Use LEFT and RIGHT arrow keys to navigate between flashcards;
Use UP and DOWN arrow keys to flip the card;
H to show hint;
A reads text to speech;
149 Cards in this Set
- Front
- Back
- 3rd side (hint)
|
Name the purpose of filtration? How does it occur? |
Filtration is used in (waste)water treatment for removal of particulates. Water Passes through filter media, particulates accumulate on surface of media or are collected in its depth. |
Screens/Granular Material |
|
|
Filter Media - Single/Dual |
Anthracite, Sand for dual media. Gravel placed at the bottom to retain the sand above and drain the water. |
|
|
|
Purpose of troughs? |
Troughs carry all the waste sludge created from particulates and are where the dirty water is (at the top of filter). These particulates are put into trough when backwashing is used. |
|
|
|
When is backwashed used |
Approximately 24-72hrs, when all voids are full, and the backwash (clean water) removes the particulates by putting the in the toughs (sent to waste) |
Voids full? |
|
|
Enhanced Backwashing (2 other methods alongside backwash water)? |
Air injection or air scour is the injection of air pressure in the form of tiny air bubbles which scour or eliminate the small particles. Surface washing is the rotation of jets which are used to break up coagulant precipitate at the top of the medium of the filter. |
Air, surface |
|
|
Filtration Purpose to Water Treatment? |
- Removal of turbidity (regulation) - Typically follows sedimentation - Useful for pathogen removal - Granular filter effective after coagulation (particles destabilized in charge) |
|
|
|
Filtration Purpose to Waste water Treatment? |
- Removal of suspended solids in secondary effluents - In industrial streams, remove emulsified oil droplets, iron particulates |
:) |
|
|
Explain the difference between Convention/Direct/Inline Filtration? |
Conventional Filtration always has coagulation and flocculation and sedimentation prior to filtration. Direct Filtration - Skip sedimentation, but apply both coagulation and flocculation Inline Filtration - Coagulation (must remove charge) then go to filtration |
Conventional - Coagulation + Flocculation + Sedimentation + Filtration |
|
|
Where can Direct or Inline Filtration be used |
Best suited for surface waters with low turbidity (smaller particulates can be used for the filter). Flocculation removed or may occur in the actual granular media. |
Lake Ontario. |
|
|
What are the qualities of FIlter Media |
- Sufficiently Fine - prevent passage of suspended solid material (very fine = short run time but retains more small particulate) - Coarse enough to retain floc (more void space for collecting particulates) -Deep enough for long filter runs -Grading to permid cleaning by backwash |
Fine < Filter < Coarse |
|
|
How should graded media be? |
- In several layers, from top (largest, less dense) to bottom (smallest, most dense) DUAL MEDIA: Anthracite is big but light so it doesn't settle to the bottom and get mixed up after backwash |
NOT ALL THE SAME SIZE/DENSITY |
|
|
What characteristics does filtration depend on?
|
- Surface charge -pH rate of filtration Ensure coagulation is done to remove surface charge so it can stick to filter |
|
|
|
Transport/Attachment Mechanisms? |
- Transport:Sedimentation, Interception, Diffusion (depends on media size, filt. rate, viscosity, density of solids) -Attachment: Electrostatic interactions, chemical bridging, specific adsorption (depends on coagulant, water quality, filter media) |
|
|
|
When does backwash occur? |
Limiting headloss - headloss increases with impurities. Don't want to be a negative pressure (headlosses exceed depth of water above filter) - reduces filter capacity by removing dissolved O2. |
|
|
|
What is air binding? |
Dissolved air that comes out of air solution - these bubbles can take away space within filter Reduce air binding by ensuring enough head |
bubbles :) |
|
|
Backwashing depends on...? |
- headloss, effluent quality reduction, run time - don't wash too fast or media washes out - stop backwash gradually to allow media to return to desired gradation |
|
|
|
Constant Rate vs Declining Rate Flow? |
-Constant Q allows hL to increase, and rate control valve slows opens to maintain Q when media is plugged - Declining - Q decreses near end of filter run and so hL slowly increases there |
