BMP testingSewage and industrial sludges

Pulp and paper mill biosludge — BMP: 25 studies, weighted mean 100 m³ CH₄/t VS

Biological sludge from the pulp and paper industry has a low methane potential because of lignin and ash; results depend on the type of mill and technology.

rating: negative CH₄ ≈ 52 % (estimate)

Published 14 October 2024Updated 29 October 20263 min readFeedstockData Editorial Team

Photo Aleš Makovec / Wikimedia Commons, licence CC BY-SA 3.0, source file; changes: cropping

Weighted mean: 100m³ CH₄/t VS
Range: 67–209m³ CH₄/t VS
Records: 25studies
Publications: 4sources
Temperatures: 20 °C, 35 °C, 37 °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

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

Potential per tonne of fresh matter: very low (1 m³ CH₄/t); process risk: inhibitors, sulphur. Handling costs: fibres, floating layer, slow degradation. Low potential combined with process risk and handling costs.

Why? Rating factors

Potential per tonne −1

−1potential 1 m³ CH₄/t fresh matter (BMP 100 × DM 2.2 % × VS 68 %)

Process stability −1.25

−1inhibitors: natural or residues (e.g. limonene, polyphenols, antibiotics, metals)
−0.25sulphur: H₂S in the biogas (toxicity to bacteria, corrosion, desulphurisation)

Handling and costs −1

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

Total points: −3.25 · 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: high · excluding market prices

Add to the co-digestion calculator CSV data

BMP curves from 25 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 (100); 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.

Show the remaining records in the legend (13)

Records and sources

Download CSV

Source	BMP m³ CH₄/t VS	Temperature	Sample	Curve
Karlsson et al. (2011) · 1 DOI	89	37 °C · mesophilic	Mill 6 mech	end point (model curve)
Karlsson et al. (2011) · 2 DOI	97	37 °C · mesophilic	Mill 4 CTMP/Kraft	end point (model curve)
Karlsson et al. (2011) · 3 DOI	138	37 °C · mesophilic	Mill 1 mech	end point (model curve)
Karlsson et al. (2011) · 4 DOI	145	37 °C · mesophilic	Mill 3 Kraft	end point (model curve)
Karlsson et al. (2011) · 5 DOI	155	37 °C · mesophilic	Mill 5	end point (model curve)
Karlsson et al. (2011) · 6 DOI	158	37 °C · mesophilic	Mill 5 · pretreatment: particle size reduction/sample preparation (MY-D: physical treatment)	end point (model curve)
Karlsson et al. (2011) · 7 DOI	159	37 °C · mesophilic	Mill 2 sulphite	end point (model curve)
Karlsson et al. (2011) · 8 DOI	162	37 °C · mesophilic	Mill 5 · pretreatment: particle size reduction/sample preparation (MY-D: physical treatment)	end point (model curve)
Karlsson et al. (2011) · 9 DOI	167	37 °C · mesophilic	Mill 5 Kraft/CTMP	end point (model curve)
Karlsson et al. (2011) · 10 DOI	173	37 °C · mesophilic	Mill 3 · pretreatment: particle size reduction/sample preparation (MY-D: physical treatment)	end point (model curve)
Karlsson et al. (2011) · 11 DOI	175	37 °C · mesophilic	Mill 3 · pretreatment: particle size reduction/sample preparation (MY-D: physical treatment)	end point (model curve)
Karlsson et al. (2011) · 12 DOI	176	37 °C · mesophilic	Mill 2 sulphite	end point (model curve)
Karlsson et al. (2011) · 13 DOI	182	37 °C · mesophilic	Mill 3	end point (model curve)
Karlsson et al. (2011) · 14 DOI	188	37 °C · mesophilic	Mill 3	end point (model curve)
Karlsson et al. (2011) · 15 DOI	197	37 °C · mesophilic	Mill 6 mech	end point (model curve)
Karlsson et al. (2011) · 16 DOI	199	37 °C · mesophilic	Mill 5	end point (model curve)
Karlsson et al. (2011) · 17 DOI	209	37 °C · mesophilic	Mill 5 · pretreatment: particle size reduction/sample preparation (MY-D: physical treatment)	end point (model curve)
Kinnunen et al. (2015) · 1 DOI	89	35 °C · mesophilic	paper biosludge	end point (model curve)
Kinnunen et al. (2015) · 2 DOI	92	35 °C · mesophilic	paper biosludge	end point (model curve)
Kinnunen et al. (2015) · 3 DOI	93	35 °C · mesophilic	paper biosludge	end point (model curve)
Kinnunen et al. (2015) · 4 DOI	94	35 °C · mesophilic	paper biosludge	end point (model curve)
Kinnunen et al. (2015) · 5 DOI	102	35 °C · mesophilic	paper biosludge	end point (model curve)
Kolbl et al. (2014) DOI	74	38 °C · mesophilic	dehidrated Paper mill sludge	end point (model curve)
Meyer i Edwards (2014) · 1 DOI	67	20 °C · psychrophilic	(orig.: “paper sludge”): value quoted in a literature review	end point (model curve)
Meyer i Edwards (2014) · 2 DOI	68	20 °C · psychrophilic	(orig.: “paper sludge”): value quoted in a literature review · pretreatment: particle size reduction/sample preparation (MY-D: physical treatment)	end point (model curve)
Weighted mean	100	arithmetic mean 138, SD 46

