Introduction to Activated Sludge��Missouri Rural Water Fall Operations Symposium 2019��Kay Curtin, Curtin Consulting and Training LLC

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Or, Bug Farming 101

Introduction to Activated Sludge

• Principle, Structure and Function
• Operation and Maintenance
• Monitoring and Troubleshooting
• Safety and Calculations

Principle, Structure and Function

Principle of Activated Sludge

Principle of Activated Sludge

• The activated sludge is one of the secondary treatment processes that uses aerobic microorganisms in a suspended growth.
• The microorganisms are used to convert the dissolved and colloidal organics to gases and cell matter.
• The microorganisms form flocks that settle out along with fine suspended solids.

Principle of Activated Sludge

• Suspended Growth Systems
• Activated Sludge
• Attached Growth
• Rotating Biological Contactors
• Trickling Filters and bio towers
• Sand filters
• Ponds and Lagoons
• Also Suspended Growth

History of Activated Sludge

• Developed by Gilbert John Fowler at Manchester England in 1900’s�U.S. installations 1920’s
• In 1940 became widespread, CWA of 1970 increased use
• Most widely used process for wastewater

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Principle of Activated Sludge

• The activated sludge process is a wastewater treatment method in which the carbonaceous organic matter of wastewater provides an energy source for the production of new cells for a mixed population of microorganisms in an aquatic aerobic environment
• The microbes convert carbon into cell tissue and oxidized end products that include carbon dioxide and water
• In addition, a limited number of microorganisms may exist in activated sludge that obtain energy by oxidizing ammonia nitrogen to nitrate nitrogen in the process known as nitrification

Principle of Activated Sludge

Principle of Activated Sludge

• Bacteria constitute the majority of microorganisms present in activated sludge
• Bacteria that require organic compounds for their supply of carbon and energy (heterotrophic bacteria) predominate, whereas bacteria that use inorganic compounds for cell growth (autotrophic bacteria) occur in proportion to concentrations of carbon and nitrogen
• Both aerobic and anaerobic bacteria may exist in the activated sludge, but the preponderance of species are facultative, able to live in either the presence of or lack of dissolved oxygen.

Typical Activated Sludge Treatment System

Primary

Clarifier

(optional)

Waste Sludge

Aeration Basin

Secondary Clarifier

Return Sludge

Disinfection

Digester

Principle of Activated Sludge

• Aerobic Bacteria (heterotrophic)
• Fungi
• Protozoa
• Metazoa
• Nitrifying bacteria (autotrophic)
• Denitrifying bacteria (heterotrophic)

Principle of Activated Sludge

• Aerobic bacteria: uses oxygen to oxidize carbon (BOD)
• Anaerobic bacteria: Ferments carbon in the absence of oxygen yielding by-products like methane, organic acids, etc.
• Facultative bacteria: can oxidize carbon if oxygen is present, but can also go to fermentation if oxygen is not present

Principle of Activated Sludge

• Adsorption - waste adheres to the surface of the cell walls.
• Absorption - waste is taken in through the cell wall to be used for cell energy and growth.

Metabolic Waste

Products

Cell

Membrane

Bacterium

(Absorbed Organics)

Enzyme

Soluble Organics

Liquid Phase

Sorption of Degradable Organics

Principle of Activated Sludge

• Autotrophic bacteria in activated sludge reduce oxidized carbon compounds such as carbon dioxide for cell growth
• Nitrifying bacteria obtain their energy by oxidizing ammonia nitrogen to nitrate nitrogen in a two-stage conversion process known as nitrification
• Due to the fact that very little energy is derived from these oxidization reactions, and because energy is required to convert carbon dioxide to cellular carbon, nitrifying bacteria represent a small percentage of the total population of microorganisms in activated sludge
• In addition, autotrophic nitrifying bacteria have a slower rate of reproduction than heterotrophic, carbon-removing bacteria. Two genera of bacteria are responsible for the conversion of ammonia to nitrate in activated sludge, Nitrobacter and Nitrosomonas

Growth Rates

• Log growth phase
• growth only limited by time needed to reproduce
• Declining growth phase
• growth limited by environmental factors
• Endogenous phase
• growth suppressed- uses own resources

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Environment

• Food (Waste)
• Nutrients
• C:N:P:Fe 100: 5: 1: 0.5
• Oxygen, at least 1.0 mg/L
• Temperature
• Rate of growth doubles with about 10 degree C increase
• Constant population

Principle of Activated Sludge

Principle of Activated sludge

• Presence of protozoans are related to effluent quality and plant performance
• Protozoans play a secondary role in purification of aerobic wastewater
• Some protozoans can absorb soluble nutrients
• Mostly used in sludge age determination

Principle of Activated Sludge

• Protozoa

Principle of Activated Sludge

Principle of Activated Sludge

Principle of Activated Sludge

• Activated sludge is a process dealing with the treatment of sewage and industrial wastewaters
• Atmospheric air or pure oxygen is bubbled through primary treated sewage (or industrial wastewater) combined with organisms to develop a biological floc which reduces the organic content of the sewage
• The combination of raw sewage (or industrial wastewater) and biological mass is commonly known as Mixed Liquor
• MLSS can be expressed as mg/L or pounds under aeration (if the volume of the aeration basin is known
• In all activated sludge plants, once the sewage (or industrial wastewater) has received sufficient treatment, excess mixed liquor is discharged into settling tanks and the treated effluent is run off to undergo further treatment before discharge, usually disinfection or further filtration.

