BMP testingFruit, vegetables and their residues
Eggplant (fruit) — BMP: 2 studies, weighted mean 333 m³ CH₄/t VS
Aubergine (fruit, including fruit damaged by pests) has a high water content and readily available carbohydrates, so it digests well; the data come from several studies.
Photo Krzysztof Golik / Wikimedia Commons, licence CC BY-SA 4.0, source file; changes: cropping
- Weighted mean
- 333m³ CH₄/t VS
- Range
- 270–396m³ CH₄/t VS
- Records
- 2studies
- Publications
- 2sources
- Temperatures
- 35 °Cof the test
Methane in biogas
Medium methane content · ≈ 5.4 kWh/m³ of biogas
estimate from the substrate type The collected studies contain no measurement. The interval follows from the approximate composition (protein from total nitrogen (N 2.3 % DM × 6.25)) and the yields of compound groups according to FNR.
Rating for biogas plants
not rated — editorial rating for biogas plants
Not rated: no dry matter or volatile solids in the data. We calculate the rating when the dry matter and volatile solids of the material are known.
Add to the co-digestion calculator CSV data
BMP curves from 2 studies
Weighted mean Individual records
Dashed lines are a model curve (first-order kinetics, B(t) = B₀·(1 − e−kt)); the end point comes from the publication. All curves are model curves.
Cumulative methane production over the test [m³ CH₄/t VS]. The thick line is the weighted mean of all records (333); dots mark the end values given in the publications. Point at the chart to read values; click a legend item to hide or show a record.
Records and sources
Download CSV| Source | BMP m³ CH₄/t VS | Temperature | Sample | Curve |
|---|---|---|---|---|
| Yan et al. (2021) DOI | 270 | — | Eggplant (Solanum melongena) – Whole | end point (model curve) |
| Gunaseelan (2004) DOI | 396 | 35 °C · mesophilic | Brinjal whole fruit (pest infested) | end point (model curve) |
| Weighted mean | 333 | arithmetic mean 333, SD 89 | ||
Typical composition
- Volatile solids (VS)
- 91.8 % DM (range 91.1–92.6)
- Nitrogen
- 2.3 % DM
- C/N ratio
- 17.6
Median and range of the determinations reported in the publications behind this substrate's BMP records (read from: BCBPD, MY-D); dry matter: 0 determinations, volatile solids: 2 determinations. C/N was calculated as the ratio of C and N content (% DM) from the same source. No DM in the sources – the calculator has to ask for a value.
Sources: Yan et al. (2021); Gunaseelan (2004).
The composition of the raw material varies between batches — for plant calculations use an analysis of your own sample. The calculator inserts typical values automatically.
Process properties
Low confidence: the description is based on general characteristics of the substrate group, not on studies of this material. Treat it as a hint to be verified.
No published process studies
The literature we use does not describe the advantages or drawbacks of digesting this substrate beyond the BMP test results. Below are process characteristics assigned on the basis of the type of material — an editorial classification, not a study result.
- easily degradable
- sugars, starch, glycerol → fast hydrolysis and acidification (VFA), needs buffering
- acidic
- low pH of the substrate (silages, stillage, whey, fruit)
- dilutes the feed (low DM)
- low dry matter, dilutes the feed
- seasonal
- seasonal availability — requires storage
- poor in trace elements
- poor in trace elements — mono-digestion requires supplementation
- carbon-rich
- high C/N → nitrogen deficiency; combine well with nitrogen-rich substrates
- low in nitrogen
- high C/N → nitrogen deficiency; combine well with nitrogen-rich substrates
Co-digestion — what to combine it with, what to watch out for
- combines well
substrates: nitrogen-rich — e.g. Pig slurry, Poultry manure, Waste activated sludge (secondary sludge), Chlorella vulgaris, Nannochloropsis salina
A nitrogen-rich co-substrate balances the low C/N of fruit and vegetable waste (Bouallagui et al. 2009).[1]
- combines well
substrates: high alkalinity (buffer) — e.g. Cattle manure, Pig slurry, Cattle slurry, Duck slurry, Rumen and digestive tract content
Co-digestion of easily degradable substrates with dairy slurry increased the methane yield relative to slurry alone.[2]
Dosing
No source limits on the dose for this substrate.
Introduce gradually, starting with a small dose and monitoring the process (e.g. FOS/TAC, pH, gas composition).
