Source
doi:10.3389/fsufs.2025.1561457 — original publication (opens in a new tab; the file is not redistributed)
Ebel et al. 2025 — Household-scale anaerobic digestion of food waste (Bozeman, Montana)
Primary field study behind CR_039's digestate / energy-vs-nutrient framing + independent cold-climate corroboration (D03/D02 evidence, NOT a modelled NI cell)
A peer-reviewed community case study (12 households, cool-climate northern USA) running household-scale AD for biofertiliser, not biogas. It is the retrievable primary source that CR_039 cited for the “energy-vs-nutrient” framing, and it independently corroborates the cold-climate seasonality (CR_039’s own “≈6 months/yr” figure traces to Castaño et al. 2014, a separate CR_039 underlying source, not this study). Foreign context (Montana) — the transferable content is the operational pattern (cold-climate seasonality, fertiliser-first justification, user acceptance), not the Montana-specific nutrient values, which are not NI inputs.
Summary
A community-based case study in Bozeman, Montana (population ~53,000; cool-continental climate, no municipal food-waste programme at the time) deploying two household-scale anaerobic-digestion designs in 12 households over 2021–2022 — six households with a commercial Home Biogas 2 unit (1,200 L digester, up to 700 L biogas storage) and six with a research-built MSU prototype (114 L plastic drum that produces liquid digestate but does not capture biogas). Digesters were run explicitly to produce nutrient-rich digestate as biofertiliser, not for energy — methane production was not a study goal. The study characterised household food-waste composition and tracked digestate nutrient content over ~12 weeks of summer operation, and surveyed participants on the practicality of the technology. Its headline findings: household-scale AD can process food waste even in a cool climate but is seasonal — non-functional for over 6 months of the year because of cold; the fertiliser output is the defensible product (half the Home Biogas users could not extract any gas); and despite convenience/cold-climate challenges, 87% of participants would continue/recommend the technology, favouring the simpler custom-built unit. This is the primary evidence behind CR_039’s “AD as sanitation + nutrient recovery, energy a co-benefit” verdict, and it independently corroborates CR_039’s cold-climate seasonality (CR_039’s “≈6 months/yr” figure itself traces to Castaño et al. 2014, not this study).
Key claims
- claim: "COLD-CLIMATE SEASONALITY (decisive operational finding, and the transferable content for NZ). Household-scale AD 'can effectively process food waste, even in cool climates, but it also highlighted the seasonality of this approach as digesters were not functional for over 6 months of the year due to cold temperatures.' Mesophilic reactors function optimally at 35 °C, but Bozeman monthly-average air temperatures over the study period were only 15.5 °C (June 2021), 20.7 °C (July), 21.0 °C (August) and 15.4 °C (September) — matching the 30-year normals. Digestion was incomplete (final digestate pH only 5.7 vs food-waste pH 4.4; food-waste AD digestates are usually alkaline at completion) and AD activity stayed low until higher temperatures occurred. In winter the digestate had to be physically removed and the unit disassembled to prevent freezing — a task not required in the tropical areas where household AD is common. The authors flag psychrophilic digesters (functioning at 10–20 °C) as a promising future research field. Implication (consistent with CR_039): passive household-scale AD is a warm-season-only proposition in a cool-temperate climate. [primary field study, high confidence for the qualitative pattern]"
source_location: "Abstract (cold-climate willingness); §4.2 Digester operation (air temps 15.4–21.0 °C; incomplete digestion, pH 5.7 vs 4.4); §4.3 Survey (disassembly to prevent freezing of the digestate in Montana winter); §5 Conclusions ('not functional for over 6 months of the year due to cold temperatures'; psychrophilic 10–20 °C research direction)"
