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Article

Estimating Environmental and Economic Impacts of Hermetic Bag Storage Technology

by
Ma. Cristine Concepcion D. Ignacio
1,2,*,
Kurt A. Rosentrater
1 and
Dirk E. Maier
1
1
Department of Agricultural and Biosystems Engineering, Iowa State University, Ames, IA 50010, USA
2
Institute of Agricultural and Biosystems Engineering, University of the Philippines, Los Baños 4031, Philippines
*
Author to whom correspondence should be addressed.
Sustainability 2023, 15(20), 14850; https://doi.org/10.3390/su152014850
Submission received: 20 September 2023 / Revised: 12 October 2023 / Accepted: 12 October 2023 / Published: 13 October 2023
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Abstract

:
Hermetic bag storage is a growing innovative technology that can effectively mitigate insect activity in stored grain and preserve quality without pesticides. This study aimed to estimate the environmental and economic impacts of hermetic storage bags as the basis for the sustainable adoption of the technology. This study demonstrated an approach to estimate the environmental impact of using hermetic bags and their superior economic benefits for storing maize at the 1-ton scale over three years. The life cycle assessment (LCA) of six commercially available hermetic bags (AgroZ®, GrainPro, Storezo, ZeroFly®, Elite, and PICS™) from cradle to grave was evaluated and compared using the Sustainable Minds LCA software. The gas barrier liners were analyzed for structure and polymer composition using confocal microscopy and Raman spectroscopy. The results showed that bag manufacturing had the highest environmental impact contribution, with 84.6% to 90.8% of the total impacts (mPt). The carbon footprint contribution of the total service life delivered for one hermetic bag ranged from 1.1 to 1.7 kg CO2eq. The economic benefits of using hermetic bags were calculated and compared with traditional storage bag methods for one smallholder farmer using ten (10) hermetic bags storing 100 kg/bag (1 ton) of maize. The results found that using hermetic bags exhibited the highest profit of 1130 USD when used for nine months over three years, while storage loss was maintained at less than 1%.

1. Introduction

Hermetic storage bag technology is an effective chemical-free method of mitigating insect pests in grain, oilseed, and pulse storage. It is widely disseminated among smallholder farmers in low-income countries in Africa, Asia, and Central America. It is a flexible storage structure with two components: outer and inner bags. The outer bag is a woven polypropylene bag or “jute bag” designed to provide strength and protection to the stored crop. The inner bag is either a single liner made from an extruded multilayer film of different polymers with a high oxygen barrier component, or two liners of high-density polyethylene films, limiting oxygen permeability (O2) and water vapor [1]. The hermetic storage efficacy is due to the bio-generated modified atmosphere phenomena. Due to the grain respiration and metabolic activity of insect pests and microorganisms, the oxygen level inside an adequately sealed hermetic storage structure decreases, creating an inhibitory environment for insect development and mold growth [2,3,4,5]. The social and economic impacts of hermetic storage bag technology are well documented in published studies, supported by increased adoption among smallholder farmers and the commercial availability of several product types from manufacturers in several countries. The promotion of the technology benefits from ongoing efforts by government and non-government agencies encouraging improvements in the supply chain [6,7,8,9,10,11,12]. However, additional research studies are needed to address the emerging challenges and knowledge gaps associated with hermetic storage bag technology. Foremost are the gaps of (1) evaluating the technology’s environmental impacts and (2) to determining cost-effectiveness for smallholder farmers.
Losses during storage due to insect infestation and mold-induced spoilage are a major constraint for smallholder farmers in low-income countries to ensuring food security and safety [11,13,14]. Several storage technology options have been introduced to prevent post-harvest losses in grains, oilseeds, and pulses. Hermetic storage has been promoted as an economically viable option for preventing losses due to insect pests and mold growth, and for maintaining stored product quality. For example, studies have concluded that hermetic bags are economical when used for at least four months per season and reused for at least three seasons (one season represents a year) [13,15]. Other studies have proven that using hermetic bags provides direct profits to farmers and promotes the health benefits of not needing pesticides [16,17]. Although the economic benefits of hermetic storage technology have been established, the willingness of farmers to adopt the technology has been a challenge because of the purchase cost of hermetic storage bags, which is higher than conventional woven PP or jute bags. Moreover, the decision of farmers to use hermetic bags has been influenced by access to training, the availability of the technology in their area, storage capacity, seasonal price variations, weight losses, and quality [18].
The use of plastic packaging has increased tremendously over recent years, and consequently, the resulting issues of GHG emissions, disposal into landfills, and litter are rising [19]. The increase in the global production of plastic causes increases in GHG emissions that contribute to climate change. The disposal of plastic as part of the waste management stream is another concern, with plastic accumulating in land and water for decades [20,21]. The results of this study should help identify the life cycle stage of hermetic storage bag technology that contributes most to the environmental impact and carbon footprint, and options for making the technology more sustainable in low-income countries where effective solid waste management is challenging. When hermetic storage bags are introduced and become more popular, questions about this technology’s disposal and GHG emissions will be raised as concerns. So far, the environmental impacts of this technology have not been thoroughly evaluated. One study reported that most PICS bags were being reused for at least three years to store cowpea grain and recycled for other purposes, eventually lessening the technology’s environmental impact [18]. To date, there is only one published study on the GHG emissions of hermetic storage bag technology [16]. That study reported that one hermetic storage bag (90 kg capacity) causes 469 g CO2eq. Although no studies have been published comparing the environmental impacts of commercially available hermetic storage bags, many LCA studies have been published on polyethylene or plastic bags. Most studies estimated the environmental impacts in different categories, such as ecological damage, resource depletion, and human health damage from the raw material production and disposal of plastic bags [22,23,24,25].
A life cycle assessment (LCA) is a systematic approach to accounting for the environmental impacts of a product, process, service, or technology during its lifetime [26,27]. Information gathered in the assessment guides decision making and allows for comparing different products or services. Moreover, an LCA aids in measuring sustainability, in developing and implementing cost-effective solutions to address environmental burdens, and in improving an overall product or process life cycle [28,29]. The application of the LCA in agriculture has emerged over the past two decades. Studies have reported the environmental impacts of agricultural production and post-production processes [30]. For example, a life cycle evaluation of a rice production system in Italy found that from the field to the supermarket, 2.9 kg of CO2eq emissions per kg of delivered white milled rice was generated, consuming 17.8 MJ of primary energy and 4.9 m3 of irrigated water [31]. Another study assessed maize storage for small and middle-sized farmers and reported that as storage capacity increases, more energy is required and more greenhouse gas (GHG) emissions result [32]. Numerous other reports and studies have established that agricultural production and post-production operations, including storage, contribute significantly to greenhouse gas emissions [33,34].
An additional tool is the techno-economic analysis (TEA), which is used to evaluate a product, process, or service for cost-effectiveness and profit assessment. It estimates the capital cost, operating cost, and revenues over a lifetime. Moreover, this approach can be used to evaluate different scales of production or compare types of technology or product applications and understand the factors that affect profitability [29,35].
This study aimed at determining the environmental and economic impacts of hermetic storage bag technology using the LCA and TEA. It is the first attempt to estimate and compare the environmental impacts (ecotoxicity, global warming, and fossil fuel depletion) and the carbon footprint of six commercially available hermetic storage bag products. The results of this study could help provide baseline information for the successful adoption and sustainability of hermetic storage bag technology. Moreover, it will help authorities make science-based decisions on whether to include hermetic storage bags as part of a plastic ban. Furthermore, the TEA results will quantify the economic benefits of using hermetic storage bags in mitigating post-harvest loss challenges at the farm level.

