Digestion EquipmentCost-Effective Sludge Stabilization

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Sludge DigestionThe anaerobic sludge digestionprocess accelerates the naturaldecomposition of sludge, allow-ing safe, nuisance-free disposal.Over eighty years ago, anaerobicdigestion of sludges in coveredtanks was proven to be a usefulmethod of solids reduction. Sincethat time, effective digester mixinghas been demonstrated to en-hance the anaerobic digestionprocess. Experience has alsoshown that inadequate or improperdigester mixing causes difficultiessuch as reduced rates of volatilesolids destruction and gas pro-duction, rapid scum accumulation,and foaming.

Thickening of the sludges to beanaerobically digested has becomea common practice. Combiningsludge thickening with adequatedigester mixing reduces the volumerequired for effective digestionand makes the process less sub-ject to upset. Additional factorsaffecting anaerobic digestion in-clude temperature, volatile acidproduction, pH, solids concen-tration, and sludge composition.

Anaerobic Digesters• Achieve solids stabilization• Produce a dewaterable sludge• Reduce the volume of sludge

for disposal• Produce inoffensive sludge for

disposal• Produces a valuable by product

(methane gas)

Digestion EquipmentAs the anaerobic digestion pro-cess has developed, Eimco WaterTechnologies has become a leaderin the field, providing technology,

engineering and equipment de-sign. The equipment described inthis brochure is designed to pro-duce the most effective anaerobicdigestion systems available.Items offered by include:• Fixed digester covers• Buoyant digester covers• Gasholder digester covers• Sludge mixing systems• Digester heaters and heat

exchangers• Supernatant removers• Sight glasses

Digestion CoversWe provide a variety of digestercovers for specific applications.Each digester cover is constructedas a dome-shaped segment of asphere, offering maximum strengthand structural integrity. Thrustrings are installed at the peripheryof each cover to absorb all designloads without transmitting ex-cessive forces to the concretedigester wall. During erection,

covers are supported by radialbeams which add strength to thecompleted unit but are not con-sidered in structural calculations.The use of radial beams allowsthe covers to be erected quicklyand efficiently. The difficulty ofpainting and protecting truss-typesupports is eliminated.

Our digester cover designs arecompatible with all our availablemixing systems to ensure ade-quate mixing plus odor, scum, andfoaming control. A variety of ac-cessories are available with fixed,buoyant, and gasholder digestercovers to effectively interface withthe consulting engineer’s design.These accessories includemanhole covers, large diametercleanout ports, sample tubes,pressure relief vacuum breakerswith flame arresters, gas pipingnozzles, gas bonnets for gas draw-off pipes, mixer mountings, sightglasses, and pressure indicators.

Cost Effective Sludge Stabilization

2 3

The Type F digester cover is thesimplest and most economical offall our digester cover designs.A dome-shaped steel structurecovers the tank and is supportedin a vertical direction by the tankwall. The fixed cover is frequentlyused as the primary or first stagedigester in a two stage system.

Type F covers include archedradial beams attached to a centerring and a thrust ring with a side-sheet extending below liquid level.Fixed covers are supported fromstructural tubes resting on top ofthe tank wall. The required numberof arched radial beams, sidesheetsections and cover plates varieswith the tank diameter. The fixed

covers are easily insulated to re-duce heat loss using commonlyavailable roofing materials. Theentire liquid surface beneath afixed cover is open and can beagitated by a digester mixingsystem. This is a key element inpreventing scum accumulation onthe liquid surface of the digester.When a digester mixer is used,a cleanable sight glass viewingport on the digester cover can beadded for inspection of the mixeroperation.

Benefits• Simple, rugged structural

design–Low capital cost• Constant water level–Allows

maximum use of digester volume

• Easy to insulate–Efficient heatretention

• Can be sealed against the tankwall–Combats odors and foaming

• Radial loads absorbed bythrust ring–Wall design is eco-nomical, requiring design forvertical loads only

• Self-supporting dome withoutcolumns–More effective areawith high mixing efficiency

• Simple, quick erection–Lowinstallation cost

• Free water surface–Preventsscum accumulation with mixing

Fixed Digestion Covers - Type F

Type FFixed Digester Cover

Sludge DigestionThe anaerobic sludge digestionprocess accelerates the naturaldecomposition of sludge, allow-ing safe, nuisance-free disposal.Over eighty years ago, anaerobicdigestion of sludges in coveredtanks was proven to be a usefulmethod of solids reduction. Sincethat time, effective digester mixinghas been demonstrated to en-hance the anaerobic digestionprocess. Experience has alsoshown that inadequate or improperdigester mixing causes difficultiessuch as reduced rates of volatilesolids destruction and gas pro-duction, rapid scum accumulation,and foaming.

