BMP testingBioplastics and compostable packaging

PHA (polyhydroxyalkanoates) — BMP: 3 studies, weighted mean 341 m³ CH₄/t VS

PHA (PHB, PHBV, PHBH) are polyesters produced by bacteria, counted among the biopolymers most amenable to anaerobic degradation, although they have been studied in only a few studies.

CH₄ ≈ 52 % (estimate)

Published 23 September 2022Updated 29 October 20263 min readFeedstockData Editorial Team

Illustration: FeedstockData (AI, Google Gemini)

Weighted mean: 341m³ CH₄/t VS
Range: 271–484m³ CH₄/t VS
Records: 3studies
Publications: 2sources
Temperatures: 35 °C, 38 °Cof the test

Methane in biogas

≈51–54% 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 (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

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 (341); 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
Wang et al. (2018) · 1 DOI	338	38 °C · mesophilic	PHA-F	end point (model curve)
Wang et al. (2018) · 2 DOI	484	38 °C · mesophilic	PHA-S	end point (model curve)
Nachod et al. (2021) DOI	271	35 °C · mesophilic	PHBV pellets without food waste (PHBV-35)	end point (model curve)
Weighted mean	341	arithmetic mean 364, SD 109

Process properties

slowly degrading
editorial classification

Advantages

Methane potential in the Substraty.pl BMP dataset: weighted mean 340.8 m³ CH₄/t VS (SD 108.9; 3 records, 2 sources).
Most of the bioplastics tested and their blends degraded thermophilically with a high biogas yield (Narancic et al. 2018).

Drawbacks and risks

Degradation times 3-6 times longer than the retention time in commercial plants (Narancic et al. 2018).
Results depend on the composition and shape of the product (Benn and Zitomer 2018).

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

combines well
substrates: high alkalinity (buffer) — e.g. Cattle manure, Pig slurry, Cattle slurry, Duck slurry, Rumen and digestive tract content
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Dosing

No source threshold.

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

Practical requirements

Shred: shredding increases the surface available for degradation and speeds it up, but does not necessarily raise the final gas yield (FNR 2010, Ch. 3 “Triturado”).

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

Polyhydroxyalkanoates (PHA) are a family of polyesters synthesised by bacteria, which store them as a reserve material. The best known are polyhydroxybutyrate (PHB), the PHBV copolymer and PHBH. They are produced by fermentation of sugars, oils or organic waste and are used, among other things, for packaging and disposable products. They occur in the waste stream only sporadically, because production is still small compared with other plastics.

Properties relevant to digestion

PHA is degraded enzymatically by depolymerases produced by microorganisms, including anaerobic ones. The products of hydrolysis are hydroxybutyric and hydroxyvaleric acids, which in subsequent stages are converted into acetate, hydrogen and methane. Because PHA is a polyester without nitrogen and sulphur, neither ammonia nor hydrogen sulphide is a risk. The rate of degradation depends on the composition (the share of the valerate unit lowers crystallinity), molecular weight, thickness of the product and additives. Under anaerobic conditions PHA usually degrades better than PLA, but dense and crystalline products may hydrolyse slowly.

How to read the spread of results

The dataset covers several records from several publications, in different forms: PHA samples designated by letters and PHBV pellets. Differences result from the type of copolymer, the shape of the sample (pellets, film, powder), the test time and the activity of the inoculum. It is also important whether the test was run with the addition of another substrate and how the result was converted to VS. With so few records the spread is not a good measure of uncertainty, and individual values may deviate significantly from representative ones.

In biogas plant practice

PHA is not a standard raw material. If it reaches a plant, it is more likely in a mixture with other compostable packaging than on its own. Before digestion size reduction is advisable, as it increases the surface available to enzymes. Because of the possibly slower hydrolysis of thick products, an adequate retention time must be ensured. Legal requirements arise from the classification of the packaging waste and the plant's permits; the material has no specific regulations of its own in the context of digestion.

It is worth remembering that real PHA products often contain additives: fillers, plasticisers and nucleating agents. These affect crystallinity, and hence the rate of hydrolysis, so the result for the pure polymer does not always carry over to a finished package.

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 = 0.091 d⁻¹ was assumed (no kinetic data for the group – the median of all available rate constants k (93 values) was used).

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.