Quantifying and Mapping Biomass Resources in Ireland: A Holistic Assessment of Primary and Secondary Feedstocks

Abstract

European bioeconomy policies stress the need for responsible, efficient feedstock use and timely, comprehensive data on ecosystems and bioeconomic activities. This paper addresses the data gap by: (i) providing holistic county-level (sub-NUTS3) biomass maps for the Republic of Ireland (RoI), covering primary feedstocks (PFs) and secondary feedstocks (SFs, i.e., by-products and waste); (ii) identifying feedstock uses during the study period. In total, 221 feedstocks were mapped: 85 solid PFs (approx. 43 million tonnes dry matter (tDM) nationally) and 136 solid SFs (approx. 6 million tDM nationally), plus 6 liquid PFs (approx. 18 thousand million m³ nationally) and 8 liquid SFs (approx. 39 thousand million m³ nationally). The mapping indicates that environmentally sustainable bio-based value chains (BBVCs) requiring large amounts of solid or liquid SF should prioritise processing sites near major feedstock sources in the southeast and southwest of the RoI. The northwest and east coast have the lowest availability, while the west and midlands have the most variety in quantity and type of feedstock. Counties with abundant feedstocks do not necessarily have high feedstock diversity, except for Cork. Granular sub-NUTS3 mapping of quantities and fate provides a powerful foundation for future feedstock strategies and empowers stakeholders to design innovative BBVCs.

1. Introduction

The transition to an economically and environmentally sustainable Europe has been a priority for the European Commission (EC) since its first efforts to promote biotechnology research in the 1980s [1,2]. European strategies did not include the term ‘Knowledge-Based Bio-Economy’ until the early 2000s, as an effort to include other sectors of the economy under the science knowledge strategy umbrella [3]. This use of bioeconomy terminology was not strongly linked to environmentally sustainable concepts such as renewable biological resources or bio-based products until 2012, when the EC produced the first Bioeconomy Strategy 2012 [4]. It was broad in scope but was lacking interdisciplinary character. This was revised in October 2018, resulting in the ‘EU Bioeconomy Strategy’ [5], with a stronger focus on sustainability and planetary boundaries [6,7]. It focused on the key role of biological resources or feedstocks in various bioeconomy sectors, stressing the importance of timely and comprehensive data to accurately evaluate ecosystem conditions, such as land-use change and pollution [5,8,9], and to identify potential to develop bioeconomy activities. In November 2025, the new Strategic Framework for a Competitive and Sustainable EU Bioeconomy was released [10], defining actions for the ‘responsible and efficient use of biomass’, such as financing R&D to study biomass supply and demand innovations and improve methodologies, and modelling for assessing sustainably sourced biomass availability, its cumulative impacts and the provision of ecosystem services.

The circular bioeconomy provides sustainable ways to support the adaptation to and mitigation of climate change and reduce dependence on fossil fuels and polluting chemicals and materials. To support the circular bioeconomic conversion of biomass from agriculture, forestry, fisheries, and aquaculture into food, materials, products, as well as bioenergy (biomethane and/or combustion of biomass) to generate heat and electricity, minimising waste, maximising resource efficiency (i.e., biomass or feedstocks), and closing material loops within economic systems are needed [11,12,13].

Therefore, to balance economic development with biomass extraction and avoid further environmental crises, it is necessary to examine biomass availability in detail as well as the source of the biomass (waste, by-product, main raw materials, etc.) to ensure its sustainable supply within a circular economy, i.e., keeping it in use for as long as possible, preserving its value, and minimising waste generation [14,15,16].

In this context, Ireland has been working towards a balanced circular bioeconomy by incorporating by-products from processing activities, thus making valorisation economically feasible in terms of both the quantity and quality of biological resources [17]. The Irish Bioeconomy Forum [18] highlights that to develop markets and competitiveness in the circular bioeconomy framework, scenario analysis is required for ‘the development of bio-based products (...) and to quantify the opportunities in the bioeconomy in an economic sense’ [18]. Resource quantification is also mentioned by the 2023–2025 Irish Bioeconomy Action plan, stating the need to capture the flow of materials in the Irish economy [19]. Bio-based resources are plentiful in Ireland, representing a key advantage for bioeconomy development, driven by its substantial agricultural sector (occupying two-thirds of the land) and a leading agri-food industry contributing 5.7% to GDP. Forests cover 10.7% of the country and are projected to produce 8 million m³ of forest annually by 2035. Additionally, Ireland’s vast seabed, 10 times its landmass, generated a turnover of €6.5 billion and a direct economic value of €2.72 billion, which constitutes 0.9% of GNI [20,21]. Utilising by-products or waste materials from primary production, instead of primary products, as feedstocks to diversify outputs for the development of bio-based value chains (BBVCs) could, on the one hand, improve local economic development and GDP, enhance market performance, and help identify socio-economic outcomes [22], while, on the other hand, lowering environmental risks as by-products or wastes produce no, or only minimal, upstream production burdens [23].