QQQQQ |
|
|
Advantages of Constant/Declining Rate? |
Constant - expensive, complex, if valve is opened too much, particles displace due to shear Decline - Lower hL, improved quality (less shear), cheaper, also requires high water depth (disadv) |
C: |
|
|
What is hardness caused by? |
Magnesium and Calcium ions Also other multivalent cation but not common |
|
|
|
Problems with hardness? |
- May produce scale in hot water heaters/pipes - Apparently studies are done with cancer possibilities.... |
|
|
|
Types of Hardness Removal? |
- Precipitation as insoluble compounds - Reverse Osmosis - Ion Exchange |
R.O |
|
|
Carbonate vs Noncarbonate |
Carbonate - Ca And Mg carbonates precipitated by lime Non - Ca and Mg sulfates/chlorides requiring soda ash |
|
|
|
Precipitation Limits? |
0.6 meq/L CaCO3 0.2 Mg(OH)2 |
|
|
|
Variations of Lime-Soda Softening |
Excess lime treatment - remove MgOH2 at higher pH Selective calcium removal - only remove the calcium hardness Split treatment - Splitting water into one stream that requires softening and the other that doesnt |
Excess lime treatment.... |
|
|
What happens if precipitation occurs in filter? |
particulates get stuck together, increase backwash, increase void ratio, particles that used to be on an angle give a path for water to go straight through |
|
|
|
How do you drop the pH back from 10.5 to about 7? |
Recarbonation - Add CO2 to lime to neutralize excess lime Second recarbonation - lower pH and prevent scaling on filters (convers carbonate ions to bicarbonate ions) |
|
|
|
What is ion exchange softening |
Cation exchange resin usually polystyrene Ions of a particular species in solution are replaced by ions of a different species Resin regenerated by passing solution of high concentration of released ions through bed |
Regenerated with strong solution of NaCl |
|
|
What is disinfection? |
selective destruction/inactivation of disease causing organisms |
|
|
|
Primary/Secondary Disinfection? |
Primary - applying disinfectant at the treatment plant to kill pathogens Secondary - disinfectant used to prevent biofilm growth on pipe and protect water from intrusion as it travels |
|
|
|
Why do we need to do prechlorination/ |
Chlorine gas needs to be added to prevent zebra mussels from attaching to the pipe inlet and block the water to go to the plant |
|
|
|
How does UV work |
UV alters the DNA of pathogens not allowing them to reproduce inside the body |
|
|
|
What is a DBP? |
A disinfection by product are what forms when chlorine is combined with an organic material (precursor). ex. of DBP = chloroform |
|
|
|
What are the characteristics of disinfectants? |
- Toxic to microorganisms - Soluble in water and cell tissues - Stable (can be stored) - Non-toxic to humans (unless too much) - Effective over pH and temperature range - Can penetrate surfaces (cell walls) - Available in large quantities - Safe to handle - Leave an appropriate residual |
|
|
|
Why can't alum coagulation and softening happen at the same time |
Alum coagulation requires a pH of 6.5 and reduces the pH briefly, and softening with lime increases the pH and (since magnesium precipitates out at 10.5). So doing both at same time will put it at a pH range where neither coagulation nor softening would work. |
|
|
|
What are the conventional disinfectants used? |
Chlorine Chloramine (not powerful for primary disinfection) Chlorine Dioxide Ozone |
|
|
|
What are the advanced disinfectants used? |
Ozone + Hydrogen peroxide (peroxone) Ozone + UV irradiation UV alone |
|
|
|
What are the characteristics of pathogens? |
Bacterial spores Protozoan Spores Viruses Vegitatitive Bacteria |
4 categories |
|
|
Which of the following exists at high pH's? HOCl or OCL-? |
OCl-. HOCl is 80 - 90x more effective than OCl- at disinfecting |
Acid H+ is removed |
|
|
Disinfection with chlorine is dependent on what? |
Temperature and pH (pH is a major one) |
|
|
|
What can chlorine be added as ? |
- Chlorine Gas (Dangerous - higher liability cost, but more eff.) - Javex (Sodium hypochlorite - liquid) |
2 forms |
|
|
Chloramine types? |
- NH3 - monochloramine NH2CL - dichloramine - NHCL2 - Trichloramine (smells bad) |
Chlorine is added to water and ammonia forms chloramines |
|