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Principle of Activated Sludge

• Part of the settled material, the sludge, is returned to the head of the aeration system to re-seed the new sewage (or industrial wastewater) entering the tank
• This fraction of the floc is called Return Activated Sludge (RAS)
• RAS is the suspended solids removed from the activated sludge and can be expressed in mg/L or pounds per day if the flow (gallons returned) is known
• Excess sludge which eventually accumulates beyond what is returned is called Waste Activated Sludge (WAS) and can be expressed as mg/L or pounds per day if the flow (gallons) is known

Principle of Activated Sludge

• WAS is removed from the treatment process to keep the ratio of biomass to food supplied (sewage or wastewater) in balance. This is called the F:M ratio. This is calculated as pounds of influent BOD divided by the pounds of MLSS in the basin (More on this later)
• WAS is stored away from the main treatment process in storage tanks and is further treated by digestion, either under anaerobic or aerobic conditions prior to disposal
• In all activated sludge plants, once the sewage (or industrial wastewater) has received sufficient treatment, excess mixed liquor is discharged into settling tanks and the treated supernatant is run off to undergo further treatment before discharge

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Principle of Activated Sludge

• Activated sludge plants are designed to allow enough detention time for all this to happen
• Purpose
• Sufficient contact time of microorganisms with waste and oxygen
• Start the formation of flocs
• Design
• Based on time microorganisms are in the basin (SRT) (MCRT)
• Food(Waste) in pounds to Microorganisms in pounds (F:M)
• Hydraulic detention time

Principle of Activated Sludge

• Mean Cell Retention Time (MCRT or CRT) is the average time that a bacterium will spend in the activated sludge process. The desired MCRT for conventional operations will fall between 4 and 15 days. Extended aeration is longer.

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• This is determined by dividing the total pounds of MLSS under aeration by the number of pounds of solids wasted per day

Principle of Activated Sludge

• Sludge Retention Time (Sludge Age) is calculated by dividing the mass of solids under aeration by wasted solids. Basically the same as MCRT and Sludge age.

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• Sludge Volume Index is the number of milliliters of sludge from a 30 minute settling test, times 1000 (to convert to liters) divided by the concentration of MLSS (in mg/L)
• Most of the time this shows settling trends

Principle of Activated Sludge

• It is easy to take care of BOD in the system. BOD is eaten by bacteria first.

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• Then, there needs to be further treatment of nitrogen compounds

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• We depend on uptake & nitrification/

denitrification

Principle of Activated Sludge

• Nitrification is conversion of ammonia, NH₃-N (from influent) to nitrate
• Denitrificaton converts NO₃-N to nitrogen gas, N₂
• Nitrification is ammonia removal and is aerobic
• Denitrification is nitrate removal and is anoxic
• Since nitrogen gas is stripped off, denitrification is total nitrogen removal

Principle of Activated Sludge

• Aeration
• Purpose - Mixing and supplying oxygen
• Design
• 1.1 pounds of oxygen per pound BOD (conventional)
• 1.8 pounds of oxygen per pound BOD (extended aeration)
• 4.6 pounds of oxygen per pound of ammonia
• 20 cubic feet per minute of air per 1000 cubic feet of basin

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Principle of Activated Sludge

Principle of Activated Sludge

• Blowers
• Positive Displacement
• Centrifugal
• Aerators
• Course bubble
• Fine bubble
• Surface aeration
• Piping and Valves
• reduce back pressure and adjust air flow in basin

Principle, Structure and Function

Structure and Function

Typical Activated Sludge Treatment System

Primary

Clarifier

(optional)

Waste Sludge

Aeration Basin

SecondaryClarifier

Return Sludge

Disinfection

Digester

Structure and Function

• Aeration Basins
• Oxidation Ditch
• Package Plant
• Sequencing Batch Reactor

Structure and Function

• Oxidation Ditches

Structure and Function

• Package Plants

Structure and Function

• Sequencing Batch Reactor

Conventional (Plug flow)

Aeration

Clarifier

RAS

WAS

Inflow

Effluent

Step feed

Aeration

Clarifier

RAS

WAS

Inflow

Structure and Function

• In contact stabilization, primary treatment is not required. The activated sludge is mixed with influent in the contact tank where the organics are absorbed by microorganisms. The MLSS is settled in the clarifier. The returned sludge is aerated in the reaeration basin to stabilize the organics.
• The process requires approximately 50% less tank volume and can be prefabricated as a package plant for flows of 0.05 to 1.0 MGD. On the downside, this system is more complicated to control because many common control calculations do not work.
• Not usually built any more, at least in WI

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Contact Stabilization

Contact

Clarifier

Re-aeration

Inflow

Effluent

WAS

Structure and Function

• In complete mix aeration the influent and the returned sludge are mixed and applied at several points along the length and width of the basin.
• The contents are mixed, and the mixed liquor suspended solids (MLSS) flows across the tank to the effluent channel.
• The oxygen demand and organic loading are uniform along the entire length of the basin.