2. Materials and Methods

2.1. Life Cycle Assessment (LCA)

2.1.1. Goal and Scope Definition

LCA was used to estimate the environmental impacts of hermetic storage bag technology from cradle to grave. The production of plastics from pellets to bag manufacturing, delivery of bags to vendors and end users, product usage, and disposal (Figure 1) were considered as part of the system boundary for the analysis. Transport to landfills was not considered.

2.1.2. Functional Unit (FU)

The focus of this study was on estimating the environmental impacts of six commercially available hermetic storage bag products (Table 1 and Figure 2). The functional unit used in the analysis is one hermetic bag with 69 to 100 kg capacity. Hermetic bag manufacturers claim that bags can be used for at least 3 years [13,14,15]. Thus, for the purpose of this LCA analysis, the total service of one hermetic bag is 27 months (or 9 months of storage per year).

2.1.3. Polymer Composition of Gas Barrier Liners

Confocal microscopy and Raman spectroscopy were utilized to identify the hermetic storage bag gas barrier liner structure, number of layers, and polymer composition. The gas barrier liners of six commercial hermetic storage bag products were prepared in five (5) replicates for microscopic analysis by dipping samples in liquid nitrogen before slicing them (5 × 10 mm). The cross-sectioned layer of each gas barrier liner was mounted for analysis on a confocal microscope (Keyence-laser, Vk-X1000) to analyze the thickness and number of layers. Confocal microscopy uses fluorescence optics with laser light to focus on a defined spot at a specific depth within the sample. It can also create 3D images of the structures of a given sample [36,37]. Raman spectra were subsequently applied to the mounted samples and measured on a DXR Raman Microscope (Thermo Fisher, Waltham, MA, USA) with 32 scans at a 2 cm−1 resolution and a 780 nm laser excitation source, 60 mW laser power at the sample, and a 50× microscope objective. The results were analyzed with OMNIC 9.7 software (Thermo Fisher, Waltham, MA, USA) to estimate the polymer composition per layer. Raman spectroscopy is a non-destructive technique used to analyze and detect bond vibrations. It is suitable for examining polymers and their additives through a collection of reference spectra called “fingerprints” [38,39].

2.1.4. Impact Categories

Energy, water consumption, and other resources within the system were the input impacts, while greenhouse gas emissions and solid waste disposal were the output impacts. The units for energy consumption were kilo Joule (kJ) and water consumption was in liters (L). The environmental impact categories and their respective descriptions are listed in Table 2. They are provided in millipoints (mPt) and CO2eq (kg). In SM 2013 methodology, one millipoint is 1/1000th of a point [40].

