A Detailed Database of the Chemical Properties and Methane Potential of Biomasses Covering a Large Range of Common Agricultural Biogas Plant Feedstocks

Abstract

Agricultural biogas plants are increasingly being used in Europe as an alternative source of energy. To optimize the sizing and operation of existing or future biogas plants, a better knowledge of different feedstocks is needed. Our aim is to characterize 132 common agricultural feedstocks in terms of their chemical composition (proteins, fibers, elemental analysis, etc.) and biochemical methane potential shared in five families: agro-industrial products, silage and energy crops, lignocellulosic biomass, manure, and slurries. Among the families investigated, manures and slurries exhibited the highest ash and protein contents (10.3–13.7% DM). High variabilities in C/N were observed among the various families (19.5% DM for slurries and 131.7% DM for lignocellulosic biomass). Methane potentials have been reported to range from 63 Nm³ CH₄/t VS (green waste) to 551 Nm3 CH₄/t VS (duck slurry), with a mean value of 284 Nm³ CH₄/t VS. In terms of biodegradability, lower values of 52% and 57% were reported for lignocelluloses biomasses and manures, respectively, due to their high fiber content, especially lignin. By contrast, animal slurries, silage, and energy crops exhibited a higher biodegradability of 70%. This database will be useful for project owners during the pre-study phases and during the operation of future agricultural biogas plants.

1. Introduction

Biogas production has increased in the European Union, encouraged by the European “Green Deal” and the renewable energy policies [1,2]. Between 2000 and 2017, global biogas production quadrupled, from 78 to 364 TW h, which corresponds to a global yearly volume of 61 billion m³ biogas; it is shared mainly among Europe (54%), Asia (31%), and the Americas (14%) [1]. Anaerobic digestion (AD) unit numbers are increasing in Europe, supported by the need to improve green energy supplies. Among the typologies of biogas plants, agricultural biogas plants are gaining increasing interest as a valuable technology to treat agricultural residues and co-products, thereby generating energy and fertilizers and improving farmers’ incomes. In 2021, France had approximately 401 AD on farms and 285 centralized or territorial AD (Source: SINOE). In parallel, in 2018, 1555 and 9500 biogas plants were reported in Italy and Germany, respectively [1]. Nonetheless, it appears that the biogas sector is facing a shift in its development paradigm [1]. At the European level, the biogas sector is still dominated mainly by a model based on energy crops, high feed-in tariffs, and local electrical production via combined heat and power units. However, the biogas sector is now moving towards a different model, where organic wastes, agricultural by-products, as well as sequential crops are used mainly as feedstocks, and biogas is upgraded to biomethane for various applications (transportation, chemical production, heat, etc.) [1].

As the number of biogas plants has increased, securing deposits and the need for alternative feedstocks are growing. The main families of inputs for agricultural biogas plants are animal wastes (manures and slurries), lignocellulosic biomasses, energy and sequential crops and silages, and agricultural co-products. To help industrial and biogas operators, a better knowledge of the main chemical properties (organic matter, fibers, proteins, elemental analysis, C/N, COD, etc.) along with biochemical methane potential tests are needed. The C/N ratio of feedstock is another important parameter, and for a good anaerobic digestion process, the C/N ratio must be between 20 and 30 [3,4]. Indeed, if a biogas reactor has a low C/N ratio, there is potential inhibition from ammonia [3,5]. Among the chemical parameters, the content of fibers (cellulose, hemicelluloses, and lignin) and proteins is another important issue that can affect the final biodegradability of substrates [6]. Finally, the information of the elemental analysis (C, H, N, S, and O) is of prime importance, as it will allow determination of both the theoretical chemical oxygen demand (COD) and the theoretical methane potential according to the Buswell equation [7].

Aside from chemical properties, the determination of the methane potential through BMP (biochemical methane potential) tests is important. BMPs allow laboratory-scale measurement of the maximum production of methane generated by the digestion of a single substrate, and in recent decades, several national and international inter-laboratory studies have been carried out to optimize the protocol and define good practices [8,9,10]. BMP tests are a popular technique to determine the methane potential and biodegradability of organic substrates [11]. Currently, the BMP test is used for the technical and economic analysis of a project, for the design of agricultural biogas plants, and for evaluation of the process performance [8]. BMP tests can also be useful when the biogas plant unit is operating and new biomasses are to be introduced. Table 1 lists recent studies that provided detailed BMP data of different organic wastes along with the ISR (inoculum-to-substrate ratio) applied. Indeed, the ISR of the BMP is one of the crucial parameters, and the generally recommended values are between 2 and 4 [9,11]. In parallel with classical BMP tests, a theoretical one can also be estimated according to the elemental composition and the Buswell equation [12] or the COD [13], the chemical composition (lipids, carbohydrates, and proteins) [13], or using McCarty’s method [14], allowing determination of the biodegradation rate of a selected substrate.

It is of interest to note that a few publications have provided detailed methane potentials per substrate categories, and they generally provide only min., max., and mean values. Among these publications, Allen et al. (2016) reported methane potentials for 83 organic substrates covering different categories from first-, second-, and third-generation biomasses with agricultural wastes, agro-industrial wastes, food residues, and seaweeds [5]. In parallel, Garcia et al. (2019) reported a detailed methane potential database of more than 50 agricultural and food processing substrates [15]. Similarly, Godin et al. (2015) referenced the methane potential of 569 plant biomasses [16]. In parallel, other studies reported exhaustive lists of the methane potentials of 56 agricultural wastes [17], 48 maize sample silages [18], 43 crop species [19], 12 lignocellulosic biomasses [6], and 30 organic wastes [14].

To date, there is clearly a lack of information in the literature regarding data about the chemical and methane potentials of a large spectrum of agricultural biogas plant feedstocks. This publication aims to highlight the characterization of 132 substrates shared by five different families: cereal and residue (CER), energy crop and silage (ENSI), lignocellulosic matter (LCM), manure (MAN), and slurry (SLU). The selection of substrates was based on their frequency of inclusion in agricultural biogas plants. First, various chemical properties (organic matter, fibers, proteins, elemental analysis, C/N, COD, etc.) were analyzed for the 131 substrates. Then, methane potentials were assessed on these substrates and biodegradability rates (defined as the ratio of the BMP assay yield to the theoretical Buswell yield) were calculated.

Table 1. Literature data on large sets of BMP references for organic substrates. N.: number of samples, ISR: inoculum–substrate ratio, MSW: municipal solid wastes, and WWTP: wastewater treatment plant. Description of the samples can be found in the Appendix B.

Reference	Data Access	Sample Description	N. (Total Number)	ISR	Min BMP	Mean BMP (Nm3 CH4/t VS)	Max BMP
[14]	Yes	30 organic substrates, including 2 raw manures, 9 food residues, 5 invasive aquatic plants, and 6 other organic wastes	22	1	122	341	649
[20]	Yes	Reed canary grasses	14	0.8	283	348	417
[21]	Yes	11 crops	41	2	177	311	401
[22]	Yes	4 grasses and 2 legume species	61	2	265	338	422
[5]	Yes	Biomasses from first-, second-, and third-generation: 6 cereal crops, 3 oilseed rapes, 7 root crops, 5 grass silages, 2 baled silages, 8 other grass substrates, 7 dairy slurries, 4 other agricultural wastes, 4 milk processing wastes, 4 abattoir wastes, 7 miscellaneous wastes, 10 domestic and commercial food wastes, 3 alternative waste substrates, and 12 seaweeds	83	2	99	328	805
[23]	Yes	20 sludge samples	20	2–2.5	58	181	318
[17]	Yes 51/57	18 plants, 12 grasses, 5 bushes, 16 trees, 4 cereals, and 1 straw	57	3	104	219	479
[15]	Yes	5 energy crops, 8 lignocellulosic biomasses, 7 herbaceous and vegetable by-products, 7 fruit by-products, 6 livestock effluents, and 18 food by-products	50	2	71	325	729
This study	Yes	46 energy crops and silages, 5 slurries, 31 manures, 17 cereal and agro-industrial residues, and 32 lignocellulosic biomasses	131	3	63	283	551
[24]	Yes Appendix *	3 animal manures, 3 crop straws, 5 food and green wastes, 2 processing organic wastes, 1 energy grass, and 2 lignocellulosic biomasses	16	2	49	317	811
[18]	Yes Appendix *	48 maize genotypes selected for diverse maturity and biomass production	204	-	295	329	355
[16]	Yes Appendix *	17 Miscanthus, 16 switch grasses, 36 spelt straws, 37 fiber sorghums, 369 tall fescues, 21 immature ryes, and 73 fiber corns	569 (588)	2	147	389	589
[19]	Yes Appendix *	405 silages from 43 crop species	43	2	143	304	425
[25]	No	68 municipal solid wastes, 7 MSW mix, 9 raw substrates, and 18 lignocellulosic wastes	20 (102)	0.5	87	257	226
[26]	No	95 meadow grasses	95	-	51	288	406
[27]	No	57 agro-industrial biomasses, 1 macroalgae, 20 biowastes, 4 energy crops, 11 fatty wastes, 14 meat wastes, 2 co-digestion mixtures, 66 WWTP, 42 plants and vegetables, 18 agro-industrial sludges, 30 sewage sludge WWTP, and 31 municipal solid wastes	296	2–5	0	291	1344
[28]	No	33 energy crops, 15 lawn grasses, 19 hedge trimmings, and 21 wild plants	88	3	104	251	502
[29]	No	23 anaerobic sludges, 30 standard compounds, 50 household wastes, 10 agriculture wastes, 19 sewage sludges, and 6 lipid-rich wastes	138	2	39	361	943
[30]	No	48% agricultural residues, 29% animal beading wastes, 6% AD feedstock, AD digestates, lipid wastes, algae, MSW, and agro-industrial wastes	289	2.8	56	287	879
[6]	No	12 lignocellulosic biomasses	12	2	155	225	300

* data are not provided directly in the publication but in an appendix of the authors publications.

Table 1. Literature data on large sets of BMP references for organic substrates. N.: number of samples, ISR: inoculum–substrate ratio, MSW: municipal solid wastes, and WWTP: wastewater treatment plant. Description of the samples can be found in the Appendix B.

Reference	Data Access	Sample Description	N. (Total Number)	ISR	Min BMP	Mean BMP (Nm3 CH4/t VS)	Max BMP
[14]	Yes	30 organic substrates, including 2 raw manures, 9 food residues, 5 invasive aquatic plants, and 6 other organic wastes	22	1	122	341	649
[20]	Yes	Reed canary grasses	14	0.8	283	348	417
[21]	Yes	11 crops	41	2	177	311	401
[22]	Yes	4 grasses and 2 legume species	61	2	265	338	422
[5]	Yes	Biomasses from first-, second-, and third-generation: 6 cereal crops, 3 oilseed rapes, 7 root crops, 5 grass silages, 2 baled silages, 8 other grass substrates, 7 dairy slurries, 4 other agricultural wastes, 4 milk processing wastes, 4 abattoir wastes, 7 miscellaneous wastes, 10 domestic and commercial food wastes, 3 alternative waste substrates, and 12 seaweeds	83	2	99	328	805
[23]	Yes	20 sludge samples	20	2–2.5	58	181	318
[17]	Yes 51/57	18 plants, 12 grasses, 5 bushes, 16 trees, 4 cereals, and 1 straw	57	3	104	219	479
[15]	Yes	5 energy crops, 8 lignocellulosic biomasses, 7 herbaceous and vegetable by-products, 7 fruit by-products, 6 livestock effluents, and 18 food by-products	50	2	71	325	729
This study	Yes	46 energy crops and silages, 5 slurries, 31 manures, 17 cereal and agro-industrial residues, and 32 lignocellulosic biomasses	131	3	63	283	551
[24]	Yes Appendix *	3 animal manures, 3 crop straws, 5 food and green wastes, 2 processing organic wastes, 1 energy grass, and 2 lignocellulosic biomasses	16	2	49	317	811
[18]	Yes Appendix *	48 maize genotypes selected for diverse maturity and biomass production	204	-	295	329	355
[16]	Yes Appendix *	17 Miscanthus, 16 switch grasses, 36 spelt straws, 37 fiber sorghums, 369 tall fescues, 21 immature ryes, and 73 fiber corns	569 (588)	2	147	389	589
[19]	Yes Appendix *	405 silages from 43 crop species	43	2	143	304	425
[25]	No	68 municipal solid wastes, 7 MSW mix, 9 raw substrates, and 18 lignocellulosic wastes	20 (102)	0.5	87	257	226
[26]	No	95 meadow grasses	95	-	51	288	406
[27]	No	57 agro-industrial biomasses, 1 macroalgae, 20 biowastes, 4 energy crops, 11 fatty wastes, 14 meat wastes, 2 co-digestion mixtures, 66 WWTP, 42 plants and vegetables, 18 agro-industrial sludges, 30 sewage sludge WWTP, and 31 municipal solid wastes	296	2–5	0	291	1344
[28]	No	33 energy crops, 15 lawn grasses, 19 hedge trimmings, and 21 wild plants	88	3	104	251	502
[29]	No	23 anaerobic sludges, 30 standard compounds, 50 household wastes, 10 agriculture wastes, 19 sewage sludges, and 6 lipid-rich wastes	138	2	39	361	943
[30]	No	48% agricultural residues, 29% animal beading wastes, 6% AD feedstock, AD digestates, lipid wastes, algae, MSW, and agro-industrial wastes	289	2.8	56	287	879
[6]	No	12 lignocellulosic biomasses	12	2	155	225	300

* data are not provided directly in the publication but in an appendix of the authors publications.

