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Digester cleaning

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Digester Cleaning Digester Cleaning
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Page 1: Digester cleaning

Digester CleaningDigester Cleaning

Page 2: Digester cleaning

ObjectiveObjective Remove inert material, rags, hair, and high Remove inert material, rags, hair, and high

concentrations of bio-solids from digester concentrations of bio-solids from digester tankstanks

Page 3: Digester cleaning

Beneficial Consequences of Beneficial Consequences of Digester CleaningDigester Cleaning

Increase detention time of bio-solids in the Increase detention time of bio-solids in the vesselvessel

Reduce fuel costs to heat solidsReduce fuel costs to heat solids Increase digestionIncrease digestion Increase life of sludge pumpsIncrease life of sludge pumps

Page 4: Digester cleaning

Selection of digester to clean due to:Selection of digester to clean due to: Discharge pipeline clogsDischarge pipeline clogs Efficiency of digester deterioratedEfficiency of digester deteriorated Scheduled modification or repairs to vesselScheduled modification or repairs to vessel

Page 5: Digester cleaning

Anaerobic Digester IsolationAnaerobic Digester Isolation Assumption – thatAssumption – that

As much material will be pumped out to As much material will be pumped out to allow for the floating cover to rest on the allow for the floating cover to rest on the corbels.corbels.

as much of the material in the digester will as much of the material in the digester will be pumped out prior to clean out. (probe be pumped out prior to clean out. (probe vessel to ascertain grit level)vessel to ascertain grit level)

Care must be taken to not withdraw the Care must be taken to not withdraw the sludge too fast; there is a potential for sludge too fast; there is a potential for collapsing the cover by creating a vacuum. collapsing the cover by creating a vacuum. Do not pump level below grit levelDo not pump level below grit level

Page 6: Digester cleaning

Close and lock out Primary Sludge / Waste Close and lock out Primary Sludge / Waste Sludge influent line isolation valves.Sludge influent line isolation valves.

Close and lock out the recirculation (to and Close and lock out the recirculation (to and from heat exchanger) lines. Lock out the from heat exchanger) lines. Lock out the recirculation pumps.recirculation pumps.

Close and lock out the supernate (if it is the Close and lock out the supernate (if it is the secondary digester) lines and valves. secondary digester) lines and valves.

Check the gas collection line and if there is a Check the gas collection line and if there is a vacuum pump that pulls the digester gas from vacuum pump that pulls the digester gas from the digester put it in the hand mode to remove the digester put it in the hand mode to remove as much gas as possible.as much gas as possible.

When gas lines are isolated it is strongly When gas lines are isolated it is strongly suggested that the line have a blank installed suggested that the line have a blank installed to prevent gas leaking past a closed valve.to prevent gas leaking past a closed valve.

(Lock Out Tag Out Video)(Lock Out Tag Out Video)

Page 7: Digester cleaning

Open all man-ways (access points) on the Open all man-ways (access points) on the floating and/or fixed cover for ventilation to floating and/or fixed cover for ventilation to begin.begin.

It may be necessary to inject the area with an inert It may be necessary to inject the area with an inert gas (such as argon, carbon dioxide, or nitrogen) gas (such as argon, carbon dioxide, or nitrogen) and vent until a reading of lest than 2.5% and vent until a reading of lest than 2.5% combustible gas is detected. combustible gas is detected.

Care must be taken to lock out all potential electrical Care must be taken to lock out all potential electrical sources that could be an ignition point for the gas. sources that could be an ignition point for the gas.

Post signage for “no smoking”, “No open Post signage for “no smoking”, “No open flames” flames”

Monitoring the used of grinders or other spark Monitoring the used of grinders or other spark producing equipment.producing equipment.

(Ventilation Video)(Ventilation Video)

Page 8: Digester cleaning

One thing to remember is that concrete has One thing to remember is that concrete has pores and the organic matter in the concrete will pores and the organic matter in the concrete will continue to breakdown and generate gas continue to breakdown and generate gas (methane, hydrogen sulfide, and carbon (methane, hydrogen sulfide, and carbon dioxide), so the potential of the presence of dioxide), so the potential of the presence of explosive gases remains for a period of time.explosive gases remains for a period of time.

