Life Cycle Assessment of Black Soldier Fly Technology for Sustainable Manure Management in Jing-Jin-Ji: Balancing Feed Protein Production and Carbon Mitigation

Abstract

The Jing-Jin-Ji region in China has highly intensive agriculture but faces challenges of feed protein shortage and manure surplus, threatening environmental sustainability and industrial development. The black soldier fly (Hermetia illucens) is a promising sustainable feed protein source, capable of efficiently converting organic waste into high-quality insect protein to alleviate feed scarcity while mitigating waste pollution. Existing research on black soldier fly (BSF) treatment in this area is limited, lacking comprehensive benefit evaluations. This study, conducted in Hebei Province, integrated sub-county-scale manure resource mapping, life cycle assessment, and economic assessment to compare traditional composting with BSF-based manure management. Results show BSF treatment can produce 0.36 to 0.39 teragrams (Tg) of feed protein per year. Compared with conventional composting, BSF treatment reduced direct manure-treatment emissions, while additional mitigation benefits were obtained through feed-protein substitution, fertilizer substitution, and BECCS-related land-use savings. Overall, the BSF scenarios achieved a total GHG mitigation potential of 2.85–6.19 Tg CO₂eq yr⁻¹. Economically, low-technology BSF production is cost-competitive, with a total cost of $121 for treating 1 ton of fresh chicken manure. With its protein output roughly doubling the local soybean production capacity, BSF technology provides a viable, low-carbon solution to the dual challenges of feed security and waste management in intensive agricultural systems.

1. Introduction

The Jing-Jin-Ji region in China has highly intensive agriculture, with Beijing and Tianjin accounting for a significant share of the region’s poultry production and manure generation, while facing challenges of feed protein shortage and manure surplus, threatening environmental sustainability and industrial development. Hebei province, situated at the core of the Jing-Jin-Ji region, is a linchpin in China’s agricultural landscape, characterized by vast arable land and a robust livestock industry that underpin national food security [1]. In 2021, the province ranked among the nation’s top poultry producers, churning out substantial quantities of chicken meat and eggs—a testament to its role in sustaining the region’s food supply [2]. However, its unique geographical proximity to Beijing and Tianjin, combined with temperate climate conditions, has fostered a high-density poultry-farming environment that amplifies two critical challenges plaguing the entire Jing-Jin-Ji area: a stark imbalance between crop and livestock production, a heavy dependence on imported feed protein that exposes the sector to supply instability, and the resultant dual crises of feed protein shortage and manure surplus [3,4,5].

This imbalance is manifested in a severe decoupling of crop and livestock sectors. Hebei’s large-scale poultry farms alone generated 22 teragrams (Tg) of chicken manure (fresh weight) in 2021—an enormous volume that, unlike in regions with integrated agri-livestock systems, cannot be efficiently recycled into local croplands due to spatial and logistical disconnects. The consequence is twofold: On one hand, improper manure disposal leads to severe ecological degradation, water and soil pollution, and potential public health risks, with nitrogen and phosphorus runoff contaminating water bodies and soils across the Jing-Jin-Ji region; pathogen proliferation and odor nuisance further threaten environmental quality and human well-being. On the other hand, it represents a squandered opportunity to close the nutrient loop between livestock waste and crop fertilization. Concurrently, Hebei’s livestock industry struggles with a dearth of locally sourced protein-rich feeds, relying heavily on imported soybeans and other commodities [6,7]. Feed represents the largest cost component in poultry production, generally accounting for 65–70% of total production costs, while protein feed ingredients such as soybean meal are among the most expensive components and remain highly dependent on external supply [8,9]. This not only burdens producers with high costs but also renders the entire Jing-Jin-Ji livestock supply chain vulnerable to international market volatility, underscoring the region’s systemic dependence on external protein inputs.

Against this backdrop, the black soldier fly (Hermetia illucens L., BSF) emerges as a transformative solution tailored to Hebei’s role in perpetuating these regional challenges. As a saprophagous insect, BSF thrives in warm, humid environments rich in organic waste, poses no risk to humans or livestock, and does not transmit diseases. With high fecundity, a single female can lay over 500 eggs under favorable conditions, enabling rapid population growth. BSF larvae thrive on chicken manure, converting it into two valuable outputs: protein-rich insect biomass that can substitute imported feeds, and nutrient-dense frass that serves as organic fertilizer for local crops. Although recycling chicken manure as organic fertilizer is not new, BSF-based treatment goes beyond conventional manure recycling by producing both alternative feed protein and frass fertilizer, thereby linking manure management with feed substitution and greenhouse gas mitigation. The life cycle assessment (LCA) approach has been widely used in black soldier fly research to assess its environmental impacts at different life cycle stages, including resource consumption, greenhouse gas emissions, and protein replacement potential [10,11]. By integrating BSF treatment into Hebei’s poultry waste management, the technology has the potential to bridge the crop–livestock divide, transforming a regional liability—manure surplus—into an asset that addresses both feed insecurity and environmental contamination [12,13,14]. Specifically, BSF larvae reared on poultry manure produce biomass containing 40–60% crude protein, a level comparable to conventional soybean meal, offering a scientifically validated alternative feed source for the livestock industry.

Yet, while BSF shows promise in laboratory and small-scale settings, its large-scale application in Hebei’s complex agricultural ecosystem remains under-researched [15]. Recent BSF-LCA studies have evaluated insect-based feed production and agro-waste treatment at experimental or process scales, comparing BSF protein with soybean meal or fishmeal and BSF composting with conventional waste-treatment routes [16]. Unlike previous studies that mainly focused on laboratory-scale bioconversion experiments, nutrient composition analysis, or single-farm evaluations, this study integrates sub-county-scale manure resource mapping with life cycle assessment and economic assessment to evaluate the regional environmental, feed-protein, and cost implications of BSF-based chicken manure management [17]. Gaps persist in optimizing BSF breeding under local climatic conditions and assessing the economic viability of scaling up this technology within the Jing-Jin-Ji region’s industrial and policy framework. This study aims to evaluate the environmental and economic feasibility of BSF-based chicken manure management in Hebei Province. Specifically, we aim to: (1) quantify county-level chicken manure generation and treatment pathways; (2) estimate BSF-derived feed protein and frass production; (3) compare GHG emissions between conventional composting and BSF-based treatment scenarios; and (4) assess the economic costs and benefits of different manure management pathways.

2. Materials and Methods

The methodological framework consisted of five main steps. First, county-level poultry production, farm-scale distribution, and manure generation were quantified for Hebei Province in 2021. Second, BAU and BSF-based manure management scenarios were defined according to current composting practices and alternative BSF rearing systems. Third, life cycle assessment was used to calculate direct manure-treatment emissions and product-substitution benefits under each scenario. Fourth, BSF-derived product outputs, including insect protein and frass, were estimated using a mass-balance approach. Finally, the economic costs and benefits of conventional composting and BSF-based treatment pathways were assessed.

2.1. Study Region and Data Collection

This study focuses on layer and broiler chicken farms in Hebei Province, situated within the Jing-Jin-Ji region, to evaluate the environmental and economic performance of chicken manure management under different treatment scenarios in 2021. Data were systematically collected from multiple sources to ensure regional representativeness and analytical rigor. Annual agricultural and livestock data (e.g., number of farms, poultry inventory, manure treatment methods) were obtained from the Hebei Provincial Agricultural and Rural Statistical Yearbook (2022) and China Animal Husbandry and Veterinary Statistics Yearbook, disaggregated at the county level to capture spatial heterogeneity. Operational data from large-scale farms (defined as ≥10,000 layer birds or ≥50,000 broiler slaughterings annually) were sourced from the national livestock industry information platform, which detailed manure generation quantities and current treatment technologies (e.g., static composting, reactor composting). Parameters for black soldier fly (BSF) bioconversion, including feed conversion ratio (FCR), larval moisture content, and frass nutrient composition, were derived from experimental studies (

Table A1. Nutrient losses during composting.