Thickening of the sludges to beanaerobically digested has becomea common practice. Combiningsludge thickening with adequatedigester mixing reduces the volumerequired for effective digestionand makes the process less sub-ject to upset. Additional factorsaffecting anaerobic digestion in-clude temperature, volatile acidproduction, pH, solids concen-tration, and sludge composition.

Anaerobic Digesters• Achieve solids stabilization• Produce a dewaterable sludge• Reduce the volume of sludge

for disposal• Produce inoffensive sludge for

disposal• Produces a valuable by product

(methane gas)

Digestion EquipmentAs the anaerobic digestion pro-cess has developed, Eimco WaterTechnologies has become a leaderin the field, providing technology,

engineering and equipment de-sign. The equipment described inthis brochure is designed to pro-duce the most effective anaerobicdigestion systems available.Items offered by include:• Fixed digester covers• Buoyant digester covers• Gasholder digester covers• Sludge mixing systems• Digester heaters and heat

exchangers• Supernatant removers• Sight glasses

Digestion CoversWe provide a variety of digestercovers for specific applications.Each digester cover is constructedas a dome-shaped segment of asphere, offering maximum strengthand structural integrity. Thrustrings are installed at the peripheryof each cover to absorb all designloads without transmitting ex-cessive forces to the concretedigester wall. During erection,

covers are supported by radialbeams which add strength to thecompleted unit but are not con-sidered in structural calculations.The use of radial beams allowsthe covers to be erected quicklyand efficiently. The difficulty ofpainting and protecting truss-typesupports is eliminated.

Our digester cover designs arecompatible with all our availablemixing systems to ensure ade-quate mixing plus odor, scum, andfoaming control. A variety of ac-cessories are available with fixed,buoyant, and gasholder digestercovers to effectively interface withthe consulting engineer’s design.These accessories includemanhole covers, large diametercleanout ports, sample tubes,pressure relief vacuum breakerswith flame arresters, gas pipingnozzles, gas bonnets for gas draw-off pipes, mixer mountings, sightglasses, and pressure indicators.

Cost Effective Sludge Stabilization

2 3

The Type F digester cover is thesimplest and most economical offall our digester cover designs.A dome-shaped steel structurecovers the tank and is supportedin a vertical direction by the tankwall. The fixed cover is frequentlyused as the primary or first stagedigester in a two stage system.

Type F covers include archedradial beams attached to a centerring and a thrust ring with a side-sheet extending below liquid level.Fixed covers are supported fromstructural tubes resting on top ofthe tank wall. The required numberof arched radial beams, sidesheetsections and cover plates varieswith the tank diameter. The fixed

covers are easily insulated to re-duce heat loss using commonlyavailable roofing materials. Theentire liquid surface beneath afixed cover is open and can beagitated by a digester mixingsystem. This is a key element inpreventing scum accumulation onthe liquid surface of the digester.When a digester mixer is used,a cleanable sight glass viewingport on the digester cover can beadded for inspection of the mixeroperation.

Benefits• Simple, rugged structural

design–Low capital cost• Constant water level–Allows

maximum use of digester volume

• Easy to insulate–Efficient heatretention

• Can be sealed against the tankwall–Combats odors and foaming

• Radial loads absorbed bythrust ring–Wall design is eco-nomical, requiring design forvertical loads only

• Self-supporting dome withoutcolumns–More effective areawith high mixing efficiency

• Simple, quick erection–Lowinstallation cost

• Free water surface–Preventsscum accumulation with mixing

Fixed Digestion Covers - Type F

Type FFixed Digester Cover

Type GV and Type GS gasholderdigester covers are frequentlyused in the second stage of atwo-stage system or in a singlestage system. Our gasholdercovers use the shell theory designdome structure as on all otherdigester covers with added side-sheet and ballast for digester gasstorage. Submerged ballast blocksare used to maximize cover sta-bility and maintain adequate gaspressure to divert digester gas to

supply energy needs. Stored di-gester gas can be used to reducewastewater treatment plant ener-gy requirements such as heatingand power generation. Specialballasting arrangements are avail-able to increase the gas pressureunder the cover to provide thedigester heating needs, run aux-iliary boilers, generators, gasengines or meet other plant energyrequirements.

