Final Draft SPDA

Evaluation of the Integration of Anaerobic
Digestion and Composting at the Barr
Regional Bio-Industrial Park by Barr Tech
Deliverable to:
Sprague Public Development Authority
June 1, 2009
By
Paul Gamble, Craig Frear, and Dr. Shulin Chen
Washington State University
Bioprocessing and Bioproducts Engineering Laboratory

Evaluation of the Integration of Anaerobic Digestion and Composting at Barr Regional Bio-Industrial Park by Barr
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Contents
1. Introduction ----------------------------------------------------------------------------------------------------------------- 4
2. Anaerobic Digestion of High Solids at Barr Tech ------------------------------------------------------------------- 6
2.1. Business Prospects and Timing for High Solids Digestion ------------------------------------------------- 6
2.2. Technology Choice: ------------------------------------------------------------------------------------------------- 7
2.2.1. Dry, Wet, Continuous or Batch ---------------------------------------------------------------------------- 7
2.2.2. Multi or Single-Stage Digestion System ----------------------------------------------------------------- 8
2.3. Pre-treatment Components -------------------------------------------------------------------------------------- 8
2.4. Wet System Choice: Plug Flow versus Complete Mix ------------------------------------------------------ 8
2.5. Mesophilic versus Thermophilic --------------------------------------------------------------------------------- 9
2.6. Nutrient Recovery and Inhibition Removal in Reclaim Water ------------------------------------------- 9
2.7. Digester System Capital Costs ----------------------------------------------------------------------------------- 9
2.8. Phased Sizing and Potential Outputs of Digesters within Overall Project ---------------------------- 10
2.9. Revenue Scenarios ------------------------------------------------------------------------------------------------- 10
2.10. Test-Bed for Additional Research and Grant Dollars --------------------------------------------------- 10
2.11. Overall Suggestions -------------------------------------------------------------------------------------------- 10
3. Advantages of Coupling Anaerobic Digestion with Composting ---------------------------------------------- 11
4. Compost Technology Recommendation ---------------------------------------------------------------------------- 12
4.1. Other Composting Considerations ----------------------------------------------------------------------------- 15
5. Electrical Power Potential of Feedstock ----------------------------------------------------------------------------- 16
5.1. Recycled Newspaper ---------------------------------------------------------------------------------------------- 17
5.2. Source-Separated Yard Waste ---------------------------------------------------------------------------------- 18
5.3. Food Waste ---------------------------------------------------------------------------------------------------------- 20
5.4. Fats, Oils and Grease (FOG) ------------------------------------------------------------------------------------- 21
5.5. Biosolids -------------------------------------------------------------------------------------------------------------- 22
6. Regulatory Factors ------------------------------------------------------------------------------------------------------- 23
7. Diversion Analysis -------------------------------------------------------------------------------------------------------- 24
7.1. Solids Mass Balance ----------------------------------------------------------------------------------------------- 24
8. Greenhouse Gas Analysis ----------------------------------------------------------------------------------------------- 26
9. Biogas ------------------------------------------------------------------------------------------------------------------------ 28

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10. Algae Production ------------------------------------------------------------------------------------------------------ 30
11. Conclusion -------------------------------------------------------------------------------------------------------------- 32
12. References -------------------------------------------------------------------------------------------------------------- 33
13. Appendix 1: Basic Biochemistry Information ------------------------------------------------------------------- 37
13.1. Biochemical and Microbiological Principles of Anaerobic Digestion ------------------------------- 37
13.2. Hydrolysis and Liquefaction ---------------------------------------------------------------------------------- 37
13.3. Acidogenesis ----------------------------------------------------------------------------------------------------- 37
13.4. Methanogenesis ------------------------------------------------------------------------------------------------ 37
14. Appendix 2: Anaerobic Digestion 101 ---------------------------------------------------------------------------- 39
14.1. Key Parameters in AD for Solid Waste --------------------------------------------------------------------- 39
14.2. pH ------------------------------------------------------------------------------------------------------------------- 39
14.3. Temperature ----------------------------------------------------------------------------------------------------- 40
14.4. C/N ratio ---------------------------------------------------------------------------------------------------------- 40
14.5. Mixing/Agitation ------------------------------------------------------------------------------------------------ 41
14.6. Retention Time -------------------------------------------------------------------------------------------------- 42
14.7. Organic Loading Rate ------------------------------------------------------------------------------------------ 42
14.8. Toxicity ------------------------------------------------------------------------------------------------------------ 43
14.9. Ammonia-nitrogen --------------------------------------------------------------------------------------------- 43
15. Appendix 3: Various Iterations of Potential Methane Yields ----------------------------------------------- 45

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1. Introduction
Managing solid waste is a natural aspect of any human culture, and to date in the US, has been subject to
the simple landfill model. However, as land landfills have become more difficult to permit due to
NIMBY (Not In My Back Yard) concerns among others, they have been forced to rural areas away from
city centers, leading to costly transportation requirements and logistics. In addition, regions are actively
seeking methods to divert material from landfill disposal to increase their serviceable life as well as
promote a recycling standard. Thus, alternatives to this model have become more relevant (Haight 2005).
The Sprague Public Development Authority (SPDA) is in the process of facilitating the establishment of
the Barr Regional Bio-Industrial Park (BRBIP), and Barr Tech has proposed to site a joint compost and
anaerobic digestion facility at the BRBIP location in order to create “green” energy and soil amendments
from the region’s organic waste. This report outlines the technical potential of this venture.
The handling of the organic fraction (OF) of municipal solid waste (MSW) stream has become a focus in
recent times (Verstraete, Morgan-Sagastume et al. 2005), (Haight 2005). This fraction tends to be mostly
water in composition, and the solids are highly volatile. In addition to being deposited into landfills that
results in un-controlled anaerobic degradation with its negative impacts on air, water and climate, the
organic waste stream can be processed through thermal and biological methods—yielding improvement
in environmental quality while also potentially producing valuable energy or products. This report
focuses on the feasibility of handling the OFMSW through biological means.
Composting and anaerobic digestion (AD) are the primary mature biological methods for handling
OFMSW. Both techniques employ micro-organisms within related kingdom, but differ in the microbial
environment in which they degrade material: composting degrades organic matter in an aerobic (with
oxygen) environment while AD degrades organic matter in an anaerobic (without oxygen) environment.
They both reduce organic waste through their respective respiration processes by converting carbon
matter into gas- with aerobic organisms respiring carbon dioxide (CO2) and anaerobic organisms respiring
CO2 and methane (CH4) (Haight 2005), (Murphy and Power 2006). In addition they both produce
valuable by-products- a soil amendment product and a liquid fertilizer, respectively. Finally, the
OFMSW is mainly characterized as a wet waste (70-95% water), and represents a detriment to hauling
and incineration processes (Arvanitoyannis, Tserkezou et al. 2006). In the context of the Spokane area,
which utilizes incineration to dispose of a large fraction of its MSW, Hartmann and Ahring (2006) note
that AD can advantageously be coupled with incineration due to a more positive energy balance in
processing wet wastes, its superior ability to recover nutrients, and the reduction of the bottom ash from
the incineration process that has to be handled as hazardous waste.

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While both are mature technologies in their ability to affectively degrade organic matter, they differ in
their energy inputs. AD produces 100-150 kWh/ ton processed while composting consumes 30-35 kWh/
ton processed (Hartmann and Ahring 2006). In addition, AD has the potential to process material in a
much smaller area, can contain odors due, and has a more controlled ability to collect and process
greenhouse gases (GHGs) (Verstraete, Morgan-Sagastume et al. 2005). To date in the US, municipalities
have installed composting facilities as opposed to AD systems because of the lack of maturity of the AD
industry and the less intensive capital demand. The success of the AD system rests on the development of
digester configurations that operate at a high rate, can handle high solid concentrations, and can operate
with reasonable capital and operating costs. Configurations in Europe have proven this technology to be
mature in regard to operational success, however economic viability within US has few examples
(Switzenbaum, Giraldogomez et al. 1990), (Lettinga 1995). Figure 1 exhibits the three-fold increase in
electrical generation from anaerobic digesters worldwide (Demirbas and Balat 2006).
Figure 1: The upward trend in growth of electricity generated through anaerobic digestion over the past 15 years,
representing over a three-fold increase.
The AD industry has clear benefits, the most obvious of which is its production of biogas. Biogas from
AD systems is composed of 50-70% methane which can be processed for use in a number of ways. The
most prevalent use is as an input into a generator set, often referred to as combined heat and power
(CHP), in which the gas is utilized to produce electricity and the subsequent heat is used for a number of
functions including the partial internal use for maintaining desired reactor temperatures. Other uses of the
methane portion of biogas are to compress it into compressed natural gas (CNG), to purify it to pipeline
quality for localized use as natural gas, methanol, and liquid natural gas (LNG) (Demirbas and Balat
2006).

