Report No.
CM-00-2
ACKNOWLEDGMENTS
This project was partially funded by CWC’s Recycling Technology Assistance Partnership (ReTAP), through a grant from the U.S. Environmental Protection Agency, with supporting funds from the National Institute of Standards and Technology Manufacturing Extension Partnership (NIST MEP).
E & A Environmental Consultants, Inc. was instrumental in completion of this project. The Woodland Park Zoo and Soos Creek Composting also contributed to the research project. FINAL Prepared for:
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Disclaimer CWC disclaims all warranties to this report, including mechanics,
data contained within and all other aspects, whether expressed or
implied, without limitation on warranties of merchantability, fitness
for a particular purpose, functionality, data integrity, or accuracy
of results. This report was designed for a wide range of
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complexity and levels of data input.
Carefully review the results of this report prior to using
them as the basis for decisions or investments.
Table of Contents
1 Introduction..................................................................................................................................................
1
2 Summary.............................................................................................................................................................
3
3 Compost Facility Runoff Characteristics...............................................................................
8
4 Regulations...................................................................................................................................................
14
5 Process Water Management Capacity Characteristics
of Composting Methods
17
5.1 Factors that Influence the Water Management Capacities of Composting
Processes
17
5.2 Comparison of Composting Methods.........................................................................................
19
6 Best Management Practices..............................................................................................................
23
6.1 Source Reduction of Process Stormwater Runoff..........................................................
23
6.2 Process Water Recycle.......................................................................................................................
24
6.3 Reuse of Process Water......................................................................................................................
24
7 Management Practice Case Study: Compost Tea (Zoo Broo) Production at Woodland
Park Zoo
25
7.1 Potential Fertilizer Value of Process Runoff....................................................................
25
7.2 Bench Scale Pasteurization
Tests..............................................................................................
29
7.3 Pasteurization Process Alternatives for Woodland Park Zoo............................
34
7.4 Zoo Broo Product Nutrient Testing
Characteristics....................................................
41
7.5 Product Bottling and Distribution...........................................................................................
42
7.6 Zoo Broo Customer Survey...............................................................................................................
43
7.7 Zoo Broo Economics..............................................................................................................................
44
7.8 Zoo Broo Marketing.............................................................................................................................
44
8 Management Practice Case Study: Soos Creek Organics Composting Facility Water
Management Evaluation...............................................................................................................................................................
46
8.1 Calibrating the Energy and Water Balance Model.......................................................
46
8.2 Comparison of Rainfall Management Alternatives.....................................................
47
Appendices: Appendix A: Water
Capture and Evaporation Spreadsheet Model Appendix B: Lab
Reports Appendix C: Survey
Form and Information Sheet Appendix
D: Soos Creek Energy Spreadsheets
and Runoff Mgmt. Alternative
Comparison
List of Tables:
Table
1: Composting Process
Water Management Alternatives Table
2: Major Types of
Pollutants in America's Waterways and Aquifers Table 3: Comparison of Yard Debris Composting
Runoff with Regulation and Other Sources Table
4: Pollutants of Concern
in Leachate as Defined by DOE Table
5: Potential Water
Removal Comparison of Compost Technologies Table
6: Growth and Potassium
Treatment Differences Table 7: N:P:K of Commercial Fertilizer Products
and Woodland Runoff as Packaged and as Mixed Table
8: Market Value of
Commercially Available Organic Fertilizer Products Table
9: Runoff Assumptions
Table
10: Container Dimensions Table
11: Heat Profile Every
15 Minutes Table 12: Propane BTU Calculations Table 13: Fecal Coliform Reduction for Pasteurization
Tests Table 14: Nutrient Content of Woodland Park Compost
Facility Runoff Table 15: Nutrient Comparison Table 16: Economics of the Two Methods of Pasteurization Table 17: Composting Process Water Management Alternatives
List of Figures:
Figure
1: Bench Scale Pasteurization
Temperatures Figure
2: Fecal Coliform Reduction
through Pasteurization Figure
3: Temperature Profile
for In-Pile Pasteurization Test Figure
4: Temperature Profile
for Propane Pasteurization Test Figure
5: Fecal Coliform Reduction
Results
1 Introduction
The purpose of this project
is to evaluate and prioritize methods for compost facilities' management
of rainfall runoff. The runoff
contains contaminants that could cause problems if they migrate offsite. Therefore, compost facilities capture and treat
the runoff before release or reuse.
These techniques often require large amounts of space and are
quite costly. This report
explores and evaluates several methods to reduce, reuse, or recycle
the runoff. Another water source that occurs with some
composting systems – condensate – is not considered in this report.
Two existing compost sites
were used to demonstrate and test these techniques. Soos Creek Organics (Kent, WA) and the Woodland Park Zoo (Seattle,
WA). Soos Creek is a medium-scale
yard debris composter, and the Woodland Park Zoo compost yard produces
Zoo Doo from animal manure and bedding material. Both sites are on the west side of the Cascades,
and therefore are inundated with rain in the fall, winter, and spring.
Neither site is under cover.
The Soos Creek site was used
to examine techniques to minimize the quantity of runoff generated,
and therefore reduce the burden of treatment and disposal. Different feedstocks and composting techniques
generate varying levels of microbial activity, and therefore use different
amounts of water during the process.
The more water that is used by the process, the less runoff
is generated. Different compost
techniques require varying amounts of impervious surface, and therefore
generate vastly different quantities of runoff.
The Soos Creek site was used to develop energy and runoff models,
which show the quantity of runoff generated for a given storm from
different compost technologies. In
addition, management techniques were examined to determine how to
reduce runoff from the site.
The Woodland Park Zoo compost
facility is quite a bit smaller than Soos Creek, but some of the same
concerns exist regarding the runoff.
The Zoo produces a compost product (Zoo Doo) which has a strong
market and public acceptance in Seattle.
At this site, after analysis of nutrient content and testing
following pathogen reduction, the project manager determined that
it might be feasible to produce a compost tea (liquid plant food)
from the runoff. This product (Zoo Broo) could be sold as a companion product to
the Zoo Doo, and in fact might generate a substantial revenue stream. The Zoo made some product and gave it away
at its quarterly compost sale. The
response was quite positive, based on the surveys returned.
2
Summary
This project has revealed that
there are several methods of reducing, reusing, and recycling process
and non-process runoff as well as leachate from compost operations. Modification of operation technique and operating
procedures can eliminate up to 90% of the runoff generated from a
facility. These estimates
are based on the energy and water needs of a system before and after
optimizing the conditions for microbial growth.
This optimization is achieved by:
·
Managing
composting process so that moisture and heat release occur at the
same place in the pile.
·
Manage the
composting process such that evaporated moisture is released to the
atmosphere.
·
Inducing
air in quantities sufficient to evenly distribute oxygen throughout
the pile and remove heat (by evaporating water) when above the temperature
set point.
·
Reducing
pad space by changing pile configuration to extended pile instead
of windrows (with space between).
·
Covering
the compost process areas, and/or:
·
Diverting
rainfall pad water away from the active composting areas, thus preventing
contamination.