	Co-Substrate	Manure/Co-Substrate Ratio	TC (%)	TN (%)	N2O-N (Loss) (%)	NH3-N (Loss) (%)	CH4-C (Loss) (%)
SC	Straw	83:17	32.3	2.42	0.43	18.09	0.007
WC	Straw	83:17	32.3	2.42	0.47	14.38	0.445
TC	Straw	83:17	32.3	2.42	1.52	26.54	0.383
RC	Straw	83:17	32.3	2.42	1.15	18.09	0.879

) and validated against international datasets [18,19].

Based on these data sources, poultry farms were further grouped into large-, medium-, and small-scale systems according to China Animal Husbandry Statistics. Because county-level farm-scale data were incomplete, the proportion of large-scale poultry production in each county was estimated using a regression-based approach and then corrected to match the observed provincial total. Annual chicken manure production was calculated by multiplying poultry numbers, feeding duration, and manure excretion coefficients. Because farm-specific feed formulations were unavailable, manure composition parameters were assumed to represent conventional corn–soybean meal-based poultry diets commonly used in commercial layer and broiler production. The C/N ratio is closely related to manure composition, nitrogen transformation, and biological treatment performance; it was considered an important manure-quality factor in this study. However, farm-specific C/N measurements were not available at the regional scale. Therefore, the influence of C/N ratio was represented indirectly using literature-derived manure composition, nitrogen-loss parameters, composting emission factors, and BSF bioconversion parameters. These data and assumptions were used as inputs for the subsequent LCA, product-output estimation, and cost–benefit analysis. Detailed calculation procedures, correction methods, manure excretion coefficients, BSF bioconversion parameters, composting emission factors, and life cycle inventory data are provided in Appendix A.

GHG calculations followed an IPCC-based manure management framework. Technology-specific and regional parameters, such as composting N₂O emission factors, were adjusted using the peer-reviewed literature where appropriate [20]. The life cycle inventory data were obtained from the built-in databases of SimaPro 9.0, including Ecoinvent and Agri-footprint. Transportation emissions were excluded due to inconsistent regional logistics data and because this study focused on farm-gate manure treatment and on-farm BSF bioconversion processes.

2.2. Scenario Definition and System Boundaries

To ensure comparability, the BAU and BSF scenarios were defined under consistent system boundaries, including manure treatment processes and product-substitution benefits generated by each treatment pathway. Construction-related GHG emissions from treatment infrastructure and equipment, including composting facilities, cement ponds, and automated BSF rearing tanks, were also included in the life cycle boundary and quantified using material inventory data provided in Appendix A. Two contrasting scenarios were constructed to compare conventional practices with BSF-based innovation (Figure 1).

2.2.1. Business-As-Usual (BAU) Scenario

BAU scenario reflects the current practices of chicken manure management in Hebei. We distinguished in detail the differences across farm scales, between layer and broiler production, and among various manure management (

Table A3. Nutrient production during bioconvertion (BSF).

	Fertilizer	Production Capacity (kg)	Emission Factor (kg/kg)
Layer	N	3.53	7.76
	P	2.69	2.33
	K	2.75	0.66
Broiler	N	3.86	7.76
	P	2.94	2.33
	K	3.01	0.66

,

Table A4. BECCS parameters during bioconvertion (BSF).

		Production Capacity	Unit	Emission Factor (kg/kg)
CP	BSF protein	65	kg t−1	3.24
	Saving land	676	m2 kg−1	1.54
AU	BSF protein	70	kg t−1	3.24
	Saving land	724	m2 kg−1	1.54

,

Table A5. (A) Business as usual (BAU) -total consumption and carbon emission factor for treating chicken manure (dry matter); (B) Black soldier fly (BSF) -total consumption and carbon emission factor for treating chicken manure (dry matter).

