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BMP testingFruit, vegetables and their residues

Citrus seeds — BMP: 3 studies, weighted mean 676 m³ CH₄/t VS

Mandarin and orange pips are a compact waste from juice production and citrus processing, rich in lipids and fibre; they require comminution and careful dosing.

rating: goodCH₄ ≈ 52 % (estimate)

Published Updated 3 min readFeedstockData Editorial Team

Photo Scott Bauer, USDA / Wikimedia Commons, public domain, source file; changes: cropping

Weighted mean
676m³ CH₄/t VS
Range
581–732m³ CH₄/t VS
Records
3studies
Publications
2sources
Temperatures
35 °Cof the test

Methane in biogas

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 (carbohydrate-dominated (no protein or fat characteristics)) and the yields of compound groups according to FNR.

How we calculate it and what the zones mean

Rating for biogas plants

good — editorial rating for biogas plantsStable, usually accepted without a fee

Potential per tonne of fresh matter: very high (239 m³ CH₄/t); no particular threats to stability. Handling costs: fibres, floating layer, slow degradation.

Why? Rating factors

Potential per tonne +3

  • +3potential 239 m³ CH₄/t fresh matter (BMP 676 × DM 37.3 % × VS 94.7 %)

Process stability 0

  • 0no factors

Handling and costs −1

  • −0.5fibres, floating layer — shredding and intensive mixing
  • −0.5slow degradation — long retention time

Total points: 2 · thresholds: ≥ 2.5 very good, ≥ 1 good, below — neutral; negative with cumulative process risk.

Editorial rating per the methodology · confidence of the rating: low · excluding market prices

Add to the co-digestion calculator CSV data

BMP curves from 3 studies

Weighted mean Individual records

BMP curves: Citrus seedsCumulative methane production over time for 3 records and the weighted mean of 676 m³ CH₄/t VS. 3 of the curves are model curves (first-order kinetics).0200400600800051015202530time [d]m³ CH₄/t VSGunaseelan (2004): 732 m³ CH₄/t VS (model curve)Sanjaya et al. (2016) · 1: 581 m³ CH₄/t VS (model curve)Sanjaya et al. (2016) · 2: 658 m³ CH₄/t VS (model curve)mean676

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 (676); 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
SourceBMP
m³ CH₄/t VS		TemperatureSampleCurve
Gunaseelan (2004) DOI73235 °C · mesophilicMandarin seedsend point (model curve)
Sanjaya et al. (2016) · 1 DOI58135 °C · mesophilicFresh ripe orange seedend point (model curve)
Sanjaya et al. (2016) · 2 DOI65835 °C · mesophilicRooten orange seedend point (model curve)
Weighted mean676arithmetic mean 657, SD 76

Typical composition

Dry matter (DM)
37.3% (range 37.1–37.5)
Volatile solids (VS)
94.7 % DM (range 94.7–94.7)

Median and range of the determinations reported in the publications behind this substrate's BMP records (read from: MY-D); dry matter: 2 determinations, volatile solids: 1 determination.

Sources: Gunaseelan (2004); Sanjaya 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

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.

slowly degrading
slow degradation, requires a long retention time
fibrous
lignocellulose, long fibres → floating layer, harder mixing, slow degradation
seasonal
seasonal availability — requires storage
variable composition
high variability of composition between batches

Dosing

The sources do not give a safe share of this substrate in the feed.

Introduce gradually, starting with a small dose and monitoring the process (e.g. FOS/TAC, pH, gas composition).

Sources of the process data

  1. Biochemical methane potential of fruits and vegetable solid waste feedstocks
  2. Mesophilic batch anaerobic digestion from fruit fragments
  3. Biochemical methane potential and biodegradability of complex organic substrates
  4. Effects of size and thermophilic pre-hydrolysis of banana peel during anaerobic digestion, and biomethanation potential of key tropical fruit wastes
  5. 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

Citrus fruit pips arise in the production of juices, in the processing of mandarins and oranges, and in catering. Citrus fruits in Poland are imported, so larger waste streams appear in fruit processing plants, juice plants and wholesale sorting plants. Pips usually make up a small part of the mass of the fruit and go to waste together with peels and pomace, but in studies they are sometimes analysed separately.

Properties relevant to digestion

Seeds have a lower moisture content than the rest of the fruit, and in the dry matter, alongside fibre (cellulose, lignin in the seed coat), there are lipids and storage protein. A high fat content means a potentially high gas yield, but also a risk of accumulation of long-chain fatty acids (LCFA), which at high loading inhibit methanogens. Citrus seeds contain limonoids that give bitterness, and residues of essential oils (limonene) may have antimicrobial effects. The compact, hard structure limits the availability of components until the seeds are ground. There is no typical danger of rapid acidification, as with the pulp.

How to read the spread of results

The dataset contains several records from several sources: mandarin pips and orange pips, fresh and from spoiled fruit. Differences result from the species, ripeness and condition of the fruit, but above all from the degree of comminution: ground seeds release gas faster and more completely than whole ones. The fat content, test length and inoculum also have an effect. If a test was stopped before lipid degradation had finished, the result is underestimated. All the records come from mesophilic studies.

In biogas plant practice

Citrus pips are an additive of limited significance, usually introduced together with other fruit wastes. They should be shredded and the dose kept low, in order to avoid loading with fats and the action of essential oils. The material tolerates storage well, because it is relatively dry, but pips collected from wet waste quickly go mouldy. Waste from fruit processing is classed as waste, so its acceptance requires appropriate entries in the installation's permits. In a mixture with slurry, process safety increases thanks to the buffering capacity and the supply of trace elements.

The value of pips as an additive is limited by their small mass in the waste stream, so separate collection is usually not worthwhile; it is more sensible to include them in the balance of the whole citrus waste and to monitor the combined share of oils and lipids in the feed.

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

  1. 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
  2. Sanjaya, A.P.; Cahyanto, M.N.; Millati, R. (2016). Mesophilic batch anaerobic digestion from fruit fragments. Renewable Energy 98, 135–141. DOI: 10.1016/j.renene.2016.02.059 DOI

All sources of the site: bibliography.

Other substrates in the group “Fruit, vegetables and their residues”