In addition to these techniques, this report
also shows that it is feasible to produce a product from the process
runoff and leachate generated at a compost facility.
The runoff, a disposal problem and a costly management burden,
can be treated with heat in order to achieve complete pathogen destruction.
The two trial tests of pasteurization generated results indicating
that the pathogens can be controlled by heat generated within the
pile, and by heat generated from burning propane.
The results also show that re-growth does not occur within
the first three weeks. The product, from the standpoint of pathogens,
is safe for use by consumers.
Summary of Best
Management Practice (BMP) Case Studies
The first case study considers
methods of managing stormwater at the Soos Creek Organics Facility.
Most composting facilities generate runoff, and are faced with high treatment and disposal costs. Applying the principles of waste reduction, reuse and recycling to compost facility runoff management is an elegant solution to a problem currently experienced by many compost facility operators.
The following BMP methods were
evaluated for Soos Creek:
§
Separation of Process Water
and Storm Water on the Composting Pad – Since winter time yard debris quantities are generally reduced significantly,
the option of reducing the operating size of the pad becomes available.
§
Larger volume compost piles – Larger composting piles will do a better job of capturing water because
of increased level surface area.
Larger piles will also do a better job of retaining generated
heat. The expected result would be increased rainfall
capture and evaporation.
§
Larger volume piles with low
rate aeration – Optimum heat utilization
can be achieved by adding a minimal aeration system to the larger
composting piles. The aeration
will provide a continuous supply of air to capture and carry away
the evaporated moisture.
§
Extended Aerated Static Pile
– This established composting
process generates far more energy than needed to evaporate all rain
falling on the surface. It
is considered as a comparison baseline. § Structural Cover – A structural method of reducing process water is to cover the composting area. This prevents the rainfall from contacting the composting material except as desired by the operator.
During this project, a spreadsheet
model was developed to determine the quantity of runoff generated
from different composting technologies and management practices. Application of this model to Soos Creeks situation
indicates that a significant reduction in process water runoff can
be accomplished by seasonally modifying the composting process. The results of the alternative comparison for
that facility are provided on Table 1.
All alternatives have assumed volumes of 15,000 cubic yards
of material on site, and a pile depth of 12 feet.
Table 1 - Composting Process Water Management Alternatives
1large static pile (no aeration) 2extended aerated static pile composting
The second case study involved producing a compost tea product at Seattle's Woodland Park Zoo.
The organic and nutrient content of the runoff was used to develop a valued product. Pathogens in the runoff were treated prior to reuse. This project tested two methods of pasteurization. Lab testing determined that both methods provided complete pathogen destruction.
Pasteurization
Method 1 – Buried Containers - This method uses the residual
heat of the pile to heat and pasteurize the liquid. Containers, if placed in the core of the pile,
were heated to the temperature of the pile core. See the photos below.
The temperatures must exceed
55o C for three consecutive days or 70o C for
30 minutes.
Pasteurization Method 2 – Propane
Burner - The second method of pasteurization
uses a propane burner to heat a 55-gallon drum of process runoff.
The process was heated to 70o C (approximately 158o
F in approximately 100 minutes. The propane required to pasteurize 100 gallons
of process runoff using this method would be approximately 1.1 gallons
of propane. Therefore, fuel
costs for pasteurizing 100 gallons of runoff would be approximately
$1.10.
The compost tea produced in
these tests was bottled and labeled as Zoo Broo. The product was distributed with a survey form at the Fecal Fest
sponsored by the Zoo.
The Zoo Broo drew favorable response from the
test market distribution, and nearly all participants liked the product
and would be willing to pay $6 per gallon.
The test batch of Zoo Broo cost approximately $1.75 per gallon
to make, which indicates a good potential profit margin. This does not even take into consideration avoided cost of having
to dispose of the runoff. The
production of compost tea solves a problem and puts the nutrients
present in the runoff to good use on plants rather than in the surface
waters of the state, where they can cause substantial environmental
damage.
3 Compost Facility Runoff Characteristics
The recycling concepts
of reduction, reuse, and recycling have useful parallels when considering
runoff management. Use of
these concepts in runoff management are best understood in conjunction
with the regulatory framework that differentiates between non-process
stormwater runoff and composting process water based on physical contact
between water and the solid waste feedstocks.
Reduction would therefore involve actions that prevent rainfall
from falling on compost piles or working surfaces where feedstock
residuals are normally present. Providing a structural cover or reducing the
size of the composting area would reduce the quantity of process water. Reuse would involve capturing process water
and using it for moisture control in the composting process. Recycling could take one of three forms. First, by treating process water and discharging
it to the environment, the water becomes part of the hydrologic cycle
along with the other rainfall. Second,
using the heat generated in the composting process, the water vapor
is recycled to the atmosphere to again fall as rain. Third, process water can be treated to produce
a plant growth product.
To discuss the management
of water from a compost facility we need to define the runoff fractions.
The quality of the water and the need for management facilities
differ for each of these fractions. The runoff fractions that should be considered
for a compost facility include:
1.
Stormwater
(non-process) runoff
2.
Leachate
from the composting material
3.
Process stormwater
runoff
Stormwater (non-process) runoff - Stormwater is the moisture
that falls on the compost site but does not have contact with the
compost. Thus, this wastewater
is not contaminated with pathogens or nutrients.
Examples of stormwater runoff includes water from roofs of
structures or water from paved areas, such as parking spaces, where
no compost product or input materials are stored or processed.
In all cases the preferred method of managing this
fraction is to keep stormwater runoff physically separate from the
compost operation. Procedures
for managing this fraction are well established and relatively simple. The objective is to minimize the quantity of water that comes in
contact with the composting operation.
Stormwater is covered by a specific set of regulatory requirements.
Leachate from the composting material - Leachate is free water draining
from a compost pile that has been an integral part of the compost
pile matrix for a sufficient time to solubilize organic and inorganic
compounds. Leachate includes
rainfall that percolates through the pile.
Depending on the feedstock quality, rate of decomposition and
stability of the composting material, the leachate can reach high
concentrations of organic compounds (BOD and COD), nutrients, and
salts. If the feedstock material includes heavy metals,
toxic organics, or pathogenic organisms, these materials can be present
in leachate. Yard debris generally
has relatively low concentrations of heavy metals and toxic organics
but can have pathogenic organisms, such as salmonella, or pathogenic
indicators, such as fecal coliform.
Because compost materials have a large capacity to hold moisture
and evaporate large quantities during the composting process, an operational
objective should be to keep the quantity of leachate produced to a
minimum or none at all.
Process stormwater runoff - This fraction includes any
runoff from the composting site that results from precipitation that
does not flow through the composting mass.
This includes runoff from the pile sides and composting pad
areas adjacent to the piles, including any areas where compost or
input materials are stored or processed, such as tip areas or loading
areas. Equipment wash down water would also be included in this category.
The character of precipitation has a direct effect
on runoff quality and quantity. Runoff
control at compost facilities may be significantly different in Washington's
two primary climate zones. These
zones are the wet temperate climate west of the Cascade mountains
and the dry climate to the east that is relatively hot in summer and
cold in winter. The runoff control solutions for a long wet
winter will likely be different than for the snow melt and thunderstorm
conditions of the east side.