2.1.5. Life Cycle Impact Assessment

Using Sustainable Minds 2013 (SM 2013) LCA software, LCA was carried out for the six hermetic storage bag products. The input material characteristics for each product are summarized in Table 1. Energy and water consumption data were assessed with EioLCA using the 2002 Purchaser Price Model (Table 3). The model was run using 1 million United States dollars (USD) of economic activity in the overall plastic packaging materials, film, and sheet sector.
Three performance indicators of environmental impacts (mPt/bag) and carbon footprint (kg CO2eq/bag) for bag manufacturing, transportation, use, and end of life (landfill) were estimated using SM 2013 LCA software. The assumptions are listed in Table 4. The SM 2013 software uses TRACI 2.1 impact categories developed by the U.S. Environmental Protection Agency (EPA), North American normalization, and weighting values developed by the EPA and National Institute for Standards and Technology (NIST) for evaluating potential ecological and human health impacts of products used in North America.
The total environmental impact for each hermetic storage bag type is expressed as a single score indicator (mPt), representing a total impact score from the 10 TRACI environmental impact categories listed in Supplemental Material Table S1 [40]. This score relates the hermetic bag storage technology environmental impacts to the overall environmental impacts in the US. Thus, a bag type with a high score means contributing more of an impact.

2.1.6. Sensitivity Analysis

The sensitivity of the analysis was based on “what if” questions to determine the impact of the total service delivered (no. of storage season) and bag material on the total environmental impacts. This study used specifications as listed in Table 5 for the sensitivity analysis.

2.2. Techno-Economic Analysis (TEA)

2.2.1. Description of the Analysis

The TEA only accounted for the typical bag storage methods used by smallholder farmers in low-income countries. These include woven polypropylene (PP) bags, PP bags with insecticide applied to the stored product, and hermetic storage bags. Two types of hermetic bags were considered based on the number of gas barrier liners used in practice: (a) one multilayer extruded film (hermetic bag A) and (b) two high-density polyethylene (HDPE) films (hermetic bag B). Table 6 shows the independent variables and scenarios used in the analysis. Within the scope of the study, the economic impacts assessed were for one smallholder farmer using ten (10) hermetic bags storing 100 kg/bag (1 ton) of maize at a safe storage moisture content of 13.5% for one season (3, 6, or 9 months) and using the bags for up to three seasons.

2.2.2. Method of Data Collection

Secondary information was accessed from various sources, including journals, articles, field reports, and other online sources as listed in Table 6. The secondary data provided information about the production and post-production data on maize in Sub-Saharan African countries. Other information used for the economic analysis included the capital cost of a bag (100 kg) and insecticides (USD/bag), adoption cost (USD/bag), and transportation cost (USD/bag) as the annual operating costs. Other data collected included the average selling price of maize, discount prices due to grain damage, and loss of sales due to weight loss. These were used to calculate the benefits as a function of the storage method used for different storage periods (3, 6, and 9 months) per season.

2.2.3. Analytical Approach

Annual costs for each storage method were calculated based on a 3-, 6-, and 9-month period, which included costs for purchasing the bags, insecticides, adoption, and transportation. Annual benefits were assessed based on discounts due to damage, loss of sales due to weight loss, and market selling price. Economic impacts were then calculated for each storage method as the profit (USD) and storage loss (%) for the entire lifetime of the bags (Table 7). Furthermore, the total operating costs were projected to increase annually by 12% due to price inflation in Sub-Saharan African countries [47]. Transportation costs considered for traditional and hermetic storage bags were related to time and assumed to decrease with the increase in storage duration because the opportunity for transportation is high during peak production [48].

3. Results and Discussions

3.1. Life Cycle Assessment (LCA)

3.1.1. Polymer Composition of Gas Barrier Liners

To accurately estimate the allocation of the environmental impacts of different commercially available hermetic storage bag products, the polymer structure and composition of gas barrier liners were identified. Figure 3 shows the confocal images of each commercially available hermetic bag gas barrier liner. The AgroZ®, GrainPro, Storezo, and ZeroFly® bags showed a multilayer structure with three layers, consistent with manufacturers’ specifications as a coextruded liner of polyethylene (PE) with a gas barrier layer.
After identifying the number of layers for the coextruded gas barrier liners (AgroZ®, GrainPro, Storezo, and ZeroFly® bags), polymer identification was performed using Raman spectroscopy to estimate the film composition. The results extracted from the confocal and Raman microscopes revealed structural and compositional differences (Table 8). The composition of each layer was identified using a spectral search to compare the spectra from the layer with those in the Raman Polymer Library. All Raman peak assignments for PE, PA6 (Nylon), PP, and EvOH are compiled in Supplementary Material Table S2.