Type GV covers use a verticalguide arrangement with the guidesattached to the tank wall. Guidedevices, spanning from the topto the bottom of the cover side-sheet, are engaged to stabilizethe cover and protect the coverfrom substantial wind loads.

Where the sidesheet is exposedto high wind loads, with coverextended beyond the top of theconcrete wall, even greater stabilityis required.

Gasholder Digester Covers - Type GS & Type GV

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Type GS covers are an option tomeet this need. In these designs, a45° spiral guide track is attachedto the cover sidesheet, engagingguide devices located in the di-gester wall. Any applied wind loador overturning moment simplycauses the gasholder cover tospiral downward into the tankwhile remaining level. This designallows the gasholder cover side-sheet to extend farther above thetank wall while maintaining coverstability.

Benefits• Simple construction–Low capital

and installation cost• Lower ballasting and spiral

guides available–Extra stableconfiguration

• Dome shell design–Flexiblecover design

• Cover is designed to move ver-tically–Allows large liquid levelvariations

• Gas storage volume–Used forplant energy requirements

• Operates at high pressure–Candivert gas to where it is requiredto supply plant energy needs

• No trusses to paint or protect–Low maintenance cost

• Easily insulated–Conservesheat in cold climates

Type GV Gasholder Cover

Type GS Gasholder Cover

Type GV and Type GS gasholderdigester covers are frequentlyused in the second stage of atwo-stage system or in a singlestage system. Our gasholdercovers use the shell theory designdome structure as on all otherdigester covers with added side-sheet and ballast for digester gasstorage. Submerged ballast blocksare used to maximize cover sta-bility and maintain adequate gaspressure to divert digester gas to

supply energy needs. Stored di-gester gas can be used to reducewastewater treatment plant ener-gy requirements such as heatingand power generation. Specialballasting arrangements are avail-able to increase the gas pressureunder the cover to provide thedigester heating needs, run aux-iliary boilers, generators, gasengines or meet other plant energyrequirements.

Type GV covers use a verticalguide arrangement with the guidesattached to the tank wall. Guidedevices, spanning from the topto the bottom of the cover side-sheet, are engaged to stabilizethe cover and protect the coverfrom substantial wind loads.

Where the sidesheet is exposedto high wind loads, with coverextended beyond the top of theconcrete wall, even greater stabilityis required.

Gasholder Digester Covers - Type GS & Type GV

4 5

Type GS covers are an option tomeet this need. In these designs, a45° spiral guide track is attachedto the cover sidesheet, engagingguide devices located in the di-gester wall. Any applied wind loador overturning moment simplycauses the gasholder cover tospiral downward into the tankwhile remaining level. This designallows the gasholder cover side-sheet to extend farther above thetank wall while maintaining coverstability.

Benefits• Simple construction–Low capital

and installation cost• Lower ballasting and spiral

guides available–Extra stableconfiguration

• Dome shell design–Flexiblecover design

• Cover is designed to move ver-tically–Allows large liquid levelvariations

• Gas storage volume–Used forplant energy requirements

• Operates at high pressure–Candivert gas to where it is requiredto supply plant energy needs

