Open and Closed Black Soldier Fly Systems Tradeoff Analysis

Abstract

When it comes to waste management, it is essential to consider human and environmental safety, financial feasibility, and social benefits. So often, one of these factors takes priority over the others. However, integrated social, environmental, and economic benefits are more apparent with insect-based waste treatment technology like the Black Soldier Fly (BSF) system. BSF waste treatment is an innovative and adaptable technique that offers sustainable benefits to communities in developing countries because it can be designed to be as simple or complex as required. Depending on the local context, simple (open) systems based on naturally occurring flies or more complex (closed) systems based on captured fly colonies are viable. However, what are the environmental tradeoffs when choosing between these two systems? The surge in the use of both BSF systems makes this consideration imperative. Furthermore, until now, the environmental and social impacts of open BSF waste treatment systems have not been compared. The environmental tradeoffs in implementing an affordable, socially accepted, open BSF biowaste treatment system are explored in this study to address this gap. Co-production for delivering public services was used to develop an accepted BSF system through a case study by applying qualitative interaction research methodologies. A Life Cycle Assessment (LCA) was then used to compare the environmental impacts of natural ovipositing BSF systems compared to captured BSF systems. Natural ovipositing BSF (open) systems, in comparison, have reduced climate change (33%) and water, land, and energy use (55%, 37% and 32%) while also motivating the development of socially accepted infrastructure measured through community engagement. This mixed-methods approach facilitates the development of contextually appropriate technology in low-income communities in developing and developed countries while also reducing environmental consequences.

1. Introduction

Climate change concerns, increasing food demand, environmental deterioration, human health concerns, and the recognized value of organic waste have driven interest in a closed-loop solution to waste management. Insect farming through insect-based waste treatment has become a viable solution [1]. The treatment of organic waste using fly larvae was mentioned almost a century ago [2]. By treating biowaste (organic waste), producing alternative protein for feed, and preventing eutrophication, the benefits of insect-based waste management or insect farming are appreciable to humans, animals, and the environment. This interdependency between humans, animals, and the environment includes health risks. Therefore, proper biowaste management is a key component of the One Health concept, as it recognizes that the health of people is closely connected to that of animals and the environment [1]. The benefits have also been proven economically, as evidenced by the proliferation of insect rearing in developed and developing economies. Insect-based biowaste treatment mitigates food waste and nutrient loss [3] while generating byproducts that include alternative protein sources beneficial to humans, livestock and pets, input for biofuel production, pharmaceuticals, and regenerative agriculture [4]. These advantages have seen an increase in the adoption of insect-based waste treatment systems, with Black Soldier Fly (BSF) insect production recognized as the fastest-growing sector [5]. Black Soldier Fly larvae (BSFL) are the most favored species for animal feed amongst insect producers [6,7,8] because of attributes that include a waste reduction potential of 50–80% [9], high-quality protein conversion [10], efficient reduction of the occurrence of harmful bacteria [6], lower greenhouse gas emissions with less residue in comparison to livestock production [6], and efficacy in digesting almost all types of organic waste [9].

Black Soldier Fly larvae (BSFL) production can be classified based on two factors: scale, i.e., large, medium, or small, and system design, i.e., natural or captured fly populations. Large-scale BSFL systems are geared toward protein production and can process up to 200 tons of waste daily. Medium-scale systems focus on waste treatment and cater to local markets, treating up to 10 tons of waste per day [10]. In contrast, small-scale BSFL systems are typically run by farmers and hobbyists, treating less than 1 ton of waste daily. BSF production systems are also categorized by the mode of BSFL reproduction. These can be systems based on the natural oviposition of naturally occurring BSF (open systems) or the rearing of captured BSF (closed systems) [9,11]. Open BSF systems (OSs) attract wild female BSF to a pile of exposed biowaste [11]. The adult flies lay clutches of eggs close to decomposing waste, so newly hatched larvae fall into the food source. Specialized equipment is unnecessary as the system is self-sustaining, requiring minimal infrastructure, and can be run using a wide range of containment configurations from exposed basins of organic waste to wooden or cement structures [5,8]. Feeding larvae bioconvert the organic waste into insect biomass, a nutrient-rich feed used in animal husbandry. The BSF larvae can be harvested from the residue by manually sorting the larvae from the leftover residue (frass), or harvesting can be based on the self-migratory behavior at the prepupae stage when BSFL self-harvest by exiting the residue to pupate [12,13,14]. Empirical studies of OSs were first conducted in the USA. The study involved wild BSFL in the bioconversion of chicken manure using concrete basins beneath a caged hen house [15]. Since then, a plethora of OS designs have been available, with videos and descriptions provided on the internet [8]. OSs are typically small-scale operations run by micro or traditional farmers and composting enthusiasts [5,10].

