Wastewater Treatment Flashcards
What are its physical characteristics? Colour Odour Temperature Solids
Colour - grey to light brown
Odour - “fresh” - musty, “old” rotten egg
Temperature: varies seasonally
Solids: floatable, dissolved, suspended, settleable
What are its chemical characteristics?
Organics
Inorganics
Organics - Human, animal, vegetable waste
Measured as BOD and COD
Alkalinity
Inorganics - nitrogen, phosphorous, dissolved material
Biological characteristics:
Define Pathogenic and Non-pathogenic
Pathogenic - disease producing
Non-pathogenic - harmless, most prevalent
What are the stages in preliminary treatment and are the three functions?
Screening and Grit removal
- removal of untreatable solids
- protection of subsequent equipment
- improvement of the performance of other processes
Notes:
• A portion of suspended solids and organic matter
(BOD) is removed from the wastewater
• this is usually accomplished with physical operations
such as: settling ,sedimentation, clarification
What is grit?
- Sand
- Cinders
- Rocks
- Cigarette filter tips
- Coffee grounds
- Non-putrescible material
Why is grit removed?
• Prevent clogging of the subsequent unit
operations
• Avoid overloading biological reactors
• Avoid damaging mechanical parts of the WWT
process (grits are abrasive)
How to remove grit?
- Aerated grit chamber
- Non- aerated grit chamber
(old wastewater can be odorous)
What are Biological Unit Processes?
• Biological Unit Processes: Consist of treatment
methods whereby the removal of contaminants is
brought about by biological activity.
• Used to remove colloidal and dissolved biodegradable
organics.
What is Substrate?
• Most organic constituents in wastewater can serve as food (substrate) to provide
energy for microbial growth.
• Organic substrate is measured as BOD, COD or alternatively as TOC
Organic substrate is a mixture of sugars, fats, proteins, etc.
Denoted by generic “S”
eg. BOD5(initial) = S0
What is Biomass?
- Biomass is measured as volatile suspended solids (VSS).
- Biomass nutritional patterns or trophic levels are distinguished on the basis of two criteria: the energy and carbon source.
- Mostly bacteria
Denoted by generic “X” (Micro-organisms)
How do we measure bacteria? Mixed liquor volatile solids (MVLSS) = 80% of TSS
Growth of bacteria:
1) Water treatment - Number(i.e # coliforms/100mL)
2) Wastewater Treatment - Mass (i.e mg/L)
Biomass Classification o Trophic Levels: Energy Source
What are Phototrophs?
If light is the primary energy source, micro-organisms are known as phototrophs.
Biomass Classification o Trophic Levels: Energy Source
What are Chemotrophs?
If redox reactions extract energy from chemicals, micro-organisms are known as chemotrophs.
Biomass Classification o Trophic Levels: Carbon Source
What are Autotrophs (or lithotrophs)?
If CO2 or HCO3- is the principle carbon source, micro-organisms are known as autotrophs (or lithotrophs).
Biomass Classification o Trophic Levels: Carbon Source
What are Heterotrophs (or organotrophs)?
If organics are the principal carbon source, micro-organisms are known as
heterotrophs (or organotrophs).
What are photoautotrophs?
Give examples
• Organisms obtaining energy from light and carbon from CO 2 .
• Ex: Algae, plants, Chlorobium (green sulfur bacteria), Chromatium (purple sulfur bacteria) and Cyanobacteria (blue-green algae).
What are photoheterotrophs?
Give examples
• Organisms obtaining energy from light and carbon from organic material (ex: alcohols,
carbohydrates, fatty acids etc.)
• Ex: Rhodospirillium (purple non-sulfur bacteria) and green non-sulfur bacteria.
What are chemoautotrophs?
Give examples
• Organisms obtaining carbon from CO 2 and energy from the oxidation of inorganic
compounds.
• Ex: Beggiatoa (H 2 S oxidized to SO 4-2 ), Thiobacillus (elemental sulfur S to H 2 S), Nitrosomonas
(NH 3 to NO 2- ), Nitrobacter (NO 2- to NO 3- ), Hydrogenomonas (H 2 to H 2 O), and Thiobacillus
ferrooxidans (Fe +2 to Fe +3 ).
What are Chemoheterotrophs?