• No trusses to paint or protect–Low maintenance cost

• Easily insulated–Conservesheat in cold climates

Type GV Gasholder Cover

Type GS Gasholder Cover

Our Type B and Type BC digestercovers are used as the first stagein a two stage digestion systemor where gas is stored in someexternal receptacle. They areused on digesters where it isdesirable to vary the liquid levelover a wide range during thecourse of operation. As on all ourdigester covers, a dome-shapedsteel structure is designed in ac-cordance with accepted shell de-sign theory. A peripheral buoyantchamber is added and the coverfloats directly on the digester con-tents. Precast concrete ballastblocks are placed on Type B coversto maintain a specified gas pres-sure. Type BC covers incorporatethe ballast as precast panels whichform the roof over the buoyantchamber as an economical alter-native. A cross-sectional view of

the Type B or Type BC cover re-veals that the peripheral chamberlooks very similar to a catamaran,an extremely stable floating con-figuration. A major portion of thebuoyant volume which keeps thecover afloat is located at the coverperiphery. This feature providesthe Type B or Type BC cover withexcellent resistance to tipping.Slides and anti-rotational guidespermit vertical movement with-out rotation or binding. The domedcenter portion of the cover pro-vides a free liquid surface to allowvigorous agitation for maximumscum dispersal when mixing isused. Digester gas is forced to thecenter of the doomed cover forcollection rather than allowing it tocollect at the periphery where itcould possibly be vented to the at-mosphere causing the cover to tip.

Benefits• Cover is designed to move ver-

tically–Allows large liquid levelvariations

• Easily constructed and erect-ed–Low installation cost

• No trusses–Easy to paint andprotect

• Catamaran cross section–En-sures stability

• Free water surface–Preventsscum accumulation with mixing

• Anti-rotational guides and roll-ers–Prevents listing or binding

• Gas collected at center of thedome–Prevents tipping of thecover

• Easily insulated–Conservesheat in cold climates

• Buoyant chamber can use pre-cast roof slabs–Lower capitalcosts

Buoyant Digester Covers - Type BC and Type B

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A “Clean” Liquid Seal EliminatesGas and VOC Emissions, ImprovesService Access and ReducesDigester MaintenanceHydroSeal® digester covers areone of our latest innovations foranaerobic digestion. A “clean”water seal between the digestertank and cover provides com-plete gas containment in normaloperation and reduces digestermaintenance. Because the side-skirt, guides and ballast membersare located in the seal waterlaunder there is no direct sludgecontact and maintenance accessis greatly improved. Rag and sed-iment accumulation on guide andballast surfaces is eliminated andin most designs, ballast membersremain easily accessible for oper-ating pressure adjustment. Hydro-Seal covers are available for newor existing tankage and are fullycompatible with all our sludgemixers.

HydroSeal® Gasholder Covers for Anaerobic Digesters

No components come in contact with sludge

Side sheet operatesindependent of sludgestorage in clean area

Guide systemcontained in clean area

Separate launder and“clean” seal liquidwith no annular gap

Feature / Function Benefit

Positive Seal

100% gas containment.

Effective odor andVOC emissions control.

Clean environment,no rags, sediment ordebris accumulation onside sheet or ballast.

Aesthetically pleasing.

Easy, low-cost installation.

Accessible for ease ofmaintenance.

Corrosion resistant.

Long, trouble-free life,easier inspection.

Variable sludge storagecapabilities.

Lower equipment cost.

Will not become coated withdried sludge, rags, etc.

Length dependent only ongas storage needs.

Accessible for inspection.

Easier maintenance.

Greater stability.

Increased life.

Type B Buoyant Cover

Our Type B and Type BC digestercovers are used as the first stagein a two stage digestion systemor where gas is stored in someexternal receptacle. They areused on digesters where it isdesirable to vary the liquid levelover a wide range during thecourse of operation. As on all ourdigester covers, a dome-shapedsteel structure is designed in ac-cordance with accepted shell de-sign theory. A peripheral buoyantchamber is added and the coverfloats directly on the digester con-tents. Precast concrete ballastblocks are placed on Type B coversto maintain a specified gas pres-sure. Type BC covers incorporatethe ballast as precast panels whichform the roof over the buoyantchamber as an economical alter-native. A cross-sectional view of

the Type B or Type BC cover re-veals that the peripheral chamberlooks very similar to a catamaran,an extremely stable floating con-figuration. A major portion of thebuoyant volume which keeps thecover afloat is located at the coverperiphery. This feature providesthe Type B or Type BC cover withexcellent resistance to tipping.Slides and anti-rotational guidespermit vertical movement with-out rotation or binding. The domedcenter portion of the cover pro-vides a free liquid surface to allowvigorous agitation for maximumscum dispersal when mixing isused. Digester gas is forced to thecenter of the doomed cover forcollection rather than allowing it tocollect at the periphery where itcould possibly be vented to the at-mosphere causing the cover to tip.