Closed BSF systems (CSs) introduce more control to insect production by breeding captured BSF. Although BSFLs are adaptable to a wide range of abiotic parameters, temperature and humidity control is vital for productivity. A CS, therefore, includes two units, with one feeding into the other. The rearing unit houses the breeding colonies, from where eggs are acquired and added to organic waste in the waste treatment unit [8]. The eggs hatch into BSFL that feed on and bioconvert the waste into insect biomass. A CS uses a range of harvesting mechanisms, from simple sieving arrangements to highly mechanized strategies. CSs can be small-, medium- or large-scale operated.

Table 1. Comparing open and closed BSF systems.

BSF System	Pros	Cons
Open	Suitable for farmers with limited time for larval production [8].	Adaptable for large-scale production [8].
	Climate control is not required [5,6].	BSFL yields vary strongly with seasons because oviposition rates are weather-dependent [8,16].
	Simple designs with comparable procedures [8].	Required disposal of residue halts production [2,8].
	Facilitates waste treatment in remote and challenging locations [10].	Applicable only in regions with naturally occurring BSF [2,8].
	Adaptable to the technological and operational requirements and future increased demand of the local context [10].	High chitin and less digestible migrating prepupae are harvested [8].
	Provides an accessible solution to poor sanitation infrastructure for low- and middle-income countries with favorable weather [11].	Low-efficiency model that lacks an established or secured market. Meeting increased demand will be challenging [2,10,11].
	BSF do not transmit pathogens and rarely enter dwellings, unlike house flies (Musca domestica) [12,15].	Lacks quality control and assurance of the products. Hygiene standards are unregulated [10].
	Through colonization, BSF eliminates the presence of house flies [15].	BSF colonization, although vital for high biomass production, is dependent on natural conditions, which makes it unpredictable [11].
	Self-adjusts larval development duration in response to waste scarcity, thus allowing for the manipulation of larvae population and storage [15].	Reduced opportunities for administering process improvement interventions [2].
Closed	The units can be split for efficiency and mutual benefit. Large-scale centralized facilities can produce BSF eggs efficiently and cost-effectively. While small-scale farmers use the hatched eggs in growing the biomass-rich BSFL [8].	Requires two separate units, one for rearing and another for larvae growth [8].
	Increased production facilitates contracts with the animal feed sector and other industries [10].	Egg rearing is unsuitable for small-scale farmers due to its complexity and time requirement [8].
	High-quality control and hygiene standards [10].	High energy input required for lighting, mechanization, climate control and automation [7,8,9].
	Emissions and all waste generated can be centrally controlled [10].	Capital intensive investment [2,10].
	Abiotic conditions like temperature and humidity are easily controlled [9].	Transportation costs for hauling large waste quantities with minimal adaptability for changes in the waste source [10].

provides a comparison of OSs and CSs.

The varied BSF production methods by rearing system or scale have appropriate applications determined by the local context and affordability. Small- and medium-scale insect producers are located all over the world, including in Costa Rica [17], Indonesia [6], Kenya [18], and Guinea Republic [19], and Mali [16], and they are well-suited for countries and communities with inexpensive labor and limited access to protein feed [8]. However, the literature covering field studies centers predominately on scaling CS production, with a limited number focused on simple, affordable OSs [8,15,18,20]. According to surveys conducted by the World Bank, 76% of insect farms in Africa are small scale, and 39% are operated in the open air, while only 4% are large scale and are climate-controlled [5]. Small-scale BSF production offers numerous benefits but is not without limitations, which include unpredictable production, human health concerns, geographic suitability, and profitability. However, the increasing interest and proliferation of small-scale OSs in tropical low-income communities necessitate an assessment of their environmental impacts in comparison to an equally sized CS. This study aims to comparatively assess both systems’ greenhouse gas emissions and land, energy, and water use. The assessment will be a valuable tool for informing decision- and policy-makers on BSF farming.

A Life Cycle Assessment (LCA) is an established method of assessing or evaluating the environmental impacts of a process, product or service throughout its entire life span. However, LCAs recorded and published in Africa are limited, which is concerning because LCAs are required to identify potential tradeoffs when transitioning between environmental solutions [21]. When the environmental impacts of a proposed solution are unknown, it could have hidden and dire consequences. So far, LCAs of BSF biowaste treatment in Africa have solely focused on the waste reduction potential of dipteran insect species on animal manure [22,23], i.e., BSF, Hermetia illucens (L. Diptera, Stratiomyidae) and the common housefly, Musca domestica (L. Diptera: Muscidae). Therefore, this research intends to expand this repository by assessing the potential tradeoffs when introducing or substituting different BSF biowaste treatment methods, thus also advancing African LCA representation.

