A new method for converting foodwaste into pathogen free soil

Transcription

Journal of Cleaner Production xxx (2015) 1e9
Contents lists available at ScienceDirect
Journal of Cleaner Production
journal homepage: www.elsevier.com/locate/jclepro
A new method for converting foodwaste into pathogen free soil
amendment for enhancing agricultural sustainability
Pramod Pandey a, b, *, Mark Lejeune c, Sagor Biswas a, Daniel Morash c, Bart Weimer a,
Glenn Young d
a
Department of Population Health and Reproduction, Veterinary Medicine School, University of California, Davis, CA, 95616, USA
Division of Agriculture and Natural Resources (ANR), University of California, Davis, CA, USA
California Safe Soil, 1030 Riverside Parkway, West Sacramento, CA, 95606, USA
d
Department of Food Science and Technology, University of California, Davis, CA, USA
b
c
a r t i c l e i n f o
a b s t r a c t
Article history:
Received 23 July 2015
Received in revised form
8 September 2015
Accepted 11 September 2015
Available online xxx
Increasing emphasis on controlling the uses of chemical fertilizers requires identifying safe Organic Soil
Amendments (OSA) to use as alternatives. Converting organic waste, such as foodwaste into an OSA can
be an option. Such approaches are also an attempt to make beneficial use of the enormous amount of
foodwaste generated globally. In this study we conducted a pathogen challenge to determine the inactivation of three foodborne pathogens in an OSA derived from a complex foodwaste stream. Further, the
physiochemical characteristics of the OSA were assessed at pilot-scale experiments. The inactivation of
three most common foodborne pathogens (Escherichia coli O157:H7, Salmonella enterica subspecies
enterica sv Typhimurium LT2, and Listeria monocytogenes) was determined using bench-scale tests,
simulating the process adopted at a pilot-scale facility. The pilot-scale facility uses three processes
(enzyme digestion (55e57 C), pasteurization (75e77 C), and acidification treatments) for producing the
OSA. In addition, the yields and nutrient characteristics of the OSA were analyzed using 16 pilot-scale
batch tests. The results showed that the process adopted in this study for converting foodwaste to the
OSA produced a soil amendment with non-detectable levels of E. coli O157:H7, Salmonella LT2, and L.
monocytogenes. The yield of the OSA was 84e96% of the initial foodwaste inputs, and organic matter and
C: N ratio of the OSA were 20e25% and 12:1, respectively. We anticipate that the results presented here
will help in enhancing agricultural sustainability.
© 2015 Elsevier Ltd. All rights reserved.
Keywords:
Foodwaste
Pathogens
Organic soil amendment
Public health
Nutrients
1. Introduction
Food production in the U.S. uses approximately 50% of its land,
and utilizes 80% of the total fresh water consumed. About 40% of
total food production, however, goes as waste (Gunders, 2012),
which is equivalent of $165 billion each year. In contrast, currently
more than a billion people are chronically malnourished (Foley
et al., 2011). In theory, the total food waste produced in North
America and Europe can potentially feed the world's hungry three
times over (Stuart, 2009). Alternatively, it can reduce the application of chemical fertilizers considerably if the use of soil amendment derived from food waste is adopted extensively.
* Corresponding author. Department of Population Health and Reproduction,
Veterinary Medicine School, University of California, Davis, CA 95616, USA.
E-mail addresses: [email protected], [email protected] (P. Pandey).
Recycling foodwaste for producing products, such as OSA and
bioenergy, has received a great level of interest recently. Organic
waste treatment processes such as composting processes (i.e.,
windrow composting, vermicomposting, and powered composting) (VermiCo, 2013; Purkayastha, 2012; Munnoli et al., 2010;
Shivakumar et al., 2009) and anaerobic digestion processes (Shin
et al., 2010; Quiroga et al., 2014; Dai et al., 2013; Bernstad et al.,
2013; Rounsefell et al., 2013) are promising technologies. Previous studies (Parthan et al., 2012; Broitman et al., 2012; Levis and
Barlaz, 2011; Levis et al., 2010; Diggelman and Ham, 2006; Lundie
and Peters, 2005; Ayalon et al., 2001) have assessed the waste
treatment costs of the various treatment processes. Many factors
including the application of the digestate (i.e., soil amendment),
waste transport, gas collection and energy recovery, and the inclusion of environmental benefits are reported to influence the
waste treatment costs. For example, Ayalon et al. (2001) suggested
that the most cost-effective means to treat the degradable organic
http://dx.doi.org/10.1016/j.jclepro.2015.09.045
0959-6526/© 2015 Elsevier Ltd. All rights reserved.