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Digester systems traditionally focus on particular types of organic waste- or feedstock- which have been
proven to be easily digestible, stable, and economical (Bolzonella, Battistoni et al. 2003). They generally
focus on three waste streams: municipal water waste (biosolids), manures, and OFMSW. This report will
focus mainly on the processing of OFMSW, but can draw upon similarities amongst the three. Each
system lends itself to what is termed co-digestion, or the processing of multiple wastes in one vessel. The
advantages of co-digestion are that it allows for cost-savings due to the processing of multiple wastes at a
single facility. Co-digestion also facilitates wastes that are difficult to process in biological systems
because they must be mixed with other wastes, such as liquid wastes high in protein or fat (Kabouris, C.
et al. 2008). These possibilities can be drawn upon because often the design of their systems allows for
excess handling capacity that can be augmented with various beneficial waste streams.
Although literature focuses on the beneficial reasons for processing wet, organic waste through AD
systems, there are numerous synergies between AD and composting systems, and those are highlighted in
section 3.
2. Anaerobic Digestion of High Solids at Barr Tech

2.1. Business Prospects and Timing for High Solids Digestion
High solids digestion in the US is in its infancy, with no commercial operations presently being run.
Reasons for this center around the (1) technological hurdles present in high solids digestion, (2) high
capital costs which have precluded use in a US environment not ripe with governmental incentives, (3)
waste stream management systems which up until now have not given rise to large volumes of available
municipal or industrial high solid OFMSW ready for digestion, and (4) previous non-focus on conversion
technologies that contribute positively to greenhouse gas reductions while also producing renewable
energy (Mata-Alvarez, Macé et al. 2000). It is the authors’ belief that conditions now exist in the US
whereby large volumes of OFMSW can be attained consistently and at reasonably high tipping fees for
the purpose of digestion (Arvanitoyannis, Tserkezou et al. 2006), (Verstraete, Morgan-Sagastume et al.
2005), . These positive conditions result from ever-growing governmental and consumer driven pressures
that have resulted in new desires for effective collection programs, reduction in landfill use, and
development of renewable energy and renewable products (De Baere 2006). Much of the consumer-
driven pressures are particularly centered within the US in the Pacific Northwest and California and as
such, development of a Washington-based project is uniquely advantageous. This is especially true given
Washington State’s unique landfill concerns and approach towards green and OFMSW waste
management that requires extensive transportation costs to a limited number of landfill or processing

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sites. Note, though the European experience, which has years of extensive organic waste management,
has resulted in increasing competition for available organic resources, leading to tipping fees becoming
variable and often severely depressed (Van Opstal 2006).
2.2. Technology Choice:
2.2.1. Dry, Wet, Continuous or Batch
OFMSW has been commercially treated using a variety of AD technological options. These technological
options can be classified into the following groups:
Dry versus Wet: The distinction here is that the waste material can be directly handled, as is, at a high
solid concentration (TS = 20-25%) or diluted to a solids content that has a more manageable flow and
mixing level (TS < 15%). Although designs operating with lower TS and more manageable flow and
mixing regimes have a longer and more reliable history than recently developed dry systems, concerns
arise from the need for available reclaim water, reclaim water not concentrated in inhibitors, effective
means toward consistently diluting to a desired solids content, and a need for a larger reactor volume
because of the dilution. Alternatively, dry systems despite their smaller footprint, have concerns regarding
high mixing/pumping energy costs, poor substrate/bacterial interaction and therefore reduced kinetics,
and engineering concerns regarding loading/unloading of the waste material.
Continuous versus Batch: Systems can be designed to continually or semi-continuously be fed in such a
manner that the increased volume to the reactor automatically results in a release of digested fraction
equal in volume, thus resulting in a continuous or semi-continuous operation. In batch mode, the entire
digester is fed with waste, allowed to react, and then wasted all as one at which point a new batch is
started (Lissens, Vandevivere et al. 2001), (Bolzonella, Fatone et al. 2005). Continuous operation can be
ideal in how it smoothly interfaces with the incoming feed to the waste facility and allows for reduced
storage space, odors, etc. On the other hand, continuous feed could be potentially problematic in regard to
short-circuiting thus allowing non-digested material to be released from the digester, or in how to
smoothly accomplish a steady loading and unloading of waste (Metcalf and Eddy 2003).
It is the belief of the authors that engineering gains accomplished through wet operation resulting from
reclaim water dilution, can offset costs in extra reactor volume, especially since the anticipated feedstock
to this operation will be relatively wet in nature and require on average only a dilution from 22% to 15%.
Put another way, the increase in reactor volume and associated capital costs due to this dilution rate,
although appreciable, are warranted by the fact that a wet digestion with its engineering benefits in regard
to mixing, pumping, kinetics can occur. The negatives of wet digestion can be overcome at this projected
facility as there will be plenty of reclaimable water from the digester effluent, plenty of storage capacity

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on-site to utilize the reclaimed water, and proven commercial systems and designs to accomplish an
effective reclaimed water operation. A significant unknown is the possible inhibitory effects of long-term
use of the reclaim water resulting from the digestion effluent, but this will be discussed in another point.
2.2.2. Multi or Single-Stage Digestion System
Multi versus Single Step: Waste streams with highly biodegradable material such as is often present in
OFMSW can result in rapid acidification that in turn can lead to a lowering of the pH which sours,
inhibits or even fails the digester. A common mechanism for avoiding this concern is to separate the
acidifying and methane-forming steps into separate reactors so that each can perform optimally at their
own preferred conditions and not adversely affect the down-stream step (Raynal, Delgenes et al. 1998),
(Nguyen, Kuruparan et al. 2007), (Yu, Samani et al. 2002). Proponents against such a multi-stage
approach emphasize the increased cost required by multiple reactors and the difficulty in managing and
maintaining the separate biological conditions especially given the fact that the AD biological consortia is
naturally synergistic and complimentary, and as such, ideally can be inferred that vital steps should not be
artificially separated.
2.3. Pre-treatment Components
Pretreatment will be based on the specifications of the digestion system chosen and vendor preference and
experience. Options to be discussed with AD vendors are physical separation (trommel screen- 4”
screens in literature), size reduction through grinding or shredding, aerobic drum digesters with 2-3 day
residence time, thermophilic aerobic and anaerobic hydrolysis, and the possibility of integrating the
composting process as a hydrolysis/ acidification step. The reviewers recommend to Barr Tech to place
an emphasis on the digester technology providers to clearly deliver a specification for its digester
feedstock as well as methods for accomplishing that specification.
2.4. Wet System Choice: Plug Flow versus Complete Mix
Plug-flow systems are traditionally designed for systems with 10-15% TS, while complete-mix have been
designed for more moderate TS even though they can go higher. But the cost and difficulty of mixing
gets problematic and expensive. Plug-flow still supplies adequate substrate/bacteria contact but in natural
hydraulic plug environment without need for expensive mixing. Axial mixing could be an addition benefit
to the system as it will overcome any failure of the hydraulic plug that might occur with diverse
feedstocks. Also, plug-flow is friendlier not just to high solids, but potential inert material in the system.

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2.5. Mesophilic versus Thermophilic
Mesophilic digestion has reduced costs, easier and more stable operation, and greater control over odor
and inhibition as compared to thermophilic operation. In contrast, the increased temperature operation of
thermophilic systems allows for enhanced kinetics and therefore greater vector reduction, pathogen
control and increased biogas production (Mackie and Bryant 1995). Much of the thermophilic benefits are
mitigated in this particular project as effluent solids will be composted, thus reducing the need for
enhanced pathogen control within the digester itself. Recognizing the on-going regulatory debate
regarding AD treatment of OFMSW, it would be wise to consider a mesophilic system capable of
producing enough excess thermal heat to operate a pre- or post-hygenization step.
2.6. Nutrient Recovery and Inhibition Removal in Reclaim Water
Nutrient recovery is an essential aspect of digester processes that expect to use reclaimed digester water
as well as a potentially viable means to extract agricultural nutrients. The Bioprocessing and Bioproducts
Engineering Laboratory (BBEL) is currently pilot-testing novel ammonia and phosphorous recovery
technologies with invested industrial partners. This aspect of the operation, namely nutrient management,
will also be closely monitored by regulators. Such being the case, strong consideration should be made
regarding installation and utilization of nutrient recovery technologies, especially given its abilities to
control inhibitors, maintain nutrient management regulations, and develop additional saleable products for
the project.
2.7. Digester System Capital Costs
The reviewer finds it difficult to attain reliable project price quotes from the numerous different
technology suppliers, especially given that no formal RFP has been completed for the project. Personal
communications and extensive literature search has led, though, to the following conclusions regarding
high solids digestion in the US. As a result, some key inferences can be made regarding costs as they
apply to technologies. European technology is exorbitantly high in capital cost. Related to the earlier
discussion, capital costs could be lower for US wet systems as compared to European- and in particular
European dry systems- because of their increased reliability, reduced operation and maintenance, etc. US
systems have been designed to operate economically in a non-advantageous governmental policy
environment, although the environment is getting better. Based on the reviewer’s experience examining
bids, it is important to understand that bids do not necessarily compare apples and oranges, and Barr Tech
needs to be mindful that the bids are comparable in what they are supplying or not supplying—not just
dollars.