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Complete mix (small basins)

RAS

WAS

Aeration

Clarifier

Inflow

Effluent

Structure and Function

Extended Aeration

• Can be a large conventional aeration tank
• Can be a oxidation ditch
• Extended aeration does not require primary treatment. It utilizes a large aeration basin where a high population of microorganisms is maintained.
• It has a channel in the shape of a race track, with rotors being used to supply oxygen and maintain circulation. Typically the process produces high-quality effluent and less volatile activated sludge

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Structure and Function

Structure and Function

• Aeration is biggest part of the process
• Several functions to aeration
• Aeration-provides oxygen to aerobic and facultative bacteria for oxidation of organic materials in wastewater
• Mixing-bubbles moving through water provides mixing which enables bacteria, oxygen, nutrients and organic matter to combine
• It is important that the operator has control, and uses control to operate the plant
• Many controls are available to operators to control different functions

Structure and Function

• Other controls:
• Return activated sludge-
• Returning activated sludge allows control of solids, bacteria and food (BOD) (More in the calculations section)
• Usually from 30 to 120 % of influent flow

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• Waste Activated Sludge-
• Used to maintain the biological level in the activated sludge system by ridding the system of extra sludge generated by the reproduction of bacteria

Structure and Function

• Wasting is controlled by either a constant MLSS in aeration, or:

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• A constant sludge age

Operation and Maintenance

Operation

Operation

• Advantages
• Small Space
• Excellent Effluent
• Allows Operator Control

• Disadvantages
• High Energy Use
• Upsets
• Requires Operator Control

• Activated sludge process consists of living organisms, it requires operator attention to ensure that there is a continuous suitable environment for the microorganisms

Operation

• Operators strive to maintain ideal conditions for bacterial growth
• pH range 6.8-7.4
• Temperature 60^oF
• No “shock” loadings
• DO 1-2 mg/L (usual is 1.5-2 mg/L)
• Good mixing
• No toxic loadings
• Proper nutrient balance

Operation

DO Control

• Controlling air header valves

Operation

DO Control

• Increasing or decreasing blower output
• Sheaving
• Changing size changes speed of blower
• Lower MLSS means

a higher DO

Operation

DO Control

• Adding more blowers

Operation

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DO Control

• In oxidation ditches, raise the water level for higher DO, and lower for lower DO.

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• Or, remove brushes or paddles from the rotor.

Operation

Operation

DO Control

• Clean blower inlet filters

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• Switch to Fine Bubble Diffusers for a much better Oxygen Transfer Efficiency

DO Control

• Cleaning diffusers

Operation

Operation

DO Control

• Cleaning diffusers
• Acid? Or other cleaners

Operation

DO Control

• Control plant side streams
• Side streams high in BOD, solids, nutrients or toxins will affect DO

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• The more efficient your process, the better the sidestream

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Operation

Normal characteristics of Activated Sludge:

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• Color should be brown golden brown
• Should have a musty odor
• Settling test should be about 30%
• Supernatant should be clear w/little or no floc
• Sludge age for conventional systems would be 6-10 days

Operation

Anaerobic Activated Sludge:

• Color will be dark brown to black
• Dark, greasy foam
• Will have a septic odor
• Settlability will be poor
• Caused by under-aeration, not moving sludge through the system fast enough, or high Sludge Volume Index (SVI) (sludge age)

Operation

Bulking Activated Sludge:

• Color will be from light brown to gray
• SVI will be <200
• Sludge settles slowly w/ clear supernatant
• Clarifier blanket will be unusually high
• Microscope shows a lot of filaments present

Conditions that favor filament growth

• Low DO
• F:M ratio too high or low
• Nutrient imbalances

Filamentous Bulking

Operation

Excessive solids may look like bulking

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• Both may have a high final clarifier sludge blanket and even loss of solids over the weir

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• Excessive solids can be confirmed if the sludge settles well, SVI is in the 90-150 range and little or no filaments are present under a microscope

30 Minute Settling Test

Operation

Rising Sludge

• Sludge looks normal in settle test but will rise if left longer than the 30 minute test
• Gas bubbles from denitrification will get caught in the sludge and make it lighter than water
• Happens quite often in winter when there is incomplete nitrification/denitrification due to the cold weather
• Can be confirmed by running the nitrogen series of tests (ammonia, nitrate, nitrite) or by running CBODs

Rising Sludge

Operation

Running cBODs??

• BODs are supposed to measure oxygen uptake through bacteria oxidizing organic material
• This also catches oxygen uptake from nitrification
• cBOD adds a chemical to the BOD test that inhibits nitrification, which then measures true “ carbonaceous BOD”
• Difference should be zero if nitrification/ denitrification is working properly

Operation

As long as we are talking about nitrification and denitrification….

• Optimal temperature for the process is 60^oF to 90^oF
• Growth rate of nitrifying bacteria increases as temperature increases and so on

How to prevent denitrification (nitrate to nitrogen gas, thus floating sludge)

• Reduce Sludge blanket in clarifier (waste)
• Reduce aeration to prevent nitrification (denite cannot happen w/o nitrification) IF you don’t have ammonia nitrogen limits in your permit

Operation

• Reduce sludge age to inhibit nitrification (waste)
• Maintain enough DO in the system to prevent anaerobic conditions in clarifier

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Operation

What does young sludge look like?

• Billowy white foam

Operation

What does young sludge look like?