(A)
Composting Method		Project	Raw Materials	Consumption	Unit	Emission Factor	Unit	Factor Source
Static composting		Ground	Cement	0.0041	m2/t	215	kg CO2 eq/m2	SimaPro 9.0-Ecoinvent and Agri-footprint
		Roof	PVC Plastic	0.0128	kg/t	2	kg CO2 eq/kg	SimaPro 9.0-Ecoinvent and Agri-footprint
Windrow composting		Ground	Cement	0.0043	m2/t	215	kg CO2 eq/m2	SimaPro 9.0-Ecoinvent and Agri-footprint
		Roof	PVC Plastic	0.0135	kg/t	2	kg CO2 eq/kg	SimaPro 9.0-Ecoinvent and Agri-footprint
		Aeration Pump	Aluminum alloy (die-cast aluminum)	0.0034	kg/t	20	kg CO2 eq/kg	SimaPro 9.0-Ecoinvent and Agri-footprint
		Aeration Pipes	Silica	0.0015	kg/t	15.7	kg CO2 eq/kg	SimaPro 9.0-Ecoinvent and Agri-footprint
		Flipper	Carbon steel	0.0426	kg/t	0.951	kg CO2 eq/kg	SimaPro 9.0-Ecoinvent and Agri-footprint
		Electricity		38	kWh/t	0.7901	Kg CO2/kWh	Government Official Website
Trough composting		Ground	Cement	0.0043	kg/t	215	kg CO2 eq/m2	SimaPro 9.0-Ecoinvent and Agri-footprint
		Roof	PVC Plastic	0.1855	kg/t	2	kg CO2 eq/kg	SimaPro 9.0-Ecoinvent and Agri-footprint
		Composting aisle	Cement	0.0021	kg/t	215	kg CO2 eq/m2	SimaPro 9.0-Ecoinvent and Agri-footprint
		Aeration Pump	Aluminum alloy (die-cast aluminum)	0.0034	kg/t	20	kg CO2 eq/kg	SimaPro 9.0-Ecoinvent and Agri-footprint
		Aeration Pipes	Silica	0.0015	kg/t	15.7	kg CO2 eq/kg	SimaPro 9.0-Ecoinvent and Agri-footprint
		Flipper	Carbon steel	0.0426	kg/t	0.951	kg CO2 eq/kg	SimaPro 9.0-Ecoinvent and Agri-footprint
		Electricity		38	kWh/t	0.7901	Kg CO2/kWh	Government Official Website
Reactor composting		Ground	Cement	0.0001	kg/t	215	kg CO2 eq/m2	SimaPro 9.0-Ecoinvent and Agri-footprint
		CFCS-40	Stainless steels	0.1142	kg/t	0.00000188	kg CO2 eq/kg	SimaPro 9.0-Ecoinvent and Agri-footprint
		Electricity		63	kWh	0.7901	Kg CO2/kWh	Government Official Website
(B)
Composting Method	Process	Project	Raw Materials	Consumption	Unit	Emission Factor	Unit	Factor Source
Cement pool	-	Ground	Cement	3.82	m2/t	215	kg CO2 eq/m2	SimaPro 9.0-Ecoinvent and Agri-footprint
		Roof	Polyethylene	0.006	kg/t	2.19	kg CO2 eq/kg	SimaPro 9.0-Ecoinvent and Agri-footprint
		Thermal Air Drying System	Polypropylene	0.046	kg/t	0.808	kg CO2 eq/kg	SimaPro 9.0-Ecoinvent and Agri-footprint
			Stainless steels	0.443	kg/t	1.88	kg CO2 eq/kg	SimaPro 9.0-Ecoinvent and Agri-footprint
			Rock wool	0.88	kg/t	1.14	kg CO2 eq/kg	SimaPro 9.0-Ecoinvent and Agri-footprint
		Electricity		0.66	kWh/t	0.7901	Kg CO2/kWh	Government Official Website
Automated breeding tanks	Tray cleaning	-	Chromium steel pipe	0.372	kg/t	4.90	kg CO2 eq/m2	SimaPro 9.0-Ecoinvent and Agri-footprint
			Tap water	1004.2	kg/t	0.0015	kg CO2 eq/kg	SimaPro 9.0-Ecoinvent and Agri-footprint
			Potassium hydroxide	11.15	kg/t	2.52	kg CO2 eq/m2	SimaPro 9.0-Ecoinvent and Agri-footprint
			Sodium hydroxide, without water, in 50%	55.79	kg/t	1.35	kg CO2 eq/kg	SimaPro 9.0-Ecoinvent and Agri-footprint
	Climate control	Carbon steel	Polyethylene terephthalate	0.0127	kg/t	1.06	kg CO2 eq/kg	SimaPro 9.0-Ecoinvent and Agri-footprint
		Air conditioner	Steel, low-alloyed, hot rolled	0.2	kg/t	1.92	kg CO2 eq/kg	SimaPro 9.0-Ecoinvent and Agri-footprint
	Dry larvae and frass storage	Paloxes	Polyethylene, low density, granulate	0.3	kg/t	3.24	kg CO2 eq/kg	SimaPro 9.0-Ecoinvent and Agri-footprint
	Process control and lights	Lamp	Electronics	0.0014	kg/t	288	kg CO2 eq/kg	SimaPro 9.0-Ecoinvent and Agri-footprint
		Computer	Electronics	0.0055	kg/t	162	kg CO2 eq/kg	SimaPro 9.0-Ecoinvent and Agri-footprint
	Grinding and feeding	Shredder	Chromium steel pipe	0.44	kg/t	4.9	kg CO2 eq/kg	SimaPro 9.0-Ecoinvent and Agri-footprint
		Feeder	Chromium steel pipe	0.18	kg/t	4.9	kg CO2 eq/kg	SimaPro 9.0-Ecoinvent and Agri-footprint
	Reactor	Rolls	Chromium steel pipe	2.76	kg/t	4.90	kg CO2 eq/kg	SimaPro 9.0-Ecoinvent and Agri-footprint
		Steel table plate	Chromium steel pipe	0.36	kg/t	4.90	kg CO2 eq/kg	SimaPro 9.0-Ecoinvent and Agri-footprint
		Roller balls	Chromium steel pipe	0.73	kg/t	4.88	kg CO2 eq/kg	SimaPro 9.0-Ecoinvent and Agri-footprint
		Pusher	Chromium steel pipe	1.18	kg/t	4.90	kg CO2 eq/kg	SimaPro 9.0-Ecoinvent and Agri-footprint
		Pusher plate	Chromium steel pipe	0.00	kg/t		kg CO2 eq/kg	SimaPro 9.0-Ecoinvent and Agri-footprint
		Conveyor frame	Aluminium, primary, cast alloy slab from continuous casting	0.10	kg/t	4.90	kg CO2 eq/kg	SimaPro 9.0-Ecoinvent and Agri-footprint
		End table frame	Aluminium, primary, cast alloy slab from continuous casting	0.84	kg/t	17.45	kg CO2 eq/kg	SimaPro 9.0-Ecoinvent and Agri-footprint
		End table conveyor	Aluminium, primary, cast alloy slab from continuous casting	0.12	kg/t	17.46	kg CO2 eq/kg	SimaPro 9.0-Ecoinvent and Agri-footprint
		Trays	Polyethylene, low density, granulate	0.18	kg/t	17.51	kg CO2 eq/kg	SimaPro 9.0-Ecoinvent and Agri-footprint
		40×40 end scaffolds	Aluminium, primary, cast alloy slab from continuous casting	2.21	kg/t	2.19	kg CO2 eq/kg	SimaPro 9.0-Ecoinvent and Agri-footprint
		Main 40 × 80 scaffolds	Aluminium, primary, cast alloy slab from continuous casting	0.02	kg/t	2.19	kg CO2 eq/kg	SimaPro 9.0-Ecoinvent and Agri-footprint
		Brace	Chromium steel pipe	0.16	kg/t	2.19	kg CO2 eq/kg	SimaPro 9.0-Ecoinvent and Agri-footprint
	Harvesting handler	Harvesting handler	Aluminium, primary, cast alloy slab from continuous casting	0.034	kg/t	17.48	kg CO2 eq/kg	SimaPro 9.0-Ecoinvent and Agri-footprint
			Aluminium, primary, cast alloy slab from continuous casting	0.005	kg/t	11.89	kg CO2 eq/kg	SimaPro 9.0-Ecoinvent and Agri-footprint
			Steel, low-alloyed, hot rolled	0.014	kg/t	1.92	kg CO2 eq/kg	SimaPro 9.0-Ecoinvent and Agri-footprint
			Aluminium removed by drilling, computer numerical controlled	0.012	kg/t	11.90	kg CO2 eq/kg	SimaPro 9.0-Ecoinvent and Agri-footprint
	Sieving	-	Chromium steel pipe	0.097	kg/t	4.9	kg CO2 eq/kg	SimaPro 9.0-Ecoinvent and Agri-footprint
	Blanching	Blanching	Chromium steel pipe	0.01	kg/t	4.91	kg CO2 eq/kg	SimaPro 9.0-Ecoinvent and Agri-footprint
			Tap water	890.12	kg/t	0.0015	kg CO2 eq/kg	SimaPro 9.0-Ecoinvent and Agri-footprint
	Drying	Dryer	Chromium steel pipe	0.478	kg/t	4.90	kg CO2 eq/kg	SimaPro 9.0-Ecoinvent and Agri-footprint
		Dried larvae conveyor	Aluminium, primary, cast alloy slab from continuous casting	0.012	kg/t	17.45	kg CO2 eq/kg	SimaPro 9.0-Ecoinvent and Agri-footprint

and

Table A6. Mean data on the output of bioconversion of poultry manure by BSF in different studies.

Item	Cement Ponds	Automated Feeding Tanks
Percentage reduction in dry weight of manure (%)	45.57 1	45.57 1
	40.55 2	40.55 2
Moisture content of insect frass (%)	30	30
Insect moisture content (%)	75	75
FCR	6.43	6

Note: ¹ for layer manure, ² for broiler manure.

). In Hebei, we differentiated manure treatment ways, including static composting (SC), windrow composting (WC), trough composting (TC), and reactor composting (RC). The distribution of manure treated by each pathway was derived from farm-scale manure management statistics and county-level poultry production data, with detailed calculation procedures and pathway-specific manure amounts provided in Appendix A. Static composting was treated as an open or semi-open system with limited mechanical aeration and turning. Windrow composting was considered a semi-open system with periodic turning and aeration. Trough composting was treated as a semi-enclosed system with structured composting channels, periodic turning, and aeration. Reactor composting was considered an enclosed and mechanically aerated system. Because this study conducted a regional-scale LCA based on statistical data rather than on-site composting process monitoring, farm-specific temperature and humidity data were not available. Therefore, the effects of composting conditions were represented using technology-specific emission factors and literature-based composting parameters following the IPCC-based manure management calculation framework.