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2.8. Phased Sizing and Potential Outputs of Digesters within Overall Project
Operation should be designed, engineered, and constructed in phases that take into account the infancy of
the OFMSW collection program, the potential long-term growth rate of their collection program, and final
collection capability. Thus, target initial reactor size based on the desired potential MW range. In terms
of engines, certain units can be selected to take advantage of scales and phases, and keeping engines the
same size to reduce potential replacement/ maintenance costs would be prudent.
2.9. Revenue Scenarios
Business proformas need to include the potential for several additional revenue streams and have
discussions regarding risk assessment on their potential availability and/or volatility. Additional revenue
streams to be looked at include the tipping fees, electrical sales, tax credits, carbon credits, RECs, sales or
offsets of utilizing excess thermal energy, extramural grants/loans, federal bio-methane incentives, etc.
Extensive discussions should be made with USDA, DOE, EPA, State Regulatory Agencies, and CTED
regarding stimulus funds and regular RFP calls regarding industrial and even research grants.
2.10. Test-Bed for Additional Research and Grant Dollars
Bioproduct and Bioprocessing Engineering Laboratory’s work with state AD installations warrants
continued use of its working methodology—namely to utilize the commercial installation as a source of
outreach, education and basic and industrial research and demonstration. The Sprague facility will be the
first of its kind in the US in regard to this type of industrial OFMSW digestion, and as such, we need to
use its presence as much as possible. In return the Sprague facility can receive valuable recognition,
political will, on-going updates to existing technology and capabilities and access to research dollars and
potentially new next generation technologies. With this in mind it would be wise to consider test-bed
development and integration in the initial construction plans so to best facilitate later use of the facilities
in test-bed studies.
2.11. Overall Suggestions
In summary, the following are recommended as areas of focus and discussion when developing the AD
component of this project:
• Barr-Tech should actively consider AD integration into their business opportunity;
• Barr-Tech must make careful consideration into their choice of technology regarding dry vs. wet;
batch vs. continuous; mesophilic vs. thermophilic; single vs. multi-stage; and European vs. US.
In review and decision-making the above analysis of respective strengths and weaknesses as it
applies to this unique application and project should be considered;

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• Long-term analysis regarding end-use of biogas product should be considered in regard to use of
either CHP and/or combinations with other fuel upgrade options;
• Considerations should be made regarding phased build-outs and integration of slip-stream
infrastructure for use of facility as a test-bed;
• Specific attention should be made and discussions made with all perspective technology providers
regarding the unique concerns of this particular project- namely concerns regarding reclaim
water separation and utilization, VFA inhibition and pH control as it relates to feedstock choice,
feedstock ratio and relationship to technology choice, and nutrient removal and recovery;
• Need for auxiliary equipment and potential back-ups particularly as it applies to storage and pre-
treatment of OFMSW;
• Potential revenues from projected final scale as compared to projected capital costs
• Means to reduce capital payout through grants, and test-bed operation.
3. Advantages of Coupling Anaerobic Digestion with Composting
The advantages of coupling AD with composting are numerous. The first revolves around the need to
have a pasteurization step in any biological process handling large amounts of organic waste. Because
the technology is in its infancy in the US, there are not standards that dictate processes to reduce
pathogens to a sanitary level. Therefore, it is assumed that a sanitation step will be required when
handling any type of organic waste, similar to the composting industry. Pasteurization in the AD industry
would entail maintaining 55°C for a period of time (3 hours), which would effectively kill targeted
pathogens known to propagate in organic waste- mainly from the Genus Escherichia and Salmonella.
The strength of integrating the two systems is that the pasteurization step in the AD process can be
eliminated and conducted in the composting process (Poggi-Varaldo, Trejo-Espino et al. 1999).
The second major advantage of the integration is the ability to limit the solid retention time (SRT) of the
feedstocks in the digester system because of the ability to further stabilize the solid substrate in the
composting process. Typical analysis of substrate conversion to biogas is a steep initial gain of biogas
production in the first 20-30 days followed by a slower degradation for the remaining degradation of
solids. This is directly related to properties of most feedstock and the systematic availability for
microbial life to degrade those properties. Cellulose (complex and simple sugars), amino acids (proteins),
and lipids (fats) are the organic compounds that are the most readily available for initial microbial
degradation followed by the hemi- and ligno-cellulose fractions- which are often considered recalcitrant
to degradation in AD systems. The latter compounds make up the structural components of wood and
plant cells walls, and are more effectively degraded in the aerobic composting systems (Poggi-Varaldo,

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Trejo-Espino et al. 1999). By having the ability to process the hemi- and ligno-cellulose fractions in a
composting system, digesters can be designed to smaller volume as their operation will not attempt to
degrade these portions. Some facilities are sized to do so because the solid by-product presents a disposal
problem for their operation. Furthermore, windrow turners in the composting process physically beat
fiber, thereby creating more surface area for microbial degradation.
Finally, with a proper design of the preprocessing system, this coupling allows for the targeting of a much
larger array of feedstock possibilities. Obviously, AD systems are extremely susceptible to contamination
due to sensitivity in pumping and solids extraction systems, and this inability to handle wastes precludes
them from extracting readily available organic fractions of some waste streams. By designing a
pretreatment system that is capable of extracting targeted fraction of feedstock for AD, the remaining
fraction can be degraded with the less finicky composting process, thereby processing the entire stream.
Figure 2: One conception of the Unit Operation of integrating AD with composting. This conception involves a 4”
trommel pre-screening process that would create a feedstock for the AD process. The 4” overs would be ground and
sent to compost.
Aerobic composting and
curing
Finished Screening
Grind
Unit Operation Basics
Reaction
Product
Separation
Product
Purification
Airlift Separation and
De-Stoning
Compost
(3/8"
minus)
Products
Overs
material (3/
8" over)
Traditional Compost System4"
Over
4"
Minus
Anaerobic
Digestion Solids
Supernatant
Feedstock
Pre-screening of Feedstock Coupling AD with
Composting
Prescreen
4. Compost Technology Recommendation
Composting is the aerobic decomposition of organic waste. Like AD, degradation proceeds in a
methodical process such that some compounds (sugars, proteins, and fats) are more readily available than
structurally fibrous portions of biomass- the ligno-cellulosic portion. But unlike AD, the aerobic
decomposition of organic waste is a much more efficient process in terms of degradation rates,
exemplified by the elevated temperatures in large-scale composting processes. Another substantial

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difference between AD and composting is that the composting system is not enclosed and inaccessible
like the AD system, and therefore requires relatively less deliberation. Parameters that are necessarily
monitored are the C:N ratio, the moisture content, the oxygen concentration in the compost pile, particle
sizing of pre-processing size reduction, pH, and windrow temperature.
The factors that go into choosing an aerobic composting system are the ability to get it permitted, its
process efficiency, operation and maintenance costs (O&M), energy requirements, site weather patterns,
odor constraints, and capital costs. Generally, composting systems fall into three categories: turned
windrow, forced air windrows (negative or positive pressure), and in-vessel. In-vessel systems are
primarily considered for areas where odor is the major constraint or in situations where feedstock must be
entirely contained for permitting processes. Neither of these are primary considerations for this project,
so this system is eliminated from consideration.
Although odor is always a primary consideration, the above judgment of downgrading odor as a major
consideration is possible due to the location of the facility. It is proposed to be located as a piece of an
8,500 acre parcel well isolated from residential zoning, so it is of relatively little concern. Permitting too
will be based on site engineering and not odor constraint, which is often the case, so is not being
considered as a major concern in choosing a composting system.
If a recommendation were to be made based solely on suitability of climate and capital expenditure, a
turned windrow system would be the best choice. Forced air systems are excellent designs for
maintaining increased degradation rates, but this will not be necessary when coupling AD with
composting; the higher caloric value feedstocks will be degraded in the AD process, thereby partially
relieving the necessity of a high-rate aerobic system. The necessary capital for building the in-ground
infrastructure as well as the on-going pumping costs associated with forced-air systems makes this option
less desirable for a case in this climate. In addition, a primary cost of forced air systems is the covers for
the windrows that repel water while acting as a permeable membrane for gaseous exchange are
potentially an excessive cost due to this facility’s proposed location and the associated annual
precipitation levels (14.61
inches per year). In addition, a turned windrow system offers further physical
maceration that a forced-air system does not, and this will be beneficial considering the fibrous nature of
the digestate solids coming out of the digester system.