Developing bio-based products and services requires detailed knowledge of resource availability. Currently, researchers, industry players, and policymakers rely on traditional national statistics to assess emerging BBVC potential. However, traditional national statistics often lack the granular details or update frequency needed for regional decision-making in a rapidly evolving circular bioeconomy. Existing mapping studies partially address this gap and specific studies have arisen (

Table 1. Comparison of mapping projects, activities and available information. N/A: not applicable. N.d.: no data.

Name	Resolution	Country (s)	Number of Feedstocks	Primary Feedstocks	Secondary Feedstocks	Uses/Fate
CAFIPLA project [24]	NUTS0 to NUTS3	EU-27	13	N/A	Urban waste, Agriculture, Industry	N/A
S2Biom project [25]	NUTS3	EU-28	50	Forest biomass	Agriculture, Forestry, Perennial crops and other biowastes	Yes
Zero Waste Scotland [27]	NUTS0	1	n.d.	N/A	Waste materials, Industry by-products, Agricultural crop residues, Sewage sludges	Yes
Central Statistics Office of Ireland [29]	NUTS0 to NUTS3, sometimes Below NUTS3	1	N/A	Agriculture, Forest, Industry, Flow of materials	N/A	Yes (data type specific)
ICT-BIOCHAIN project [26]	Below NUTS3	2 (26 counties + 8 provinces)	20	Forest biomass	Lignocellulose, Horticulture, Manure, Olive, Algae	Yes
This study (InformBio project [30])	Below NUTS3	1 (26 counties)	221	Grass Livestock (meat and milk-derived products) Energy crops and plants Forestry Tillage Horticulture Pulses Marine	Manure Forestry Straw from tillage Other secondary feedstocks from tillage Slaughterhouse arisings from livestock Horticulture Pulses Drink industry and organic waste Marine Energy crops and plants	Yes

), such as that by Günther, et al. [24], who mapped 13 residue types from municipal waste, agricultural by-products, and industrial residues from NUTS0 to NUTS3 for 27 EU countries, not including primary feedstocks; Panoutsou, et al. [25], who covered 50 feedstocks from agriculture, forestry, perennial crops and other biowastes at NUTS3 level for 28 countries in the EU, focusing on lignocellulosic biomass; or Attard, et al. [26] and Zero Waste Scotland [27], who reported biomass arisings below NUTS3 level, but for fewer than 20 feedstocks each. Although these studies achieve NUTS3 or below and some cover primary feedstocks, they lack a broad range of feedstocks as they span many countries and, while some [25,26,27] include information on current feedstock uses, it is either only at national scale or limited by the small number of feedstocks covered. Nationally, in Ireland, there are initiatives such as BioMap [28], which maps businesses in the RoI and Northern Ireland, detailing their locations and type of feedstock processed, although no quantities are disclosed publicly. There is also the Central Statistics Office (CSO) [29], which collects and displays primary feedstock quantities from agriculture, forestry, material flows, industry, etc., at national and, in some cases, at below NUTS3 level.

Therefore, through the InformBio project [31], this study tries to address this gap to quantify, characterize and map a wide range of Ireland’s regional feedstocks for use within the bioeconomy across 26 counties, including fate of feedstocks [26,27,32,33], by: (1) providing a holistic biomass mapping exercise in Ireland at county level (a level under NUTS3, i.e., the administrative sub-divisions or Local Authority Areas of Ireland [34]), from both primary and secondary (i.e., by-products and wastes) biomass availability [35]; and (2) to provide current uses of biomass, i.e., biomass fates, to assess its availability. These data can underpin the development of BBCVs by providing sufficient data for future BBVC feedstock (primary and secondary) environmental assessments, enhancement of secondary feedstock use, and overall reducing the upstream environmental burdens, helping to develop more sustainable bio-based products and services.

2. Materials and Methods

Definitions of the terminology used in this study are provided in

Table 2. Definitions of terminology.

Name	Definition
Feedstock	A raw material that goes into a process or plant as input to be converted into a product [36]. Biomass regardless of its value (waste, by-product, co-product, input, output) is considered feedstock.
Primary feedstock	Biomass for which agriculture crops, silviculture fields, fish or livestock are grown, caught or raised. Moreover, biomass used as input for industrial or other processing to generate main products. Examples of primary feedstocks are grains, meat, dairy, timber, beverages, etc.
Secondary feedstock	Biomass that is obtained from a production process that does not aim to produce this form of biomass as a primary product. Secondary feedstocks can be grouped into by-products, co-products, and waste. Examples are straw or barley spent grain from brewing
Category	The classification of sub-sectors associated per raw material.
Material	A raw material considered a feedstock. The detail of the types of materials studied can be found in Appendix A.
Fate	The current use of the outputs of a process. It applies to both primary and secondary feedstocks. Feedstocks may have several uses; therefore, fate is provided in proportions (%).
Forest biomass generated naturally	Secondary feedstocks generated from the trees and that do not necessarily result from processing within the wood industry, e.g., needles/leaves, branches, bark, stumps, roots, cones, etc., as opposed to the timber itself, which is considered primary feedstock.
Forest processing feedstocks	Secondary feedstocks from the wood industry.
Harvested forest feedstocks	Primary feedstock collected from forests by thinning or felling from the timber production