Page 9: Digester cleaning

Process: SafetyProcess: Safety Lock Out, Tag Out all piping, electrical, or Lock Out, Tag Out all piping, electrical, or

mechanicalmechanical Open all possible portalsOpen all possible portals Vent with explosion proof blower Vent with explosion proof blower Confined SpaceConfined Space

Entry Permit Documenting ConditionsEntry Permit Documenting Conditions Atmosphere TestingAtmosphere Testing Fall Protection / retrieval (secure ladder)Fall Protection / retrieval (secure ladder) Agree upon method to maintain communicationAgree upon method to maintain communication

• Hand signalsHand signals• Tugs on retrieval lanyardTugs on retrieval lanyard• (Confined Space Video)(Confined Space Video)

Page 10: Digester cleaning

PPEPPE• GlovesGloves• Rubber BootsRubber Boots• Hard HatHard Hat• Hearing protectionHearing protection• Wash hands frequently with clean water and soapWash hands frequently with clean water and soap• (PPE Video)(PPE Video)

Page 11: Digester cleaning

Entry Procedures Entry Procedures Have a rescue plan prior to entrance of vesselHave a rescue plan prior to entrance of vessel

Notify crew of rescue optionsNotify crew of rescue options We notify closest fire department prior We notify closest fire department prior

to man entry and upon last exit of day.to man entry and upon last exit of day.

Page 12: Digester cleaning

Monitor Atmosphere ContinuouslyMonitor Atmosphere Continuously Calibrate meterCalibrate meter Test various levels of interior prior to entry.Test various levels of interior prior to entry.

Position tester suction hose in area man is working Position tester suction hose in area man is working when entry occurswhen entry occurs

Install ladder and secure prior to useInstall ladder and secure prior to use Never carry tools or equipment while Never carry tools or equipment while

climbing down latter – Use bucket and ropeclimbing down latter – Use bucket and rope Safety watch monitors entry person at Safety watch monitors entry person at all timesall times Use a comfortable harness and Use a comfortable harness and

retractable retrievable deviceretractable retrievable device

Page 13: Digester cleaning

COLLAPSED ROOF AN ADDITIONAL COLLAPSED ROOF AN ADDITIONAL CONFINED SPACE DANGERCONFINED SPACE DANGER

Page 14: Digester cleaning

Confined Space Entrance EquipmentConfined Space Entrance Equipment BlowerBlower HarnessHarness TesterTester Retrieval WinchRetrieval Winch LadderLadder

Page 15: Digester cleaning

Confined Space Entrance EquipmentConfined Space Entrance Equipment HarnessHarness

Page 16: Digester cleaning

Confined Space Entrance EquipmentConfined Space Entrance Equipment TesterTester

Page 17: Digester cleaning

Confined Space Entrance EquipmentConfined Space Entrance Equipment Retrieval WinchRetrieval Winch

Page 18: Digester cleaning

DBI Sala Sealed SRLDBI Sala Sealed SRL Sealed SRL, 130ft 3/16&#34 galv steel wire rope, indicator hook w/3401123 mounting bracket & 9503578 Sealed SRL, 130ft 3/16&#34 galv steel wire rope, indicator hook w/3401123 mounting bracket & 9503578