1
http://www.weatherbase.com/weather/weather.php3?s=659754&refer=

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Yet considering the feedstock, a forced-air system makes sense. The State of Washington regulates its
solid waste through the Department of Ecology (Ecology), and Ecology has delineated different organic
wastes into different types in its code named “Solid Waste Handling Standards (SWHS), Chapter 173-350
WAC2
.” (Table 1).
Table 1: Definitions of feedstocks delineated by Washington Department of Ecology “Solid Waste Handling
Standards, Chapter 173-350 WAC”
Type 1 feedstocks
Means source-separated yard and garden wastes, wood wastes, agricultural
crop residues, wax-coated cardboard, pre-consumer vegetative food wastes,
other similar source-separated materials that the jurisdictional health
department determines to have a comparable low level of risk in hazardous
substances, human pathogens, and physical contaminants.
Type 2 feedstocks
Means manure and bedding from herbivorous animals that the jurisdictional
health department determines to have a comparable low level of risk in
hazardous substances and physical contaminants when compared to a type 1
feedstock.
Type 3 feedstocks
Means meat and postconsumer source-separated food wastes or other similar
source-separated materials that the jurisdictional health department
determines to have a comparable low level of risk in hazardous substances
and physical contaminants, but are likely to have high levels of human
pathogens.
Type 4 feedstocks
Means mixed municipal solid wastes, post-collection separated or processed
solid wastes, industrial solid wastes, industrial biological treatment sludges, or
other similar compostable materials that the jurisdictional health department
determines to have a comparable high level of risk in hazardous substances,
human pathogens and physical contaminants.
SWHS states that food waste must be composted in such a way as to minimize vectors and odor emission.
As regulation is often based on precedent, food waste and biosolids are often required to be composted in
a covered system. Such being the case, a covered, forced-air system is an excellent composting technique
to meet regulatory requirements while effectively degrading the projected in-coming feedstocks. Beyond
its ability to be permitted for a wider array of feedstocks, a forced-air system has many positive attributes
including more controlled aeration, ability to maintain moisture and contain odors, and the ability to

2
http://www.ecy.wa.gov/programs/swfa/facilities/350.html

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maintain heat in the winter. Barr Tech has indicated that it will be collecting Type 1 and Type 4 waste
with the potential to also process Type 3 in the future. As the compost facility will be the primary
processor of organic material while the AD system is built and utilized as a back-up/ overflow system,
Barr Tech needs to be capable and permitted to handle all materials that may be future feedstock for AD.
Further design consideration ought to take into account the novelty of this facility. As there is little
precedent in the US for the further processing of digestate that originated from source-separated food
waste digested solids (rather than biosolids), there naturally is little precedent to the permitting of such a
facility. Such being the case, it is the recommendation of this paper to maintain options within the design
of the future growth of the compost facility’s outlay. It is possible that scientific progress may pave the
way for the acceptance of less capitally intensive composting techniques, or that food waste solids coming
out of a digestion system may no longer be classified as the food waste as the digestion process had
changed its composition. As Barr Tech will be on the cutting edge of this industry, it will be setting many
precedents. By maintaining the possibility of a hybrid composting system, it may increase its potential to
degrade and handle higher volumes of feedstock.
In addition to the AD system, which will have a substantial outlay, all compost facilities, regardless of
what composting system will be run, will require a pre-processing mechanism (grinding, pre-screen and
grinding combination, or another configuration), site equipment (loaders, lube truck(?), box trucks), and
post-composting separation (trommel screen, de-stoner, air-lift separator), not to mention grading, surface
improvements, and a pond system.
4.1. Other Composting Considerations
• Odor Management Plan- Because odor is the primary killer of all composting operations, a
proactive approach to odor management and monitoring is essential. There are tools on the
market that quantify odor in the field, and measurements should be taken and recorded daily to
address any odor complaint made.
• Compost Quality- There is many markets for compost sales, all of which demand different levels
of processing. It is important for the design of the composting process to understand who the end
user of the compost will be. This will allow for proper sizing of the composting pad.
• Grinding- Electric vs. Diesel; Mobile vs. Stationary- Grinding is the bottleneck of composting
processes, and the options should be weighed. Major manufacturers have tub, horizontal, and

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vertical grinders, all of which have the potential to run on diesel or electric power. In designing
the compost facility, it will be essential to consider power needs if electric grinding is chosen.
Another consideration is whether or not all grinding will be done at a central location, if there will
be grinding stations throughout the facility, or if there will be mobile grinding capabilities. Much
of this decision will be based on the specification of the digestion system feedstock, and if the
grinding for the digestion system and the composting system will have specifications independent
of each other, which is possible. Regardless, the success of a compost facility hinges on the pre-
process’s ability to segregate material that can cause major damage to a grinder.
• Clopyralid Testing- Based on the history of the region, it will be important for the successful
sale of compost to provide data that the non-degradable broad leaf herbicide ingredient
Clopyralid is not present in the product. As the region has a history with the persistence of this
chemical in its compost product, it will be important for consumer confidence and liability
reasons to be assured that this product is not in the compost product.
• Curing and Storage- Make sure to calculate curing and storage into the facility design. Because
the region produces very little feedstock in the winter months, it will be necessary to stockpile
material for Spring sales as well as have a strategy for screening it without it being too wet.
5. Electrical Power Potential of Feedstock
Table 2: The estimated volumes of methane gas and electrical potential of proposed feedstock to Barr Tech.
Appendix 3 outlines various volumes of feedstock and minor adjustments in the properties of those feedstocks.
Feedstock Source Projected Tons
per Year
Methane
Potential (L CH4/
g VS)
Volume of
Methane (ft3
)
Electrical
Potential (MW)
Recycled
Newspaper 15,000
0.09
(Clarkson and Xiao 2000)
(Owens and Chynoweth
1993)
3.8835 x 107
0.42
Source-Separated
Yard Waste 50,000
0.19
1993)
5.6152x 107
0.61

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Feedstock Source Projected Tons
per Year
Methane
Potential (L CH4/
g VS)
Volume of
Methane (ft3
)
Electrical
Potential (MW)
Source-Separated
Food Waste
40,000
0.35
(Mtz.-Viturtia, Mata-
Alvarez et al. 1995)
(Banks, Chesshire et al.
2008)
5.3821x107
0.58
Fats, Oils, and
Grease
15,000
1.01
(Kabouris, C. et al. 2008)
1.516x108
1.66
Total 120,000 3.0041 x 108
3.28
Waste Heat Total 2.927 MW Net
(Banks et al 2008)
5.1. Recycled Newspaper
Newspaper and paper as a whole are taken into different consideration than the more wet wastes due to its
high variability in lignin content. For office paper, the lignin content was reported as 3.6% while the
lignin content for unprinted newspaper and printed newspaper was reported as 30.3% and 31.3%
respectively (Clarkson and Xiao 2000). Their results for methane potential resulted in units of volume
per gram of COD (chemical oxygen demand), which is a difficult comparison with wet wastes because
the study was conducted over long time periods (300 days) in order to attempt to degrade typically
recalcitrant fractions. The study noted that the lack of degradation may have been due to the soy-based
printing inks, which may have limited the bacterial adhesion to the cellulose substrate, thereby impeding
degradation.
More realistic results to base substrate methane potential were reported in Owens and Chynoweth (1993).
This study also emphasized the lignin content being the main consideration of the paper type in its
determination to degrade and ultimately produce biogas. This paper reported lignin contents of
newspaper in the 20% range. Lignin, which is often referred to as ligno-cellulose in biochemical terms,
has been determined as a decent indication of methane potential as it is a decent tool in approximating the
percentage of a substrate available for high-rate degradation (Buffiere, Loisel et al. 2006). Total Solids
(TS) and Total Solids/ Volatile Solids (VS/TS) were reported as 91.4% and 97.9% (Owens and
Chynoweth 1993). Again, it is important to emphasize with this feedstock that the VS/TS figure is not as
good of a benchmark for degradation as is typical for more wet wastes, which lack substantial lignin
content. VS are determined by combusting the dry solids from a sample at 550°C, which essentially