• Billowy white foam
• Mixed liquor looks thin
• Poor settling
• Low DO
• Straggler floc in effluent (small pieces of floc in the supernatant part of a settle test)
• Sludge age > 4 days
• High F:M ratio (not enough bacteria present to use the food)

Operation

What does old sludge look like?

• Aeration basin has a leathery brown color with greasy looking bubbles

Operation

What does old sludge look like?

• Aeration basin has a leathery brown color with greasy looking bubbles
• Final clarifier settling would be rapid, but pin floc would be present in the straw colored effluent

Operation

What does old sludge look like?

• Aeration basin has a leathery brown color with greasy looking bubbles
• Final clarifier settling would be rapid, but pin floc would be present in the straw colored effluent
• Sludge age is < 12 days
• F:M is low (Not enough food for the bacteria present)
• Endogenous respiration at this point (like a digester)

Operation

How are solids made?

• Bacteria grow by division with the proper environment
• If one does not waste, there will eventually be more bacteria than food
• At this point bacteria start dying
• After enough bacteria die, leftover cellular matter accumulates
• These solids takes up space, blocking remaining bacteria from contact with oxygen, food, etc.

Operation

• For every pound of BOD removed a portion of that pound remains in the system as bacteria
• High rate AS produces 0.75lbs of solids per pound of BOD removed
• Conventional AS produces 0.55lbs of solids per pound of BOD removed
• Extended aeration produces 0.15lbs of solids per pound of BOD removed

Operation

So how do we maintain proper solids concentration?

• Young sludge: stop or slow down wasting and increasing return sludge rates
• This increases sludge concentration under aeration
• Decrease F:M ratio
• Increase sludge age
• Old sludge: Increase wasting and decrease return sludge
• This reduces sludge under aeration
• Increase F:M ratio
• Reduces sludge age

Operation

Why increase waste sludge and decrease return sludge?

• Decreasing return means less sludge is pumped from the clarifier to the head of the plant
• This allows the solids to settle and get thicker
• When this sludge is wasted out it is thicker and removes more solids than thinner sludge
• More solids can be removed with less energy

less storage, less acreage, less gasoline etc.

Operation

• Why increase return and decrease wasting?
• Same reason, decrease in sludge wasting allows the sludge to get thicker and more solids are returned per gallon

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• Most newer activated sludge plants can return up to 100% of flow, but…

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• MUST MONITOR F:M FOR PROPER TREATMENT

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Operation

• Wasting sludge keeps the plant working at a level that uses almost all the BOD coming into the plant, the trick is determining how much sludge to waste
• What should we consider when figuring this out?
• Process design
• Mode of treatment
• Influent flow & loadings
• Concentration of solids in return sludge
• Settlability of sludge in final clarifier

Operation

• First determine how you measure the sludge being moved:
• Gallons per day
• Pounds of solids
• Time?
• Some plants just let pumps pump for a period of time and usually do not have a means of measuring exact amounts of sludge
• This form of wasting is called “By guess by golly”

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Operation

• We will go through wasting rate and F:M calculations a bit later

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• F:M is not a good tool for wasting – it uses the BOD test in the calculation

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• Constant SRT or Constant MLSS????

Operation

Basic design concepts:

F:M-the normal range of F:M is 0.2 to 0.4, but it could run from 0.1-0.5

• Wasting rate must be increased if F:M ratio is low (less than 0.2), and must be decreased if its too high (over 0.4)

Sludge age-normal range is 6 to 10 days (could be as low as 3 days)

• Increase or decrease waste rate to arrive at the desired sludge age

Operation

Constant MLSS-normal range is 1800 mg/L to 2500 mg/L (could run from 1000 mg/L to 3000 mg/L)

• Increase or decrease waste rate to get to the MLSS concentration desired in the system
• This is OK, but does not take into account fluctuation in loadings
• Must anticipate nitrification/denitrification needs in winter-you must be able to have solids to waste to “jumpstart” the process in winter
• Carry slightly higher solids concentration going into winter

Operation

• Hydraulic loading
• There are times when the plant can be hydraulically over-loaded (flood, sudden snow melt, hard rain, extreme I&I)
• Usually the final clarifier (source of the solids be returned/wasted) can exceed it’s flow
• Floc has a density close to water so it can go over the weirs and be lost to the process
• In this case you will lose treatment for a time
• Stop wasting and build up new solids

Operation

• Older plants are experiencing overloading with changes to population

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• I&I changes through the years

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• Cities need to FIX THEIR COLLECTION SYSTEMS FIRST

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• Addition of excessive returns can overload the clarifier

Operation

• The number of microorganisms present in the treatment plant is estimated by measuring the mixed liquor suspended solids.
• MLSS consists of both organic and inorganic materials. Muni waste is about 70% organic.
• Since organic material can burn, the mixed liquor volatile suspended solids are the ideal measure of the microorganisms in the process.
• If you do not use the MLVSS you can still get pretty close by estimating 70% volatile. If you were to burn the MLSS sample in a muffle furnace, you will have a MLVSS.)

