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Confectionery waste — BMP: 6 studies, weighted mean 318 m³ CH₄/t VS

Confectionery waste (wafers, bars, sugar, jelly sweets) is an energy-rich substrate with sugars and fat; the risks are rapid acidification and heterogeneity of composition.

rating: neutralCH₄ ≈ 63 % (estimate)

Published Updated 3 min readFeedstockData Editorial Team

Photo Mshuang2 / Wikimedia Commons, licence CC0 1.0, source file; changes: cropping

Weighted mean
318m³ CH₄/t VS
Range
200–506m³ CH₄/t VS
Records
6studies
Publications
3sources
Temperatures
36 °C, 39 °Cof the test

Methane in biogas

High methane content · ≈ 6.3 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); fat-rich (process classification)) and the yields of compound groups according to FNR.

How we calculate it and what the zones mean

Rating for biogas plants

neutral — editorial rating for biogas plantsNo clear advantages — worth charging a fee for accepting it

Potential per tonne of fresh matter: very high (104 m³ CH₄/t); process risk: fats, acidification. Handling costs: physical contaminants (packaging, plastics).

Why? Rating factors

Potential per tonne +3

  • +3potential 104 m³ CH₄/t fresh matter (BMP 318 × DM 35.2 % × VS 93.4 %)

Process stability −1.25

  • −1fats: risk of accumulation of long-chain fatty acids (LCFA), flotation and overloading
  • −0.25acidification: rapid degradation / acidic pH, risk of VFA accumulation, needs buffering

Handling and costs −1

  • −1physical contaminants (packaging, plastics) — depackaging and separation

Total points: 0.75 · thresholds: ≥ 2.5 very good, ≥ 1 good, below — neutral; negative with cumulative process risk.

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

Add to the co-digestion calculator CSV data

BMP curves from 6 studies

Weighted mean Individual records

BMP curves: Confectionery wasteCumulative methane production over time for 6 records and the weighted mean of 318 m³ CH₄/t VS. 6 of the curves are model curves (first-order kinetics).0200400600051015202530time [d]m³ CH₄/t VSPilarska et al. (2018) · 1: 317 m³ CH₄/t VS (model curve)Pilarska et al. (2018) · 2: 408 m³ CH₄/t VS (model curve)Pilarska et al. (2018) · 3: 506 m³ CH₄/t VS (model curve)Alkanok et al. (2014): 200 m³ CH₄/t VS (model curve)Koch et al. (2020) · 1: 340 m³ CH₄/t VS (model curve)Koch et al. (2020) · 2: 344 m³ CH₄/t VS (model curve)mean318

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 (318); 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
Pilarska et al. (2018) · 1 DOI31739 °C · mesophilicWafers (W)end point (model curve)
Pilarska et al. (2018) · 2 DOI40839 °C · mesophilicChocolate bars (CB)end point (model curve)
Pilarska et al. (2018) · 3 DOI50639 °C · mesophilicFilled wafers (FW)end point (model curve)
Alkanok et al. (2014) DOI20036 °C · mesophilicsugar wasteend point (model curve)
Koch et al. (2020) · 1 DOI340—Tic Tacsend point (model curve)
Koch et al. (2020) · 2 DOI344—Gummi bearsend point (model curve)
Weighted mean318arithmetic mean 352, SD 101

Typical composition

Dry matter (DM)
35.2% (range 35.2–35.2)
Volatile solids (VS)
93.4 % DM (range 93.4–93.4)

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

Sources: Alkanok et al. (2014).

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

  • easily degradable
  • fat-rich
  • carbon-rich
  • physical contaminants
  • 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 potential in the Substraty.pl BMP dataset: weighted mean 317.5 m³ CH₄/t VS (SD 101.4; 6 records, 3 sources).
  • Sugars and fat give a high potential per unit of mass (Long et al. 2012).

Drawbacks and risks

  • Chocolate fat -> LCFA (Long et al. 2012).

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

Dosing

No source-based threshold; shared limit with fats.

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

Practical requirements

  • Remove foreign contaminants before dosing: material from biowaste may contain interfering substances, and the co-substrate should be free of them (FNR 2010, Ch. 3).

Sources of the process data

  1. Hagos et al. (2017). Anaerobic co-digestion process for biogas production: progress, challenges and perspectives. Renew. Sustain. Energy Rev.
  2. Weiland, P. (2010) Biogas production: current state and perspectives. Applied Microbiology and Biotechnology
  3. Long et al. (2012). Anaerobic co-digestion of fat, oil, and grease (FOG): A review of gas production and process limitations. Process Saf. Environ. Prot.
  4. FNR (2010). Guía sobre el Biogás – Desde la producción hasta el uso (hiszp. wydanie „Leitfaden Biogas”, GIZ 2013)

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

What it is and where it comes from

Confectionery waste consists of wafers, chocolate bars, filled products, sugar, jelly sweets and dragees that do not meet quality standards or have passed their use-by date. It arises in production plants, wholesalers and shops. It often arrives at the biogas plant together with packaging, which must be separated. The dataset includes samples of wafers, chocolate bars, filled wafers, supermarket sugar and small sweets, tested mainly at mesophilic temperature.

Properties relevant to digestion

The composition depends on the product: wafers are mainly starch and fat, chocolate contains cocoa fat, sugar and milk protein, and sugar and jelly sweets are almost pure carbohydrates. A high concentration of readily available sugars causes very rapid acidification, and fats, especially in chocolate, can at a larger dose cause LCFA inhibition and foaming. The low nitrogen-to-carbon ratio requires combining with protein-rich materials or a buffer. Some sweets contain gelatine or milk, so they have components of animal origin.

How to read the spread of results

The results are wide, because the item combines very different products: from almost pure sugar to chocolate and filled wafers. The value is determined by the share of fat, which increases the potential per gram of VS, and by starch and sugars. Comminution, the presence of packaging residues, the substrate-to-inoculum ratio, adaptation of the inoculum to fat and sugar, temperature and test length also have an effect. The dataset does not describe a uniform waste, so the values must be related to the specific product.

In biogas plant practice

Confectionery waste is a valuable, very high-yielding co-substrate, which must be dosed carefully, at a small share and with monitoring of pH and volatile acids. It requires separation of packaging (depackaging) and shredding. For stable supplies, use of a buffer tank is advisable. Products containing components of animal origin (milk, gelatine) are subject to the rules on animal by-products, and food products not used for consumption are waste within the meaning of the Waste Act, so acceptance requires the installation's permit.

For the operator it is also important that confectionery waste contains a lot of sucrose, which is fermented almost immediately. As a result, short-term spikes in gas production may be large, and these are followed by a fall if the process becomes acidified. Stable, small doses are better than large occasional portions.

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 = 0.232 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. Pilarska, A.A.; Pilarski, K.; Wolna-Maruwka, A.; Boniecki, P.; Zaborowicz, M. (2018). Use of Confectionery Waste in Biogas Production by the Anaerobic Digestion Process. Molecules 24(1), 37. DOI: 10.3390/molecules24010037 DOI
  2. Alkanok, G.; Demirel, B.; Onay, T.T. (2014). Determination of biogas generation potential as a renewable energy source from supermarket wastes. Waste Management 34(1), 134–140. DOI: 10.1016/j.wasman.2013.09.015 DOI
  3. Koch, K.; Hafner, S.; Astals, S.; Weinrich, S. (2020). Evaluation of Common Supermarket Products as Positive Controls in Biochemical Methane Potential (BMP) Tests. Water 12(5), 1223. DOI: 10.3390/w12051223 DOI

All sources of the site: bibliography.

Other substrates in the group “Food and catering waste”