DIGESTION: MANAGING

BLENDED WASTES

ROBERT CASE – CITY OF FLINT

WATER POLLUTION CONTROL SUPERVISOR

CHAD ANTLE – BIOWORKS ENERGY

CHIEF EXECUTIVE OFFICER

CITY OF FLINT

WATER POLLUTION CONTROL, 2008

Flint’s Solids Handling, 2008

PUBLIC – PRIVATE PARTNERSHIP

2008

Began with Governor’s Trade Mission

Center of Energy Excellence with Kettering University

Energy Production – Major Goal

MEDC Grant + SBI Funding = Capital Improvements

Processing Cost Savings Provides Operating Revenue

CITY’S GOALS AND OBJECTIVES

Reduce operating

costs

Minimize capital

expenditures

Maintain or

enhance reliability

of solids

processing

Promote

sustainable

operations

SWEDISH BIOGAS INTERNATIONAL

GOALS AND OBJECTIVES

Implement Digestion Process

Produce Energy - Biogas

Business Expansion, Revenue Increase

Rehabilitation of Flint’s Solids Facilities

FLINT BIOGAS PLANT - PHASE I

Ground

breaking08/09/2010

Seed sludge

loading05/16/2011

• Production

startup

• Cost

savings

begins

08/2011

Thru

09/2011

Ex. North Digester

Existing

Biosolids

Incinerator

Biogas

Digestate

Storage

Sludge

from

Treatment

Plant

Digested

Biosolids to

Incinerator

Gas

Holder

Digestate

StorageTo Boiler

ACCOMPLISHMENTS

2011

REFURBISHED NORTH DIGESTER

• NEW MIXING SYSTEM

• NEW HEATING SYSTEM

• NEW CONTROL SYSTEM

REPLACED GAS SPHERE WITH NEW

DIGESTATE STORAGE TANK

NEW PUMP HOUSE

NEW SLUDGE FORCE MAINS

NEW CENTRIFUGES

SBI revenue depends on cost

savings

Cost savings declined

•Lower sludge volume

•Reduced natural gas cost

Value of Biogas

City forced

to

abandon incineration

Unexpected

Changes

THE NEW ORDER

SBI exits North

Americaoperations

BioWorksEnergy

acquires N. America operations

BioWorks

negotiates

new contract

with Flint

Stable and Sustainable Revenue Base

Long Term Commitment to Partnership

I

• Landfilling to replace incineration

• Use biogas to generate lower electricity costs

II

• Enhance biogas production – pursue outside wastes

• Blend high energy outside wastes with dilute municipal sludge

III

• Digest the blended wastes

• Produce electricity with internal combustion engine generator

STEP BY STEP: The New Order

ADVANTAGES

Greatly

increased

gas

production

Increased

revenue

Tipping

fees

Diversion

of high

strength

wastes

Improved

utilization

of assets

Flint Solids Handling, 2015

Municipal Biosolids

High Strength Wastes

2015 GOALS INCREASE VOLUME

OF EXTERNAL

SUBSTRATES

INSTALL

ELECTRICAL POWER

GENERATION

CONSTRUCT

BIOSOLIDS

LOADING FACILITY

DECOMMISSION

INCINERATION

BLENDED WASTES

MUNICIPAL WWTP SLUDGE

(PRIMARY, WAS, TWAS)

1 to 8% total solids

60 to 90 % Volatile Solids

55 to 65% Methane Content

Heterogeneous MIX – Good for Digestion

Relatively Low “Energy Density”

Contains both MACRO/Micro Nutrients required for

stable process

EXTERNAL SUBSTRATES

(FOOD PROCESSING WASTES, ORGANIC PROCESS, ETC)

TS% - Large Variations, Rheology Not Directly

Related to TS%

30 to 100% Volatile Solids

45 to 75% Methane Content

Homogeneous Mix – Can Be Difficult to Digest as a

Mono-Culture

Higher Energy Densities Than WWTP Sludge

May Lack Macro/Micro Nutrients

Proper Combination of the Two - Better Than Either Component

Increased gas

production

Micro-

Biological

diversity

Potentially higher

degradation of solids

Increased

revenue

(Tip fees,

power

generation)

BENEFITS

OF

BLENDED

WASTES

How do I

put it

together?

REALLY…

Is this

necessary?

ADMINISTRATIVE CONCERNS

Substrate

Variability

• Unknown

factors

• Unwanted

effects

• NPDES

compliance

• Polymer

consumption

Delivery

• Acceptable

transfers

• Limited

delivery

window

• Labor

resources

Sustainability

• Must achieve

desired results

• Reliable Staff

• Who is the

“Cavalier”?

PROCESS CONCERNS

SUBSTRATE VARIABILITY

The Unknown and Sometimes Unwanted Impacts

IMPACTS

Thickening and

dewatering

performance may

vary

RESPONSIBLITY

Owner must insure

compatibility with

digestion system

and NPDES limits

TESTING

Substrates should

be tested prior to

system injection,

before problems

arise

SUBSTRATE

PROVIDER

Not responsible for

the WWTP.

Responsible only to

get rid of their

waste reliably.

QUANTIFY

Recycle Streams

and nutrient Loads

should be projected,

with testing and

modeling

GAS QUANTITY/QUALITY CONCERNS

• Flow Rates

• Pressure/Vacuum Relief Valves

• Flare

• Gas storage

• Water separation

GAS HANDLING

SYSTEM

DESIGN

• Changes in energy content

• Increases in Hydrogen Sulfide

• Dilution of siloxanes (mg/M3)

• Higher chemical (Carbon/F3Cl

2) costs

BIOGAS

QUALITY

STEADY SUBSTRATE SUPPLY

• Not always as advertised!

• Marketing and procurement of long term contracts

• Competitive pricing

• Economic Development – Educate

planners/administrators of the benefit potential

MANAGEMENT

• Sufficient daily supply

• Long term contracts – Hard to come by

• Tip Fees are Volatile – competition for substrates

• Educating administrators regarding the entire process

CHALLENGES

• Must be “Right-Size” for efficient processing

• Under utilization of capital improvements if substrates

don’t materialize

• Laboratory QA/QC of Substrates – Insure material is as

planned

RISKS

PRACTICAL ISSUES OF

BLENDED WASTES

Proportions of the desired mix and how to achieve it

Order of addition (Municipal sludge versus

substrates)

Higher gas production than expected

Rapid Rise – Underestimated gas production +

insufficient Mixing = rapid expansion in gas/liquid

matrix

Flaring of gas instead of power generation = lost

revenue

ECONOMICS OF BLENDED WASTES

Tip Fees

Additional Energy

Production

• Power production

• Avoidance of natural gas usage

• Renewable energy credits

Added nutrient value for land app

Higher energy

consumption through

higher mixing requirements

+/- Impacts to residuals

processing

Recycle streams –impacts to

plant

Increased employee

labor

QUESTIONS?