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Bruce R. Johnson P.E. BCEE and Glen T. Daigger, PhD, NAE, P.E. BCEEAdvances in Solids Reduction Processes at Wastewater Treatment Facilities: NBP Webcast, April 28th, 2010

1B U I L D I N G S U S T A I N A B L E S O L U T I O N S

Applications of Variable Environmental Conditions on Biological Sludge

Production in Wastewater Treatment

Outline

• Introduction• Sludge Reduction Overview• Mechanisms of Biological Sludge Reduction• Modeling of Biological Sludge Reduction• Conclusions

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Why is Sludge Production Important?

Limited disposal paths and more constraints

Landfill 38%• restrictive regulations• lower public acceptance• restricted access fororganic wastes

Agriculture 51%• restrictive regulations• lower public acceptance• competition with manure• restricted available land

Incineration 11%• restrictive regulation (air emission)• lower public acceptance

US Biosolids production is approximately 7 million dry tons

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• lower public acceptance

Favorable drivers for sludge reduction technologies

yper year

Introduction

• Reduction of solids disposal costs and quantities is of great interest to Utilities around the worldof great interest to Utilities around the world– WERF Project CTS-05-3: Evaluation of Processes to

Reduce Activated Sludge Solids Generation and Disposal• There are a wide range of sludge reduction

technologies offeredN f th t h l i ll d t d

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• None of these technologies are well understood– Theoretical Basis– Design Basis– Modeling Approaches

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Introduction

• The technologies fall into three major categories according to the methods they use to improve according to the methods they use to improve degradability– Mechanical

• The physical breaking up of cells and agglomerations– Chemical

• Changing the chemical makeup of the constituents

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Changing the chemical makeup of the constituents– Biological

• Creating conditions that improve biodegradability– Combinations of the three methods

Introduction

• This presentation is focused on the principals behind i i bi l i l d d bilitimproving biological degradability– Mechanisms– Modeling– Examples

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Where Can We do Solids Reduction?

Primary Treatment

Pl t

Headworks

PS to Digestion

WAS to Digestion

Plant Effluent

Secondary Treatment

Plant Influent

Digestion

Dewatering/ Disposal

H i ti Th hili

Pretreatment

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• Extended Aeration

• Cannibal™• Ozonation• Others?

• Homogenization• Sonication• Thermal

Hydrolysis• Electrical Fields

• Thermophilic Digestion

• Phased Digestion • Acid/Enzymatic

Hydrolysis• Others?

Where Can We do Biological Solids Reduction?

Primary Treatment

Pl t

Headworks

PS to Digestion

WAS to Digestion

Plant Effluent

Secondary Treatment

Plant Influent

Digestion

Dewatering/ Disposal

H i ti Th hili

Pretreatment

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• Extended Aeration

• Cannibal™• Ozonation• Others?

• Homogenization• Sonication• Thermal

Hydrolysis• Electrical Fields

• Thermophilic Digestion

• Phased Digestion • Acid/Enzymatic

Hydrolysis• Others?

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So What are Waste Solids????

Waste Solids

Biodegradable Non-Biodegradable

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SlowFast Very Slow InorganicOrganic

The Essence of Solids Reduction

Biological Sludge Reduction

• Occurs in Secondary TreatmentL l d – Long sludge age

– Reduced yields with non-aerated zones– Cannibal Solids Reduction Process

• Improved Anaerobic Digestion is achieved with Advanced digestion techniques

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– pH changes– temperature changes

• What do these processes have in Common?

