Introduction to WW Collection & Treatment Flashcards
- Collection system = sanitary sewer system = piping + pump stations + manholes that transport wastewater from sources (industries, homes, and businesses) to a wastewater treatment plant.
- Sewerage = collection + treatment facilities
- Sewage = spent water or wastewater
- Sewers = part of the collection system
Alpha
Pumping or Lift Station
- Pumping or Lift Station to lift the water to a higher elevation where gravity can take care of it
- Lift Stations can be used to lift sewage into treatment plant.
- After pumping, the plant is designed to operate under gravity flow to the point of discharge at the receiving stream.
Preliminary & Primary Treatment (Chap 3 & 4)
Preliminary & Primary Treatment (Chap 3 & 4)
Which type of pump can be used to lift sewage into treatment plant?
Preliminary & Primary Treatment (Chap 3 & 4)
A Screw Pump, or Archimedes Pump, can be used to lift sewage into treatment plant.
Where? In lift station, small plants
What? To move WW (i.e. solids, which can’t get stuck)
What are the types of preliminary treatment?
Preliminary & Primary Treatment (Chap 3 & 4)
1) Screening – the removal of objectionable items that may be troublesome in future treatment.
2) Grit Removal
3) Primary Clarifier
4) Equalization – the balancing of flow over time, resulting in consistency in quantity and quality.
5) pH adjustment – the chemical balancing of hydrogen ions to neutralize the wastewater for future treatment
1) SCREENING - Why is Screening useful?
Preliminary & Primary Treatment (Chap 3 & 4)
Screening reduces overall solids loading by reducing:
- Floatable solids
- Dissolved solids
- Settleable solids
Reducing solids reduces :
- Power requirements
- Equipment maintenance
- Pump, Pipes, Mixers, and Diffusers can clog
- Chemical enhancers
- Organic loading to biological treatment
1) SCREENING - What are the types of screens in preliminary treatment?
Preliminary & Primary Treatment (Chap 3 & 4)
1) Course Screens
- Bar screen mechanical
- Bar screen manual
2) Static Screen
3) Rotating Screen
- with external feed
- with internal feed
4) Disc filters
1) SCREENING - What are the characteristics of a mechanical bar screen?
Preliminary & Primary Treatment (Chap 3 & 4)
- Fixed vertical bars of steel mounted in an open channel
- Debris trapped by the submerged bars restrict the flow raising the liquid level upstream of the screen.
- Level sensing device triggers mechanical rake, which drops down and rakes in an upward motion cleaning the screen.
- Screenings are dropped into a container or receiving conveyor.
- Most screens are equipped with torque overload switches that will stop the unit before serious damage is caused.
1) SCREENING - What are the characteristics of a manual bar screen?
Preliminary & Primary Treatment (Chap 3 & 4)
Bar Screen: Manual
- Fixed vertical bars of steel mounted in an open channel
- Debris trapped by the submerged bars restrict the flow raising the liquid level upstream of the screen.
- No Level sensing device – operator must manual rake clean the screen.
- Screenings are rake up onto the floor where they dewater via a floor drain.
1) SCREENING - What are the characteristics of a static screen?
Preliminary & Primary Treatment (Chap 3 & 4)
Static Screen:
- No moving parts
- Low capital costs
- Pre-treat fibrous and non-grease bearing wastes
- Features stainless steel screen panel in a flat or curved form set into cabinet.
1) SCREENING - What are the characteristics of a rotating screen?
Preliminary & Primary Treatment (Chap 3 & 4)
- Slow rotating, horizontally mounted cylinder wrapped in a synthetic cloth.
- Wastewater is delivered via headbox. Solids larger than the clear openings in the cylinder are retained on the outside surface. As the drum rotates, these solids are carried out of the water up toward the other side of the drum where they are scraped off by a “doctor blade”.
- EXTERNAL FEED filters have wastewater applied to the outside of the filter with solids adhering to the outside while the filtered water passes through the drum.
- INTERNAL FEED filters have wastewater fed from inside the drum. Wastewater cascades by gravity and falls slowly onto the bottom of the cylinder. Solids are captured on the inside of the drum and are carried toward the discharge end
1) SCREENING - What are the characteristics of a disc filter?
Preliminary & Primary Treatment (Chap 3 & 4)
- Mesh (=maille) covered discs which rotate on a common shaft.
- Wastewater is introduced between the discs & rises to cover about 1/3 of the discs diameter.
Solids form a pre-coat of solids on the discs, which help filter out solid while the liquid drains through the disc. - Water sprays, mounted above the water level, are used to wash trapped solids of the mesh screening.
1) SCREENING - What is BLINDING of screens?
Preliminary & Primary Treatment (Chap 3 & 4)
- Blinding is when solids build up on the screen to a point where the openings on the screen are blocked and water can no longer pass through the screen.