2. Materials and Methods

2.1. Sampling

Feedstocks were collected in thirty agricultural biogas plant units operating with agricultural feedstocks on the national level. Of these, 75% were operating in wet AD and 25% in dry AD. These 132 inputs are regrouped into five main families: cereal and agro-industrial co-products (CER), energy crop and silage (ENSI), lignocellulosic matter (LCM), manure (MAN), and slurry (SLU). A description of the dataset is available in the Appendix A (

Table A1. Description of the substrates analyzed within the families, where SD is standard deviation, DM is dry matter, FM is fresh matter, VS is volatile solids, BMP exp is the BMP measured, and BMP is the maximum methane potential based on CHNS composition.

Family	Type	Sub Type	DM	VS	VS/DM	BMP exp			Biodegradation	C/N	Carbon		Hydrogen		Nitrogen		Sulfur		Oxygen
			Mean	Mean	Mean	Mean	SD	CV(%)			Mean	SD	Mean	SD	Mean	SD	Mean	SD	Mean
			(% FM)			(Nm3 CH4/t VS)			%		(% DM)		(% DM)		(% DM)		(% DM)		(% DM)
ENSI	Millet	---	22.9	20.8	0.91	267.9	11.9	4%	61	54.1	42.7	0.1	5.3	0.1	0.8	0.1	0.2	0.1	41.9
ENSI	Sorghum	---	18.4	16.2	0.88	361.8	4.1	1%	79	28.2	42.3	0.0	5.6	0.2	1.5	0.1	0.3	0.2	38.5
ENSI	Mix	Sorghum, Millet, and Sunflower mix	16.5	14.9	0.90	406	10.9	3%	87	19.1	43.1	0.1	6.0	0.0	2.3	0.0	0.3	0.0	38.8
ENSI	Sorghum	Sucro variety	15.5	14.3	0.92	351.3	8.5	2%	79	25.1	42.6	0.3	6.0	0.0	1.7	0.0	0.2	0.0	41.8
ENSI	Sorghum	Vega variety	16.1	14.8	0.92	360.4	6.4	2%	79	19.5	43.4	0.1	5.9	0.0	2.2	0.1	0.2	0.0	39.9
ENSI	Mix	Vega sorghum variety and San Lucas sunflower variety	21.5	19.1	0.89	286.9	17.1	6%	67	25.3	41.5	0.1	5.3	0.1	1.6	0.2	0.3	0.1	40.4
ENSI	Mix	Sunflower, Millet, and Guizotia abyssinica	16.7	14.5	0.87	312.7	4.6	1%	68	27.6	42.0	0.1	5.4	0.2	1.5	0.1	0.4	0.3	37.6
ENSI	Mix	Sunflower, Millet, and Guizotia abyssinica	17.6	15.7	0.89	318.4	0.9	0%	69	30.4	42.8	0.2	5.5	0.0	1.4	0.1	0.2	0.1	39.1
ENSI	Mix	---	18.6	16.5	0.89	337.1	32.1	10%	70	32.8	42.5	0.1	6.1	0.1	1.3	0.2	0.2	0.0	38.6
ENSI	Millet and Clover	---	15.9	14.1	0.89	374.1	1.7	0%	85	26.6	40.6	0.0	5.8	0.2	1.5	0.3	0.2	0.0	40.6
ENSI	Maize	---	35.2	33.9	0.96	272.1	5	2%	63	47.5	42.6	0.3	6.5	0.1	0.9	0.2	0.1	0.0	46.2
ENSI	Mix	Residue	23.3	22.9	0.98	371.5	16.9	5%	81	62.4	45.5	0.2	6.6	0.1	0.7	0.1	0.1	0.0	45.1
ENSI	Sorghum	Sucro variety	31.3	29.9	0.96	332.7	21.5	6%	79	73.8	43.5	0.3	5.8	0.0	0.6	0.0	0.2	0.0	45.6
ENSI	Mix	Sorghum (Pacific graze), Millet (Robusta), Vetch (Bingo and Massa), and Clover (Tabor)	26.6	23.9	0.90	269.4	3.3	1%	64	27.1	40.3	0.0	5.7	0.1	1.5	0.1	0.2	0.0	42.4
ENSI	Millet and Clover	---	29.7	26.0	0.88	275.8	4.1	1%	61	21.9	41.4	0.0	5.5	0.2	1.9	0.2	0.6	0.0	38.3
ENSI	Millet and Clover	---	27.1	24.9	0.92	303.7	17.3	6%	69	23.3	42.6	0.2	5.8	0.2	1.8	0.2	0.3	0.2	41.3
ENSI	Millet and Clover	---	27.1	24.9	0.92	285.2	4	1%	65	31.5	42.9	0.1	5.6	0.0	1.4	0.1	0.2	0.0	42.1
ENSI	Sorghum	---	19.8	18.0	0.91	285.6	2.1	1%	64	54.5	41.8	0.0	6.0	0.1	0.8	0.1	0.1	0.0	42.2
ENSI	Maize	---	36.5	35.3	0.97	336	20.4	6%	82	47.9	41.8	0.2	6.4	0.2	0.9	0.2	0.2	0.1	47.4
ENSI	Rye and Vetch	---	49.4	45.9	0.93	255.1	10.9	4%	62	40.2	42.3	0.3	5.3	0.2	1.1	0.1	0.2	0.0	44.1
ENSI	Rye and Vetch	---	28.3	26.7	0.94	284.6	14.7	5%	68	58.8	42.8	0.2	5.6	0.3	0.7	0.1	0.2	0.1	45.0
ENSI	Mix	---	28.9	25.8	0.89	368.7	4.3	1%	81	57.0	41.8	0.2	5.8	0.1	0.7	0.1	0.2	0.0	40.7
ENSI	Mix	Faba bean, Rye, and Radish	20.3	18.8	0.92	300.1	0.7	0%	72	29.4	42.0	0.2	5.5	0.0	1.4	0.1	0.2	0.0	43.2
ENSI	Mix	Faba bean, Triticale, and Radish	17.5	16.1	0.91	294.3	6.2	2%	70	30.2	41.0	0.3	5.7	0.1	1.4	0.1	0.3	0.0	43.1
ENSI	Mix	Grass	54.6	46.6	0.85	253.9	14.4	6%	55	25.7	39.7	0.2	5.8	0.1	1.5	0.2	0.3	0.0	37.9
ENSI	Mix	Sorghum and Maize	32.1	28.4	0.89	315.9	1.8	1%	74	51.5	38.7	0.2	6.1	0.2	0.8	0.2	0.3	0.2	42.8
ENSI	Mix	Peas, Vetch, Oats, and Beans	27.0	24.5	0.91	331	15	5%	67	20.6	45.0	0.0	6.1	0.0	2.2	0.2	0.2	0.0	37.4
ENSI	Maize	---	33.0	32.1	0.97	319.1	10.7	3%	73	44.4	44.4	0.2	6.4	0.1	1.0	0.0	0.1	0.0	45.4
ENSI	Sorghum	---	35.9	33.1	0.92	272.6	3.7	1%	62	51.7	43.9	0.3	5.3	0.1	0.8	0.0	0.2	0.2	42.0
ENSI	Mix	Moha and Clover	50.3	44.8	0.89	282.5	11.2	4%	58	34.9	43.9	0.2	6.0	0.1	1.3	0.1	0.2	0.0	37.7
ENSI	Rapeseed	---	18.2	17.2	0.94	432.5	5.6	1%	93	79.4	44.4	0.3	6.4	0.2	0.6	0.1	0.5	0.5	42.4
ENSI	Grass	---	27.8	24.7	0.89	264.3	15	6%	57	25.2	41.5	0.2	6.1	0.1	1.6	0.2	0.2	0.0	39.3
ENSI	Sorghum	---	23.6	21.2	0.90	305.3	3	1%	69	45.0	40.8	0.0	6.0	0.0	0.9	0.1	0.2	0.1	41.8
ENSI	Sunflower	---	15.6	14.1	0.90	290.7	0.9	0%	63	44.1	41.7	0.2	6.3	0.0	0.9	0.1	0.2	0.0	41.2
ENSI	Grass	---	17.2	13.5	0.78	406.3	4.8	1%	70	34.6	42.8	0.1	5.8	0.2	1.2	0.0	0.2	0.0	28.2
ENSI	Maize	---	28.5	27.2	0.96	376.3	31.1	8%	89	43.3	43.1	0.1	5.9	0.3	1.0	0.1	0.1	0.0	45.4
ENSI	Alfalfa	---	69.0	62.4	0.90	271	0.1	0%	60	26.7	42.9	0.2	5.7	0.0	1.6	0.1	0.2	0.0	40.0
ENSI	Sorghum	---	24.7	23.3	0.94	289.8	10.9	4%	67	43.3	43.6	0.1	5.8	0.1	1.0	0.1	0.2	0.1	43.7
ENSI	Grass	Ray-grass	17.6	16.7	0.95	393.3	26.5	7%	87	66.5	44.5	0.0	6.0	0.0	0.7	0.1	0.2	0.1	43.1
ENSI	Maize	---	19.8	19.4	0.98	418	4.2	1%	90	42.1	46.8	0.1	6.3	0.1	1.1	0.1	0.2	0.1	43.4
ENSI	Grass	---	21.3	18.9	0.89	461.2	3.7	1%	100	23.8	41.4	0.2	5.9	0.0	1.7	0.0	0.4	0.1	39.2
ENSI	Maize	---	33.6	32.4	0.96	383.9	1.5	0%	85	45.6	44.6	0.2	6.4	0.2	1.0	0.1	0.1	0.0	44.4
ENSI	Maize	---	30.2	28.8	0.95	335.1	10	3%	75	42.2	43.6	0.2	6.5	0.1	1.0	0.1	0.1	0.0	43.9
ENSI	Grass	---	23.4	21.3	0.91	403.2	14.2	4%	90	29.3	42.9	0.2	5.7	0.1	1.5	0.2	0.3	0.0	40.8
ENSI	Grass	---	39.9	36.1	0.91	187.2	11.5	6%	40	49.5	42.4	0.3	6.4	0.1	0.9	0.0	0.3	0.0	40.6
ENSI	Maize	---	32.0	30.3	0.95	301.1	7.4	2%	71	37.7	42.2	0.1	6.2	0.1	1.1	0.2	0.3	0.0	44.9
MAN	Mix	Manure and Spates	32.1	17.3	0.54	253.4	14.9	6%	38	27.2	31.7	0.1	4.4	0.2	1.2	0.1	0.4	0.0	16.2
MAN	Cattle	After phase separation, Straw	15.3	13.8	0.90	321.9	16.8	5%	80	15.8	39.8	0.0	5.4	0.0	2.5	0.1	0.5	0.0	41.8
MAN	Horse	---	8.0	5.3	0.66	237.6	14.3	6%	42	22.4	35.8	0.1	5.0	0.2	1.6	0.1	0.3	0.0	23.8
MAN	Cattle	Straw	27.7	25.1	0.91	257.7	14.9	6%	63	45.9	40.3	0.2	5.5	0.2	0.9	0.1	0.2	0.0	43.7
MAN	Cattle	Straw	16.6	14.3	0.86	236	21.7	9%	51	30.7	41.8	0.1	5.3	0.3	1.4	0.0	0.2	0.1	37.8
MAN	Cattle	Fern	27.6	24.1	0.87	162	5.7	4%	33	32.6	43.2	0.3	5.6	0.0	1.3	0.2	0.2	0.0	36.9
MAN	Cattle	Straw	43.1	34.5	0.80	191.3	8.4	4%	39	54.2	40.6	0.1	4.8	0.2	0.7	0.1	1.4	0.3	32.7
MAN	Horse	---	81.6	69.1	0.85	258.2	11.9	5%	57	49.6	40.8	0.1	5.1	0.2	0.8	0.1	0.8	0.1	37.1
MAN	Poultry	---	57.2	35.3	0.62	216.8	6.9	3%	49	12.0	28.7	0.3	4.0	0.3	2.4	0.0	0.4	0.1	26.2
MAN	Poultry	---	75.9	58.0	0.76	263.8	1.9	1%	63	15.3	34.7	0.3	4.7	0.2	2.3	0.0	0.6	0.1	34.3
MAN	Pig	---	31.6	27.0	0.85	217.8	13.5	6%	50	19.5	38.8	0.1	5.6	0.1	2.0	0.3	0.4	0.0	38.7
MAN	Cattle	Straw, after 1 month conservation	17.0	13.0	0.76	198.6	17.3	9%	38	29.2	39.5	0.1	5.3	0.0	1.4	0.3	0.7	0.2	29.7
MAN	Turkey	---	68.3	52.3	0.77	173	1.1	1%	37	13.5	36.6	0.2	5.1	0.1	2.7	0.3	0.5	0.0	31.6