- claim: "FERTILISER-FIRST, NOT ENERGY (the energy-vs-nutrient framing CR_039 leans on). Household-scale biodigesters 'can degrade food waste effectively but typically do not generate enough biogas to meet entire household needs, making them more suitable for fertilizer production than for generating energy.' The digesters in this study were run for biofertiliser: the MSU prototype captures no gas at all, and methane-enhancing carrier materials were deliberately not added 'since methane production was not a goal of the study.' Crucially, half of the households using the commercial Home Biogas unit 'reported being unable to extract biogas, negating the only potential advantage this system might have over the MSU model.' A participant summarised it: 'I did not have success with the gas … Wasting the gas is more than offset by the fertilizer and reduced landfill components.' [primary field study; directly supports the AD-as-nutrient-recovery verdict]"
source_location: "§1 Introduction (household digesters more suitable for fertilizer than energy); §3.3 Digester comparison (MSU model captures no biogas; carrier materials omitted, methane not a goal); §4.3 Survey + participant quote (half of Home Biogas users could not extract gas)"
- claim: "STUDY DESIGN & DIGESTER SCALES. Two designs across 12 households in Bozeman, MT (pop. ~53,000), 2021–2022: (1) commercial Home Biogas 2 (Beit Yanai, Israel) — a 1,200 L plug-flow digester tank storing up to 700 L biogas; (2) an MSU-built prototype — a 114 L plastic drum producing effluent biofertiliser without biogas capture. Six households received each. The study explicitly targets the feasibility of decentralised household AD for 'towns and small cities of around 50,000 residents or fewer located in cool climates.' Decentralised AD designs generally range 0.65–150 m³; the upper end is unsuitable for households. [primary; design parameters directly stated]"
source_location: "§3.3 Digester comparison (Home Biogas 2: 1,200 L tank / 700 L gas; MSU model: 114 L drum, no gas capture; 6 + 6 households); §3.1 Case study (Bozeman ~53,000, 2021–2022); §1 Introduction (~50,000-resident cool-climate towns); §2.3 (decentralised AD 0.65–150 m³)"
- claim: "DIGESTATE NUTRIENT CONTENT (Montana-specific; illustrative, NOT an NI input). Over ~12 weeks, digestate N, P, K, S, pH and conductivity all increased significantly (p < 0.05). Mean total C and N across all digestate samples were 2,093.3 ± 1,956.8 and 246.7 ± 206.6 mg l⁻¹ (highly variable, and lower than literature values — attributed to the shorter operating period and low temperatures). Final digestate C:N ratio averaged 6.6 (6.57 ± 2.23 Home Biogas; 10.25 ± 3.99 MSU), down from food-waste C:N of 12.1–25.7. Potassium: 857.14 mg l⁻¹ (Home Biogas) and 1,212.5 mg l⁻¹ (MSU). Average ammonia was 88.7 mg l⁻¹ — well below the ~650 mg l⁻¹ methanogenesis-inhibition threshold — while the NH3-N-to-total-N ratio rose from 0.09 in the food waste to 0.25 in the digestate, evidence that digestion did occur. [primary; foreign-context nutrient values — corroborates the digestate-biofertiliser mechanism, not calibrates any NZ figure]"
source_location: "§4.2 Digester operation & digestate characterization + Table 4/Table 5 (mean C 2,093.3 / N 246.7 mg l⁻¹; ammonia 88.7 mg l⁻¹; NH3-N:TN 0.09→0.25; K 857.14 / 1212.5 mg l⁻¹; C:N 6.57 / 10.25); Abstract (mean C:N 6.6)"
- claim: "FOOD-WASTE FEEDSTOCK (heterogeneity + C:N). Average wet weight of household food waste was 1.9 kg per 2-week collection period (range 0.4–5.3 kg, depending on household size). Food-waste C:N ratios varied by type — 12.1–18.6 for vegetable waste and 20.8–25.7 for fruit waste — against an optimal AD C:N of 20–30, so a balanced fruit-plus-vegetable feedstock is needed to avoid ammonia accumulation. Household food waste is heterogeneous and season/diet-dependent, which the authors classify into 12 categories to improve planning certainty. (Context: roughly one-third of US food is wasted, ~600 g per person per day.) [primary; feedstock characterisation]"
source_location: "§4.1 Food waste characterization (1.9 kg/collection, 0.4–5.3 kg range; veg C:N 12.1–18.6, fruit 20.8–25.7); §2.2 (optimal AD C:N 20–30); §1 Introduction (one-third US food wasted, ~600 g/person/day)"
- claim: "USER ACCEPTANCE (survey, n = 28 respondents from all 12 households; Cronbach's α = 0.71, acceptable). Despite convenience and cold-climate challenges, 87% of respondents said they would continue using / recommend household-scale AD once feasibility issues are addressed. 64% reported a shift in perception, most citing new awareness of the volume of food waste they generate. Participants found the simpler custom-built MSU unit more user-friendly and feasible than the commercial Home Biogas unit (assembly ~0.5 h vs ~1.5 h); 42% found assembly difficult and 33% found disassembly / biofertiliser extraction 'somewhat difficult.' Both models produced an occasionally-uncomfortable odour. Takeaway: user-friendliness and design tailored to household needs and local climate are decisive for adoption. [primary; human-subjects survey, IRB-approved]"