- Screens should be checked at least once per shift for operation and solids separation.
What are comminutors or grinders?
Preliminary & Primary Treatment (Chap 3 & 4)
Comminutors, or grinders, are shredding (with teeth) and screening devices widely used in wastewater treatment plants and pumping stations.
Comminutors break down wastewater solids in plant headworks and pump stations.
Some plants do not have screenings, only comminutors that would only shred and send pieces downstream (risk of clogging pumps).
Some recent comminutors can run backward to unblock stuff.
2) GRIT - What is the purpose of grit chambers?
Preliminary & Primary Treatment (Chap 3 & 4)
Purpose: to remove inorganic material referred to as grit. Grit includes sand, eggshells, bone chips, coffee grounds, etc.
Grit chambers slowing down velocity, settling solids, MAX 1 FEET PER SECOND to let grease and sand settle down. Not treated yet, still raw water, which means bad odors
Grit is removed to prevent abrasion of pumps and to reduce deposits in pipe lines, channels, and digesters.
2) GRIT - What are the 2 types of Grit Chambers?
Preliminary & Primary Treatment (Chap 3 & 4)
1) Square Clarifier (detritus tank): designed so that the horizontal velocity is 1.0 feet per second (fps) at maximum flow. Chain and Flight grit collector at the bottom of the tank.
2) Aerated Tanks: It has became common practice to use aerated grit chambers.
Aeration also provides pretreatment of the waste by removing odors and inducing flocculation of the organic material making primary clarification more effective.
3) PRIMARY CLARIFIER - What is the purpose of primary clarifier?
Preliminary & Primary Treatment (Chap 3 & 4)
Purpose: to remove settleable organics and floating scum (grease and oils).
Primary clarifiers are either circular or rectangular. They are very similar to sedimentation basins used in water treatment.
Td (Detention Time): 90 – 150 min at average flow (Avg 2 hr)
4) FLOW EQUALIZATION - What is flow equalization and what are its advantages?
Industrial wastewaters vary greatly in QUANTITY (flow) and QUALITY, which affect downstream treatment processes.
Therefore, flow equalization by diverting the flow above average in tanks or blending all incoming flows in a holding tank.
Benefits: operating process at constant flow / loadings, reducing shock loads, and equalization of chemicals (less pH variability)
5) pH Adjustment
- Neutralization is important part of corrosion control.
The lower the pH, the greater rate of corrosion. - Solubility of heavy metals are effected by pH. Most metals are soluble at low pH and precipitate when pH is increased.
- Buffering Capacity The amount of acid or alkaline needed to change the pH.
5) pH Adjustment - What are pH ranges set by regulatory statute (= “Quality Criteria for Water”)?
pH ranges set by regulatory statute; “Quality Criteria for Water”:
Domestic water pH 5.0 to 9.0
Freshwater Aquatic pH 6.5 to 9.0
Marine Aquatic pH 6.5 to 9.5
5) pH Adjustment - Which chemicals are used to lower pH?
Higher pH levels can be lowered with acidic compounds, such as:
- Sulfuric acid (H2SO4) – cheapest and most readily available. Dark, oily
- Hydrochloric acid (HCl), also know as muriatic acid. Fumes
- Carbon dioxide (CO2)
- Sulfur dioxide (SO2)
5) pH Adjustment - Which chemicals are used to increase pH?
Lower pH levels can be raised with alkaline compounds, such as:
- Calcium oxide (CaO), also known as lime
- Slaking – mixing lime and water
- Hydrated lime (Ca(OH)2)
- Sodium hydroxide (NaOH), (25% or 50%)
- Ammonia (NH3)
- Magnesium oxide (MgO)
- Magnesium Hydroxide (Mg(OH)2)
- Sodium Carbonate (Na2CO3), also known as soda ash)
5) pH Adjustment - What type of pump most typically is used to pump chemicals?
= Diaphragm pump
5) pH Adjustment - What is the use of a titration curve and what does it involve?
Titration Curves:
- Used to measure changes in pH.
- Involves drop by drop addition of one solution (reagent / titrant) into another solution (wastewater) until an endpoint is reached.
5) pH Adjustment - What are the buffers to calibrate pH?
3 pH buffers (=solution en bouteille): 4, 7, and 10
to clean and calibrate pH sensors (=electrodes)
5) pH Adjustment - What is the unit of pH?
pH is measured in SU (Standards Units)
5) pH Adjustment - What is the optimum pH range for effluent = receiving stream?
There is optimum pH range for any given wastewater.
- Effluent (receiving stream) typically needs to be pH 6-9
5) pH Adjustment - What is ceriodaphnia?
Ceriodaphnia = Test with trouts, if they are ok and reproduce
5) pH Adjustment - What is ORP?