There are many types of pollutants present in America's waterways and aquifers. Table 2 describes the major types of pollutants, their sources, and their effects. These constituents can be considered beneficial or pollutant, depending on where they are in the environment. Generally, organic matter and nutrients (fertilizers) are beneficial in soils but harmful in surface waters when present in high concentrations. Overloading the soils can lead to migration to surface and ground waters, which can, in turn lead to high levels of plant and algae growth. This causes premature aging or eutrophication of bodies of water.
Table 2 - Major
Types of Pollutants in America's Waterways and Aquifers
A previous CWC project entitled
"Evaluation of Compost Facility Runoff for Beneficial Reuse",
describes data gathered to quantify the benefits and potentially
undesirable characteristics of liquid runoff from four different compost
facilities. The facilities
included a very large yard debris and foodwaste composter, a medium
sized yard debris facility, a facility affiliated with a university
composting manures and brush, and a zoo manure compost facility.
Runoff samples from the four facilities were taken during storm
events and normal daily operations. Several parameters were examined in each of
the runoff samples.
That data indicates that the
range of constituents expected for runoff from composting facilities
are as shown in Table 3. Typical
concentration ranges (in mg/L unless noted) for the runoff are compared
to the general permit stormwater benchmark values and to the characteristics
of raw sewage:
Table 3: Comparison of Yard Debris Composting Runoff
with Regulation and Other Source
1 Clean Washington Center Study
entitled "Evaluation of Compost Facility Runoff for Beneficial
Reuse" 2 Stormwater General Permit 1200-Z
(7/22/97). WA DEQ indicates
possible future changes for compost facilities 3 Only for landfills accepting
biosolids and wastewater treatment facilities
It is clear that runoff from
a yard debris composting facilities may require appropriate management
prior to discharge. Discharge
of process water without treatment would have a major negative effect
on surface water quality and fisheries.
There may also be some potential of public health impacts.
Certainly, such a discharge would have an impact on measured
levels of indicator organisms in receiving waters.
In addition, failure to capture the organic and nutrient
content of the runoff is a waste of potentially valuable resources.
By keeping these substances in the compost or diverting to
a separate product, the value of these materials can be realized.
4 Regulations
The purpose of a process or
non-process runoff or leachate treatment system is to transform the
untreated water into an effluent suited for disposal or reuse, such
that the wastewater can be disposed of in conformance with public
health and environmental regulations. The State of Washington Department
of Ecology (DOE) has produced a compost facility resource guideline,
which outlines proper practices for compost facilities in order to
produce a high quality product without creating a nuisance to the
surrounding area. Part of this document is devoted to a discussion
of process runoff and leachate from these facilities. The draft handbook describes regulations for
treating this material in order to allow discharge to the storm sewer
system. The document does
not address reuse, only treatment and disposal.
The DOE defines two types of
water, making the distinction between leachate and stormwater runoff. Leachate, or industrial wastewater, is "water
or other liquid that has been contaminated by dissolved or suspended
materials due to contact with solid waste or gases therefrom"
(Chapter 173-304 WAC). Leachate
is also included in the definition of industrial wastewater in Chapter
173-216 WAC, the State Waste Discharge Program and in Chapter 173-240
Submission of Plans and Reports for Construction of Wastewater Facilities. Runoff from a site is defined as any water that lands on site but
does not come in contact with active compost or mixing piles. Therefore, put simply, leachate touches active
compost and raw materials, stormwater runoff does not. The DOE definition of leachate includes both
leachate and process stormwater runoff, as described in this report,
whereas the definition of stormwater (non-process) runoff, as used
in this report, is identical to the DOE definition.
A compost facility in Washington
State currently has the choice of three regulatory permitting alternatives
to address the leachate (process runoff) generated by their facility.
These three alternatives are:
· National
Pollutant Discharge Elimination System (NPDES)
permit · State Waste
Discharge permit · Zero discharge
(leachate and process water storage)
Table 4 - Pollutants
of Concern in Leachate as Defined by DOE
(DOE Compost Handbook)
The alternative that a facility
will use depends upon the features incorporated into its design. For both the NPDES permit and the State Waste
Discharge permits, the leachate and process runoff water must be treated
before it is discharged. In
addition, the surface and ground water quality standards (Chapter
173-201A WAC and Chapter 173-200 WAC, respectively)
(draft DOE Compost Handbook) must be complied with.
If the leachate is to be discharged to surface water, an NPDES
permit is required, with treatment by All Known Available and Reasonable
Methods of Treatment (AKART). The
DOE makes AKART determinations on a case-by-case basis (draft DOE
Compost Handbook).
If leachate or process water
is to be discharged to a sewage treatment plant or to the ground water,
a State Waste Discharge permit must be obtained.
If the discharge is to a delegated
Publicly Owned Treatment Works
(POTW), a permit is required directly from the treatment facility. A delegated facility is one to which the state
has delegated authority to regulate pretreatment of incoming wastewater.
The DOE must be contacted for a list of these facilities. Land treatment of treated leachate or process
water is an example of discharging to ground water. Soil absorption
is one technique that can effectively treat waste water. Partially treated wastewater is discharged below the ground surface
where it is absorbed and treated by the soil as it percolates to the
groundwater. For example,
in a subsurface soil absorption system, the pretreatment unit should
remove nearly all settleable solids and floatable grease and scum
so that a reasonably clear liquid is discharged into the soil absorption
field. This discharge allows the field to operate more efficiently. Likewise, for a surface discharge system, the
treatment unit should produce an effluent that will meet applicable
surface discharge standards. If
this option is used, an engineering report must be submitted to the
DOE for review and approval.
Zero discharge requires the
containment of all leachate and process runoff water generated at
a facility or the prevention of production of leachate and process
water. This can be accomplished by composting under
a roof or in an enclosed building, or by storing leachate and process
water in a tank or lagoon. Storage
lagoons must be lined with impervious material.
Stormwater (runoff) discharge to surface water or to
the municipal storm sewer must be covered under the Baseline General
Stormwater Permit. This permit
covers stormwater only, not industrial wastewater (leachate and process
water). The purpose of the permit is to incorporate
Stormwater Pollution Prevention Plans into the design of facilities,
to prevent overflow events and contamination
of the surrounding waters.
The DOE Stormwater Unit will assist facility managers in deciding
what stormwater permits are appropriate for their facilities (draft
DOE Compost Handbook). Steps required to get DOE and Health Department
approval for land application as a nutrient reuse technique would
include approval of pre-treatment techniques, nutrient loading expectations,
water balance for the site, and assurance that the pollutants would
not reach surface or ground water.
This type of a reuse will be evaluated on a case-by-case basis.
5 Process Water Management Capacity Characteristics of Composting Methods
5.1 Factors that Influence the Water Management Capacities of Composting Processes
The capacity of a composting facility to manage rainfall
on site depends on the rainfall intensity, feedstock processed, and
composting methods. 5.1.1 Rainfall IntensityClimatic conditions at the composting site together
with regulatory requirements for use of a design statistical rainfall
intensity and duration probability determine the quantity of rain
per unit area that must be managed over a given time period.