3.1.2. Ecotoxicity, Fossil Fuel Depletion, Greenhouse Gas Emission, and Carbon Footprint

Among the six products, PICS™ had the highest value of 2.6 × 10−2 mPt/bag, 2.3 × 10−2 mPt/bag for ecotoxicity and fossil fuel depletion, respectively (Figure 4). AgroZ® had the lowest value (8.9 × 10−3 mPt/bag) for ecotoxicity and fossil fuel depletion (1.9 × 10−2 mPt/bag), i.e., 66% lower in ecotoxicity and 43% lower in fossil fuel depletion than PICS™.
Ecotoxicity is the environmental impact caused by chemicals or substances that adversely affect all living things. Plastics are considered solid waste but also as hazardous waste due to the chemicals used in their production processes that could be ingested by animals, adsorbed in water, and bio-accumulated in soil [49,50]. The raw materials PE, PP, Nylon, and EvOH used to manufacture these gas barrier liners are made from non-renewable resources (i.e., petroleum-based polymers). The two liners of the PICS ™ and Elite bags weigh 400 g per unit bag and are made from polyethylene resin. This higher amount of polymer resin used in each product results in a greater ecotoxicity and fossil fuel depletion than the coextruded gas barrier liners.
ZeroFly® accounted for the highest global warming impact (2.5 × 10−2 mPt/bag), and Storezo for the lowest (1.6 × 10−2 mPt/bag). The coextruded films consist of two to three polymer types. Utilizing more than one raw material for bag manufacturing results in higher GHG emissions.
Figure 5 shows the carbon footprint of each hermetic storage bag product for the total service life delivered, i.e., 27 months of use. ZeroFly® had the highest value of 1.7 kg CO2eq/bag for one bag and Storezo had the lowest value (1.1 kg CO2eq/bag). These results suggest that the multilayer coextruded and double HDPE gas barrier films fall within a narrow carbon footprint range from bag manufacturing to landfill disposal.
Carbon dioxide emissions for polyethylene and polypropylene are reported to range from 2.5–3 kg CO2eq/kg and 3.4 kg CO2eq/kg, respectively [51]. Nylon is estimated to produce 6.5 kg CO2eq/kg [52], while EvOH produces 2.5 kg CO2eq/kg [53]. One study utilized a value of 0.5 kg CO2eq/kg PICS™ bag as the GHG emissions for packaging maize, but failed to mention whether the value included the disposal and life span of the bags considered in the calculation [18]. The results of this study point to more realistic values because the analysis considered the cradle-to-grave approach for hermetic storage bag technology.

3.1.3. Impacts of the Life Cycle Stage

Figure 6 shows the environmental impacts for each life cycle stage of hermetic storage bag technology. Bag manufacturing dominated across all products ranging in impact from 84.6% to 91.9%. Bag manufacturing had the greatest environmental impact because of the substantial fossil fuel depletion and global warming potential of petroleum-based polymer processing. The technology usage period (storage period) contributed 6.4% to 13.5% of the impact, while transportation and end-of-life stages had the least impact ranging from 0.7% to 0.9%. The 27 months of useful service life assumed in this study requires the strength of liner material and structural integrity of the hermetic storage bag to last for three harvest and storage cycles. If the use cycle is reduced to just one season or increases to five seasons, then the environmental impact changes to 0.09 mPt/bag and 0.11 mPt/bag, respectively (Table 9). The results indicate that if bags are only used for one season (9 months only), then the manufacturing contribution increases to 94.4% while decreasing to 82.5% when used for five seasons. Moreover, as expected, the environmental impact contribution of the use life stage increased with the total service delivered.
Although landfill disposal is used in the analysis of the end of service life, the impact is substantially smaller than the bag manufacturing and use stages. Nevertheless, the problem of plastic solid waste still hinders the technology’s long-term sustainability. In consultation with plastic packaging industries, research institutions and academia are working to develop new bio-based and eco-friendly materials to replace petroleum-based packaging materials. Some examples of biopolymers currently under investigation include thermoplastic starch (TPS), polylactides (PLA), poly-hydroxybutyric acid (PHB) and its copolymers (PHAs), and polymer fills [51,54]. In 2020, a new hermetic storage bag product (Tigoun bag) was introduced that supposedly consists of 80% renewable and biodegradable materials [55]. Unfortunately, a sample could not be obtained in time for inclusion in this study. However, assuming such a high renewable and biodegradable content in the gas barrier liner of the hermetic bag product with the lowest total impact in this study would change the distribution of the environmental impact of the four life cycle stages investigated to 86.9% for bag manufacturing, 10.9% for use period, 1.3% for transportation, and 0.6% for end of life. Shown in Table 10 are the total impacts for the service delivered in terms of CO2eq emission per bag when different bag material is used for storage.
Currently, manufacturers promote extending the service life of hermetic bags as a key solution to mitigating their environmental impact. Recommendations include the proper handling and use of the product to increase longevity, encouraging users to ensure that grains are cleaned and free from debris (e.g., stones, sticks, metals) that could damage liners, storing bags in clean areas away from direct sunlight and extreme heat, avoiding damage by rodents and sharp objects that could puncture liners, carefully handling bags during filling and emptying, and patching small holes or tears with tape to maintain air tightness [27,56]. Manufacturers also suggest that once gas barrier liners lose airtightness due to holes and punctures, farmers should use them to store crops that are less susceptible to pests, and making plastic ropes and mats, rain-shedding wearables, and window covers from the material [56]. However, this study clearly identifies the need to improve the bag manufacturing process, and specifically, replacing petroleum-based polymers with renewable and biodegradable materials is one approach.