Within the system boundaries of these traditional manure treatment, both GHG emission sources and indirect GHG reductions resulting from organic fertilizer substitution for chemical fertilizers were considered (Figure 1a). Specifically, emission sources include: GHG emissions from equipment construction (e.g., concrete pits for static composting), energy use (ventilation, machinery), and biological processes (CH₄ from anaerobic pockets, N₂O from nitrogen transformations, and indirect N₂O via NH₃ volatilization). Offset mechanisms include: emission reductions from substituting synthetic NPK fertilizers with composted manure (1:1 nutrient replacement ratio, based on local soil testing data).

2.2.2. Black Soldier Fly (BSF) Scenario

In the BSF scenario, chicken manure is used to rear BSF, converting chicken manure into insect biomass and frass. The system boundary includes three main stages: BSF larval hatching, chicken manure bioconversion, and product substitution (Figure 1).

Two technological pathways were designed according to the BSF rearing systems applied in the manure bioconversion stage: BSF-A adopts a low-input way, using traditional cement ponds with manual operation. This system requires minimal capital investment and has a longer larval processing cycle (14-day larval cycle). BSF-B represents a high-input alternative. It employs automated breeding tanks with controlled temperature and humidity. This system enables shorter larval cycles (12-day cycle) and improves resource efficiency. We considered the applicability of BSF systems for farms of different scales. Therefore, we developed scenarios in which farms of varying sizes adopt different BSF rearing systems. Details are provided in Appendix A.

In the product-substitution stage, BSF-derived protein meal was assumed to replace conventional soybean protein on a protein-equivalent basis, following previous studies on insect protein substitution and mini-livestock production in China [21,22]. BSF frass was assumed to substitute synthetic NPK fertilizers according to its nutrient-equivalent N, P, and K contents. Accordingly, two avoided-burden credits were included in the BSF scenario. First, the land theoretically saved from local soybean protein production was assumed to be reallocated to bioenergy production with carbon capture and storage (BECCS), representing a scenario-based carbon removal pathway rather than a guaranteed land-use outcome [23]. Second, avoided GHG emissions from synthetic NPK fertilizer production due to frass substitution were credited to the system.

To test the influence of land-use assumptions, an additional no-BECCS scenario was included, in which BSF-derived protein was still assumed to substitute soybean protein, but the theoretically saved cropland was not credited with BECCS-related carbon removal. This scenario was used to distinguish mitigation from manure treatment and product substitution from the additional land-based carbon mitigation benefit.

2.3. Manure Production

The chicken manure production (Q) was calculated as the product of feeding volume (N), feeding period (T, days), and the excretion coefficient (P). The detail calculation formula can be referred to Wang et al. (2006) [24].

$$Q_{i,j}=N_{i,j}\times T_j\times P_j$$

(1)

where Q: annual manure production; N: feeding volume (number of chickens); T: feeding period (days); P: excretion coefficient (Table A5); i: the county of Hebei province; and j: the type of chicken (layer and broiler). Equation (1) was used to calculate chicken manure production from poultry numbers, feeding duration, and daily excretion coefficients, following Wang et al. [24].

2.4. GHG Emissions Calculation

GHG emissions from manure management were calculated following the 2006 IPCC Guidelines for National Greenhouse Gas Inventories and the 2019 Refinement to the 2006 IPCC Guidelines [25,26], which provide methods for estimating CH₄ and N₂O emissions from livestock manure storage and treatment systems. Construction-related emissions from treatment infrastructure and equipment, energy-related emissions during operation, direct CH₄ and N₂O emissions from manure treatment, and indirect N₂O emissions associated with NH₃ volatilization were included in the life cycle GHG calculation. The 100-year global warming potentials of CH₄ = 28 and N₂O = 265 were adopted from the IPCC Fifth Assessment Report. GHG emissions were calculated for the BAU and BSF scenarios using Equations (2) and (3), respectively.

$$E_{BAU-Net}=E_{Equipment}+E_{Energy}+E_{Process-{CH}_4}+E_{Process-N_{2}O}+E_{Process-{NH}_3\left(Indirectly\right)}-E_{Of}$$

(2)

where E_BAU-Net: net GHG emissions from chicken manure composting in the BAU scenario, Gg CO₂eq year⁻¹; EEquipment: GHG emissions from equipment construction, Gg CO₂eq year⁻¹; EEnergy: GHG emissions from energy consumption, Gg CO₂eq year⁻¹; EProcess-CH₄: CH₄ emissions from treatment processes, Gg CO₂eq year⁻¹; EProcess-N₂O: N₂O emissions from treatment processes, Gg CO₂eq year⁻¹; EProcess-NH₃: NH₃ (indirect) emissions from treatment processes, Gg CO₂eq year⁻¹; Eof: the GHG reductions from chicken manure compost products as organic fertilizers replacing chemical synthetic N, P, K fertilizers, Gg CO₂eq year⁻¹; and detailed parameters and calculations can be found in the Appendix A. Equation (2) was adapted from the IPCC manure-management emission accounting framework [25,26].

$$E_{BSF-Net}=E_{Equipment}+E_{Energy}+E_{Process-{CH}_4}+E_{Process-N_{2}O}+E_{Process-{NH}_3\left(Indirectly\right)}-E_{Of}-E_{feed-land}$$

(3)

where E_BSF-Net: net GHG emissions from chicken manure composting in the BSF scenario, Gg CO₂eq year⁻¹; $E_{Equipment}$: GHG emissions from equipment construction, Gg CO₂eq year⁻¹; $E_{Energy}$: GHG emissions from energy consumption, Gg CO₂eq year⁻¹; $E_{Process-{CH}_4}$: CH₄ emissions from treatment processes, Gg CO₂eq year⁻¹; EProcess-N₂O: N₂O emissions from treatment processes, Gg CO₂eq year⁻¹; $E_{Process-{NH}_3\left(Indirectly\right)}$: NH₃ (indirect) emissions from treatment processes, Gg CO₂eq year⁻¹; $E_{Of}$: the GHG reductions from frass as organic fertilizers replacing chemical synthetic NPK fertilizers, Gg CO₂eq year⁻¹; and $E_{feed-land}$: GHG reduction from using saved land for BECCS and avoiding soybean production, Gg CO₂eq year⁻¹. Detailed parameters and calculations can be found in Appendix A. Equation (3) extended the IPCC-based framework by incorporating BSF product-substitution and BECCS-related mitigation credits [22,23,24,25,26,27].

2.5. Analytical Methods for Cost–Benefit Analysis

In order to assess the potential for the bioconversion of chicken manure by black soldier fly and to evaluate the economic benefits and costs of the treatment process, the methodology and implications of the equations are presented in this section.

