Introduction to WW Collection & Treatment

Question 1

• 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

Answer 1

Alpha

Question 2

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)

Answer 2

Preliminary & Primary Treatment (Chap 3 & 4)

Question 3

Which type of pump can be used to lift sewage into treatment plant?

Preliminary & Primary Treatment (Chap 3 & 4)

Answer 3

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)

Question 4

What are the types of preliminary treatment?

Preliminary & Primary Treatment (Chap 3 & 4)

Answer 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

Question 5

1) SCREENING - Why is Screening useful?

Preliminary & Primary Treatment (Chap 3 & 4)

Answer 5

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

Question 6

1) SCREENING - What are the types of screens in preliminary treatment?

Preliminary & Primary Treatment (Chap 3 & 4)

Answer 6

1) Course Screens
- Bar screen mechanical
- Bar screen manual
2) Static Screen
3) Rotating Screen
- with external feed
- with internal feed
4) Disc filters

Question 7

1) SCREENING - What are the characteristics of a mechanical bar screen?

Preliminary & Primary Treatment (Chap 3 & 4)

Answer 7

• 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.

Question 8

1) SCREENING - What are the characteristics of a manual bar screen?

Preliminary & Primary Treatment (Chap 3 & 4)

Answer 8

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.

Question 9

1) SCREENING - What are the characteristics of a static screen?

Preliminary & Primary Treatment (Chap 3 & 4)

Answer 9

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.

Question 10

1) SCREENING - What are the characteristics of a rotating screen?

Preliminary & Primary Treatment (Chap 3 & 4)

Answer 10

• 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

Question 11

1) SCREENING - What are the characteristics of a disc filter?

Preliminary & Primary Treatment (Chap 3 & 4)

Answer 11

• 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.

Question 12

1) SCREENING - What is BLINDING of screens?

Preliminary & Primary Treatment (Chap 3 & 4)

Answer 12

• 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.

Question 13

What are comminutors or grinders?

Preliminary & Primary Treatment (Chap 3 & 4)

Answer 13

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.

Question 14

2) GRIT - What is the purpose of grit chambers?

Preliminary & Primary Treatment (Chap 3 & 4)

Answer 14

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.

Question 15

2) GRIT - What are the 2 types of Grit Chambers?

Preliminary & Primary Treatment (Chap 3 & 4)

Answer 15

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.

Question 16

3) PRIMARY CLARIFIER - What is the purpose of primary clarifier?

Preliminary & Primary Treatment (Chap 3 & 4)

Answer 16

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)

Question 17

4) FLOW EQUALIZATION - What is flow equalization and what are its advantages?

Answer 17

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)

Question 18

5) pH Adjustment

Answer 18

• 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.

Question 19

5) pH Adjustment - What are pH ranges set by regulatory statute (= “Quality Criteria for Water”)?

Answer 19

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

Question 20

5) pH Adjustment - Which chemicals are used to lower pH?

Answer 20

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)

Question 21

5) pH Adjustment - Which chemicals are used to increase pH?

Answer 21

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)

Question 22

5) pH Adjustment - What type of pump most typically is used to pump chemicals?

Answer 22

= Diaphragm pump

Question 23

5) pH Adjustment - What is the use of a titration curve and what does it involve?

Answer 23

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.

Question 24

5) pH Adjustment - What are the buffers to calibrate pH?

Answer 24

3 pH buffers (=solution en bouteille): 4, 7, and 10

to clean and calibrate pH sensors (=electrodes)

Question 25

5) pH Adjustment - What is the unit of pH?

Answer 25

pH is measured in SU (Standards Units)

Question 26

5) pH Adjustment - What is the optimum pH range for effluent = receiving stream?

Answer 26

There is optimum pH range for any given wastewater. | - Effluent (receiving stream) typically needs to be pH 6-9

Question 27

5) pH Adjustment - What is ceriodaphnia?

Answer 27

Ceriodaphnia = Test with trouts, if they are ok and reproduce

Question 28

5) pH Adjustment - What is ORP?

Answer 28

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

Question 29

What is the main objective of preliminary treatment?

Answer 29

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

Question 30

What are the units / components of Preliminary Treatment process?

Answer 30

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

Question 31

What is Advanced Primary Treatment?

Answer 31

Enhanced removal of suspended solids and organic matter from the WW. Typically accomplished by chemical addition or filtration known as coagulation and flocculation.

Question 32

What is the main objective of Secondary Treatment?

Answer 32

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

Question 33

What are the units / components of Secondary Treatment process?

Answer 33

- Activated sludge process - Oxidation ponds and lagoons - Trickling filter

Question 34

What is the main objective of Tertiary Treatment?

Answer 34

Removal of residual suspended solids (after secondary treatment) usually by granular medium filtration or micro screens.

