EST Flashcards
What are the 8 types of common water pollutants?
1) Suspended solids
2) Oxygen-demanding waste
3) Nutrients
4) Salts
5) Heavy metals
6) Organic compounds such as
7) Pathogens
8) Thermal Pollution
What are examples of heavy metals?
As, Cr, Cu, Pb, Hg, Fe and Zn`
What are examples of organic compounds?
C- and H- containing substances
Polycylic aromatic hydrocarbons
Oils, Fats and Phenols
What are examples of salt pollutants
Chloride, sulfate and phosphate
Oxygen consumption by biodegradable wastes is due solely to the oxidation of carbon compounds. True or false?
False.
Oxygen consumption can be due to both oxidation of carbon and nitrogen compounds.
For Carbonaceous Biochemical Oxygen Demand, organic matter is assumed to be oxidised to ____ and ____
CO2, H20
In a standard 5 day BOD test, a 300ml BOD bottle is filled with a ______ sample, seeded and incubated in the dark at ____ for ____ days
water, 20C, 5 days
What factors would affect the biodegradation rate constant (k)?
Type of wastewater sample
Temperature of wastewater sample
Ability of microorganisms to utilise waste in sample
Well-treated sewage has a higher biodegradation rate constant than raw sewage. True or false?
False. Raw sewage typically
has a higher k value than well-treated sewage.
Define Chemical Oxygen Demand
The amount of oxygen to chemically oxidise the organics present in wastewater.
BOD5 > COD for a normal wastewater sample. True or false?
False. COD > BOD5 because more compounds can be oxidised chemically than biologically.
Besides the higher presence of compounds that can be oxidised chemically than biologically, what is another reason for high COD values?
Inorganic substances that can react with potassium dichromate (K2-CR2-O7 may be present
Chemical oxidation can be carried out by ________ in an ____ medium in ___ hours
Chemical oxidation can be carried out by potassium dichromate (K2-CR2-O7) in an acid medium in 3 hours
Provide 4 ways by which pollutants degrade water quality
- Reduction of dissolved oxygen through aerobic biodegradation
- Production of unstable and foul-smelling products through anaerobic biodegradation
- Eutrophication
- Adverse impacts on human health
Write the equation for the oxidation of nitrogen
N2 -> NH3 -> NO2- -> NO3-
Write the equation for nitrification
NH4+ + 2O2 NO3- + Water + 2H+
Write the equation for anaerobic decomposition of organic compouds
Organic matter -> CO2 +H2O + new cells + H2S/NH3/CH4
Examples of foul-smelling products produced through anaerobic biodegradation include…
Hydrogen sulfide, H2S
Ammonia, NH3
Methane, CH4
Examples of stable products produced through aerobic biodegradation include…
Nitrates, NO3-
Phosphates, PO43-
Sulfates, SO42-
Describe the 5 stages of eutrophication
Oligotrophic: Deep, clear, cold nutrient poor water with minimal aquatic life
Mesotrophic: Nutrients, and sediment begin to accumulate. Increasing populations of aquatic life disappear
Eutrophic: Nutrient rich, relatively shallow, warmer water with much plant growth and other aquatic organisms. Algal blooms occur.
Senescent: Very shallow, overgrown with emerging rooted plant life.
Both primary and secondary standards are designed to protect public health by setting guidelines on the amount of harmful substances in water. True or false?
False. Secondary standards consist of guidelines that apply to the aesthetic qualities of water, which do not pose a health risk.
Both secondary and primary standards are enforceable by law. True or false?
False. Only primary standards are enforceable by law.
List down 5 differences between ground and surface water
GW has constant composition. SW has varying composition.
GW has no dissolved oxygen. SW has dissolved oxygen.
GW has little to no colour. SW has color.
GW has high hardness. SW has low hardness.
GW has little turbidity. SW has high turbidity.
Water hardness is generally expressed in terms of ____ (mg/L)
CaCO3
What is the method available for removal of colloids?
Coagulation: Neutralise the surface charge of colloids so they will adhere to form larger floc.
and Flocculation: Bring colloidal particles in contact so they will form a larger floc and settle
What are 2 commonly used coagulants?
Al3+ as sulfate salts
Fe3+ as chloride salts
Why must the coagulation process take place under rapid mixing?
Allow coagulant to be quickly and uniformly dispersed in water
What are the 2 methods available for hardness removal?
- Lime-soda reaction: Hydrated lime (Ca-OH2) is added to hard water.
- Ion exchange: Reversible exchange of ions between resin and solution
What is the method available for removing suspended solids?
Filtration: Passing through solution through a porous medium such as sand, coal and mixed media
What is the method available for removing pathogens?
Disinfection with chlorine: Sodium hypochlorite or calcium hypochlorite is added to water
Chlorine disinfection _______ the microbe cells and disrupts the organisms’ ______
penetrates, metabolism
Chlorine added beyond the breakpoint dosage will be available as free chlorine residual for water disinfection. True or false?