Typical composition

Dry matter (DM): 2.2% (range 0.6–19.7)
Volatile solids (VS): 68 % DM (range 65–78.4)

Median and range of the determinations reported in the publications behind this substrate's BMP records (read from: MY-D); dry matter: 14 determinations, volatile solids: 3 determinations.

Sources: Karlsson et al. (2011); Kinnunen et al. (2015); Kolbl 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

slowly degrading
fibrous
sulphur-rich
low in nitrogen
contains inhibitors
editorial classification

Advantages

Methane potential in the Substraty.pl BMP dataset: weighted mean 99.6 m³ CH₄/t VS (SD 46.2; 25 records, 4 sources).
Thermophilic co-digestion of primary and secondary sludge from a paper mill is feasible at an OLR of approx. 1 kg VS/(m³·d) (Bayr et al. 2012).

Drawbacks and risks

Lignin does not degrade in the process (Bayr et al. 2012).
pH adjustment and N supplementation required (Bayr et al. 2012).

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
Slurry supplies N, alkalinity and trace elements.^[1][2]

Dosing

No source-based limit on the share in the mix. Bayr et al. (2012), thermophilic CSTR reactors: primary sludge from a paper mill — feasible at an OLR of 1–1.4 kg VS/(m³·d) and an HRT of 16–32 d, and the highest tested OLR of 2 and HRT of 14–16 d might be possible once pH stability is confirmed; co-digestion of primary and secondary sludge at an OLR of 1 and an HRT of 25–31 d. These are whole-reactor loadings in a laboratory test, not a limit on the share of a component, so max_share is not given. Allow for pH adjustment and nitrogen deficiency.

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

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

Biological sludge from the paper industry arises in the wastewater treatment plants of mills producing pulp and paper. The wastewater is poor in nitrogen and phosphorus and contains lignin compounds and polysaccharides from wood, and its treatment by the activated sludge method gives a surplus of biomass. The dataset contains many records from a study of many mills, described as mechanical pulp, CTMP/kraft and kraft, as well as from other studies.

Properties relevant to digestion

The sludge contains bacterial biomass, cellulose fibres and fine wood fractions, and ash from fillers. Lignin compounds and tannins are poorly degradable and can inhibit microorganisms. Bacterial biomass has cell walls that hinder degradation, and the share of readily available components is small. Wastewater from kraft mills contains sulphur, which can increase the hydrogen sulphide content of the biogas. The sludge has a low N-to-C ratio because of the nitrogen-poor wastewater, although the bacteria themselves contribute nitrogen.

How to read the spread of results

The spread results from differences between mills: the type of pulp produced (mechanical, chemical), wastewater quality, treatment technology, sludge age and fibre share. Dewatering, storage and size reduction also have an effect, as do the test conditions: temperature, inoculum, substrate-to-inoculum ratio and length. A large number of records come from one study comparing many mills, so not all of them are independent.

In biogas plant practice

Paper industry sludges are rarely digested on their own because of the low yield. They can be a supplement to mixtures with a higher content of readily available substrates or be subjected to pretreatment. Their main advantage is that they arise at the plant, which limits transport. They are industrial waste (group 03), and their management requires permits; they often go to incineration or composting.

Compared with municipal sludges, paper sludge contains fewer readily available compounds and more ash, which explains why the results are lower. Pretreatment, such as heating or milling, is sometimes studied, but its cost-effectiveness on an industrial scale depends on local conditions.

Because the spread is large, it is worth running 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

Results after pretreatment (4) — excluded from the mean

Source	BMP m³ CH₄/t VS	Pretreatment	Sample
Karlsson et al. (2011)	240	enzymatic	Mill 5
Karlsson et al. (2011)	239	physical-enzymatic	Mill 5
Meyer i Edwards (2014)	97	unspecified	paper sludge
Meyer i Edwards (2014)	66	enzymatic	paper sludge

Bibliography

All sources of the site: bibliography.