Question 35

What are the units / components of Tertiary Treatment process?

Answer 35

``` Membrane filtration and separation Dechlorination and disinfection systems Reverse Osmosis systems Ion exchange Activated carbon adsorption Physical / Chemical treatment ```

Question 36

``` What are the functions of the different water treatment units? Screening Sedimentation Coagulation Chemical methods Filtration Disinfection Softening Aeration, chemicals use ```

Answer 36

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

Question 37

What is the main process of primary treatment?

Answer 37

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.

Question 38

What is the removal efficiency of primary treatment process?

Answer 38

30% for BOD (Biological Oxygen Demand) | 60% for TSS (Total Suspended Solids)

Question 39

What is the main process of secondary treatment?

Answer 39

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

Question 40

What are some examples of suspended film system vs fixed film system?

Answer 40

Suspended film system: - activated sludge system - lagoon system - oxidation ditch Fixed film system: - Trickling filter - RBC - Rotating Biological Contactor

Question 41

What is the process for suspended film system vs fixed film system?

Answer 41

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.

Question 42

What is a lagoon system?

Answer 42

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.

Question 43

What is an oxidation ditch?

Answer 43

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

Question 44

What does activated sludge refer to?

Answer 44

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)

Question 45

What is the definition of activated sludge?

Answer 45

ACTIVATED SLUDGE: floc or solid formed by microbes

Question 46

What is the definition of FOOD to MICROORGANISMS RATIO (F:M)?

Answer 46

FOOD to MICROORGANISMS RATIO (F:M): control measure used to evaluate the amount of food available per pound of mixed liquor suspended solids (microbes)

Question 47

What is the definition of MIXED LIQUOR?

Answer 47

MIXED LIQUOR: combination of return activated sludge and wastewater (primary effluent) that flows into the aeration tank.

Question 48

What is the definition of MEAN CELL RESIDENCE TIME (MCRT)?

Answer 48

MEAN CELL RESIDENCE TIME (MCRT): average length of time a mixed liquor suspended solid particle remains in the activated process

Question 49

What is the definition of MIXED LIQUOR SUSPENDED SOLIDS (MLSS)?

Answer 49

MIXED LIQUOR SUSPENDED SOLIDS (MLSS): the suspended solids concentration in the mixed liquor. Common qualitative reference to the amount of microbes in the activated sludge process.

Question 50

What is the settleometer test?

Answer 50

Settleability is how quickly the sludge will settle at the bottom of the secondary clarifier. The test is performed in a cylindrical apparatus called a settleometer (cylindrical beaker).

Question 51

What is the definition of MIXED LIQUOR VOLATILE SUSPENDED SOLIDS (MLVSS)?

Answer 51

MIXED LIQUOR VOLATILE SUSPENDED SOLIDS (MLVSS): the organic concentration within the mixed liquor suspended solids.

Question 52

What is the definition of RETURN ACTIVATED SLUDGE (RAS)?

Answer 52

RETURN ACTIVATED SLUDGE (RAS): the solids returned from the secondary clarifier to the head of the aeration tank.

Question 53

What is the definition of SETTLEABILITY?

Answer 53

SETTLEABILITY: process control test used to evaluate the settling characteristics of the sludge.

Question 54

What is the definition of SLUDGE AGE?

Answer 54

SLUDGE AGE: process control measure that measures the length of time a particle of suspended solids has been undergoing aeration in the activated sludge process.

Question 55

What is the definition of SLUDGE VOLUME INDEX (SVI)?

Answer 55

SLUDGE VOLUME INDEX (SVI): process control test that evaluates the age/settling ability of the sludge. Requires Settled Sludge result and MLSS result.

Question 56

What is the definition of WASTE ACTIVATED SLUDGE (WAS)?

Answer 56

WASTE ACTIVATED SLUDGE (WAS): refers to the solids (microbes) being removed from the activated sludge process.

Question 57

What is the process with activated sludge in the aeration basin and clarifier-settler?

Answer 57

- Wastewater is mixed with return activated sludge (RAS). This mixture is known as Mixed Liquor. - The mixed liquor is aerated for a specified period of time (6-8 hours). The microbes feed on the available organic matter (primary feeders = bacteria; secondary feeders = protozoa) - The process produces stable solids and more microbes. The quantity of solids in the system increases (activated sludge). - Activated sludge is separated from the wastewater by clarification (in the clarifier-settler) - Settled activated sludge are then returned to the head of the aeration tank. - Excessive solids are removed from the system (WAS)

Question 58

What are the factors affecting activated sludge?