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leaves only the mineral portion as ash. Chanakya, Sharma et al.(2009) reported as much as 50% of the
solids remained undegraded after a 30 day solid retention time (SRT), indicating that this material will
provide solid material for the composting process.
The most relevant value for the methane potential of printed and unprinted newsprint is 0.10 and 0.08 L
CH4/ g VS added (Owens and Chynoweth 1993), so 0.09 L CH4/ g VS will be used for calculations.
Based on the estimation of 15,000 (dry3
) tons per year of this feedstock, TS of 92%, a VS/TS ratio of
97.6, 3.8835 x 107
ft3
CH4 per year can be expected. Based on the conversion of electricity of a Guascor
710 generator set (9.4 ft3
CH4/ KWH), with a 90% running time (10% downtime), this feedstock has the
potential to produce 424.4 KW/ yr.
5.2. Source-Separated Yard Waste
Source-separated yard waste, often referred to as simply yard waste, has been measured to be as much as
14.6% of the total municipal solid waste stream (Yu, Samani et al. 2002). Estimation of potential gas
production for source-separated green waste will be the least accurate approximation of methane potential
of all the feedstock due to seasonal and household type of variation. Krogmann (1999) did an extensive
study of the types of green waste that originated from different types of housing units. For the purpose of
this study, the assumption is made that the primary source of green waste is from single, suburban
households.
Because of the variability, the ability to compost this fraction when it is highly woody in composition will
be one of the great advantages of coupling the anaerobic digestion and aerobic composting. Owens and
Chynoweth (1993) broke the fraction of a yard waste sample down into its components, which they
identified as grass, leaves, and branches. Their characterization of these fractions was analyzed for TS
and VS/TS, and the results for grass, leaves, and branches were 37%, 56.4%, and 70.8% and 88.1%, 95%,
and 93.9%, respectively. It is relevant to note that one minus TS is the Moisture Content (MC), and that
grass and leaves generally may not be ideal for incineration based on elevated levels of inherent moisture.
This study also combined all three of the fractions to create a 1:1:1 blend, which was characterized by TS
and VS/TS values of 50.4% and 92%. Of note, this experiment was conducted in the state of Florida, and
did not specify the time of year the samples were taken. It did state the grass was a turf grass common to

3
This is assuming the material is not preprocessed in a wet fractionation or is not co-mingled with a wet fraction.

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North Florida yards and that the leaves and branches were “fresh”. So this feedstock is probably more
indicative of a spring time scenario, which is ideal as it is likely that the leaf, branch, and grass waste
from the fall collection will be more suitable for straight composting.
Table 3 represents the tonnage by month of yard waste that was hauled to the Royal City facility in the
year 2007. This appeared to be a representative year based on the trends of the previous 4 years. The
fractions of grass, leaf, and branch tonnage are based on best estimates and are subject to change if more
accurate information becomes available. Similarly, the assumption that little to none of the yard waste
feedstock will be conducive for anaerobic digestion after the month of September is being made. This
fraction will be better suited for the composting process. In addition, this fraction will probably be best
applied to the compost facility as it will be the bulk of the material that is processed for the spring sale of
compost.
Table 3: Tonnage by month based on 2007 statistics. The grass, leaf, and branch fractionations are best
approximations
Tonnage total Assumption of
Grass Tonnage
Assumption of
Leaf Tonnage
Assumption of
Branch Tonnage
January 600 0
February 1250 0
March 3300 2000 1300
April 5300 4800 500
May 6800 6000 800
June 6050 5500 550
July 4450 4000 450
August 4550 4000 550
September 3950 2000 1000 950
October 4750 1000 3000 750
November 5600 1000 4000 600
December 500 0 100 400
The methane potential reported by Owens and Chynoweth (1993) of the grass, leaf, and branch fraction
was 0.209, 0.123, and 0.134 L CH4/ g VS added respectively. This study measured the “ultimate methane
yield”, which is a measure of the feedstock’s methane potential over a long period of time- 90 days in this
case. Obviously, no anaerobic digestion process will process the material for that period of time. In the

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case of the grass fraction, it appears from the graph that the degradation rate significantly decreased at a
value of 0.19 L CH4/ g VS added at approximately 30 days. This is the value that will be applied to
methane potential calculations. It should be assumed that the methane potential of grass will decrease
through the summer and fall, although there is no literature support for this assumption. But for the
purpose of this study, the value above will be applied to the methane potential of this feedstock. The
assumption will also be made that leaves and branches will not be put through an anaerobic system due to
their low methane potential and difficult handling attributes. Therefore, the methane potential calculation
will be made based on the assumption that only the grass yard waste fraction from the months of March –
September will be added to the anaerobic digestion system. With that in mind, the material available for
anaerobic digestion would be 28,300 tons. The methane potential for this fraction of the waste stream is
estimated at 5.6152x 107
ft3
CH4. Yu et al. (2002) found a 67% VS destruction. Based on the conversion
of electricity of a Guascor 710 generator set (9.4 ft3
CH4/ KWH), with a 90% running time (10%
downtime), this feedstock has the potential to produce 613.7 KW/ yr.
5.3. Food Waste
Barr Tech has approximated that it can divert 40,000 tons of source-separated food waste primarily from
grocery stores. Industry has named this fraction pre-consumer food waste, but is also identified in
scientific literature as source-separated food waste, often referred to as the source-separated organic
fraction of municipal solid waste (SSOFMSW). Other types of SSOFMSW may include pre- and post-
consumer food waste, but the major similarity is that this fraction has been separated from MSW at the
source. In contrast, mechanically separated organic fraction of municipal solid waste (MSOFMSW) is
physically separated from raw MSW via physical, biological, chemical separation methods, or
combinations of the three. For the purpose of this study, only SSOFMSW will be outlined for future
considerations. Ultimately, the goal is to find a value that will accurately predict the methane potential of
the incoming feedstock at Barr Tech.
Lee et al. (2009) took food waste leachate from a Korean food processing plant (SSOFMSW), where the
leachate was the result of a grinding process, a screening process, and a screw press process. The MC of
the material was 84% and the VS/TS was 91%. The study digested the leachate at different temperatures
of 25°C, 35°C, 45°C, and 55°C, and yielded a methane potential of 0.37 L CH4/ g VS, 0.403 L CH4/ g
VS, 0.351 L CH4/ g VS, and 0.275 L CH4/ g VS, respectively. Banks et al. (2008) did a mesophilic
digestion trial of SSOFMSW which was composed of household food waste and restaurant and catering

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waste. Their study achieved 67% VS destruction and a methane potential of 0.3654 L CH4/ g VS.
Habiba et al. (2009) collected food waste from markets, and ground the material. The TS of the material
was 6.8% and the VS/TS was 82.5%. The digester was a sequenced batch reactor (SBR) and was run at
35°C. The VS removal was 81.2% and the methane potential after a 65day SRT was 0.35 L CH4/ g VS.
Mtz.-Viturtia et al. (1995) also collected SSOFMSW from a central market in Barcelona and achieved
methane yields of 0.2 to 0.63 L CH4/ g VS with organic loading rates (OLRs) ranging from 3 to 12.5 g
VS/ L d. These were achieved with an HRT of 18 days, and the VS destruction was around 72%.
Zhang et al. (2007) reported a methane potential of SSOFMSW of 0.348 L CH4/ g VS and 0.435 L CH4/ g
VS after 10 and 28 days of digestion. This feedstock had a MC of 70% and a VS/TS ratio of 83%. The
VS destruction after 28 days was 81%. It should be noted that 80% of the methane potential was
achieved after 10 days, exemplifying the fact that the production of methane is not linear. This feedstock
was source-separated food waste from an urban restaurant collection, and the preprocessing of this
material was through a trommel fit with 4” screens and then ground to 1/16”. This feedstock is pre- and
post-consumer waste, and therefore does not necessarily reflect the supermarket waste that Barr Tech will
receive.
For the purpose of this study, a conservative assignment of 0.35 L CH4/ g VS will be assigned to the
incoming feedstock, with a TS of 15%4
and an 80% VS/TS. If Barr Tech collects 40,000 tons per year,
the TS will be 6,000 dry tons with 4,800 dry tons of VS. This would result in 5.3822X107
ft3
of methane.
Based on the conversion of electricity of a Guascor 710 generator set (9.4 ft3
CH4/ KWH), with a 90%
running time (10% downtime), this feedstock has the potential to produce 588 kW/ yr. 50,000 tpy of
feedstock would yield 735 kW/yr; 60,000 tpy would yield 882 kW/yr; 70,000 tpy would yield 1.03
MW/yr; 80,000 tpy would yield 1.177 MW/yr.
5.4. Fats, Oils and Grease (FOG)
FOG waste typically originates from grease traps from restaurants, and can result in severe restriction of
flow in sewage systems. It has the ability to vastly increase the biogas yield in an AD system, but also
can cause inhibition due to the low solubility and adsorption of long-chain fatty acids (LCFA), which

4
It is very important to verify the TS of the feedstock. Because of the scale of this project and the amount of
material being collected, the electrical potential figure can fluctuate greatly based on actual values.