carrying bagcarrying bag

* Stainless steel and cast aluminum housing for corrosion resistance* Stainless steel and cast aluminum housing for corrosion resistance* 130 ft. 3/16" galvanized steel wire rope for durability (50, 85 and 130 ft. lengths in galvanized or stainless steel is available)* 130 ft. 3/16" galvanized steel wire rope for durability (50, 85 and 130 ft. lengths in galvanized or stainless steel is available)* Built in retrieval winch for raising/lowering load during emergencies with built-in shock absorbing capabilities (fall arrest * Built in retrieval winch for raising/lowering load during emergencies with built-in shock absorbing capabilities (fall arrest capabilities in retrieval mode for added safety)capabilities in retrieval mode for added safety)* Input crank handle incorporates brake which will prevent movement of the load if the operator accidentally released the * Input crank handle incorporates brake which will prevent movement of the load if the operator accidentally released the handle during raising/lowering.handle during raising/lowering.* Winch drive incorporates and overload device thus reducing the possibility of injury should the worker become entangled * Winch drive incorporates and overload device thus reducing the possibility of injury should the worker become entangled during retrievalduring retrieval* Environmentally sealed design for safety, even in harsh environments* Environmentally sealed design for safety, even in harsh environments* Self adjusting disc brake for reliability* Self adjusting disc brake for reliability* Reserve lifeline retention system for added safety* Reserve lifeline retention system for added safety* Self-locking swivel snap hook with impact indicator* Self-locking swivel snap hook with impact indicator* Swiveling anchorage loop to prevent twisting of lifeline* Swiveling anchorage loop to prevent twisting of lifeline* Quick-mount bracket (model 3401065) enables user to attach to a DBI/SALA support structure with ease and carrying bag * Quick-mount bracket (model 3401065) enables user to attach to a DBI/SALA support structure with ease and carrying bag (model 9503515)(model 9503515)* Meets or exceeds all applicable industry standards including OSHA, ANSI and the stringent ANSI Z 359 * Meets or exceeds all applicable industry standards including OSHA, ANSI and the stringent ANSI Z 359

This man-rated (3-way) personal fall arrest component incorporates a self contained bi-directional retrieval winch This man-rated (3-way) personal fall arrest component incorporates a self contained bi-directional retrieval winch suitable for raising and lowering personnel in emergency rescue/retrieval situations. In the event of a fall, the self suitable for raising and lowering personnel in emergency rescue/retrieval situations. In the event of a fall, the self adjusting disk brake will stop the fall and limit the arresting forces imposed on the worker to 900 lbs. or less.adjusting disk brake will stop the fall and limit the arresting forces imposed on the worker to 900 lbs. or less. In the In the event emergency retrieval is required, you can activate the retrieval winch by simply removing the crank handle and rotating event emergency retrieval is required, you can activate the retrieval winch by simply removing the crank handle and rotating the shift knob. The device incorporates a quick-mount bracket that enables the user to attach it to a DBI/SALA support the shift knob. The device incorporates a quick-mount bracket that enables the user to attach it to a DBI/SALA support structure (tripod, davit arm, etc.) with ease.structure (tripod, davit arm, etc.) with ease.

These sealed SRL's incorporate a revolutionary patented concept that separates all dynamic components, including the These sealed SRL's incorporate a revolutionary patented concept that separates all dynamic components, including the motor spring and brake, from foreign elements such as grease, moisture and dirt. You always know your SRL is operating at motor spring and brake, from foreign elements such as grease, moisture and dirt. You always know your SRL is operating at peak efficiency, without worries about what is happening inside the housing, no matter how dirty or damp your environment. peak efficiency, without worries about what is happening inside the housing, no matter how dirty or damp your environment. The retrieval feature is one more way we're adding versatility to this product range.The retrieval feature is one more way we're adding versatility to this product range.

Similar Models:Similar Models:3400108: with stainless steel cable3400108: with stainless steel cable3400315: 50 ft. galvanized steel cable 3400315: 50 ft. galvanized steel cable 3400311: 85 ft. galvanized steel cable3400311: 85 ft. galvanized steel cable3400309: 85 ft. stainless steel cable3400309: 85 ft. stainless steel cable3400509: 130 ft. galvanized steel cable3400509: 130 ft. galvanized steel cable3400508: 130 ft. stainless steel cable3400508: 130 ft. stainless steel cable

Page 19: Digester cleaning

EquipmentEquipment Pump – Most importantPump – Most important

We use electric submergible We use electric submergible Flyst 3153 or Flyst 3153 or ABS AFP (no longer manufactured)ABS AFP (no longer manufactured)

Page 20: Digester cleaning

EquipmentEquipment DischargeDischarge

3-way tee to 2 valves3-way tee to 2 valves

Page 21: Digester cleaning

EquipmentEquipment Structure insert and service pumpStructure insert and service pump