Answer 58

- Temperature: Increase in temp. results in increase in biological activity and decrease in oxygen content. Decrease in temperature results in decrease in biological activity and increase in oxygen content. Bugs are more active in Summer, and hence there is more WAS - Return Activated Sludge (RAS) Rates: Affects F:M ratios Controls microbe population - Nutrients (Nitrogen and Phosphorus) *Ratio of BOD:N:P is 100:5:1 - Dissolved Oxygen (D.O.) Oxygen is one factor that controls the types of microbes that are dominate in the system. Too little system goes septic (< 1.0 mg/L) Too much shear biomass (pin floc) and waste energy - Organic Loading (O.L.): Affects F:M ratios Measures the amount of food available for microbes Too much food overloads treatment system results in poor treatment Too little microbes will go dormant and/or die off - pH: pH variability affects microbes Optimal range is 6.5 – 8.5 Acceptable at 6.0 – 9.0 Outside this range and the microbes will be affected An issue with industrial treatment systems -- Waste Activated Sludge Rates (WAS): Controls F:M ratios Controls microbe population Helps rid system of unwanted microbes and material - Aeration: Major supply of D.O. Mixes microbes with food to allow suitable contact time for treatment - Wastewater Toxicity: Affects microbes

Question 59

What is the ratio of BOD:N:P? What does it stand for?

Answer 59

Ratio of BOD:N:P is 100:5:1

Question 60

Which microbes are in the activated sludge ?

