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ABSTRACT
PYROLYSIS OF AGRICULTURAL WASTE PLASTIC INTO DIESEL AND EVALUATION OF THE CARBONACEOUS BYPRODUCT
AS A SOIL AMENDMENT
High density polyethylene[HDPE] from used drip irrigation tubing was
thermochemically broken down through pyrolysis at 500 °C for 20 minutes in the
presence of a clinoptilolite zeolite catalyst to produce pyrolysis oil and a carbonaceous
byproduct. The pyrolysis oil produced had a melting point of 50 °C, a boiling point of 80
°C, and a flash point of 89 °F. The melting point is higher than that of diesel fuel and the
boiling point and flash point are lower than that of diesel fuel. The high melting point
necessitates preheating before use as a fuel and prevents the pyrolysis oil from being a
direct substitute for diesel fuel. The carbonaceous byproduct, when used as a soil
amendment, increased soil water holding capacity and microbial respiration but had not
effect on cation exchange capacity. Two-percent by weight of carbonaceous byproduct
reduced soil hydraulic conductivity and increased nitrate leaching but lower treatment
levels did not affect soil hydraulic conductivity or nitrate leaching. Amended soil had a
slightly increased pH compared to the control. The properties of the pyrolysis oil can
potentially be improved by using a different catalyst or increasing the pyrolysis reaction
time from 20 minutes to several hours. The carbonaceous byproduct can be used as an
effective soil amendment that improves several important soil characteristics.
Alexis Jackson May 2019
PYROLYSIS OF AGRICULTURAL WASTE PLASTIC INTO DIESEL
AND EVALUATION OF THE CARBONACEOUS BYPRODUCT
AS A SOIL AMENDMENT
by
Alexis Jackson
A thesis
submitted in partial
fulfillment of the requirements for the degree of
Master of Science in Plant Science
in the Jordan College of Agricultural Sciences and Technology
California State University, Fresno
May 2019
APPROVED
For the Department of Plant Science:
We, the undersigned, certify that the thesis of the following student meets the required standards of scholarship, format, and style of the university and the student's graduate degree program for the awarding of the master's degree. Alexis Jackson
Thesis Author
Dave Goorahoo (Chair) Plant Science
John Bushoven Plant Science
William Wright Civil and Geomatics Engineering
For the University Graduate Committee:
Dean, Division of Graduate Studies
AUTHORIZATION FOR REPRODUCTION
OF MASTER’S THESIS
X I grant permission for the reproduction of this thesis in part or in its
entirety without further authorization from me, on the condition that
the person or agency requesting reproduction absorbs the cost and
provides proper acknowledgment of authorship.
Permission to reproduce this thesis in part or in its entirety must be
obtained from me.
Signature of thesis author:
ACKNOWLEDGMENTS
Funding for this thesis was provided in part by a Fresno State Graduate Net
Initiative Graduate Research Grant and a Fresno State Graduate Net Initiative Graduate
Research and Creative Studies Support Award.
I would like to thank my committee members Dr. Dave Goorahoo, Dr. John
Bushoven, and Dr. William Wright for providing their support and lending their expertise
during this journey.
TABLE OF CONTENTS
Page
LIST OF FIGURES ........................................................................................................... vi
STATEMENT OF THE PROBLEM .................................................................................. 1
INTRODUCTION .............................................................................................................. 3
SIGNIFICANCE OF THE PROJECT ................................................................................ 9
OBJECTIVES ................................................................................................................... 10
MATERIALS & METHODS ........................................................................................... 12
Pyrolysis of Agricultural Waste Plastic .................................................................... 12
Evaluation of the Carbonaceous Byproduct as a Soil Amendment .......................... 12
STATISTICAL ANALYSIS ............................................................................................ 15
RESULTS & DISCUSSION ............................................................................................ 16
CONCLUSIONS............................................................................................................... 25
REFERENCES ................................................................................................................. 27
LIST OF FIGURES
Page
Figure 1. Disc infiltrometer used to determine soil hydraulic conductivity. .................... 14
Figure 2a. Melting points of #1 diesel fuel, #2 diesel fuel, pyrolysis oil, and HDPE. ..... 17
Figure 2b. Boiling points of #1 diesel fuel, #2 diesel fuel and pyrolysis oil. ................... 17
Figure 2c. Flash points of #1 diesel fuel, #2 diesel fuel, pyrolysis oil, and HDPE. ......... 18
Figure 3. Mass water holding capacity of soils amended with carbonaceous byproduct ......................................................................................................... 19
Figure 4. pH of fluid vacuum extracted from saturated soil paste made with amended soil. ................................................................................................................... 20
Figure 5. ppm CO2 detected in 100 mL sample taken from respiration chamber. ........... 21
Figure 6. Hydraulic conductivity in cm/s of soils amended with carbonaceous byproduct. ........................................................................................................ 22
Figure 7. mg nitrate that leached through soils amended with carbonaceous byproduct ......................................................................................................... 23
Figure 8. mg NH4 N /L in leachate produced by the ammonium replacement method of determining cation exchange capacity. ........................................................ 24
STATEMENT OF THE PROBLEM
Enormous amounts of plastic are used annually in the United States due to the
affordability and versatility of plastic resins. A total of 34.5 million tons of plastic waste
was generated in the United States in 2015 (U.S. EPA, 2018). 75.4% of those 34.5
million tons were landfilled (U.S. EPA, 2018). Plastic is used extensively in agriculture
due to a wide range of benefits and low cost of plastic resins. The use of plastic in
agriculture experienced a 3-fold increase from 1994-2002, increasing from 521 million
pounds annually in 1994 to 1.678 billion pounds annually in 2002 (Hurley, 2008). Plastic
is typically used for drip irrigation tubing, plastic mulch, fertilizer and pesticide
containers, nursery seedling trays, silage covers, fruit bins, grain storage bags, and baling
twine. A survey of 215 California farms with gross incomes exceeding $100,000 annually
found a total of 2.57 million pounds of plastic was used on a yearly basis (Hurley, 2008).
The global market for agricultural plastic film alone was worth $5.87 billion in 2012 with
mulching and greenhouse use accounting for 85% of the market (Transparency Market
Research, 2013).