To achieve this, the study co-produced an affordable, socially acceptable, and energy-independent waste treatment system. Co-production involves the active participation of service users in the delivery of services [24] and therefore promotes social inclusion and civic engagement via public services [25]. This amalgamation of human safety and social benefits in waste management from the perspectives of government representatives, users, and the community necessitates the active involvement of all key stakeholders. The key stakeholders preferred to minimize resource inputs (financial, time, and labor) to the OS while maintaining profitability and minimizing the environmental impact. Using these design parameters, the study demonstrates that the design and operation of a decentralized biowaste treatment system can be co-produced with stakeholders to achieve a system requiring reduced water usage (28 m³ vs. 44.46 m³) and land use (1233 m² vs. 1687 m²) in comparison to the CS, the technologically more advanced system.

2. Materials and Methods

A Life Cycle Assessment was conducted with data acquired from an empirical case study that established the social acceptance of the BSF system through co-producing the BSF system with a local health organization, a BSF enterprise, the relevant regulatory agency, an academic institution and community members. The case study used naturally occurring wild BSF in an OS.

2.1. Geographical Context

Approval was sought from the University of Calgary’s Research Ethics Board (CFREB) due to the inclusion of human behavior in the study. The CFREB operates under the current version of the Tri-Council Policy Statement: Ethical Conduct for Research Involving Humans (TCPS). The review board reviewed and approved the study (REB# 21-15-33) on 3 February 2022. The National Institute for Medical Research of Tanzania also granted ethical clearance on 7 June 2022, with the Tanzanian Commission for Science and Technology (COSTECH) approving the study on 15 August 2022. All the research participants provided written informed consent.

The open BSF system is located in Kipunguni (6.91844° S, 39.17309° E), a peri-urban community in Dar es Salaam, Tanzania. The site is 19 kilometers southwest of Dar es Salaam city center and 14 kilometers northeast of the Pugu Kinyamwezi landfill. The study started in the dry season (September and October) and continued through the rainy season (December to May). Therefore, the environmental conditions varied significantly, with temperatures ranging from 27 to 40.2 °C and humidity ranging from 40 to 82.8%.

2.2. Co-Production

The co-production approach sought to incorporate priorities for human safety and social benefits in biowaste management from the perspectives of government representatives, users, and the community. This was achieved by identifying and agreeing on the BSF system requirements with the identified stakeholders and incorporating these requirements into the project’s design and operation. Some of the requirements include an income source, a user-friendly and adaptable system, minimal operator intervention, and a reliable source of heavy-metal-free biowaste. Therefore, an OS was designed to minimize the resource inputs with minimal environmental impact and economic viability. The steps taken to incorporate co-production included modifying the research design post meeting with the stakeholders and research team observations. See Figure 1 below.

Details of the co-production process, stakeholder requirements, bioreactor modifications and process improvements are detailed in a separate publication [26]. This strategy was adopted to ensure that the final product would be suitable for a low-income majority female group, thus advancing the sustained use of the OS.

2.3. BSFL Production System

2.3.1. Organic Waste Bioconversion

The OS was collaboratively co-produced with BioBuu, a BSF enterprise, and Sauti ya Jamii Kipunguni (Voice of the Community Kipunguni), a community group. The bioreactor was constructed on land owned by Sauti ya Jamii Kipunguni and was independently managed by the community group.

The OS used in the case study is made up of a bioreactor and a 4.96 × 2.93 × 0.73 m concrete enclosure with corrugated roofing that is opened one sheet at a time. A metal frame runs around the bioreactor, supporting the roofing sheets and providing substrate access to wild BSF. The bioreactor is protected by a 25 mm chicken wire mesh to prevent rodents and pests from entering. Additionally, a 20 cm wide and 17 cm deep water channel keeps the bioreactor free from ants and lizards, see Figure 2. The bioreactor comprises two identical compartments, each with a biowaste conversion section and a harvesting section where black soldier fly prepupae self-harvest using a 32-degree ramp.

Fruit and vegetable waste sourced from a neighboring retail market, 5.25 km northwest of the site, is added to a feeding section until it is filled. The waste is manually broken down into smaller chunks and weighed before its addition to a bioreactor compartment. The compartments are used rotationally so that one section has feeding larvae while the second contains BSFL residue. The section with feeding larvae is manually aerated every other day. The biowaste is kept in that section for three weeks when the waste appears biodegraded i.e., blackish in color. Within those three weeks, the BSF prepupae migrate to the harvesting section, thus self-harvesting. The study ran from the bioreactor construction in October 2022 to May 2023; however, the data used in this LCA cover information gathered with the research team on site, i.e., before project handover and the independent running of the bioreactor by the community group. Therefore, the BSF cycle in this analysis was run four times between November 2022 and January 2023, i.e., the twelve weeks occurring in this time interval.

The data collected include inputs to the system, including biowaste and water, and outputs from the system, which were BSF larvae and prepupae, leachate, frass, and waste like mango pits that were not bioconverted. Frass is a blend of fecal excrement from BSFL, particles of their exoskeleton, and leftover substrate [27].