|
When to apply chlorine? |
After alum coagulation when the pH is still relatively low - but not at the same time as alum. Alum temporarily drops pH to 4.5 before it raises again and that low pH can create Nitrogen trichloride (tricloramine) which can smell/taste bad |
Lower pH for effectiveness |
|
|
Free/Combined/Total Chlorine |
Free = residual chlorine existing in water as HOCL and OCl- Combined = residual existing in combination with ammonia (chloramines) or other organic compounds Total = difference between chlorine added and (free + combined) |
|
|
|
Breakpoint chlorination graph? |
1. Chlorine reacts with readily oxidizable substances (chlorine --> chloride) 2. Formation of mono/dichloramines with more chlorine dosage 3. Tipping point - when more chlorine results in oxidation of chloramines, N02, N2, NCl3. - reduces total chlorine residual 4. At the end of the reduction of total chlorine, additional chlorine creates an equal residual |
How does it work |
|
|
Chlorine Dioxide Usage? |
- Limited application as a disinfectant - Used more for taste/odour control - Used for destroying phenols, and Giardia -Does not form Trihalomethanes |
ClCO2 |
|
|
Advantages of ClC02 |
-Does not react with ammonia Stronger than chlorine (doesn't depend too much on pH) - Strong oxidant - taste/odour/colour control |
|
|
|
Disadvantages of ClCO2? |
- Must be generated on site - Good control required to minimize excess free chlorine |
|
|
|
Effectiveness of Ozone? (Advantages) |
- Must generate onsite and use immediately - Strong oxidizing gas - reacts with most organic and many inorganic molecules - Does not leave a residual like chlorine (need to add more) - Destroys taste, colour, odour - Organic by products produced are easily biodegradable - Inactivates cryptosporidium cysts |
|
|
|
Ozone is capable of reacting by what two mechanisms? |
- Direct reaction of ozone molecule - As hydroxyl free radical (OH-) --> way more powerful than ozone - Half life of OH much smaller (microseconds) |
|
|
|
Ozone disadvantages? |
- Most complex technology - Short half life (no residual) - Cannot be stored (must be used right away) - Very expensive for equipment |
|
|
|
How are Disinfection By-Products created? |
Treatment of surface waters or groundwater with chlorine Chlorine + precursors = DBP's |
Precursors are natural organic matter that chlorine reacts with |
|
|
Examples of Disinfection By Products? |
Trihalomethanes (THMS) ex. clhoroform, bromodichoromethane - Halacetic Acids (GAAs) ex. Monocloroacetic acid, Dichloroacetic acid |
|
|
|
Formation of DBP dependent on ? |
- Precursor type/concentration - Disinfectant type - Disinfectant - precursor ratio - pH - Contact Time - Temperature |
|
|
|
What alternatives are there to reduce formation of THMs? |
- Use alternative disinfectant - Remove precurors PRIOR to chlorination (DONT REMOVE AFTER FORMATION) - Optimize chemical coagulation - alum dosage for precursor removal (add more than just for turbidity removal) - Add powdered activated carbon to adsorb precurors - Change location of CL2 addition til after coagulation (must ensure enough contact time for adequate disinfection) |
|
|
|
Primary/Secondary Disinfectant? |
- Primary responsible for microbiological kill - Secondary - maintain dectable residual Consider: effectiveness, potential to form DBPS, cost |
|
|
|
Alternative Primary Disinfectants? |
- Chlorine Dioxide - Ozone (becoming popular) - Chloramines (not powerful as primary disinfectant) - UV light (cost effective control |
|
|
|
Filtration is given what credits? |
2.0 log Cryptosporidium/Virus - need 2 more 2.5 Giardia - need 0.5 more |
|
|
|
What concentration, and time do we use for CT? |
(C - effluent concentration and T is time for the fastest 10% of the flow to pass through the tank) |
this is a conservative estimate |
|
|
What are some reasons we use coagulation? |
-Cost time effective to settle out big particles Sedimentation works on bigger particles Filtration works on large particles and particles with destabilized charges |
|
|
|
Define coagulation/flocculation |
Coagulation - process of destabilizing colloidal particles to permit particle growth Flocculation - agglomeration of destabilized particles through mechanical mixing |
|
|
|
Applications of coagulation for (waste) water? |