. Primary feedstocks (PFs) and secondary feedstocks (SFs) were quantified for Ireland, at county level (where possible). The sectors covered are in Section 2.1. A series of expert interviews (ca. 40 interviews with Irish experts from different agriculture systems and the livestock, forestry, marine, dairy, meat, brewery and distillery sectors) was conducted to obtain information on feedstock fates (see [30] for further information) following an ethics screening/minimal risk methodology to protect interviewees’ personal data and to ensure only aggregated information is published. In case this was not possible, fates were calculated (see Section 2.2).

2.1. Mapping of Irish Feedstocks

The methodologies applied for the quantification and mapping at county-level of Irish feedstocks varied by sector and feedstock type. Quantities of solid primary feedstocks (PF—solid) per county were collated from primary sources or estimated following already developed methods (e.g., [37,38]) or transforming data from key reports and databases such as the Census of Agriculture 2020 from the CSO of Ireland [39], PastureBase Ireland [40], Ireland’s Nitrates Action Program [41], etc., to calculate, for instance, crop and grass production, utilising their yields and hectares, or animal meat, utilising the number of animals slaughtered, the carcass weights per animal and percentage of the meat per carcass.

To quantify solid secondary feedstocks (SF—solid), estimates were made using proportions based on the PF—solid weights, production quantities, and the process in which they arise and then applied to the mass of PF—solid to obtain the estimated tonnes of the SF—solid. Information on proportions of SF—solid was based on data collected from the scientific and grey literature, as well as interviews with key sectoral experts [30]. To unify units, dry matter (DM) proportion (%w/w) was applied to the feedstocks estimated in fresh weight, whenever possible. For liquid primary feedstocks (PF—liquid) and liquid secondary feedstocks (SF—liquid) (dairy and drink industry), a similar approach was followed. A summary of the methods adapted for each feedstock is provided in

Table 3. Methods to estimate the quantification of biomass by sector in Ireland.