Give examples
• Organisms obtaining both their energy and carbon from organic material.
• Ex: The majority of bacteria (Eschericia coli, Desulfovibrio, Pseudomonas, Clostridium,
Methanogens), all fungi, slimes, protozoa and animals.
• They also include saprophytes and parasites
Aerobic Processes
Free (molecular) O2 is present.
- Carbon degradation is done by chemoheterotrophic bacteria
- Nitrification is done by chemoautotrophic bacteria
Anoxic Processes
Bound oxygen forms
- Denitrification is done by chemoheterotrophs.
- Sulphate reduction (i.e. sulphanogenesis) is done by chemoautotrophs.
- Sulphate reduction is most often classed as an anaerobic process.
Anaerobic Processes
No free or combined oxygen
• Done by two groups of chemoheterotrophic bacteria.
a) Liquefaction (acidogenesis)
b) Gasification (methanogenesis)
What is the Trickling Filter (TF)?
- An aerobic, fixed-growth process in which the biomass grows on a media and the wastewater trickles down over the media allowing the BOD to be removed.
- A fixed growth process because the micro-organisms grow as a film and are “fixed” on to the media.
What is the Rotating Biological Contactor (RBCs)?
• An aerobic process in which the biomass grows on a media but this time the media is rotated into a pool of wastewater allowing the BOD to be removed.
What is Activated Sludge (AS)?
• An aerobic suspended growth process.
• The micro-organisms are grown in suspension forming brown flocculent suspended
particles.
- Often modelled as a completely-mixed reactor (CMR) with recycle.
- The model is also known as a continuous-flow, stirred tank reactor (CFSTR)
What is the goal of the AS Process?
• To remove (reduce) or stabilize organic (and inorganic) matter in the wastewater using suspended growth, aerobic microorganisms
What is Anaerobic Digestion (AD)?
• An anaerobic suspended growth process in which WAS is digested by cannibalisation
by other bacteria.
What is Fluidized Bed (FB)?
• An anaerobic process in which bacteria grow on media but this time the media is kept in suspension.
What is Upflow Anaerobic Sludge Digestion (UASBs)?
• An anaerobic process where the bacteria form large granules (rather than flocs) and the granules cluster in a blanket.
How is a water’s quality measured?
By chemical, physical and biological parameters.
What is the order of how contaminants are removed from a water/wastewater?
(i) increasing difficulty; and
(ii) decreasing size.
What is the nutrient ratio for biological growth in a sewage treatment plant? BOD5:N:P
BOD5:N:P = 100:5:1
You add nutrients to promote biomass growth
Model for Microbial Growth:
What is the name of the concept when the output is less than the input?
Microbial growth kinetics is described in terms of a Yield Coefficient (Y).
What is r(s)?
( ) = subscript
Substrate Destruction Rate (oxidation)
what is r(g)?
( ) = subscript
Biomass growth rate (synthesis)
What is k(d)X?
( ) = subscript
Endogenous Metabolism Rate (autooxidation)
Whats is k(d)?
( ) = subscript
starving factor coefficient
What is Y?
Yield coefficient = mass biomass produced/mass substrate destroyed i.e. Y = r(g)/r(s)
What is K(s)?
the one half velocity coefficient (half-saturation constant)
What is Mu(m)?
maximum specific growth rate = r(g,max)/X
What is k?
Max specific substrate destruction rate
k=Mu(m)/Y = r(s,max)/X
Treatment Models: Completely Mix with No Recycle
What processes are in involved?
Aerobic and anaerobic digesters
Aerated lagoons:
• A biological treatment process consisting of a CFSTR (Continuous Flow Stirred Tank Reactor)
• Properties are uniform throughout @ steady-state.
What is U?
The Specific Utilization Rate
U=k*S/(K(s)+S)
What is r(g)’?
Net sludge production when multiplied by volume
High F/M (food to microorganism ratio)
- > Low growth phase, maximum rate of metabolism
- > settling poor, BOD removal efficiency is low
Thus
- > excess BOD passes out through effluent
- > lots of sludge produced
Low F/M (food to microorganism ratio)
- > endogenous phase, metabolic rate is low
- > small(food) + large(bugs) = starvation
- > settling is good, BOD removal efficiency is high