2.3.2. Frass Composting

The BSFL-produced frass is moved to a 2 × 1.2 × 0.5 m drying unit, see Figure 3, after the prepupae migrate for further decomposition and BSFL harvesting. The drying unit consists of two mesh wire racks, with wooden drawers under each rack. The residue is placed on a 25 mm metal mesh, prompting leftover photophobic BSFL to burrow into the residue, thus falling into the wooden drawers for harvesting. The residue is left in the drying unit for another three weeks for curing. This results in a total processing time of six weeks, three weeks in the bioreactor and three weeks in the drying unit. The weights of the drying units’ input, i.e., BSFL residue, and its outputs, i.e., cured compost and harvested BSFL, were recorded. Water loss due to evaporation and emissions to air were not measured or recorded.

2.4. Life Cycle Assessment

This study assesses the potential environmental tradeoffs when introducing or substituting a hypothetical CS biowaste treatment for an OS. To conduct the assessment, an LCA with openLCA 2.0 software (GreenDelta, Berlin, Germany) was performed using the ecoinvent 3.91 database (ecoinvent, Zurich, Switzerland) for background data. Dimensions and data from the literature were gathered to model the CS (captured BSF system). A midpoint impact assessment was conducted using ReCiPe 2016 version 1.03. Based on the BSF LCA literature, the impact categories considered in this assessment include climate change [28,29,30], energy use [29,31], land use [29,30], acidification and eutrophication [31], and water use [30]. Elements of the standardized LCA approach were used [32,33].

2.4.1. Goal and Scope

This is a comparative study of two Black Soldier Fly waste treatment systems defined by their production method [8]. The LCA aims to (1) determine the environmental impact differences between the OS and CS BSF waste treatment systems; (2) provide recommendations intended to facilitate future research and development endeavors in assessing the environmental performance of BSF technology in developing countries with a growing interest in BSF waste treatment [5,34]; and (3) identify processes that could yield substantial improvements. The gate-to-gate attributional LCA requires no allocation, as both the open and closed systems produce the same byproducts of BSFL and frass, which are cured to produce compost.

All the inputs and outputs of the BSF systems are analyzed and assessed based on the input-based functional unit (FU) of one ton of biowaste processed daily through both BSF waste treatment systems, i.e., one ton/day. The functional unit was chosen because it allowed for comparison with the literature [13,28].

2.4.2. System Boundaries

The system boundaries used in this assessment for the OS are illustrated in Figure 4, and the boundaries for the CS are shown in Figure 5. Both systems begin with collecting waste fruit and vegetables from the retail market, and they end with BSL and compost production. Both boundaries include the BSF system construction, waste collection, and BSF production, which includes rearing for the closed system. The same cleaning and maintenance processes are assumed for both systems.

2.5. Life Cycle Inventory

Direct measurements during waste collection and construction of the OS were used as primary data, while background data like electricity, water, and the miscellaneous equipment required for rearing BSF were obtained from the literature and ecoinvent 3.91 database.

2.5.1. BSF System Construction

The materials required for the construction of the open system bioreactor and drying unit were used as primary data in the study. Volumetric and weight conversions were based on industrial supplier data sheets. Conversions also had to be made on inputting data into openLCA. For example, paint and paint thinners used in the construction were entered as “solvent for paint” using the ecoinvent database. Additionally, materials such as metal mesh, paint brushes and rollers, and PVC pipes were unavailable in the database and therefore omitted. However, the material inclusion or omission was kept consistent for both the OS and CS.

Table A1. Material used in OS construction with corresponding material input references into openLCA.