Answer 60

``` Amoebas – indicative of younger sludge Flagellates Free-Swimming Ciliates - indicative of a good settling Stalked Ciliates Rotifers Nematodes – indicative of older sludge ```

Question 61

What are activated sludge controls?

Answer 61

Activated Sludge Controls are limited to the following: - Aeration (Air Supplied) - Return Activated Sludge Rate (RAS) - Waste Activated Sludge Rate (WAS) - F:M Ratio

Question 62

Aeration systems: What is the dual purpose of aeration in the activated sludge process? Name some aeration systems.

Answer 62

Aeration serves a dual purpose in the Activated Sludge Process - Supply of Dissolved Oxygen - Mixing the Mixed Liquor Aeration systems: - Mechanical (turbine aerator) - Diffused aeration system - most common. Air from blowers at the bottom of the tank

Question 63

What is the purpose of RAS (Return Activated Sludge)?

Answer 63

Purpose is to return microbes back to aeration tank. Makes it possible to keep microbes in the system longer. In theory, RAS should be constant and approximately 20 – 40% of the incoming flow. Changes in the flow of the RAS is dependent on the sludge characteristics.

Question 64

What are the 2 types of RAS controls?

Answer 64

1) Constant RAS flow allows MLSS to be at a peak both during low and high flows. Simplistic and minimizes labor. Controlling RAS flow rates independent of the influent flow rate. Pros: Simplicity, Maximum solids loading occurs at start of peak flow periods, Requires less operational time. Cons: The F/M ratio is constantly changing. 2) Percentage of flow RAS Control is completed by automatic controls valves and is frequently changing. Controlling the RAS as a constant percentage of the influent flow Pros: Reduced MLSS concentrations variations and F/M ratio variations, Con: Clarifier is subjct to maximum hydraulic loading when the reactor contains the maximum amount of sludge

Question 65

What can be used to determine the RAS?

Answer 65

Sludge Blanket Depth, Settleability and Sludge Volume Index can all be used to determine the RAS.

Question 66

What is the purpose of WAS (Waste Activated Sludge)?

Answer 66

Waste Activated Sludge (WAS): Purpose is to waste microbes to maintain a balance between microbes and incoming food. If balance swings in favor of one or the other operational conditions can be unfavorable. Balanced aeration tank leads to a “Steady State”. Steady State is reached by controlling Sludge Age, MCRT, Volatile Solids, and MLSS concentration Wasting is usually achieved by removing a portion of the RAS. Wasting is usually 1% - 20% of the total flow.

Question 67

What is Sludge Age?

Answer 67

Sludge Age: - Measure of the length of time a particle of suspended solids has been undergoing aeration. - Based upon the ratio of solids in aeration and the incoming solids - As a control technique the operator waste just enough sludge to maintain a sludge age that produces the best effluent quality. - Sludge age can range from 3 to 30 days. - Usually less than 15 days - Conventionally 3-10 days - Extended aeration - 15 to 30 days

Question 68

What is the F:M ratio?

Answer 68

F:M Ratio: - Ratio of Food to Microbes (Food/Mass or F/M) - Ensures that treatment is running efficiently - Conventional Activated Sludge F/M is 0.2 - 0.5 - Extended Aeration and Oxidation Ditch F/M is 0.01 - 0.07 - If the ratio becomes distorted leads to operational problems. - Four things to remember: Food concentration is estimate with BOD / COD The amount of food used in the calculation is vital. Quantity of microbes in the system is approximated by MLSS. Since two approximation are used, operator should not make daily changes based upon this calculation. Rolling 7 day average would be much more useful.

Question 69

What is Mean Cell Resident Time (MCRT)?

Answer 69

Mean Cell Resident Time (MCRT): - Expresses the average time that a microbe spends in the activated sludge process. - Indicator used to determine the dominate organism. - Directly influence NITRIFICATION - Nitrification is the process of ammonia and nitrogen be converted to nitrate. - Plant with an MCRT of 15-20 days usually will nitrify. - Plant with an MCRT of 5-10 may not. - MCRT is also temperature related. The higher the temperature the less MCRT is needed to nitrify.

Question 70

What is Nitrification?

Answer 70

- Nitrification is the process of ammonia and nitrogen be converted to nitrate. - Nitrification is the biological oxidation of ammonia or ammonium to nitrite followed by the oxidation of the nitrite to nitrate – NH4 to NO2 to NO3 - Plant with an MCRT of 15-20 days usually will nitrify. - Plant with an MCRT of 5-10 may not. - MCRT is also temperature related. The higher the temperature the less MCRT is needed to nitrify.

Question 71

What is denitrification?

Answer 71

Denitrification is a microbial facilitated process where nitrate is reduced and ultimately produces nitrogen gas (N2) NO3 to N2 Can happen in clarifiers when detention time is too long

Question 72

What are respiration rates used for? What do they mean?

Answer 72

- Laboratory test that gives insight to the health of the microbes and their activity. - Values of: <4 mg O2/hr/gm MLSS – indicates microbe population not stable and healthy, possible toxic load or low biological growth. 4 -9 mg O2/hr/gm MLSS – indicates microbes slow to stabilize organics, young microbes 10 - 20 mg O2/hr/gm MLSS – system is normal > 20 mg O2/hr/gm MLSS – indicates rapidly biodegradable material, high organic loads - Best way to use RR values is to measure them daily, prepare trend chart, establish best range for your treatment facility.

Question 73

Which are ranges of values for Sludge Volume Index?

Answer 73

Sludge Volume Index: Indicator of how well sludge is settling. < 100 – old sludge, turbidity of effluent due to pin floc 100 – 200 normal operation, good settling, low turbidity > 250 – bulking sludge, poor settling, high turbidity.

Question 74

Why must Dissolved Oxygen (D.O.) Concentrations be maintained?

Answer 74

Dissolved Oxygen (D.O.) concentrations: - Must be maintained so that there is oxygen available for the microbes to stabilize organics - Residual oxygen of >1.0 mg/L is good. - If D.O. levels are too high or to low operation problems can occur.

Question 75

Why control cyanides?

Answer 75

Cyanides Are toxic to bacteria. May cause serious upsets in Activated Sludge Process. May cause hazardous gases in the sewer. Extreme toxic gases can be formed when cyanides are introduced to an acidic waste stream.

Question 76

What Toxic Waste Loads look like / cause?

Answer 76

Toxic Waste Loads * Causes an increase in D.O. in aeration basin. - An increase in D.O. without an increase in air flow is a potentially toxic event. Clarifier effluent - Floc carry-over will become visible. - This is an indication of cell death. Every effort should be made to obtain a sample of the wastewater for analysis

Question 77

What High Organic Waste Loads (high BOD loading) look like / cause?

Answer 77

High Organic Waste Loads (high BOD loading) * Causes decrease in D.O. in Aeration Basin. - A decrease in D.O. without a decrease in air flow is a potentially high organic loading event. Another indication of high organic waste loading can be observed in the clarifier. - The effluent may become more turbid. - This would indicate that the waste was incompletely treated

Question 78

Is Sequencing Batch Reactor (SBR) a recent treatment development?

Answer 78

Biological treatment process SBR’s are not a recent development as commonly thought. Between 1914 and 1920, several full-scale fill-and draw systems were in operation. Interest in SBRs was revived in the late 1950s and early 1960s, with the development of new equipment and technology. Improvements in aeration devices and controls have allowed SBRs to successfully compete with conventional activated sludge systems.

Question 79

What are the 5 steps of a Sequencing Batch Reactor (SBR) cycle?

Answer 79

Toutes les etapes du traitement dans le meme contenant / reactor --> everything happening in the same tank For industrial and smaller plants (less than 9MGD) 5 steps (cycle time %): 1) FILL - add substrate - 25% 2) REACT - reaction (bugs + air) - 35% 3) SETTLE - clarity - 20% 4) DRAW - remove effluent - 15% 5) IDLE - waste sludge - 5% Timers must be set up right. Otherwise, you would send / discharge sewer. Usually, operators will check at some time (not there 24/7).

Question 80

What are some characteristics of a Sequencing Batch Reactor (SBR) - flow, depth, etc.?

Answer 80

Flow: SBR reactor volume should be equivalent to 1.2 to 2.0 times the average daily flow. Number or Reactors: Typically two or more Reactor Depth: 10 to 20 feet working water depth TWL or top water level plus 1.5 feet freeboard. Number of Cycles per day: Normally 2 to 6 per day

Question 81

What are the characteristics of a 60min mixed liquor settling test with a Sequencing Batch Reactor (SBR)?

Answer 81

60 minute Mixed Liquor settling test. - Take 1000 ml sample of aerated activated sludge - Record results every 5 minutes for first 30 minutes. - Record results every 10 minutes for remaining 30 minutes. - Observe and record any other changes in settling sludge.

Question 82

What are some advantages of Sequencing Batch Reactor (SBR)?

Answer 82

Advantages - Equalization, primary clarification , biological treatment, and secondary clarification can be achieved in a single reactor vessel. - Operating flexibility and control. - Minimal footprint. - Potential capital cost savings by eliminating clarifiers and other equipment.

Question 83

What are some disadvantages of Sequencing Batch Reactor (SBR)?

Answer 83

Disadvantages - A higher level of sophistication is required(compared to conventional systems), especially for larger systems, of timing units and controls. - Higher level of maintenance associated with more sophisticated controls, automated switches, and automated valves. - Potential of discharging floating or settled sludge during the DRAW or decant phase with some SBR configurations. - Potential plugging of aeration devices during selected operating cycles, depending on the aeration system used by the manufacturer. - Potential requirement for equalization after the SBR, depending on the downstream processes.

Question 84

How long for the BOD test?

Answer 84

Biochemical Oxygen Demand - B.O.D. The Quantity of Oxygen Used in the Biochemical Oxidation of Organic Material. 5 Day Test *20 Degrees C

Question 85

What are the ranges for key metrics (aerator detention time, F:M, CRT) for conventional activated sludge and extended aeration activated sludge?

Answer 85

Conventional Activated Sludge Aerator Detention Time: 4 - 8 Hrs. F:M : 0.25 - 0.45 CRT: 4 - 6 Days Extended Aeration Activated Sludge Aerator Detention Time: 16 - 24 Hrs. F:M: 0.05 - 0.15 CRT: 15 - 25 Days

Question 86

Some characteristics of Fixed Growth Systems

Answer 86

- Fixed growth instead of suspended growth (activated sludge is suspended) - The purpose of all biological treatment processes is to remove dissolved organics and finely divided organic material. BOD removal - Biological treatment (fixed or suspended) utilizes biomass to convert organic material into a more stable substance. - Biomass is a clump of organic material consisting of: - Living organisms feeding on wastewater - Dead organisms - Other debris - Successful operation of biological treatment systems depends on good equipment for settling and thickening the biomass. - Fixed Growth Systems the biomass (microorganisms) are attached to a stationary or moving media.

Question 87

What are some advantages of Fixed Growth Systems ?

Answer 87