3.2. Techno-Economic Analysis (TEA)

Figure 7 shows the capital and operational costs, benefits, and profits for the different scenarios considered in the study using the data, assumptions, and equations listed in Table 6 and Table 7. The capital cost of traditional methods (PP bag with and without insecticides) ranged from 5 to 6 USD when used for three to nine months of storage per year, unlike hermetic bags (bag type A and B) that require a higher capital cost of 33 to 50 USD for ten bags of 100 kg capacity when used over three years.
The length of effective storage that minimizes crop losses and maximizes profit plays a vital role for smallholder farmers in choosing the storage method. For the scenarios evaluated, the purchase price of hermetic bags resulted in seven to nine times higher capital costs than conventional polypropylene bags with or without insecticides. Several studies [1,13,57] have reported that the first criterion farmers use to choose a storage method is its initial cost. If the new technology requires taking out a loan at interest rates as high as 20% or more, then smallholder farmers hesitate or avoid adopting new technologies and practices that initially cost more. However, among other important criteria is maintaining the quality and quantity of the stored product and its relatively easy availability. Hermetic bags have proven effective at reducing storage losses from insect pests and mold spoilage, have become more affordable and relatively easy to obtain in rural areas.
On the other hand, the highest operational costs among the storage methods was incurred when using PP bag + insecticides because of the reapplication of insecticides every three months; costs increased from 100 to 240 USD for three versus nine months of storage in contrast to hermetic bags, of which the operational cost decreased from 29 USD (three months) to 18 USD (nine months). Current practice of farmers to protect grains from insects is the application of chemical insecticides before placement in conventional (PP) bags for storage. Insecticides are readily available but are an additional expense [2,15,58]. Additionally, when farmers used insecticide, it did not stop insect damage but continued to cause weight loss of 2.5 to 12.9% compared to 1.2 to 1.5% for hermetic bags during 100 to 200 days of maize storage [5,16]. The overuse and misuse of insecticides, such as applying more or more frequently than recommended, has increased insect resistance to certain chemicals and pesticide residues on grains that are a health concern for consumers [5]. Hermetic bag storage technology does not require the chemical treatment of grains to effectively reduce losses due to insect damage, thus outweighing the benefits of the less expensive PP bag with or without insecticides.
This analysis assumed that all maize stored for each duration was sold at a given price listed in Table 6. Thus, benefits were calculated as the total sales minus the discount due to damage and loss of sales due to weight loss. Hermetic bags A and B resulted in greater benefits (Figure 7) than PP bags and PP bags + insecticide, and significantly increased with storage duration, i.e., from 13.3% to 106.9% and 2.1% to 25.5%, respectively. Grain damage and storage losses are caused mainly by insects, rodents, and fungi. Farmers reported having losses of up to 20% when using PP bags, which reduced to 8% with the application of insecticides, when stored for at least six months [13,56]. This results in higher discounts due to damage and loss of sales. Although the capital cost for hermetic bags is 7- to 9-fold higher than PP bags (with or without insecticides), the results clearly show that the benefits are substantially greater due to their better performance in preserving grain quantity and quality for three to nine months of storage per year.
Moreover, hermetic storage bags A and B resulted in greater profitability across storage duration (Figure 7). At three months of storage per year, profit margins were relatively narrow ranging from 741 to 834 USD for the four options. As the storage period increased, the difference in profit from using traditional bags (PP bag and PP bag + insecticide) to hermetic bags became larger with values of 618 to 985 USD and 536 to 1135 USD, for six months and nine months of storage per year, respectively. The profit reported in this study was expected because the operational cost of hermetic storage for each duration was less than 100 USD, while discounts due to damage and weight loss were significantly lower than the traditional storage bag options. Furthermore, the results agree with other published reports that hermetic bags provided better profit than conventional (PP) bags and insecticide-treated PP bags, and that hermetic bags were found more profitable when used for at least four months for one season [5,13,14,59].
PP bags for storage resulted in a total loss per kg maize of 12.2%, 36.9%, and 52.0% for three, six, and nine months of storage duration per year, respectively (Figure 8). Consequently, they incurred the lowest profit among the storage options and durations. A similar observation was made in several studies, which reported that losses due to grain damage when using traditional bags for at least six months to ten months would reach up to 80%, while 30% due to weight loss [2,8]. As a result, farmers tend to sell right after harvest when prices are low, resulting in low or no profit [60]. As an option, farmers apply insecticides to reduce the damage caused by insect pests. As reflected in the results, the storage loss incurred in PP bag + insecticide was reduced to 2.9%, 9.5%, and 24.2% for three, six, and nine months of storage, respectively, whereas hermetic bags A and B maintained less than 1% storage loss over the three-to-nine-month storage duration over three years of use. For this reason, the profits earned using hermetic bags were calculated as being up to twice those of PP bags (Figure 7). These results imply that storage loss reduction using an airtight bag for storing grains is superior to traditional methods and effective, as established in several published studies [15,16,17].
In summary, the economic benefits of using hermetic bags surpassed the capital cost as shown in Table 11. A farmer that will invest in ten hermetic bags and use them for a nine-month storage period will have a savings of 163 and 616 USD, due to not buying insecticides and the storage loss reduction, respectively.