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Cannibal® Solids Reduction Process

• Siemens (formerly US Filter) Cannibal process uses b th bi l i l d h i l th dboth biological and physical methods

• Versions in operation since 1998

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Cannibal Step 1 – Physical: Solids Separation Module

• Screenings and Grit (inert material)– 0.2 to 0.3 lb/lb BOD applied– dewaters to 30-40% TS– is 90% volatile– disposed in

landfill

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Cannibal Step 2 – Biological: Interchange Reactor

• WAS (<1% TS) sent to reactor• Interchange reactor SRT 10-12 d• Intermittent aeration

(SBR) controlled by ORPPortion returned

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• Portion returned to aeration basins every day

Cannibal Interchange ReactorEnvironmental Conditions

• Long periods of anaerobic/anoxic diti conditions are common

• Relies on cycling of environmental conditions

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0 6 12 18 24

Interchange Cycle, hours 2 2 18 1 1

Fill Aerate Quiesent (Anoxic/Anaerobic) Decant Mix / Decant

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Advanced Anaerobic Digestion

• Acid/Gas DigestionFi t St i l H (5 t 6) f t ti t– First Stage is low pH (5 to 6) fermentation step

– Second Stage is normally conventional Mesophillic (pH=7)

STo Dewatering

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Acid PhaseDigestion

MethanogenicDigestion

Waste Solids

Advanced Anaerobic Digestion

• Temperature Phased– Various combinations of mesophillic (35 C) and

thermophillic (55 C) staged digesters

Waste Solids To Dewatering

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ThermophillicDigestion

MesophillicDigestion

Waste Solids

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Advanced Digestion Concepts

• A recent innovation is the concept of Post Aerobic Di tiDigestion– PhD research (Kumar)– DCWASA experimental work with Dr. John Novak– Full Scale operation in Austria (Parravicinni et. al)

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MesophillicDigestion

AerobicDigestion

Waste SolidsTo Dewatering

Biological Sludge Reduction Commonalities

• Conventional digestion/treatment is limited by the t f bi d d bl lid ( i d amount of non-biodegradable solids (organic and

inorganic) in the sludge• All methods use varying environmental conditions to

improve removals• It is hypothesized that the non-biodegradable

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• It is hypothesized that the non-biodegradable organics created in one environmental condition are not totally non-biodegradable in another

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What do Variable Environmental conditions do?

Waste Solids

Biodegradable Non-Biodegradable

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SlowFast Very Slow InorganicOrganic

Modeling of Sludge Reduction

• Johnson (2008) proposed a method of modeling the C ib l lid d ti hCannibal solids reduction process where– Aerobic/Anoxic Decay products are converted

biodegradable material under anaerobic conditions• This concept was applied to Anaerobic/Aerobic

digestion

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g– Anaerobic decay products are degradable under aerobic

conditions

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Modeling of Anaerobic/Aerobic Digestion

Model Results Kumar (2006) Parravicini (2008)(2008)

Anaerobic SRT, days

20 15 30

Anaerobic VSR 55% 50% Unknown

Aerobic SRT days 12 6 6

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Aerobic SRT, days 12 6 6

Aerobic VSR 15% 23% 16%

Total VSR 62% 60% Unknown

Summary and Conclusions

• Biological Sludge Reduction Technologies– Work through the cycling of decay products through

variable environmental conditions– Can be modeled by the separate tracking of decay

products and their conversion to particulate degradable matter under different metabolic conditions

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Summary and Conclusions

• Primary HypothesisC ti l h i l d th d ti f – Conventional approach includes the production of non-biodegradable VSS. This VSS is non-biodegradable under conditions present in WWTPs

– This material may be the microbial pieces grown to protect the microbe in the environment it is grown

– In other environments it is possible that this material is at

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pleast partially degradable

– Modeling, Advanced Digestion, and the Cannibal process appears to support this hypothesis

– Principal is generally applicable throughout a WWTP

Bruce R. Johnson P.E. BCEE and Glen T. Daigger, PhD, NAE, P.E. BCEEAdvances in Solids Reduction Processes at Wastewater Treatment Facilities: NBP Webcast, April 28th, 2010

Questions?

24B U I L D I N G S U S T A I N A B L E S O L U T I O N S

Applications of Variable Environmental Conditions on Biological Sludge

Production in Wastewater Treatment