Please cite this article in press as: Pandey, P., et al., A new method for converting foodwaste into pathogen free soil amendment for enhancing
agricultural sustainability, Journal of Cleaner Production (2015), http://dx.doi.org/10.1016/j.jclepro.2015.09.045
2
P. Pandey et al. / Journal of Cleaner Production xxx (2015) 1e9
component for avoiding reducing CO2 is aerobic composting.
Another study by Levis and Barlaz (2011) assessed the various options of food waste treatment processes and estimated that
anaerobic digestion was the most environmentally beneficial
treatment option potentially because of avoided electricity generation and soil carbon storage from use of the resulting soil
amendment. The authors also reported that a traditional landfill
with energy recovery can have lower emissions than any of the
composting alternatives when a fertilizer offset was used. Another
study by Tsilemou and Panagiotakopoulos (2006) reported that
anaerobic digestion and in-vessel composting are the most costly
methods for solid waste treatment.
Although all above processes are applied for treatment the food
waste and have numerous benefits, the fate of foodborne pathogens
in these processes are not well understood. The presence of pathogens in an OSA can potentially recycle pathogens in agricultural
systems (Holden and Treseder, 2013). Pathogens associated with
growing plants have caused many foodborne outbreaks (Holden and
Treseder, 2013; Hoffmann and Anekwe, 2013). The U.S. Department
of Agriculture's Economic Research Service (USDA-ERS) estimates
that pathogens in food cause 6.5e33 million cases of human illnesses, and the cost of these illnesses is greater than $4 billion
(Buzby et al., 1996). A relatively new study by Hoffmann and Anekwe
(2013) reported cost of foodborne-illness in the USA ranging from
$14.1 billion to $152 billion. Hoffman et al. (2012) estimated that 14
foodborne pathogens cause $14.0 billion in cost of illness. Approximately 90% of this loss is caused by five pathogens: Salmonella
enterica, Campylobacter spp., Listeria monocytogenes, Toxoplasma
gondii, and norovirus. Therefore, ensuring the destruction of these
pathogens in the soil amendment, prior to application of soil
amendment (derived from food waste) into crop land is crucial for
protecting environment and mitigating human health risk.
Considering the enormous amount of food waste in global food
supply chains (Papargyropoulou et al., 2014), additional research is
needed to identify the processes capable of converting food waste
into a safe and useful by-product such as OSA. Previous studies reported soil as an important source of pathogens such as Escherichia
coli, which has been directly related to foodborne outbreaks (Perry
et al., 2013; Bolton et al., 2011). In contrast to the OSA, ongoing
excessive use of chemical fertilizers has lowered soil quality and
leads to environmental degradation (Zhu et al., 2012). Since the
global food production relies on soils (Lal, 2014; Blanco-Canqui and
Lal, 2008), which are a finite resource, they require protection.
Recently, the use of OSA has been seen as an alternative to chemical
fertilizers, which enhance crop yield as well as promote the sustainable development of agricultural industry (Zhu et al., 2012).
The goal of this research is to assess the inactivation of human
pathogens in the process of converting foodwaste into OSA. The
objectives of this study are to: 1) understand the impacts of enzyme
digestion (55e57 C), pasteurization (75e77 C) and acidification
processes on the inactivation of foodborne pathogens (E coli
O157:H7, S. enterica subspecies enterica sv Typhimurium LT2, and L.
monocytogenes) in the OSA; and 2) assess the yields and nutrient
levels of OSA derived from food waste.