ScaffoldScaffold Chain FallChain Fall

Page 22: Digester cleaning

Cleaning OperationsCleaning Operations

Attach a water pressure hose and Attach a water pressure hose and discharge hose to submersible pumpdischarge hose to submersible pump

Set up scaffolding over manholeSet up scaffolding over manhole Secure chainfall to scaffoldingSecure chainfall to scaffolding Lower pump into digester solidsLower pump into digester solids

Take care to attend to power cord to avoid Take care to attend to power cord to avoid pulling cord from connection boxpulling cord from connection box

Page 23: Digester cleaning
Page 24: Digester cleaning
Page 25: Digester cleaning
Page 26: Digester cleaning

PumpingPumping

Pump sludge from digester to the furthest Pump sludge from digester to the furthest available opening until a large pool of easily available opening until a large pool of easily pumpable fluid is formed adjacent to the pumppumpable fluid is formed adjacent to the pump

Slowly switch 2 way valves until less sludge is Slowly switch 2 way valves until less sludge is being re-circulated and a greater amount is being re-circulated and a greater amount is pumped to disposal option.pumped to disposal option.

Continue this operation of pumping/circulating, Continue this operation of pumping/circulating, lowering pump as required.lowering pump as required.

Page 27: Digester cleaning
Page 28: Digester cleaning

During this operation the valves will require opening and During this operation the valves will require opening and closing many time to assure that sufficient fluid volume is closing many time to assure that sufficient fluid volume is stored in the pump location to avoid cavitating.stored in the pump location to avoid cavitating.

Anticipate pump clogging occasionally and monitor Anticipate pump clogging occasionally and monitor discharge so that you can unclog when necessary. Add discharge so that you can unclog when necessary. Add water as needed with hose connected to pump and water as needed with hose connected to pump and additional host blasting from man-waysadditional host blasting from man-ways

Man entry will be necessary when efficiency slows. Man entry will be necessary when efficiency slows. Follow all safety practices for the entry. Follow all safety practices for the entry. Objective is to wash solids to pump with enough water to allow Objective is to wash solids to pump with enough water to allow

the pump to be able to remove the solids, but not too much that the pump to be able to remove the solids, but not too much that the majority is water instead of sludgethe majority is water instead of sludge

There is a sweet spot– too much water cleaning takes too long, There is a sweet spot– too much water cleaning takes too long, too little water and the discharge hose will clog.too little water and the discharge hose will clog.

Page 29: Digester cleaning

Disposal OptionsDisposal Options Pump to the headworks and allow the grit collection to Pump to the headworks and allow the grit collection to

remove the inert materialremove the inert material

Page 30: Digester cleaning

Disposal OptionsDisposal Options

Screen the pumped material with rotary or Screen the pumped material with rotary or inclined screens and return biosolids to another inclined screens and return biosolids to another digesterdigester

Page 31: Digester cleaning

Disposal OptionsDisposal Options Pump to sludge storage tank for land application Pump to sludge storage tank for land application

or mechanical dewateringor mechanical dewatering If land application is selected, plastics and rags may If land application is selected, plastics and rags may

cause concern with land ownercause concern with land owner Dewatering will require a storage tank with agitation to Dewatering will require a storage tank with agitation to

provided constant feed to dewatering equipmentprovided constant feed to dewatering equipment

Page 32: Digester cleaning

Mechanical DewateringMechanical Dewatering

Page 33: Digester cleaning

Mechanical DewateringMechanical Dewatering

Page 34: Digester cleaning
Page 35: Digester cleaning

Mechanical DewateringMechanical Dewatering

Page 36: Digester cleaning

Mechanical DewateringMechanical Dewatering

Page 37: Digester cleaning

Anaerobic Digester StartupAnaerobic Digester Startup Easiest is to reseed from another source Easiest is to reseed from another source

whether it is a digester on site or from another whether it is a digester on site or from another treatment facility.treatment facility.

Rule of thumb from EPA manual is that the amount Rule of thumb from EPA manual is that the amount of seed needed should be 20 times the anticipated of seed needed should be 20 times the anticipated volatile solids in the raw sludge.volatile solids in the raw sludge.