MAN	Mix	---	15.3	13.8	0.90	243.3	1	0%	56	21.4	40.9	0.1	5.9	0.0	1.9	0.0	0.3	0.0	40.9
MAN	Poultry	---	71.2	58.3	0.82	211	16.1	8%	49	8.2	36.7	0.2	5.6	0.1	4.5	0.1	0.6	0.0	34.4
MAN	Poultry	---	60.3	50.4	0.84	274.1	13	5%	69	15.5	35.3	0.0	5.6	0.1	2.3	0.3	1.0	0.2	39.5
MAN	Cattle	Straw	45.6	34.2	0.75	131.9	1.4	1%	21	51.3	43.5	0.3	5.8	0.0	0.8	0.3	0.3	0.0	24.6
MAN	Horse	---	20.2	16.4	0.81	182.6	9.9	5%	41	27.5	39.5	0.0	4.5	0.2	1.4	0.0	0.5	0.0	35.2
MAN	Cattle	Straw	69.8	61.7	0.88	233.2	15.3	7%	55	34.0	40.6	0.3	5.2	0.0	1.2	0.2	0.6	0.1	40.9
MAN	Poultry	---	49.6	40.5	0.82	185.6	8.8	5%	42	15.3	37.7	0.2	5.4	0.1	2.5	0.2	0.7	0.0	35.4
MAN	Horse	---	34.4	29.1	0.85	308.4	15.3	5%	65	55.3	40.9	0.0	5.5	0.0	0.7	0.1	0.4	0.1	37.1
MAN	Horse	---	33.2	27.0	0.81	281.2	16.2	6%	57	79.1	39.6	0.3	5.6	0.2	0.5	0.0	0.3	0.1	35.3
MAN	Zoo	---	31.3	25.5	0.81	235.3	10.7	5%	51	30.8	38.7	0.3	5.3	0.2	1.3	0.3	0.3	0.1	35.6
MAN	Cattle	Straw	22.8	20.1	0.88	166.9	7.3	4%	38	39.2	41.2	0.2	5.5	0.1	1.1	0.1	0.3	0.1	40.1
MAN	Mix	Straw	22.3	19.4	0.87	346.9	15.9	5%	73	18.6	41.1	0.1	6.1	0.2	2.2	0.1	0.3	0.1	37.2
MAN	Mix	Straw	20.9	18.1	0.86	366	7.1	2%	72	20.1	42.8	0.0	6.2	0.1	2.1	0.3	0.3	0.1	35.0
MAN	Horse	---	57.6	50.3	0.87	281.1	10	4%	62	62.4	40.7	0.1	5.7	0.2	0.7	0.1	0.5	0.0	39.8
MAN	Horse	---	51.0	44.8	0.88	240.9	13.6	6%	57	75.1	39.3	0.2	5.6	0.2	0.5	0.1	0.6	0.2	41.8
MAN	Cattle	Straw	43.1	34.5	0.80	191.4	8.3	4%	46	17.2	35.0	0.2	5.3	0.0	2.0	0.3	0.5	0.0	37.3
MAN	Cattle	Straw	33.7	27.9	0.83	223.8	9	4%	49	21.2	38.4	0.1	5.8	0.0	1.8	0.1	0.4	0.0	36.6
MAN	Horse	---	31.5	26.0	0.83	250.6	18.6	7%	60	13.5	36.2	0.0	5.6	0.1	2.7	0.3	0.6	0.0	37.3
CER	Maize Residues	Follicle	73.9	71.7	0.97	279.2	19	7%	64	33.1	43.1	0.2	6.8	0.1	1.3	0.0	0.2	0.0	45.6
CER	Wheat	Contaminated culture	86.2	84.0	0.97	317.7	2.1	1%	78	22.9	41.2	0.1	6.8	0.0	1.8	0.1	0.2	0.0	47.4
CER	Mix	Cereals	75.6	72.5	0.96	285.9	15.8	6%	64	29.4	43.0	0.3	6.7	0.1	1.5	0.0	0.1	0.0	44.5
CER	Mix	Cereal dust	89.4	80.1	0.90	300.1	5.6	2%	66	42.6	41.9	0.0	5.8	0.1	1.0	0.1	0.1	0.0	40.8
CER	Mix	Cereal residue	72.0	64.7	0.90	250.2	9.3	4%	57	11.4	40.6	0.3	6.2	0.1	3.6	0.2	0.3	0.0	39.2
CER	Maize	Fresh residue from sweet corn	24.6	24.2	0.98	314	20	6%	77	53.1	43.5	0.2	6.0	0.1	0.8	0.0	0.1	0.0	47.9
CER	Maize	Fresh residue from sweet corn	21.9	21.4	0.98	262.7	0.1	0%	63	43.3	43.5	0.2	6.2	0.1	1.0	0.0	0.2	0.1	46.6
CER	Maize	Fresh residue from sweet corn	23.9	23.3	0.97	306	5.4	2%	71	43.7	43.8	0.0	6.4	0.1	1.0	0.1	0.1	0.0	46.3
CER	Maize	Fresh residue from sweet corn	26.7	26.3	0.99	335.5	5.4	2%	78	49.6	44.6	0.2	6.3	0.0	0.9	0.1	0.1	0.0	46.5
CER	Maize	Fresh residue from sweet corn	23.6	23.1	0.98	312.3	14	4%	69	36.9	44.6	0.2	6.7	0.1	1.2	0.0	0.6	0.2	44.7
CER	Maize	Fresh residue from sweet corn	21.9	21.4	0.98	263.7	24.5	9%	60	57.8	44.0	0.3	6.7	0.0	0.8	0.2	0.04	0.1	46.4
CER	Maize	Fresh residue from sweet corn	26.5	26.0	0.98	306.8	5.2	2%	71	56.7	43.7	0.3	6.7	0.1	0.8	0.2	0.1	0.1	46.9
CER	Mix	Cereals	87.0	80.6	0.93	313.3	7.8	2%	67	12.1	43.3	0.0	6.7	0.0	3.6	0.3	0.2	0.0	38.9
CER	Maize	Flour	87.0	85.4	0.98	325.4	28.8	9%	80	37.8	41.4	0.2	6.8	0.0	1.1	0.1	0.1	0.0	48.8
CER	Mix	Cereals	77.0	71.9	0.93	328.4	7.2	2%	73	18.3	43.2	0.1	6.4	0.1	2.4	0.2	0.2	0.0	41.3
CER	Mix	Silo’s lose	79.8	74.1	0.93	320.4	14.7	5%	77	56.2	40.2	0.0	6.2	0.0	0.7	0.1	0.3	0.0	45.4
CER	Mix	Cereals	75.6	72.5	0.96	285.9	15.8	6%	66	29.8	42.4	0.1	6.7	0.1	1.4	0.1	0.3	0.0	44.9
SLU	Cattle	---	4.7	3.5	0.74	291	3	1%	51	15.7	40.5	0.2	5.4	0.1	2.6	0.1	0.5	0.0	25.6
SLU	Rabbit	---	18.4	15.9	0.86	263.8	4.7	2%	55	24.1	41.6	0.2	5.9	0.0	1.7	0.1	0.5	0.1	36.7
SLU	Cattle	---	26.3	24.2	0.92	224.1	3.7	2%	70	16.0	35.9	0.2	5.1	0.1	2.2	0.2	0.6	0.0	48.0
SLU	Duck	---	6.2	5.2	0.84	551.2	26.3	5%	100	14.2	42.1	0.2	6.1	0.1	3.0	0.2	0.4	0.1	31.9
SLU	Cattle	---	10.4	8.1	0.78	481	10.2	2%	91	27.3	39.5	0.1	5.8	0.0	1.4	0.3	0.5	0.2	30.6
LCM	Maize Residue	Cob	28.4	27.7	0.98	272.2	2.1	1%	63	497.8	44.1	0.2	6.3	0.1	0.1	0.0	0.1	0.1	47.2
LCM	Hemp	Dust	88.1	69.0	0.78	184.4	4.5	2%	36	48.5	39.6	0.1	5.3	0.0	0.8	0.0	0.2	0.0	32.5
LCM	Straw	Plant residues	88.0	83.9	0.95	277.6	7.6	3%	68	60.0	42.2	0.0	5.8	0.1	0.7	0.1	0.3	0.0	46.4
LCM	Straw	---	87.6	84.6	0.97	274.1	2.2	1%	67	77.8	42.7	0.1	6.0	0.0	0.5	0.0	0.3	0.1	47.1
LCM	Maize	Beans	42.0	36.4	0.87	246.8	13.3	5%	51	165.7	42.8	0.1	5.5	0.3	0.3	0.1	0.8	0.1	37.3
LCM	Bagasse and Straw	---	52.2	48.3	0.92	188.1	9.1	5%	42	245.9	43.3	0.1	5.7	0.2	0.2	0.1	0.3	0.1	43.0
LCM	Bagasse	---	43.2	40.9	0.95	173.7	7.2	4%	39	376.8	44.6	0.2	5.9	0.2	0.1	0.0	0.2	0.1	44.0
LCM	Straw	---	54.0	47.5	0.88	199.8	8.8	4%	42	193.6	43.4	0.1	5.4	0.2	0.2	0.0	0.2	0.0	38.7
LCM	Bagasse	---	56.7	41.2	0.73	250.6	16.5	7%	39	297.1	42.8	0.2	5.5	0.2	0.1	0.0	0.1	0.0	24.1
LCM	Straw	Waste	79.2	71.8	0.91	329.8	0.8	0%	72	79.1	42.8	0.1	5.8	0.0	0.5	0.1	0.2	0.1	41.4
LCM	Green waste	---	37.9	35.2	0.93	212.1	1.8	1%	47	136.8	43.4	0.0	5.8	0.1	0.3	0.1	0.6	0.1	42.7
LCM	Straw	---	86.5	82.2	0.95	277.6	21.8	8%	67	64.0	43.0	0.3	5.7	0.1	0.7	0.1	0.1	0.0	45.5
LCM	Hay	Meadow	86.0	80.4	0.93	289	7.1	2%	65	51.4	42.6	0.1	6.3	0.0	0.8	0.1	0.1	0.0	43.7
LCM	Straw	Plant residues	89.0	85.1	0.96	292.7	27.4	9%	70	89.0	42.5	0.1	6.1	0.3	0.5	0.0	0.2	0.2	46.4
LCM	Straw	Plant residues	87.2	83.2	0.95	298.9	2.3	1%	69	89.3	42.9	0.1	6.2	0.1	0.5	0.0	0.1	0.1	45.6
LCM	Straw	---	88.3	84.0	0.95	302.1	5.9	2%	72	73.6	42.3	0.2	6.0	0.3	0.6	0.1	0.3	0.3	46.0
LCM	Straw	---	88.8	86.0	0.97	290.6	7.1	2%	69	132.0	43.0	0.1	6.3	0.0	0.3	0.0	0.1	0.0	47.1
LCM	Straw	---	75.9	70.4	0.93	305.5	6.4	2%	70	102.2	42.9	0.0	5.7	0.1	0.4	0.0	0.2	0.0	43.5
LCM	Straw	Waste	84.9	81.3	0.96	293.7	1	0%	67	126.8	44.2	0.2	5.9	0.0	0.3	0.0	0.1	0.0	45.2
LCM	Flower residue	Lavender	88.7	81.2	0.92	200.5	9.6	5%	42	41.5	45.0	0.1	6.0	0.0	1.1	0.2	0.3	0.1	39.3
LCM	Maize	Leaf	37.8	35.0	0.93	286.3	23.3	8%	65	56.5	43.2	0.1	5.8	0.0	0.8	0.0	0.1	0.0	42.8
LCM	Straw	Plant residues	86.3	82.3	0.95	280.5	2.9	1%	69	68.3	41.5	0.3	6.0	0.1	0.6	0.1	0.2	0.1	47.1
LCM	Straw	Waste	84.5	77.3	0.92	306	23.1	8%	66	128.8	43.5	0.3	5.9	0.0	0.3	0.0	0.1	0.0	41.7
LCM	Straw	Rapeseed waste	71.9	62.9	0.87	241.4	3	1%	54	31.1	40.0	0.2	5.8	0.2	1.3	0.0	0.4	0.2	40.0
LCM	Straw	---	85.0	81.2	0.96	309.7	10.1	3%	72	162.8	43.8	0.3	5.9	0.0	0.3	0.1	0.1	0.0	45.6
LCM	Straw	Waste	83.9	78.2	0.93	283.8	8.8	3%	62	119.4	43.6	0.1	6.3	0.0	0.4	0.2	0.2	0.1	42.8
LCM	Green waste	---	44.6	34.5	0.77	178.2	0.1	0%	33	23.9	40.3	0.1	5.5	0.1	1.7	0.2	0.1	0.0	29.7
LCM	Mix	Green waste	34.4	26.4	0.77	218.9	11.6	5%	45	21.9	37.5	0.3	5.3	0.2	1.7	0.1	0.2	0.0	31.9
LCM	Green waste	---	80.6	36.9	0.46	63.1	3.4	5%	7	29.2	34.5	0.0	4.5	0.0	1.2	0.2	0.3	0.0	5.3
LCM	Flower residue	Pomace	47.1	39.6	0.84	281.1	1.7	1%	64	17.6	38.3	0.1	5.5	0.0	2.2	0.1	0.6	0.0	37.3
LCM	Straw	---	90.6	85.8	0.95	240	6.3	3%	60	406.3	41.2	0.3	5.7	0.3	0.1	0.0	0.8	0.3	46.9
LCM	Flower residue	Lavender	82.8	78.2	0.94	171.3	12.4	7%	37	68.8	44.3	0.0	6.3	0.0	0.6	0.3	0.6	0.1	42.6
LCM	Straw	Waste	88.8	82.3	0.93	267	7.4	3%	64	263.7	40.3	0.1	6.1	0.3	0.2	0.1	0.8	0.1	45.3

