The document discusses different types of lagoon systems used to treat wastewater. Aerobic lagoons use aeration to add oxygen and facilitate microbial activity to break down organic matter. Facultative lagoons contain aerobic, anaerobic, and facultative zones. Both require regular maintenance to prevent issues like damage from rodents or accumulation of material on aeration equipment. Lagoons are well-suited for warm climates and treating low to medium strength wastewaters but have limitations in cold climates and removing certain contaminants from effluent.

2.  Lagoons are deep waste stabilization ponds -like bodies of water or basins
designed to receive, hold, and treat wastewater for a predetermined period of time
by artificial means of aeration.
 In the lagoon, wastewater is treated through a combination of physical, biological,
and chemical processes.

3.  According to the microbial activity in the aerated lagoons
- Aerobic aerated lagoons
- Facultative aerated lagoons

4.  Dissolved oxygen is present throughout much of the depth of aerobic lagoons.
 They tend to be much shallower than other lagoons.
 They are better suited for warm, sunny climates, where they are less likely to
freeze.
 HRT = 2 to 10 days
 SS concentration between 60 to 300mg/l
 The BOD removal is of order of 75 to 85%
 Oxygenation requirement is of order of 0.7 to 1.3 kg per kg of BOD removed.

5. 1) The mechanical surface aerators so that solids do not settle to bottom of tank.
2) The other unit is settling tank for removal of suspended solids .

6. FACULTATIVE AERATED LAGOONS
 Three types of zones are present
 Aerobic Zone.
 Anaerobic Zone.
 Facultative Zone.
 HRT is higher than aerobic lagoons because time requires for
the solids to settle and for
 many pathogens viruses to either die off or settle out.
 Detentions time ranges from 3 to 5 days .
 BOD removal are of order 75 to 90%

7. In Series
 When lagoons operate in series, more
of the solid material in the
wastewater, such as algae, has an
opportunity to settle out before the
effluent is disposed of
In Parallel
 This system design is particularly
useful in cold climates or where
lagoons are covered with ice for parts
of the year
Two, Three, or Four Lagoons Are Better Than One Two, Three, or
Four Lagoons Are Better Than One
• Each lagoon cell has a different function to perform, and a different kind of lagoon design
may be used for each cell.

8. For Aerobic Lagoons
 Any earthen structures used as impoundments must be periodically inspected. If
left unchecked, rodent damage can cause severe weakening of lagoon
embankments.
 In submerged diffused aeration, the routine application of HCl gas in the system
is used to dissolve accumulated material on the diffuser units
 The use of submerged perforated tubing for diffused aeration requires
maintenance and cleaning on a routine basis to maintain design aeration rates

9. For Facultative Lagoons
 Most facultative lagoons are designed to operate by gravity flow.
 The system is not maintenance intensive and power costs are minimal because
pumps and other electrically operated devices may not be required.
 Earthen structures used as impoundments must be inspected for rodent damage.

10. TYPE OF LAGOON APPLICATION
Aerobic Lagoon Municipal and industrial wastewaters of low
to medium strength
Facultative Lagoon Treated raw, screened, or primary settled
municipal wastewater and biodegradable
industrial wastewaters

11. 1. The aerated lagoon are simple and rugged in operation , the only moving piece
of equipment being the aerator.
2. The removal efficiency in terms of power input are comparable to some of the
other aerobic treatment methods
3. Civil construction mainly entails earthwork, and land requirement is not
excessive.
4. Aerated lagoons require only 5 -10% as much land as stabilization ponds.
5. The aerated lagoons are used frequently for the treatment of industrial wastes.

12. 1. They are less efficient in cold climates and may require additional land or longer
detention times in these areas
2. Odour can become a nuisance during algae blooms and lagoons that are
inadequately maintained.
3. Unless they ae properly maintained, lagoons can provide a breeding area for
mosquitoes and other insects.
4. They are not very effective at removing heavy metals from wastewater.
5. effluent from some types of lagoons contains algae and often requires additional
treatment or polishing to meet local discharge standard.

13. For Aerated Lagoons
 Aerated lagoons may experience ice formation on the water surface during cold
weather periods
 Reduced rates of biological activity also occur during cold weather
 Formation of ice on Floating Aerators.
For facultative Lagoons
 The inability of the process to meet a 30 mg/L limit for TSS due to the presence of
algae in the effluent.
 Odors may be a problem in the spring and fall during periods of excessive algal
blooms and unfavorable weather conditions
Limitations

14. EXAMPLE-
Design an aerated lagoon for the following data –
Raw sewage flow- 20 MLD
Raw sewage BOD ( So) = 200mg/l
Desired BOD ( S ) = 20mg/l
Kinetic constant, y= 0.6 , Kd= 0.1 /day , f=0.68.
Hydraulic retention time ( HRT )= 6 days
Solid retention time (𝜃𝑐 ) = 10 days
Depth = 2 m, L/B = 3
Solution-
Flow rate = Q = 20,000 𝑚3
/𝑑𝑎𝑦
So = 200mg/l = .2kg/l
S= 20mg/l = .02 kg/l
HRT =
𝑉𝑂𝐿𝑈𝑀𝐸
𝑠𝑒𝑤𝑎𝑔𝑒 𝑓𝑙𝑜𝑤 𝑝𝑒𝑟 𝑑𝑎𝑦
volume = 20,000 𝑚3/𝑑𝑎𝑦 * 6 days
= 120, 000 𝑚3
Area = volume/depth
= 120, 000 𝑚3/ 2 m
= 60,000 𝑚2

15. Area = L*B
L/B =3
60,000 𝑚2= 3*B*B
B = 141.42 m
L= 424.26 m
Now,
Oxygen requirement,
𝜃𝑐=
𝑋 ∗𝑉∗( 1+𝐾𝑑 ∗𝜃𝑐 )
𝑌 ∗𝑄∗(𝑆𝑜−𝑆 )
X =
10 ∗0.6∗20,000 ∗(0.2−0.02)
120,000∗(1 +0.1∗10)
X = 0.1125 kg/ 𝑚3
O₂ required = 1.47*Q* ( So-S) -
1.42∗𝑋∗𝑣
𝜃𝑐
= 1.47*20,000* ( 0.2 – 0.02 ) -
1.42∗0.1125∗120,000
10
O₂ required = 3375 kg/day

16. Thank
you