Water - to help remove turbidity, dissolved organic matter, colour, odour causing compounds, and pathogens Wastewater - enhance removal of microorganisms in clarifiers (after biological treatment), aid in removal of non-biodegradable organics |
|
|
|
Suspended particles have often a +ve or - ve overall charge |
- |
|
|
|
What type of intermolecular bonds allow floc to build up |
van der Waals forces - when materials are very close they tend to bind to each other - need to reduce the electrostatic repulsion to allow van der Waals forces to cause particles to join |
|
|
|
What kinds of chemicals work as coagulants? |
Anything with a multivalent ion (alum, ferric chloride, ferric sulphate), and is fairly insoluble in water |
|
|
|
Name three parts of Coagulant Dose vs Turbidtiy Graph |
Charge Neutralization, Restabilization (if too much coagulant added), Sweep Flocculation |
Sweep Flocculation is last one |
|
|
How to determine optimum dosage of coagulant? |
Using a jar test - coagulation is strongly pH dependent (need pH ~ 6.5, and alum decreases pH to ~ 4.5 momentarily before raising it again), and also temperature dependent |
JAR |
|
|
What is sweep flocculation? |
Involves overdosing coagulant beyond neutralization, and the high concentration results in large, metal polymer molecules that stick to particles and form large floc, independent of surface charge. Sweep flocculation sweeps fine particles with the long chains of polymers |
|
|
|
What pH does alum work at |
approximately 6. |
Toronto (6ix) |
|
|
Explain organic polymers |
Water soluble high molecular weight organic compounds; many ionizable groups along a molecular chain - less sensitive to pH, need less mixing (minimizes floc breakup), reduces sludge protection, result in very strong, dense floc, bridging mechanism |
Polymers are bridging the destabilized the particles |
|
|
Should mixing speeds be the same in flocculators? |
No. The first mixer should be the fastest, and then it should be slower and slower for sequential mixers since floc are bigger and don't need that big of a speed to produce bigger floc (also faster mixing can break up floc) |
|
|
|
What is flocculation? |
Agitation of chemically treated water to cause small particles to coalesce into large particles (flocs) |
|
|
|
Purpose of flocculation in (waste) water? |
Water - enhance removal of turbidity in sedimentation and/or filtration Wastewater - increase removal of suspended solids in primary settling, condition industrial wastewater, improve performance of secondary settling following activated slufge |
|
|
|
Flocculation is faster when... |
- G is bigger (velocity gradient (mixing) faster) - d (particles have bigger diameter) - N (more particles per unit volume) - n (increase in the proporrtion of successful collisions) - controlled by coagulation, since they don't repel each other |
Factors affecting rate |
|
|
What is the critical time, tc? |
After the critical time tc, for mixing, the floc begins to break up. Want to mix until tc to maximize floc. |
Flocculation wise |
|
|
What's wrong with having the paddel area larger than 20-25% of the tank cross sectional area? |
Any bigger than 20-25%, the water rolls around with the paddle, and doesn't actually do any sort of mixing of the water. |
|
|
|
What is tapered flocculation? |
To mix the water quickly (high G), and as particles get bigger, they become more fragile and so reduce the G (results in growth of large, dense flocs) |
|
|
|
What is hydraulic flocculation |
Flocculation occuring through hydraulic mixing in baffled channels (no mechanical mixing). - cheap, no mixing power, but no control over G or t (dictated by flow) |
|
|
|
How does sedimentation work? |
It uses gravity to separate suspended material from water - gravity is cheap (instead of pumping), low headlosses, but main constraint is space |
|
|
|
Sedimentation applications in water treatments |
Water: pretreatment of surface water, settling of coagulated and flocculated waters prior to filtration, settling of coagulated waters in water softening, settling of water for iron/manganese removal |
|
|
|
Sedimentation applications in wastewater treatments |
Waste water - Removal of grit, other coarse solids, removal of suspended solids prior to biological treatment, removal of biological solids produced during biological treatment |