4. Conclusions

The key conclusions are:
  • The confocal and Raman spectroscopy results found differences in the polymer composition of six commercially available gas barrier liners, confirming that AgroZ®, GrainPro, Storezo, and ZeroFly® use coextruded films with an oxygen barrier layer, while PICS™ and Elite bags use liners made solely of polyethylene.
  • The life cycle assessment (LCA) of six commercially available hermetic bags from cradle to grave found that the bag manufacturing stage had the highest (84.6% to 90.8%) environmental impact contribution among all the life cycle stages. In terms of environmental impact and carbon footprint for the 27-month service life evaluated for the technology, the key findings include:
    • The PICS™ bag had the highest value of 2.6 × 10−2 mPt and 3.3 × 10−2 mPt for ecotoxicity and fossil fuel depletion, respectively.
    • The ZeroFly® bag had the highest global warming impact contribution of 2.5 × 10−2 mPt.
    • The carbon footprint ranged from 1.1 to 1.7 kg CO2eq per bag.
  • The economic analysis of adopting hermetic storage bag technology predicted net profits of 829, 979, and 1130 USD per 10 bags for the crop storage periods of three, six and nine months, which were substantially higher than the initial capital costs of 38, 41, and 45 USD, respectively. Savings from eliminating insecticides and reducing storage losses contributed substantially to the net benefits.

Supplementary Materials

The following supporting information can be downloaded at: https://www.mdpi.com/article/10.3390/su152014850/s1, Table S1: TRACI impact categories, normalization and weighting factors used to create the SM2013 impact factors; Table S2: Main Raman assignments for polymer found in the multilayer films. References [38,39,40,61,62,63,64] are cited in the Supplementary Materials.

Author Contributions

All authors contributed to the study conception and design. M.C.C.D.I.: Investigation, Visualization, Formal analysis, Writing—original draft & editing; K.A.R.: Writing—review & editing; D.E.M.: Supervision, Writing—review & editing. All authors have read and agreed to the published version of the manuscript.

Funding

This research was funded by The Rockefeller Foundation (Grant 2018 FOD 004), the Foundation for Food and Agriculture Research (Grant DFs-18-0000000008), and the Iowa Agriculture and Home Economics Experiment Station.

Institutional Review Board Statement

Not applicable.

Informed Consent Statement

Not applicable.

Data Availability Statement

Data is contained within the article or Supplementary Material.

Acknowledgments

The authors would also like to acknowledge that part of the study was conducted at the Food Packaging Research Laboratory of the Food Science and Human Nutrition Department, College of Agriculture and Life Sciences, Iowa State University.

Conflicts of Interest

The authors declare no conflict of interest.

