BMP testingFruit, vegetables and their residues

Longan peel, seed and waste — BMP: 3 studies, weighted mean 190 m³ CH₄/t VS

Longan (Dimocarpus longan) is a tropical fruit; the dataset includes peels, seeds and shredded waste from several studies, so results depend on the composition of the fractions.

CH₄ ≈ 52 % (estimate)

Published 23 February 2024Updated 29 October 20263 min readFeedstockData Editorial Team

Photo Dinkun Chen / Wikimedia Commons, licence CC BY-SA 4.0, source file; changes: cropping

Weighted mean: 190m³ CH₄/t VS
Range: 87–235m³ CH₄/t VS
Records: 3studies
Publications: 2sources
Temperatures: —of the test

Methane in biogas

≈51–53% CH₄

Medium methane content · ≈ 5.2 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 1.1 % DM × 6.25)) and the yields of compound groups according to FNR.

How we calculate it and what the zones mean

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.

Editorial rating per the methodology

Add to the co-digestion calculator CSV data

BMP curves from 3 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 (190); 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
Odedina et al. (2017) DOI	235	—	Chopped longan waste	end point (model curve)
Zhao et al. (2016) · 1 DOI	87	—	Longan (Dimocarpus longan) – Peel	end point (model curve)
Zhao et al. (2016) · 2 DOI	202	—	Longan (Dimocarpus longan) – Seed	end point (model curve)
Weighted mean	190	arithmetic mean 174, SD 78

Typical composition

Volatile solids (VS): 94.3 % DM (range 91–97.7)
Nitrogen: 1.1 % DM
C/N ratio: 42.2

Median and range of the determinations reported in the publications behind this substrate's BMP records (read from: BCBPD); 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: Zhao et al. (2016).

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

fibrous
slowly degrading
seasonal
variable composition
dilutes the feed (low DM)
editorial classification

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.

Advantages

Methane yield in the compendium: median 202 (range 87-235) m³ CH₄/t VS, 3 records from 2 studies (weighted mean 190).

Drawbacks and risks

Longan waste (chopped) gave a lower yield than ground banana peels (Odedina et al. (2017))

Co-digestion — what to combine it with, what to watch out for

combines well
substrates: easily degradable — e.g. Maize silage (whole crop), Food waste, Sorghum, whole crop, Whey, Beet leaves and tops
In BMP studies, easily degradable substrates increased the yield of the mixture with slurry (synergy in some mixtures).^[1]

Dosing

No source limits on the dose for this substrate.

Sources of the process data

The co-digestion calculator will assess a specific mixture containing this substrate.

What it is and where it comes from

Longan (Dimocarpus longan), known as the dragon's eye, is a fruit tree grown in South-East Asia and southern China. The fruit is sold fresh, dried or canned. The waste consists of the thin, brittle peel, the large glossy seeds and processing residues. The dataset contains several records from several studies: shredded processing waste, and peels and seeds separately. In Poland the fruit is only an imported commodity.

Properties relevant to digestion

Longan peels contain polyphenols and tannins, and the seeds contain starch and phenolic compounds in a hard coat. These fractions decompose more slowly than the flesh, which is rich in sugars. Shredded waste from processing plants is a mixture of fractions, so its composition is less predictable. Grinding improves enzyme access to the starch in the seeds. The material has a low protein content and a high C/N ratio, which favours combining it with nitrogen-rich wastes.

How to read the spread of results

The records concern different fractions of the fruit (peels, seeds, mixed waste), so variation is natural. There are also differences between studies: one examined shredded waste, in another the fractions were separated, and the temperature was not given in the data taken from the compilations. The variety, ripeness, degree of comminution, the share of seeds in the sample and the adaptation of the inoculum to polyphenols all have an effect. It should not be assumed that the value for mixed waste can be reproduced from the results for individual fractions without knowing the proportions.

In biogas plant practice

For a Polish biogas plant, longan is a curiosity from the literature. In fruit-producing countries, waste from processing plants can supplement the mix. Seed shredding, pH monitoring and gradual dosing because of the polyphenols are then recommended. Regardless of the country, investment decisions are best based on a BMP test of the actual waste batch, because the proportions of the fractions vary between processing plants.

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.

Full methodology and correction policy

Bibliography

All sources of the site: bibliography.