2. Materials and methods
2.1. Conversion of food waste into OSA
The process described in this research (Fig. 1) uses hydrolysis,
pasteurization, and stabilization processes for converting foodwaste into an OSA. The first step involves food waste (organic
waste) collection from supermarkets located within 50 miles of the
food waste processing center. Organic food waste (discarded food
from produce, meat, bakery, & deli departments) is collected from
Fig. 1. Schematic of process flow used in converting food waste into soil amendment.
super markets in double wall insulated containers suitable for
perishable food storage and transported in refrigerated (temperature 5e8 C) trucks within 2 days of being removed from the shelf
at the supermarket. The second step involves an enzymatic digestion at 55e57 C to digest the food waste. In a vessel digester, slurry
is mixed with a cocktail of enzymes designed to digest the diverse
foodwaste streams received from the supermarkets. The digestion
process takes place for 3 h. In the third step, digested food waste is
pasteurized in order to kill any remaining human pathogens. After
pasteurization, the solution is screened with a sieve (74 mm) for
separating the larger particles from the solutions. The fourth step
involves stabilization i.e., decreasing the pH of pasteurized foodwaste to a pH of 2.8e3.0. In the stabilization process, the pH of the
pasteurized emulsion is lowered by adding phosphoric acid to
preserve the emulsion and prevent microbial activity in the
emulsion. After 2.5 h of the stabilization process, the final product
(i.e., OSA), Harvest-to-Harvest (H2H), is transferred to a storage
tank, and then it is supplied as an OSA. The process of converting
foodwaste into OSA has been tested at a pilot-scale plant, designed
by California Safe Soil, LLC (CSS; West Sacramento, CA). CSS collects
unsold food, such as produce, bakery, and delicatessen department
waste materials, in insulated containers for use in this process.
2.2. Pathogen challenge study
A batch-scale experiment was designed (Fig. 2) to test the
pathogen inactivation and survival in the OSA at each stage (i.e.,
thermophilic digestion, pasteurization, and stabilization) of the
process. The experiment was conducted inside a biosafety cabinet
(level II) to minimize the pathogen risks to the personnel involved
in the experiment as well as possible ambient contamination. The
unstablized OSA used in the pathogen challenge study was received
from CSS immediately before starting batch-scale experiments. The
experiment was performed in three stages: 1) enzyme digestion
(55e57 C for 150 min); 2) pasteurization (75e77 C for 30 min);
and 3) acidification (room temperature (22e25 C) for 120 min). To
control the temperature of the OSA in a reactor used for digestion,
3
2.4. Yield and nutrient characteristics of the OSA
In addition to the pathogen test, nutrient characteristics of the
OSA were assessed. For nutrient characterization, the OSA samples,
taken from a total of 16 independent pilot-scale batch tests, were
analyzed (results are discussed later) using standard methods
(APHA, 1999). Nutrient characteristics such as organic matter (OM),
nitrogen (N), phosphorous (P), and potassium (K) were measured.
The elements such as calcium (Ca), sulphur (S), magnesium (Mg),
sodium (Na), Iron (Fe), aluminum (Al), copper (Cu), zinc (Zn), crude
protein, crude fat, and total carbohydrates were also measured.
3. Results and discussion
3.1. Pathogen challenge results
The analysis of the initial OSA (prior to inoculation) showed no
detectable E. coli O157:H7, S. Typhimurium LT2, and L. monocytogenes. After the OSA inoculation with pathogens, the OSA
samples were analyzed again, and pathogen levels in the OSA were
greater than 6 orders of magnitude. Subsequently, pathogen levels
in the OSA were tested at the end of each process and the results are
discussed in the following subsections.
Fig. 2. Schematics of bench-scale experiment.
we regulated the temperature of the water jacket (Fig. 1) utilizing a
heating plate (Thermolyne Corporation, Dubuque, IA, U.S.). The
stirring of the OSA was performed using an overhead mixer
(CAFRAMO Model#BDC250U1) in all the three stages. During the
thermophilic and pasteurization processes, stirring speed was 50
RPM, and during the acidification process, the stirring speed was
200 RPM, which creates uniformity in the OSA emulsion as well as
helping to aerate the OSA.
2.3. Pathogen inoculation and enumeration
To test the pathogen inactivation, the OSA (i.e., H2H product)
was inoculated with pathogens (E. coli O157:H7, Salmonella.
Typhimurium LT2, and L. monocytogenes). To prepare inoculum,
fresh pathogen culture of E. coli O157:H7 (ATCC #35150), S.