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typically are comprised of 14-24 carbon atoms. Kabouris et al. (2008) measured co-digestion of sludge
with FOG as well as digestion of FOG alone. Their sample had TS and VS/TS values of 32.6% and
96.2%, respectively. It reported methane yields of 1.01 L CH4/ g VS and VS destruction on average to be
71.2%.
Barr Tech estimates that it will have the potential to collect 15,000 tons of FOG. Using the TS, VS/TS,
and methane yield per g VS delineated above, FOG has the potential to yield 1.516X108
ft3
of methane
gas. Based on the conversion of electricity of a Guascor 710 generator set (9.4 ft3
CH4/ KWH), with a
90% running time (10% downtime), this feedstock has the potential to produce 1.663 MW/ yr5
.
5.5. Biosolids
There are many names for human wastes that are processed at waste water treatment plants (WWTPs)
including primary sludge, secondary sludge, sewage sludge, and biosolids. Primary sludge usually refers
to settled solids from the primary clarifier, so it has not undergone any biological oxidation. Secondary
sludge refers to microbial biomass that has accumulated through growth on the soluble and suspended
nutrients (substrate) in the waste water treatment process. This biomass is then either recycled to
inoculate the incoming waste water or settled in the secondary clarifier, and is also known as Activated
Sludge (AS) or Waste Activated Sludge (WAS). Both sewage sludge and biosolids are more general
terms: sewage sludge can refer to incoming solids to a WWTP or a mixture of out-going primary and
secondary sludge while biosolids refer to the collective solids to be composted and/or land applied after
separation from the clarifier systems at WWTPs. In the literature, sewage sludge tends to be sludge that
has not undergone a treatment post-WWTP process while biosolids tend to be ready for land application.
Naturally, there is much information regarding multiple types of solids digestion from a WWTP. This
section will attempt to find a consensus in the research to determine a suitable descriptor for the anaerobic
digestion of sewage sludge. Gavala et al. (2003) examined the digestion of mixed sludge (primary and
secondary) under mesophilic and thermophilic conditions. They found that primary sludge under
mesophilic and thermophilic conditions produced methane potentials of 0.474 L CH4/ g VS and 0.3059 L
CH4/ g VS, respectively, while secondary sludge under mesophilic and thermophilic conditions produced

5
Again, keep in mind that FOG has inhibitory effects on digesters, so this figure may not be attainable. It will be
essential to base the loading of FOG on previous experience of the chosen digester design.

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methane potentials of 0.185 L CH4/ g VS and 0.2433 L CH4/ g VS, respectively. Unfortunately, the study
did not list the attributes of the primary and secondary sludge feed, so TS and VS/TS information is not
available. Kim et al. (2003) co-digested sewage sludge with a feed mixture typical of Korean food waste.
The sludge was referred to as only “sewage sludge”, so there is no differentiation of primary or secondary
sludge. The sludge had TS and VS/TS values of 3.04% and 49%, respectively. The study reported
methane potentials of 0.116 and 0.163 L CH4/ g VS for mesophilic and thermophilic conditions,
respectively. Rintala et al. (1996) evaluated sewage sludge that was a mixture of primary and secondary
sludge that had a TS and VS/TS of 14% and 57% respectively. The methane yield under a mesophilic
temperature was 0.22 L CH4/ g VS. No VS destruction was provided. Appels et al. (2008) focused
mainly on modeling, but provided data on VS destruction. They found that in a high-rate, fully mixed
mesophilic anaerobic digestion system, VS destruction on day 15, 20, and 30 was 56%, 60%, and 65.5%
respectively. Habiba et al. (2009) conducted a co-digestion experiment with various mixtures of
foodwaste and Activated Sludge digested at mesophilic temperatures. Their study achieved a VS
destruction of 55.4% and a methane yield of 0.168 L CH4/ g VS. Finally, Metcalf and Eddy (2003) lists
TS of untreated primary sludge, digested primary sludge, and untreated activated sludge as 6%, 4%, and
1% respectively and VS/TS as 65%, 40%, and 70% respectively.
Although Barr Tech has specified that it will process the biosolids it will receive in the compost facility, it
is worth considering the feedstock’s potential within an AD system. Barr Tech has indicated that it can
collect 15,000 tons of digested secondary sludge, and for the purpose of this report, a conservative
methane yield of 0.10 L CH4/ g VS is assigned. Metcalf and Eddy (2003) suggests a range of TS from 2-
5% with a typical value being 4%, and a VS/TS range from 30-60% with a typical value being 40%.
Since Barr Tech has indicated that this feedstock will be composted, a calculated methane potential will
be excluded for the time being. Also, bear in mind that the TS value is before dewatering. TS for a
dewatered sludge was reported as 67% (Desalegn, Binner et al. 2008).
6. Regulatory Factors
Compost facilities in the State of Washington must adhere to WAC 173-350-220, and those can be found
here: http://apps.leg.wa.gov/wac/default.aspx?cite=173-350-220. Based on the definitions section, it
appears that most of the feedstock will be classified as Type I, and may be Type III depending on if meat
is present. The biosolid portion appears to be a Type IV waste. Permitting will be based on interaction
with the Lead Enforcement Agency (LEA), County and State regulators.

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7. Diversion Analysis
Figure 3 is a mass balance analysis of the in-coming feedstock and also delineates the diversion of
materials. As the combination of AD and composting is still a relatively new endeavor, the mass of
compost that can be derived from the digested solids is not represented in the literature. One of the most
relevant applications of the mass balance equation is in the avoided haul. The City and County of
Spokane have three waste management options currently: the local incinerator, a Royal City compost
facility (134 miles one way according to Mapquest.com), and Roosevelt landfill (283 miles one way
according to Mapquest.com). BRBIP is 22 miles from the transfer station (personal communications with
Larry Condon), representing a significant decrease in long-hauling of waste. Specifically, if the 47,100
tpy were hauled to Barr Tech versus Royal City, assuming a one-way haul weight of 23 tons, 2,048 loads
were hauled in 2007. There is a one-way difference between BRBIP and the Royal City compost facility
of 112 miles, so a round trip difference of 224. Thus, based on 2007 tonnages, hauling Spokane’s yard
waste to BRBIP would avoid 458,752 miles driven by a long haul tractor-trailer (only half of those miles
with a full load).
7.1. Solids Mass Balance
Table 4: Solid mass balance of the projected feedstocks at Barr Tech.
Feedstock6
Initial
Mass
(tons)
TS
(%)
VS/TS
(%)
% VS
Reduction-
AD
Process
Non-Volatilized
VS + non VS- TS
% VS
Reduction7
-
Compost
Process
(Nakasaki, Tran
et al. 2009)
Projected
Dry
Tonnage
of
Compost
Recycled
Newspaper
15,000 92% 97.6% 33.6%
331+8,943=9,274
(dry tons)
40%
5,564
Source
Separated
Yard
Waste
(Grass)
28,300 37% 88.1% 67%
3,044+1,246=4,290
(dry tons)
40% 2,574
Source
Separated
Yard
Waste
(leaves and
branches)
21,700
–not to
be
digested
64% 94% n/a
21,700 (wet tons)
13,054 (dry tons)
1993)
40% 7,832
Food
Waste
40,000 15% 80% 70%
1,200+1,440=
2,640 (dry tons)
40% 1,584
Fats. Oils, 15,000 32.6% 96.2% 71.2% 185+1,354=1,539 40% 923

6
Feedstock material referenced in Table 3.
7
This value is conservative. Nakasaki, Tran et al (2009) reported degradation rates of 40-50%.

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Feedstock6
Initial
Mass
(tons)
TS
(%)
VS/TS
(%)
% VS
Reduction-
AD
Process
Non-Volatilized
VS + non VS- TS
% VS
Reduction7
-
Compost
Process
(Nakasaki, Tran
et al. 2009)
Projected
Dry
Tonnage
of
Compost
and Grease
(FOG)
(dry tons)
Biosolids
15,000
– not to
be
digested
67% n/a
15,000 -(wet tons)
10,050 (dry tons)
50%
(Desalegn,
Binner et al.
2008)
6,030
Total 24,507
Sample calculation:
Estimating yardage for sale is difficult because tonnage conversions are usually based on wet tonnage.
Wet tonnage is difficult to calculate because that will be based on the ability to dewater the digestate from
the AD system, and those values vary greatly in the literature. Metcalf and Eddy (2003) note that the
percent moisture will vary by up to 20% depending on if a chemical flocculent is added as well as the
variability in dewatering methods.
For the purpose of compost facility design, solids tonnages can be attained by conferring with the
preferred digester vendor and determining the typical moisture content that their dewatering technology
achieves, and apply that figure to the feedstocks coming out of the digester system.
Figure 3 combines the methane mass balance outlined in Table 2 and the solid mass balance in Table 4.
Note that the final masses and volumes of compost were omitted due to the reasons outlined above.