For purposes of runoff management, rainfall during the wet
season must be considered in order to provide on-site control. To date, the Washington Department of Ecology has used the 10 year
statistical wet year as the basis for compost facility runoff management. Based on historical correlations of monthly
rainfall distribution, the 10 year return interval peak three month
period would have an estimated rainfall total of 27.9 inches. In other words, looking forward to a wet season
the probability is 9 of 10 that less than 27.9 inches will fall during
the peak three month period. If
the compost facility's runoff management system is designed to handle
27.9 inches of rain, then excess, unmanaged rainfall will probably
occur one year out of ten. 5.1.2 FeedstocksFeedstocks display varying degradation energy levels. Energy is also released at varying rates.
For example, grass is composed of primarily high level of energy
constituents with a high fraction that is quickly degradable while
tree trimmings are also high energy but have a small fraction that
is degradable and a very slow degradation rate. Generally, the quantities and energy levels
of yard debris vary seasonally. Typically,
as winter quantities are reduced, the available degradation energy
is also reduced. The reduced
quantities allow reduction in the composting area from which rainfall
becomes process water. The
reduced degradation energy results in a lower potential for water
evaporation. 5.1.3 Evaporation CapacitySeasonal variations in energy available for evaporation
of water are a known constraint.
In the Pacific Northwest, the peak winter rains occur when
yard debris consists of the lowest energy materials.
The low energy level has increased the challenge for composters
to maintain desirable composting conditions in the piles while controlling
the impact of runoff. 5.1.4 Water Holding CapacityComposting materials have the ability to absorb and
hold quantities of water greater than present upon delivery to a composting
facility. This capacity could
be used to incorporate rainfall moisture in the final product rather
than allowing it to contribute to the site runoff.
However, moisture content is a critical parameter for a number
of factors, including screening.
Overly moist compost sticks to the larger particles during
screening and provides a poor product yield.
Also, the addition of process or leachate moisture to compost
product can result in contamination with undesirable bacterial indicator
organisms. For these reasons, the moisture holding capacity of the material
cannot always be fully utilized for runoff reduction.
Moisture content of final compost is an important factor
for a number of marketing reasons as well. Additional moisture increases the weight of the compost, which increases
transportation costs. Wet
compost is also more difficult to apply, which reduces its value to
the end user. 5.1.5 Volumetric Water Management CapacityA calculation of energy available in yard debris using
the following assumptions indicates that a cubic foot of winter yard
debris has sufficient energy to evaporate 36 pounds of water:
§
90% Volatile
Solids (VS)
§
45% degradable
fraction
§
600 lb./cubic
yard density
§
50% initial
moisture content
§
Sufficient
detention time to release degradable energy
§
6,500 BTU
of energy released / lb of degraded organics
§
1,010 BTU
required to evaporate 1 lb of water
§
Insignificant
energy used to heat solids mass
As will be discussed in the following assessment, by
stacking the piles deeper, the rainfall falling on the pile is decreased
while the energy available to evaporate the rainfall is increased. However, this capability is not useful unless
the water falling on the surface of the pile can be evaporated by
the released energy. Some
composting processes do not effectively accomplish the needed distribution
of water through the pile. These
factors are all important from an operational perspective since they
impact the amount of leachate and/or process runoff produced, which
needs to be treated. They are also important from a compost product
perspective, as a very wet composting mass will not stabilize as quickly
and will produce a lower quality compost in the same time period. 5.2 Comparison of Composting Methods
Site layout determines the relative areas of composting
material and working surface on which rain will fall. This is important because the composting material
has the capability of absorbing rainfall whereas the impervious working
surface converts almost all rainfall into runoff. Since the working surface near composting activity
normally has organic debris that is pulverized by operations traffic,
this runoff carries a load of soluble and suspended organic matter
(i.e., process runoff).
The type of composting process used and the resulting
pile configuration is the primary factor determining the capability
to control site runoff. Appendix
A contains a spreadsheet model analysis of a range of composting processes
used in the Pacific Northwest. Since
rainfall is an areal phenomenon, the runoff management parameters
of interest are also areal. For
example, deeper piles reduce the amount of rainfall on the active
composting area. Deeper piles normally also reduce the associated
impervious surface in aisles and for peripheral pile access. Therefore, the pile depth (mass per area) is
a critical factor. Equally
important is the evaporative energy contained in the feedstock. A deeper pile has more energy per unit area and therefore more evaporative
capacity per inch of rainfall.
Table 5 provides a summary of the analysis results
for typical conditions and for a range of processing technologies. The technologies considered include:
§
Big pile - Large consolidated static
piles with minimal turning and long duration as practiced by GroCo
Inc., Kent, WA and Pacific Topsoils, Inc., Bothell, WA.
Built with stacking conveyors and track dozers.
§
Machine turned windrow (MTW) - Traditional windrow composting
turned frequently with a straddle type machine with rotating drum
mounted flails.
§
Loader turned windrow (LTW) - Windrows formed and turned
infrequently with front end loaders.
§
Extended aerated static pile
(EASP)
- Aerated static piles with insulated exterior surface. Typically formed and broken down with loaders. Temperature controlled by forced aeration. This variation uses the mass bed configuration.
§
Scat turned aerated mass bed
(STAMB)
- Mass bed piles turned with a lifting face/side cast turning device
as practiced by Land Recovery, Inc., Puyallup, WA.
Temperature is controlled by forced aeration. Moisture control is provided during turning.
§
Excavator turned aerated mass
bed (ETAMB) - Same as previous except that piles are deeper and turned with excavators.
This method (although unaerated) is used by facilities in Vancouver,
B.C. and Portland, Oregon.
Table 5 - Potential Water Removal
Comparison of Compost Technologies
The energy of degradation can only be utilized for
evaporation of rainfall if:
1.
Sufficient
moisture is present to allow the microbes to degrade the available
organics.
2.
The rainwater
can be placed in proximity to the energy release.
3.
The evaporated
moisture is removed from the pile without condensing. These factors are highly influenced by the composting
process used. While the big
pile approach has a large amount of energy available, the rainfall
is not distributed through the pile.
The moisture is therefore available neither for maintaining
a moist environment nor for cooling the pile.
The machine turned windrow pile is so spread out that the rainfall
exceeds the capacity of the material for evaporation.
Turning allows only two minutes of air release (volume approximately
equal to pile volume) every three to five days.
The result is over saturation and cooling of the piles such
that the energy is not released efficiently.
Loader turned windrows are an improvement in terms of potential
energy and distribution of the water throughout the pile.
The aerated static pile process is excellent at controlling
and utilizing moisture that falls on the piles but is seldom available
for handling runoff from impervious surfaces due to the static nature
of the system. Aeration is a very effective method of removing
moisture from the composting piles.
Piles are aerated three to five minutes every 15 minutes, and
therefore much higher volumes of
hot steamy air is released.
The turned and aerated mass bed systems provide the optimum
combination of aeration to carry off the evaporated moisture and turning
which provides the opportunity to uniformly add water.