True
In disinfecting a wastewater solution, chlorine dosage should not exceed the breakpoint chlorination. True or false?
False. Before the breakpoint dosage, no free chlorines are available for disinfection.
Free available chlorine is defined as HOCl and OCl-. True or false?
True
Municipal wastewater = Domestic wastewater. True or false?
False. Municipal wastewater = Domestic wastewater
+ Treated Industrial wastewater
Define treatment efficiency
The ratio of the amount of pollutants removed to the amount of pollutants in the raw untreated wastewater
What is the main goal of wastewater treatment?
To remove as much pollutants as possible before the treated water (effluent) can be discharged back to the environment.
Protect aquatic life
Protect wildlife that depend on rivers and ocean waters
Improve scenic and recreational value of water bodies
The goal of primary treatment is to remove all biological pollutants. True or false?
False. Secondary and tertiary treatment remove majority of the BOD and bacteria.
Tertiary treatment removes 99% of all BOD5. True or false?
True. It provides added treatment where secondary treatment is inadequate.
Secondary treatment does not completely remove pathogenic bacteria and viruses. True or false?
True. Tertiary treatment is required to provide additional treatment.
Primary treatment is focused on physical operations, while secondary treatment is focused on biological treatment. True or false?
True.
Sedimentation tanks are only rectangular in size. True or false?
False. Sedimentation tanks may either be round or rectangular.
The purpose of mechanical scrappers in sedimentation tanks is to remove settled solids (also known as raw sludge).
True.
Domestic wastewater consists of which two types of sewage?
Domestic sewage and sanitary sewage
What is the purpose of the outlet zone?
For collection of clarified effluent
What is the purpose of the sludge zone?
For collection of raw sludge
What is the purpose of the inlet zone?
For distribution of influent
What is the purpose of settling zone?
For separation of suspended solids from wastewater
A typical sedimentation tank can hold wastewater for __ to __ hours
2 to 3 hours
What are the 4 requirements of aerobic biological treatment?
- Availability of microorganisms
- Good contact between micro-organisms and organic waste
- Availability of oxygen
- Favorable temperature and residence time for micro-organisms to work
What are the 3 methods available for removing oxygen-demanding materials?
Trickling Filter: Wastewater is sprayed on a bed of coarse rock. Microorganisms grow on the surface of the rock and feed on organic matter.
Activated Sludge: Wastewater is broken down by an active massive clump of microorganisms known as activated sludge
Oxidation Pond:
Wastewater is broken down by microorganisms grown in shallow or deep ponds
Attached-growth process is the process by which microorganisms grow in activated sludge. True or false?
False. Attached-growth process -> Coarse bed in Trickling Filter
Suspended-growth process is the process by which microorganisms grow in trickling filter. True or false?
False. Suspended growth -> Activated sludge
The rocks used in trickling filter process are 25- 100 um diameter.
False, the rocks used in trickling filter process are 25- 100mm in diameter.
Why is it important to recirculate the clarified effluent to the trickling filter?
It brings the wastewater into contact with the active micro-organisms more than once.
It prevents the slime from drying out in the night, when flows may be too low to keep the filter continuously wet
Explain why some of the activated sludge is diverted to disposal instead of recirculation to the aeration tank
Prevent excess activated sludge from clogging up the aeration tank
How is “aeration” achieved in the aeration tank in activated sludge process?
Compressed air is bubbled through submerged porous diffusers
In an activated sludge system, how long is the wastewater typically aerated for?
6- 8 hours
Definition of Mixed-Liquor Suspended Solids (MLSS)
The total amount of organic and mineral suspended solids in the mixed liquor
Definition of Mixed-Liquor Volatile Suspended Solids (MLVSS)
The organic matter, micro-organisms, and cellular debris in MLSS
MLSS is approximately 60- 70% of MLVSS. True or false?
False. The other way round - MLVSS is 60- 70% of MLSS since it only consists of the organic matter/microorganisms of the solids.
How would you determine the MLSS?
- Obtain aliquot of mixed liquor
- . Filter it
- Dry filter residue at 105C
- Weigh solid residue
How would you determine the MLVSS?
- Dry MLSS further at 600- 650C
2. Weigh solid residue
What is the hydraulic retention time?
The average time spent by the liquid in the aeration tank of activated sludge process.
HRT = V/Q
Why is a low F/M ratio desirable??
Means that microorganisms are “starved”, leading to more efficient wastewater treatment.
How would you control the F/M ratio in activated sludge process?
By controlling the amount of activated sludge diverted to disposal. The higher the disposal rate, the lower the ratio.
Suggest modifications to the conventional activated sludge process to
1) Increase BOD removal
2) Reduce aeration periods
1) Reduce F/M ratio, increase aeration period
2) Increase F/M ratio
High rate activated sludge process involves high/low F/M loading and short/long aeration period.
high F/M loading, short aeration period
How are dissolved oxygen levels maintained in the aerobic ponds?