Sector	Origin of Biomass	Type of Feedstock	Method	References	Replicability in Other Countries
Agriculture	Arable crops, horticultural crops, energy, and other crops	PF	Multiplication of the national yields (tDM/ha) of the crop by the hectares available for each crop per county.	[42,43,44,45,46,47,48,49,50,51,52,53,54,55,56,57]	Yes, providing yields data and crop hectares data are available at the desired resolution.
		SF	Proportions of each secondary feedstock were gathered from the literature and stakeholder interviews. These were used to estimate secondary feedstock quantities based on primary feedstock quantification per county.	[58,59,60,61,62,63,64,65,66,67,68,69,70]	Proceed with caution. Proportions from interviews are only applicable to Irish context. See Appendix B for detail.
	Rushes	PF	Multiplication of yield (tDM/ha) by hectares of GLEY soil per county.	[71,72,73]	Proceed with caution. Proportions from interviews are only applicable to Irish context. See Appendix B for detail.
	Grass and the potential surplus of grass	PF	Estimation of grass production on pasture and silage land and the proportion used by cattle. Grass and pasture production was estimated using an adapted methodology from XD Consulting [37]. Only the first cut of silage was considered in this study. To estimate the proportion used by cattle, the methodology of McEniry et al. [38] was applied.	[37,38,74,75,76,77,78,79]	Proceed with caution. Irish-specific method relying on Irish reference data. It is recommended to adapt the method to the characteristics of each country.
	Livestock on the farm (manures and slurries)	SF	Animal head per county was used to estimate the average production of slurry or manures produced by each type of animal studied. For cattle and sheep, housing days and proportion of stored manure was applied. For cows, housing days and slurry storage was calculated using the Statutory Instruments Regulations for 2022 (S.I. No. 113 of 2022) [80], from Ireland’s Nitrates Action Program [41]. For pigs, national tonnes of manure produced, and livestock head numbers was applied. For chicken Thia Hennessy [81] report was used to extract approx. yearly tonnes of manure.	[41,80,81,82,83,84,85,86,87,88,89,90,91]	Yes, providing head count, housing days, and proportion of slurry/manure/animal data are available at the desired resolution.
	Food loss and waste	SF	Food loss and waste (FLW) proportions up to farm level were calculated following Attard et al. (2022) [58] in combination with the production numbers calculated for arable crops, horticultural crops, energy, and other crops as primary feedstocks in Ireland. Additionally, national Irish municipal solid waste and other organic wastes information from 2021 was obtained from the EPA National Waste Statistics [92].	[58,92]	Proceed with caution. Irish-specific method relying on Irish reference data. It is recommended to adapt the method to the characteristics of each country.
Forestry	Forest biomass	PF	National Forest Inventory (NFI) total growing stock volume (m3) data per species group and county [93] was used to estimate tDM of harvested forest primary feedstock for selected species [94] by dividing it by the national mean annual harvested standing volume (m3) by species group data [95].These species-group proportions were then applied uniformly to each county’s growing stock to estimate harvested volume (m3) per species group and county. Then, estimated harvest volumes (m3) were transformed to tDM of forest feedstock per county by obtaining NFI data on tonnes of carbon stock by county and carbon pool (tree aboveground, tree belowground, deadwood, litter, soil) and multiplying the carbon pool data by two as described in the NFI Field Procedures and Methodology [96].	[93,94,95,96]	Proceed with caution. Irish-specific method relying on Irish reference data. It is recommended to adapt the method to the characteristics of each country.
	Forest biomass generated naturally	SF	Weight proportions of different types of needles/leaves, branches, barks, roots, stumps, and cones per species were identified from the literature and applied to the estimated harvested tDM.	[97,98,99,100,101,102,103]	Yes, providing forest biomass data are available at the desired resolution.
	Forest processing industry	SF	Factors obtained from the COFORD 2018 report [104] were used to estimate secondary feedstocks quantities, including bark, sawdust and woodchip from the 2020 total wood removals (CSO “Forest Wood Removals” database [105])	[104,105]	Proceed with caution. Irish-specific method relying on Irish reference data. It is recommended to adapt the method to the characteristics of each country.
Animal Industry	Meat industry biomass	PF	The approach assumed that meat production starts at slaughterhouse level, hence, the number of livestock slaughtered by county was used to estimate meat quantities generated in Ireland. To quantify the tonnes of meat produced by type of livestock, the animal weights, carcass weights and percentage of the meat per carcass were obtained.	[84,85,106,107,108,109,110,111,112,113,114,115,116]	Yes, providing number of livestock slaughtered data are available at the desired resolution.
		SF	The national fifth-quarter production from slaughterhouses was estimated and classified as co-products, red offal, white offal, and categories 1–3 under relevant regulations [117,118]. Edible and inedible carcass shares by animal type, animal weight, average carcass weight, and meat share in the edible carcass were compiled from the literature. Appendix B and Appendix C delve into the details of the calculations of these feedstocks.	[106,107,108,112,113,114,115,116,117,118,119,120,121,122,123,124,125,126]	Yes, providing number of livestock slaughtered data are available at the desired resolution.