|
|
|
Types of Sedimentation |
Type 1 - Discrete/Free Settling - constant speed Type 2 - Flocculant Settling - variable speed depending on particle size/mass (settle faster) Type 3 - Zone/Hindered Settling (high Susp. solids), particles settle with a new interface Type 4 - Compression Settling (compression of compacting mass on bottom) |
4 of them |
|
|
Three forces surrounding Type I settling |
Gravity Buoyancy Drag |
|
|
|
What is the overflow rate? |
The velocity that a particle has to sink so that it is guaranteed to be removed. (=h/t, where h is the depth of the tank, and t is the time for the water to travel from the left to right side of the tank) |
|
|
|
Does the effectiveness of a settling tank depend on its depth? |
No. Increasing the depth, makes the particles travel twice as far, but also keeps the particles in the tank for twice as long so it all cancels out. In practice, need to provide depth to avoid resuspension of sludge |
|
|
|
Explain hindered or zone settling |
Solid flux, G = concentration, c x velocity, v |
|
|
|
How do you find the limiting flux? |
Find Cu, maximum allowable concentration, (where at the bottom of it solids are being pumped out), draw a tangent line going through the second hump from the left (lower one) and connect it to the y-axis |
|
|
|
Explain high rate settling |
A shallow tank used to minimize construction costs, ex. parallel plate settlers - particulates don't all have to go as far deep to settle out High rate settling requires less than 20% of total area compared to conventional settlers. |
|
|
|
Name some physical, two chemical, and one biological treatment method |
Physical - settling, filtration, flocculation, screening, gas transfer Chemical - coagulation, softening Biological - anaerobic digestion |
|
|
|
Types of Waste water? |
Sanitary, industrial, stormwater, infilitration/inflow |
|
|
|
Raw sludge disposal methods? |
Mechanical dewatering Landfill Incineration Anaerobic Digestion |
|
|
|
Uses and Sources of Water? |
Domestic, Recreational, Agricultiral, industrial |
|
|
|
Objectives of water treatment |
1. safe 2. appealing 3. reasonable cost to facilities |
|
|
|
What needs to be removed in water throughout treatment |
Pathogenic organisms (bacteria, viruses), suspended materials, hazardous contaminants, odours, unpleasant tastes/colour |
|
|
|
Objective of wastewater |
To clean wastewater such that it may be discharged into the natural environment again. |
|
|
|
What needs to be removed in wastewater throughout treatment |
Suspended, floatable materials, biodegredable organics, pathogenic organisms, nutrients, toxic compounds |
|
|
|
What is the limitation of standards? |
Standards are imaginary lines between good and bad, so anything below the standard is magically acceptable, but a small amount over would be horrible? |
|
|
|
Define MAC and IMAC |
Maximum acceptable concentration - certain substances that are known or suspected to cause adverse effects on health For substances where there is insufficient toxicological data to derive a MAC, interim values are recommended |
|
|
|
Who sets the water treatment standards? |
Canadian guidelines adopted as provincial standards (provincial governments MOE, MOH) |
|
|
|
Measurements of Organic Content in Waste water (3 types of demand measurement) |
- Biochemical Oxygen Demand = most common - Chemical Oxygen Demand - Total Organic Carbon |
|
|
|
What is BOD |
Biochemical Oxygen Demand is the measurement of dissolved oxygen used by microorganisms in biochemical oxidation of organic matter. BOD determines the approximate quantity of oxygen required to stabilize organic matter |
|
|
|
Problems with the laboratory Method of BOD measurement? |
Most wastewaters will run out of oxygen in the bottle Wastewatter may not contain organisms to start the process Solutions: Dilute wastewater, spike seed organisms |
|
|
|
Why do we use BOD5 |
O2 uptake is commonly first order decay, shorter than 5 days makes measurement too imprecise, while longer measurements cause interference from nitrification problems |
|
|
|
Nitrification? |
NH3 + Oxygen becomes N03- > organisms that perform nitrification in wastewater take 6-10 days to acclimatize and begin. Nitrification reduces the amount of dissolved oxygen |