``` Advantages: Simplicity in operation Can treat all portions of soluble BOD Low energy requirements Less land requirements Easy to design and install Less affected by shock loads and settleability problems (more affected by hydraulic surges) Less maintenance Less production of solids ```

Question 88

What are some disadvantages of Fixed Growth Systems ?

Answer 88

Disadvantages: Hydraulic surges Temperature sensitive Dependent on other treatment steps (grit removal & screening) Susceptible to “blind” or “interfere” with inefficient treatment.

Question 89

Trickling filters (with distributor arm, media, underdrain). What is the main process?

Answer 89

A fixed growth “filter” that contains media which is covered in bio-mass (micro-organisms). Wastewater (influent) is applied (trickled) at a controlled rate, causing contact between the waste and the bio-mass. “Filter” is somewhat misleading…does not separate out solids from liquid stream. Treatment occurs when biomass absorbs and use the dissolved organics as the wastewater cascades randomly through the voids in the media. Bio-mass is AEROBIC in nature, needs oxygen to grow and thrive. Oxygen is derived from air naturally circulating through the media.

Question 90

Fixed Growth - Trickling Filters | What are the components of a trickling filter?

Answer 90

From top to bottom: - Distribution System / Arm - Filter media - Underdrain system - Containment Structure - Auxiliary Equipment

Question 91

Fixed Growth - Trickling Filters | What are some characteristics of the FILTER MEDIA?