Material	Quantity	Unit		openLCA Entry	Unit	Assumptions	Reference
Bioreactor Construction
Sand	2	tons		2	tons	2–3 tons capacity truck used in hauling sand. 2 tons assumed usage because of leftover
Bricks	130	pieces		707.629	kg	30 cm × 14 cm × 9 cm. 1440 kg/m3 density for 5.4433 kg per brick.
Gravel	270	kg		270	kg	15 bags of gravel @ 18 kg/bag
Cement	215	kg		215	kg	5 bags of cement @ 43 kg/bag
Wire mesh	7	pieces		39.56	kg	Welded Wire Mesh—1 kg/m2 (Ref No. 100. 200 × 200 mm, 4 mm wire size) 1 × 2 m wire sheets assumed (8 in total with metal roof). Total wire mesh weight for bioreactor installation was 39.56 kg ((4.3 length × 2.3 width/1 × 2 mesh size) × 8 mesh count)	https://www.weldedwiresupplier.com/products/reinforcingbarmesh.html (accessed on 7 December 2023)
Hardwood beams (2 × 2″)	4	pieces		0.03794	m3	2 × 4 × 12 kiln-dried wood weighing 7.2 kg (from reference) • volumetric estimation: 0.335 ft3 (0.167 ft × 0.167 ft × 12 ft), i.e., 0.009486 m3	https://www.engineeringtoolbox.com/green-kiln-dried-pressure-treated-lumber-weights-d_1860.html (accessed on 7 December 2023)
Hardwood beams (1 × 6″)	4	pieces		0.0564	m3	2 × 4 × 10 kiln-dried wood weighing 5.85 kg • volumetric estimation: 0.498 ft3 (0.083′ × 0.5′ × 12′), i.e., 0.0141 m3	https://www.engineeringtoolbox.com/green-kiln-dried-pressure-treated-lumber-weights-d_1860.html (accessed on 7 December 2023)
Nails (2″)	1	kg	1	0	kg	Added to roofing sheet weight
Nails (4″)	0.5	kg	0.5	0	kg	Added to roofing sheet weight
Metal Roofing
Square pipe (1 × 1″)	12	pieces		29.5884	kg	5.436 lbs (0.453 lbs/foot weight for 1 × 1″ for 12 ft) i.e., 2.4657 kg per piece	https://www.industrialtube.com/square-structural-tubing/ (accessed on 7 December 2023)
Hinge (3″)	12	pieces		0	kg	Not available in ecoinvent; therefore, ignored
Paint thinner	2	liters		1.554	kg	6.49 lbs (2.94 kg) for 1 gallon (3.785 L). All paint and thinners entered as “Solvent for paint” in openLCA	https://www.amazon.com/Klean-Strip-GKPT94400-Paint-Thinner-1-Gallon/dp/B000GF49M4 (accessed on 7 December 2023)
Red oxide	2	liters		0		Not available in ecoinvent; therefore, ignored
Black gloss	2	liters		0		Not available in ecoinvent; therefore, ignored
Tin nails	1	kg	1	0	kg	Added to roofing sheet weight
Wire mesh	1	piece	4.945	0	kg	Added to bioreactor construction wire mesh
Aluminum roofing sheets (10 ft 30-gauge)	6	pieces	21.78	24.28	kg	3.63 kg/sheet (8 lbs—8 ft 31-guage used). Weight of nails included here as openLCA entry	https://www.homedepot.com/p/8-ft-Corrugated-Galvanized-Steel-31-Gauge-Roof-Panel-13513/202092961 (accessed on 7 December 2023)
Painting
Paint (gray)	10	liters		0		Not available in ecoinvent; therefore, ignored
Paint (white)	1	litres		0		Not available in ecoinvent; therefore, ignored
Miscellaneous
Chicken wire (3 m)	1	piece		0		Not available in ecoinvent; therefore, ignored
PVC Pipes and elbows	2	pieces		0		Not available in ecoinvent; therefore, ignored
Bucket (20 L)	2	pieces		0		Not available in ecoinvent; therefore, ignored
Metal net	1	piece		0		1 m
Paint brush	2	pieces		0		Not available in ecoinvent; therefore, ignored
Roller	1	piece		0		Not available in ecoinvent; therefore, ignored
Drying Unit
Metal Pipes (2 × 2″)	8	pieces		7.076	kg	Square pipe—7.076 kg (15.6 lbs @1.3 lbs/ft for 2″ × 2″ at 12 ft)	https://www.industrialtube.com/square-structural-tubing/ (accessed on 7 December 2023)
Aluminum roofing sheets	8	pieces		18.15	kg	3.63 kg/sheet (8 lbs—8 ft 31-guage used). Accounting error suspected; five pieces used	https://www.homedepot.com/p/8-ft-Corrugated-Galvanized-Steel-31-Gauge-Roof-Panel-13513/202092961 (accessed on 7 December 2023)
Wire mesh	2	pieces		4.945	kg	4.945 kg (Ref No. 100. 200 × 200 mm, 4 mm wire size)	https://www.weldedwiresupplier.com/products/reinforcingbarmesh.html (accessed on 7 December 2023)
Wood	1	piece		0.0141	m3	One piece of 1 × 6″ wood assumed for wooden trays—0.0141 m3

in Appendix A provides details of the construction materials, assumptions made in measurement conversions, supplier references and the data omitted from the assessment.

2.5.2. Waste, Waste Collection and System Sizing

The same mode of transportation, a gasoline-powered flatbed tricycle, and distance to the waste collection point (10.5 km) were assumed for both systems. However, this was modeled as a passenger vehicle in openLCA. The fruit and vegetable waste composition was based on the Kenyan proximate analysis of the Kamau JM et al. and Gold et al. substrate databases [35,36]. The fruits and vegetables collected and modeled include kale, cabbage, pumpkin leaves, spinach, tomato, pawpaw, banana, avocado, zucchini, cucumber, mango, and watermelon.

Establishing the functional equivalence began with using the OS dimensions, shown in Figure 1, as a reference. The daily average biowaste added to the OS was 21.14 kg. This was calculated based on the monthly inputs provided in

Table 2. Monthly biowaste collection by the open system.