2.5.1. Estimation of Product Output

Product outputs from BSF treatment were estimated using a mass-balance approach based on published BSF bioconversion studies. Key parameters, including manure dry matter reduction, frass moisture content, larval moisture content, FCR, and larval crude protein content, were extracted from experimental studies and summarized as mean values in Appendix A (Table A1). The percentage of dry weight reduction of manure was 45.57% and 40.55% for layers and broilers, respectively, and the moisture content of insect sand was 30%, while the moisture content of insects was 75%, and the FCR was 6.43 and 6, respectively. According to (Table A1), we can use Equation (4) to estimate the production of feed protein yield (kg) from fresh chicken manure after its bioconversion by black soldier fly:

$$PR={\displaystyle \frac{W_{fresh weight}}{FCR}}\ast \left(1-MC\right)\ast {Pr}_c$$

(4)

where PR: the production of black soldier fly protein after BSF bioconversion; W_{fresh weight}: the amount of chicken manure (fresh weight); FCR: feed conversion ratio of black soldier fly; MC: insect moisture content; and Prc: the protein content of BSF. Equation (4) was based on a mass-balance calculation using BSF feed conversion ratio, larval moisture content, and crude protein content [19,28].

Equation (5) was used to estimate the organic fertilizer yield after manure treatment:

$$OF=W_{fresh weight}\ast \left(1-MC\right)\ast (1-R)$$

(5)

where OF: amount of organic fertilizer (dry weight); W: the amount of chicken manure (fresh weight); MC: the moisture content of fresh chicken manure; and R: percentage reduction in dry weight of manure. Equation (5) was based on a mass-balance calculation using manure moisture content and dry matter reduction during BSF bioconversion [28].

2.5.2. Production Cost and Benefit Analysis

Manure treatment will incur costs for equipment construction, electrical energy consumption, composting materials, labor, and other costs. The cost of each manure treatment way consists of fundamental costs and operating costs [27]. Fundamental costs cover land cost, infrastructure investment and equipment cost. Operating costs consist of labor, energy, equipment maintenance, and auxiliary materials. Equipment maintenance is estimated at 3% of the equipment cost [29].

Data on production costs of chicken manure composting equipment in the BAU scenario were obtained [20]. Composted chicken manure can be returned to the field as organic fertilizer in BAU scenario [30]. Therefore, the BAU scenario cost mainly consists of the net cost of the four types of compost minus the benefit of the compost product as an organic fertilizer, with the following formula (Formulas (6) and (7)).

$$\begin{array}{c}{Net Cost}_{BAU}=({\displaystyle \sum _{i,j,k}}\begin{array}{c}{\displaystyle \frac{{Cost}_{land,i,j,k}}{P_{land}}}+\left({\displaystyle \sum _x}{\displaystyle \frac{{Cost}_{infrastructure,x,i,j,k}}{{DF}_x}}\right)+\left({\displaystyle \sum _y}{\displaystyle \frac{{Cost}_{equipment,y,i,j,k}}{{DF}_y}}\right)\\ +{Cost}_{operating,i,j,k}-{Price}_{Organic fertilizer})\ast Q_{i,j,k}\end{array}\end{array}$$

(6)

where Net Cost_BAU: BAU scenario net cost of manure treatment in Hebei province ($); Costland: the cost of land ($/t dry weight manure); Pland: the land-use period (year); Cost infrastructure: the cost of infrastructure ($/t manure); Q: annual manure production (t); DFx: the depreciation factor; Cost equipment: the cost of equipment ($/t manure); Cost operating: the cost of operating ($/t manure), including: labor, energy, equipment maintenance, and auxiliary materials; Price Organic fertilizer: price of the total amount of organic fertilizer derived from 1 ton of dry chicken manure ($/t manure); i: the county of Hebei province; j: the type of chicken (layer and broiler); k: the different ways of manure treatment (SH, WC, TC, RC); and x: the type of different infrastructure. Infrastructure includes pad construction, drainage and roof construction (excluding RC). y: the type of different equipment; equipment includes composting channel (TC), aeration equipment (WC, TC), turning machine (WC, TC), and composting reactor (RC). Equation (6) was adapted from cost-assessment methods for manure composting systems [20,29].

The BSF scenario mainly involves cement pool (BSF-A) and automated farming tanks (BSF-B). The cement pool data is from practical production research, and detailed information is in (

Table A2. Nutrient production during composting (BAU).

Fertilizer	Production Capacity (kg)	Emission Factor (kg/kg)
N	0.0124	7.76
P	0.0099	2.33
K	0.0108	0.66

), where the black soldier fly cement pool bioconversion takes into account the utilization of black soldier fly after chicken manure treatment, and, therefore, drying equipment is needed. The establishment of an automated modular system for organic waste using black soldier fly was performed, and the paper introduced the equipment process and economic benefits in detail [30]. In BSF scenario, the black soldier fly can be used as a substitute for soybean feeds, and the frass produced by the conversion of chicken manure can be used as organic fertilizer. Therefore, the net cost of the BSF scenario is the production cost minus the income from products, which is calculated as follows:

$${Net Cost}_{BSF}=({\displaystyle \sum _{i,j}}\begin{array}{c}{\displaystyle \frac{{Cost}_{land,i,j,k}}{P_{land}}}+\left({\displaystyle \sum _x}{\displaystyle \frac{{Cost}_{infrastructure,x,i,j}}{{DF}_x}}\right)+\left({\displaystyle \sum _y}{\displaystyle \frac{{Cost}_{equipment,y,i,j}}{{DF}_y}}\right)\\ +{Cost}_{operating,i,j}-{Price}_{Organic fertilizer}-{Price}_{BSF protein})\ast Q_{i,j,k}\end{array}$$

(7)

where Net Cost_BSF: BSF scenario net cost of manure treatment in Hebei province ($); Costland: the cost of land ($/t dry weight manure); Pland: the land-use period (year); Cost infrastructure: the cost of infrastructure ($/t manure); Q: annual manure production (t); DF: the depreciation factor; Cost equipment: the cost of equipment ($/t manure); Cost operating: the cost of operating ($/t manure), including: labor, energy, equipment maintenance, and auxiliary materials; Price Organic fertilizer: price of the total amount of organic fertilizer derived from 1 ton of dry chicken manure ($/t manure); Price BSF protein: total price of BSF protein derived from 1 ton of dry chicken manure ($/t manure); i: the county of Hebei province; j: the type of chicken (layer and broiler); and x: the type of different infrastructure. Infrastructure includes pad construction, drainage and roof construction (For the AU, infrastructure investment, equipment cost, and land cost were aggregated as total fundamental cost). y: the type of different equipment. Equipment includes drying equipment (CP) and automated breeding system equipment (For the AU, drying units, rearing equipment, conveyors, and control components were integrated, and their costs were included as fundamental cost). Equation (7) was adapted from techno-economic assessment methods for BSF-based organic-waste treatment systems [29,31].

2.6. Sensitivity Analysis

To evaluate the robustness of the results, a one-at-a-time sensitivity analysis was conducted for selected technical, environmental, and economic parameters. For the BSF scenarios, the tested parameters included FCR, larval crude protein content, and equipment cost. For the BAU composting scenario, direct GHG emission factors and unit operating costs were tested. Each parameter was varied by ±20% around the baseline value, while all other parameters were kept constant. The effects on BSF-derived protein production, GHG mitigation results, composting emissions, and economic costs were compared with the baseline results. Detailed results are provided in Appendix A.