and

Table A2. Description of the substrates analyzed within the families: fibers, protein content, and COD, where SD is standard deviation, DM is dry matter, VS is volatile solids, and COD is the chemical oxygen demand.

Family	Type	Sub Type	Cellulose		Hemicelluloses		Lignin		Protein	COD
			Mean	SD	Mean	SD	Mean	SD	Calculated	Calculated
			(g/100g DM)		(g/100g DM)		(g/100g DM)		(% DM)	(g COD/g CxHyOz)
ENSI	Millet	---	28.6	1.4	17.7	1.1	22.3	0.3	4.9	1.3
ENSI	Sorghum	---	21.7	0.0	10.8	0.2	21.1	0.3	9.4	1.4
ENSI	Mix	Sorghum, Millet, and Sunflower mix	22.7	0.3	12.7	0.2	19.4	0.1	14.1	1.4
ENSI	Sorghum	Sucro variety	25.1	0.5	12.1	0.6	18.1	0.1	10.6	1.3
ENSI	Sorghum	Vega variety	22.8	0.7	13.7	0.4	20.0	0.9	13.9	1.4
ENSI	Mix	Vega sorghum variety and San Lucas sunflower variety	24.7	0.2	10.1	0.1	26.7	0.7	10.3	1.3
ENSI	Mix	Sunflower, Millet, and Guizotia abyssinica	17.3	0.3	7.1	0.1	26.6	1.3	9.5	1.4
ENSI	Mix	Sunflower, Millet, and Guizotia abyssinica	17.9	0.1	8.6	0.2	25.6	0.3	8.8	1.4
ENSI	Mix	---	22.6	0.8	9.2	0.2	25.1	0.3	8.1	1.4
ENSI	Millet and Clover	---	29.6	0.2	19.1	0.3	19.6	0.5	9.5	1.3
ENSI	Maize	---	47.7	1.5	11.5	0.5	11.4	0.2	5.6	1.3
ENSI	Mix	Residue	13.5	0.3	9.0	0.2	14.0	0.1	4.6	1.3
ENSI	Sorghum	Sucro variety	31.4	0.4	18.0	0.5	17.8	0.1	3.7	1.2
ENSI	Mix	Sorghum (Pacific graze), Millet (Robusta), Vetch (Bingo and Massa), and Clover (Tabor)	30.3	2.5	14.2	0.5	19.7	0.8	9.3	1.3
ENSI	Millet and Clover	---	22.4	0.4	15.4	0.3	22.2	1.0	11.8	1.4
ENSI	Millet and Clover	---	12.9	0.4	6.6	0.1	18.6	1.8	11.4	1.3
ENSI	Millet and Clover	---	11.2	0.1	6.4	0.1	21.0	0.2	8.5	1.3
ENSI	Sorghum	---	28.3	0.6	17.2	0.4	18.7	0.1	4.8	1.3
ENSI	Maize	---	49.9	0.6	12.6	0.4	11.4	0.2	5.5	1.2
ENSI	Rye and Vetch	---	25.8	0.0	15.1	0.0	22.1	0.1	6.6	1.2
ENSI	Rye and Vetch	---	26.7	0.0	17.4	0.0	20.6	0.1	4.5	1.2
ENSI	Mix	---	22.3	0.4	13.3	0.5	19.5	0.4	4.6	1.3
ENSI	Mix	Faba bean, Rye, and Radish	19.6	0.6	10.6	0.1	22.4	0.1	8.9	1.2
ENSI	Mix	Faba bean, Triticale, and Radish	17.5	0.0	8.8	0.0	18.1	0.2	8.5	1.2
ENSI	Mix	Grass	21.7	0.0	12.3	0.0	28.9	0.5	9.6	1.4
ENSI	Mix	Sorghum and Maize	22.0	0.5	15.4	0.3	17.8	0.3	4.7	1.2
ENSI	Mix	Peas, Vetch, Oats, and Beans	21.9	0.3	10.7	0.3	20.2	0.8	13.7	1.5
ENSI	Maize	---	45.5	1.0	10.5	0.3	13.3	0.4	6.2	1.3
ENSI	Sorghum	---	30.5	0.6	20.5	0.2	24.5	0.5	5.3	1.3
ENSI	Mix	Moha and Clover	28.4	0.1	13.5	0.5	19.2	1.0	7.9	1.5
ENSI	Rapeseed	---	25.7	1.2	10.2	1.0	27.4	0.3	3.5	1.4
ENSI	Grass	---	21.5	0.5	11.7	0.2	27.1	0.2	10.3	1.4
ENSI	Sorghum	---	31.6	0.2	14.0	0.1	22.9	0.3	5.7	1.3
ENSI	Sunflower	---	20.9	0.4	9.1	0.2	22.8	0.8	5.9	1.4
ENSI	Grass	---	29.9	0.2	16.9	0.2	25.7	1.6	7.7	1.7
ENSI	Maize	---	41.1	0.4	11.7	0.8	16.5	0.8	6.2	1.2
ENSI	Alfalfa	---	23.6	0.7	9.2	0.1	21.5	0.6	10.1	1.4
ENSI	Sorghum	---	29.8	0.3	13.1	0.8	16.8	0.4	6.3	1.3
ENSI	Grass	Ray-grass	31.9	1.6	14.1	0.9	21.9	1.6	4.2	1.3
ENSI	Maize	---	27.3	0.2	18.4	0.1	20.0	0.7	6.9	1.4
ENSI	Grass	---	24.9	0.2	14.8	0.5	19.5	0.3	10.9	1.4
ENSI	Maize	---	52.3	3.5	11.2	0.9	15.4	0.6	6.1	1.3
ENSI	Maize	---	41.3	1.2	9.6	0.4	13.1	1.3	6.5	1.3
ENSI	Grass	---	21.1	0.7	9.7	0.2	18.1	0.7	9.1	1.3
ENSI	Grass	---	26.0	0.4	13.7	0.3	18.4	1.1	5.3	1.4
ENSI	Maize	---	37.1	0.5	11.6	0.0	19.9	1.3	7.0	1.3
MAN	Mix	Manure and Spates	28.7	0.8	14.8	0.4	52.3	2.9	7.3	2.0
MAN	Cattle	After phase separation, Straw	24.5	0.6	17.5	0.5	26.0	0.7	15.7	1.2
MAN	Horse	---	25.3	2.5	14.2	0.6	48.7	2.2	10.0	1.7
MAN	Cattle	Straw	25.6	0.1	18.2	0.2	29.4	1.0	5.5	1.2
MAN	Cattle	Straw	22.5	1.8	15.3	0.0	34.9	0.6	8.5	1.4
MAN	Cattle	Fern	20.0	0.7	14.5	1.1	36.3	1.2	8.3	1.4
MAN	Cattle	Straw	29.2	1.4	16.3	0.6	34.9	0.4	4.7	1.5
MAN	Horse	---	29.1	0.9	17.1	0.5	32.3	0.3	5.1	1.4
MAN	Poultry	---	16.6	0.4	13.6	0.2	35.4	2.9	14.9	1.4
MAN	Poultry	---	16.8	0.1	13.5	0.2	36.3	0.5	14.2	1.3
MAN	Pig	---	19.6	1.7	11.6	0.8	36.8	0.1	12.4	1.3
MAN	Cattle	Straw, after 1 month conservation	18.8	0.8	13.6	0.3	48.5	2.6	8.5	1.6
MAN	Turkey	---	21.7	0.7	21.5	0.2	22.8	0.5	17.0	1.5
MAN	Mix	---	19.6	0.6	12.8	0.0	31.2	2.3	12.0	1.3
MAN	Poultry	---	20.1	0.2	14.4	0.1	23.5	0.6	28.1	1.4
MAN	Poultry	---	22.1	1.0	17.4	0.7	20.0	0.4	14.2	1.2
MAN	Cattle	Straw	13.6	0.1	8.8	0.1	52.0	1.9	5.3	1.9
MAN	Horse	---	20.0	0.5	12.7	0.4	56.5	3.7	9.0	1.3
MAN	Cattle	Straw	29.2	1.4	16.9	0.2	30.4	0.3	7.5	1.3
MAN	Poultry	---	19.1	0.3	17.1	0.1	26.4	0.2	15.4	1.4
MAN	Horse	---	35.0	1.3	20.0	1.3	27.2	1.3	4.6	1.4
MAN	Horse	---	31.8	0.0	18.9	0.0	27.1	0.1	3.1	1.4
MAN	Zoo	---	21.9	0.2	15.2	0.1	38.6	1.6	7.8	1.4
MAN	Cattle	Straw	19.1	0.3	11.5	0.1	40.1	4.0	6.6	1.3
MAN	Mix	Straw	20.2	0.2	14.9	0.4	28.6	0.1	13.8	1.4
MAN	Mix	Straw	18.9	0.2	12.7	0.1	35.7	2.7	13.3	1.5
MAN	Horse	---	31.6	0.2	20.0	0.1	27.1	0.5	4.1	1.3
MAN	Horse	---	29.6	0.6	19.9	0.1	34.6	0.3	3.3	1.2
MAN	Cattle	Straw	28.5	0.2	15.7	0.1	36.4	0.0	12.8	1.3
MAN	Cattle	Straw	25.0	1.0	18.1	0.6	43.2	0.2	11.3	1.4
MAN	Horse	---	20.7	0.5	16.4	0.4	28.3	0.7	16.8	1.3
CER	Maize Residues	Follicle	49.0	1.2	10.8	0.5	12.0	0.0	8.2	1.3
CER	Wheat	Contaminated culture	59.3	1.1	6.0	0.1	5.5	0.5	11.3	1.2
CER	Mix	Cereals	50.2	0.6	7.9	0.3	14.2	0.0	9.1	1.3
CER	Mix	Cereal dust	29.7	0.4	21.3	0.3	21.4	1.2	6.1	1.3
CER	Mix	Cereal residue	33.3	1.7	14.7	1.2	16.1	0.1	22.3	1.4
CER	Maize	Fresh residue from sweet corn	29.5	1.5	16.1	1.5	15.4	0.4	5.1	1.2
CER	Maize	Fresh residue from sweet corn	25.8	0.4	18.9	0.2	16.4	0.0	6.3	1.2
CER	Maize	Fresh residue from sweet corn	29.5	0.1	19.0	0.2	16.2	0.1	6.3	1.3
CER	Maize	Fresh residue from sweet corn	29.5	0.2	20.5	0.0	12.2	0.1	5.6	1.3
CER	Maize	Fresh residue from sweet corn	29.0	0.3	19.9	0.0	12.9	0.3	7.6	1.3
CER	Maize	Fresh residue from sweet corn	27.6	0.4	16.8	0.6	16.3	0.2	4.8	1.3
CER	Maize	Fresh residue from sweet corn	28.4	0.1	18.9	0.1	14.0	0.1	4.8	1.3