Algae photosythesis
Aerobic ponds are shallow ponds less than or equal to 2 m in depth. True or false?
False. Should be 1 m in depth at most.
Suggest one tertiary treatment method to remove P
chemical precipitation
Suggest one tertiary treatment method to remove N
denitrification
gas stripping
Suggest one tertiary treatment method to remove NH3
Volatilisation
Suggest one tertiary treatment method to remove residual SS
Ultrafiltration
Suggest one tertiary treatment method to remove toxics and organics
Carbon adsoprtion
Suggest one tertiary treatment method to remove heavy metals
Ion Exchange
Reverse Osmosis
Phosphorus removal can be achieved using these 3 types of chemical compounds
FeCl3
Alum
Lime
What is the consequence to pH in using alum or FeCL3 vs lime?
Alum or FeCl3 would reduce pH, while lime increases pH
Unit operations for chemical precipitation
Reaction basin; for precipitation
Settling tank; for precipitate removal
How can alum or FeCL3 be added directly to an activated sludge process?
Added before the wastewater enters primary sedimentation tank
Added directly to activated sludge aeration tank
Why is it not recommended to add FeCls / alum directly to the settling tank
It may deprive the secondary biological treatment of needed nutrients
Why is it not recommended to add lime to the aeration tank?
The high pH required to form precipitate may be detrimental to microorganisms
Unit operations for nitrification
Reaction basin; for nitrification reaction
Tertiary settling tank; to clarify effluent and return sludge to reaction basin
Secondary reaction basin; for denitrification reaction
Unit operations for gas stripping
Stripping column; for stripping of NH3 from water using air
Activated carbon filter; for removal of NH3 from air
Will you expect the ultimate BOD of wastewater to be different at different temperatures?
No, Ultimate BOD will not change with temperature. It is the amount of oxygen consumed when all the biodegradable material in the sample has been broken down by microorganisms.
Why is 5 days normally used as a reference for BOD?
To measure only CBOD and not include NBOD.
Historically, 5 days was time taken for Thames River to meet the ocean.
How do you increase the removal efficiency of a sedimentation tank unit?
Longer residence time in sedimentation tank.
Laminar region in sedimentation tank.
“A low F/M ratio means that the micro-organisms in the aeration tank are “starved”,
leading to a more efficient wastewater treatment.”
From the sentence, it seems like the
lower the F/M ratio, the higher is the treatment efficiency. Is this true? Explain.
Statement only true to a certain extent.
F/M ratio cannot go lower than a minimum.
Below minimum, treatment efficiency will suffer.
What are the 3 ways by which solid waste can be classified?
Point of origin
Nature of material
Heat content of waste
What are the different types of point of origin for solid waste?
Domestic
Commercial
Industrial
Street
Demolition
Contruction
What are the different types of nature of material?
Organic or Inorganic
Combustible or non-combustible
Putrescible or non-putrescible
What is putrescible waste?
Contains organic matter capable of being decomposed by microorganisms
Cause obnoxious odors
Be capable of attracting or providing food for birds or animals
What is municipal solid waste?
Common ordinary household and commercial waste
Examples of municipal solid waste
Papers
Packing materials
Metal cans
What is hazardous solid waste?
Waste that has harmful effects on human health or the environment.
Storage for MSW vs hazardous waste
MSW: Use disposal bins or plastic bags
Hazardous waste: Use specific type of containers
Handling for MSW vs hazardous waste
MSW: Normal handling
Hazardous waste: Handled as little as possible to minimise risk of exposure
Discard into designated container so that subsequent sorting is not necessary
Transport for MSW vs hazardous waste
MSW: Normal handling
Hazardous waste: Minimise risk of exposure during loading and unloading of truck
Use secondary containment to hold waste
Packaged securely to minimise chance for spills
Sturdy containers are used to survive impact of accident
Treatment for MSW vs hazardous waste
MSW:
Recovery of useful fractions from waste
Disposal of residues into environment
Hazardous wastes:
Treatment on-site for certain types of waste or off-site treatment facility
What are examples of primary pollutants?
Particulate Matter (PM) Volatile Organic Compounds (VOCs) Sulfur Oxides (SOx) Nitrogen Oxides (NOx) Oxides of Carbon (CO and CO2) Lead (Pb) Choro-Fluro Carbons (CFCs)
What are examples of secondary pollutants?
Peroxy Acetyl Nitrate (PAN)
Aldehydes
Ozone (O3)
What is the difference between primary and secondary pollutants?
Primary pollutants exist in the form which they were produced. Secondary pollutants are formed from primary pollutants.
5 ways a material can deteriorate due to air pollution
Direct chemical attack
Abrasion
Indirect chemical attack
Deposition and removal
Electro-chemical corrosion
What are the 4 main zones in a sedimentation tank?
Inlet zone, outlet zone, settling zone, sludge zone