3. Results

3.1. Chicken Manure Production and Treatment Rate

In 2021, the total production of chicken manure in Hebei province reached 22 Tg yr⁻¹ (fresh weight), with layers contributing 81% and broilers contributing 19%. Among the 17.7 Tg yr⁻¹ of layer manure produced, approximately 43% originated from large-scale industrial farms with a stock of over 10,000 birds per farm (Figure 2a). For broiler manure, large-scale farms with an annual slaughter of over 50,000 birds per farm accounted for 78% of the 4.3 Tg produced (Figure 2b). This distribution pattern is consistent with global trends, where large-scale poultry operations are increasingly dominant in manure production [31]. Generally, large-scale chicken farms are more likely to adopt new technologies, such as using black soldier fly to convert chicken manure into insect protein, compared to medium and traditional-scale farms. This is in line with international studies showing that larger farms have greater access to capital and expertise for technology adoption.

There were significant spatial variations in chicken manure production and the contributions of large farms at the county level in 2021 (Figure 2c,d). Similar spatial heterogeneities have been reported in other regions globally (e.g., in the Midwestern United States [32]). This complexity makes it challenging to estimate greenhouse gas (GHG) emissions from the entire chicken manure treatment and recycling chain. Firstly, chicken manure production varied among counties, as indicated by the bar lengths in Figure 2. Some counties in northeastern Hebei had notably higher broiler manure production; for instance, two out of 167 counties were responsible for 9.6% of broiler manure production (Figure 2d). In contrast, layer manure production was more concentrated in southern Hebei and was more evenly distributed among counties compared to broiler manure (Figure 2c,d). Secondly, counties with high layer and broiler production were not necessarily the ones where large-scale farms were the main contributors. For example, a few counties had an extremely high proportion of manure production from large-scale farms (over 90%), yet these counties accounted for only a small portion of the total chicken manure production, as shown by the dark-blue shading; darker areas indicate a higher proportion of large-scale farms (Figure 2c,d).

Currently, static composting is the dominant technology for treating chicken manure in Hebei province, accounting for 94% and 87% of layer and broiler manure treatment, respectively (Figure 2a,b). This is in contrast to some developed countries where more advanced composting technologies are more prevalent (e.g., in Europe, reactor composting is widely used in many regions [33,34]). Although more efficient but costly advanced composting technologies, like reactor composting, can significantly reduce nitrogen losses and GHG emissions compared to traditional static composting, they are less commonly adopted by farms, mainly due to the high initial investment in equipment (

Table 1. The detailed costs of different types of composting equipment and black soldier fly treatment technologies, and related benefits.

		BAU				BSF-A	BSF-B
Category	Project	SC	WC	TC	RC	CP	AU
	Coverage area (m2)	267	141	141	8.5	20	2.5
Fundamental cost	Infrastructure investment ($/t)	2.42	2.39	2.39	0.05	0.75	453
	Equipment cost ($/t)	-	9.9	10	20	14
	Land cost ($/t)	0.46	0.24	0.24	0.01	11.40
Operation cost	Electricity consumption ($/t)	-	2.74	2.74	4.57	12	1657
	Labor cost ($/t)	6.2	6.2	6.2	6.2	64
	Maintenance costs ($/t)	0.07	0.37	0.38	0.60	0.42
	Accessories materials expense ($/t)	17	17	17	15	17
	Depreciation cost($/t)	2.88	13	13	20	26	453
Total cost per ton dry weight of manure ($)		26	39	39	46	120	2110
Price	Organic fertilizer/frass ($/t)	154	154	154	154	841	841
						912	912
	BSF protein ($/t)	-	-	-	-	201	215
Net economic cost per ton dry weight ($/t)		−128	−115	−115	−108	−165 1	1811 1
						−172 2	1804 2

Notes: SC: static composting. WC: windrow composting. TC: trough composting. RC: reactor composting. CP: cement pool based black soldier fly treatment. AU: automated feeding tanks based on black soldier fly treatment. ¹ for layer manure, ² for broiler manure. BAU including SH. WC. TC. RC. BSF-A: CP. BSF-B: AU. Organic fertilizer/frass: price of the total amount of organic fertilizer derived from 1 ton of dry chicken manure ($/t manure). BSF protein: total price of BSF protein derived from 1 ton of dry chicken manure ($/t manure).

). Moreover, there were significant differences in chicken manure composting technologies at the county level. While static composting was dominant in most counties, especially for layer manure treatment, there were exceptions for broiler manure treatment, with some counties having a high proportion of manure treated by reactor composting and trough composting (Figure 2d). These findings emphasize the need for county-specific cost–benefit analyses of chicken manure treatment strategies, similar to the regional-based optimization approaches proposed in the international literature [28].

3.2. GHG Emissions Under the Business-As-Usual Scenario

A life cycle assessment was employed to trace GHG emissions from chicken manure treatment at the provincial and county levels in Hebei. The boundaries of GHG emissions calculation are presented in Figure 1. In 2021, the total GHG emissions were estimated to be 0.6 Tg CO₂ eq yr⁻¹, with layer manure contributing 79% and broiler manure contributing 21% (Figure 3a,d). Large-scale farms contributed around 59% of the total emissions from all chicken manure, but this contribution varied from 51% for layer manure emissions to 85% for broiler manure emissions (Figure 3a,d).

The detailed GHG emission flows and the contributions of different composting technologies were quite similar for layer and broiler manure treatment. This similarity is due to comparable emission factors and the dominance of static composting in chicken manure treatment (Figure 3a,d). The total emissions from static composting of all chicken manure were 466 Gg CO₂eq yr⁻¹, accounting for 75% of the total emissions. Reactor composting emissions were 35 Gg CO₂eq yr⁻¹, representing 6% of the total, while strip-stack composting and trough composting emissions were 58 Gg yr⁻¹ and 42 Gg CO₂eq yr⁻¹, respectively (Figure 3a–d). These emission patterns are consistent with some previous studies on poultry manure treatment in Asia [28,35], but the overall emission levels in Hebei are relatively high compared to some regions with more advanced treatment technologies.

Most of the GHG emissions occurred during the composting period, with direct N₂O emission being the main contributor. Although composting manure requires ventilation to supply oxygen for microbes, many studies have observed N₂O emissions during composting [36]. This is partly because the cessation of ventilation can create anaerobic conditions, and in large composting piles, ventilation may not provide sufficient oxygen throughout. In total, N₂O emissions accounted for 64% of the total GHG emissions from chicken manure treatment in Hebei in 2021 (Figure 3a,d). Indirect N₂O emission, via NH₃ emission, was the second-largest source, accounting for 24% of the total GHG emissions. Ammonia emission is a major issue in manure composting; high temperatures and forced ventilation during composting promote its release from the manure heap into the atmosphere, leading to indirect N₂O emission in the environment. Higher nitrogen losses during composting also reduce the manure’s ability to replace synthetic nitrogen fertilizers. Additionally, anaerobic conditions during composting, even with a relatively low carbon-to-nitrogen ratio in chicken manure, favor the production of methane (CH₄), which accounted for 8.1% of the total emissions (Figure 3a,d). The GHG emissions from energy use and other materials during chicken manure composting were relatively low compared to other emission sources. Composted manure can substitute synthetic nitrogen fertilizer, helping to reduce GHG emissions during fertilizer manufacturing, with a total reduction of 0.8 Gg CO₂eq yr⁻¹ (Figure 3a,d). The detailed GHG emission flows of different composting technologies were also dominated by direct and indirect N₂O emissions during the composting process (Figure 3a–d).