Care must be taken
in the use of runoff for pile moisture control to prevent contamination
of material that has satisfied pathogen treatment standards. Addition of process runoff-derived moisture
or leachate prior to time and temperature controls is the recommended
operating strategy. Also,
use of biofiltration for odor control results in a significant portion
of the evaporated moisture being captured as condensate.
Condensate can be a management issue as significant as process
runoff.
6 Best Management PracticesMost composting facilities could effectively use a
combination of methods for managing
process and non-process rainfall runoff.
Applying the principles of
waste reduction, reuse and recycling to compost facility runoff
management is an elegant solution to a problem currently experienced
by many compost facility operators.
Although a variety of potential solutions have been proposed,
none are capable of fully addressing the technical constraints associated
with stormwater runoff. A blend of strategies as described below can
be adapted to the specific needs of each facility.
6.1
Source Reduction
of Process Stormwater Runoff
The most positive method of control is to prevent rainfall
from coming in contact with feedstock or composting materials. This can be accomplished by constructing a
cover and diverting the runoff to a stormwater management system or
by reducing the operating area upon which contact can occur.
Structural cover is completely effective but expensive.
Temporary covers have also been used but can create problems
by restricting air flow. Temporary covers are only effective if the
water diverted from the pile does not come in contact with material
on the operating surfaces.
During winter the quantity of materials processed normally
declines. The volume reduction
can allow processing on a smaller portion of the operating surface. By providing a curb or some other physical
separation of the pad, it is possible to divert runoff from the separated
area to the stormwater management system, thereby reducing the volume
of process water produced. The
winter operating area could be reduced even more by using a space
conserving composting process during the
winter.
6.2
Process Water
Recycle
Once rainfall has contacted feedstock material it can
be recycled for other uses or reused in the composting process. Recycle options include producing a marketable
product or returning the water to the hydrologic cycle.
6.2.1
Compost Tea
Product
The organic and nutrient content of the process water runoff or leachate can be used to develop a product. An in depth discussion of this option is outlined in Section 7.
6.2.2
Evaporation
Evaporation returns the moisture to the atmosphere
where it will eventually be converted to some form of precipitation. As shown earlier, the material has excess energy
for evaporation provided that it is properly processed to take advantage
of the available energy.
6.2.3
Treatment
and Discharge
Treatment and discharge to surface or groundwater is
another recycling options. Treatment
at the site or at a wastewater treatment facility are available but
potentially costly options. Treatment
requirements may vary depending on the receiving water body but are
in general very stringent. As
new information is developed, regulatory constraints also change;
thus, the treatment process must be very flexible or easily modified
to meet new requirements.
6.3
Reuse of
Process Water
Process water, as well as collected stormwater runoff,
can be used in the early phases of composting as a source of moisture
for the composting process. If
stormwater runoff is collected, it can also be used later in the composting
process without degrading compost quality.
Storage of water can be expensive due to the high seasonal
volume of rain in parts of Washington.
7 Management Practice Case Study: Compost Tea (Zoo Broo) Production at Woodland Park Zoo
7.1 Potential Fertilizer Value of Process Runoff
The process runoff from compost facilities were analyzed
as part of a previous study ("Evaluation of Compost Facility
Runoff for Beneficial Reuse") and was found to have many of the
qualities of conventional fertilizers, as well as commercially available
organic fertilizers. However,
in order to make a product suitable for sale, the runoff must not
have pathogen contamination. Pathogens can be reduced or eliminated through
pasteurization. Pasteurization,
as defined by the EPA for wastewater treatment, is a process by which
the liquid is heated to at least 70o C for a minimum of
30 minutes. When these conditions are met, the liquid is
considered pasteurized and ready for public use. This case study evaluated pasteurization procedures for runoff generated
at the Woodland Park Zoo in Seattle, using two methods of elevating
temperatures:
1.
Container
in the active composting pile.
2.
Heating with
a propane burner.
There are many types of pollutants generated at composting facilties. These constituents can be considered beneficial or pollutant, depending on where they are in the environment. Pathogens (bacteria, viruses, parasites, etc.) present in agricultural return flows, whether from cattle, horses, humans, leaking septic systems, and storm drains make water into which these materials are introduced unsafe for consumption or recreation.
The process runoff and leachate from the Woodland Park Zoo contains extremely high levels of fecal coliform bacteria, which precludes its reuse as a fertilizer product. Fecal coliform is an indicator organism for all pathogenic organisms. High concentrations of pathogens could cause illness if ingested accidentally (from materials on hands, or through children eating soil, etc.). Pathogens can be destroyed through heat processes such as composting or pasteurization, as directed by the EPA.
In a previous CWC funded project ("Evaluation of Compost Facility Runoff for Beneficial Reuse"), the runoff liquid was used in growth trials in comparison to MiracleGro. Table 6 shows a summary of data from these growth trials. The nutrient content of runoff from the four composting facilities varies, but compares favorably to the nutrient content of MiracleGro fertilizer. Potassium levels in the runoff are 5.5 and 2.7 times higher than that of the fertilizer solution Marigolds and radishes were grown to compare bud generation and root growth. Root growth differences were significantly better for the runoff applications. Potassium encourages root growth and increases plant resistance to disease. It produces larger, more uniformly distributed xylem vessels throughout the root system. Xylem vessels are a complete tissue in the vascular system of higher plants, and function chiefly in support and storage. The xylem typically constitute the woody element of the plant. Potassium increases size and quality of fruit and vegetables and increases winter hardiness (Western Fertilizer Handbook, Horticulture Edition, 1985).
Table 6 - Growth and Potassium Treatment Differences
Micronutrients (calcium, magnesium, zinc, etc.) also play a role in the production of flowers in ornamentals and in the development of root systems. Strong production of flowers is recognized as a sign of a balanced nutrient (macro and micro) loading. Growth studies that use compost as a medium have shown strong flower production when compared to other potting mixes, and this has been determined to be affected by the micronutrients present in the compost (Gouin). Because the runoff is from a compost facility, it is likely that there are balanced micronutrients present. Because of budget constraints, the lab analyses performed for this project did not include full micronutrient analysis. Historical data from the large yard debris composting facility gathered before the start of this project indicate the presence of many micronutrients in the process stormwater runoff.
Also, it has been shown that
an unbalanced nutrient loading will push top (green) growth in root
based crops (Gouin). The data
from the growth study shows that in all of the radish groups on which
nutrients were applied, the average root growth and the average green
weights were higher than those for the control.
Furthermore, the plant groups treated with runoff showed increased
root growth over the fertilized group.
This increase indicates that the nutrient balance was more
appropriate for root growth in the process runoff groups than for
the fertilized group. The
better balance is most likely because of the presence of the micronutrients
in the process runoff. In addition to higher levels of potassium and the potential
presence of micronutrients, the runoff might have elevated levels
of humic acids. Humic acids
are present in compost and are known to stimulate shoot and root growth. They consist of organic materials that are
difficult to breakdown. Humic
acids would likely be present in any runoff that comes in contact
with the composting process or the finished product.