The example given was:The example given was:• if the anticipated raw sludge is 4% solids, 80% volatile, and if the anticipated raw sludge is 4% solids, 80% volatile, and

1000 gallons will be pumped.1000 gallons will be pumped.• 8.34 x .04 x .8 x 1000 = 270 lbs of volatile solids in the raw 8.34 x .04 x .8 x 1000 = 270 lbs of volatile solids in the raw

sludgesludge• 270 lbs x 20 = 5,400 lbs of seed material270 lbs x 20 = 5,400 lbs of seed material• If the seed sludge is 5% solids, 50% volatile, this would If the seed sludge is 5% solids, 50% volatile, this would

equal about 25,900 gallons of seed.equal about 25,900 gallons of seed.

Page 38: Digester cleaning

Factors:Factors: Availability of seed sludge Availability of seed sludge Ability to control the feed rate into the digesterAbility to control the feed rate into the digester Type of FeedType of Feed

Assuming No Seed Available Assuming No Seed Available Fill digester with raw (primary sludge from the Fill digester with raw (primary sludge from the

primary clarifiers) and sewage; or a combination of primary clarifiers) and sewage; or a combination of Primary Sludge and Waste Activated. The Primary Sludge and Waste Activated. The amounts/percentage of each flow (Primary Sludge amounts/percentage of each flow (Primary Sludge from the Primary Clarifiers, Waste Activated from from the Primary Clarifiers, Waste Activated from the Final Clarifiers, and/or raw wastewater) is the Final Clarifiers, and/or raw wastewater) is subject to debate from the people who are suppose subject to debate from the people who are suppose to know. But if the ratio isn’t correct foaming can be to know. But if the ratio isn’t correct foaming can be a problem on start up. a problem on start up.

Page 39: Digester cleaning

Heat the sludge as it is being pumped into the digester (by pumping Heat the sludge as it is being pumped into the digester (by pumping through a heat exchanger) or once the tank is full. Temperature through a heat exchanger) or once the tank is full. Temperature should be brought up to normal operating settings in a reasonable should be brought up to normal operating settings in a reasonable time frame, the operating temperature for most digesters is 95 time frame, the operating temperature for most digesters is 95 degrees F; but this varies with the mode of operation.degrees F; but this varies with the mode of operation.

Begin mixing as soon as the material reaches the operating level.Begin mixing as soon as the material reaches the operating level. Begin feeding primary/raw sludge from the primary clarifier at a Begin feeding primary/raw sludge from the primary clarifier at a

uniform rate (gpm) and consistency (normally 3 <> 5 %) to be uniform rate (gpm) and consistency (normally 3 <> 5 %) to be determined by past operational records and by the condition of the determined by past operational records and by the condition of the digester being started up.digester being started up.

MonitorMonitor Quantity of material added to the digester to fill it upQuantity of material added to the digester to fill it up Raw Sludge (Total and Volatile Solids)Raw Sludge (Total and Volatile Solids) Sampling of the digester contents for Total and volatile solids Sampling of the digester contents for Total and volatile solids Volatile acids. Alkalinity, and pH of contentsVolatile acids. Alkalinity, and pH of contents Alkalinity is important to monitor; if it is too low the digester will go Alkalinity is important to monitor; if it is too low the digester will go

sour due to a low pH. It may be necessary to have some product on sour due to a low pH. It may be necessary to have some product on hand to adjust the pH and add alkalinity to the digester. Sodium hand to adjust the pH and add alkalinity to the digester. Sodium Hydroxide, Lime Slurry, Soda Bicarb, Soda ash are some common Hydroxide, Lime Slurry, Soda Bicarb, Soda ash are some common products used.products used.

Temperature, gas production, carbon dioxide levelsTemperature, gas production, carbon dioxide levels Estimates of a few days up to 2 weeks for the digester to return to Estimates of a few days up to 2 weeks for the digester to return to

full operational status.full operational status.

Page 40: Digester cleaning
Page 41: Digester cleaning

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