3.3. GHG Mitigation Potential Under the BSF Scenario

Certain insects and worms, such as the BSF and earthworm, can thrive in harsh environments like chicken manure. After proper treatment, their larvae and bodies can be used as livestock feed. Rearing them in manure can significantly reduce manure stock and reconnect decoupled crop–livestock production. BSF-derived insect protein has the potential to replace feed proteins like soybean, saving land for BECCS, thus offering great potential for GHG mitigation [22]. The remaining substrate, frass, can be used as an organic fertilizer to replace synthetic NPK fertilizer [37,38]. This concept of using BSF for manure management and resource recovery has been widely explored in international research, with similar findings on its potential benefits [19,39].

Based on the current situation, two scenarios were developed, both using BSF to convert chicken manure into valuable insect protein but with different BSF production technologies. Scenario BSF-A involves producing BSF in traditional cement ponds, which have relatively low costs but a lower turnover rate. Scenario BSF-B uses advanced automated breeding tanks. These two technologies represent the two main methods of BSF-based insect protein production, and understanding the GHG emissions and costs associated with them is crucial.

In BSF-A, the dry BSF larva production is expected to be 857 Gg yr⁻¹ (dry matter), with 690 Gg yr⁻¹ from layer manure and 167 Gg yr⁻¹ from broiler manure. In BSF-B, due to better management, the dry BSF larva production will increase to 918 Gg yr⁻¹. Based on the 41.9% protein content of BSF larva, the produced insect protein is 359 Gg yr⁻¹ in BSF-A and 385 Gg yr⁻¹ in BSF–B (Figure 4e,f). For comparison, the total soybean production in Hebei province in 2022 was approximately 230 Gg yr⁻¹ [39], which is over half of the insect protein produced from chicken manure, considering the similar protein content of dry BSF larva and soybean. This insect protein is expected to replace soybeans from the Chinese market, given China’s emphasis on food security. When corrected by the multiple-harvest index in China, this would save 0.37–0.40 Mha yr⁻¹ of cropland [40]. If the saved cropland is used for BECCS, it could potentially reduce GHG emissions by 6.9 Tg CO₂eq yr⁻¹ in BSF-A and 7.25 Tg CO₂eq yr⁻¹ (Figure 4e,f). Meanwhile, the 5233 Gg yr⁻¹ of frass produced, a high-quality organic material, could potentially substitute 24 Gg yr⁻¹ of N fertilizer, 18 Gg yr⁻¹ of P fertilizer, and 19 Gg yr⁻¹ of K fertilizer. This substitution would reduce GHG emissions by 213 Gg CO₂eq yr⁻¹ due to reduced energy use and related N₂O losses during fertilizer manufacturing. The significantly higher GHG emission reduction in BSF-A and BSF-B scenarios compared to the BAU scenario is mainly due to over-fertilization in the BAU scenario, where applied compost manure does not effectively replace synthetic fertilizers (Figure 4).

During BSF-A and BSF-B, the additional requirements for materials, basic structures (such as cement and steel), and energy consumption (for drying BSF larvae) result in GHG emissions of 4.17 Tg CO₂eq yr⁻¹ and 1.18 Tg CO₂eq yr⁻¹, respectively (Figure 4e,f). However, the GHG emissions during BSF-treated manure, including CH₄, direct and indirect N₂O, are much lower compared to traditional composting technologies (Figure 3 and Figure 4). Specifically, the total GHG emissions during BSF treatment are 92 Gg CO₂eq, while in the BAU scenario, it is 576 Gg CO₂eq yr⁻¹ (Figure 3 and Figure 4). This indicates that BSF treatment directly reduced manure-treatment emissions by 484 Gg CO₂eq yr⁻¹ compared with conventional composting. The larger overall mitigation potential was mainly derived from additional system benefits, including soybean-protein substitution, fertilizer substitution by frass, and BECCS-related land-use savings. This difference may be attributed to the black soldier fly’s continuous peristaltic movement, which creates numerous holes and tunnels, enhancing the oxygen concentration in the waste and inhibiting the production of two greenhouse gases [41]. The application of BSF-A and BSF-B could reduce the overall GHG emissions from chicken manure by 7.11 Tg yr⁻¹ and 7.47 Tg yr⁻¹, respectively, compared to the current situation. These results are consistent with international studies on the superiority of BSF-based manure treatment in reducing GHG emissions [42].

The spatial distribution of GHG emissions under the BAU scenario exhibited clear regional disparities, largely consistent with chicken manure production patterns (Figure 2c–d). Emissions were notably higher in central-southern and northeastern counties, particularly those dominated by layer production. Most counties showed layer manure emissions ranging from 1 to 4 Gg CO₂eq yr⁻¹, while only nine counties exceeded 8 Gg CO₂eq yr⁻¹ but contributed over 20% of total layer emissions. For broilers, emissions ranged from 0.1 to 1 Gg CO₂eq yr⁻¹, with just four counties exceeding 4 Gg CO₂eq, accounting for 16% of broiler-related emissions. Under the BSF scenario, these high-manure regions also exhibited the greatest mitigation potential, especially for layer manure. In BSF-A, 20% of counties achieved GHG reductions exceeding 20 Gg CO₂eq yr⁻¹, while BSF-B increased this proportion to 54%, with mitigation hotspots concentrated in the northeastern and central-southern parts of the province. These results highlight a strong spatial convergence between emission hotspots and reduction opportunities.

Because the BECCS-related credit strongly influenced the overall mitigation results, we further evaluated a no-BECCS scenario. When BECCS-related carbon removal was excluded but soybean-protein and fertilizer substitution credits were retained, the GHG results changed from −2.85 to 2.88 Tg CO₂eq yr⁻¹ for BSF-A and from −6.19 to −0.19 Tg CO₂eq yr⁻¹ for BSF-B. This indicates that BECCS was a major driver of the negative GHG balance, while BSF treatment still reduced direct manure-treatment emissions and provided additional substitution benefits through insect protein and frass production.

3.4. Total Cost of Chicken Manure Treatment Under Two Scenarios

A comprehensive comparative analysis of the economic costs and benefits of the BAU scenario and the BSF scenario was conducted. The results indicate that the BSF scenario has significant economic advantages. In the BAU scenario, total treatment costs ranged from $26 to $46 per ton of dry manure, with SH being the most cost-effective and RC the most expensive (Table 1). The cost differences were primarily driven by equipment depreciation costs, especially in WC, TC and RC systems. Despite the operational expenses, all BAU composting methods generated net negative costs due to the sale of compost as organic fertilizer. This results in the net economic cost of treating chicken manure in Hebei Province to be −$838 million every year (Figure 5).

The BSF scenario also performs well in terms of revenues, despite having relatively high costs. BSF-A, based on cement pool systems, had a moderate treatment cost of $120/t. While BSF-B, involving automated rearing tanks, incurred an extremely high cost of $2109.6/t, largely due to the high depreciation and maintenance costs of precision equipment. However, the benefit from both frass and dried BSF larvae significantly offset these costs. In BSF-A, the net cost reached −$164.6/t for layer manure and −$172/t for broiler manure, indicating higher cost-effectiveness compared to traditional composting methods. If scaled across Hebei Province, cement pool-based BSF treatment could yield a total net economic benefit of $1160 million (Figure 5). In contrast, BSF-B incurred a much higher treatment cost of $1798–1805/t, primarily due to substantial capital and operational expenses associated with automated rearing systems. While BSF-B may be more suitable for large-scale farms with advanced infrastructure, further reductions in investment and operational costs are essential to enhance its broader applicability and economic feasibility [43,44].

These results are consistent with those of previous studies, which have shown that although BSF farming requires a high initial investment, its long-term economic benefits in resource recovery and recycling are significant [42]. Additionally, the high-value insect proteins and organic fertilizers produced during BSF farming can substitute external resources, reducing the overall environmental impact of the farming system [45].