A large majority of this plastic is not recycled due to a myriad of obstacles
including high transportation costs, tonnage and cleanliness requirements imposed by
recycling centers, and lack of nearby recycling centers willing to accept agricultural
waste plastics (Hurley, 2008). The difficulty of transporting waste plastics is exacerbated
by the bulky nature of the plastics and the challenge of compressing plastics into a form
that is easier to transport (Goldy, 2005). Commercial balers experience difficulty when
baling waste plastics; plastic frequently becomes caught on any protrusions and belts
break under the weight of the plastic (Goldy, 2005). Additionally, the supply of
agricultural waste plastics is irregular with a majority of plastics disposed of during
narrow periods of time (Hurley, 2008). Farmers in areas where recycling facilities are
2 2
available frequently must wait in long lines to drop off their plastics (Hurley, 2008).
Recycling of agricultural waste plastics in California ranged from 13% among melon
growers to 46% among nurseries (Hurley, 2008).
Agricultural plastic waste currently is economically unfeasible to recycle for a
majority of farmers. It was economically unfeasible to mix agricultural waste plastics
with recycled juniper to make fuel cubes (Jaeger, 2006). It was also economically
unfeasible to use baling twine as a fuel source, as a component of rubber composite
shingle, or as a reinforcing agent in concrete (Randall Conrad and Assoc. Ltd., 2000).
Disposal in landfills remains the most common way of handling agricultural plastic waste
(Hurley, 2008).
INTRODUCTION
Plastics are derived from petroleum which is the same material that gasoline and
diesel fuels are derived from. Plastics and fuels like diesel are both composed of
hydrocarbons. The primary difference between plastic and diesel is the length of those
hydrocarbons. Diesel hydrocarbons are 12-25 carbons in length (Auxilio et al., 2017)
whereas hydrocarbons found in plastics can be thousands of carbon atoms in length.
Pyrolysis is a thermolytic breakdown of organic matter in the presence of high
temperatures and an anaerobic environment. Pyrolysis can be used to break hydrocarbons
down into hydrocarbons with shorter molecule lengths. This process can convert the
hydrocarbons found in plastic into shorter chain hydrocarbons mimicking those found in
gasoline and diesel fuel (Wongkhorsub and Chindaprasert, 2013). There are several
methods of pyrolysis including thermal reactors (Auxilio et. al., 2017), microwave
induced pyrolysis (Khaghanikavkani et al., 2013), and plasma arc pyrolysis (Puncochar et
al. 2012). Pyrolysis of plastic produces fluid products (oil vapor and gas) and a solid
residue. The products of pyrolysis vary greatly depending on the type of plastic used as
feedstock, the type of catalyst used, and the temperatures the plastic was exposed to
during pyrolysis (Hamidi et al., 2013). Kumar et al. (2015) found that pyrolysis of linear
thermoplastic polymers produced straight chain hydrocarbons. Pyrolysis oil can contain
hydrocarbons ranging from C5-C80 (Almeida and Marques, 2016). Pyrolysis of low
density polyethylene [LDPE] and high density polyethylene [HDPE] in a batch reactor
with the catalyst HZSM-5 produced 70.7% and 72.6% gas respectively (Marcilla,
Beltran, and Navarro, 2009). Pyrolysis of HDPE in a fixed bed reactor for 2 hours and 40
minutes produced 38.5% pyrolysis oil at 330 °C and 76% pyrolysis oil at 425 °C (Khan et
al., 2016). This liquid fuel oil produced from pyrolysis of HDPE at 330 °C-490 °C was
within all ASTM D975 diesel fuel specifications (Khan et al., 2016). Pyrolysis of
polyethylene and polypropylene in an autoclave pyrolysis reactor at 300 °C – 500 °C for
4 4
3 hours produced 60%-80% pyrolysis oil and 5%-10% carbonaceous residue
(Wongkhorsub and Chindaprasert, 2013). This pyrolysis oil contained a mixture of C10-
C30 hydrocarbons (Wongkhorsub and Chindaprasert, 2013). Pyrolysis can be carried out
at temperatures ranging from 300 °C – 900 °C with higher temperatures decreasing the
formation of hydrogen, methane, aromatic compounds, and acetylene (Donaj et al.,
2012). However, higher pyrolysis temperatures increase the proportion non-condensable
gas produced (Scheirs, 2006). Catalysts can exert substantial influence on the
composition of the final product of pyrolysis of waste plastic. A large array of catalysts
have been used including silica-alumina, zeolites, AlCl3, alumina and FCC catalysts,
nanocrystalline zeolites, mesostructured catalysts like MCM-41, and fused metal
tetracloroaluminatos (Almeida and Marques, 2016). Zeolitic and clay based catalysts with
higher acidity and surface area were selective for gasoline fraction hydrocarbons (Auxilio
et al., 2017). Catalysts with higher acidity and surface area produced lower levels of
olefins and higher levels of aromatics (Auxilio et al., 2017).
A carbonaceous residue is a byproduct of pyrolysis (Hamidi et al., 2013) and this
carbonaceous residue may have properties similar to biochar, a carbon-rich product
produced from pyrolysis of biomass that is often used as a soil amendment. Biochar is a
material produced through thermal degradation of organic matter in the absence of
oxygen. Biochar can be produced from any organic material including corn stover, rice
hulls, woodchips, and biosolids. Biochar is differentiated from charcoal by application to
soil. Charcoal is not typically used as a soil amendment and is instead used as a fuel.
Biochar improves many aspects of soil and has a variety of other benefits besides
improving soil. Biochar reduces nitrous oxide and ammonia emissions from soil,
improves plant productivity, improves soil structure, and improves nutrient retention
(Mandal et al., 2016).
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Terra preta is an anthropogenic deposit of dark soil created by indigenous farmers
in the Amazonian basin. Terra preta is much more fertile than the surrounding soils
which are typically infertile Arenosols, Ferralsols, Acrisols, and Lixisols (Glaser, 2006).
Terra preta is created through large additions of charcoal, broken pottery, plant material,
manure, and bones (Glaser, 2006). Organic carbon in terra preta is very stable. Terra
preta deposits were created in pre-Columbian times with some deposits reaching 7,000
years of age (Glaser, 2006). Terra preta contains seventy times more charcoal than
surrounding soils and three times more organic matter, nitrogen, and phosphorus than
untreated soils (Glaser, 2006). Terra preta soils on average yield twice as much as
untreated soils (Glaser, 2006). The high productivity of terra preta soils is due to the very
high content of biochar in the soil that averages 50 Mg ha−1 m−1 (Glaser, 2006).