Operation

How to calculate MLSS

• A well-mixed sample is filtered through a weighed standard glass-fiber filter and the residue retained on the filter is dried to a constant weight at 103 to 105°C
• The increase in weight of the filter represents the total suspended solids

(A-B) X 1000                

• MLSS mg/L= sample volume, mL
• An important component to monitor daily

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Operation

Now let’s talk F:M ratios

• First let’s define F:M. F:M is the measure of the FOOD PROVIDED each day to the MICROOGANISM mass in your process. F:M is usually thought of as an activated sludge thing, but it can be applied to all processes in some way. The food in this case is the waste (BOD) coming into the plant (Influent). Oxygen demand gives us the idea of how much food is available for the microorganisms to eat. This is measured by the oxygen depletion over a five day period. This gives us an answer in mg/L or ppm of food availability.

Operation

Now lets do some calculations

• Influent BOD (or COD) mg/L x Flow (MGD) x 8.34 lbs/gal

MLSS (or MLVSS) mg/L x Volume of tank (MG) x8.34lbs/gal

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8.34 cancels out

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• BOD mg/L x MGD

MLSS mg/L x Volume

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Operation

• Example: your flow is 500,000 gallons a day, the influent BOD result from your test is 200 mg/L. Your MLSS is 1500 mg/L and your aeration basin holds 200,000 gallons.

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Here is the calculation:

• 200 mg/L x 0.5 MGD = 100 = 0.333

1500 mg/L x 0.2 MG 300

Operation

• If you increase your MLSS to 2500 mg/L:
• 200 x 0.5 = 100 = 0.2

2500 x 0.2 500

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• If you decrease your MLSS to 500 mg/L:
• 200 x 0.5 = 100 = 1.0

500 x 0.2 100

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Operation

• Look at this number. What does it mean? What this number means is the pounds of food to pounds of microorganisms. So in example 1 there is 0.333 pounds of food to 1 pound of bugs.
• The ratio is a base for which we can judge what is going on in the plant.
• If the ratio changes, something is happening. Several symptoms show up at different ratios.

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Operation

• Usually anything over 1.0 is high, 1.0 to 0.5 is medium and anything less than 0.5 is low.
• What is a high ratio and what is a low ratio. It really doesn’t make a difference; the ratio that works best in your plant is what you want.
• As a rule, high F:M shows a young sludge age. Low F:M shows an increased sludge age.
• Low F:M ratios usually bring on foams, bulking and other problems. High F:M usually doesn’t allow the maximum treatment in the plant.

Operation

• Don’t be afraid to waste!!
• Poop will keep coming into the plant giving you an everlasting supply of poop bacteria

Operation and Maintenance

Maintenance

Maintenance

Common maintenance for blowers & diffusers:

• Centrifugal blowers
• Lubrication Check pressures (Intake and Discharge)
• Clean filters
• Check Drive belts and couplings
• Positive Displacement blowers
• Lubrication
• Check inlet suction & discharge pressure
• Check belts and couplings
• Check pressure relief valve
• Check motor amperage
• Clean air filters

Maintenance

Note about PD blowers in winter

• If the filters are blocked with snow or ice, a negative pressure on the suction side could cause damage to the filters, compressor or drive motor

Maintenance

• Diffusers
• Check surface aeration patterns
• Check airline pressure reading
• Check for unequal aeration patterns
• Clean or replace as necessary
• Blower maintenance records
• Pressure checks
• Vacuum checks
• Amperage draw
• Dates of routine maintenance, belt condition, alignment, lubrication, vibration, bearing temperatures, etc.

Maintenance

Common maintenance for oxidation ditch paddles

• Bearings (lubrication)
• Belts or chain drive
• Shaft lubrication
• Drive motor operations

Maintenance

When work has to be done on aeration basins watch for several things:

• If groundwater is high the basin could float
• If you are working on a package plant make sure that the metal walls can hold the pressure of the water

Maintenance

Clarifier maintenance

• Check gear oil and drive system-belt, chain and gears
• Check rubber parts-scum collection parts
• Check tank condition-cracks, pressure relief valve, etc.
• Inspect weirs-for level and condition of metal-with and without flow
• Use a transit to check level of weirs
• Weirs should be:

Level, Free of algae or debris plugs

Maintenance

Watch sludge blanket depth with:

• Sludge judge
• Photoelectric cell
• Air lift tubes

Monitoring and Troubleshooting

Monitoring

Monitoring

What you should see in:

• Young sludge-
• Free swimming ciliates
• Grazing ciliates
• Light fluffy floc
• Organisms will generally be smaller and have relatively greater motion
• 8-10 day old sludge-
• Floc well developed
• More brown than golden colored
• Single stalked ciliates to several headed
• May see an occasional rotifer

Monitoring

• Old sludge-
• Floc will be granular and dark
• Rotifers and nematodes will be very common

Monitoring

• Some basic equipment for monitoring
• DO meter: used to monitor DO levels throughout the plant
• 1000 ml beaker or settleometer: used for 30 minute settling test
• Sludge blanket finder: sludge judge used to measure where and how high the sludge is in the system
• Microscope

Monitoring

Use your eyes

• Bulking sludge has a clear supernatant over a light brown, gray or white sludge
• Sludge blanket will be near the surface
• Too many solids in the system
• High clarifier blankets
• Often with solids going over the weirs
• Nocardial foam
• Thick, scummy light colored foam on basins and possibly on clarifier
• Confirm with microscope

Monitoring

Monitoring

• Return rates too low
• Sludge blanket build-up in the final clarifiers
• Thin mixed liquor
• Return rates too high
• No sludge blanket in the final clarifiers
• Thin RAS

Monitoring

Monitoring

Where would you sample for MLSS?