3.5. Sensitivity Analysis

The one-at-a-time sensitivity analysis first showed that BSF-derived protein production was most sensitive to FCR and larval crude protein content. A 20% decrease in FCR increased protein production to 449 Gg and 481 Gg under the cement pond and automated systems, respectively, whereas a 20% increase in FCR reduced protein production to 299 Gg and 321 Gg. Larval crude protein content showed a proportional effect on protein output and substitution-related mitigation. For the BAU scenario, a ±20% change in direct GHG emission factors changed total composting emissions from 494 to 741 Gg CO₂eq yr⁻¹, compared with the baseline value of 618 Gg CO₂eq yr⁻¹, while static composting remained the dominant emission source. A ±20% change in unit operating cost altered BAU total operating costs from $271 million to $407 million, but did not change the overall economic interpretation because organic fertilizer revenue partly offset treatment costs. For the BSF scenarios, changes in FCR and larval protein content also affected the overall GHG mitigation results through feed-protein substitution and BECCS-related land-use savings. The baseline mitigation results of −2852 and −6193 Gg CO₂eq yr⁻¹ changed to −4576 and −8006 Gg CO₂eq yr⁻¹ when FCR decreased by 20%, and to −1702 and −4984 Gg CO₂eq yr⁻¹ when FCR increased by 20%, under the cement pond and automated systems, respectively. Equipment cost affected only the economic performance of BSF systems, with automated systems showing much higher sensitivity to capital cost uncertainty than cement pond systems. Overall, the sensitivity analysis indicates that the main conclusions are generally robust under the tested parameter ranges, although key technical, emission, and economic parameters should be further validated using region-specific data (

Table A14. Sensitivity analysis of key parameters in BAU and BSF scenarios.

System	Parameter	Baseline	−20%	20%	Main Affected Output
BSF	FCR	6.43/6.00	5.14/4.80	7.72/7.20	Protein output, GHG mitigation
BSF	Larval crude protein content	0.419	0.335	0.503	Protein output, substitution benefits
BSF	Equipment cost	28.34/631.30 $ t−1	−20%	20%	Economic cost
BAU	Direct GHG emission factor	baseline	−20%	20%	Composting GHG emissions
BAU	Unit operating cost	baseline	−20%	20%	Economic cost

).

3.6. Implications for Future Research and Policy

The findings of this study offer several important implications for both future research and policy-making. From a research perspective, further investigations are needed to optimize the BSF-based manure treatment technologies. Research could focus on improving the efficiency of BSF breeding in both cement ponds and automated tanks, reducing the associated GHG emissions during the production process, and enhancing the quality of the resulting insect protein and frass. Long-term field trials are also required to assess the sustainability of substituting synthetic fertilizers with BSF-derived frass and the potential impacts on soil health and crop yields. In addition, because composted manure and BSF-derived frass may be applied to agricultural soils, product quality and soil safety should be monitored before field application. In China, organic fertilizer products and agricultural soils are regulated by relevant standards, such as NY/T 525-2021 for organic fertilizers and GB 15618-2018 for soil contamination risk control of agricultural land. Therefore, future deployment of BSF-based manure management should include monitoring of nutrient composition, trace metals, and potential contaminants, as well as product tracking systems to ensure safe use in agricultural production. Additionally, although anaerobic digestion is an important alternative for chicken manure treatment and biogas production, it was not included as an independent scenario in this study because our analysis focused on comparing current composting practices with BSF-based manure bioconversion for feed protein and frass production. Future studies could further evaluate anaerobic digestion alone or its integration with BSF treatment in hybrid systems to develop more comprehensive manure management strategies.

The C/N ratio is an important manure-quality factor affecting microbial activity, organic matter decomposition, nitrogen transformation, BSF larval growth, and GHG emissions during manure bioconversion. In general, excessively low C/N ratios may increase NH₃ volatilization and nitrogen losses, potentially inhibiting microbial activity and larval performance, whereas excessively high C/N ratios may limit nitrogen availability and slow organic matter degradation, thereby reducing composting efficiency and BSF bioconversion performance. In this study, the influence of C/N ratio was represented indirectly through literature-derived manure composition, composting emission parameters, and BSF bioconversion parameters. Therefore, we discuss the potential role of C/N ratio and related process-level factors as an important source of uncertainty in BSF-based manure treatment. Because this study was conducted as a regional-scale LCA based on statistical data and literature-derived parameters, farm-specific C/N ratios, complete manure chemical compositions, composting temperature and humidity, particle size, layer depth, and maturation time were not directly measured. Instead, representative manure composition and process parameters were adopted from published studies and summarized in Appendix A, including TC and TN contents, composting N₂O-N, NH₃-N, and CH₄-C losses, and BSF bioconversion parameters such as manure dry matter reduction, frass moisture content, larval moisture content, and FCR. These parameters were used to represent the effects of manure quality and treatment conditions on composting emissions and BSF performance. Nevertheless, process-level factors may substantially influence composting efficiency, nitrogen losses, larval growth, substrate reduction, and frass quality. In addition, the mitigation benefits associated with soybean-protein substitution, land-use savings, and BECCS should be interpreted as scenario-based potential, and transportation emissions were excluded due to inconsistent regional logistics data and the farm-gate system boundary. Future studies should combine regional-scale LCA with farm-level monitoring and spatially explicit transport data to improve the accuracy of manure treatment and mitigation assessments.

In terms of policy, BSF-based manure treatment should be promoted through stepwise demonstration and region-specific deployment rather than immediate large-scale adoption. Policy support could include pilot subsidies for suitable farms, technical training, market certification for BSF-derived feed protein and frass, and product safety standards to ensure environmental and feed safety. Policy-makers should also encourage research and development in this area by funding relevant projects and facilitating knowledge-sharing between researchers and industry stakeholders. Before broader adoption, practical constraints, including investment capacity, product utilization, market demand, transportation logistics, and farm-level management capacity, should be carefully evaluated. Furthermore, given the significant spatial variations in chicken manure production and treatment, county-level policies should be tailored to the specific characteristics of each region to maximize the effectiveness of manure management strategies.

4. Conclusions

Using life cycle assessment, this study evaluated the environmental and economic performance of traditional composting in Hebei’s large-scale chicken manure management and the substantial potential of BSF technology to address feed protein shortage and manure surplus in Jing-Jin-Ji. The results suggest that BSF treatment has the potential to convert 22 Tg yr⁻¹ of chicken manure into 359–385 Gg yr⁻¹ of feed protein. BSF treatment reduced direct manure-treatment emissions compared with conventional composting and generated additional mitigation benefits through feed-protein substitution, fertilizer substitution, and BECCS-related land-use savings. Without BECCS-related carbon removal, the GHG results were substantially reduced, highlighting the importance of land-use assumptions in interpreting the mitigation potential. Under the scenario assumptions used in this study, the overall GHG mitigation potential was estimated at 2.85–6.19 Tg CO₂eq yr⁻¹. Low-technology BSF systems (e.g., cement ponds) are cost-competitive, while automated systems, despite higher upfront costs, offer significant long-term resource recovery benefits. Overall, BSF-based manure treatment shows promise as a potential option for improving manure management, feed-protein substitution, and GHG mitigation in intensive agricultural regions. Future research should strengthen regional parameter validation, field-scale monitoring, transport assessment, and market feasibility analysis before large-scale deployment.