Typhimurium LT2 (ATCC #700720), and L. monocytogenes (ATCC #
BAA- 679D-5) was prepared in the lab prior to starting the
experiment. Difco LB Broth Miller (LuriaeBertani) growth media
was used for growing E. coli O157:H7 and S. Typhimurium LT2, and
BBL Brain Heart Infusion was used to grow L. monocytogenes. A
fresh culture of each pathogen was collected (4 ml) and pelleted
using micro-centrifuge at 8000 RPM for 10 min. The cell pellets
were mixed (i.e., dissolved) with the OSA, and stirred for 10 min at
room temperature before use in the process treatments. Samples
of E. coli O157:H7, S. Typhimurium LT2, and L. monocytogenes were
streaked (i.e., plated) on MacConkey II Agar (Becton, Dickinson
and Company, Sparks, MD, USA), Difco XLD Agar (Becton, Dickinson and Company, Sparks, MD, USA), and PALCAM Agar (with
selective supplement) (HiMedia Laboratory Pvt Ltd, Mumbai, India) plates, respectively, for enumerating the pathogens. All the
samples were tested in triplicates. A pH meter (Omega Engineering, INC., Stamford, CT, USA) equipped with a pH and temperature
probe was used to measure the pH and temperature during the
experiment.
3.1.1. Inactivation of E coli O157:H7
Fig. 3 shows E. coli O157:H7 inactivation in the enzyme digestion, pasteurization, and acidification steps of the process. The
durations of each process step is shown by horizontal lines with
both end arrows. The space between vertical dotted lines indicate
time (approximately 10 min), which was required for phase change
i.e., time for changing the temperatures from ambient to thermophilic and thermophilic to pasteurization. The results of the three
experiments (Run 1, Run 2, and Run 3) are shown indicating inactivation of E. coli O157:H7 in the OSA.
Initial E. coli O157:H7 levels in the OSA (before inoculation) was
non-detectable. The levels of E. coli O157:H7 in the inoculum (i.e.,
pure culture) were 2.8 109, 1.7 109, and 1 109 CFU/mL in Run1,
Run 2, and Run 3, respectively (shown as red (in the web version)
circles in Fig. 3). The pellets of E. coli O157:H7 were dissolved in the
OSA, which resulted in enhanced E. coli O157:H7 levels in the OSA.
After inoculation, increased E. coli O157:H7 levels in the OSA were
6.1 107, 1.7 107, and 8.0 106 CFU/mL in Run1, Run 2, and Run 3,
respectively (shown as green (in the web version) triangles in Fig. 3).
After 150 min of digestion (at the end of thermophilic process
(55e57 C for 150 min)), E. coli O157:H7 levels in Run 1 were nondetectable (shown as ND in Fig. 3). Subsequently, the OSA was
pasteurized (at 75e77 C for 30 min), which also showed ND levels
of E. coli O157:H7. After pasteurization, acidification process was
carried out (pH was decreased to 2.8e3.0). During the acidification
process, continuous mixing of the OSA (200 rpm for 150 min) was
provided, and the samples collected after the acidification process
also showed ND levels of E. coli O157:H7 in the OSA.
3.1.2. Inactivation of S. Typhimurium LT2
Fig. 4 shows S. Typhimurium LT2 inactivation in digestion,
pasteurization, and acidification processes. The levels of S. Typhimurium LT2 in inoculum were 4.3 109, 3.1 109, and
5.2 109 CFU/mL in Run 1, Run 2, and Run 3, respectively (shown as
red (in the web version) circles in Fig. 4). During Run 1, Run 2, and
Run 3, initial S. Typhimurium LT2 levels were 7.4 107, 1.1 108,
and 2.8 107 CFU/mL, respectively. Similar to E. coli O157:H7
inactivation, S. Typhimurium LT2 inactivation in digestion,
pasteurization, and acidification processes are shown in Fig. 4. In
Run 1, S. Typhimurium LT2 levels were reduced from 7.4 107 CFU/
mL to ND after the thermophilic process. In Run 2, S. Typhimurium
4
Fig. 3. E. coli 0157:H7 inactivation in digestion, pasteurization, and acidification processes (ND ¼ not detected) (detection limit was 1 colony at 100 dilution).