Sources of the process data
- Improvement of fruit and vegetable waste anaerobic digestion performance and stability with co-substrates addition
- Biochemical methane potential and biodegradability of complex organic substrates
- Compositional components and methane production potential of typical vegetable wastes
- Biochemical methane potential of fruits and vegetable solid waste feedstocks
- Effects of size and thermophilic pre-hydrolysis of banana peel during anaerobic digestion, and biomethanation potential of key tropical fruit wastes
- Effect of particle size on biogas generation from biomass residues
The co-digestion calculator will assess a specific mixture containing this substrate.
What it is and where it comes from
Aubergine (eggplant, Solanum melongena) is a fruiting vegetable grown in the open field and under cover, important in Asia and the Mediterranean basin. As a waste it arises during sorting: fruit that is too small, misshapen, or damaged mechanically or by pests. In Poland it is grown on a smaller scale, mainly under cover. The dataset contains whole fruit and fruit infested by pests, tested under mesophilic conditions and with no temperature stated.
Properties relevant to digestion
The fruit has a very low dry matter content (a few per cent) and consists of readily available carbohydrates, fibre and a small amount of protein. The lignin content is low, and the seeds contain somewhat more components that are harder to degrade. Rapid degradation of sugars can lead to acidification at a high dose. Substances characteristic of nightshades (solanine in green parts) are present in amounts that are not a limitation at typical doses, but are worth bearing in mind. Water makes thickening more difficult.
How to read the spread of results
Records from several studies differ in the degree of ripeness and damage of the fruit (fruit infested by pests may be partly spoiled), size reduction, variety and conversion to VS. Temperature (some records do not state it), inoculum, the substrate-to-inoculum ratio and test length also have an effect. A small number of records is too few to indicate a range typical for aubergine.
In biogas plant practice
Aubergine is a good co-substrate for plants accepting waste from vegetable and fruit sorting facilities, in a mixture with material of higher dry matter content. Because it spoils easily, it should be processed quickly or ensiled. The seeds and flesh must be size-reduced, and dosing should be even. Fruit and vegetable waste is usually classified as waste (group 02), and its acceptance requires installation permits; plant material is not subject to the regulations on animal by-products.
For comparison with other fruiting vegetables, aubergine has relatively many seeds and much fibre, which improves the structure of the material but requires good size reduction. It is also worth remembering that this entry is based on a small number of records, so it is mainly indicative and does not replace a test on your own waste.
Methodology in brief
BMP is the amount of methane obtained from volatile solids (VS) in a batch test, given in m³ CH₄ per tonne of VS (numerically the same as NmL CH₄/g VS in the publications) and converted to normal conditions (0 °C, 101.325 kPa). The weighted mean gives each publication a total weight of 1, split equally between its results for the substrate — a paper testing twenty varieties does not outweigh a paper with a single sample. In inter-laboratory programmes the unit is the laboratory (total weight 1), and within it the weight of a test grows with the number of bottles (replicates). Results after pretreatment (e.g. thermal, chemical, enzymatic) are shown separately and are not included in the mean.
Solid lines are curves measured in the tests. Where a publication gives only the final result, we draw a first-order kinetic model, B(t) = B₀·(1 − e−kt): only the end point comes from the publication, and the shape of the curve serves purely as visualisation — do not read the production on a particular day from it. For this substrate k = 0.245 d−1 was assumed (median of rate constants k reported in the sources and/or fitted to the mean measured curves).
The statistics describe the spread of published results — a descriptive compilation, not a meta-analysis or a guarantee of plant yield.
Bibliography
- Yan, H.; Cai, F.; Wang, L.; Chen, C.; Liu, G. (2021). Compositional components and methane production potential of typical vegetable wastes. Environmental Science and Pollution Research 28(38), 54177–54186. DOI: 10.1007/s11356-021-15798-y DOI
- Gunaseelan, V. (2004). Biochemical methane potential of fruits and vegetable solid waste feedstocks. Biomass and Bioenergy 26(4), 389–399. DOI: 10.1016/j.biombioe.2003.08.006 DOI
All sources of the site: bibliography.
Other substrates in the group “Fruit, vegetables and their residues”
Citrus seeds — BMP: 3 studies, weighted mean 676 m³ CH₄/t VS
676 m³ CH₄/t VS weighted mean from 3 studies
good — editorial rating for biogas plants≈52 %
Potato peels — BMP: 5 studies, weighted mean 234 m³ CH₄/t VS
234 m³ CH₄/t VS weighted mean from 5 studies
neutral — editorial rating for biogas plants≈56 %
Lettuce — BMP: 6 studies, weighted mean 256 m³ CH₄/t VS
256 m³ CH₄/t VS weighted mean from 6 studies
≈57 %
Durian shells — BMP: 2 studies, weighted mean 93 m³ CH₄/t VS
93 m³ CH₄/t VS weighted mean from 2 studies
≈52 %