Approximately 1,824 billion tons of organic carbon are stored in the first meter of
soil and about 3,012 billion tons within the first two meters (Sanderman et al., 2017).
Loss of organic carbon from the top 2 m of soil due to human activities is estimated at
about 133 billion tons with the rate of loss accelerating over the last two centuries
(Sanderman et al., 2017). Loss of organic carbon leads to problems like degraded soil
structure and yield loss. Adding biochar to soil sequesters carbon from the atmosphere in
a stable form that does not readily mineralize back into CO2. Carbon dioxide levels in the
atmosphere have been rising and the rate of increase in those carbon dioxide levels has
also been rising. Global carbon dioxide emissions for 2018 increased 2.7% over global
carbon dioxide emissions for 2017 and reached a record high (Le Quere et al., 2018). The
concentration of carbon dioxide in the atmosphere has increased from 277 parts per
million in 1750 to 405 parts per million in 2017 (Le Quere et al., 2018). This rapid
increase in the carbon dioxide content of the atmosphere is believed to be causing
harmful climate change that could potentially cause enormous economic losses and
trigger mass human migration as regional rainfall patterns shift and sea levels rise.
6 6
Biochar could be used to sequester carbon while reversing a centuries-long trend of
carbon loss from soil due to human activities.
Soils amended with biochar have an increase in surface area due to high levels of
micropores in biochar (Lone et al., 2015). Amendment with biochar also improves cation
exchange capacity, water holding capacity, and hydraulic conductivity while
simultaneously reducing soil tensile strength (Lone et al., 2015). This reduction in soil
tensile strength allows better root penetration though soil. Biochar produced from poultry
manure increased the availability of Mn, P, Cu, and Zn when added to soil (Inal et al.,
2015). Beans grown in soil amended with biochar and processed poultry manure had
higher concentrations of Ca, Fe, Zn, N, P, K, Cu and Mn (Inal et al., 2015). Soil amended
with the same processed poultry manure and biochar increased the Zn, Cu, Mn, N, P, and
K levels of corn (Inal et al., 2015). Shoot dry weight and plant uptake of K and N
increased after biochar application in komatsuna, a Japanese leaf vegetable in the
Brassicaceae family (Zang Oo et al., 2018). Biochar drastically increases the availability
of certain nutrients critical to plant growth and this results in better uptake by plants and
higher yields.
Amendment with biochar reduces nitrous oxide (N2O) emissions from soil (Zang
Oo et al., 2018). Biochar reduces N2O emissions by decreasing the relative abundance of
nitrate-oxidizing and ammonia-oxidizing bacteria in soil (Liu et al., 2014). Biochar also
has an alkalizing effect on soil which increases the production of N2 and reduces the
production of NO and N2O (Obia et al., 2015). Nitrogen oxides (NOx) are major air
pollutants that react to form particulate matter and smog. High levels of NOx lead to acid
rain which is deleterious to both plant and fish life and damages stone buildings.
Retaining nitrogen in soil by reducing N2O emissions reduces the need for nitrogen
fertilizers. Nitrous oxide is also a potent greenhouse gas and reducing N2O emissions
will be beneficial for mitigating climate change.
7 7
Biochar provides substrate for microbial activity and this heavily alters the soil
biota in amended soils. Soils amended with biochar have higher levels of microbial
biomass and faster rates of microbial growth (Glaser, 2006). Biochar produced from
woody materials retains an internal layer of bio-oil that functions like glucose for
increasing microbe growth (Lone et al., 2015). Some arbuscular mycorrhizal and
ectomycorrhizal fungi increase in the presence of biochar (Lehmann et al., 2006). This
increase in beneficial arbuscular mycorrhizal fungi may be a driving factor behind the
increased availability of Zn, P, Mn, and Cu in biochar amended soils. The effects on
microbial activity are still seen in terra preta soils where the biochar was added hundreds
or even thousands of years ago (Glaser, 2006). Biochar may reduce pathogen presence in
the soil by increasing beneficial microbe populations. Biochar additions to soil decreased
the relative abundance of gram-negative bacteria and fungi decreased (Lehmann et al.,
2006). Additionally, gram-positive anaerobic bacteria increased in abundance (Lehmann
et al., 2006).
Biochar can form complexes with heavy metals through adsorption (Tan, Liu, and
Xiao, 2018). This reduces the availability of the heavy metals and mitigates the
deleterious effects of heavy metal contamination of soils. Organic pollutants are also
reduced in biochar amended soils (Lone et al., 2015). This can be detrimental by reducing
the efficacy of pesticides. The sorption ability of biochar can exceed the sorption ability
of natural soil organic matter by a factor of 10-100 (Lone et al., 2015). The sorption
ability of biochar is highly dependent on feedstock and temperature at which the biochar
was produced. High temperatures tend to produce more surface area but lower levels of
amorphous organic matter (Tan, Liu, and Xiao, 2018).
Unfortunately, the mechanisms by which biochar improves soil are poorly
understood. Biochar addition to soil had generally been found to be beneficial but the
results of studies can be inconsistent (e.g. biochar produced from woody materials has a
8 8
much more pronounced effect than biochar produced from grass) (Lone et al., 2015). The
extremely wide definition of biochar also adds to the inconsistent results. Biochar
produced from widely different feedstocks ranging from human feces to woody biomass
produced under widely different conditions ranging from low temperature smoldering to
fast pyrolysis at over 1000 F is all lumped under the same umbrella term of biochar. The
complex interactions between soil microbes, crops, and their environment are also poorly
understood. General trends in soil microbial populations can be ascertained but the exact
interactions occurring in the soil are elusive. The beneficial properties of biochar have
been strongly supported by a large body of evidence. Both biochar and the carbonaceous
byproduct of pyrolysis of waste plastic are rich in carbon and are produced through
pyrolysis. The carbonaceous byproduct of pyrolysis of waste plastic may have properties
similar to biochar.