	Dairy industry biomass	PF	Raw milk production per county was estimated by multiplying dairy cattle numbers by average milk yield per cow. Milk intake per county was assessed using the Board Bia directory and interviews to identify the 8 largest processors by county, with their annual intake inferred from company websites. Dairy product production per county was estimated using total milk intake percentage from Eurostat national data [127], corroborated with Eurostat’s “Milk collection and dairy products data” [128] and CSO “Dairy Products Production” data [129].	[79,127,128,129,130,131]	Proceed with caution. Irish-specific method relying on Irish reference data. It is recommended to adapt the method to the characteristics of each country.
		SF	Dairy secondary feedstocks have been estimated through interviews with Teagasc and International Dairy Federation representatives as well as Eurostat [128] data for dairy wastes. Dairy wastewater from dairy industries was also calculated using the 2013 EPA report “The Characterisation of Dairy Waste and the Potential of Whey for Industrial Fermentation” [132].	[58,120,128,132]	Proceed with caution. Irish-specific method relying on Irish reference data. It is recommended to adapt the method to the characteristics of each country.
	Other animal biomass	PF	To estimate the eggs laid per county the national total in Ireland, and the county-level laying stock numbers [133,134] were used assuming equal egg production per stock. The eggs per county were then multiplied by an average egg weight of 63 g [135]. To calculate the national and per county wool volume, Gillespie et al.’s (2022) methodology [136] was followed.	[86,121,134,135,136]	Yes, providing laying stock data are available at the desired resolution.
		SF	Egg loss and eggshell weight was obtained from the literature, and a ratio was applied to the egg weight estimate to quantify the arising of egg waste. Wool loss proportion was obtained from DAFM’s report [121] and applied to the calculated volume.	[58,121,125]	Yes, providing laying stock data are available at the desired resolution. Proceed with caution with wool loss proportion as this followed an Irish-specific method relying on Irish reference data. It is recommended to adapt the method to the characteristics of each country.
Drink Industry	Beer industry	PF	Litres of beer produced was estimated per county and size of brewery in Ireland. The size, number and county location of breweries was obtained from online directories. Beer production was estimated using Board Bia’s report [137] and applying a growth factor from Umego and Barry-Ryan’s data [138].	[137,138,139,140,141,142,143]	Irish-specific method relying on Irish reference data. It is recommended to adapt the method to the characteristics of each country.
		SF	Brewer Spent Grain (BSG) was calculated using proportion for BSG per 100 L of beer from the literature.	[144]	Irish-specific method relying on Irish reference data. It is recommended to adapt the method to the characteristics of each country.
	Spirits industry	PF	Interviews identified three major distilleries in Ireland, detailing locations and production capacities. The distillery map by whiskeys.ie and official websites, along with the Irish Whiskey Booklet [145], helped estimate their sizes and production. Umego and Barry-Ryan [138] report was used to finalize Litres of Pure Alcohol (LPA) production estimates per scale.	[138,145]	Irish-specific method relying on Irish reference data. It is recommended to adapt the method to the characteristics of each country.
		SF	Secondary feedstock proportions were calculated in two ways; over total LPA production and over material input, using the literature case studies as reference [146].	[146]	Irish-specific method relying on Irish reference data. It is recommended to adapt the method to the characteristics of each country.
	Cider industry	PF	Cider production in Ireland was quantified using the Irish Cider Market Report (2020) [147], the locations and production volumes of 12 craft cider producers [148,149] and 2 industrial producers [150,151] was utilised.	[147,148,149,150,151]	Irish-specific method relying on Irish reference data. It is recommended to adapt the method to the characteristics of each country.
		SF	Interviews and literature review revealed the proportion of dry fibre/pulp from apple and the ratio of apples used per 10,00 litres of cider.	[58,148,152]	Irish-specific method relying on Irish reference data. It is recommended to adapt the method to the characteristics of each country.
Marine	Finfish and shellfish	PF	The Bord Iascaigh Mhara (BIM) annual aquaculture 2022 report [153] and Ireland’s Marine Atlas [154], with GIS data were used to estimate production by county.	[153,154]	Irish-specific method relying on Irish reference data. It is recommended to adapt the method to the characteristics of each country.
	Aquaculture cultivation of seaweeds	PF	Ireland’s Marine Atlas and the BIM review of the Irish seaweed aquaculture sector and strategy for its development to 2030 [155] were used to quantify seaweed cultivation (wet tonnes) in Ireland.	[155,156]	Irish-specific method relying on Irish reference data. It is recommended to adapt the method to the characteristics of each country.
	Landings of finfish and shellfish	PF	The landings of finfish and shellfish were identified via direct consultation with the CSO [157].	[157]	Yes, providing landing data are available at the desired resolution.
	Seaweed harvesting	PF	The 2022 Socio-Economic Study of Seaweed Harvesting in Ireland report [158] was used to obtain wet tonnes of seaweed harvested in Ireland.	[158]	Irish-specific method relying on Irish reference data. It is recommended to adapt the method to the characteristics of each country.
	Finfish, shellfish and crustacean	SF	The processing destination was identified, followed by the quantity of species destined for said processing, or if otherwise, it was not processed at all, and finally, which types of secondary products and its proportions were generated per each processing type.	[159,160,161,162,163]	Yes, publicly available national-level data and proportions were utilised.