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Figure 3: The mass balance of the projected in-coming tonnages to be processed at Barr Tech
Electricity Generation
CHP Unit
(electrical generator)
Assume 9.4 ft3
CH4/ KWh
90% running time
Volume of Methane Gas
Composting
Digester Solids and Compost Feedstock
Anaerobic Digestion
Recycled Newsprint
15,000 tpy incoming
0.09L CH4/ g VS
92% TS
97.6 VS/TS
Source Separated Yard Waste
50,000 tpy incoming
AD fraction: 28,300 tpy
0.19 L CH4/ g VS
37% TS
88.1 VS/TS
Food Waste
40,000 tons incoming
0.35 L CH4/ g VS
15% TS
80% VS/TS
Fats, Oil, and Grease (FOG)
15,000 tpy incoming
1.01 L CH4/ g VS
32.6 TS
96.2 VS/TS
Total Incoming Tonnage: 120,000 tpy
Recycled Newspaper
VS Destruction 33.6
Recovered solids: dry 9,274 tpy
VS Destruction: 67%
4,290 dry tpy +21,700 wet tpy= 24,744
Food Waste
VS Destruction: 70%
Recovered solids: dry 2,640 tpy
VS Destruction: 71.2%
Recovered solids: dry 1,539 dry tpy
Biosolid
15,000 tpy incoming
25% TS
40% VS/TS
Recycled Newsprint
3.8835 x 107
ft3
CH4
5.6152x 107
ft3
CH4
Food Waste
5.3822X107
ft3
CH4
1.516X108
ft3
CH4
Total: 3.0041 x 108
ft3
CH4
Recycled Newsprint
0.42 MW
0.61 MW
Food Waste
0.58 MW
1.66 MW
Total: 3.289 MW
B a s i c M a s s B a l a n c e
5.854 MW Gross
2.927 MW Net
(Banks et al 2008)
Waste Heat
Pretreatment
8. Greenhouse Gas Analysis
The US EPA has identified AD technology as a preferred waste management approach for a variety of
environmental reasons including its ability to mitigate greenhouse gas emissions (EPA 2007).
Specifically, the AD process allows for the accelerated production and harness of methane for production
of combined heat and power; resulting in reductions in greenhouse gas emissions due to a combination of
methane conversion (greenhouse contributor 21x that of carbon dioxide) to carbon dioxide and fossil fuel
displacement. Both types of greenhouse gas reductions can be quantified and given a monetary equivalent
based upon what are now US-based voluntary programs but which could soon become legislated and
mandated government programs. The two types of reductions are now commonly called carbon credits
and RECs, with carbon referring to a specific sequestration process for greenhouse gases which in this
case is the harness and conversion of methane to carbon dioxide while RECs refer to the renewable
energy that offsets any baseline fossil fuel requirement that otherwise would have been utilized.

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Because of its co-digestion and combined heat and power (CHP) production, the Barr Tech digester
operation has the potential for reducing greenhouse gas emissions and correspondingly generating
additional project revenues via both above described avenues: organic fraction municipal solid waste
(OFMSW) methane entrapment as calculated against an assumed baseline landfill management and fossil
fuel emission offsets from use of the biogas in CHP renewable energy. The ensuing discussion and
calculations as summarized in Table 5 refer to the individual calculations and outputs for these two
avenues as calculated against the projected flow and power production rates. It should be noted, though,
that at present, digesters do have commercial mechanisms for receiving carbon credits from manure
methane entrapment but no mechanism similarly exists for receiving methane carbon credits from
OFMSW. However, the protocol is being developed and reviewed as we speak. Additionally, many
contracts with power companies place the RECs in the hands of the power company and not in the hands
of the project developer. Thus, decisions regarding the impact potential credits have on project viability
should be made with full transparency with respect to these as of yet undefined factors, namely: unsettled
and changing climate legislation, correlated volatility in prices received for credits, non-established
OFMSW credit protocol, and non-negotiated agreement with the power company regarding RECs
assignment.
The Barr Tech project plans to co-digest OFMSW substrates. Just as in the case of an already developed
manure protocol where the AD treatment is set against a baseline liquid manure storage system, the
OFMSW digestion can be set against an assumed baseline represented by landfill treatment. A potential
protocol utilizing a landfill baseline as suggested by Murphy and McKeogh (2006) can be used as a
means for predicting a possible carbon credit for the project. In their study, they have determined that
anaerobic decay of OFMSW in a landfill results in a maximum of 65% VS destruction, 1 m3
of biogas per
kg VS destroyed, 55.5% methane content in biogas, and 0.396 kg CH4/m3
biogas produced. Note that
these values will be used to determine how much carbon dioxide equivalents and therefore credits could
result from anaerobic decay of the Barr Tech flow IF it were to go to landfill. This is what is meant by a
baseline protocol, the actual amount of methane produced by the Barr Tech digester is NOT used in
determining the carbon credits but rather what the baseline process would have produced if it had not
been avoided through development of the Barr Tech AD component.
The following equation utilizing the above parameters to calculate the CO2e produced:

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where is the mass flow rate to the digester in units of kg/yr; VS% is the mean volatile solids content for
the mixed waste entering the digester; and 21 is the multiplication factor for methane. The resulting
calculation shows baseline emissions of 172.97 MMt of CO2e/yr. An average carbon credit price on the
Chicago Climate Exchange for 2008 (CCX 2008) was $5.50/ton equivalent with a 50% commission fee,
thus yielding a projected project income of $475.70.
Beyond the carbon credits there is the potential for RECs based upon fossil fuel offsets through the use of
the biogas in combined heat and power operations. The Chicago Climate Exchange calculates their
energy offsets at a rate of 0.4 metric tons of CO2e/MWh electricity generated (CCX, 2008). Given that the
Barr Tech project aims to produce 2 MW or 17,520 MWh, this amounts to 7,000 metric tons of CO2e
which with the earlier quoted prices from CCX amounts to an annual RECs income of $15,750.
Thus, the projected annual combined reductions in terms of carbon dioxide equivalents are 7,173 Metric
tons of CO2 while the associated income would be $16,225.70. Please note though the volatility in prices
received for the credits and project proformas should be adjusted accordingly.
Table 5: Carbon Credits at Barr Tech
Annual Production OFMSW Credit RECs Total
tons C-Eq $ tons C-Eq $ Tons C-Eq $
Barr Tech 172.97 475.70 7,000 15,750 7,173 16,225.70
9. Biogas
The electrical capacities of the specified feedstocks are outlined in the feedstock section above, and
delineate the potential for 3.289 megawatts of power. As simple visual diagram- Figure 4- exemplifies
how an operation needs to choose whether electricity that is generated is used to power on-site equipment
or sent back to the grid.

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Figure 4: This figure exemplifies the need for a facility to delineate whether all electricity generated on-site can be
used in its operation, thereby eliminating the need to connect to the grid (Tsagarakis 2007).
But it is worth exploring the potential for transportation fuels. To be attractive as a motor gasoline, a fuel
must contain desirable volatility, anti-knock resistance (related to octane rating), good fuel economy,
minimal deposition on engine component surfaces, and complete combustion and low pollutant emissions
(Demirbas and Balat 2006). One advantage of methane is that it is the cleanest burning alternative fuel,
and exhaust emissions form methane based fuels are much lower than those of gasoline-powered vehicles.
Of the alternative fuels identified, methanol, liquid natural gas (LNG), and compressed natural gas (CNG)
are potentially derived from methane.
Methanol is a methyl alcohol, and is produced by combining methane with water to produce methanol
and carbon monoxide. It was popularized in the 1970s and tests have shown promising results with a 85-
100% blend as a transportation fuel in automobiles, trucks, and buses (Demirbas 2007). One drawback is
that 1 Liter of gasoline is equivalent to 2.2 L of methanol, so larger tanks would be required.
Both liquid natural gas (LNG) and compressed natural gas are typically associated with mined natural
gas, which naturally is a much higher percentage of methane than digester biogas. Both LNG and CNG
produced from an AD system would have to be upgraded to approximately 96% methane before being
considered suitable for vehicular engines (Houdkova, Boran et al. 2008). LNG needs to be mentioned,
but for the purpose of this project, is an unrealistic use of the methane gas. LNG is produced by
condensing methane at extremely low temperatures (-162°C), and therefore economies of scale are

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crucial. CNG production has successful examples outlined in the literature. Houdkova, Boran et al.
(2008) described a WWTP that co-digested ley and biosolids in Vasteras, Sweden which produced,
scrubbed, and piped biogas to a bus depot where it was compressed. The CNG was then stored for use.
The GHG emissions associated with the use of CNG represented a net reduction when replacing the use
of fossil fuels.
Figure 5: Figure 5 outlines the variety of choices possible in the utilization of biogas (Houdkova, Boran et al. 2008)
10.Algae Production
While anaerobic digestion and composting represent harnessing microbial systems to produce valuable
by-products, the application of algal biotechnologies represents the potential to utilize the organism itself.
There are three primary uses of algae in the literature: the lipid fraction that algae produce, the potential
for algae to recover nutrients from anaerobic digestion effluent, and the use of algae as a slow release
fertilizer.
The differences between algae and high-lipid producing plants are vast. Algae’s doubling time (i.e.
growth) is very short, it doesn’t need arable land, it can be grown continuously, its biomass is
homogeneous, it contains no ligno-cellulose, it can grow off waste nutrients, and its yield per unit area is
extremely high. All these represent great potential for algal bio-processing for production of high-
density, liquid fuel (Rittmann 2008). Rittmann (2008) further calculated that lipid yields can be as high
as a hundred fold higher than high-lipid producing plants per acre. The three main questions that the