Some of the main effects attributed to humic substances on
plant growth are an enhanced germination rate, stimulation of root
initiation, accelerated water uptake, enhanced cell elongation, and
mobilization of microelements (Inbar, Chen, & Hoitink).
The runoff contains nutrients
as well. Limited tests done
to-date indicate that the N:P:K ratio of the runoff from Woodland
Park is approximately 5:1:10 on a dry weight basis.
More testing will be required to determine runoff variability. There are many commercially available organic
fertilizer products. The
concentrations of nutrients in Woodland Park compost runoff compare
favorably to these products. For
example, Alaska Fish Emulsion and MiracleGro crystals are sold in
a concentrated form with instructions for dilution in order to properly
apply nutrients
The directions on the MiracleGro
box indicate that one tablespoon should be mixed with one gallon of
water. Alaska Fish Emulsion
is mixed at a rate of three tablespoons per gallon of water. After mixing, the liquids have the N:P:K ratios (on a wet weight
basis) as shown below in Table 7.
The Woodland Park Zoo runoff, for comparison, is also shown. As can be seen, the runoff, if cleaned of its
pathogen contamination, could be used straight out of the tank on
yard plants, gardens, flowers, etc.
If it is diluted by water at three parts water, one part runoff,
it can be used on most houseplants.
This is based on the most recent nutrient analysis.
Table 7 – N:P:K of Commercial Fertilizer
Products and Woodland Runoff as Packaged and as Mixed
As can be seen above, the process runoff from the Woodland
Park compost facility has many of the qualities of conventional fertilizers,
as well as other commercially available organic fertilizers. This is likely true for numerous other compost
facilities that compost high nitrogen products, such as animal manures
or biosolids, as well. The
pollutant of concern is pathogen contamination.
In order to make a product suitable for sale, the runoff must
be rid of pathogen contamination.
Pathogens can be reduced or eliminated through pasteurization.
Pasteurization, as defined by the EPA for wastewater treatment,
is a process by which the liquid is heated to at least 70o
C for a minimum of 30 minutes. When
these conditions are met, the liquid is considered pasteurized and
ready for public use. This
section describes the results of a bench scale thermodynamic pathogenic
reduction test for the runoff generated at the Woodland Park Zoo.
There are many commercially
available organic fertilizer products.
The retail value of commercially available products are shown
below. As can be seen, the
values are quite high, and the concentrations of nutrients in process
runoff compare favorably. The
values of the five products are shown in the Table 8.
For example, Alaska Fish Emulsion is sold in a concentrated
form with instructions for dilution in order to properly apply nutrients.
Side panel information informs the consumer that the product
contains an N:P:K ratio of 5:l:l, which is diluted for application. The solids content is approximately 18%, and
is sold in half-gallon sizes. The half-gallon plastic jugs sell at
the retail level for $7.99.
Table 8 - Market Value of Commercially
Available Organic Fertilizer Products
7.2
Bench Scale Pasteurization Tests
A small pasteurization unit was used at the Zoo to demonstrate that pasteurization
is a suitable alternative for treating runoff. In order to determine whether the system would
accomplish pathogen destruction, a small bench scale pasteurization
was conducted. Pasteurization,
by EPA’s definition, requires that a contaminated liquid be held at
or above 70o C for a period of at least 30 minutes.
This small bench scale was conducted using a two-gallon kettle
on a small natural gas stove. A
five-gallon bucket of runoff was collected from the runoff containment
basin at the zoo compost facility.
Three sample jars were filled with this material and marked
samples 1-raw, 2-raw, and 3-raw. These samples were placed in a cooler for delivery
to the lab and marked 4-clean, 5-clean, and 6-clean. The two-gallon cooking pot was filled with
runoff from the bucket and placed on the stove burner. Temperatures were recorded as the liquid heated
up to ensure that 70o C was exceeded for at least 30 minutes.
The temperatures achieved and maintained are shown in Figure
1.
The energy (propane) and time required to produce a product for sale for
the runoff was calculated. Table
9 shows the assumptions made regarding the runoff,
the ambient temperatures, heat value of propane, and heat transfer
efficiency. These assumptions
allow for the calculation of propane use, in gallons per hour. Table 10 shows the demonstration container dimensions and R value
of the materials.
Table
9- Runoff Assumptions
Table 10 - Container Dimensions
Table 11 shows the heat profile of the tank every 15
minutes, using the assumptions in Tables 9 and 10. This table shows how long it takes for the liquid to come up to
70o C, and how many gallons of propane is required to do
so. This, in turn, can be used to calculate cost
per gallon of process runoff treated.
Table 11 - Heat Profile Every 15 Minutes
Conductive heat
loss based on surface area, insulation, and ambient/compost temp difference Btu release based
on propane properties and burning efficiency 1 ASHRAE Handbook 1985 Fundamentals
As can be seen in Table 11, 70o C is reached
in just under three hours. This,
plus an additional 30 minutes at 70o C, is the time required
to pasteurize. As can be seen,
100 gallons of runoff can be pasteurized in under four hours by using
approximately one gallon per hour of propane (approximately four gallons
total).
After the desired temperatures were achieved, three samples of the pasteurized
product were bottled and placed in the cooler for delivery to the
lab. Lab results (Appendix
B) indicate extremely high levels of fecal coliform in the raw feedstock
(clean samples; >2,400,000 MPN/100 ml).
The state limit for fecal coliform in fresh surface water used
for water supply or recreation is 43 MPN/100 ml.
After pasteurization, all samples tested out at < 18 MPN/100
ml (>99.999% removal), below the detection limit of 18 for the
test dilution. These results indicate a complete removal of
pathogen contamination in the runoff samples, rendering the product
safe for use. Figure 2 shows
the results, on a logarithmic scale.
This detection limit can be lowered with a different test dilution,
and in future tests the lower detection limit will be obtained.
All "after" results are below detection limit for the test.
Earlier calculations from Section 7 indicate that approximately 975 BTU’s
are required per gallon of runoff to raise the temperature from 10o
C to 75o C and keep it there for 30 minutes to meet pathogen
reduction requirements. Propane
has 90,000 BTU’s per gallon, so approximately 0.03 gallons of propane
is required per gallon of runoff.
The test results for this task indicate that the
product can be pasteurized to treat pathogen contamination. It also appears that the nutrient content is
suitable for application either as it comes out of the pasteurization
unit, or with a 3:1 dilution rate.
These results are based on one grab sample.
These results are quite encouraging, and it looks as if the
product has good potential for reuse.
7.3 Pasteurization Process Alternatives for Woodland Park Zoo
The Woodland Park Zoo Compost Facility is a low tech
composting operation. The
system is essentially a static pile, which is turned with a front-end
loader every two weeks. Zoo
personnel are interested in developing a simple method of pasteurizing
their runoff to produce a product for sale to the public.
In an effort to help the Zoo achieve this goal, E&A recommended
that two methods be tested for ease of operation and for reliability
of pasteurization results. Samples were tested for pathogen reduction
and for nutrient content. This
report describes the two methods tested and the results of those tests.