Aeration basin representative sample from several locations

Monitoring

Where would you sample for Sludge Settlability Test?

Aeration overflow to the clarifier

Monitoring

Where would you sample Dissolved Oxygen?

Anywhere you need to

Monitoring

Where do you sample for WAS concentration?

From waste pump or wasting system

Monitoring

Where do you sample for RAS settlability?

RAS return line

Monitoring

One of the easiest and most used daily monitoring test is settlability

• Procedure:
• Use a settlometer, 1000ml graduated cylinder or any container that will hold 1000mls and has measurements on the side
• Fill to 1000 mls with well mixed sample taken from the aeration basin
• Allow to settle
• Note where sludge settles in 30 minutes, or at measured intervals

Monitoring

• Dilution of mixed liquor sample in settling test/What does it show?
• Excessive solids concentration, or under utilized young sludge
• A large concentration of filamentous organisms
• If the mixed liquor sample is diluted 50% with tap water, and the resulting settling test indicates the same settling rate and settles to about the same volume in 30 minutes, the cause of the poor settling is filamentous organisms. If the diluted sludge is not related to filamentous organisms. Consideration must be given to wasting more sludge to reduce an excessive sludge inventory

Monitoring and Troubleshooting

Troubleshooting

Foaming & Bulking in Wastewater Treatment

Biological

• Foaming/Bulking is caused primarily by filamentous organisms that are overgrowing.

Foaming & Bulking

• Five Major Steps to Control Foaming/Bulking
• Bulking
• Foaming
• Causes
• Diagnosing
• O&M

Description of Bulking

• Bulking is an overgrowth of the bacterial macrostructure (called “bridging”) to the point where there is interference with compaction and settling

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• Floc formation depends on a “macrostructure” of filaments to which other bacteria may attach and settle

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Bulking Problem

Foaming Problems

Foaming Problems

Foaming/Bulking Causes

• Foaming generally is a symptom of a plant that is not running at peak efficiency. Something is off, either seasonally or in plant operation.
• Some foaming and bulking can be caused directly by “excessive” operation.
• Too much or too little oxygen for example.

Foaming/Bulking Causes

• FOG (Fats Oils Grease)

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Foaming/Bulking Causes

• FOG adds a nutrient that is slow to biodegrade (bacteria cannot eat it fast enough).
• FOG inhibits aeration (thick covering of grease doesn’t let air into the water).
• FOG is a nutrient that certain filamentous organisms prefer.

Foaming/Bulking Causes

• Wasting and Returning rates are out of balance (WAS/RAS).
• Leads to F:M imbalances that favors problem organisms.
• You must know what is the best F:M for your system
• Seat of your pants plus some calculations

Sphaerotilus-false branching

F:M Is What Its All About

• Plant Flow (MGD)
• Influent BOD (mg/l)
• Aeration Basin Volume (MG)
• MLSS or MLVSS (mg/l)
• WAS Flow (MGD)
• Aeration Basin D.O. (mg/l)
• 30minute Settleable Solids

• Sludge Age
• SVI
• F:M

Controlling F:M

RAS

“Leftover” food

Some Bacteria

WAS

Leaves the system

Controlling F:M�

• Activated Sludge
• Decrease F:M
• Slow Wasting (gives the sludge some “concentration)
• Increase RAS
• Increase F:M
• Increase WAS (less “concentrated sludge)
• Decrease RAS

Why F:M As a Monitor?

• The ratio is a base for which we can judge what is going on in the plant.
• If the ratio changes, something is happening. Several symptoms show up at different ratios.
• Usually anything over 1.0 is high, 1.0 to 0.5 is medium and anything less than 0.5 is low.
• What is a high ratio and what is a low ratio. It really doesn’t make a difference; the ratio that works best in your plant is what you want.
• As a rule, high F:M shows a young sludge age. Low F:M shows an increased sludge age.
• Low F:M ratios usually bring on foams, bulking and other problems. High F:M usually doesn’t allow the maximum treatment in the plant.

Controlling Sludge Age

• Wasting old sludge
• Increase waste rates
• Return activated sludge
• Slow return to rid more sludge
• Increase return to add more nutrients to mixed liquor

In the End

• If the plant is working correctly, you will not experience foaming/bulking, even though these organisms are ever-present.
• The use of wasting, returning and monitoring will lead you to control your plant.
• Keeping everything clean (FOG) helps incredibly.

In the End

• Use ordinances to control FOG.
• Know what F:M ratio is best for your plant.
• Make sure there is enough DO
• Watch your sludge in the clarifier, if it starts to rise slow down wasting.
• (This may be different in cold weather)
• Always know that the foam or bulking is an esthetic issue, watch for your permitted results!

Nitrification/Denitrification Connection

• In winter we tend to see a lot of final clarifiers that have floating sludge or smaller clumps of floating solids called “pin floc”.
• Remember three things; In winter the bacteria that deal with nitrogen do not like to work very well. They are most susceptible to temperature and toxicity. When this happens we usually see ammonia bubbles form and mix in with the sludge, thus floating the sludge in large clumps or in pin floc.