SIGNIFICANCE OF THE PROJECT
Farmers have indicated in surveys that offering on-farm pickup of waste plastics,
easing cleanliness and tonnage requirements, and offering more recycling facilities would
encourage them to recycle their waste plastics (Hurley, 2008). Farmers travel an average
of 10.6 miles to dispose of waste plastics but would be willing to drive 150% farther if
recycling their plastic was offered for free (Hurley, 2008). Strawberry growers spent $16-
$18 per acre on landfill disposal fees but California farmers would be willing to pay an
average of $91 per ton for on-farm pick up for recycling (Hurley, 2008). This evidence
indicates there is substantial interest in recycling of agricultural waste plastics and that
farmers are willing to spend more than they currently do to dispose of plastic waste.
Pyrolysis of waste plastic can be carried out on mixes of different plastic resins and can
be carried out on a small scale. Plastics do not need to be cleaned or sorted prior to
pyrolysis. Due to this, pyrolysis does not necessitate the cleanliness and tonnage
requirements that traditional recycling imposes. Pyrolysis facilities can be much smaller
than traditional recycling facilities due to the small amount of material required for
pyrolysis and small pyrolysis units can be transported. The mobility of small pyrolysis
units allows a single unit to process plastic from multiple plastic drop-off sites and even
allows on-farm pyrolysis of waste plastics. Multiple plastic drop-off points and on-farm
pyrolysis mitigate the challenge of transporting waste plastics for recycling. Pyrolysis has
been successfully used to produce liquid oils that can safely be used in diesel engines
(Wongkhorsub and Chindaprasert, 2013). Pyrolysis has the potential to convert over a
billion pounds annually (Hurley, 2008) of non-recyclable agricultural plastic waste into
fuel while also generating a beneficial soil amendment, similar to biochar, as a byproduct.
OBJECTIVES
The objectives of this research project are:
1. Determine the physical or chemical properties of liquids derived from pyrolysis of
agricultural waste plastic that are relevant for use as a potential fuel.
Null Hypothesis: There are no differences between the physical or chemical
properties of the liquids derived from pyrolysis of agricultural waste plastic and
the ASTM standards for diesel fuel.
2. Determine the effects, as a soil amendment, of the carbonaceous byproduct
remaining after pyrolysis of agricultural waste plastic. The effects on soil water
holding capacity, soil pH, cation exchange capacity[CEC], hydraulic conductivity,
and microbial respiration are determined.
Null hypotheses: Carbonaceous byproduct derived from pyrolysis of agricultural
waste plastic has no effect on soil pH.
Carbonaceous byproduct derived from pyrolysis of agricultural waste plastic has
no effect on soil cation exchange capacity.
Carbonaceous byproduct derived from pyrolysis of agricultural waste plastic has
no effect on soil water holding capacity.
Carbonaceous byproduct derived from pyrolysis of agricultural waste plastic has
no effect on soil microbial respiration.
Carbonaceous byproduct derived from pyrolysis of agricultural waste plastic has
no effect on soil hydraulic conductivity.
11 11
3. Determine the effects of the carbonaceous byproduct on nitrate leaching if enough
of the carbonaceous byproduct is produced.
Null hypothesis: Carbonaceous byproduct derived from pyrolysis of agricultural
waste plastic has no effect on nitrate leaching.
MATERIALS & METHODS
Pyrolysis of Agricultural Waste Plastic
A custom device capable of maintaining the high temperatures and anaerobic
environment necessary for pyrolysis was designed and fabricated. Used drip irrigation
tubing was obtained from commercial agricultural operations. 350 g of used drip
irrigation tubing was placed into the pyrolysis device and 1 g of clinoptilolite zeolite
catalyst added. The pyrolysis device was then sealed. The pyrolysis device was heated to
940 °F (500 °C) and the waste plastic allowed to break down for 20 minutes. The
pyrolysis device was then allowed to cool to temperatures safe for handling. A sample of
the liquid products of the pyrolysis was taken. Any carbonaceous residue remaining in
the pyrolysis device was collected for evaluation as a soil amendment. The pyrolysis
device was cleaned of any solid or liquid residues and another 350 g of plastic and 1 g of
zeolite catalyst placed into the pyrolysis device. The cycle of adding plastic, heating,
sampling, and cleaning was repeated 10 times. All liquid samples were sent to a fuel
analysis laboratory for analysis of melting point, boiling point, and flash point.
Evaluation of the Carbonaceous Byproduct as a Soil Amendment
Sandy loam soil was collected from the CSUF campus. The carbonaceous
byproduct was mixed with the sandy loam soil at rates equivalent to 0.1%, 0.5%, and 2%
by weight of the carbonaceous byproduct.
1. The water holding capacity of the amended soil was measured by adding
water to a known mass of amended soil to form a saturated paste and allowing the soil to
equilibrate for 24 hours. The saturated soil was weighed and then dried at 105 °C for one
week. The dry soil was weighed and the amount of water lost recorded.
2. The pH of the amended soil was measured by moistening amended soil to
field capacity and allowing to soil to sit in an open container for 20 days. This allowed
13 13
long-term effects on pH to potentially be detected. After 20 days a saturated paste was
made from the soil and fluid from 150 g of saturated soil was vacuum extracted. The pH
of the extracted fluid was measured using a pH probe.
3. Soil microbial respiration was determined by moistening the amended soil
to field capacity and waiting 24 hours. After 24 hours, a 50 g portion of soil was
transferred to a 6 in diameter 5 in tall cylindrical chamber. The cylindrical chamber was
sealed with a lid with rubber stoppers and CO2 allowed to accumulate for 30 minutes at a
temperature of 26 Co. The CO2 produced by soil microbial activity was then measured
using a Draeger tube apparatus as described by Soil Quality Institute (2001).
4. A disc infiltrometer was used to determine hydraulic conductivity of the
amended soil. A 250 mL beaker was filled with amended soil and a disc infiltrometer
placed flat on the surface of the soil (Figure 1). The disc infiltrometer was set to a suction
of 2 cm and water flows from the disc infiltrometer into the soil. Water level readings are
taken every 30 seconds for 300 seconds. The hydraulic conductivity of the soil was
calculated using the method in Zhang (1997).
5. The effects of the carbonaceous byproduct on nitrate leaching was
determined by lining a funnel with filter paper and placing 40 g of amended soil into the
funnel. 40 mL of a 20 ppm nitrate solution was applied to the soil. The fluid was allowed
to percolate through the soil until no more liquids dripped from the funnel. All fluid that
percolated through the soil was collected. The solutions that percolated through the soil
were filtered through filter paper and the nitrate content of the solutions determined using
an AQ2 Discrete Analyzer. The filter paper used to filter the solution was weighed to
determine the mass of solution retained by the filter paper. The total amount of nitrate in
the solutions retained by the filter paper and the solutions that percolated through the soil
was determined.
