Biogas yield and rate: compare the same basis
Amon and Boxberger’s 2000 paper concerns digestion of farmyard manure. Its yield and Austrian policy context belong to the study; they are not a guaranteed output, current subsidy or engineering specification.
The diagram in words: Fresh mass × dry-matter fraction → × volatile-solids fraction → Apply a stated gas-yield basis.
What is the difference between biogas yield and production rate?
Yield relates gas output to a stated feedstock basis; rate also concerns how quickly output is reached. Compare the gas definition, mass denominator, reference conditions and observation period together. The fictional conversion and preserved batch-study table below illustrate why a similar final yield does not imply the same production timing.
Compare the whole manure chain, not one favourable stage · After biogas: what to do with digestate
Name what the tonne represents
The source abstract reports a biogas yield of 320 m³ per tonne of volatile solids. A tonne of volatile solids is not a tonne of fresh manure. Keep fresh mass, dry matter, volatile solids and gas volume on separate lines before discussing yield.
An explicit fictional conversion
Suppose one fresh tonne contains 25% dry matter, and volatile solids are 80% of that dry matter. The implied volatile-solids mass is 1 × 0.25 × 0.80 = 0.20 t. Applying the source’s 320 m³/t VS as an illustrative reference gives 64 m³ per fresh tonne. The fractions are invented; the result is not a prediction for your feedstock.
Gas volume is not electricity output
To estimate usable energy you would still need the gas composition, volume reference conditions, conversion system, efficiency and operating consumption. The source yield does not by itself supply these inputs. A biogas volume should not be silently relabelled as methane volume.
Prepare an evidence request
List feedstock analyses, retention conditions, source of the yield estimate, measurement convention, anticipated outputs and missing inputs. Record which claims are measured and which are modelled. Have a qualified project team evaluate actual safety, design and compliance rather than using this teaching calculation as an operating instruction.
| Field | Example or check |
|---|---|
| Invented fractions | 25% dry matter; 80% VS in dry matter |
| VS mass | 0.20 t per fresh tonne |
| Illustrative gas volume | 0.20 × 320 = 64 m³; not guaranteed |
The same final yield can arrive at a different time
A five-page contribution in the RAMIRAN 2008 proceedings by Cristina González-Fernández and Pedro A. García-Encina provides a second reading case. The batch tests used swine slurry at 35°C and three substrate-COD/inoculum-VS ratios: 1, 2 and 3. They are not fresh-mass ratios.
In words: R1 reached 90% of its final methane on day 22; R2 and R3 took 52 days. All three were followed to day 66. Similar final yields therefore did not mean equal production rates.
| Sample | COD/VS ratio | Days to 90% | Final L CH₄ at STP/g initial VS |
|---|---|---|---|
| R1 | 1 | 22 | 0.345 |
| R2 | 2 | 52 | 0.341 |
| R3 | 3 | 52 | 0.340 |
Table 1 on printed p. 107 supplies the VS-based yields; the timing comes from pp. 108–109. The archived PDF also contains a separate COD-based yield row whose units should not be silently substituted for this VS row.
A completed reading check
- Name the output: methane at standard temperature and pressure, rather than total biogas.
- Copy the basis: initial volatile solids. Do not compare these numbers directly with the earlier 320 m³ of biogas per tonne of VS.
- Copy the endpoint: time to 90%, as well as the final yield. The reported delay is 52 − 22 = 30 days; the endpoint-time ratio is 52/22 ≈ 2.36. That is not a 2.36-fold increase in methane volume.
- Keep the experimental setting: batch bottles, the stated feedstock and inoculum, blanks and replication. A retention time or full-scale design requires its own evidence.
- Write the conclusion narrowly: “These batches reached similar final methane yields at different rates.” This does not rank every feedstock, establish a universal optimum ratio or predict a farm’s performance.
Download the three-row endpoint table as CSV
Read the source editions
Preserved RAMIRAN contribution, printed pp. 105–109. The publisher also lists a 2009 journal article with the same title. They are distinct editions; the numerical worksheet here uses the preserved proceedings pages, not an assumed complete reading of the journal article.
Document evidence
- 2000 PA24.pdf · 6 pages.