CER	Mix	Cereals	29.3	0.9	10.9	0.3	18.7	0.4	22.3	1.5
CER	Maize	Flour	60.9	0.4	7.2	0.1	6.2	0.5	6.8	1.2
CER	Mix	Cereals	50.6	1.3	7.3	0.6	10.6	0.1	14.8	1.4
CER	Mix	Silo’s lose	51.6	0.7	10.7	0.5	18.7	0.5	4.5	1.2
CER	Mix	Cereals	49.3	1.9	6.8	0.3	13.3	0.3	8.9	1.3
SLU	Cattle	---	8.7	0.0	7.7	0.3	38.6	1.1	16.1	1.8
SLU	Rabbit	---	20.6	0.7	13.5	0.1	28.6	0.0	10.8	1.4
SLU	Cattle	---	26.4	0.7	20.0	0.9	28.8	0.1	14.0	1.0
SLU	Duck	---	13.2	0.1	23.5	1.3	19.1	0.1	18.6	1.6
SLU	Cattle	---	17.8	0.0	12.7	1.0	33.8	0.9	9.0	1.6
LCM	Maize Residue	Cob	29.0	0.6	26.0	0.4	19.8	0.1	0.6	1.2
LCM	Hemp	Dust	19.5	0.8	8.9	0.0	28.2	0.0	5.1	1.5
LCM	Straw	Plant residues	28.5	0.3	17.5	0.2	16.3	0.3	4.4	1.2
LCM	Straw	---	30.9	0.5	18.3	0.2	17.0	0.4	3.4	1.2
LCM	Maize	Beans	33.6	1.5	22.7	0.7	19.4	0.5	1.6	1.4
LCM	Bagasse and Straw	---	30.1	2.5	18.2	1.7	17.6	1.5	1.1	1.3
LCM	Bagasse	---	32.1	0.2	15.7	0.2	22.8	0.7	0.7	1.3
LCM	Straw	---	31.7	0.2	20.6	0.3	23.1	0.4	1.4	1.4
LCM	Bagasse	---	33.4	0.6	21.2	0.4	30.9	2.9	0.9	1.9
LCM	Straw	Waste	25.3	1.7	24.1	1.8	21.3	2.1	3.4	1.3
LCM	Green waste	---	31.9	0.7	13.8	0.4	17.9	1.3	2.0	1.3
LCM	Straw	---	30.5	0.8	18.5	0.3	18.8	0.5	4.2	1.2
LCM	Hay	Meadow	26.8	2.0	19.9	1.9	23.7	2.2	5.2	1.3
LCM	Straw	Plant residues	30.1	0.3	17.8	0.1	18.3	0.5	3.0	1.2
LCM	Straw	Plant residues	31.3	0.0	17.4	0.1	18.3	1.2	3.0	1.3
LCM	Straw	---	29.2	0.9	18.9	0.3	14.7	0.4	3.6	1.2
LCM	Straw	---	32.3	0.7	18.3	0.4	15.7	0.6	2.0	1.2
LCM	Straw	---	30.3	0.0	20.2	0.1	24.6	1.1	2.6	1.3
LCM	Straw	Waste	31.4	0.9	22.0	0.7	18.4	0.3	2.2	1.3
LCM	Flower residue	Lavender	20.8	0.7	12.1	0.5	30.8	0.1	6.8	1.4
LCM	Maize	Leaf	25.7	1.7	20.8	1.5	27.5	1.8	4.8	1.3
LCM	Straw	Plant residues	26.2	1.1	16.6	0.9	19.5	1.4	3.8	1.2
LCM	Straw	Waste	30.2	1.7	23.8	1.1	26.0	1.1	2.1	1.3
LCM	Straw	Rapeseed waste	24.5	1.5	11.7	0.8	23.7	2.0	8.1	1.3
LCM	Straw	---	29.8	0.2	19.7	0.3	20.9	1.1	1.7	1.2
LCM	Straw	Waste	27.8	2.1	21.5	1.4	23.7	1.3	2.3	1.3
LCM	Green waste	---	18.3	1.2	11.1	0.7	46.0	0.2	10.6	1.6
LCM	Mix	Green waste	16.8	1.6	12.5	1.1	50.2	4.2	10.7	1.5
LCM	Green waste	---	15.4	0.8	12.9	0.9	42.1	1.5	7.4	2.8
LCM	Flower residue	Pomace	17.1	0.8	7.8	0.0	17.1	0.6	13.6	1.3
LCM	Straw	---	31.5	0.7	17.0	0.7	27.9	2.5	0.6	1.2
LCM	Flower residue	Lavender	24.5	0.9	10.7	0.5	30.0	0.1	4.0	1.4
LCM	Straw	Waste	29.2	0.3	20.1	0.0	26.6	0.1	1.0	1.2

).

2.2. Elemental Composition and Fiber Analysis

The elemental composition of each feedstock was assessed by an elemental apparatus (varioMicro V4.0.2, Elementar^®, Langenselbold, Germany), after being dried at 60 °C until constant weight and ground into 1 mm particles using a centrifuge mill (SR 200, Retsch, Haan, Germany). Each COD was then calculated on the basis of this analysis using Equation (1) [31]:

$$COD \left(\frac{gCOD}{gCxHyOz}\right)=8\times \frac{4x+y-2z}{12x+4+16z}$$

(1)

The protein content was estimated on the basis of the nitrogen elemental composition multiplied by 6.25 [32].

For fiber analysis (e.g., cellulose, hemicelluloses, and lignin-like), 80 mg of sample was hydrolyzed with 0.85 mL of H₂SO₄ acid (72%) for 1 h at 30 °C in continuously shaken tubes for thorough mixing (450 rpm) using closed vessels to prevent evaporation. Then, 23.8 mL of deionized water was added, and the vessels were heated to 121 °C for one hour under magnetic agitation (450 rpm). After cooling, the insoluble residue was separated by filtration through 1 µm glass fiber paper (GFF, WHATMAN^®, Maldstone, UK) into a soluble phase (structural carbohydrates) and a solid phase (lignin and ash). The filtrate was further filtered using nylon filters (0.2 μm) and analyzed for glucose, xylose, and arabinose by high-performance liquid chromatography (1260 infinity II technology, Agilent, Santa Clara, CA, USA) equipped with a Hi.Plex H coupled to a UV detector. The crucible and the fiberglass paper were dried at 105 °C for 24 h to determine the content of Klason lignin-like material by weighing. The cellulose-like and hemicelluloses-like contents were determined using the following equations:

$$\mathrm{Cellulose}-\mathrm{like} \left(\% \mathrm{DM}\right)=\frac{\mathrm{Glucose} \left(\% \mathrm{DM}\right)}{1.11}$$

(2)

$$\mathrm{Hemicelluloses}-\mathrm{like} \left(\% \mathrm{DM}\right)=\frac{\mathrm{Xylose} \left(\% \mathrm{DM}\right)+ \mathrm{Arabinose} \left(\% \mathrm{DM}\right)}{1.13}$$

(3)

where 1.11 is the conversion factor of polymers based on glucose-to-glucose monomers, and 1.13 is the factor for converting polymers based on xylose (arabinose and xylose) into monomers [33].

2.3. Biochemical Methane Potential Measurement (BMPexp)

The procedure for BMP tests has been well-documented in a previous study [30] and followed the inter-laboratory study recommendations [8,34]. Feedstocks were stored at 5 °C if the storage period was less than or equal to three days or at −20 °C if the storage period exceeded three days and thawed at 6 °C before testing. Used inoculum was agitated, maintained at 38 ± 1 °C, and fed regularly with green grass and wastewater sludge at the laboratory of APESA facility. Regular checks were performed by measuring the pH, dry matter, and volatile solids. DM and vs. were obtained by loss on ignition (same as for feedstocks), and the pH was assessed using a 340i pH meter fitted with Sentix^® electrodes (WTW, Weilheim, Germany). The main properties of the inoculum were TS (% fresh mass): 3.8 ± 0.3%; vs. (% TS): 64.4 ± 1.5%; pH: 8.3 ± 0.2; volatile fatty acids (VFAs): 300 mg eq. acetate L⁻¹; and ammonium content: 2.1 g N-NH₄⁺ L⁻¹. The inocula complied with the quality criteria proposed by [10].