Month	Biowaste (kg)
November	632
December	616
January	655
Monthly Average	634.33 (+/−19.6 STD)

. The volumetric space occupied by the OS and drying unit is 8.47 m³. In achieving the FU of 1 ton of biowaste added per day, the space required for the OS becomes 400.78 m³, equivalent to operating 47 OSs.

Table A2. Calculation of OS and CS BSF bioreactor sizing.

Labels	Sum of Waste (kg)	Larvae Harvested (kg)	Frass Harvested (kg)	Frass Dried (kg)	Count of Larvae Application
January	655	7.76836	60	33	15
November	632	0.575	34.75	10	18
December	616	2.75994	143.25	20.5	14
Monthly Average Waste	634.33
STD	19.60
Daily Average Waste	21.14
Open System Sizing
Data-based Unit size (area)		(4.96 × 2.93) + (0.5 × 1.2)		15.13	m2 (bioreactor and drying unit)
Data-based Unit size (volume)		15.1328 × 0.56		8.47	m3 (same height assumed)
Calculated Unit area (@ 1 ton waste/day)		(1000 × 15.1328) ÷ 21.14		715.69	m2
Calculated Unit volume (@ 1 ton waste/day)		(1000 × 8.47) ÷ 21.14		400.78	m3
Number of open systems needed to treat 1 ton waste/day		400.78 ÷ 8.47		47
Closed System Sizing
187 m2 @ 1 ton/day (based on [13] Figure 5)		187 × 2.74		512.4	m3 (assuming 9 ft i.e., 2.74 m ceiling)
Comparing Sizes
# Closed to Open system for 1 ton/day		187 ÷ 715.69		0.3	area based
# Closed to Open system for 1 ton/day		512.38 ÷ 400.78		1.3	volume based

in Appendix A provides the calculations.

One ton of biowaste per day can be processed in a CS measuring 187 m² [13], and assuming 2.74 m ceilings (9 feet), the space required is 512.38 m³. Therefore, using the simple equation shown in Equation (1):

Closed to open system ratio = CS capacity/OS capacity,

(1)

A total of 1.3 times CS volumetric space is needed in comparison to the OS. This ratio was applied when inputting construction materials into openLCA for the CS.

2.5.3. BSF, BSFL Production and Breeding

In the modeling, the processes of BSF breeding and BSFL production are where the open and closed systems diverge. However, the elementary composition of the flies used in the analysis remained the same for both systems and was sourced from the literature. The number and assumed weight of the BSF are the same for both systems and were derived from studies conducted by Dortmans et al. and Gougbedji et al. [13,37]. The BSFL output for both systems is based on the data acquired from the case study. The BSFL harvest months of December, January, and February were used in line with the timeline for biowaste bioconversion, see

Table 3. Monthly biowaste collection in the open system.

Month	BSF Harvest (kg, Wet Weight)	Frass Harvest (kg, Dry Weight)
December	3.0	8
January	7.26	10
February	2.25	6
Monthly Average	4.17	8
At 1 ton/day biowaste	197.19	378.35

. BSFL are harvested after the prepupae have migrated to the bioreactor harvesting section, and this occurred every three to four weeks, i.e., once a month. According to the referenced literature [12,28,38,39,40], not all the larvae become prepupae after 14 days, although all the prepupae and larvae can be harvested and processed for animal feed.

The prepupae output based on one ton of biowaste processed daily is 197.19 kg for the OS and CS. In the case study, 7% of the waste was discarded because biowaste like mango and avocado seeds did not biodegrade in the allocated six weeks. The remaining difference in the input mass, waste added to the bioreactor (1 ton) to output mass, biomass harvested through the BSFL and the dried frass (354.46 kg) was attributed to emissions during bioconversion, like water, CO₂ and CH₄. In a BSFL waste treatment material flow analysis, Guo et al. demonstrated an 84% loss of total water from the biowaste [38]. The loss was to the BSF prepupae, the compost (cured frass), and the environment. The loss in this case study to the environment is assumed to be the 35% (354.46 kg) difference in the input and output mass.

The animal feed replacement of the BSFL in terms of the protein content is quantified based on proximate analysis of the BSFL from the case study. Therefore, 42% protein content resulted in 82.82 kg of protein. The values are consistent with the literature [29,38] and were entered as trout feed in the assessment and used for both systems. Other inputs required in rearing and harvesting BSFL in a closed system are listed in

Table 4. Inventory for the closed BSF system per ton of biowaste (wet weight).

Closed System Process	Parameter	Source
BSF Rearing	70,000 flies	[13]
	700 g weight of flies	[37]
	2.88 kWh (electricity)	[28]
	3.57 kg compost	[28]
	3.1 kg chicken feed	[28]
BSFL Bioconversion and Harvesting	2.93 kWh (electricity)	[28]
	664 liters of water	[28]

.

The production of BSFL as an insect for feed was modeled as silkworm cocoon rearing in the openLCA assessment, with the appropriate inputs and outputs used, as listed in Table 4. The other byproduct, BSF frass, which required curing, was modeled as a composting facility for both systems. The frass harvesting over the study period is provided in Table 3.

