 A trunk sewer, shown in Figure 3.5, has a flow capacity of 4.0 m3/s. If the flow to the sewer is exceeded, it will not be able to transmit all the sewage through the pipe, and backups will occur. Currently, three neighborhoods contribute to the sewer, and their maximum (peak) flows are 1.0, 0.5, and 2.7 m3/s. A builder wants to construct a development that will contribute a maximum flow of 0.7 m3/s to the trunk sewer. Would this cause the sewer to exceed its capacity?

24. Combining Single-Material Flow Streams
Solution

25. Ex 5) A stream flowing at 10 m3/s has a tributary feeding into it with a flow of 5 m3/s. the stream's concentration of chloride upstream of the junction is 20 mg/L, and the tributary chloride concentration is 40 mg/L. find the downstream chloride concentration. **Tributary : a river or stream that flows into a larger river or a lake Solution Outline black box for problem under study. So the black box is the stream and concentration plus flow rates feeding into the black box from stream and tributary. while the effluent is chloride concentration and stream discharges

26. Ex 6) 18,925 m3/d of wastewater, with a concentration of 10 mg/L of a conservative pollutant is released into a stream having an upstream flow of 37,850 m3/d and pollutant concentration of 3 mg/L. what is the concentration in ppm just downstream? ** conservative : pollutant which doesn’t growth up or consumed inside the stream meaning no reaction coming out due to such pollutant. Solution Upstream and downstream are black box boundary parameters for current problem. So the influent is coming from upstream and effluent out off the black box at downstream.

27. Ex 7) A river with a 400 ppm of salts ( conservative substance) and an upstream flow of 25 m3/s receives an agriculture discharge of 5 m3/s carrying 200 mg/l of salts. The salts quickly become uniformly distributed in the river. A municipality just down -stream withdraws water and mixes it with enough pure water (no salt) from another source to deliever water having no more than 500 ppm salts to its customers. What would be the mixture ratio of pure water to river water?

28. Ex 8) A lagoon with volume of 1200 m3 has been receiving a steady flow of conservative waste at a rate of 100 m3/day for a long time to assume the steady state conditions apply. The waste entering the lagoon has a concentration of 10 mg/l. assuming completely mixed condition. a) What would be the concentration of pollutant in the effluent leaving the lagoon? b) If the input waste concentration suddenly increased to 100 mg/l, what would be the concentration in the effluent?