Benefits• Cover is designed to move ver-

tically–Allows large liquid levelvariations

• Easily constructed and erect-ed–Low installation cost

• No trusses–Easy to paint andprotect

• Catamaran cross section–En-sures stability

• Free water surface–Preventsscum accumulation with mixing

• Anti-rotational guides and roll-ers–Prevents listing or binding

• Gas collected at center of thedome–Prevents tipping of thecover

• Easily insulated–Conservesheat in cold climates

• Buoyant chamber can use pre-cast roof slabs–Lower capitalcosts

Buoyant Digester Covers - Type BC and Type B

6 7

A “Clean” Liquid Seal EliminatesGas and VOC Emissions, ImprovesService Access and ReducesDigester MaintenanceHydroSeal® digester covers areone of our latest innovations foranaerobic digestion. A “clean”water seal between the digestertank and cover provides com-plete gas containment in normaloperation and reduces digestermaintenance. Because the side-skirt, guides and ballast membersare located in the seal waterlaunder there is no direct sludgecontact and maintenance accessis greatly improved. Rag and sed-iment accumulation on guide andballast surfaces is eliminated andin most designs, ballast membersremain easily accessible for oper-ating pressure adjustment. Hydro-Seal covers are available for newor existing tankage and are fullycompatible with all our sludgemixers.

HydroSeal® Gasholder Covers for Anaerobic Digesters

No components come in contact with sludge

Side sheet operatesindependent of sludgestorage in clean area

Guide systemcontained in clean area

Separate launder and“clean” seal liquidwith no annular gap

Feature / Function Benefit

Positive Seal

100% gas containment.

Effective odor andVOC emissions control.

Clean environment,no rags, sediment ordebris accumulation onside sheet or ballast.

Aesthetically pleasing.

Easy, low-cost installation.

Accessible for ease ofmaintenance.

Corrosion resistant.

Long, trouble-free life,easier inspection.

Variable sludge storagecapabilities.

Lower equipment cost.

Will not become coated withdried sludge, rags, etc.

Length dependent only ongas storage needs.

Accessible for inspection.

Easier maintenance.

Greater stability.

Increased life.

Type B Buoyant Cover

Mechanical Mixing Systems - Type EDT and Type RDT

8 9

Rectangular Flotators

Mechanical Mixing Systems

Conventional PropellerA conventional three-bladedweedless marine type propeller,as shown above in a sludge mixingapplication, clearly demonstratesits propensity for fouling. Mixingefficiency is severely reduced andmechanical problems, such asmotor overload and bearing dam-age, is greatly increased. Mainte-nance was required for cleaningat least once every two weeks.

EIMIX® PropellerAn EIMIX propeller was installedin place of the marine type pro-peller. After three years of continu-ous operation, the EIMIX propellerwas removed from the draft tubeand is shown in the above photo.These photos testify to the superiorability of the EIMIX propeller toeliminate accumulation of materialswhile retaining high operatingefficiency with low maintenance.

Digester MixersEffective anaerobic digestion ishighly dependent upon efficientmixing. When tank contents arenot vigorously mixed, stratificationoccurs and the tank volume is noteffectively utilized. Most waste-water treatment facilities incor-porate thorough and completemixing to ensure uniform temper-ature, and solids distribution andmicroorganism contact with incom-ing sludge. High-rate digestionprocesses effectively handle highsolids loadings with shorteneddetention time through the properapplication of digester mixing.EIMIX sludge mixers minimizescum formation, distribute heatthroughout the digester, complete-ly mix the digester contents, andevenly distribute volatile acids andnutrients. Several types of sludgemixers are available to pumplarge volumes of sludge throughdraft tubes. These mixers act aslow head, high volume sludgepumps, utilizing explosion proofmotors to drive specially designed,vertical sludge mixing propellers.Use of a reversing motor enablesthese mixers to operate in eitherdirection, maximizing systemflexibility. We use the uniqueEIMIX sludge mixer propeller that

prevents fouling and is capableof pumping upward or downwardwith equal efficiency. The sludgemixer upper bearing is located wellabove liquid level, next to the motor,and the lower bearing is locatedadjacent to the propeller. Usingthis configuration, bearing spanis increased and overhung loadsare negligible resulting in extendedbearing life. The entire EIMIX mix-ing assembly is removable withoutdewatering or depressurizing thedigester. Pumping capacity varieswith mixer motor horsepower (from5 to 20 HP) and ranges up to 23,000gallons per minute.

