1. Individual Household Treatment Systems (Septic Tanks)

4. Sizing Septic Tank Volume:
Vol = (Average Flow Rate per hour)(1 hr)
Size of Tile Field:
Determined by “perc” test

5. Centralized Wastewater Treatment System:

6. Sedimentation Tank Principles:

7. The trajectories of particles entering the
top of the tank at depth h = 0 are illustrated below.

10. Clarifier (Sedimentation Tank) Design:
Primary: Hydraulic detention time = 2 hrs
Overflow rate = 40 m3/m2-day
Secondary: Overflow rate = 15 m3/m2-day
Depth = 1.3 m

11. Biological Treatment Principles:

12. The quantity of new biomass produced is a function of the growth rate of the microbes.
Under aerobic conditions “cell yield” varies from about 0.1 to 0.4 g cells per g of BOD5 used.
Under anaerobic conditions “cell yield” is much lower – 0.05 g cells per g BOD5

13. Essential Elements of Activated Sludge Process

15. Activated Sludge Design Parameters:
F/M = 0.3 kg BOD5/kg MLSS-day
Volumetric loading: 0.8 kg BOD5/m3-day
Hydraulic residence time = 5 hrs
Air supplied = 60 m3/kg BOD5

17. Biofilm Systems Biofilm a biological slime layer bacteria in biofilm
degrade organics
biofilm will develop
on almost anything

18. Trickling filter

19. Trickling Filter Design Parameters:
Hydraulic loading: 10 m3/m2-day
Depth: 2 m

21. Anaerobic Digestion Gas Raw Sludge In Heated to 95oF Digested
Sludge Out
Gas
Raw
Sludge In
Mixing
Floating
Cover
Supernatant

22. Anaerobic Digester Design Parameters:
Solids loading: 2 kg/m3-day
Solids retention time = 20 hrs
Note that anaerobic digestion is considered to be a mesophilic process where optimum temperature is 350C ( 90oF)

23. Gas (methane) production rate in anaerobic digesters:
0.4 m3 per kg biomass digested
(biomass digested = waste biomass from aerobic process, i.e., activated sludge, trickling filter)
This methane can be used to heat the digester.