In deciding what method to test, an effort was made
to use some of the heat generated by the composting process. The Woodland Park Zoo Compost Facility uses
a turned static pile system. The
piles are built and turned every two weeks.
This infrequent turning leaves heat undisturbed in the pile
for two weeks straight. Since
one of the byproducts of the process is waste heat, it would be desirable
to tap this energy source to help heat the liquid for pasteurization. This excess heat can be utilized in one of
two ways to meet EPA pathogen reduction criteria. The first way would be to disturb the piles during the two weeks
of high temperature, place the barrels of process water in the piles,
and monitor the water temperature.
Once the water reaches the 70o C required temperature
for 30 minutes, the barrels can be removed.
The second alternative would be to bury the process water barrels
earlier in the process and allow the piles and the water to reach
55o C for three days, when the barrels can be removed or
left in position until the pile starts to cool down after two weeks
or so.
The second method of pasteurization consisted of setting
up a propane burner under a 55-gallon drum filled with runoff. The temperature of the containerized liquid
was monitored to reach greater than 70o C for 30 minutes. This method is a field test of the bench scale
pasteurization described in the previous section of this report.
7.3.1 Pasteurization Method 1 – Buried Containers
Five barrels (two 15 gallon plastic barrels and three
5-gallon glass jugs) were filled with liquid runoff from the site. Each container was sampled for pathogen analysis.
The two plastic barrels were rigged with an air-bleeding valve,
which was vented out the top of the pile.
One glass jar had a bleeder valve which was routed to a 5-gallon
bucket of water, to create a seal but allow air to bleed up through
the water. Two of the glass
jars were simply sealed tight.
Each container had a thermocouple wire feeding through
the top into the liquid. The
opposite end came out of the barrel through a compression fitting
and out through the top of the pile.
This end of the wire has a two-pronged plug, which is plugged
into a digital temperature meter, allowing for monitoring of the liquid
temperatures. Please see the photos below.
The front-end loader operator placed a one-foot deep
layer of feedstocks on the pavement.
The five containers were placed on the layer of feedstock,
and covered with additional feedstock to a height of five to six feet. The thermocouple wire was fed through a pressure
fitting and out the top of the pile.
Pile temperatures were monitored along with the temperatures
of the liquid in the container. It
was hoped that the temperature of the liquid would exceed 55o
C for three consecutive days. As
can be seen in Figure 3, all five jugs exceeded this time and temperature
relationship, and in fact exceeded 70o C for the thirty
minutes required for pasteurization.
7.3.2 Pasteurization Method 2 - Propane Heater
The second method of pasteurization used is a field
test of the bench scale test performed earlier in the project. A heavy-duty propane burner was set up with
a 55-gallon drum of runoff over it.
A thermocouple wire was inserted into the liquid through the
top, and temperatures were monitored over the course of the heating. The heating data, volume of liquid, and thermodynamics
calculations were used to estimate large scale propane needs and heat
transfer estimates. Please
see the photos of this pilot process below.
The temperature profile is shown in Figure 4.
Figure 4 - Temperature
Profile for Propane Pasteurization Test
The propane burner chosen is rated at 36,000 BTU’s
per hour. Propane provides
approximately 90,000 BTU’s per gallon.
The runoff started at approximately 75o F (24oC),
and was heated to 70o C (approximately 158o
F). One BTU will heat one pound of water one-degree
Fahrenheit. The 55 gallons
of water weighs approximately 458 pounds.
In order to heat 458 pounds of water from 75 to 158o F, approximately 38,000 BTU’s are required.
The length of time that the liquid took to heat to 70o
C was approximately 100 minutes. This means that the heat transfer and loss
efficiency (based on the burner rating of 36,000 BTU’s per hour, 38,000
BTU’s required to heat the water, and 100 minutes to do so) was 60%. A 60% transfer and loss efficiency means that
for this system, 40% more propane is required than the amount calculated
without considering efficiency or loss.
The 38,000 BTU’s required to heat the liquid means that with
losses and transfer efficiency, approximately 53,000 BTU’s are required. Again, propane provides 90,000 BTU’s per gallon,
so this test required 0.6 gallons of propane. The transfer efficiency could be maximized and losses minimized
with shielding of the burner and insulation of the container. This
test was performed without insulation or shielding.
After 70o C was reached, the propane was cut back
substantially.
Table 12 – Propane BTU Calculations
Using these assumptions, the propane required to pasteurize
100 gallons of runoff using this method would be approximately 1.1
gallons of propane. These
results are essentially identical to the pilot study discussed in
Section 7.1.1. Industrial quantities of propane sell for approximately
one dollar per gallon. Therefore,
fuel costs for pasteurizing 100 gallons of runoff would be approximately
$1.10. This is a very small
cost when considering the potential revenues generated from 100 gallons
of product. Survey results (see Section 7.6) indicate that
the product could easily sell for $6 per gallon.
7.3.3 Results of Two Pasteurization Tests
Both pasteurization
tests yielded results showing complete reduction of pathogens.
The tests showed that levels of fecal coliform (the indicator
organism) were very high in the water running off the site.
The results were orders of magnitude higher than the allowable
limit for the surface waters of the state (the state limit for fecal coliform in fresh surface water used for water
supply or recreation is 43 MPN/100 ml).
Table 13 – Fecal Coliform Reduction
for Pasteurization Tests
After the desired temperatures were achieved, three samples of the pasteurized
product were bottled and placed in the cooler for delivery to the
lab. Lab results (Appendix
B) indicate extremely high levels of fecal coliform
in the raw feedstock (as high as 9,200,000 MPN/100 ml). After pasteurization,
all samples tested out at < 2 MPN/100 ml (>99.99998% removal),
below the detection limit of two for the test dilution. These results indicate a complete removal of
pathogen contamination in the runoff samples, rendering the product
safe for use.
At the time of the propane testing, four samples were taken from the containers
with the product of the in-pile pasteurization test. The liquid had been sitting for three weeks,
and no re-growth was seen (all samples were < 2 MPN/100 ml). Figure 5 shows the results, on a logarithmic
scale, of the in-pile pasteurization test, the propane pasteurization
test, and re-growth samples.
Figure 5 - Fecal Coliform Reduction Results
Both of the methods of pasteurization yielded results
indicating that pathogens can be reduced to a level acceptable for
use by the public. The lack
of re-growth indicates complete destruction of the pathogens, despite
a detection limit above zero.
7.4
Zoo Broo Product Nutrient Testing Characteristics
The
product from each of the containers from the in-pile pasteurization
test was sampled and analyzed for nutrients in order to determine
a recommended dosage for use on household and garden plants.
Table 14 contains the nutrient data from the samples.
Table 14 – Nutrient Content
of Woodland Park Compost Facility Runoff
*wet weight analysis
The lab results indicate that the liquid has an average solids content of
approximately 0.3% solids, nitrogen of 0.01%, 0.00% phosphorus, and
0.01% potassium. These percentages
are calculated on a wet weight basis, or as the material appears in
the container. Considering
the percent solids content, Table 14 also shows the dry weight solids
content for N, P, and K.