The BMP tests were carried out under mesophilic conditions in duplicate, and 500 mL reactors were filled with 300 mL of an inoculum/substrate ratio of 3 g VS/g VS. After filling, each bottle was flushed with N₂ gas for 30 s, incubated at 39 °C, and degassed after 1 h. Each day, manual homogenization was performed, and biogas production followed using an electronic manometer device (Digitron 2023P, Digital Instrumentation Ltd., London, UK) and expressed in normal liters (at 0 °C, 1.013 hPa). Once a week, the gas composition was analyzed by gas chromatography (Varian GC-CP4900, Agilent, Santa Clara, CA, USA) equipped with two columns. For O₂, N₂, and CH₄, a Molsieve 5A PLOT column at 110 °C was used, and for CO₂ analysis, a HayeSep A set at 70 °C was used. The injector and detector temperatures were set at 110 °C and 55 °C, respectively. Two standard gases for calibration were used: one composed of 9.5% CO₂, 0.5% O₂, 81% N₂, and 10% CH₄, and the other composed of 35% CO₂, 5% O₂, 20% N₂, and 40% CH₄ (special gas from Air Liquide^®, Paris, France). The BMP tests concluded when the biogas production reached a stationary state and did not vary for more than 0.5% during three consecutive days. Blank (inoculum only) and positive controls (cellulose, Tembec^®, Montréal, QC, Canada) were run in parallel in duplicate.

The theoretical BMP was calculated on the basis of the elemental characterization (CxHyOzNnSs) using Equation (4) (Achinas and Euverink, 2016):

$$BMPth (LC{H}_4/kg VS)=\frac{22.4\times \left(\frac{x}{2}+\frac{y}{8}-\frac{z}{4}-\frac{3n}{8}-\frac{s}{4}\right)}{12x+y+16z+14n+32s}$$

(4)

where 22.4 is the molar volume of an ideal gas.

Finally, the percentage of biodegradation is the ratio between the experimental BMP and the theoretical BMP.

$$Biodegradation \left(\%\right)=\frac{BMPexp}{BMPth}$$

(5)

3. Results

3.1. Chemical Composition of the Various Biomasses

The feedstock compositions are described in Figure 1 (overall and for each family, more data are available in SD Table 1). Among the five families, the distribution was as follows: 47% energy crops and silages, 32% lignocellulosic biomasses, 31% manures, 17% cereal co-products and residues, and 5% slurries. The minimum, maximum, and average values of the different chemical properties (DM, VS, C/N, fibers, proteins, and COD) are shown for all the families in Table A1 and Table A2. In order to have a better sense of the inter-family variability, the most important parameters (i.e., VS/DM, COD, C/N, and protein content) are presented as boxplots (Figure 1) and the fiber compositions as radar graphs (Figure 2).

First of all, higher ash contents were reported for manures and slurries compared with the other families investigated. In terms of proteins, higher contents were also reported for manures and slurries. Indeed, mean protein contents of 10.4 and 13.7% DM were reported for animal manures and slurries, respectively. By contrast, lignocellulosic biomasses exhibited the lowest protein content, at 3.9% DM. Allen et al. (2016) reported protein contents varying from 12.3% DM to 18.5% DM for different animal slurries [5]. Similarly, Li et al. (2013) estimated protein contents of 13.7% DM, 17.5% DM, and 21% DM for swine, dairy, and chicken manures, respectively. Li et al. (2013), on the other hand, reported lower values ranging from 2.5% DM to 5.6% DM for lignocellulosic biomasses [24]. The chemical oxygen demand is another important parameter in anaerobic digestion monitoring, as it can allow determination of mass balances and the theoretical methane potential [13]. Little variability in the main COD was observed for the five families, with values ranging from 1.3 to 1.5 g/g VS. Scarce information is available in the literature regarding these parameters, as only Labatut et al. (2011) have reported it for a range of 30 substrates (mono- and co-digestion). For manure, they found a COD ranging from 0.7 to 1.3 g/g, with a mean of 1.0, which is considerably lower than our values, and higher values for biowaste substrates, with a mean of 6.4, ranging from 0.9 to 28.8 g/g [14]. The fiber content (i.e., cellulose, hemicelluloses, and lignin) was also reported for the five families, and higher contents were observed for lignocellulosic biomasses and manures, similar to the values previously reported in the literature [6,14,24].

Finally, the C/N ratio was also reported for the five families. The C/N ratio is a very important parameter for the long-term continuous digestibility of a substrate. Ideally, it should be between 25:1 and 30:1 to facilitate optimal growth of micro-organisms [5]. For this parameter, high variabilities were observed with higher values of C/N for lignocellulosic biomasses, with a median of approximately 90 and an average of 132. All the other groups have means or averages between 19 and 40. Yet, the C/N ratio is based on the elemental analysis, requiring dry samples. Volatilization of ammoniacal nitrogen or volatile compounds can differ depending on the substrate. A comparison of these results with C/N ratios in the literature points out that an overestimation occurred for slurry and manure families [15,35,36]; similar results are obtained for CER and LCM [5,15], whereas ENSI family C/N ratios are underestimated [5,15,37,38]. Extrapolations cannot be readily performed, as they can depend on the feedstock composition, type, harvest, storage, etc. As an example, manure C/N ratio means have been found to be approximately 16 for cattle manure, 9 for poultry manure, and they are higher for horse manure (between 15 to 150, depending on the type and proportion of litter) [35,36,39].

3.2. Biochemical Methane Potential of Feedstock

Another important parameter in the monitoring and optimization of agricultural biogas plants is the value of the methane potential. Methane potentials were assessed in this study by BMP tests performed on the 132 agricultural substrates shared in five families: cereals and agro-industrial co-products, lignocellulosic biomass, energy crops and silages, animal manures, and slurries (Figure 3).

As shown in Table 1, a large variability in methane potentials was observed among the different families, with methane potentials ranging from 63 Nm³ CH₄/t VS (green waste) to 551 Nm³ CH₄/t VS (duck slurry), with a mean value for the 132 organic samples of 284 Nm³ CH₄/t VS.

3.2.1. Cereal and Agro-Industrial Residues (CER)

The first family investigated was cereal and agro-industrial residues (n = 17). The cereals were obtained from the cereal agro-industry and silos, whereas the maize was from the sweet corn industry. Methane potentials of 298, 301, and 318 Nm³ CH₄/t VS were reported for cereal residues, sweet corn residues, and wheat residues, respectively. Garcia et al. (2019) reported a similar methane potential, with values of 345 Nm³ CH₄/t VS for a mix of cereals [15]. Luna DeRisco et al. (2011) also investigated the methane potentials of grain mill residues, and methane potentials of 274–386 Nm³ CH₄/t VS were reported [40]. In parallel, Garcia et al. (2019) also reported methane potentials ranging from 204 to 345 Nm³ CH₄/t VS for ten agro-industrial co-products (from the vegetables and fruits industry) [15].

3.2.2. Manures (MAN)

The methane potential of various animal manures was investigated. Manures are organic matter, derived mostly from animal feces and urine but also normally containing plant materials (generally wheat straw) that have been used as bedding for animals. Methane potentials of 173, 210, 217, 230, 235, and 250 Nm³ CH₄/t VS were determined for turkey, cattle, pig, poultry, zoo, and horse manures. Such data are in the same range as the values reported in the literature [24,41,42]. Kafle and Chen (2016) investigated the methane potential of five different livestock manures (dairy manure (DM), horse manure (HM), goat manure (GM), chicken manure (CM), and swine manure (SM)). The BMPs of DM, HM, GM, CM, and SM were determined to be 204, 155, 159, 259, and 323 Nm³ CH₄/t VS, respectively [41]. Similarly, Cu et al. (2015) also reported methane potentials of various animal manures, and the highest BMP in this study was from piglet manure at 443.6 Nm³ CH₄/t VS, followed by cow, sow, chicken, rabbit, buffalo, and sheep manures at 222, 177.7, 173, 172.8, 153, and 150.5 Nm³ CH₄/t VS, respectively [42]. Similarly, Garcia et al. (2019) reported methane potentials of 97, 128, 200, and 208 Nm³ CH₄/t VS for bovine, pig, rabbit, and poultry manures, respectively [15]. Yang et al., 2021 also reported methane potentials of 160 Nm³ CH₄/t VS for dairy manure, 200 Nm³ CH₄/t VS for goat manure, and 325 Nm³ CH₄/t VS for swine manure [43]. It can be observed that the methane potentials of our studies are in the same range as the literature data, although some differences can be observed for the same manure families, as the methane potential can be influenced by the type of farm, the duration of storage, and the storage method. Finally, Carabeo-Perez et al. (2021) also investigated the methane potential from various herbivorous animal manures. Methane yield potentials of 245, 326, and 112 Nm³ CH₄/t VS were obtained for horse, rabbit, and goat manures, respectively, influenced by the difference in their digestive systems to digest the grass feedstock [44]. Finally, Li et al. (2013) determined methane potentials of 51, 295, and 321 Nm³ CH₄/t VS for dairy, chicken, and swine manure, respectively [24].

3.2.3. Animal Slurries (SLU)

Animal slurries are manure in liquid form, i.e., a mixture of excrements and urine of domestic animals, including water and/or small amounts of litter. Slurry methane potentials were also investigated in this study, with methane potentials ranging from 263 to 551 Nm³ CH₄/t VS. As shown in Figure 3, a high variability was observed for cattle slurries, which can be explained by differences in the storage type and duration. In terms of liquid manures, little information is available in the literature [5,14]. Labatut et al. (2011) reported a methane potential of 261 Nm³ CH₄/t VS for liquid dairy manure. Allen et al. (2016) investigated the methane potentials of different slurries (dairy, pig, and beef). Methane potentials of 99 and 311 Nm³ CH₄/t VS were reported for pig and beef slurries, respectively. In terms of dairy slurries, methane potentials ranging from 136 to 239 have been reported [5]. Garcia et al. (2019) also reported methane potentials of 35 and 137 Nm³ CH₄/t VS for bovine and pig slurries, respectively [15].

3.2.4. Silages and Energy Crops (ENSI)

Silages and energy crops are another type of substrate generally found in agricultural biogas plants. In our study, of the 46 organic substrates investigated, the methane potentials ranged from 187 Nm³ CH₄/t VS to 461 Nm³ CH₄/t VS. For instance, average methane potentials of 320, 342, and 352 Nm³ CH₄/t VS were reported for sorghum, corn, and grass samples, respectively. The methane potentials of silages and energy crops have been widely investigated in the literature in recent decades, and the values obtained in this study are in the same order [5,15,18,19]. For instance, Garcia et al. (2019) investigated the methane potential of five energy crops and reported methane potentials ranging from 253 Nm³ CH₄/t VS (millet, Panicum milliaceum L.) to 351 Nm³ CH₄/t VS (triticale, Triticum aestivum L.). Similarly, Allen et al. (2016) reported the methane potential of 18 energy crops, and the methane potentials ranged from 281 Nm³ CH₄/t VS (winter oats) to 398 Nm³ CH₄/t VS (turnips). Similarly, Allen et al. (2016) also investigated the methane potentials of different silages and reported methane potentials varying from 311 Nm³ CH₄/t VS (Savazi grass silage) to 433 Nm³ CH₄/t VS (silage bales). Finally, Hermann et al. also investigated the methane potentials of 43 crops, including main and secondary crops, catch crops, annual grass, and perennial crops [19].