Type EDT MixerExternal Draft Tube (EDT) mixersare self contained units whichprovide a tangential flow patternwithin the digester. They are themost efficient system availablefor high rate digestion. Maximumenergy input occurs at the periph-ery of the tank near the surfaceto enhance surface turbulenceand prevent scum accumulation.Easy access for maintenance isachieved by mounting the mixeroutside of the tank. Removal of thedrive assembly for maintenance isachieved without losing digestergas or dewatering the tank.

Type RDT MixerRemovable Draft Tube (RDT) mix-ers are mounted on the digestercover with the draft tubes anddrive assemblies both being easilyremovable. For maximum mixingcapability, several RDT mixers canbe distributed around the coveron large digesters. Flow can bedirected upward or downward withperiodic reversing of direction.

Types RDT-V and RDT-L mixersincorporate telescoping exten-sions at the bottom of the drafttube. With type RDT-L, flow ispumped downward through thedraft tube toward the digesterbottom. In large diameter digesterapplications, an RDT mixer can

be installed at the center of thedigester tank to operate in con-junction with the EDT mixers atthe tank periphery to give addi-tional scum breaking and mixingcapacity.

Benefits• Rotating equipment and draft

tubes are supplied as a unit–Easy installation

• Forward and reverse operation–Alters flow and increasessystem flexibility

• Specially designed propeller–Eliminates accumulation of debris

• Machined, lower mechanicaloil seals–Decreases mainte-nance costs

• Large diameter draft tube pro-peller–Provides low head lossand effective utilization of mixingenergy

• Heat exchange jackets–Effectivedigester heating for low cost

• Mixers are located at the tankperiphery and/or on the digestercover–More effective sludgemixing and easy access

• Strong surface agitation–Effec-tive scum break-up

• Can be worked on while thedigester remains in service–Easier maintenance

• High degree of mixing intensity–Eliminates short circuiting andincreases the active digestervolume

EIMIX® Mixing PropellerThe propeller is designed specif-ically to eliminate accumulation ofstringy and fibrous material on thepropeller which can cause bearingand seal damage and drive motoroverload. Flow is directed awayfrom the hub by the specially de-signed propeller blade which alsopermits operation in either upwardor downward flow without chang-ing the pumping rate.

Type RDT-V Sludge MixerType EDT Sludge Mixer Type RDT Sludge Mixer Type RDT-L Sludge Mixer

Mechanical Mixing Systems - Type EDT and Type RDT

8 9

Rectangular Flotators

Mechanical Mixing Systems

Conventional PropellerA conventional three-bladedweedless marine type propeller,as shown above in a sludge mixingapplication, clearly demonstratesits propensity for fouling. Mixingefficiency is severely reduced andmechanical problems, such asmotor overload and bearing dam-age, is greatly increased. Mainte-nance was required for cleaningat least once every two weeks.

EIMIX® PropellerAn EIMIX propeller was installedin place of the marine type pro-peller. After three years of continu-ous operation, the EIMIX propellerwas removed from the draft tubeand is shown in the above photo.These photos testify to the superiorability of the EIMIX propeller toeliminate accumulation of materialswhile retaining high operatingefficiency with low maintenance.