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Figure 1. System boundary, inputs, and outputs used for life cycle assessment (LCA) of hermetic bag storage technology.
Figure 1. System boundary, inputs, and outputs used for life cycle assessment (LCA) of hermetic bag storage technology.
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Figure 2. Hermetic bag storage brands considered in the study: (a) GrainPro, (b) PICS™, (c) Elite, (d) ZeroFly®, (e) AgroZ®, and (f) Storezo.
Figure 2. Hermetic bag storage brands considered in the study: (a) GrainPro, (b) PICS™, (c) Elite, (d) ZeroFly®, (e) AgroZ®, and (f) Storezo.
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Figure 3. Confocal microscopy images of gas barrier liners of hermetic storage bags at 50× magnification.
Figure 3. Confocal microscopy images of gas barrier liners of hermetic storage bags at 50× magnification.
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Figure 4. Environmental impacts of commercially available hermetic bag storage products use for 27 months.
Figure 4. Environmental impacts of commercially available hermetic bag storage products use for 27 months.
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Figure 5. Carbon footprint of hermetic bag storage for 27 months of total service delivered from cradle to grave.
Figure 5. Carbon footprint of hermetic bag storage for 27 months of total service delivered from cradle to grave.
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Figure 6. Environmental impacts of life cycle stages of hermetic storage bag technology.
Figure 6. Environmental impacts of life cycle stages of hermetic storage bag technology.
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Figure 7. Capital and operational cost, benefits, and profits for each storage method used for 3, 6, and 9 months of storage per year in 3 years. Assumption: one smallholder farmer storing 1 ton of maize. PP (polypropylene bag); PP + I (polypropylene bag with insecticide); HB A (hermetic bag type A); HB B (hermetic bag type B).
Figure 7. Capital and operational cost, benefits, and profits for each storage method used for 3, 6, and 9 months of storage per year in 3 years. Assumption: one smallholder farmer storing 1 ton of maize. PP (polypropylene bag); PP + I (polypropylene bag with insecticide); HB A (hermetic bag type A); HB B (hermetic bag type B).
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Figure 8. Storage loss incurred for four storage bag options over 3 years of usage. Assumption: one smallholder farmer storing 1 ton of maize. PP (polypropylene bag); PP + I (polypropylene bag with insecticide); HB A (hermetic bag type A); HB B (hermetic bag type B).
Figure 8. Storage loss incurred for four storage bag options over 3 years of usage. Assumption: one smallholder farmer storing 1 ton of maize. PP (polypropylene bag); PP + I (polypropylene bag with insecticide); HB A (hermetic bag type A); HB B (hermetic bag type B).
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Table 1. Characteristics of hermetic storage bags.
Table 1. Characteristics of hermetic storage bags.
Hermetic Storage Bag BrandComponentsMaterialCapacityLengthWidthWeight
kgcmcmg
AgroZ®outer bagwoven polypropylene10012080100
inner liner bagmultilayer liner 13075150
GrainProouter bagwoven polypropylene6912080100
inner liner bagmultilayer liner 11070150
Storezoouter bagwoven polypropylene7512080100
inner liner bagmultilayer liner 13075150
ZeroFly®outer bagwoven polypropylene10012580100
inner liner bagmultilayer liner 13070150
Eliteouter bagwoven polypropylene10512075150
inner liner bag2 HDPE liners 13074250
PICS™outer bagwoven polypropylene10013775100
inner liner bag2 HDPE liners 13770300
Table 2. Environmental impact categories and descriptions.
Table 2. Environmental impact categories and descriptions.
CategoriesDescription
EcotoxicityEcosystem impacts of the emission of toxic substances into air, water, and soil can occur on global, continental, or local scales; the plastic industry contributes to the toxicity caused by the emissions of toxic substances [28].
Fossil Fuel DepletionThe extraction of natural gas, oil, and coal reserves at a rate higher than nature replenishes them. Feedstock in manufacturing of plastics [40].
Global WarmingIncreasing temperature in the lower atmosphere, caused by the emission of greenhouse gases (e.g., CO2, methane, and nitrous oxides), which reflect or absorb infrared radiation from the Earth’s surface. This causes regional climate changes, the melting of polar ice and glaciers, and sea-level rise [28].
Table 3. Data inventory for energy and water consumption for six commercially variable hermetic storage bags.
Table 3. Data inventory for energy and water consumption for six commercially variable hermetic storage bags.
InventoryAgroZ®GrainProStorezoZeroFly®ElitePICS ™
Energy (kJ/bag)333333332525
Water (L/bag)1021021021027676
Table 4. Assumptions utilized in LCA impact assessment.
Table 4. Assumptions utilized in LCA impact assessment.
Life Cycle StageDescription
Bag manufacturingExtrusion process (film) using virgin polymer resin
TransportationTransport, combination truck, average fuel mix (350 km)
UseRespiration rate of dry corn (MC < 14%) 0.34 mg CO2/(kg·h) [41] was used to calculate the carbon dioxide produced by maize during storage. Carbon dioxide as by-product of respiration is an indicator of maize deterioration during storage [42]. Assumption: All CO2 produced by maize during storage is released to the environment after opening the bag.
End of lifeLandfill disposal (transport to landfill was not considered)
Table 5. Parameter specifications used for sensitivity analysis.
Table 5. Parameter specifications used for sensitivity analysis.
Total Service Delivered (Storage Season) *Bag Material (Weight)
±280% Biopolymer barrier liner (PLA/PE) (250 g)
Coextruded barrier liner (150 g)
PE gas barrier liner (250 g)
PP bag (150 g)
Jute sack (900 g)
* The study used 3 storage seasons (27 months or 9 months of storage per year) of total service delivered for one hermetic bag. Thus, 1 season = 9 months of total service delivered; 5 storage seasons = 45 months of total service delivered.