Answer 91

Supplies surface area on which the bio-mass may attach and grow. Encourages thin slime layer, which contains micro-organisms. Bio-mass breaks down organic material (BOD). Can be stone or synthetic material Material should be stacked to allow spaces for water and air to penetrate and small particles to pass through preventing plugging. Media should be uniform in size. Plastic media / synthetic media provides greater surface area for microbial growth – allowing for higher organic loading. Higher surface area comes from the ability to form plastic media. Plastic sheets are welded together in either a vertical or horizontal configuration (pg 41. Vol. II) “Plugging” is a major concern for filter media and must be protected against. Good primary settling is essential to prevent suspended solids overloading.

Question 92

Fixed Growth - Trickling Filters | What are some characteristics of the DISTRIBUTION SYSTEM?

Answer 92

System which applies the wastewater to the filter media. Typically two types: FIXED or ROTARY - Rotary type: Consists of a perforated distributor arm (two or four in number). Wastewater is pumped from a central well to the arms. Pressure from the wastewater exiting the perforated arm moves the distributor in a circular motion. - Fixed Nozzle: Series of stationary spray nozzles which feed the wastewater over the top of the filter media. Many disadvantages: difficult to main, short circuit, etc.

Question 93

Fixed Growth - Trickling Filters | What are some characteristics of the UNDERDRAIN SYSTEM?

Answer 93

Underdrain System: Consists of pre-cast concrete, fired ceramic, or plastic blocks laid over a filter floor. Supports filter media. Constructed in a manner that allows air to circulate and to collect the effluent that passes through the media (open channel). Access ports are built at the front and end of the open channel.

Question 94

Fixed Growth - Trickling Filters | What are some characteristics of the Containment Structure?

Answer 94

Containment Structure: Housing for the media. Usually made of concrete or steel Wall is usually built 4-5 feet higher than media to prevent splashing, spraying and staining. Standard rock filters have a depth of 8 feet of media High rate filters have media depths of 16-24 feet Occasionally ventilation ports are built into the base of the wall to allow for air circulation

Question 95

Fixed Growth - Trickling Filters | What are some characteristics of the Auxiliary Equipment?

Answer 95

Auxiliary Equipment: - Filter Pump Station – pumping station that pumps raw wastewater to the filter and recycles flow to the top of the media when needed. Recycle is the key to supply adequate flow to the filter at all times. - Secondary Clarifier – catches pass through solids and is the key to achieving high effluent quality. - Solids Processing Equipment – biological treatment converts soluble BOD into particulate biological solids. These solids have to be managed via solids processing to keep effluent clean.

Question 96

What is Sloughing?

Answer 96

Sloughing – periodic discharge of large quantities of slime growth (microbes) with the filter effluent

Question 97

Fixed Growth - Trickling Filters

Answer 97

Aeration Vital to keep biological biomass aerobic (w/oxygen) Spaces / voids between media must stay clear and free flowing (no restriction of oxygen) Dissolved oxygen (D.O.) should be between 3 - 6 mg/L for rock media and 4 – 8 mg/L for synthetic Blowers (forced air) can be used but normally oxygen is supplied by atmospheric transfer, therefore aeration is indirectly controlled by other operations. Optimal air movement will assure optimal pollutant removal.

Question 98

Fixed Growth - Trickling Filters | Process Controls - Aeration

Answer 98

Aeration Vital to keep biological biomass aerobic (w/oxygen) Spaces / voids between media must stay clear and free flowing (no restriction of oxygen) Dissolved oxygen (D.O.) should be between 3 - 6 mg/L for rock media and 4 – 8 mg/L for synthetic Blowers (forced air) can be used but normally oxygen is supplied by atmospheric transfer, therefore aeration is indirectly controlled by other operations. Optimal air movement will assure optimal pollutant removal.

Question 99

Fixed Growth - Trickling Filters | Process Controls - Recirculation

Answer 99

Recirculation Purpose is to increase contact time of BOD with microbes. This increase contact time increase treatment efficiency. Process in which filter effluent is recycled and brought back into contact with biomass more than once. Usually expressed as a ratio (ie: 1:1, 2:1) *If flow is 1 MGD, and ratio is 1:1, total flow through filter is 2 MGD Increase hydraulic loading; aids in sloughing & prevention of nuisance organisms.

Question 100

Fixed Growth - Trickling Filters | Process Controls - Distributor Speed

Answer 100

Distributor Speed Rate at which influent is applied to filter. Rate of 2-3 cycles per minute is normal. Can slow down to < 1 cycle per minute. Distributor speed can control organic and hydraulic loading to filter. Operator can distributor arm therefore control sloughing of solids / excessive buildup by hydraulic load. Prevents excessive buildup of biomass. Sloughing should be controllable, uniform and continuous.

Question 101

Fixed Growth - Trickling Filters | Process Controls - Clarification

Answer 101

Clarification Essential for efficient solids removal. Solids should be removed before GASIFICATION or DENITRIFICATION, both which cause gas production that will allow the solids to rise. Elevated solids pumped back to filter via recirculation will hamper operation.