Nitrification/Denitrification Connection

• To diagnose this, look at a sample of the floating sludge under a microscope on a wet mount and you will see tiny bubbles.
• Nitrogen management at your plant will have to be determined. If there is a system to handle nitrogen at your plant it will have to be tweaked to run correctly.
• Second, if the sludge in your clarifier goes septic you will also see floating sludge. To diagnose this measure the dissolved oxygen in the bottom of your clarifier.
• How do you treat septic sludge?

Nitrification/Denitrification Connection

• Lastly, there may be filamentous bacteria bulking in the clarifier. Once again some microscope work helps to diagnose this.
• To really check this out, check your SVI. If it is less than 100 then filament are not the cause, if it is over 100, this indicates that filaments could be a problem.

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Nitrification/Denitrification Connection

• Next to last, carrying the correct F:M ratios will help the plant run correctly
• When the plant runs correctly you will not experience floating sludges
• Check your F:M ratios, most are WAY TOO LOW
• How do you correct??
• WASTE

Nitrification/Denitrification Connection

• BOD:TKN ratio can measure nitrification efficiency
• 2.5 or less should show good nitrification
• MCRT of 10 days or more ensures complete nitrification
• Lower temps may increase detention time required
• Generally, a F:M of <0.3 allows for nitrification

Nitrification/Denitrification Connection

• If BODs are climbing, /sludge is floating, Perform a CBOD and TKN
• BOD and TSS should be close to the same number
• IF BOD is very high and the CBOD is close to TSS (much lower than the BOD), you are experiencing partial nitrification
• Go over your numbers and waste

Nitrification/Denitrification Connection

• Finally, Really watch your hydraulic loading
• A lot of plants are over loading…hydraulically…especially older plants
• Don’t mistake hydraulic overloading with BOD underloading

Troubleshooting

• How does an organic overload affect a plant?
• Microorganisms are sensitive to changes in food source
• Too much food (organics) means not enough bacteria to use the food
• This means the bacterial action is still going on in the clarifier
• F:M ratio increases immediately
• DO drops

Troubleshooting

• To fix we would:
• Increase return rate
• Decrease or stop wasting
• Increase air to system
• All these steps keeps the solids (bacteria) in the system and increases the bacteria’s chances of using the organics

Troubleshooting

• How does a toxic load affect a plant?
• Bacteria are sensitive to toxins, so a highly toxic load will reduce the number of bacteria that can use the organics in the water or even kill the plant
• When bacteria die they stop respiring, so DO goes up
• You may get white foam, as the plant is starting back up
• If one knows in advance that a toxic is coming, it can be bypassed until the flow is past the plant

Troubleshooting

• If the toxin gets into the plant:
• Increase aeration
• Waste sludge out of the process
• Start looking for new bugs to seed the plant
• NEVER BRING BACK SOLIDS FROM THE DIGESTER
• The plant will come back in a few weeks
• Notify DNR of problems
• Find the source, hopefully not owned by the mayor
• Have good ordinances and use them

Troubleshooting

• Other Affects:
• Return from the thickener that is high in solids:
• This increases the amount of solids return which reduces the F:M ratio
• Could cause “old” sludge to form quickly
• Fix by additional wasting

Troubleshooting

• Other Affects:
• Decanting of an overloaded aerobic digester
• Same as above
• Fix is to haul sludge out of the plant

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• Anaerobic digester supernatant high in solids and BOD
• Increases growth of organisms
• Increases DO requirements
• Fix by increasing DO and Hauling sludge

Troubleshooting

Other Affects:

• Poorly operating mechanical sludge dewatering equipment
• Could return high solids
• Could return high BOD
• Fix by increasing DO and waste out solids

Troubleshooting

Low dissolved oxygen causes and cures:

• Not enough air supplied
• Fix by opening inlet valve, increasing speed of the blower or turning on another blower
• Consider fine bubble diffusers
• Excessive loading
• Reduce the loading to the system by flow equalization or by placing more aeration basins in service

Troubleshooting

• Poor air distribution
• Clean diffusers to ensure good oxygen transfer and mixing
• Consider auxiliary mixers
• What about ditches with solids build-up?
• Lower the depth to better mix the basin
• Younger sludge will not settle as quickly

Troubleshooting

• Physical and visual indicators:
• Foam:
• Light/Billowy foam indicates too young of a sludge age OR a surfactant discharge
• Dark thick foam indicates too old of a sludge
• Foaming can be attributes to industrial/chemical discharges and/or filamentous organisms
• Color:
• Chocolate-brown color indicates a healthy aerobic system
• Dark or black sludge indicates low DO

Troubleshooting

• Physical and visual indicators:
• Color:
• Unusual colors are usually attributable to discharges of dyes or other industrial products
• Odor:
• Healthy aerobic systems should have a slightly musty odor
• A rotten egg smell indicates a septic condition due to low DO

Troubleshooting

• Physical and visual indicators:
• Turbulence:
• A completely mixed aeration basin should have uniform turbulence patterns throughout the basin
• Non-uniform turbulence may indicate plugged air diffusers, malfunctioning mixing equipment or poor air distribution

Safety

Safety

• Chemicals are a fact of life in wastewater treatment – save your SDS sheets.
• What are the safety considerations for chemical usage and storage at a WWTP?
• What is considered a Hazardous Spill in Missouri?
• What is considered a Treatment Plant Overflow or a Sewer System Overflow in Missouri?