LT2 levels were reduced from 1.1 108 CFU/mL to ND. Similarly, S.
Typhimurium LT2 levels in Run 3 were reduced from 2.8 107 CFU/
mL to ND, indicating no survival. The results of acidifications are
also shown in Fig. 4. The OSA samples testing after the acidification
process also showed ND levels of S. Typhimurium LT2 indicating no
survival of S. Typhimurium LT2 in the OSA.
3.1.3. Inactivation of L. monocytogenes
Fig. 5 shows the inactivation of L. monocytogenes in the OSA. In
Run 1, the level of L. monocytogenes in inoculum was 6.0 108 CFU/
mL. In Run 2, the level of L. monocytogenes in inoculum was
2.1 109 CFU/mL, while in Run 3, L. monocytogenes level in inoculum was 1.2 109 CFU/mL (shown as red (in the web version)
circles in Fig. 5).
After inoculum mixing in the OSA, the levels of L. monocytogenes
in the OSA were 5.0 106, 4.3 108, and 3.0 106 CFU/mL in Run 1,
Run 2, and Run 3, respectively (shown as green triangles in Fig. 5).
Subsequently, thermophilic digestion in all three runs resulted ND
levels of L. monocytogenes in the OSA. In all the three runs (Run 1,
Run 2, and Run 3), the levels of L. monocytogenes at the end of
5
Fig. 4. Salmonella Typhimurium LT2 inactivation in digestion, pasteurization, and acidification processes (ND ¼ not detected) (detection limit was 1 colony at 100dilution).
pasteurization and acidification were also ND. Enzyme digestion,
pasteurization and acidification results are shown in Fig. 5.
3.2. Yield and nutrient characteristics of the OSA
3.2.1. OSA yield
In addition to the pathogen challenge study (discussed in section 3), the OSA was analyzed to estimate the process yield, which is
shown in Fig. 6. The figure shows the average values of 16 batch
tests. The input weights of produce, meat, fine scree overs, and total
foodwaste are shown in Fig. 6. The OSA yield (OSA weight (kg) ⁄ total
waste input (produce, meat, fine screen overs)) is also shown in the
figure. The input of produce weight varied from of 494.8e1057.6 kg
(average ¼ 736.8 kg; stdev ¼ ± 174 kg). The weight of meat changed
from 100.2 to 319.7 kg (average ¼ 170.0 kg; stdev ¼ ± 59.0 kg). The
fine screen overs weight varied from 72.6 to 408.2 kg
(average ¼ 143.3 kg; stdev ¼ ± 98.1 kg). The total foodwaste input
weight varied from 800 kg to 1449.8 kg (average ¼ 1050 kg;
6
Fig. 5. Listeria monocytogenes inactivation in thermophilic, pasteurization, and acidification processes (ND ¼ not detected) (detection limit was 1 colony at 100dilution).
stdev ¼ 237.5 kg), which produced the average OSA of 970.6 kg
(variation from 680 kg to 1271 kg with stdev of 191.4 kg) resulting
in the OSA yield of 89%. The OSA yield varied from 86% to 96%
(stdev ¼ 3%).
3.2.2. OSA nutrient characteristics
Fig. 7A and B showed the nutrient characteristics (i.e., crude
protein, crude fat, total carbohydrate, N, P, K) of the OSA. The
descriptive statistics of the micro and macro nutrients including
metals are shown in Table 1. The proportion of crude protein and
crude fat in the OSA were 5.82% and 7.97%, respectively. The proportion of total carbohydrates was 8.18% (Fig. 7A). Fig. 7B shows the
average of total N, P, K contents of the OSA. Total N varied from 0.81%
to 1.16%, and total P varied from 0.38% to 0.92% (Table 1). The average
of total N was 0.93% (±0.1), while the average P was 0.56% (±0.1). The
total K varied from 0.25 to 0.42%, with average of 0.36 (±0.04).
The moisture content and organic matter content of the OSA
varied from 72 to 75% and 15.9e26.7%, respectively. The average C:
Table 1
Characteristics of the organic soil amendment.