, clarifying the applicability of these to other countries as some of these methods could be transferred providing similar data availability can be found for other countries; Appendix B describes these methods in depth.

2.2. Fate of Irish Feedstocks

Estimates of fractions of available biomass used for different purposes were made based on various data sources listed below and stakeholder interviews. Appendix D details in-depth methods used to estimate biomass fate, i.e., fate estimations for harvested forest feedstocks using adjusted wood flow proportions from COFORD study [104] and CSO “Forest Wood Removals” statistics [105]; fate estimations of dairy products using CSO intake statistics [127] and Eurostat data [128]; fate estimations of meat and dairy wastes using the EPA GeoPortal website (2015 version updated in 2021) [72], the European Pollutant Release and Transfer Register [164], the EPA licenses website [165], and the EPA waste classification [166]; and the fate estimations of marine species destined for processing/industry using the FAOSTAT destock app FishstatJ app (Version 4.03.05 from 2023) [167], as well as the Socioeconomic Study of Seaweed Harvesting in Ireland [158].

2.3. Analysis

For the quantification analysis at county level (

Table 4. Counties and regions analysed along with their respective province.

County	Region	Province
Carlow	Southeast	Leinster
Cavan	Midlands	Ulster
Clare	West	Munster
Cork	Southwest	Munster
Donegal	Northwest	Ulster
Dublin	East coast	Leinster
Galway	West	Connacht
Kerry	Southwest	Munster
Kildare	East coast	Leinster
Kilkenny	Southeast	Leinster
Laois	Midlands	Leinster
Leitrim	Northwest	Connacht
Limerick	Southwest	Munster
Longford	Midlands	Leinster
Louth	East coast	Leinster
Mayo	West	Connacht
Meath	East coast	Leinster
Monaghan	Midlands	Ulster
Offaly	Midlands	Leinster
Roscommon	West	Connacht
Sligo	Northwest	Connacht
Tipperary	Southeast	Munster
Waterford	Southeast	Munster
Westmeath	Midlands	Leinster
Wexford	Southeast	Leinster
Wicklow	East coast	Leinster

), as non-normal feedstock quantity distributions with heavy-tailed behaviour were observed after descriptive analysis (skewness ranged from 0.945 ± 0.456 to 4.906 ± 0.456 (median 2.133 ± 0.456), while kurtosis ranged from 0.702 ± 0.887 to 24.542 ± 0.887 (median 4.904 ± 0.887)), non-parametric Tukey’s Hinges percentiles (25%, 50% and 75%) [168] were utilised to classify counties as high, intermediate, and low-feedstock zones in terms of quantity. IBM SPSS Statistics (Version 30) was used for the descriptive analysis.

2.4. Limitations of the Study

This study compiles methods to estimate feedstock availability in Ireland and that could be adapted to other EU countries, providing availability of similar data at the desired resolution. These estimations provide theoretical availability rather than technically, economically or legally recoverable feedstocks, but for the overview of the regulations for meat by-products and wastes and classification of these according to EU regulations, indicating potential utilisation. However, the majority of these methods inherently introduce uncertainty to quantifications in the mapping, brought by variability in conversion factors, single year data availability (e.g., grass), unavailability of certain data (e.g., methods for dairy and drink industries), thus the interpretation of results should therefore be approached with caution. The compiled estimates are intended to support future research and project planning, while recognising that the highest level of certainty can only be achieved through on-site observations that account for seasonality, logistic constraints, other competing uses, etc., and through assessments of the technical, economic and regulatory and policy factors that determine actual availability.

3. Results

3.1. Mapping of Studied Irish Feedstocks

3.1.1. Total Irish Feedstocks at National Level

From the vast number of feedstocks available in Ireland, a starting number of 252 distinct feedstocks were investigated. To standardize the results, it was necessary to quantify feedstocks in terms of DM content. For cases where DM factors were unknown (45 feedstocks), those feedstocks were excluded from the data, leading to a final count of 207 feedstocks represented in tonnes of DM (tDM). Moreover, a total of 14 liquid feedstocks (m³) were incorporated as well, bringing the overall count to 221 feedstocks.

Approximately 49 million tDM of total solid feedstocks studied were identified in Ireland. This included approximately 43 million tDM of PF and 6 million tDM of SF across all sectors. In parallel, liquid feedstocks identified totalled to around 58 billion m³, consisting of around 18 billion m³ of PF and approximately 39 billion m³ of SF. Overall, 85 PFs and 136 SFs were mapped. See

Table 5. Estimated quantities of feedstocks (tDM) with types and categories details.

Physical State of Feedstock	Type of Feedstock	Category of Feedstock	Estimated Arisings (tDM)	Total (tDM)
Solid	PF	Grass	27,051,322	43,671,711
		Livestock (meat and milk-derived products)	6,224,152
		Energy crops and plants	3,837,687
		Forestry	3,669,809
		Tillage	2,517,547
		Horticulture	244,103
		Pulses	64,013
		Marine	63,078
	SF	Manure	2,153,066	6,219,221
		Forestry	2,212,664
		Straw from tillage	1,162,243
		Other secondary feedstocks from tillage	250,956
		Slaughterhouse arisings from livestock	177,794
		Horticulture	163,037
		Pulses	32,152
		Drink industry and organic waste	45,904
		Marine	16,816
		Energy crops and plants	4590
Solid feedstocks total (tDM)				49,890,932
Physical state of feedstock	Type of Feedstock	Category of Feedstock	Estimated arisings (m3)	Total (m3)
Liquid	PF	Drink industry	850,060,000	18,502,893,200
		Dairy industry	17,652,833,200
	SF	Drink industry	1,725,926,982	39,671,552,749
		Dairy industry	37,945,625,766
Liquid feedstocks total (m3)				58,174,445,949

for detailed quantification regarding feedstock types and categories.

3.1.2. Total Irish Feedstocks at County Level

Analysis have identified that out of the six counties with the largest volumes of solid and liquid feedstock across the nation, five are in the southwest and southeast.

Four out of six counties identified as having intermediate amount of total solid feedstocks (SF—total) are in the west and southeast. Five out of seven counties identified as having an intermediate amount of total liquid feedstock (LF—total) are in the east coast and southeast.

In contrast, eight counties in the midlands and the east coast with the lowest amounts of SF—total, and 10 counties with the lowest amounts of LF—total are also found in those regions (

Table 6. Regional distribution of total solid and liquid feedstock quantities in the Republic of Ireland.

