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WASTE SOLIDS REDUCTION TECHNOLOGIES
December 4, 2009
Timothy Shea, Ph.D., PE, BCEE, Julian Sandino, Ph.D., PE
Why Reduce Sludge Generation?
• Reduce costs (capital and O&M) in sludge processing and ultimate disposal/reuse.
• Maximize potential benefits of sludge processing (e.g. optimized energy balance in WWTP)
• Reduce carbon footprint
Secondary Enhancements
PS to Digestion
WAS to Digestion
Primary Treatment
Activated Sludge
Plant Effluent
Secondary Treatment Headworks
Plant Influent
Solids Handling
Dewatering/ Disposal
• Extended Aeration • Cannibal™ • Biolysis®O
• Homogenization • Sonication • Thermal Hydrolysis
• Thermophilic Digestion • Phased Digestion • Acid/Enzymatic Hydrolysis
CannibalTM
• USFilter Cannibal™ builds on the “extended aeration” concept
CannibalTM
• Biological Solids Destruction – Continuous – cycling ML between the main plant and I/C tank – anaerobic/aerobic cycling in the I/C tank
• Physical Solids Separation – Intermittent – 250-micron fine screens – organic material – Hydrocyclone units – inerts/grit material – 20 to 30 percent of the solids reduction
• Solids Inventory Purging – Annual – low yield (0.1 lb TSS /lb BOD)
CannibalTM
• Small to medium size plants (w/o anaerobic digestion …)
• Major Cost Items – covered I/C tanks and appurtenances (pH and ORP
meters, mixer, ) – odor control system – SSM
• Recent Cost quote for Fillmore, CA (1.8 mgd): – $1.1Million USFilter supplied equipment – excludes 0.5MG concrete tank, piping, odor
control, I/C tanks decanter, sludge pumps, etc.
CannibalTM
• Advantages – waste solids reduction – processing and hauling costs reduction – integration with most AS systems possible
• Disadvantages – Single vendor – more complex system – odor issues (I/C reactor and screens) – biogas value of volatile solids LOST – not applicable to conventional biological phosphorus
removal systems
Digestion Pretreatment
PS to Digestion
WAS to Digestion
Primary Treatment
Activated Sludge
Plant Effluent
Secondary Treatment Headworks
Plant Influent
Solids Handling
Dewatering/ Disposal
• Extended Aeration • Cannibal™ • Biolysis®O
• Thermal Hydrolysis • Pressure Release
• Thermophilic Digestion • Phased Digestion • Acid/Enzymatic Hydrolysis
• Disrupt cellular/ organic material that is slower to breakdown: – Increase hydrolysis of complex organics and production of
VFAs and hydrogen – Increase digestion rates & stability – Increase gas production – Increase volatile solids (VS) reduction – Reduce solids for dewatering & reuse/disposal – Reduce filamentous foaming – Reduce viscosity – Improve dewatering
• Lesser value in hydrolyzing primary sludge
Digestion Pretreatment – Why?
Thermal Hydrolysis: CAMBI
• Origins in Norway • High pressure-high temperature process: thermal
hydrolysis of dewatered sludge under pressure using live steam.
• Hydrolyzed and pasteurized sludge digested at greater VSLRs (smaller vessels).
• Heat recovery minimizes the energy consumption. • Application in mid-size treatment works (100 mgd
capacity range) at Aberdeen, Scotland and Ringsend, Dublin.
• Class A biosolids • Reduced volume
• >35% solids • 60 V.S. destruction
Methane
Dewatering 35-40% DS Dewatering 30 - 37% DS
Pre-Heat Tank
Flash Tank
Steam
Reactor
1 Solids are dewatered To ~15 %
5 Reactor pressure is rapidly released,flashing solids to the flash tank. • Flashing causes cells to
rupture • Steam is returned to
Pre-Heat • Hydrolyzed solids have reduce
viscosity
Anaerobic Digester • 60% C.O.D. conversion
• 50% reduction in digester volume • increased gas production • foaming eliminated
Pressure in reactor is reduced to 60 psi. • Steam is returned to Pre-Heat 4
2 Solids mixed with return steam and Water, so about 12%
8-10 % solids digester feed at 1 00 o F
Solids are heated by direct steam addition to 320 o F and 90 psi for 45 minutes • Class A time v. temp. • Organic compounds are
solubilized
3
CAMBI at Ringsend WWTP • 1,200,000 population equivalent • 40,000 dry tons per year (81%VS) • Dewatering (15%TS) • Thermal (steam) hydrolysis with
heat recovery (for digesters) • Anaerobic digestion (60% VSD)
Biogas co-generation w/ heat recovery
• Digested sludge (50%VS) to dewatering and heat drying
CAMBI Claimed Performance
Parameter Mesophilic AD
CAMBI + Meso AD
Digester Feed (%TS) 4-6 12-15
VSLR (kg VS/m3/d) 1.5 3.5
VS Destruction (%) 40-55 55-65
Pathogen content Class B Class A
Dewatered Cake TS (%) 20-25 30-35
Thermal Hydrolysis
• Advantages: – Enhanced VSLRs – Requires smaller digesters – Produces a Class A biosolids – Improved dewaterability of digested solids – Total destruction of microbiota from WAS,
thereby reducing/eliminating foaming in digesters.
Thermal Hydrolysis
• Disadvantages: – Process complexity (substantial contractor
retrofit at Aberdeen and Ringsend). – The process requires the use of high pressure
steam, a need that has not been met well in municipal treatment works in the United States.
– There is considerable cost uncertainty with the process given the problems encountered.
Pressure Release
• Macerate WAS to homogenize • Increase pressure (12 Bar) with PC pump • high pressure mixer, flow into disintegration
nozzle. • As the flow exits the nozzle, cavitation
occurs rupturing cell structure • Sludge can be passed through system three
times before discharge to the digesters.
Pressure Release
Vendor claims • A minimum 20%
increase in Biogas production.
• A minimum 15% reduction in dehydrated sludge volume
• Carbon augmentation for BNR
Crown Disintegrator Wiesbaden WWTP - 60m3/hr
Homogenization/Pressure Release - MicroSludgeTM
• NaOH to weaken cell membranes and reduce viscosity (pH 9 to 10)
• Chopper pump to break up agglomerates
• Screen to 800 µm to remove non-cellular debris
• Homogenizer pressure 82,700 kPa (12,000 psig) for cell lysis
Questions?