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industry appears to be testing are whether to grow the algae in complex photobioreactors, open ponds, or
raceways, whether to cultivate algae species (Eukaryotes) or cyanobacteria (Prokaryotes), and what the
importance of CO2 concentrations are.
Mulbry, Kondrad et al. (2008) studied the growth of algae from raw dairy pond effluent and digester
effluent (also called supernatant) from a manure based anaerobic digestion system. This study was
conducted over 4 years (2003-2006), and the primary parameters of interest were biomass growth as a
function of loading rates of nitrogen and effectiveness of uptake of nutrients. In terms of loading rates, it
found that the lowest loading rate- 0.3 g TN (Total Nitrogen) m-2
d-1
- produced approximately 2.5 g DW
(Dry Weight) m-2
d-1
while the highest loading rate- 2.5 g TN (Total Nitrogen) m-2
d-1
- yielded
approximately 25 g DW (Dry Weight) m-2
d-1
. Nitrogen and Phosphorus percentages in the biomass
reached a maximum of 7% and 1% (dry weight basis), respectively. As for the algae’s ability to
affectively scrub nutrients from the effluent, the study found that for loading rates lower than 1 g TN,
0.15 g TP m-2
d-1
, algal biomass accounted for approximately 70-90% of the input N and P. For higher
loading rates, algal biomass represented a decreased value of 50-80%. Also of note, the study found no
significant difference in algal productivity or nutrient uptake for the raceways with CO2 supplementation.
Obviously, the ability of algae to uptake waste effluent nutrients is substantial and this study represents an
interesting technology to do so.
Mulbry, Westhead et al. (2005) also investigated the ability of algae to uptake nutrients from dairy
operations with the premise that anaerobic digester effluents tend to volatilize large amounts of ammonia
N during storage. The alternative of nutrient uptake by algae presents a means of fixing nitrogen in a
form that can be transported and potentially applied as a slow release fertilizer. The study found that 3%
of total algae N was in a mineral form at day zero, and that after 21 days, 30-33% of algae N was plant
available. The results concluded that there was no difference in plant growth (cucumber and corn)
between the algae amended soil and fertilizer (Garden-tone 4-4-6) amended soil. The study did note that
it did not analyze the potential for pathogen growth, and this should be considered if this endeavor were
ever launched. But the study provided positive results for algae based fertilizers.

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11.Conclusion
Bioprocessing and Bioproducts Engineering Laboratory (BBEL) deems the combination of composting
and anaerobic digestion part of an intelligent and effective model for handling organic waste as well as
viable means for the production of “green” power. Based on the proposed in-coming feedstock to Barr
Tech, anaerobic digestion has the potential to produce biogas that would translate into 3.2 megawatts of
electricity. According to Department of Energy (DOE) 2001 statistics, this would provide “green”
electricity for approximately 2,600 households8
. If Barr Tech met its goal of 2.0 megawatts of “green”
energy production, that would provide for electricity for approximately 1,650 households. Due to the
proximity to Spokane, Barr Tech would divert over 450,000 miles of long-haul to alternate disposal sites
over the course of a year, and sequester approximately 7,100 metric tons of carbon equivalents through its
anaerobic digestion process. Its compost facility would return over 24,000 dry tons of organic material
back to the soil. The potential also exists to produce algae from the digester effluent for multiple
purposes. Finally, Barr Tech would be the first facility of its kind in the US to target source separated
food waste for the purpose of anaerobic digestion as well as beign the first facility to couple composting
and anaerobic digestion in one operation.
BBEL recommends that laboratory scale data be collected to correlate the actual feedstock Barr Tech will
be collecting with the information presented in the literature. As such, BBEL provides its best
approximation of potential outcomes, but highly recommends laboratory verification.
BBEL would like to acknowledge Community, Trade and Economic Development (CTED) for funding
this study as well as the Sprague Public Development Authority (SPDA) for administering the grant. In
particular, Pam Kelley has worked tirelessly to promote every aspect of success. BBEL would also like
to thank the Condon Brothers of Barr Tech for providing their time and information.

8
http://www.eia.doe.gov/emeu/recs/recs2001/enduse2001/enduse2001.html - Website specifies 1.21 KW
household
-1
year
-1

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13. Appendix 1: Basic Biochemistry Information
13.1. Biochemical and Microbiological Principles of Anaerobic Digestion
The AD process is accomplished through biological conversion of organics to methane and carbon
dioxide in an oxygen-free environment. The overall conversion process is often described as a three-stage
process which may occur simultaneously in an anaerobic digester. These stages are: (1) hydrolysis of
insoluble biodegradable organic matter; (2) production of acid from smaller soluble organic molecules;
and (3) methane generation. The three-stage scheme involving various microbial species can be described
as follows: (1) hydrolysis and liquefaction; (2) acidogenesis; and (3) methane fermentation.
13.2. Hydrolysis and Liquefaction
Hydrolysis and liquefaction are the breakdown of large, complex, and insoluble organics into small
molecules that can be transported into microbial cells and metabolized. Hydrolysis of the complex
molecules is catalyzed by extra-cellular enzymes such as cellulase, protease and lipase. Hydrolysis may
be conducted using separate aerobic, thermal, chemical, or enzymatic means. Essentially, organic waste
stabilization does not occur during hydrolysis; the organic matter is simply converted into a soluble form
that can be utilized by the bacteria (Parkin and Owen 1986).
13.3. Acidogenesis
The acidogenesis stage is a complex phase involving acid-forming fermentation, hydrogen production and
an acetogenic (acetic acid-forming) step. Once complex organics are hydrolyzed, acidogenic (acid-
forming) bacteria convert sugars, amino acids and fatty acids to smaller organic acids, hydrogen, and
carbon dioxide. The products formed vary with the types of bacteria as well as with environmental
conditions. The community of bacteria responsible for acid production may include facultative anaerobic
bacteria, strict anaerobic bacteria, or both (e.g. Bacteroides, Bifidobacterium, Clostridium, Lactobacillus,
Streptococcus). Hydrogen is produced by the acidogenic bacteria including hydrogen-producing
acetogenic bacteria. Acetogenic bacteria such as Syntrobacter wolini and Syntrphomonas wolfei convert
volatile fatty acids (e.g. propionic acid and butyric acid) and alcohol into acetate, hydrogen, and carbon
dioxide, which are used in methanogenesis. These microorganisms are related and can tolerate a wide
range of environmental conditions. Under standard conditions, the presence of hydrogen in solution
inhibits oxidation, so that hydrogen bacteria are required to endure the conversion of all acids (Novaes
1986); (Parkin and Owen 1986).
13.4. Methanogenesis
The formation of methane, which is the ultimate product of anaerobic treatment, occurs by two major
routes. Formic acid, acetic acid, methanol, and hydrogen can be used as energy sources by the various
methanogens. The primary route is the fermentation of the major product of the acid forming phase,
acetic acid, to methane and carbon dioxide. Bacteria that utilize acetic acid are acetoclastic bacteria
(acetate splitting bacteria). The overall reaction is:
CH3COOH → CH4 + CO2
The acetoclastic group comprises two main genera: Methanosarcina and Methanothrix. During the
thermophilic digestion of lignocellulosic waste, Methanosarcina is the dominant acetoclastic bacteria
encountered in the bioreactor. About two-thirds of methane gas is derived from acetate conversion by
acetoclastic methanogens. Some methanogens use hydrogen to reduce carbon dioxide to methane
(hydrogenophilic methanogens) according to the following overall reaction (Novaes 1986); (Morgan,
Evison et al. 1991):

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4H2 + CO2 → CH4 + 2H2O
A basic outline of the pathways of anaerobic metabolism is given as Figure 6. Under most circumstances
in treating solid wastes, acetate is a common end product of acidogenesis. This is fortunate because
acetate is easily converted to methane in the methanogenic phase. Due to the difficulty of isolating
anaerobes and the complexity of the bioconversion processes, much still remains unsolved about
anaerobic digestion (Cheong and Hansen 2007).
Complex
polymers
Cellulose,
Other polysaccharides,
Proteins, Lipids
Monomer
CO2 + H2 Acetate
Propionate
Butyrate
Ethanol
Simple sugars
Amino acids
Fatty acids
Acidogens Acidogenesis
Acetate
AcetogenesisHomoacetogens
CH4
Methanogens
CO2 +H2 Acetate
Homoacetogens
Methanogens
Methanogenesis
Methanogens Acidogens Acidogenesis

Figure 6: Scheme of anaerobic metabolism pathways

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