|
|
|
Limitation of BOD test |
takes 5 full days only measures biodegredable organics (no toxic wastes) 5 days may not be enough time for slow degradable organics (cellulose) |
|
|
|
What is Chemical Oxygen Demand? |
Measure of oxygen required to oxidize matter using a strong chemical oxidant (potassium dichromate) Organic matter is destroyed by chromic and sulfuric acid and converted to CO2 and water |
|
|
|
Advantages of COD |
Higher values than BOD since more organics can be chemically oxidized can correlate COD with BOD for lots of wastes Analysis takes hours instead of 5 days |
|
|
|
What is Total Organic Carbon? |
Instrument that measures the total organic carbon in a sample (doesn't mention type of organic carbon) |
|
|
|
What is the DO-Sag Model |
Simultaenous action of deoxygenation and reaeration The replacement of dissolved oxygen occurs through the water surface exposed to atmosphere |
|
|
|
Limitation of the Streeter Phelps Model? |
Additional processes can occur: (removal of BOD by adsorption/sedimentation, addition of BOD by tributary inflow, Addition of BOD or removal of DO by benthal layer [scummy layer at bottom - lots of organisms], addition of oxygen by photosynthesis, removal of oxygen by respiration], |
|
|
|
Define Biological Treatment |
Anything that is in suspended solid form is easy to remove, but dissolved organic pollution is heavily in wastewater Use microorganisms (usually bacteria) to eat organic pollution. Dissolved organics creates new bacteria when its eaten but bacteria are easy to remove by settling or filtration |
Biological Treatment Requires: 1. Conversion of dissolved organics into suspended matter (by bacteria) 2. Removal of bacteria |
|
|
Considerations for Biological Treatment |
Aerobic Treatment is fastes, products are inoffensive Must add O2 and mixing How much time, how much oxygen/bacteria required, how much sludge produced |
|
|
|
Microbial Metabolism - Organisms require what substrates? |
1. Source of energy (pollution = food) 2. Carbon source - for synthesis Inorganic elements - N & P Trace elements - S, Cu, Mg |
|
|
|
Difference between heterotrophs and autotrophs? |
hetero- use organic carbon to form cell tissue auto- derive cell carbon from Co2 |
|
|
|
4 Methods of Oxygen Utilization |
Aerobic - require molecular oxygen Anoxic - tolgerate absence of O2 but need other electron acceptor (NO3) Anaerobic - use carbon as electron acceptor Facultative - exist with or without oxygen (use O2 when available - ex. E. Coli) |
|
|
|
Importance of Algae and Protozoa? |
Algae - supply oxygen (photosynthesis) Protozoa - consume bacteria, act as polisher for bio. wastewater effluent |
|
|
|
How do bacteria reproduce? |
Binary Fission |
|
|
|
Phases of bacteria Reproduction? |
Lag phase - takes time for bacteria to acclimatize to environment before reproduction (or if water is changed bacteria stop eating) Log growth - food excess (reproduction exponentially limited by own rate of reproduction) Stationary phase - food becomes limiting (growth rate equals death rate) Log death - no more food (bacteria eat each other) |
|
|
|
Define growth yield |
Amount of biomnass produced per unit amount of substrate utilization |
|
|
|
What is Xv |
Measure of mass of bacteria eating the pollution (commonly [not 100% accurate] the VSS in water sample - TSS contains some inorganic, VSS mostly due to bacteria in a bio treatment system) |
|
|
|
What is the Endogenous Phase of growth kinetics |
Little food is left so bacteria consume each other |
|
|
|
What are the 5 kinetic parameters of growth kinetics of biomass? |
Y, ke, K(Ks), k, um k = um/Y |
|
|
|
What are the three types of reactors? |
Batch Reactor Continuously/completely stirred tank reactor CSTR Plug Flow Can occur in different combinations |
|
|
|
Batch Reactors? |
Absence of continuous inflow or outflow (dC/dt = r) |
|
|
|
CSTR Reactors? |
Continuous Stirred Tank Reactor - needs instantaneous and complete mixing [makes the concentration inside the reactor the same as the effluent concentration] Can also have reactors in series (more efficient) |
|
|
|
(Dis)Advantages of CSTR Series reactors |
Efficient Flexibility in Operations/Locations More complex More costly (operations, maintenance, construction) |
|
|
|