14 14
6. Cation exchange capacity was determined using the ammonium
replacement method in Gavlak, Horneck, and Miller (2005).
Figure 1. Disc infiltrometer used to determine soil hydraulic conductivity.
STATISTICAL ANALYSIS
Pairwise T tests were used to determine any statistically significant differences
between untreated soil and soil amended with carbonaceous byproduct.
RESULTS & DISCUSSION
Pyrolysis of HDPE drip irrigation tubing produced 8% carbonaceous byproduct
and 63% pyrolysis oil. The pyrolysis oil was a solid, waxy substance at room
temperature. This is consistent with pyrolysis oil produced from polyethylene and
polypropylene that was separated from municipal waste (Wongkhorsub and
Chindaprasert, 2013). The pyrolysis oil had a melting point of 50 °C, a boiling point of
80 °C, and a flash point of 89 °F. HDPE used as feedstock to produce the pyrolysis oil
has a melting point of 125 C and a flash point of 645 F (National Pipe & Plastics Inc.,
2011). #1 Diesel fuel has a melting point of -20 °C, a boiling point of 150 °C and a flash
point of 125 °F (Citgo Petroleum Corporation, 2018a). #2 diesel fuel has a melting point
of -30 °C, a boiling point of 282 °C, and a flash point of 125 °F (Citgo Petroleum
Corporation, 2018b). The flash point and boiling point of the pyrolysis oil is lower than
in #1 or #2 diesel fuel (Figures 2c and 2b) but the melting point is higher than in #1 or #2
diesel fuel (Figure 2a). The high melting point renders the pyrolysis oil solid at room
temperature whereas diesel fuel is liquid at room temperature. The flash point of the
pyrolysis oil also falls below the legal minimum of 100 °C for #1 diesel fuel. The solid
nature of the pyrolysis oil at room temperature necessitates preheating before use in an
engine and prevents direct use of the pyrolysis oil as a substitute for diesel fuel.
Khan et al., 2016 successfully produced pyrolysis oil that met ASTM standards
for diesel fuel. Khan et al., 2016 used a fixed bed pyrolysis reactor and a reaction time of
160 minutes. The longer reaction time produced shorter chain hydrocarbons that were
liquid at room temperature. A reaction time of 20 minutes produced hydrocarbons that
were solid at room temperature. Some catalysts are selective for a specific fraction of
hydrocarbons (Auxilio et al., 2017). A catalyst that is highly selective for diesel-fraction
hydrocarbons can be used to produce pyrolysis oil that meets ASTM diesel fuel
standards.
17 17
Figure 2a. Melting points of #1 diesel fuel, #2 diesel fuel, pyrolysis oil, and HDPE.
Figure 2b. Boiling points of #1 diesel fuel, #2 diesel fuel and pyrolysis oil.
0
50
100
150
200
250
300
Diesel #1 Diesel #2 Pyrolysis Oil
De
gre
es
C
Boiling Point
Boiling Point (Celsius)
18 18
Figure 2c. Flash points of #1 diesel fuel, #2 diesel fuel, pyrolysis oil, and HDPE.
Biochar is a close analogue of the carbonaceous byproduct. Biochar is produced
through pyrolysis of biomass. The carbonaceous byproduct is produced through pyrolysis
of plastic waste. Biochar, when used as a soil amendment, increases soil water holding
capacity (Lone et al., 2015). Biochar has a very high surface area and the high level of
microporosity gives biochar its beneficial properties like increasing soil water holding
capacity (Lone et al., 2015).
Soils amended with as little as 0.1% of carbonaceous byproduct by weight
experienced a statistically significant increase in mass water holding capacity (P<0.01).
Amendment with 0.1% carbonaceous byproduct increased water holding capacity by 5%
and amendment with 0.5% carbonaceous byproduct increased water holding capacity by
18% compared to the control (Figure 3). The 0.5% and 2% treatment levels had greater
water holding capacity than the 0.1% treatment level (P<0.05). Yu et al., 2017, found that
soil water holding capacity is proportional to the amount of biochar added to soil. The
carbonaceous byproduct behaved very similar to biochar and increased water holding
capacity. Larger increases in water holding capacity were observed after larger
0
100
200
300
400
500
600
700
Diesel #1 Diesel #2 Pyrolysis Oil HDPE
De
gre
es
F
Flash Point
Flash Point (F)
19 19
incorporations of carbonaceous byproduct; the 0.5% and 2% treatment levels had a
significantly higher water holding capacity than the 0.1% treatment level.
Figure 3. Mass water holding capacity of soils amended with carbonaceous byproduct
Soil amended with carbonaceous byproduct can retain more water and this can
improve productivity in dryland farming systems by retaining more moisture from
rainfall (Jeffrey et al., 2011). Biochar application to soils resulted in a mean yield
increase of 10% (Jeffrey et al., 2011). The similar properties of biochar and the
carbonaceous byproduct indicate that the carbonaceous byproduct may have a similar
positive effect on yields when used as a soil amendment.
The 0.5% and 2% treatment levels had a statistically significant increase in pH
compared to the control and 0.1% treatments (Figure 4). Biochar has an alkalizing effect
on soils (Obia et al., 2015) and the carbonaceous byproduct had a similar effect. This
alkalizing effect reduces the amount of N2O and NO produced by soil (Obia et al., 2015).
Soil pH affects the availability of nutrients in the soil and excessively acidic (pH<5) soils
negatively impact yield (Brown et al., 2008). The alkalizing effect of the carbonaceous
A
B
CC
12.5
13
13.5
14
14.5
15
15.5
16
16.5
17
17.5
Control 0.1% 0.5% 2.0%
% M
ass
Wat
er
Co
nte
nt
Mass Water Content %
Mass Water Content
20 20
byproduct increases the pH of soils and could potentially increase crop yields when used
as an amendment in acidic soils.
Figure 4. pH of fluid vacuum extracted from saturated soil paste made with amended soil.
Soils amended with biochar have higher levels of microbial biomass and faster
rates of microbial growth (Glaser, 2006). Biochar has a high surface area and provides a
substrate for microbial activity. Soil amended with 2% by weight of carbonaceous
byproduct had significantly higher microbial respiration than untreated soil (P<0.001).