1600
1200
Quantitiy (kg)
7
800
400
0
Produce
Meat
Fine Screen Overs Total Foodwaste OSA Yield
Input
Raw Inputs
Characteristics
Average
Min
Max
STD
n
Organic Matter (OM), %
Calcium (Ca), %
Sulphur (S), %
Magnesium (Mg), %
Sodium (Na), %
Iron (Fe), ppm
Aluminum (Al), ppm
Copper (Cu), ppm
Zinc (Zn), ppm
Total N, %
Total P, %
Total K, %
Crude protein, %
Crude fat, %
Total carbohydrates
21
0.13
0.07
0.03
0.13
109.8
69.5
6.3
15.3
0.93
0.56
0.36
5.82
7.97
8.18
15.9
0.1
0.05
0.02
0.09
34
9
2
5
0.81
0.38
0.25
5.06
4.05
6.08
26.7
0.15
0.25
0.04
0.23
790
602
35
106
1.16
0.92
0.42
7.25
15.15
11.01
2.76
0.02
0.05
0.004
0.04
182.7
143.9
8.3
24.4
0.10
0.14
0.04
0.62
2.64
1.41
16
16
16
16
16
16
16
16
16
16
16
16
16
16
16
Note: n ¼ number of samples.
Fig. 6. Input of foodwaste and organic soil amendment yield.
N ratio was 12:1. The ranges of secondary nutrients and micronutrients such as Ca, Mg, and S in the OSA were 0.1e0.15%,
0.02e0.04, and 0.05e0.25%, respectively. The Fe, Al, Cu, and Zin
varied from 34 to 790, 9e602, 2e35, 5e106, respectively.
Field trail data of strawberry plant growth using the OSA are
shown in Fig. 8. When the OSA (i.e., H2H) was mixed with Grower
Standard (GS) (chemical fertilizers typically used by farmers), the
weight of the whole plant was increased by 25%. The root and shoot
weights were increased by 69 and 4% (Fig. 8A), respectively. The
increase in fresh weight is shown in Fig. 8B. The fresh weight of
strawberry was increased by 32% when the OSA was mixed with GS
compared to only GS. The fresh weight of strawberry was increased
by 40% when the OSA was applied alone compared to the GS alone.
Further, the H2H can be particularly useful for orchard crops. Once
the orchard crops are planted, it is challenging to incorporate solid
composts into the soil without disturbing the root structure. In
contrast, the H2H can be applied with the irrigation water through
the existing drip system. The use of H2H is likely to reduce nitrate
runoff into the ground water because it is applied right to the root
zone, and hence increased nutrient availability to the plants. Field
trial data showed that the use of H2H resulted in reduced nitrate
fertilizer applications and increased on strawberry yields.
Considering the benefits of the OSA in plant growth, the nutrient
characteristics of the OSA, and non-detectable pathogens in the
OSA, the approach described here for the OSA production can be a
potential method for converting the food waste into a soil
amendment. In the past, many human pathogen infections were
related to food products (Akhtar et al., 2014; Tauxe et al., 2010), and
the disposal of contaminated food waste into the environment can
12%
(A)
Proportions (%)
10%
8%
6%
4%
2%
0%
Crude Protein
Crude Fat
Total Carbohydrates
Product contents
1.2
(B)
1
Fractions
0.8
0.6
0.4
0.2
0
N
P
N, P, K contnets
K
Fig. 7. Organic soil amendment characteristics: A) protein, fat, and carbohydrate
contents; and B) total N, P, and K values of the OSA.
Fig. 8. Strawberry plant growth under with soil amendment application and without
soil amendment application: A) whole plant, root, and soot growth; B) fresh weight
growth.
8
potentially disseminate the foodborne pathogens in soil and water
and subsequently in food crops. As an example, Scallan et al. (2011)
reported Salmonella as the leading cause of food borne illnesses in
the USA, and many of these illnesses were linked with agriculture
farms.
In North-America and Europe, foodwaste per capita is
95e115 kg/year, while in sub-Saharan Africa and South/Southeast
Asia food waste is 6e11 kg/year, amounting to global food loss more
than 1.3 billion tons each year (Gustavsson et al., 2011). Approximately 33% of the food produced for human consumption is lost or
discarded globally (FAO, 2011). The results of this study showed the
OSA yield greater than 80% while converting the foodwaste into soil
amendment. Further, the proposed food waste conversion is not
energy intensive. The digestion and pasteurization require heat,
which was produced using a natural gas boiler. The modest amount
of electric power is used to run the pumps, grinders, and agitators,
which are not energy intensive devices. The capital requirements
are quite modest, compared with the alternative technologies such
as anaerobic digestion and composting, with a far smaller environmental footprint, and a more valuable finished product.
