BMP testingFruit, vegetables and their residues
Spinach — BMP: 2 studies, weighted mean 227 m³ CH₄/t VS
Spinach is a delicate, watery leafy waste, rich in protein and nitrates; it ferments readily, but at a larger share increases the risk of ammonia in the feed.
Photo Nillerdk / Wikimedia Commons, licence CC BY 3.0, source file; changes: cropping
- Weighted mean
- 227m³ CH₄/t VS
- Range
- 158–296m³ CH₄/t VS
- Records
- 2studies
- Publications
- 2sources
- Temperatures
- 37 °Cof the test
Methane in biogas
Medium methane content · ≈ 5.8 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 4.7 % DM × 6.25)) and the yields of compound groups according to FNR.
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.
Add to the co-digestion calculator CSV data
BMP curves from 2 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 (227); 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 |
|---|---|---|---|---|
| Cai et al. (2019) DOI | 296 | — | Spinach (Spinacia oleracea) | end point (model curve) |
| Yan et al. (2017) DOI | 158 | 37 °C · mesophilic | Spinach | end point (model curve) |
| Weighted mean | 227 | arithmetic mean 227, SD 98 | ||
Typical composition
- Volatile solids (VS)
- 76.7 % DM (range 76.7–76.7)
- Nitrogen
- 4.7 % DM
- C/N ratio
- 8
Median and range of the determinations reported in the publications behind this substrate's BMP records (read from: BCBPD); dry matter: 0 determinations, volatile solids: 1 determination. C/N was calculated as the ratio of C and N content (% DM) from the same source. No DM in the sources – the calculator has to ask for a value.
Sources: Cai et al. (2019).
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
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.
No published process studies
The literature we use does not describe the advantages or drawbacks of digesting this substrate beyond the BMP test results. Below are process characteristics assigned on the basis of the type of material — an editorial classification, not a study result.
- dilutes the feed (low DM)
- low dry matter, dilutes the feed
- seasonal
- seasonal availability — requires storage
- poor in trace elements
- poor in trace elements — mono-digestion requires supplementation
- variable composition
- high variability of composition between batches
Co-digestion — what to combine it with, what to watch out for
- combines well
substrates: nitrogen-rich — e.g. Pig slurry, Poultry manure, Waste activated sludge (secondary sludge), Chlorella vulgaris, Nannochloropsis salina
A nitrogen-rich co-substrate balances the low C/N of fruit and vegetable waste (Bouallagui et al. 2009).[1]
Dosing
No source limits on the dose for this substrate.
Sources of the process data
- Improvement of fruit and vegetable waste anaerobic digestion performance and stability with co-substrates addition
- Prediction of methane production performances based on determination of organic components for different vegetable wastes
- Study on biomethane production and biodegradability of different leafy vegetables in anaerobic digestion
- Effects of size and thermophilic pre-hydrolysis of banana peel during anaerobic digestion, and biomethanation potential of key tropical fruit wastes
- Effect of particle size on biogas generation from biomass residues
The co-digestion calculator will assess a specific mixture containing this substrate.
What it is and where it comes from
Spinach (Spinacia oleracea) is grown in Poland mainly as a raw material for the frozen food industry and as a fresh vegetable. The waste arises in sorting, blanching, leaf cleaning and salad production, and also in the form of field surpluses. The stream is seasonal and usually concentrated at processing plants.
Properties relevant to digestion
Spinach leaves contain more than ninety per cent water. The dry matter has a high protein share, which means a lower C/N ratio than in most vegetable wastes, and contains sugars, pectins and fibre with low lignin. Spinach accumulates nitrates and contains oxalic acid, but at typical shares in the feed these are not a significant problem. The higher protein increases the potential for ammonia release, so at a high share of spinach it is worth monitoring the ammonium nitrogen concentration. Hydrolysis proceeds quickly, and the material spoils quickly.
How to read the spread of results
The dataset contains several records from several sources, including a record without a stated temperature and a mesophilic one, described as leafy vegetable waste from China (the sample code in the study corresponds to spinach). The differences may arise from variety, leaf age, protein content dependent on fertilisation, chopping, the way the sample was prepared and the inoculum. In a very watery material the accuracy of the volatile solids determination is also of great importance.
In biogas plant practice
Spinach is a supplement to the feed, best in a mixture with a material of higher dry matter and higher C/N, such as maize silage or straw. Chopping is not a problem, but the feed spoils quickly and gives off odours, so it should be used within a day or two. Waste from processing and trade counts as waste and requires appropriate provisions in the plant's permit. Residues from the farm's own holding are treated as agricultural products.
Caution makes sense particularly at plants sensitive to ammonia, for example those operating at thermophilic temperatures or with a feed rich in poultry slurry; there even a moderate addition of protein materials raises the ammonium nitrogen concentration.
In the case of spinach from frozen food processing, it should be remembered that blanched leaves have a different composition from fresh ones, because some of the sugars and mineral salts are washed out and the cells are partly destroyed, which speeds up hydrolysis.
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 = 0.245 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.
Bibliography
- Cai, F.; 1. Biomass Energy and Environmental Engineering Research Center, College of Chemical Engineering, Beijing University of Chemical Technology, Beijing 100029, China; Yan, H.; Zhang, R.; Liu, G.; Chen, C.; 2. Department of Biological and Agricultural Engineering, University of California, Davis, CA 95616, USA (2019). Prediction of methane production performances based on determination of organic components for different vegetable wastes. International Journal of Agricultural and Biological Engineering 12(3), 154–159. DOI: 10.25165/j.ijabe.20191203.4705 DOI
- Yan, H.; Zhao, C.; Zhang, J.; Zhang, R.; Xue, C.; Liu, G.; Chen, C. (2017). Study on biomethane production and biodegradability of different leafy vegetables in anaerobic digestion. AMB Express 7(1), 27. DOI: 10.1186/s13568-017-0325-1 DOI
All sources of the site: bibliography.
Other substrates in the group “Fruit, vegetables and their residues”
Other leafy and stem vegetables (bok choy, amaranth, garlic chives, garlic shoots, water dropwort, toon sprouts, zucchini and turnip leaves) — BMP: 8 studies, mean 253 m³ CH₄/t VS
253 m³ CH₄/t VS weighted mean from 8 studies
≈58 %
Citrus fruit (whole, pulp) — BMP: 5 studies, weighted mean 353 m³ CH₄/t VS
353 m³ CH₄/t VS weighted mean from 5 studies
neutral — editorial rating for biogas plants≈52 %
Rambutan seeds — BMP: 3 studies, weighted mean 449 m³ CH₄/t VS
449 m³ CH₄/t VS weighted mean from 3 studies
good — editorial rating for biogas plants≈52 %
Cabbage outer leaves and stems — BMP: 5 studies, weighted mean 320 m³ CH₄/t VS
320 m³ CH₄/t VS weighted mean from 5 studies
neutral — editorial rating for biogas plants68 %