Digester MixersEffective anaerobic digestion ishighly dependent upon efficientmixing. When tank contents arenot vigorously mixed, stratificationoccurs and the tank volume is noteffectively utilized. Most waste-water treatment facilities incor-porate thorough and completemixing to ensure uniform temper-ature, and solids distribution andmicroorganism contact with incom-ing sludge. High-rate digestionprocesses effectively handle highsolids loadings with shorteneddetention time through the properapplication of digester mixing.EIMIX sludge mixers minimizescum formation, distribute heatthroughout the digester, complete-ly mix the digester contents, andevenly distribute volatile acids andnutrients. Several types of sludgemixers are available to pumplarge volumes of sludge throughdraft tubes. These mixers act aslow head, high volume sludgepumps, utilizing explosion proofmotors to drive specially designed,vertical sludge mixing propellers.Use of a reversing motor enablesthese mixers to operate in eitherdirection, maximizing systemflexibility. We use the uniqueEIMIX sludge mixer propeller that

prevents fouling and is capableof pumping upward or downwardwith equal efficiency. The sludgemixer upper bearing is located wellabove liquid level, next to the motor,and the lower bearing is locatedadjacent to the propeller. Usingthis configuration, bearing spanis increased and overhung loadsare negligible resulting in extendedbearing life. The entire EIMIX mix-ing assembly is removable withoutdewatering or depressurizing thedigester. Pumping capacity varieswith mixer motor horsepower (from5 to 20 HP) and ranges up to 23,000gallons per minute.

Type EDT MixerExternal Draft Tube (EDT) mixersare self contained units whichprovide a tangential flow patternwithin the digester. They are themost efficient system availablefor high rate digestion. Maximumenergy input occurs at the periph-ery of the tank near the surfaceto enhance surface turbulenceand prevent scum accumulation.Easy access for maintenance isachieved by mounting the mixeroutside of the tank. Removal of thedrive assembly for maintenance isachieved without losing digestergas or dewatering the tank.

Type RDT MixerRemovable Draft Tube (RDT) mix-ers are mounted on the digestercover with the draft tubes anddrive assemblies both being easilyremovable. For maximum mixingcapability, several RDT mixers canbe distributed around the coveron large digesters. Flow can bedirected upward or downward withperiodic reversing of direction.

Types RDT-V and RDT-L mixersincorporate telescoping exten-sions at the bottom of the drafttube. With type RDT-L, flow ispumped downward through thedraft tube toward the digesterbottom. In large diameter digesterapplications, an RDT mixer can

be installed at the center of thedigester tank to operate in con-junction with the EDT mixers atthe tank periphery to give addi-tional scum breaking and mixingcapacity.

Benefits• Rotating equipment and draft

tubes are supplied as a unit–Easy installation

• Forward and reverse operation–Alters flow and increasessystem flexibility

• Specially designed propeller–Eliminates accumulation of debris

• Machined, lower mechanicaloil seals–Decreases mainte-nance costs

• Large diameter draft tube pro-peller–Provides low head lossand effective utilization of mixingenergy

• Heat exchange jackets–Effectivedigester heating for low cost

• Mixers are located at the tankperiphery and/or on the digestercover–More effective sludgemixing and easy access

• Strong surface agitation–Effec-tive scum break-up

• Can be worked on while thedigester remains in service–Easier maintenance

• High degree of mixing intensity–Eliminates short circuiting andincreases the active digestervolume

EIMIX® Mixing PropellerThe propeller is designed specif-ically to eliminate accumulation ofstringy and fibrous material on thepropeller which can cause bearingand seal damage and drive motoroverload. Flow is directed awayfrom the hub by the specially de-signed propeller blade which alsopermits operation in either upwardor downward flow without chang-ing the pumping rate.

Type RDT-V Sludge MixerType EDT Sludge Mixer Type RDT Sludge Mixer Type RDT-L Sludge Mixer

Digester HeaterType DH digester heaters supplythe hot water necessary to main-tain proper digester temperature.Extra heating capacity can besupplied to heat building with hotwater systems, or supply hot waterwherever else it might be required.Digester gas burners and controlsfeature an automatic switch-overto auxiliary fuels such as naturalgas or oil when digester gas is notof adequate supply. Maximum useis made of available digester gasprior to the burning of any auxiliaryfuel. The boiler employed in theDH unit is of a forced draft design.It is the most efficient available,extracting the most heating capac-ity from the available fuel.

Heat ExchangerThe Type HX concentric tube heatexchangers can be used in con-junction with a Type DH digesterheater as a package or suppliedseparately. The Type HX heatexchanger is a simple, ruggedpiece of equipment employingcounter current flow to transferthe maximum amount of heat fromhot water to sludge. A tube-in-tubedesign is employed using heavyduty, removable cast iron returnbends for long life and ease ofmaintenance.

