1. Wastewater Treatment
• On-site
• Municipal

7. Chemical Oxygen Demand
Oxygen equivalent of the organic matter that can be oxidized by a
strong oxidizing agent (potassium dichromate) in an acid medium.
COD > BOD5: (a) Because more compounds can be oxidized chemically
than can be oxidized biologically and
(b) Because BOD5 does not equal ultimate BOD
COD: 3 h
BOD: 5 d

8. On-site wastewater treatment

12. Septic Systems
Septic Tank – settling, flotation and anaerobic degradation

18. Septic Systems
Drain field (cross-section) – aerobic degradation

19. 0.04 to 0.05 m3 per capita or 1/3 to 1/2 of septic tank capacity

21. Municipal Wastewater
Treatment Systems
•Pretreatment – removes materials
that can cause operational
problems, equalization optional
•Primary treatment – remove
~60% of SS and ~35% of BOD
(by: settle/float) (no removal: soluble pollutants)
•Secondary treatment – remove
~85% of BOD5 and solids
(removes: soluble BOD 5, biological processes/speed-
up natural processes, not significant N, P, HMs,
pathogens)
•Advanced treatment (AWT) – varies:
95+ % of BOD5, SS, N, P, bacteria
(Chemical treatment/filtration/land application/soil-
crop system)
(Sparkling clean, colourless, odourless, effluent)

23. Bar racks
• Purpose
– remove larger objects
• Solid material stored in
hopper and sent to
landfill
• Mechanically or
manually cleaned

26. Grit Chambers
• Purpose: remove inert
dense material, such as
sand, broken glass, silt and
pebbles
• Avoid abrasion of pumps
and other mechanical
devices
• Material is called “grit”

27. MUNICIPAL WASTEWATER TREATMENT PLANT
Aeration Primary
Secondary
Tanks Clarifiers
Clarifiers
Return Sludge
Pumping Facility Sludge
Thickeners
Anaerobic
Digestors

32. Primary Settling
Basins

33. Primary Settling

37. Secondary Treatment
• Provide BOD removal beyond what is achieved
in primary treatment
– removal of soluble BOD
– additional removal of suspended solids
• Basic approach is to use aerobic biological
degradation:
organic carbon + O2 → CO2
• Objective is to allow the BOD to be exerted in
the treatment plant rather than in the stream

38. How is this accomplished?
• Create a very rich
environment for growth
of a diverse microbial
community

39. Basic Ingredients
• High density of microorganisms (keep
organisms in system)
• Good contact between organisms and wastes
(provide mixing)
• Provide high levels of oxygen (aeration)
• Favorable temperature, pH, nutrients (design
and operation)
• No toxic chemicals present (control industrial
inputs)

40. Wastewater Microbiology
1.1 Role of Microorganisms:

42. Bacteria: single-celled organisms
no particular species is selected as “the best”
Fungi: multicellular, nonphotosynthetic, heterotrophic
require only half as much nitrogen as bacteria
Algae: uni-/multicellular, net production of oxygen
Protozoa: single-celled
Rotifers and Crustaceans: animals- aerobic, multicellular
chemoheterotrophs
• Rotifers-consume bacteria, small particles of organics
• Crustaceans: shell structure, present in underloaded ponds
presence indicate-> DO, << organic matter

69. ASP/TF
Attached growth/fixed film/stationary microbial population
No filtering/straining process
Depth = 1-3 m
Dia. < 60 m
Rocks = 25 – 100 mm dia.
Openings too large to strain out solids
Surface area : large where microbes cling/grow/feed on organics

72. Problems
Under high organic loadings:
slime growth – prolific, plug voids, flooding,
air circulation/ O2 for microbes – restricted
system failure
Solution: alternate media
modules/ corrugated plastic sheets, plastic rings

79. Oxidation Ponds
Small communities
Collective term for all types of ponds
Originally:
Oxidation pond – that received partially treated WW
Sewage lagoon - that received raw WW
Waste stabilization pond – all inclusive
pond/lagoon to treat organic WW
Self purification: DO furnished through photosynthesis + surface re-aeration

80. Classification:
Aerobic – shallow, < 1 m, DO throughout the entire depth, by photosynthesis
 Facultative – 1- 2.5 m, zones: anaerobic lower, facultative middle, aerobic upper
 Anaerobic – deep ponds, high organic loadings, anaerobic throughout
 Maturation/tertiary/polishing –polishing effluents from other biological processes
 Aerated lagoons – oxygenated through surface/diffused air aeration

81. Aerobic Ponds.
Shallow
Light penetrates to bottom
Active algal photosynthesis throughout
Daylight hours – large amount of O2 by photosynthesis
Darkness hours–wind mixing of shallow water mass, high degree of surface aeration
Aerobic bacteria predominate

82. Anaerobic Ponds.
Aerobic/anaerobic – function of (a) organic loading and (b) availability of DO
Anaerobic – BOD5 load > O2 production from photosynthesis
To reduce photosynthesis – decrease surface area, increase depth
Turbid – due to reduced metal sulfides,
Reduced light penetration, negligible algal growth
3 stage anaerobic degradation of complex wastes
1st stage: hydrolysis of organic matter
2nd stage (acid fermentation): complex organics broken to short-chain acids+ alcohols
3rd stage (methane fermentation): converted to gases ( primarily CH4 and CO2)

83. Facultative Ponds:
Most common, small communities
Long retention – take care of fluctuations in Q and BOD5
Less capital/operating/maintenance costs

84. Facultative Ponds:

86. Design
BOD load not > 22 kg/ha.d on smallest cell
- To prevent anaerobic conditions
DT (considering total volume of all cells, excluding bottom 0.6 m in vol.)=6 months
- To provide enough storage to hold WW in winter/when receiving stream is frozen
-To provide enough storage to hold WW in summer/when flow in receiving stream
is low to absorb even a small amount of BOD.

90. UPFLOW ANAEROBIC SLUDGE BLANKET REACTOR