3.2.5. Lignocellulosic Biomasses (LCM)

The methane potentials of 33 lignocellulosic biomasses were also investigated. The methane potentials ranged from 63 Nm³ CH₄/t VS (green waste) to 330 Nm³ CH₄/t VS (barley straw). Lower methane potentials were observed for green waste residues, likely due to their high content in fibers, and especially in lignin, which has been shown to be poorly degraded in the anaerobic digestion process [19,45]. Similar methane potentials on lignocellulosic biomasses have been reported previously in the literature [6,15]. Indeed, Monlau et al. (2012) reported the methane potentials of twelve lignocellulosic biomasses ranging from 155 Nm³ CH₄/t VS (sunflower stalks) to 300 Nm³ CH₄/t VS (Jerusalem artichoke tubers). Similarly, Garcia et al. (2019) reported methane potentials ranging from 282 Nm³ CH₄/t VS (coconut fibers) to 425 Nm³ CH₄/t VS (corn, Zea mays L.). Similarly, Dinuccio et al. (2010) reported methane potentials ranging from 225 to 424 Nm³ CH₄/t VS [46]. Perennial crops exhibited the lowest methane potentials, with values ranging from 203 Nm³ CH₄/t VS (cup plant) to 260 Nm³ CH₄/t VS (tall wheatgrass). The highest methane potential of the various crops investigated was reported for forage triticale, with a methane potential of 371 Nm³ CH₄/t VS.

3.3. Practical Implementation of this Database

To assist the reader and user in exploiting this publication, a summary table is provided in

Table 2. Chemical composition of the families (FM: fresh matter; DM: dry matter; and VS: volatile solids). Families: cereals and residues (CER), energy crops and silage (ENSI), lignocellulosic matter (LCM), manures (MAN), and slurries (SLU).

Family	CER	ENSI	LCM	MAN	SLU
Sample number	17	46	33	31	5
DM (% FM)	21.9–89.4 57.2	15.5–69.0 27.3	28.4–90.6 71.2	8.0–81.6 39.2	4.7–26.3 13.2
VS (% FM)	21.4–85.4 54.3	13.5–62.4 25.0	26.4–86.0 64.3	5.3–69.1 31.8	3.5–24.2 11.4
C (% DM)	40.2–44.6 42.8	38.7–46.7 42.6	34.5–45.0 42.2	28.7–43.5 38.7	35.9–42.1 39.9
H (% DM)	5.8–6.9 6.5	5.2–6.6 5.9	4.5–6.3 5.8	3.8–6.3 5.4	5.1–6.0 5.6
N (% DM)	0.6–3.8 1.4	0.5–2.3 1.2	0.1–2.3 0.6	0.4–4.6 1.6	1.6–2.8 2.2
S (% DM)	0.1–0.7 0.2	0.1–0.9 0.2	0.1–1.0 0.3	0.2–1.6 0.5	0.4–0.7 0.5
C/N	11.4–57.8 37.3	19.1–79.4 39.2	17.6–497.8 131.7	8.2–79.1 31.4	14.2–27.3 19.5
Cellulose-like (% VS)	25.8–60.9 39.0	11.2–52.3 27.1	15.4–33.6 27.4	13.6–35.0 23.4	8.7–26.4 17.3
Hemicellulose-like (% VS)	6.0–21.3 13.7	6.4–20.5 12.6	7.8–26.0 17.5	8.8–21.5 15.7	7.7–23.5 15.5
Lignin-like (% VS)	5.5–21.4 14.1	11.4–28.9 20.3	14.7–50.2 24.2	20.0–56.5 34.9	19.1–38.6 29.8
Proteins (% DM)	4.5–22.5 9.1	3.5–14.1 7.7	0.6–13.6 3.9	3.1–28.1 10.4	9.0–18.6 13.7
COD (g/g (CxHyOz))	1.2–1.5 1.3	1.2–1.7 1.3	1.2–2.8 1.4	1.2–2.0 1.4	1.0–1.8 1.5
Family	CER	ENSI	LCM	MAN	SLU
BMPth (Nm3 CH4/t VS)	407–469 434	410–582 449	400–920 466	397–659 466	320–568 483
BMP (Nm3 CH4/t VS)	250–336 300	187–461 324	63–330 251	132–366 237	224–551 362
BMP (Nm3 CH4/t FM)	56–278 164	41–169 78	23–254 167	13–178 75	10–54 35

with the main physicochemical parameter and methane potential values for the various substrate families investigated in this study. As previously discussed, the methane potentials ranged from 63 Nm³ CH₄/t VS (green waste) to 551 Nm³ CH₄/t VS (duck slurry), with a mean value for the 132 organic samples of 284 Nm³ CH₄/t VS.

To better understand the ability of the various organic wastes that were tested to be degraded in the AD process, a biodegradation yield (based on the ratio of the experimental and theoretical BMP) was calculated using the Buswell formula. The family biodegradation yields are presented in Figure 4.

A majority of families presented a good biodegradation rate, with means between 52 and 73%. Lower degradation rates of only 52 and 56% were reported for manure and lignocellulosic matter, respectively. As manure is a mixture of feces and bedding material, depending on the bedding material used and its concentration, it is not surprising to find similar results between these two families [47]. The biodegradability of organic substrates has been well-documented in the literature for various organic substrates [5,14,15,17,24]. Regarding lignocellulosic biomasses, Triolo et al. (2012) reported biodegradability indices of 32.7%, 39.9%, 44.9%, and 66.6% for wood cuttings, hedge cuttings, wild plants, and lawn cuttings, respectively. Similarly, Li et al. (2013) reported biodegradability indices of 51%, 54%, and 62% for corn stover, wheat straw, and rice straw, respectively. Similarly, Li et al. (2013) reported biodegradation rates of 10%, 63%, and 68% for dairy manure, chicken manure, and swine manure, respectively. Garcia et al. (2019) also reported biodegradability indices varying from 30% to 70% for different animal manures samples. Such lower biodegradation rates for LCM and MAN families can be explained by the higher fiber contents in such biomasses, especially lignin content, which is poorly degraded in the AD process [6,45]. The high nitrogen concentration in animal manures can also be a limiting factor of the expression of the methane potential [42].

In parallel, other families investigated in this study exhibited higher biodegradability rates of 69%, 72%, and 73% for cereal and agro-industrial residues, energy crops and silages, and slurries, respectively. Allen et al. (2016) reported biodegradability indices for sixteen silages from second-generation crops, and three-quarters of the samples exhibited biodegradation rates higher than 75%. Similarly, Garcia et al. (2019) reported biodegradabilities varying from 80% to 100% for various energy crops (i.e., millet, barley, maize, sorghum, and triticale). Garcia et al. (2019) also reported high biodegradabilities of 80% and 90% for flour and cereals. In terms of slurry samples, the results in the literature are more contrasted [5,15]. Indeed, biodegradabilities varying from 20% to 60% have been reported. Such variation can be explained by the difference in the origins of animal slurries as well as the storage duration and typology.

4. Discussion

At the end of 2018, annual production of biomethane from AD in the EU corresponded to 2.3 billion m³, with 18,202 biogas plants in operation [1]. Europe is the world leader in biogas electricity production, far ahead of the USA (2.4 GW) and China (0.6 GW) [1]. At the European level, the methanization sector will greatly develop in the years to come with projections up to 64.2 billion m³ in the EU by 2050; this would represent an energetic potential of approximately 640 TW h/year and would require a 30-fold growth of the current biomethane sector [1].

AD will continue to grow in the future, but it is clear that the sector should have better control of not only the management and the use of the deposits but also the identification of new sources of deposit. The BMP test remains an essential tool for characterizing new deposits and determining their pricing.

This publication and the results (Table 1) are intended to contribute to providing data to the scientific community and biogas developers regarding the values of methane potentials and biodegradability indices of different organic substrates and complete previous studies on the subject (

Table A3. Literature references of BMP performed on large samples, biogas production and biochemical characterization are indicated for each families of substrates. DM: dry matter; VS: volatile solids, HCell: hemicellulose, Cell: cellulose, COD: chemical oxygen demand, Prot: proteins, and BMP: biochemical methane potential.