Feedstock Type	Feedstock Quantity	Regions
Total Solids	High quantity	Southeast and southwest
Total Solids	Intermediate quantity	West and southeast
Total Solids	Low quantity	Midlands and east coast
Total Liquids	High quantity	Southeast and southwest
Total Liquids	Intermediate quantity	Southeast and east coast
Total Liquids	Low quantity	Midlands and west

).

In other words, Co. Cork, Kilkenny, Tipperary, Limerick, Kerry and Galway were identified as having high quantity of SF—total, with approx. 7.1, 3.9, 3.8, 3.6, 2.7 and 2.3 million tDM respectively. Seven counties (Co. Meath, Wexford, Mayo, Cavan, Clare, Waterford and Donegal) were identified as having intermediate quantity with approx. 2.2, 2.0, 1.99, 1.96, 1.6, 1.5, 1.4 million total tDM respectively. In comparison, the remaining 13 counties were identified as having low quantity of SF—total, being at the bottom of the list Co. Dublin, Longford and Louth with approx. 479, 638 and 673 thousand tDM respectively. This is visualised in the colour graduated county-level maps from Figure 1.

With regards to LF, Co. Kilkenny, Cork, Cavan, Kerry, Tipperary and Limerick were those identified with high quantity of LF—total, with approx. 16.5, 11.8, 10.8, 5.9, 3.39, 3.36 thousand million m³, respectively. Counties Sligo, Waterford, Wexford, Meath, Louth, Laois, and Dublin were identified with intermediate quantity with approx. 2100, 524, 481, 396, 355, 284, 267 million m³, respectively. The remaining 13 counties were identified as low quantity of LF—total. with Co. Leitrim, Co. Roscommon and Co. Longford LF—total at the bottom with approx. 18, 50 and 67 million m³, respectively.

At county level, the ratio of SF—solid to SF—liquid volume (Figure 1) has a mean of 0.17% with a standard deviation (SD) of 0.06%. For SF—liquid this ratio is 0.85 with a SD of 1.30. The following subsections provide details on the quantities and types of both primary and secondary feedstocks studied in each county in Ireland.

3.1.3. Primary Feedstocks at County Level

Counties in the southwest and southeast were identified as having high quantity of PF—solid (five out of seven counties), and PF—liquid (five out of six counties). Counties identified as having intermediate quantity for PF—solid were those in the midlands and west (four out of six counties) and for PF—liquid, the southeast and the east coast (four out of seven counties). The midlands and northwest were identified as having low quantity of PF—solid (seven out of 13), and the midlands and the west for PF—liquid (

Table 7. Regional distribution of primary solid and liquid feedstock quantities in the Republic of Ireland.

Feedstock Type	Feedstock Quantity	Regions
Primary Solids	High quantity	Southeast and southwest
Primary Solids	Intermediate quantity	Midlands and west
Primary Solids	Low quantity	Midlands and northwest
Primary Liquids	High quantity	Southeast and southwest
Primary Liquids	Intermediate quantity	Southeast and east coast
Primary Liquids	Low quantity	Midlands and west

).

In other words, Co. Cork, Kilkenny, Limerick, Tipperary Kerry, Galway and Meath were identified as having high quantity of PF—solid, with approx. 6.3, 3.7, 3.4, 3.3 2.4, 1.98 and 1.93 million tDM, respectively. Counties Cavan, Wexford, Mayo, Clare, Waterford, and Laois were identified as having intermediate quantity of PF—solid, approx. 1.8, 1.7, 1.6, 1.4, 1.3 and 1.2 million tDM, respectively. The rest 13 counties were identified as low quantity of PF—solid, with Co. Dublin showing the lowest PF—solid arisings with 367 thousand tDM (Figure 2). In Appendix E,

Table A22. Estimations of quantifications on primary feedstocks (PFs) in tonnes dry matter (tDM) by county and category. No data: “- “.