Question 102

Fixed Growth - Trickling Filters | Process Controls - Temperature:

Answer 102

Temperature: Biomass is affected by climate and temperature. Cold temperatures decrease biological activity Warm temperatures increase biological activity HOT temperatures sterilizes biomass. Blower air can be warmed to heat filter. Recirculation water can be heated to warm filter. Can increase recirculation in winter time to warm up water to trickling filter

Question 103

Trickling Filters from an operational standpoint : Advantages and disadvantages

Answer 103

+++ - One of the most trouble-free types of treatment available - Requires very little operating attention and operational control changes compared to other biological treatments - Recovery quickly from organic overloads because filter acts like a sponge and treats great amounts of BOD in a short a period of time. - Steady hydraulic load is optimal and should be controlled by recirculation. - -- - Difficulties arise from hydraulic overloads - Ponding – result from loss of voids / spaces between the filter media. Can cause odor and filter efficiency - Odors - Filter Flies (Psychoda): nuisance insect that prefer wet/dry environments, lays larvae between and on media and on filter walls. Mostly found on intermediate filters. - Sloughing: the act of biomass falling off the media

Question 104

Trickling Filters | Ponding: causes & solutions

Answer 104

Ponding – result from loss of voids / spaces between the filter media. Causes: Excessive biomass growth Lack of primary clarification Media size too small or not uniform Poor or improper media quality (breaks up) Uncontrollable sloughing (toxic or shock load) Excessive insect or snail growth in media openings ``` Solutions: Increase hydraulic load / recirculation rate Adjust distributor arm to balance flow Replace media to one uniform size Spray filter with high pressure wash Hand turn media Dose filter with chlorine (5 mg/L) Flood filter, will cause sloughing Shut down filter, dry out media, than rake ```

Question 105

Trickling Filters | Odors: causes & solutions

Answer 105

Odors Causes: Results from lack of proper ventilation/air through filter (anaerobic) Stale influent Results from septicity (ponding) Solutions: Increase air flow, force air if needed Keep influent aerated and fresh Prevent ponding / septicity