Reference	N.	Sample Familly	Sample Description	DM	VS	HCell	Cell	Lignin	COD	Prot	BMP (mL CH4/g VS)
[14]	2	Manures	Dairy and Separated liquid manure	58–124 91 g/kg	41–102 71 g/kg	10% VS	32% VS	14% VS	71–129 100 g/kg	6% VS	243–261 252
	9	Food residue	Cheese whey, Plain pasta, Meat pasta, Used vegetable oil, Ice cream, Fresh dog food, Cola beverage, Cabbage, and Potatoes	71–991 274 g/kg	60–989 274 g/kg	0–0 0% VS	0–36 3% VS	0–0 0% VS	91–2880 642 g/kg	0–19 10% VS	216–649 390
	1	Switchgras	Switchgrass	930 g/kg	905 g/kg	42% VS	49% VS	8% VS	707 g/kg	1% VS	122
	1	Silage	Corn silage	217 g/kg	201 g/kg		12% VS		-	14% VS	296
[25]	20	Municipal solid wastes	Municipal solid wastes	94–99 97% RM	53–90 74% RM	-	-	ND–0.4 0.1 g/g VS	38–279 145 g/g VS	29–89 52 g/g VS	87–357 226
[26]	95	Grass	Meadow grass	51	288	-	-	-	-	-	406
[18]	204			295	329						355
[17]	9	Lawn cuttings	Meadow grass, Grass mixture, White clover, and Short bluegrass	-	-	22% VS	28% VS	6% VS	-	16% VS	298–404 333
	9	Hedge cuttings	Oval-leaved privet, Ivy, Beech hedge, Chokeberry, and Ground-elder	-	-	12% VS	28% VS	16% VS	-	12% VS	149–277 203
	16	Wood cuttings	Birch tree, Plane tree, Willow, and Cypress	-	-	12% VS	24% VS	24% VS	-	10% VS	138–245 177
	17	Wild plants	Northern bluegrass, Green foxtail, Bamboo, Common reed, Tufted hair-grass, Reed canary grass, Chrysanthemum, and Dandelion	-	-	24% VS	38% VS	10% VS	z	8% VS	106–319 227
	6	Crops	Maize, Wheat straw, and Sugar beet	-	-	30% VS	28% VS	4% VS	-	8% VS	223–479 404
[27]	58	Agro-industrial wastes	Solid food processing waste and non-conformed end products	-	4–99 52% DM	-	-	-	-	-	66–845 396
	1	Macroaglae	-	-	56% DM	-	-	-	-	-	238
	20	Biowaste	Household organic waste	-	3–88 42% DM	-	-	-	-	-	185–845 370
	4	Energy crops	Maize and switch grass	-	89–94 92% DM	-	-	-	-	-	211–370 264
	11	Fatty waste	Industrial sludge digester with fatty feedstock	-	0–29 13% DM	-	-	-	-	-	53–1321 475
	14	Meat waste	Slaughterhouse waste or stale meat	-	23–96 70% DM	-	-	-	-	-	172–594 475
	2	Co-digestion mix		-	83% DM	-	-	-	-	-	185
	66	Municipal solid wastes	Fresh wastes collected from different localisation and after different treatment	-	15–85 60% DM	-	-	-	-	-	26–423 211
	42	Plant and Vegetable	Wheat and barley residues, Potatoes, Tomatoes, etc.	-	42–95 81% DM	-	-	-	-	-	0–449 264
	18	Agro-industrial sludges	Sludges produced from agro-industrial WWTP	-	2–80 18% DM	-	-	-	-	-	0–687 317
	30	Sewage sludge WWTP	Different WWTP at different process steps (pre-treated or not)	-	11–84 66% DM	-	-	-	-	-	13–343 172
	31	Stabilised municipal solid waste	Landfill drillings	-	14–66 40% DM	-	-	-	-	-	0–264 132
[20]	14	Leaf	Reed canary grass	-	-	22–36 31% DM	16–29 26% DM	1–5 3% DM	-	-	321–388 352
		Steam	Reed canary grass	-	-	24–34 30% DM	21–41 35% DM	1–10 7% DM	-	-	283–417 344
[24]	3	Manures	Chicken, Dairy, and Swine manures	26–39 32% FM	20–29 23% FM	15–28 22% DM	11–20 17% DM	2–17 8% DM	-	13–20 17% DM	51–322 223
	3	Crops straws	Corn stover, Wheat straw, and Rice straw	85–93 89% FM	77–82 79% FM	25–30 27% DM	41–42 42% DM	8–11 10% DM	-	3–6 4% DM	241–281 256
	5	Food and green wastes	Kitchen waste, Fruit and vegetable, Used animal/vegetable oil, and Yard waste	4–100 60% FM	3–100 57% FM	0–20 7% DM	0–21 10% DM	0–11 5% DM	-	0–21 9% DM	183–811 531
	2	Processing organic wastes	Vinegar residue and Rice husk	90–92 91% FM	74–85 80% FM	18–33 26% DM	23–41 32% DM	12–20 16% DM	-	3–12 7% DM	49–253 151
	1	Energy crops	Switchgrass	91% FM	87% FM	32% DM	43% DM	11% DM	-	3% DM	246
	2	Lignocellulosic biomass	Chenopodium album leaf, seed, and stalk	84–86 85% FM	78–83 81% FM	17–19 18% DM	20–39 30% DM	8–16 12% DM	-	3–17 10% DM	171–262 217
[28]	88	All		-	87–96 92% DM	9–76 57% DM			-	-	104–502 251
[16]	18	Miscanthus	Miscanthus giganteus	-	-	25% DM	44% DM	9% DM	-	4% DM	263
	16	Switchgrass		-	-	33% DM	40% DM	7% DM	-	4% DM	213
	36	Spelt straw		-	-	31% DM	44% DM	7% DM	-	2% DM	275
	37	Fiber sorghum	Winter and Autumn	-	-	22–25 24% DM	33–42 37% DM	5–7 6% DM	-	4–7 5% DM	363–438 400
	369	Tall Fescue	Spring, Summer, and Autumn	-	-	22–25 24% DM	25–29 27% DM	4–4 4% DM	-	9–11 10% DM	400–425 408
	21	Immature rye		-	-	18% DM	22% DM	2% DM	-	9% DM	525
	73	Fiber corn	Winter and Autumn	-	-	2–4 3% DM	20–20 20% DM	18–18 18% DM	-	5–7 6% DM	313–400 356
[29]	23	Anaerobic sludges	Effluent from anaerobic digesters	-	-	-	-	-	-	-	32–214 73
	30	Standard compounds	Cellulose, Starch, and Gelatine	-	-	-	-	-	-	-	289–407 361
	50	Household wastes	Fruit and vegetable waste, Milk waste, Meat waste, and Co-digestion mixtures	-	-	-	-	-	-	-	214–900 461
	10	Agriculture wastes	Wheat straw, Bamboo waste, and Banana stem	-	-	-	-	-	-	-	139–300 224
	19	Sewage sludges	Primary and secondary Sludge and Co-digestion mixtures	-	-	-	-	-	-	-	171–429 353
	6	Lipid rich wastes	Butter and Oil wastes	-	-	-	-	-	-	-	793–943 891
[5]	6	Cereal crops	Barley, Wheat, Triticale, and Oats	54–69 62% FM	49–67 58% FM	-	-	-	-	-	281–366 336
	3	Oil seed rapes	Macerated, Whole crop, and Not macerated	88–93 91% FM	85–89 87% FM	-	-	-	-	-	215–646 393
	7	Root crops	Potatoes, Turnips, Sugar beet, Energy beet, and Fodder beet	11–26 19% FM	10–25 18% FM	-	-	-	-	-	306–399 349
	5	Grass silages	Grass silage and Fresh grass	12–29 19% FM	11–27 18% FM	-	-	-	-	-	368–400 385
	2	Baled silages	-	17–17 17% FM	15–16 15% FM	-	-	-	-	-	428–433 431
	8	Other grass substrates	Silage, Hay, Savazi grass, Silage effluent, Grass digestate, Fresh maize, and Maize silage	6–87 29% FM	3–82 27% FM	-	-	-	-	-	127–394 324
	7	Dairy slurries	-	6–9 7% FM	4–7 6% FM	-	-	-	-	-	136–239 201
	4	Other agricultural wastes	Beef slurry, Pig slurry, Poultry manure, and Farm yard manure	5–51 21% FM	4–30 14% FM	-	-	-	-	-	99–311 194
	4	Milk processing wastes	Sludges with or without dissolved air floatation	4–16 9% FM	3–9 7% FM	-	-	-	-	-	189–787 473
	4	Abattoir wastes	Mix, paunch content, and Sludges	13–20 17% FM	11–18 15% FM	-	-	-	-	-	166–404 286
	7	Miscellaneous wastes	Bakery waste, Brewing stillage, Grocery waste, Fish offal mix, Bread waste, Park and grass waste, and WWTP	9–66 32% FM	7–64 29% FM	-	-	-	-	-	247–592 396
	10	Domestic and commercial food wastes	Rural and urban food waste, Food wastes from canteens and restaurants, and Centralised collection centre combining the two types or not	22–95 37% FM	19–88 32% FM	-	-	-	-	-	274–535 329
	3	Alternative wastes	Recycled paper, Used cooking oil, and Grease trap wastes	27–100 72% FM	26–99 68% FM	-	-	-	-	-	254–805 434
	12	Seaweeds	9 brown & 3 green Seaweeds	13–78 23% FM	8–46 15% FM	-	-	-	-	-	101–341 213
[19]	24	Main and secondary crops	Sugar beet, Barley/ryegrass, Maize, Triticale, Marrow stem kale, Rye/triticale, Potatoes, Oat/forage Pea/false flax, Rye, Sundangrass, Forage sorghum, Rye/fodder vetch, Barley/turnip rape, Oat, Amaranth, Quinoa, Rapeseed, Sunflower, Forage pea, and Buckwheat	9–59 33% FM	81–97 92% DM	2–25 15% DM	3–37 27% DM	1–13 6% DM	-	4–19 9% DM	210–399 294
	10	Catch crops	Triticale, Barley, Rye, Landsberger mix, Sudengrass hybrid, Forage sorgum, Ryegrass, Phacelia, Fodder radish, and Buckwheat/phacelia	9–58 24% FM	73–96 90% DM	0–24 17% DM	24–34 30% DM	2–9 5% DM	-	5–26 11% DM	235–376 311
	4	Annual grass and legume mix	Ryegrass, Clover, Alfalfa clover, and Alfalfa	15–48 28% FM	85–93 90% DM	11–18 14% DM	26–29 28% DM	4–7 5% DM	-	7–20 14% DM	240–388 307
	5	Perennial crops	Tall wheatgrass, Countru mallow, Jerusalem artichoke, Miscanthus, and Cup plant	14–40 28% FM	85–97 90% DM	5–24 16% DM	28–42 33% DM	7–13 10% DM	-	4–15 9% DM	179–259 228
[30]	58	Solid manure		2–99% FM	1–92% DM	-	-	-	-	-	129–366 225
	7	Animal slurries				-	-	-	-	-	225–551 293
	3	Slaughterhouse waste				-	-	-	-	-	186–664 349
	16	Mix of AD feedstock				-	-	-	-	-	90–253 101
	6	AD digestats				-	-	-	-	-	214–405 304
	36	Grass and intermediate crops				-	-	-	-	-	191–444 304
	24	Cereals and crop residues				-	-	-	-	-	191–388 304
	26	Silages				-	-	-	-	-	186–495 338
[30]	38	Lignocellulosic plants				-	-	-	-	-	62–326 270
	15	Grape marcs				-	-	-	-	-	79–219 129
	3	Algae				-	-	-	-	-	146–169 165
	25	Food wastes and biowastes				-	-	-	-	-	96–518 338
	10	Sludges				-	-	-	-	-	56–776 259
	3	Effluents				-	-	-	-	-	225–281 276
	3	Fat and lipid wastes				-	-	-	-	-	596–878 630
	2	Products and wastes from meat				-	-	-	-	-	203–388 293
	2	Organic fraction of municipal waste				-	-	-	-	-	281
[21]	41	Energy crops	Barley, Clover, Cup plant, Grassland, Maize, Millet, Potatoes, Rye, Sugar beet, Sunflower, and Triticale	88–94 91% FM	79–89 85% FM	3–28 18% DM	5–39 27% DM	0–11 4% DM	-	4–20 9% DM	177–401 311
[22]	43	Grasses	Lolium perenne, Dactylis glomerata, Poa pratensis, and Fescuta pratensis	87–94 91% FM	78–88 84% FM	21–32 26% DM	20–36 29% DM	2–7 4% DM	-	6–20 11% DM	314–422 353
	18	Legumes	Trifolium pratense and Repens	88–93 90% FM	80–85 82% FM	3–22 11% DM	16–33 25% DM	5–9 7% DM	-	13–29 21% DM	265–346 301
[13]	2	Biowaste	Banana peel waste, Tomato waste, and	11% FM	83% DM	-	-	-	2 g O2/g VS	-	329
	1	Effluent	Winery wastewater	3% FM	65% DM	-	-	-	3 g O2/g VS	-	251
	10	Plants		?	?	?	?	?	?	?	111–379 229
	21	Vegetables		?	?	?	?	?	?	?	186–443 314
	24	Fruits		?	?	?	?	?	?	?	185–529 314
	7	Cereals		?	?	?	?	?	?	?	261–325 293
	12	Manures		?	?	?	?	?	?	?	154–325 211
	17	Diet		?	?	?	?	?	?	?	250–775 432
	10	Sludges		?	?	?	?	?	?	?	164–711 411
	4	Beverage wastewaters		?	?	?	?	?	?	?	250–593 411
	18	Organic fraction of municipal solid wastes		?	?	?	?	?	?	?	175–571 464
	8	Other		?	?	?	?	?	?	?	207–443 379
[23]	20	Sludges	10 primary and 10 bioglogical Sludges	5–46 21% FM	4–33 15% FM	-	-	-	1–2 2% VS	0–60 28 mg BSA/g VS	58–318 181

in Appendix B). In parallel, this study is intended to be a tool for the sizing, optimization, and operation of the biogas sector. All the data obtained for the different feedstocks are available in the Appendix A.

It could be interesting in the future to extend this work and to generate an overall synthesis of all the BMP values listed in the literature by taking into account the studies using a protocol based on the recommendations of interlaboratory guidelines carried out at the international level [10,34]. In parallel, the growing development of the biogas sector requires the mobilization of new resources and organic biomasses, and it will be interesting in the future to focus studies on the evaluation of the methanogenic potential of atypical biomasses (i.e., algae, paper sludges, biodegradable plastics, insect excrements, etc.). An extended open-source BMP database (based on BMP values validated by experts) could be very useful in the future in order to improve the biogas development as well as the monitoring of the energetic performances of biogas plants. Indeed, Holliger et al. (2017) compared methane production from BMPs with biogas production from the same organic materials in full-scale installations [48]. Holliger et al. (2017) highlighted that the measured weekly methane production accounted for 94.0 ± 6.8 and 89.3 ± 5.7% of the calculated weekly methane production for two biogas plants, respectively [48].

Short-term (i.e., 1–2 months), batch-mode anaerobic digestion tests, such as the biochemical methane potential (BMP) assay, are intended primarily to determine methane yields and the biodegradability of substrates [14]. Nonetheless, such testing may fail to truly predict the performance of full-scale anaerobic reactors. For this purpose, semi-continuous laboratory-scale experimental methods are complementary to chemical and BMP analysis. Semi-continuous flow reactors are designed to emulate the conditions of commercial-scale digesters and study their overall performance over time, taking into account co-digestion benefits and potential inhibition.

5. Conclusions

In this study, a characterization of 132 common agricultural feedstocks (shared in five families) was carried out in terms of physical properties and methane potentials. Of the various families investigated, manures and slurries exhibited the highest ash and protein contents (10.3–13.7% DM). A high degree of variability in terms of the C/N ratio was observed among the various families, with values ranging from 19.5% DM (slurries) to 131.7% DM (lignocellulosic biomass). In terms of biodegradability, lower values of 52% and 57% were reported for lignocelluloses biomasses, and manures due to their high content in fibers, especially lignin. The AD sector will continue to grow in the future, and such studies can be used as a reference for any operator/manager of units or public authority/financial provider in the future.