Oxidation-Reduction Potential (ORP) –
- ORP is the electrical potential to transfer electrons from one compound or element to another.
- ORP is a measurement that indicates the degree to which a substance is capable of oxidizing or reducing another substance.
- The higher the reading, the more oxidizing the substance is.
- Measured in millivolts (mv). Scale is +/- 1400 millivolt
What is the main objective of preliminary treatment?
Removal of waste water constituents (rags, sticks, floatable grits, and grease) to reduce maintenance or operational problems.
Removal of a portion of the suspended solids and organic matter from the WW
What are the units / components of Preliminary Treatment process?
1) - Screening = for removal of floating matter
- Grit Chamber = for removal of sand and grits
- Comminutors = grinder for grinding large suspended solids
- Primary Clarifier (can be considered as primary treatment, not preliminary)
2) Sedimentation (primary settling tank)
Coagulation (secondary setting tank)
Flocculation
What is Advanced Primary Treatment?
Enhanced removal of suspended solids and organic matter from the WW. Typically accomplished by chemical addition or filtration known as coagulation and flocculation.
What is the main objective of Secondary Treatment?
Removal of biodegradable organic matter (insoluble or suspension state) and suspended solids. Disinfection is also typically included in the definition of conventional secondary treatment.
There can be secondary treatment with nutrient removal
What are the units / components of Secondary Treatment process?
- Activated sludge process
- Oxidation ponds and lagoons
- Trickling filter
What is the main objective of Tertiary Treatment?
Removal of residual suspended solids (after secondary treatment) usually by granular medium filtration or micro screens.
What are the units / components of Tertiary Treatment process?
Membrane filtration and separation Dechlorination and disinfection systems Reverse Osmosis systems Ion exchange Activated carbon adsorption Physical / Chemical treatment
What are the functions of the different water treatment units? Screening Sedimentation Coagulation Chemical methods Filtration Disinfection Softening Aeration, chemicals use
Screening: floating matter
Sedimentation: suspended matter
Coagulation: suspended matter, as part of colloidal matter and bacteria
Chemical methods: Iron, Manganese, etc.
Filtration: remaining colloidal dissolved matter, bacteria
Disinfection: pathogenic bacteria, organic matter and reducing substances
Softening: hardness
Aeration, chemicals use: color, odor, taste
What is the main process of primary treatment?
SEDIMENTATION is primary treatment process. It is a PHYSICAL water treatment process used to settle out suspended solids in water under the influence of gravity.
What is the removal efficiency of primary treatment process?
30% for BOD (Biological Oxygen Demand)
60% for TSS (Total Suspended Solids)
What is the main process of secondary treatment?
BIOLOGICAL w/ activated sludge process. WW containing organic matter is aerated in an aeration basin in which micro-organisms metabolize the suspended and soluble organic matter
What are some examples of suspended film system vs fixed film system?
Suspended film system:
- activated sludge system
- lagoon system
- oxidation ditch
Fixed film system:
- Trickling filter
- RBC - Rotating Biological Contactor
What is the process for suspended film system vs fixed film system?
Suspended film system: stir and suspend microorganisms in WW, which absorb organic matter & nutrients from WW. Then, settle as sludge
Fixed film system: microorganisms are cultured on substrates such as rocks, sand or plastic. WW is spread over the substrate. Nutrients and organic matter are absorbed by micro-organisms as they grow in size.
What is a lagoon system?
In-ground earthen basin on which the WW is detained for a specific time and then discharged. Take advantage of natural aeration and microorganisms in the WW to remove sewage.
What is an oxidation ditch?
Modified form of “extended aeration” of activated sludge process. The ditch consist of a long continuous channel oval in shape with two surface rotors placed across the channel.
Oxidation ditch –> Clarifier –> Effluent
What does activated sludge refer to?
Activated Sludge:
Refers to a Biological treatment system
Use SUSPENDED GROWTH
Require Aeration tank, Aeration equipment, Settling tanks, Return/Waste sludge support equipment.
Wastewater is fed continuously
Microbes, “Bugs”, STABILIZE waste
Microorganisms are referred to as activated sludge
Microbes are separated out from the MIXED LIQUOR after settling in Secondary Clarifier and are returned back the aeration tank while the SUPERNATANT is sent on to further treatment.
Food is organic waste (BOD)
What is the definition of activated sludge?
ACTIVATED SLUDGE: floc or solid formed by microbes
What is the definition of FOOD to MICROORGANISMS RATIO (F:M)?
FOOD to MICROORGANISMS RATIO (F:M): control measure used to evaluate the amount of food available per pound of mixed liquor suspended solids (microbes)
What is the definition of MIXED LIQUOR?
MIXED LIQUOR: combination of return activated sludge and wastewater (primary effluent) that flows into the aeration tank.