Several organic material liquid plant food products are available for sale
to the public. Table 15 shows
the nutrient content of the runoff and of each of the organic plant
supplements. The supplements
report N:P:K levels. It is
assumed that these N:P:K levels are for the material as it sits in
the bottle (the labels do not indicate whether this is the case).
The labels also do not indicate a % solids content, so it is
not possible to calculate the nutrient content on a dry weight basis,
which would allow for an accurate even comparison.
The recommended dosages for use on household plants and gardens
are also shown in Table 15.
Table 15 – Nutrient Comparison
Based
on a comparison to the Maxi Crop, which requires one tablespoon per
gallon of water, the recommended dosage for the Zoo Tea will be approximately
one-half cup per gallon of water.
This dilution is less than some of the other products (such
as Alaska Fish Emulsion) but will provide nutrients and organics for
plant growth.
7.5
Product Bottling and Distribution
After completion of the two pasteurization tests and review of the lab test results, the product was bottled for distribution to the public. A label was developed for the pilot project in order to ensure that consumers knew what the bottles contained after bringing them home. The label incorporates graphics currently used in Zoo Doo marketing materials, and also contains dilution instructions for the user.
The majority of the product produced in the two pasteurization tests was bottled for distribution during the fall Fecal Fest (Zoo Doo sale). Eighty gallons were bottled, leaving about fifteen gallons for use on zoo grounds and other projects. Bottles were filled by hand for this test, using a double action barrel pump (available at any hardware stores for $15). Once filled, the bottles were placed back in their boxes and stacked under the Fecal Fest canopy, ready for distribution.
7.6 Zoo Broo Customer Survey
During the fall Fecal Fest at the zoo, the quarterly compost sale of Zoo Doo, the purchasers had the opportunity to take home a one gallon jug of Zoo Broo. Approximately 80 gallons of the product were given away, along with a survey form and a self addressed stamped envelope. The survey was designed to gain information about the consumers impression of the product. There was no attempt to gather plant growth information. It was felt that if we required this information, the surveys would not be returned. The survey form, informational sheet, and a sheet filled out with the average responses are all contained in Appendix C. Overall, the results indicated a very favorable response to the product. Nearly everyone indicated that they would pay $6 per gallon for the product. A few people indicated that the smell was quite bad, but it didn’t seem to diminish their overall opinion of the product. At this printing, 35% of the surveys have been returned.
7.7 Zoo Broo Economics
The test product was produced on a small scale. Still, with the small economy of scale, the
product would produce a large gross profit.
Outlined below are the economics of the two methods of pasteurization.
Capital costs are neglected for this particular test, because
they were insignificant and would be paid for with the first 100 gallon
batch. The propane burner
and tank were approximately $75, the barrels for burying in the pile
were approximately $100. A
one hundred gallon batch of Zoo Broo could yield $600 gross sales.
Table 16: Economics of the Two Methods of Pasteurization
*bottle - $0.58, sticker - $0.05
7.8 Zoo Broo Marketing
Zoo Doo, Woodland Park’s compost product, already has
good product visibility from several years of product marketing. This name recognition will allow Woodland Park
to rapidly introduce a related product.
Because of this, the cost of product marketing would be very
minor as compared to other facilities that might have to spend significant
resources to launch a new product.
Any and all product marketing costs would reduce the revenue
generated by the product producer.
8 Management Practice Case Study: Soos Creek Organics Composting Facility Water Management Evaluation
8.1
Calibrating
the Energy and Water Balance Model
The spreadsheet model developed for this evaluation
uses expected typical values for degradation energy and energy release
rates during the composting process.
Specific operating data from Soos Creek was used to calibrate
the model for the currently used composting process.
The calibrated model was then used to evaluate potential benefits
from using water and energy management techniques.
The model calibration period is October 1998 through
May 1999. During this period,
Soos Creek hauled approximately 2.8 million gallons of process water
from the site at a considerable expense.
During this time, the facility had approximately 15,000 cubic
yards of composting materials on site.
The composting was done in 24 loader turned windrows that were
approximately 30 feet at the base, 150 feet long, and 12 feet high.
The composting energy spreadsheet model (Appendix D)
used to compare the moisture management characteristics of several
composting configurations was adapted for use in evaluating alternatives
for Soos Creek. The nearby
Landsburg station was used as the estimate of rainfall at the site
during the evaluation period. During the period of interest (October 1998
through May 1999) the Landsburg
rainfall was 56.92 inches. This
compares to 43.65 inches for the same period at Sea-Tac Airport. The peak three-month rainfall period was December
1998 through February 1999. During
this period 33.5 inches of rain fell at Landsburg. About 60 percent of the wet season rainfall
fell between December 1, 1998 and February 28, 1999. Assuming that runoff is consistent during the period of interest,
it is estimated that 1,650,000 gallons of process water was generated
and hauled by Soos Creek during December through February, 1999. Using the model to back calculate the energy
utilization that would result in that much process water runoff, it
was estimated that 65% of the energy available from the composting
process was utilized by Soos Creek for evaporation during this period.
8.2
Comparison
of Rainfall Management Alternatives
Several variations in compost processing and site management
were compared for impact on the quantity of process water runoff that
would need to be managed by Soos Creek.
The intent of this evaluation is that Soos Creek would modify
their composting process on a seasonal basis to minimize the generation
of process water runoff. The
alternatives compared include:
§
Separation of Process Water
and Stormwater on the Composting Pad – Since winter time yard debris quantities are generally
reduced significantly, the option of reducing the operating size of
the pad becomes available. A
simple curb across the pad would be used to divert runoff away from
the composting area. The seasonally
separated part of the pad would need to be cleared and swept by late
September in preparation for the rainy season.
§
Larger compost piles – Larger composting piles
will do a better job of capturing water because of reduced slope area. Larger piles will also do a better job of retaining
generated heat. Heat retention
will increase the utilization of available energy. This alternative may reduce movement of oxygen
into the center of the pile and thereby increase the odor potential.
§
Larger piles with low rate
aeration –
Optimum heat utilization can be achieved by adding a minimal aeration
system to the larger composting piles.
The aeration will provide a continuous supply of air to capture
and carry away the evaporated moisture.
The aeration rate must be sufficient to carry the majority
of the moisture out of the pile without re-condensing.
This alternative will also help to control odors.
Low rate aeration will likely result in high temperatures in
the piles.
§
Extended Aerated Static Pile
–
This established composting process generates far more energy than
needed to evaporate all rain falling on the surface.
It is provided as a comparison baseline.
§
Structural Cover – A structural method of reducing
process water is to cover the composting area. This prevents the rainfall from contacting
the composting material except as desired by the operator. This gives a high level of moisture control. Storage facilities may be necessary to allow
utilization of rainfall for composting moisture control.
The results of the modeling evaluation indicate that
significant reduction in process water runoff can be accomplished
by seasonally modifying the composting process.
The results of the alternative comparison for the Soos Creek
Facility are provided on Table 17.
All alternatives have assumed volumes of 15,000 cubic yards
and a depth of 12 feet.
Table 17 - Composting Process Water
Management Alternatives
1large static pile (no aeration) 2extended aerated static pile
composting
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