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BMP testingSewage and industrial sludges

Dairy wastewater biological sludge — BMP: 2 studies, weighted mean 293 m³ CH₄/t VS

Biological sludge from a dairy wastewater treatment plant is a material of highly variable composition; records from several studies differ markedly, which reflects its heterogeneity.

rating: negativeCH₄ ≈ 66 % (estimate)

Published Updated 3 min readFeedstockData Editorial Team

Photo Wehrle Werk AG / Wikimedia Commons, licence CC BY-SA 4.0, source file; changes: cropping

Weighted mean
293m³ CH₄/t VS
Range
125–461m³ CH₄/t VS
Records
2studies
Publications
2sources
Temperatures
35 °C, 37 °Cof the test

Methane in biogas

High methane content · ≈ 6.6 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 5.6 % DM × 6.25); 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

negative — editorial rating for biogas plantsMay endanger process stability — not worth taking even with a large payment

Potential per tonne of fresh matter: low (22 m³ CH₄/t); process risk: fats, protein / nitrogen, inhibitors. No additional handling requirements. Low potential combined with process risk and handling costs.

Why? Rating factors

Potential per tonne 0

  • ±0potential 22 m³ CH₄/t fresh matter (BMP 293 × DM 9.4 % × VS 81 %)

Process stability −2

  • −1fats: risk of accumulation of long-chain fatty acids (LCFA), flotation and overloading
  • −0.5protein / nitrogen: risk of ammonia inhibition at higher shares
  • −0.5inhibitors: natural or residues (e.g. limonene, polyphenols, antibiotics, metals)

Handling and costs 0

  • 0no factors

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

Low potential combined with process risk and handling costs.

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

Add to the co-digestion calculator CSV data

BMP curves from 2 studies

Weighted mean Individual records

BMP curves: Dairy wastewater biological sludgeCumulative methane production over time for 2 records and the weighted mean of 293 m³ CH₄/t VS. 2 of the curves are model curves (first-order kinetics).01002003004005000510152025303540time [d]m³ CH₄/t VSRico et al. (2014): 125 m³ CH₄/t VS (model curve)Browne et al. (2013): 461 m³ CH₄/t VS (model curve)mean293

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 (293); 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
Rico et al. (2014) DOI12535 °C · mesophilicdewatered biological sludge from dairy factory (DSL1)end point (model curve)
Browne et al. (2013) DOI46137 °C · mesophilicbio treatment sludge from cheese processing · pretreatment: particle size reduction/sample preparation (MY-D: physical treatment)end point (model curve)
Weighted mean293arithmetic mean 293, SD 238

Typical composition

Dry matter (DM)
9.4% (range 9.4–9.4)
Volatile solids (VS)
81 % DM (range 81–81)
Nitrogen
5.6 % DM
C/N ratio
7.8

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. C/N was calculated as the ratio of C and N content (% DM) from the same source. DM from a single determination – indicative value.

Sources: Browne et al. (2013).

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

  • fat-rich
  • protein-rich
  • variable composition
  • contains inhibitors
  • 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 293.0 m³ CH₄/t VS (SD 237.6; 2 records, 2 sources).
  • When it contains milk fats, the potential increases (Long et al. 2012).

Drawbacks and risks

  • Composition highly variable.
  • Residues of disinfectants and salts from washing may inhibit (Chen et al. 2008).
  • Protein -> ammonia.

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

Dosing

No source-based threshold; start low.

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

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. Chen, Cheng, Creamer (2008). Inhibition of anaerobic digestion process: A review. Bioresour. Technol.
  5. Appels et al. (2008). Principles and potential of the anaerobic digestion of waste-activated sludge. Prog. Energy Combust. Sci.

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

What it is and where it comes from

Sludge from a dairy wastewater treatment plant arises in the biological treatment of wastewater from dairies, cheese plants and milk processing plants. It contains surplus bacterial biomass (activated sludge) and often also milk fats and proteins captured in the flotation process. The dataset contains several records: dewatered biological sludge from a dairy and sludge from the biological treatment of wastewater from cheese processing. The sludge is thickened and dewatered and then sent for management.

Properties relevant to digestion

The composition depends on whether fat flotation is used at the treatment plant and how far the sludge is mixed with fats. Bacterial biomass has cell walls that hinder degradation, so activated sludge digests less well than primary sludge. If the sludge contains a lot of milk fat, the potential rises, but so does the risk of VFA inhibition. A high protein content favours ammonia. Sludge from a treatment plant also contains salts (from washing with chemicals) and may contain residues of disinfectants.

How to read the spread of results

The records differ greatly, and this divergence is typical. Sludges from different plants differ in treatment technology, sludge age, the presence of fats, the degree of dewatering and the way they are stored. The substrate-to-inoculum ratio, temperature and test length also have an effect, and sludge after dewatering is sometimes less accessible than fresh sludge. The small number of records does not allow a typical value to be indicated.

In biogas plant practice

Sludges from dairy treatment plants are sometimes digested in treatment plant digesters or together with other dairy wastes. They require monitoring of fat and ammonia, and the digestate must be managed in accordance with the rules. Sewage sludge from the food industry is waste (group 02 or 19), and its acceptance requires a permit. If it contains components of animal origin, it may be subject to the rules on animal by-products.

For the operator it is also important that sludges from the food industry are usually richer in organic matter than municipal sludges, but their quantity and composition depend on the production profile. It is therefore worth carrying out regular tests and avoiding planning on the basis of single literature values.

Because the description of the dataset is brief, it is necessary to run a BMP test of your own.

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

  1. Rico, C.; Diego, R.; Valcarce, A.; Rico, J.L. (2014). Biogas Production from Various Typical Organic Wastes Generated in the Region of Cantabria (Spain): Methane Yields and Co-Digestion Tests. Smart Grid and Renewable Energy 05(06), 128–136. DOI: 10.4236/sgre.2014.56012 DOI
  2. Browne, J.D.; Allen, E.; Murphy, J.D. (2013). Evaluation of the biomethane potential from multiple waste streams for a proposed community scale anaerobic digester. Environmental Technology 34(13-14), 2027–2038. DOI: 10.1080/09593330.2013.812669 DOI

All sources of the site: bibliography.

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