What is Plug Flow Reactor |
Can consider PFR as an infinite series of CSTRs. As subsections become infinitely smaller, mass balance converts to a form related to changes in C relative to distance x from the PFR influent |
|
|
|
Does a CSTR outperform a PFR? Or other way around? |
RFP outperforms a CSTR - in CSTR concentration inside reactor is equal to the outflow concentration (very low). In PFR the lowest concentration is outflow (higher average concentration) |
|
|
|
What is activated sludge? |
most widely used system for wastewater - it involves the production of an activated mass of microorganisms capable of stabilizing a waste aerobically (microorganisms actively convert dissolved pollution into new cell mass) |
|
|
|
Important consequences of activated sludge |
proper reactor design to give desirable (BOD in effluent) and Mixed liquor volatile suspended solids (mass of bacteria) rate of sludge production oxygen requirements |
|
|
|
Assumptions for reactor design? |
All biological activity occurs only in the reactor Bacteria do not lose their activity in clarifier or while being recycled |
|
|
|
Difference between thetax and thetad |
theta x for sludge retention time theta d for hydraulic retention time |
|
|
|
What does increase thetax do? |
Makes the process more efficient (lowers Se) but increases Xv. But there is a practical limit to Xv. (F:M ratios) |
|
|
|
What does increasing the tank size do |
Tank size doesn't affect Se. A bigger tank results in higher HRT, but fewer organisms per volume. Therefore theta x is the most important factor for effectiveness |
|
|
|
What is Se |
Soluble BOD in effluent of clarifier (also contains some cells that don't settle which exert some BOD) |
|
|
|
The rate of solids produced is the sum of what? |
Sum of: Rate of new cell material growth as a result of substrate utilization (>80% sludge) Rate of nonbiodegredable particulates entering inflow Rate of production of nonbiodegredable parts of new cell growth |
|
|
|
F:M Ratio? |
Food to Microorganism Ratio
= QSo/VXv Low to medium ratio are best (bacteria are a little hungry) |
|
|
|
Rate of Metabolism vs F:M graph parts |
Endogenous - Good settling (small F:M) Declining Growth - Medium F:M Exponential growth - Poor Settling (High F:M) |
|
|
|
Optimum Activated Sludge Retention Time (thetax) and MLVSS (Xv - concentration of biomass)? |
SRT - 5-7 days (high rate systems 3-5 days, and extended aeration system 20 days) Xv 1500 - 5000 mg/L |
|
|
|
What is sludge volume index? |
SVI measures the settleability of the sludge - (efficiency of settling out bacteria to remove them in clarifier) SVI should be between 50-150 Too high SVI --> check thetax, O2, F:M |
|
|
|
What is sludge bulking |
A high SVI indicates sludge bulking which is slow settling due to growth of poorly-settling organisms Common under low F:M, low O2, low pH, nature of the organics in wastewater |
|
|
|
Application of oxygen in a reactor? |
Bubbled oxygen or air Mechanical mixing/aeration |
|
|
|
Nutrient Requirements of Activated Sludge? |
Nitrogen, Phosphorus Bacterium - C5H7NO2 |
|
|
|
What is a completely mixed reactor |
It's a variation in activated sludge treatment where no recycle occurs but not very efficient (no control over SRT) |
|
|
|
Plug flow reactors are more or less efficient? |
More, (Higher S at fron end which means a faster substrate utilization rate). Also endogenous decay near reactor effluent yields good settling sludge |
|
|
|
What is plug flow with tapered aeration |
Apply tapered O2 more at the front less at the rear (more efficient use of O2 - more biological activity where S is greater) |
|
|
|
What is plug flow with step aeration |
Apply wastewater at different states in treatment to maintain a F:M |
|
|
|
What is Extended Aeration |
Activated sludge with a high hydraulic retention time (>1 day) High thetax means poorer settling of sludge |
|
|
|
Contact stabilization? |
ALlows smaller tankage
Less efficient, more prone to process upset Basically long HRT in stabilizign tank results in starved biomass. then its mixed with influent S and starved biomass ensures rapid utilization of S at high F:M |
|
|
|
Sequencing Batch Reactors? |
Operate in batch mode rather than continuous flow (reality, treat continuous flow using many SBR in parallel) |
|