Supernatant RemoverWithdrawal of supernatant atvarious levels in the digester canbe accomplished by use of a su-pernatant remover. A rotatabledrawoff pipe is manually operatedthrough a vertical zone up to 20

feet in diameter by an externalworm gear assembly. Locationof the drawoff pipe inlet is easilynoted by a pointer. The cleanablesight glass, allows the operator avisual inspection of the removalprocess.

Digester Heating Equipment and Accessories

10 11

Cleanable Sight GlassThe Type K-2 sight glass is usedfor right angle flow applications.Sludge is clearly visible through apyrex glass pipe-section to permitobservation and inspection ofcontents without withdrawingsamples. The Type K-3 sight glassis used in straight through flowapplications. A light shines throughtwo tempered glass windows onopposite sides of an inner chamber.

Both Type K-2 and Type K-3 sightglasses have internal neoprenewipers and cleaning rod handleswith provision for dispensing clean-ing solvent on the inside of theglass. To allow inspection throughthe digester cover, the 8” x 16”weldable sight glass can be used.The assembly can also be pro-vided with a solvent dispenserwhen required.

K-3 Sight GlassSolvent Hand PumpDual Wiper

Packing Gland

Light

K-2 Sight Glass

8” x 16” Sight Glass

Sight Glass Body

Gaskets

Glassport

Packing GlandAssembly

Handle

Wiper with DoubleSqueegee

Shade7

6

2

4

5

3

1

7

6 2 3 1 4 5

6 3 1

5

4

Digester HeaterType DH digester heaters supplythe hot water necessary to main-tain proper digester temperature.Extra heating capacity can besupplied to heat building with hotwater systems, or supply hot waterwherever else it might be required.Digester gas burners and controlsfeature an automatic switch-overto auxiliary fuels such as naturalgas or oil when digester gas is notof adequate supply. Maximum useis made of available digester gasprior to the burning of any auxiliaryfuel. The boiler employed in theDH unit is of a forced draft design.It is the most efficient available,extracting the most heating capac-ity from the available fuel.

Heat ExchangerThe Type HX concentric tube heatexchangers can be used in con-junction with a Type DH digesterheater as a package or suppliedseparately. The Type HX heatexchanger is a simple, ruggedpiece of equipment employingcounter current flow to transferthe maximum amount of heat fromhot water to sludge. A tube-in-tubedesign is employed using heavyduty, removable cast iron returnbends for long life and ease ofmaintenance.

Supernatant RemoverWithdrawal of supernatant atvarious levels in the digester canbe accomplished by use of a su-pernatant remover. A rotatabledrawoff pipe is manually operatedthrough a vertical zone up to 20

feet in diameter by an externalworm gear assembly. Locationof the drawoff pipe inlet is easilynoted by a pointer. The cleanablesight glass, allows the operator avisual inspection of the removalprocess.

Digester Heating Equipment and Accessories

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Cleanable Sight GlassThe Type K-2 sight glass is usedfor right angle flow applications.Sludge is clearly visible through apyrex glass pipe-section to permitobservation and inspection ofcontents without withdrawingsamples. The Type K-3 sight glassis used in straight through flowapplications. A light shines throughtwo tempered glass windows onopposite sides of an inner chamber.

Both Type K-2 and Type K-3 sightglasses have internal neoprenewipers and cleaning rod handleswith provision for dispensing clean-ing solvent on the inside of theglass. To allow inspection throughthe digester cover, the 8” x 16”weldable sight glass can be used.The assembly can also be pro-vided with a solvent dispenserwhen required.

K-3 Sight GlassSolvent Hand PumpDual Wiper

Packing Gland

Light

K-2 Sight Glass

8” x 16” Sight Glass

Sight Glass Body

Gaskets

Glassport

Packing GlandAssembly

Handle

Wiper with DoubleSqueegee

Shade7

6

2

4

5

3

1

7

6 2 3 1 4 5

6 3 1

5

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Digestion EquipmentCost-Effective Sludge Stabilization

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