Taking 80% yield as an example, there is a potential of producing
more than 1 billion tons of soil amendment each year from food
waste alone. The remaining solids screened from OSA production
may be used as feed for pork or chicken production, or pet food,
increasing the potential beneficial use of food waste. In the past 50
years, global fertilizer use has increased by 500% (Tilman et al.,
2001; Foley et al., 2011) for enhancing crop production, which
has impacted the ecosystem adversely. If the ongoing chemical
fertilizer uses need to be continued, then this trend will most likely
degrade freshwater and marine ecosystems further.
Current food waste production is huge; however, it can be
trapped for soil amendment production at a large scale in costeffective manner. As an example, supermarkets already optimize
the distribution of goods offered for sale at their stores through
networked food distribution centers (DC). Co-locating the food
waste conversion plants with the DCs can be an option. In the
proposed system, double wall insulated food waste storage containers will be provided by CSS to supermarkets to collect food
waste inside the back of their stores. These containers filled with
food waste will be back hauled to the DCs in otherwise empty truck
(a “free backhaul”). Subsequently, the containers will be shuttled to
the food waste conversion plants located in the vicinity of the DCs.
In this manner, every major supermarket in every major city can be
linked with food waste conversion plants. Since the process has no
significant air emission, liquid effluent, solid waste, or nuisance
odors, it is possible to obtain all necessary operating permits in
urban areas.
Developing the capability of converting food waste produced
globally (greater than a billion tons annually) into OSA can help in
controlling adverse impacts of chemical fertilizers on ecosystems.
Therefore, identifying suitable methods capable of converting food
waste into OSA, which are relatively safe to the environment, can be
a viable option. Previous researchers have studied various food
waste recycling processes, such as anaerobic digestion (Shin et al.,
2010; Zhang et al., 2007; Kim et al., 2011), however the effect of
the digestion process on pathogen inactivation (such as S. Typhimurium LT2, L. monocytogenes, and E. coli O157:H7) was not verified
well. Currently, there is little research focusing on understanding
food system that include the chain of activities connecting food
production, processing, distribution, consumption, and waste
management are available (Pothukuchi and Kaufman, 2000;
Lundqvist et al., 2008; Parfitt et al., 2010; Parizeau et al., 2015),
which are crucial for improving the agricultural sustainability and
waste utilization. In summary, the pathogen challenge study presented here showed inactivation of pathogens in OSA derived from
food waste. Pathogen levels (S. Typhimurium LT2, L. monocytogenes,
and E. coli O157:H7) in the OSA were reduced from 7 to 8 orders of
magnitude to ND level indicating the reduced microbial risk to the
environment and public health. Further, a nutrient analysis of the
OSA and a preliminary field trial showed enhanced plant growth
when the OSA was mixed with the GS. We anticipate that the results and analysis provided in this research will help in improving
the existing food waste treatment processes as well as deriving new
methods for producing microbially safe OSAs, hence, will improve
waste recycling.
4. Conclusions
The results showed that the processes adopted in this study for
converting food waste into organic soil amendment (OSA) reduced
the pathogen levels from 7 to 8 orders of magnitude to nondetectable levels indicating that the final OSA product has minimal risk of pathogens. The food waste recycling approach presented
in this research produced OSA with organic matter and C: N ratio of
21% and 12:1, respectively. Field trials of strawberry plant growth
showed that the plant growth was increased by 25% when the OSA
was added with grower standard chemical fertilizer. We anticipate
that the results presented here will help in improving the understanding of pathogen inactivation in food waste as well as
improving the existing food waste recycling processes.
Acknowledgment
Authors thank California Safe Soil (CSS), LLC for providing the
support to carry out the pathogen challenge study. Authors also
thank Division of Agriculture and Natural Resources (ANR), University of California, Davis for supporting the work.
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A new method for converting foodwaste into pathogen free soil

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