Table 6. Assumptions and data used for techno-economic analysis for different storage scenarios of one smallholder farmer storing 1 ton of maize.
Table 6. Assumptions and data used for techno-economic analysis for different storage scenarios of one smallholder farmer storing 1 ton of maize.
AssumptionsValueRemarks/References
Storage bag method
   Polypropylene bag (PP)
   PP bag + insecticide (PP + I)
   Hermetic bag type A (HB A)
   Hermetic bag type B (HB B)
Storage duration (months) per season369
Service life (months) for 3 seasons91827
Interest rate, per annum0.20.20.2[43]
Bag cost (USD/bag − 100 kg capacity) [44]
   Polypropylene bag0.5
   Hermetic bag A4.0
   Hermetic bag B3.0
Insecticides, USD/bag (reapply every 3 months)1.21.21.2[17,45]
Adoption cost
   Bagging labor (USD/bag)0.50.50.5[9]
   Insecticide application (USD/bag)111[9]
Transportation
   PP bag, USD/bag0.800.650.5[46]
   Hermetic bag, USD/bag0.360.210.06[46]
Discounts due to damage, %
   10–20% damaged: 8%
   >20% damaged: 16%		 [20]
Damaged grain, %
   PP bag183550[20,45,46]
   PP bag + insecticide<5<610 to 20
   Hermetic bag A<5<5<10
   Hermetic bag B3.53.54
Loss Sales (weight loss, %)
   PP bag4.220.936[20,45]
   PP bag + insecticide2.58.212.9
   Hermetic bag A0.30.61.0[45]
   Hermetic bag B0.50.71.0
Market prices, USD/kg0.300.350.40[20,45]
All Bags Lifetime, year 3 [20,45]
Table 7. Equations used for the TEA calculations.
Table 7. Equations used for the TEA calculations.
Analyses (Units Included)Equations (Units Included)
Storage duration (SD), (months/season)
(1)
SD = months of storage per season
Total service life (TSL), (months/bag)
(2)
TSL = SD (months/season) × 3 seasons
Total storage bag capacity (TSC), (kg/total service life)
(3)
TSC = bag capacity (kg) × 10
Annuity (A), USD
(4)
A = P ((I (1 + I)N)/((1 + I)N − 1)), P = principal value (purchase cost of bag, USD), I = interest rate/12, N = total service life in months
Capital cost (CC), USD
(5)
CC = bag purchase cost (USD/bag) × 10
Bagging cost (BC), (USD/total service life)
(6)
BC = cost of bagging (USD/bag) × 10
Insecticides and application cost (IC), (USD/total service life)
(7)
IC = (insecticide cost (USD/bag) × 10) + (application cost (USD/bag) × 10)
Transportation cost (TrC), (USD/total service life)
(8)
TrC = transportation (USD/bag) × 10
Total operational cost (TOC), (USD/total service life)
(9)
TOC = bagging cost (USD/total service life) + (insecticides and application cost) + transportation cost (USD/total service life)
Total cost (TC), (USD/total service life)
(10)
TC = TOC (USD/total service life) + (annualized CC for entire service life)
Discount due to grain damage (DGD), (USD/total service life)
(11)
DGD = TSC (kg/total service life) × market price (USD/kg) × discount
Loss of sales (LOS), (USD/total service life)
(12)
LOS = TSC (kg/total service life) × market price × weight loss
Total benefits (TB), (USD/total service life)
(13)
TB = (TSC (kg/total service life) × market price (USD/kg)) − DGD (USD/total service life) − LOS (USD/total service life)
Profit (P), (USD/total service life)
(14)
P = TB (USD/total service life) − TC (USD/total service life)
Storage loss (SL), (%)
(15)
SL = ((TSC (kg/total service life) × market price (USD/kg)) − (TB (USD/total service life)))/(market price(USD/kg)/TSC (kg/total service life)) × 100
Table 8. Polymer composition and thickness (± standard deviation) of gas barrier liners of hermetic storage bags.
Table 8. Polymer composition and thickness (± standard deviation) of gas barrier liners of hermetic storage bags.
Hermetic Storage Bag TypeNumber of Layer (s)CompositionTotal Thickness, μmLayer Thickness, μm
1st2nd3rd
AgroZ®3PE-Nylon-PE82.5 ± 1.250.1 ± 2.68.9 ± 0.623.5 ± 3.2
GrainPro3PE-Nylon-PE81.8 ± 1.037.2 ± 0.39.1 ± 0.935.5 ± 0.9
Storezo3PE-EvOH-PE79.8 ± 1.834.4 ± 0.210.2 ± 0.935.7 ± 0.9
ZeroFly®4PE-PP-Nylon80.0 ± 0.839.1 ± 0.911.1 ± 0.229.7 ± 0.4
Elite1PE74.5 ± 0.5
PICS ™1PE75.5 ± 0.4
Table 9. Effect of total service delivered of one hermetic bag on environmental impacts *.
Table 9. Effect of total service delivered of one hermetic bag on environmental impacts *.
Life StagesAverage Total Impacts (%)
Current (3 Seasons)−2 Seasons+2 Seasons
Bag manufacturing88.9694.4182.48
Transportation1.020.960.84
Use9.193.6615.92
End of life0.840.960.76
Total impacts (mPt/bag)0.100.090.11
* Current = 3 storage seasons (27 months or 9 months of storage per year); −2 seasons = 9 months total service delivered; +2 storage seasons = 45 months total service delivered.
Table 10. Scenarios of using different bag material of 100 kg capacity for grain storage of 27 months.
Table 10. Scenarios of using different bag material of 100 kg capacity for grain storage of 27 months.
Bag Typekg CO2eq/bagTotal Impacts (mPt/bag)Bag Manufacturing (% of Total mPt)
80% Biopolymer barrier liner (PLA/PE)1.70.0986.9
Coextruded barrier liner1.10.0579.7
PE gas barrier liner1.20.0885.9
PP bag1.10.0369.2
Jute sack4.90.3696.4
Table 11. Economic benefit of using ten hermetic bags for storing 1 ton of maize for 3 years.
Table 11. Economic benefit of using ten hermetic bags for storing 1 ton of maize for 3 years.
3-Month Storage6-Month Storage9-Month Storage
Capital cost (USD)384145
Savings for not buying insecticide (USD)89163163
Savings for storage loss reduction (USD)106381616
Profit per 10 bags (USD)8299791130
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Ignacio, M.C.C.D.; Rosentrater, K.A.; Maier, D.E. Estimating Environmental and Economic Impacts of Hermetic Bag Storage Technology. Sustainability 2023, 15, 14850. https://doi.org/10.3390/su152014850

AMA Style

Ignacio MCCD, Rosentrater KA, Maier DE. Estimating Environmental and Economic Impacts of Hermetic Bag Storage Technology. Sustainability. 2023; 15(20):14850. https://doi.org/10.3390/su152014850

Chicago/Turabian Style

Ignacio, Ma. Cristine Concepcion D., Kurt A. Rosentrater, and Dirk E. Maier. 2023. "Estimating Environmental and Economic Impacts of Hermetic Bag Storage Technology" Sustainability 15, no. 20: 14850. https://doi.org/10.3390/su152014850

APA Style

Ignacio, M. C. C. D., Rosentrater, K. A., & Maier, D. E. (2023). Estimating Environmental and Economic Impacts of Hermetic Bag Storage Technology. Sustainability, 15(20), 14850. https://doi.org/10.3390/su152014850

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