Safety

• Aeration basins can be dangerous
• Besides drowning, aerated water is less dense than water, so it is harder to float
• Life vest or ring doesn’t really help
• Aerated water also has the potential to make bacteria and other small organisms airborne, which makes it a disease hazard
• Empty tanks are confined spaces and must be entered with proper training and equipment
• Also a fall hazard

Safety

• And speaking of fall hazards….

Safety

• Remember, empty tanks are often a Confined Space

Safety

• Gas builds up in pipes and can rip them apart.
• Clean lines with water when shutting down if possible

Calculations

Calculations

• Volume of tanks
• Rectangle or square=Length x Width x Height

Given length=30 feet

width=12 feet

Depth=10 feet

So volume=length x width x height

=30 x 12 x 10

=3600 cubic feet (ft³)

1 ft³=7.5 gallons or 7.48 if you’re an engineer

Volume = 3600 x 7.5 = 27,000 gallons

Calculations

Calculate Volume of tanks

• Area Round=3.14 x radius x radius x depth

Given tank diameter = 30 feet

tank depth = 12 feet

So volume=3.14 x radius x radius x depth

=3.14 x 15 x15 x 12

=8480 square feet (ft2)

1 ft3 7.5 gallons

Volume = 8480 x 7.5 = 63,600 gallons

Calculations

Calculate percent BOD removal or efficiency

• Works for any component % removal

% BOD removal=Conc (in)-Conc (out) X 100

Conc (in)

Given: Raw BOD=200 mg/L

Final Eff BOD=15 mg/L

200-15 X 100 = 92.5%

200

Calculations

Calculate loadings in pounds per day

• Loadings (pounds/Day)=

Conc (mg/L) x Flow (MGD) x 8.34

Given: Conc Influent BOD=150 mg/L

Flow=1 MGD

Loadings (pounds/day)=150 x 1 x 8.34

=1250 pounds per day

Calculations

• Sometimes aeration basin loading is expressed as pounds of BOD per 1000 cubic feet of tank volume
• Loading=Pounds of BOD/Day

Tank Volume (ft³)/1000

Given: Pounds/Day of BOD=1250 pounds/Day

Tank Volume=30,000 ft³

=1250 = 42 pounds/1000 ft³/Day

30

Calculations

Calculate SVI

• SVI=Mixed Liquor 30 minute settle volume (ml) x 1000

Mixed liquor concentration mg/L

Given: 30 minute settle test=300 ml

Mixed liquor concentration=2400 mg/L

SVI=300 x 1000 = 125

2400

Calculations

• Calculate detention time V/F
• 1^st calculate volume
• 2^nd calculate flow/hour
• 3^rd calculate detention time

Given Tank length=50 feet

Tank width=12 feet

Tank depth=10 feet

Flow rate =180,000 GPD

1 ft3 = 7.5 gallons

Calculations

1^st Volume:50 x 12 x 10 x 7.5=45,000 gallons

2^nd Flow/Hour=GPD=180,000=7500 GPH

24 24 hr/day

3^rd detention time=Volume

Flow rate

=45,000 = 6 hours of detention time

7500

Calculations

• Calculate sludge age

Given: Volume of Aeration Basin=140,000 gallons

MLSS=2400 mg/L

Volume of sludge wasted=5000 gallons

Conc of waste sludge=9600 mg/L

Sludge age=Pounds of MLSS

Pounds of sludge solids wasted/Day

Sludge age=Conc (mg/L) x Volume (MG) x 8.34

Conc (mg/L) x Flow (MG) x 8.34

=2400 x .14 x 8.34 = 2800 pounds

9600 x .005 x 8.34 400 pounds

=7 days

Calculations

• Now, in reverse, how many gallons of sludge should be wasted to have a 7 day sludge age?

Sludge age=Mixed Liquor Suspended Solids

Sludge solids wasted/Day

=MLSS

Desired sludge age

​

=Conc (mg/L) x Vol (MG) x 8.34

Desired sludge age

Calculations

= 2400 x .14 x 8.34

7

= 2800

7

= 400 pounds/day

= 400

9600 x 8.34

=.005 MG or 5000 gallons/day

Calculations

• Calculate a F:M ratio

F:M= BOD loading to aeration basin

pounds of solids in aeration basin

F:M=Conc (mg/L) x Flow (MG) x 8.34

Conc (MG/L) x Volume (MG) x 8.34

Given: Primary Eff BOD=120 mg/L

Inf flow=1 MGD

MLSS=2400 mg/L

Aeration Volume=170,000 gallons

Calculations

F:M=120 x 1 x 8.34

2400 x .17 x 8.34

F:M=0.29

Calculations

• Calculate different volumes and concentrations

Formula for proportional equation

V=volume

C=concentration

V₁ x C₁=V₂ x C₂

Given: Vol of Waste sludge=5000 gal

Conc of waste sludge=9600 mg/L

Vol of thickened sludge=3000 gal

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Calculations

Find concentration of thickened sludge

• V₁ x C₁=V₂ x C₂

5000 x 9600 = 3000 x C₂

C2=V₁ x C₁

V₂

=5000 x 9600

3000

=16,000 mg/L

Thank you!�

For questions or more information, call Kay at 715.340.8827