1. Wastewater Treatment
Secondary Treatment

2. Problem:
Using Velz equation, determine the filter depth of a low rate trickling filter, if settled ultimate BOD is 100 mg/L and desired effluent BOD5 is 20 mg/L . Assume
BOD5 = 68% of ultimate BOD
Removable influent BOD=95%
BOD removable rate constant k=0.18

3. Problem:
A low rate trickling filter has a diameter of 40 m and depth of 1.5 m. assuming the waste removal rate constant as 1.90/d and filter media constant n=0.67, using Eckenfelder's Equation, determine the treatment efficiency of the trickling filter for a wastewater flow of 2 MLD having 200 mg/L BOD5

4. Problem:
Using Rankin's Equation, determine the treatment efficiency of a two-stage trickling filter system designed for the following conditions:

5. Waste Stabilization Ponds
Known as oxidation ponds.
are the simplest biological systems available for the treatment of wastewater.
They are employed for the treatment of both domestic wastewaters and industrial wastewater.

7. Removal Mechanism
When the raw wastewater is fed to the basin after screening, the suspended solids settle to the pond bottom by gravity due to the long retention time.
The soluble organic matter is upper top and intermediate layer are decomposed (oxidized) under aerobic and facultative conditions to carbon dioxide, nitrates, or phosphate and water by micro-organisms (bacteria) present in the waste.
The solids settled at the bottom of ponds are decomposed to stable end products by anaerobic bacteria.
Required oxygen supplied by ?

8. classification of Ponds
1- Aerobic Ponds
Generally m deep and have classified as low rate and high rate aerobic ponds.
2- Anaerobic Ponds
Generally m deep in which anaerobic conditions prevail throughout the pond except for a surface zone of few centimeters.
Usually installed with facultative ponds in series.
Removal of soluble BOD5 is up to 85%

9. classification of Ponds
3- Facultative Ponds
Generally m deep and three zones exist throughout the pond depth, aerobic zone at the surface, anaerobic zone at the bottom and facultative zone at the mid depth of the pond.
Stabilization of organic solids achieved by aerobic bacteria in the aerobic zone, by anaerobic bacteria at the bottom and by facultative bacteria in the middle zone.
4- Maturation Ponds
Generally m deep are normally used after facultative ponds to destruct the faecal organisms.

10. Design Consideration
A first order BOD removal rate is normally assumed in the design of aerobic and facultative ponds and the value of rate constant , K is reported to vary from 0.05 to 1.0 per day depending on hydraulic and operational characteristics of the pond.
The hydraulic loading rate gives detention time t of the pond which is the time required for BOD reactions to be completed.

12. Design Criteria
Normally waste stabilization pond is designed based on organic loading and hydraulic loading criteria. For rectangular ponds, L:B ratio of 3:1

13. Problem:
Design an aerobic waste stabilization pond to treat 4.0 MLD flow of sewage having 200 mg/L BOD5 for a desired effluent BOD5 of 20 mg/L.
Assume BOD removal rate constant to be 0.20 /d at 20o C and the pond dispersion factor as 0.5. the wastewater treatment in summer and winter are 35o C and 25o C respectively. Individual pond area and depth should not be more than 3.0 hectares and 1.2 m respectively.