Soil amended with 2% carbonaceous byproduct produced 64% more CO2 than the control
treatment (Figure 5). Soils amended with 0.1% or 0.5% carbonaceous byproduct did not
have any statistically significant change in microbial respiration compared to the control.
Microbial respiration is an indirect indicator of soil health and beneficial arbuscular
mycorrhizal and ectomycorrhizal fungi increase in the presence of biochar (Lehmann et
al., 2006). Arbuscular mycorrhizal and ectomycorrhizal fungi increase the availability of
essential plant nutrients including phosphorus (Mcgonigle and Murray, 1996). The
carbonaceous byproduct had a beneficial effect on soil microbial respiration. The
AA
BB
6.5
6.6
6.7
6.8
6.9
7
7.1
7.2
7.3
7.4
7.5
Control 0.10% 0.50% 2%
pH
pH
21 21
carbonaceous byproduct may have a beneficial effect on the relative abundance of
beneficial soil microbes due to the similarity between the carbonaceous byproduct and
biochar.
Figure 5. ppm CO2 detected in 100 mL sample taken from respiration chamber.
The carbonaceous byproduct was hydrophobic in nature. The carbonaceous
byproduct readily adhered to skin but could not be washed off, without soap. Amendment
with 2% by weight of carbonaceous byproduct reduced soil hydraulic conductivity by
40% (P<0.05). Lower treatment levels, 0.1% and 0.5%, did not adversely impact soil
hydraulic conductivity (Figure 6). The adverse effect on soil hydraulic conductivity may
be related to the hydrophobic properties of the carbonaceous byproduct. Freshly made
biochar is hydrophobic but oxidation by air and water make the surface of biochar
hydrophilic over time (Basso et al., 2012). The carbonaceous byproduct used in this study
was stored in airtight plastic bags and was exposed to minimal water and air. These
storage conditions minimized oxidation of the carbonaceous byproduct. Oxidation may
make the carbonaceous byproduct hydrophilic. A hydrophilic carbonaceous byproduct
A A A
B
0
100
200
300
400
500
600
700
800
900
Control 0.10% 0.50% 2%
PP
M C
O2
Microbial Respiration
ppm CO2
22 22
may increase soil hydraulic conductivity. Soils with low hydraulic conductivity, like
soils with a high sodium absorption ratio (Oster et al., 1999), suffer from poor water
infiltration. Improving soil hydraulic conductivity improves water infiltration.
Figure 6. Hydraulic conductivity in cm/s of soils amended with carbonaceous byproduct.
Amendment with carbonaceous byproduct did not affect the amount of nitrate
leaching from the soil at the 0.1% and 0.5% treatment levels (Figure 7). Amendment with
2% carbonaceous byproduct increased nitrate leaching by 5.6% compared to the control
(p<0.01). Nitrate leaching results in nitrate contamination of groundwater and excessive
intake of nitrate can adversely affect human health (Harter et al., 2012). The
carbonaceous byproduct was expected to reduce nitrate leaching. Biochar can reduce
nitrate leaching (Yao et al., 2012) and increases nitrogen use efficiency of crops (Chan et
al., 2007) when used as a soil amendment. However the properties of biochar vary
depending on the feedstock and temperature at which the biochar was manufactured.
Biochar made from Brazilian pepperwood reduced the amount of phosphate leaching
from a sandy soil but biochar made from peanut hulls increased phosphate leaching from
A
AA
B
0
0.0002
0.0004
0.0006
0.0008
0.001
0.0012
Control 0.10% 0.50% 2%
cm/s
Soil Hydraulic Conductivity
Soil HydraulicConductivity
23 23
sandy soil (Yao et al., 2012). Biochar made from switchblade grass can hold 450% of its
weight in water and biochar made from hemlock can hold 270% of its weight in water
(Yu et al., 2017). Biochar produced at temperatures ranging from 250 ºC – 750 ºC
increased soil water holding capacity from 7%-16% (Novak et al., 2009).A higher water
holding capacity reduces nitrate leaching by retaining water and nitrate dissolved in the
water.
Figure 7. mg nitrate that leached through soils amended with carbonaceous byproduct
Elemental analysis of the carbonaceous byproduct was not within the scope of this
research. The carbonaceous byproduct may have contained nitrogenous compounds that
falsely inflated nitrate readings. The exact interactions between the carbonaceous
byproduct and the soil matrix were beyond the scope of this research. This makes it
difficult to determine the exact mechanisms responsible for the increase in nitrate
leaching.
The carbonaceous byproduct did not significantly alter soil cation exchange
capacity (Figure 8). Cation exchange capacity is a measure of how well a soil can hold
A
A
A
B
1.02
1.04
1.06
1.08
1.1
1.12
1.14
1.16
1.18
1.2
Control 0.10% 0.50% 2%
mg
Nit
rate
Le
ach
ed
Nitrate Leaching
Nitrate Leaching
24 24
cationic nutrients like potassium or magnesium. The carbonaceous byproduct used in this
project experienced minimal oxidation. Oxidation of biochar produces carboxylic
functional groups that increase the cation exchange capacity of the biochar (Cheng et al.,
2006). Incubation at 30 °C and 70 °C increased the cation exchange capacity of biochar
by 53% and 538% respectively (Cheng et al., 2006). Oxidizing the carbonaceous
byproduct may result in a significant increase in cation exchange capacity.
Figure 8. mg NH4 N /L in leachate produced by the ammonium replacement method of
determining cation exchange capacity.
A
AA A
0
5
10
15
20
25
Control 0.10% 0.50% 2%
mg
NH
4 N
/L in
Le
ach
ate
Cation Exchange Capacity
Cation Exchange Capacity
CONCLUSIONS
Enormous amounts of waste plastic are produced by California agriculture and
this plastic is largely disposed of in landfills. This project demonstrated that used
irrigation tubing can be converted into diesel-like fuel through pyrolysis. The pyrolysis
oil that was produced during this project had a high melting point and was unsuitable for
use as a direct diesel fuel substitute. Pyrolysis oils that fall within ASTM specifications
for diesel fuel have been successfully produced (Khan et al., 2016). The properties of the
pyrolysis oil could potentially be improved by longer pyrolysis times (Khan et al., 2016;
Wongkhorsub and Chindaprasert, 2013) or a different catalyst (Auxilio et al., 2017).