2.5.4. Assumptions

Table 5. List of assumptions.

Assumption	References
Incoming biowaste is manually sorted and grinded, i.e., broken to BSFL digestible sizes. Therefore, water and energy use in the closed system are ignored.	Case study, [28,38]
Waste generated post-BSFL bioconversion is left on farmland, is biodegradable and reabsorbed into the soil.	Case study
BSFL produced through the OS and CS are equivalent. The production rates remain consistent through different seasons of the year.
Composting in the drying unit is the same for both systems, with impacts equivalent to composting in a composting facility.	ecoinvent 3.91
Mass losses from the input biowaste, particularly in curing the residue, are predominately due water loss to the environment. Climate control was ignored in the CS. Materials required in the installation of windows, doors, and electrical wiring for producing illumination for BSF mating in the CS were also excluded. Energy input required in the construction of the OS was not measured and therefore assumed as equal for both OS and CS, and it was not included in the assessment.	[38] Case study

below provides a summary of the assumptions used in the analysis.

3. Results

The construction of the OS and CS had the most significant contributions across impact categories for both systems. Appropriately, the construction of the bioreactor and drying unit made the most significant contributions to the GWP, fossil fuel depletion, and acidification. See

Table 6. Total impact category indicators and contributions for the open (OS) and closed (CS) systems.

Month	Water Use [m3]		GWP100 [kg CO2-Eq]		FFP [kg oil-Eq]		Land Use [m2·a crop-Eq]		Acidification [kg SO2-Eq]		Eutrophication [kg P-Eq]
	OS	CS	OS	CS	OS	CS	OS	CS	OS	CS	OS	CS
Bioreactor Construction	24.62	32.01	4590.16	5967.21	705.28	916.87	1100.86	1431.12	10.37	13.49	0.70	0.92
Drying Unit Construction	3.83	4.97	144.76	188.18	32.33	42.03	131.28	170.66	0.40	0.52	0.07	0.09
Biowaste Collection	0.10	0.10	42.42	42.42	12.38	12.38	0.92	0.92	0.08	0.08	0.01	0.01
BSFL Rearing	-	7.17	-	160.87	-	20.03	-	84.30	-	0.27	-	0.01
Total	28.55	44.26	4777.34	6358.69	749.99	991.30	1233.06	1687.05	10.86	14.36	0.78	1.02

.

The results are analyzed using the impact category in the subsequent sections. BSFL rearing makes the largest contribution to the water usage impact, see Figure 6. This is due to soybeans predominately produced in Brazil [41]. Water use was also the most significant percentage impact category difference between both systems, as shown in Figure 6.

3.1. Global Warming Potential

The global warming potential was higher for the CS, Figure 6, with the increase attributable to the increased use of construction material and the energy required to produce the soybeans used as feed for rearing the BSFL, Figure 7.

3.2. Land Use

Second to water use, the CS impacts agricultural land use next, showing 33.82% in Figure 6. This impact is also attributable to the cultivation of soybeans for the rearing of BSFL. See Figure 8.

4. Discussion

Previous to this study, BSF waste treatment LCAs in Africa have focused on the waste reduction potential of dipteran insect species on animal manure [23]. The impact categories examined in this article were based on the literature and explore the environmental impact differences of two BSF systems. Climate change has an associated impact with BSF waste treatment [28,29,30], with others including energy use [29,31], land use [29,30], acidification and eutrophication [31], and water use [30].

As an energy-intensive process when run on an industrial scale [42], BSFL rearing contributes significantly to climate change, fossil fuel use potential, and water use [43]. Conservative measurements were used in sizing the CS BSF facilities. While Dortmans et al. [13] suggest 150 m² as a rule of thumb for a facility processing 1 ton of biowaste daily, Komakech et al. suggest a 5250 m² (75 m × 70 m)-sized facility [31].

Sensitivity Analysis

A sensitivity analysis was conducted to determine the extent of the environmental impact of the production infrastructure on the CS and the corresponding difference in environmental impacts. Accelerated depreciation of production equipment has been observed in humid tropics, shortening their service life to 15 years [22]. In contrast, built infrastructure for insect farming is assumed to have a 25-year life span [22]. An analysis of the CS with the infrastructure is conducted based on the 15-year depreciation of equipment CSE (15 Y) and the 25-year depreciation CSE (25 Y).

Table A3. Calculation of material weights required for the equipment used in a CS.