source_location: "§4.3 Survey (87% would continue/recommend; 64% perception shift / food-waste awareness; MSU more user-friendly; assembly 1.5 h vs 0.5 h; 42% assembly difficult, 33% disassembly difficult; odour); §3.4 (n = 28, Cronbach's α 0.71); Abstract"Neobiome Intelligence relevance
AD is not a modelled NI calculation cell — there is no biogas/AD technology in the engine’s ④ technologies.csv; it is classed Conditional in the strategic technology options and stands as EDT-page evidence. This source is the retrievable primary behind CR_039’s energy-vs-nutrient framing (a claim CR_039 previously carried only as a synthesis citation), and it independently corroborates CR_039’s cold-climate seasonality:
- D03 (water/waste/circular) — the stronger justification. Corroborates the AD-as-sanitation + nutrient-recovery framing with a real field deployment: the digesters were run for digestate biofertiliser, not gas, and half the gas-capable units produced no usable gas. Reinforces the anaerobic_digestion “household Out / community Conditional” verdict from an independent cool-climate geography.
- D03 — cold-climate seasonality (independent corroboration). This study found digesters “not functional for over 6 months of the year due to cold temperatures,” with incomplete digestion at 15–21 °C ambient and winter disassembly to prevent freezing — a finding parallel to CR_039’s, though CR_039’s own “≈6 months/yr” figure traces to Castaño et al. 2014 (a separate CR_039 underlying source), not this study.
- D02 (food) — digestate as biofertiliser closing the nutrient loop. Household food waste → stabilised nutrient-rich digestate applied to home gardens/lawns; the food↔waste nutrient link.
Foreign-context caveat: all nutrient/temperature/cost specifics are Bozeman, Montana. The transferable content is the operational pattern and user-acceptance evidence, not the Montana nutrient numbers — none are used to calibrate an NI figure. NZ-specific AD gaps (RT_269 dairy primary, RT_272 NZ community deployment) remain open.
Notes
- Open access, downloaded authoritative primary — no retrieval-provenance block required (not AI-prepared). Frontiers in Sustainable Food Systems 9:1561457, published 21 May 2025, DOI 10.3389/fsufs.2025.1561457, CC-BY. Read verbatim via
pdftotext -layout(17 pp). - Scope limits stated by the authors: results are from summer conditions and may differ in colder seasons/other climates/food-procurement habits; the study is a qualitative case study (n = 12 households, n = 28 survey respondents), not a controlled experiment — inter-household variability in feedstock is high and confounds digester-model comparisons (“it was not possible to determine whether these differences were due to food waste inputs or digester design”). Treat the nutrient numbers as illustrative, not benchmark.
- Not an energy study. Gas yield / methane content were not measured; the paper cannot speak to biogas energy output — for that side of the AD verdict see CR_039 and the Malawi techno-economic corroboration (RT_027).
- Funding: US EPA “Supporting Anaerobic Digestion in Communities” grant — an advocacy-adjacent funder, but the paper reports candid negatives (seasonality, gas-extraction failures, odour), so no framing discount applied beyond the summer-only scope caveat.
Research targets
Documents to retrieve
- RT_273 — ADVANCED (not fully resolved). This source delivers the Ebel 2025 (Bozeman MT) leg of RT_273 — cold-climate household-AD operational outcomes + digestate-biofertiliser evidence. The Feng 2016 solar-heated-digester design leg of the same target is not delivered here and remains the residual, so RT_273 stays open.
Research gaps
- (none new — the NZ AD residuals stay on their existing targets: RT_269 NZ dairy-AD primary; RT_272 any NZ community-scale digester deployment.)
Connections
Links to
Sources (1): CR_039
Technologies (1): Biogas (community-scale,…
Referenced by
EDT domains (2): D02: Smart Food Systems & Agriculture · D03: Water, Waste & Circular Systems
Sources (1): CR_039
Technologies (1): Biogas (community-scale,…