The carbonaceous byproduct improved the water holding capacity and increased
the microbial respiration rates of amended soils. Very high levels of carbonaceous
byproduct exceeding 0.5% of soil weight should be avoided due to potential increases in
nitrate leaching and adverse effects on soil hydraulic conductivity. Soil amended with 2%
carbonaceous byproduct had 40% lower hydraulic conductivity and 5.6% increased
nitrate leaching compared to the control. The adverse effect of carbonaceous residue on
soil hydraulic conductivity may be due to the hydrophobic properties of the carbonaceous
byproduct. Biochar becomes hydrophilic after oxidation by air and water (Basso et al.,
2012). Biochar also increases cation exchange capacity after being oxidized (Cheng et al.,
2006). Oxidation of the carbonaceous byproduct may reduce or eliminate the negative
effects of the carbonaceous byproduct on soil hydraulic conductivity. The carbonaceous
byproduct of pyrolysis of waste plastic can be effectively used as an soil amendment that
improves several aspects of soil quality including water holding capacity. The exact
interactions between the carbonaceous byproduct and the soil matrix were beyond the
scope of this research. This makes it difficult to determine the exact mechanisms
responsible for the effects observed during this research. Future work may include an
26 26
investigation of equilibrium adsorption capacity and adsorption kinetics of the
carbonaceous byproduct.
REFERENCES
Almeida, Débora, & Marques, Maria de Fátima. (2016). Thermal and catalytic pyrolysis
of plastic waste. Polímeros, 26(1), 44-51. https://dx.doi.org/10.1590/0104-
1428.2100
Auxilio, A. R., Choo, W-L., Kohli, I., Chakravartula Srivatsa, S., & Bhattacharya, S.
(2017). An experimental study on thermo-catalytic pyrolysis of plastic waste using
a continuous pyrolyser. Waste Management, 67, 143-154.
https://research.monash.edu/en/publications/an-experimental-study-on-thermo-
catalytic-pyrolysis-of-plastic-wa
Basso, A., et al. (2012). Assessing Potential of Biochar for Increasing Water-Holding
Capacity of Sandy Soils. GCB Bioenergy, 5(2), 132–143., doi:10.1111/gcbb.12026.
Brown, T., et al. (2008). Lime Effects on Soil Acidity, Crop Yield, and Aluminum
Chemistry in Direct-Seeded Cropping Systems. Soil Science Society of America
Journal, 72(3), 634. doi:10.2136/sssaj2007.0061.
Chan, K. Y., et al. (2007). Agronomic Values of Greenwaste Biochar as a Soil
Amendment. Soil Research, 45(8). 629., doi:10.1071/sr07109.
Cheng, C, et al. (2006). Oxidation of Black Carbon by Biotic and Abiotic Processes.
Organic Geochemistry, 37(11), 1477–1488, doi:10.1016/
j.orggeochem.2006.06.022.
Citgo Petroleum Corporation. (2018a) Safety Data Sheet CITGO No. 1 Diesel Fuel, All
Grades. Citgo, www.docs.citgo.com/msds_pi/AG1DF.pdf.
Citgo Petroleum Corporation. (2018b). Safety Data Sheet CITGO No. 2 Diesel Fuel, All
Grades, Low Sulfur. Citgo, www.docs.citgo.com/msds_pi/AG2DF.pdf.
Donaj, P. J., Kaminsky, W., Buzeto, F., & Yang, W.(2012). Pyrolysis of polyolefins for
increasing the yield of monomers’ recovery.Waste Management (New York, N.Y.),
32(5), 840-846. http://dx.doi.org/10.1016/j.wasman.2011.10.009. PMid:22093704.
Gavlak, R. G., Horneck, D. A., and R. O. Miller. (2005). Soil, Plant, and Water
Reference Methods for the Western Region. WREP-125.
Glaser, B. (2006). Prehistorically modified soils of central Amazonia: a model for
sustainable agriculture in the twenty-first century. Philos Trans R Soc Lond B Biol
Sci. 362(1478).
Goldy, Ron. (2005). Baling Used Agricultural Plastic. College of Agriculture & Natural
Resources, Michigan State University, https://www.canr.msu.edu/uploads/files/
Research_Center/SWMREC/special_reports/bale_plastic_2005.pdf
28 28
Harter, T., et al. (2012). Addressing Nitrate in California's Drinking Water with a Focus
on Tulare Lake Basin and Salinas Valley Groundwater. Report for the State Water
Resources Control Board Report to the Legislature. Center for Watershed Sciences,
University of California, Davis. http://groundwaternitrate.ucdavis.edu.
Hurley, Sean. (2008). Postconsumer Agricultural Plastic Report. California Integrated
Waste Management Board
Inal, A., Gunes, A., Sahin, O., Taskin, M., and Kaya, E. (2015). Impacts of biochar and
processed poultry manure, applied to a calcareous soil, on the growth of bean and
maize. Soil Use and Management. 31 (1),106-113.
Jaeger, W. E (2006). Economic Analysis of the Cost of producing Juniper-Plastic Fuel
Cubes in the Upper Klammath Basin. A report prepared for ORE-CAL RC&D, PO
Box 785, Dorris, CA.
Jeffery, S., et al. (2011). A Quantitative Review of the Effects of Biochar Application to
Soils on Crop Productivity Using Meta-Analysis. Agriculture, Ecosystems &
Environment, 144(1), 175–187., doi:10.1016/j.agee.2011.08.015.
Hamidi, Nasrollah, et al. (2013). Pyrolysis of Household Plastic Wastes.” British Journal
of Applied Science and Technology, 3(3), 417–439.
Khaghanikavkani E, Farid MM, Holdem J, Williamson A. (2013). Microwave Pyrolysis
of Plastic. J Chem Eng Process Techno.4(150). doi:10.4172/2157-7048.1000150
Khan, M., Sultana, M., Al-Mamun, M., and Hasan, M. (2016). Pyrolytic Waste Plastic
Oil and Its Diesel Blend: Fuel Characterization. J Environ Public Health.
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4940549/
Kumar, P. Senthil, et al. (2015). Conversion of Waste Plastics into Low-Emissive
Hydrocarbon Fuels through Catalytic Depolymerization in a New Laboratory Scale
Batch Reactor. International Journal of Energy and Environmental Engineering,
8(2), 167–173. doi:10.1007/s40095-015-0167-z.