By Main Constituent	Units Needed for 1 ton/day 15 Years	Units Needed for 1 ton/day 25 Years	Weight per Unit (kg)	Total Weight (kg) 15 Years	Total Weight (kg) 25 Years	Reference (Literature)	Reference (Manufacturers)
Plastic				1388.22	2313.71			Plastic injection molding assumed
Conversion crates	800	1333.33	1.60	1280.00	2133.33	[13]	Vegcrates	Ventilated plastic crates for shrimp
Pupation crates	23	38.33	1.60	36.80	61.33	[13]	Vegcrates	Ventilated plastic crates for shrimp
Egg media	50	83.33	0.05	2.41	4.02	[13]	Amazon	Biochemical Ball Filter Media
Hatchling crate	11	18.33	1.60	17.60	29.33	[13]	Vegcrates	Ventilated plastic crates for shrimp
Egg media	160	266.67	0.05	7.71	12.85	[13]	Amazon	Biochemical Ball Filter Media
Nursery Larvero	17	28.33	1.60	27.20	45.33	[13]	Vegcrates	Ventilated plastic crates for shrimp
Collection container	17	28.33	0.95	16.15	26.92		Uline	20 liter bucket assumed
Egg media holder	32	53.33	0.01	0.35	0.59		Amazon	Aquarium Nylon Bag mesh
Metal				284.00	473.33			Chromium steel production
Ventilation frames	120	200.00	1.20	144.00	240.00		Amazon	32 × 22.9 × 15.4 cm assumed
Pallet trolley	1	1.67	10.60	10.60	17.67		Amazon	177.8 cm × 74.98 × 34.98 cm assumed
Shredder	1	1.67	10.60	10.60	17.67		Amazon	177.8 cm × 74.98 × 34.98 cm assumed
Dark cage frame	1	1.67	8.92	8.92	14.87		Amazon	59.99 × 35 × 150 cm assumed
Love cage frame	2	3.33	8.92	17.84	29.73		Amazon	59.99 × 35 × 150 cm assumed
Hatching frame	2	3.33	8.92	17.84	29.73		Amazon	59.99 × 35 × 150 cm assumed
Larvero frame	6	10.00	10.60	63.60	106.00		Amazon	177.8 cm × 74.98 × 34.98 cm assumed
Mobile fly harvester	1	1.67	10.60	10.60	17.67		Amazon	177.8 cm × 74.98 × 34.98 cm assumed
Fabric				8.15	13.58
Love cage	5	8.33	1.36	6.79	11.32		Alibaba	75 × 75 × 115 cm assumed
Dark cage	1	1.67	1.36	1.36	2.26		Alibaba	75 × 75 × 115 cm assumed
Wood				399.56	665.93
Pallets	20	33.33	18.64	372.80	621.33		Global Industrial	101.6 × 121.92 cm assumed
Working table	2	3.33	8.92	17.84	29.73		Amazon	59.99 × 35 × 150 cm assumed
Working table	1	1.67	8.92	8.92	14.87		Amazon	59.99 × 35 × 150 cm assumed

in Appendix A provides a breakdown of the equipment required in the CS but not in the OS. The list is based on the inventory provided by EAWAG [44]. Items common to the CS and OS and therefore excluded from the analysis include sieves, grinders, scales and balances, high-pressure cleaners and a washing machine.

All three scenarios, CS, CSE (15 Y), and CSE (25 Y), have the highest impact process contributor as BSFL rearing and bioreactor construction, see Figure 9.

The most significant difference in impact between the CS (15 Y) and CSE (25 Y) is eutrophication, see Figure 10. The reduction in the quantity of plastic-based equipment showed a significant drop in the land use impact. On the other hand, water use had the most considerable effect on the change in depreciation.

Therefore, the more equipped a CS is for BSFL rearing, the higher the environmental impact that is expected. Some systems use conveyor belts to move the BSFL and compost [4], translating to more energy that the system utilizes. Additionally, semi-centralized CS systems, which require a central BSF-rearing facility with decentralized bioconversion facilities [10,45], will necessitate additional emissions and impacts from material transport between locations.

5. Conclusions

The increased environmental impacts of large-scale CSs can be reduced by switching to OSs or running a combination of both systems where possible. Although an OS has minimal environmental impact, it is often overlooked due to scaling challenges. However, to achieve sustainable development and promote beneficial interactions between humans, animals, and the environment (One Health), an OS should be explored as a viable and scalable biowaste solution. This study aims to pave the way for research in this area.

This analysis made several assumptions, including the avoidance of greenhouses in rearing BSFL because of the associated challenges with maintaining the appropriate abiotic conditions, i.e., climatic control. Materials for framing and installing windows, doors, ventilation systems, and electrical wiring for producing light critical to BSF mating were also excluded because of the limitation of establishing the appropriate inventory. These parameters, which were not included in the CS and not required in the OS, indicate a conservative estimate of the difference in environmental impacts between the systems.

Further research is required, particularly in obtaining a complete inventory of the CS, to determine a more accurate assessment of the difference between the systems. However, this study provides a template that can be enhanced in the future. The study results confirm that the OS is a viable alternative to a centralized CS, producing less environmental impact. Overall, the study supports the OS as a viable solution to organic waste treatment, which is important for ensuring a sustainable future.