Question 106

``` Trickling Filters Filter Flies (Psychoda): causes & solutions ```

Answer 106

Filter Flies (Psychoda): nuisance insect that prefer wet/dry environments, lays larvae between and on media and on filter walls. Mostly found on intermediate filters. Causes: Not enough hydraulic load Alternating wet/dry environment Partial clogged media voids Solutions: Increase recirculation rate / hydraulic loads Keep media orifices clear Use approved insecticides Flood filter (24 hours) Dose with chlorine (1 mg/L) Minimize natural sanctuaries (bushes/weeds) Adjust distributor arm so spray hits outside wall

Question 107

Trickling Filters | Sloughing: causes & solutions

Answer 107

Sloughing: the act of biomass falling off the media Causes: Organic overload Low recirculation rate Toxic/shock loads Solutions: Increase recirculation rate / hydraulic loads Slow down distributor arm

Question 108

Fixed Growth - RBCs (Rotating Biological Contactors) | What is it and how does it work?

Answer 108

Fixed growth biological treatment systems Consist of plastic discs (media) mounted on a long horizontal rotating shaft. Biomass grows on media Media than rotates into and out of the wastewater. When the media is exposed to the atmosphere oxygen transfer (transpiration) occurs, supplying the biomass with the needed oxygen to survive.

Question 109

Fixed Growth - RBCs (Rotating Biological Contactors) | What are RBCs Major Components?

Answer 109

- Tankage: structure for the RBC equipment (shaft/discs). Tank size is designed for 1 hour hydraulic contact time. - Baffles: weir structures providing separation between stages of RBC reactors. - Filter Media: Media is made from high density polyethylene (HPDE) Standard and High Density media available. Difference is in the spacing between the discs. High density spacing is closer and allows for more treatment (nitrification) Standard media – 90,000 to 100,000 sq. ft of media High Rate Media – 120,000 to 180,000 sq.ft of media Media discs circular in shape and approximately 12 feet in diameter - Shafts (axe central): are usually steel in nature and 25 ft long. - Covers: Made of fiberglass / molded plastic Protect biomass from freezing, biomass from rain and washing off of discs, etc. - Drive Mechanism: Used to rotate RBC

Question 110

Fixed Growth - RBCs (Rotating Biological Contactors) | What are RBCs Process Controls?

Answer 110

FLOW - Preliminary and primary treatment is necessary for solids removal - Slough solids must be captured via secondary clarifier - Recirculation is not practiced on RBCs unless weak influent or seeding is necessary - Flow is applied vertical or horizontal across the media INSPECTIONS / TESTING - Daily inspections of shafts, biomass and D.O. measurements on effluent leaving each stage Biomass Inspection: - Thin, brown color and evenly distributed - HEAVY, SHAGGY biomass represents organic overload - Overload = insufficient number of RBC on line or high industrial load - WHITE, GRAY SPLOTCHES indicate Beggiatoa or Thiothrix bacteria. Nuisance filamentous bacteria that reduce removal capability of RBC, cause poor settling in secondary clarifiers. They occur mostly in high sulfide concentrations and septicity wastes (low D.O.) - Reversing the rotation of the RBC helps slough off biomass when it becomes too heavy - D.O. Inspection: Low D.O. in the RBC indicates high organic loading. D.O. levels of 0.5 to 1.0 mg/L in first stage RBC and D.O. Levels of 2.0 to 3.0 mg/L in the last stage RBC Nitrification requires 4 to 5 mg/L in the last stage. Recirculation is not typical but can be very helpful in replenishing D.O., helping diminish nuisance bacteria

Question 111

Fixed Growth - RBCs (Rotating Biological Contactors) | What are most common operational concerns?

Answer 111

- Equipment Problems - Nuisance insects (snails) - Cold Weather - Biological - Excessive sloughing - Corrosion - Foam

Question 112

Fixed Growth - RBCs (Rotating Biological Contactors) | Details about operational problem: EQUIPMENT PROBLEMS

Answer 112

Equipment Problems RBC Shaft failures / drive bearing failures (attributed to poor maintenance) Trickling filters failed distributor arm, media collapse, bearing problems

Question 113

Fixed Growth - RBCs (Rotating Biological Contactors) | Details about operational problem: NUISANCE INSECTS

Answer 113

Nuisance insects Snails most common, inhabit fixed growth systems RBC grow on lightly loaded or nitrifying stages TF grow on horizontal or rock media Harmless but cause problems (equipment / ponding) Eliminate by applying chlorine (1-2 mg/L) and caustic bath Screen effluent and harvest

Question 114

Fixed Growth - RBCs (Rotating Biological Contactors) | Details about operational problem: BIOLOGICAL

Answer 114

Biological Changes in biomass of fixed growth great indicator Aerobic organisms require oxygen to breakdown organics and do most of the work on fixed growth HETEROTROPHIC organisms are singled cell bacteria which use carbon as an energy source, settle well and have a high BOD removal rate. AUTOTROPHIC organisms use inorganic chemical as an energy source. NITROSOMONAS and NITROBACTER breakdown and remove ammonia (nitrifiers) Wrong type of bacteria dominates treatment efficiency decreases Biological (cont) FILAMENTOUS are long hair-like bacteria that cause bulking sludge, which causes poor settleability and carry over of solids. IRON bacteria (filamentous) causes iron hydroxide (rust) to plate out on the the organism itself, increasing the weight of the organisms by 10-50 times, leads to excessive sloughing and shaft failure. Low D.O. can cause ANAEROBIC bacteria leading to odors. Low pH can cause fungus, filter flies, worms and NOCARDIA Toxic loads can strip biomass Lack of nutrient (P and N) can lead to nuisance organisms.

Question 115

Fixed Growth - RBCs (Rotating Biological Contactors) | Details about operational problem: EXCESSIVE SLOUGHING

Answer 115

Excessive Sloughing Biomass falling off media in abundance Causes PONDING, excessive solids in effluent Organic overloads, hydraulic overloads and toxic loads can cause excessive sloughing

Question 116

Fixed Growth - RBCs (Rotating Biological Contactors) | Details about operational problem: CORROSION

Answer 116

Corrosion Metal failure caused by Microbial Induced Corrosion (MIC) Biological activities by filamentous bacteria produce hydrochloric acid Acid accumulates at joints and welds and corrodes metal Covered filters do not release VOC and they become concentrated, condense on exposed surfaces causing corrosion Low pH, alkalinity, chemical additions, recycle streams and industrial wastewaters can cause corrosion.

Question 117

Fixed Growth - RBCs (Rotating Biological Contactors) | Details about operational problem: FOAM

Answer 117

Foam: WHITE FOAM indicates young biological activity..dissipates when biological activity increase and biomass age increases. DARK BROWN FOAM is caused by NOCARDIA, a filamentous organism, and occurs when biomass is too old. Traps air bubbles and solids, rises to the surface where it appears dark in color. Condition worsens with abundance of oil and grease Controls: sprays and control of biology

Question 118

Fixed Growth - RBCs (Rotating Biological Contactors) | Details about operational problem: COLD WEATHER

Answer 118

Cold Weather Biological activity slows down For every drop of 10 F BOD removal rate decreases 50% on fixed film. Cover units Reduce air around filter Windbreaks to protect from wind Adjust sprays for even distribution, warm influent