Lehmann, J, Gaunt J, Rondon M. (2006). Bio-char sequestration in terrestrial
ecosystems—a review. Mitig. Adapt. Strat. Global Change. 11, 395-419.
Le Quere, C., Andrew, R., Friedlingstein, P., Sitch, S., et al. (2018). Global Carbon
Budget 2018. Earth Syst. Sci. Data, 10, 2141-2194.
Liu, L., et al. (2014).Effect of Biochar on Nitrous Oxide Emission and Its Potential
Mechanisms. J Air Waste Manag Assoc. 64(8),894-902.
www.ncbi.nlm.nih.gov/pubmed/25185392.
Lone, A., Najar, G., Ganie, M., Sofi, J., and Ali, T. (2015). Biochar for Sustainable Soil
Health: A Review of Prospects and Concerns. Pedosphere 25 (5): 639-653.
29 29
Mandal, S., et al. (2016). Application of Biochar Produced From Biowaste Materials for
Environmental Protection and Sustainable Agriculture Production. Environmental
Materials and Waste, 73–89. doi:10.1016/b978-0-12-803837-6.00004-4.
Marcilla, A., Beltrán, M. I., & Navarro, R. (2009). Thermal and catalytic pyrolysis of
polyethylene over HZSM5 and HUSY zeolites in a batch reactor under dynamic
conditions. Applied Catalysis B: Environmental, 86(1-2), 78-86.
http://dx.doi.org/10.1016/j.apcatb.2008.07.026.
Mcgonigle, T., and Murray H. (1996). Mycorrhizae, Phosphorus Absorption, and Yield
of Maize in Response to Tillage. Soil Science Society of America Journal, 60(6),
1856, doi:10.2136/sssaj1996.03615995006000060034x.
National Pipe & Plastics Inc. (2011). Material Safety Data Sheet -HDPE. National Pipe
& Plastics Inc. www.nationalpipe.com/pdf_files/msds-hdpe.pdf.
Novak M., et al. (2009). Characterization of designer biochar produced at different
temperatures and their effects on a loamy sand. Annals of Environmental Science.
3(1). 195–206.
Obia, A., et al. (2015). Effect of Soil PH Increase by Biochar on NO, N2O and N2
Production during Denitrification in Acid Soils. Plos One, 10(9).
doi:10.1371/journal.pone.0138781.
Oster, J.D., I. Shainberg, and I.P. Abrol. (1999). Reclamation of salt-affected
soil.Agricultual Drainage, Agronomy monograph no. 38. 315–346.
Puncochar, M, et al. (2012). Development of Process for Disposal of Plastic Waste Using
Plasma Pyrolysis Technology and Option for Energy Recovery. Procedia
Engineering, 42, 420-430. doi:10.18411/a-2017-023.
Randall Conrad and Assoc. LTD. (2006). The Market Feasibility of
Recycling/Recovering Post Consumer Polypropylene Baler Twine in Alberta. A
research report submitted to the Poly-Twine Market Feasibility Steering Committee,
Canadian Plastics Industry Association. http://www.cpia.ca/files/files/
files_baler_twine_study.pdf,
Sanderman, J., Hengl, T., and Fiske, G. (2017) Soil carbon debt of 12,000 years of human
land use. PNAS. 114 (36) 9575-9580.
Scheirs, J. (2006). Overview of commercial pyrolysis processes for waste plastics. In J.
Scheirs, & W. Kaminsky (Orgs.), Feedstock recycling and pyrolysis of waste
plastics (pp. 383-434). Hoboken: John Wiley & Sons.
Soil Quality Institute. (2001). Soil Quality Test Kit Guide. Natural Resources
Conservation Service, USDA.
www.nrcs.usda.gov/Internet/FSE_DOCUMENTS/nrcs142p2_050956.pdf.
30 30
Tan, G., Liu, Y., and Xiao, D. (2018). Influence of different pyrolysis methods on the
sorption property of rice straw biochar, Separation Science and Technology,
https://www.tandfonline.com/doi/abs/10.1080/01496395.2018.1553981?journalCod
e=lsst20
Transparency Market Research. (2013). Agricultural Films (LDPE, LLDPE, HDPE,
EVA/EBA, Reclaims and Others) Market for Greenhouse, Mulching and Silage
Applications - Global Industry Analysis, Size, Share, Growth, Trends and Forecast,
2013 - 2019. Transparency Market Research.
www.transparencymarketresearch.com/report-toc/996.
U.S. EPA. (2018). Advancing Sustainable Materials Management: 2015 Fact Sheet
Assessing Trends in Material Generation, Recycling, Composting, Combustion
with Energy Recovery and Landfilling in the United States.
https://www.epa.gov/sites/production/files/2018-07/documents/
2015_smm_msw_factsheet_07242018_fnl_508_002.pdf
Wongkhorsub, C, and N. Chindaprasert . (2013). A Comparison of the Use of Pyrolysis
Oils in Diesel Engine. Energy and Power Engineering, 5, 350–355.
doi:10.4236/epe.2013.54B068.
Yao, Y., et al. (2012). Effect of Biochar Amendment on Sorption and Leaching of
Nitrate, Ammonium, and Phosphate in a Sandy Soil. Chemosphere, 89(11)1467–
1471., doi:10.1016/j.chemosphere.2012.06.002.
Yu, O., et al. (2017). Characterization of Biochar and Its Effects on the Water Holding
Capacity of Loamy Sand Soil: Comparison of Hemlock Biochar and Switchblade
Grass Biochar Characteristics. Environmental Progress & Sustainable Energy,
36(5), 1474–1479., doi:10.1002/ep.12592.
Zang Oo, A., Sudo, S., Matsuura, S., Win, K., and Gonai, T. (2018). Aerated Irrigation
and Pruning Residue Biochar on N2O Emission, Yield and Ion Uptake of
Komatsuna. Horticulturae. 4(4), 33
Zhang, R. (1997). Determination of Soil Sorptivity and Hydraulic Conductivity from the
Disk Infiltrometer. AGRIS: International Information System for the Agricultural
Science and Technology, Hillsdale, N.J. : B.L. Erlbaum Associated, 1982.
agris.fao.org/openagris/search.do?recordID=US199705
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