County	PFtDM_Energy	PFtDM_Forestry	PFtDM_Grass	PFtDM_Horti	PFtDM_Livestock	PFtDM_Marine	PFtDM_Pulses	PFtDM_Tillage	Total
Carlow	131,291.49	33,983.24	433,710.65	17,063.43	3064.70	-	4333.40	140,963.76	764,410.6
Cavan	253,796.34	75,712.07	1,048,713.65	1047.89	429,434.84	-	89.07	311.94	1,809,105.7
Clare	173,255.61	258,387.59	979,093.20	217.92	2480.67	26.72	-	798.20	1,414,259.9
Cork	467,550.00	450,791.55	3,987,713.02	43,103.24	1,049,632.02	6968.24	5420.79	352,138.01	6,363,316.8
Donegal	172,384.52	228,107.39	726,994.92	6259.80	5420.36	46,710.95	-	36,762.16	1,222,640.0
Dublin	111,196.31	35,670.84	89,008.63	14,594.12	673.30	951.35	6263.41	108,693.39	367,051.3
Galway	52,243.79	308,478.79	1,589,450.85	5240.35	7189.34	1437.89	42.49	23,295.17	1,987,378.6
Kerry	324,632.69	243,121.63	1,182,301.65	1633.43	692,990.99	2589.43	23.74	17,396.43	2,464,689.9
Kildare	76,985.52	24,751.03	453,129.35	9201.73	5191.51	-	6858.62	255,808.64	831,926.4
Kilkenny	120,133.92	92,849.39	1,275,571.13	13,951.58	2,073,924.48	8.31	2112.51	125,432.41	3,703,983.7
Laois	60,950.87	145,340.28	886,728.08	16,618.96	6427.32	-	2078.81	127,457.04	1,245,601.3
Leitrim	172,572.70	154,860.60	316,214.30	6.83	979.48	-	-	-	644,633.9
Limerick	308,499.25	136,548.57	1,722,490.92	441.32	1,308,827.86	-	63.92	8462.12	3,485,333.9
Longford	138,996.32	46,704.90	377,694.45	44.74	2162.02	-	6.06	3130.33	568,738.8
Louth	19,998.61	3654.37	345,847.56	10,954.69	3865.02	441.77	3477.11	159,042.04	547,281.1
Mayo	166,137.74	301,156.54	1,222,403.79	927.56	5227.83	1499.61	-	1360.24	1,698,713.3
Meath	207,636.53	23,108.84	1,367,341.55	22,887.16	8951.95	-	8488.44	298,037.67	1,936,452.1
Monaghan	96,970.06	13,256.87	819,964.00	2990.50	23,676.80	-	0.71	3812.24	960,671.1
Offaly	18,709.54	100,701.62	960,866.67	9309.46	5514.27	35.70	1508.47	75,874.84	1,172,520.5
Roscommon	70,435.65	161,610.56	814,274.94	1279.05	4533.27	-	50.29	3013.62	1,055,197.3
Sligo	95,791.15	137,007.50	426,908.90	181.76	277,320.96	6.69	-	495.04	937,712.0
Tipperary	145,781.91	227,459.99	2,523,579.59	14,658.50	288,611.56	11.04	3305.51	179,414.30	3,382,822.4
Waterford	137,683.13	119,081.50	970,836.47	8158.08	5298.31	1154.29	788.71	73,033.89	1,316,034.3
Westmeath	23,848.08	48,263.15	1,001,974.25	2786.95	4664.55	-	2155.51	43,640.82	1,127,333.3
Wexford	139,570.19	78,859.15	1,078,971.59	33,556.91	5426.61	1202.42	14,740.47	375,230.27	1,727,557.6
Wicklow	150,635.09	220,341.20	449,537.55	6987.41	2661.77	33.52	2204.82	103,942.46	936,343.8

displays estimated quantities of PF—solid.

Regarding PF—liquid (Appendix E,

Table A24. Quantification of primary feedstocks (PFs) and secondary feedstocks (SFs) in m³ by county and category. No data: “- “.

County	PFm3_Drink Industry	PFm3_Dairy	SFm3_ Drink Industry	SFm3_Dairy	Totals
Carlow	952,256.28	101,646,000.00	7,553,000.00	-	110,151,256.280
Cavan	-	2,221,927,100.00	-	8,623,421,815.17	10,845,348,915.170
Clare	1,304,512.56	197,080,300.00	8,134,000.00	-	206,518,812.560
Cork	308,148,569.60	3,697,843,700.00	1,344,000,069.35	6,470,136,141.08	11,820,128,480.030
Donegal	1,963,537.68	125,363,400.00	1,743,000.00	-	129,069,937.680
Dublin	226,992,005.11	16,941,000.00	23,240,000.00	-	267,173,005.110
Galway	1,611,281.40	222,491,800.00	1,162,000.00	-	225,265,081.400
Kerry	18,583,120.48	1,578,252,800.00	8,715,000.00	4,311,710,907.59	5,917,261,828.070
Kildare	1,209,025.12	115,763,500.00	-	-	116,972,525.120
Kilkenny	1,065,589.61	3,570,347,000.00	7,553,000.00	12,935,132,722.76	16,514,098,312.370
Laois	604,512.56	284,044,100.00	-	-	284,648,612.560
Leitrim	650,000.00	10,164,600.00	7,553,000.00	-	18,367,600.000
Limerick	1,020,102.17	1,208,133,800.00	-	2,155,855,453.79	3,365,009,355.960
Longford	50,000.00	66,634,600.00	581,000.00	-	67,265,600.000
Louth	13,972,358.45	107,293,000.00	234,068,611.89	-	355,333,970.340
Mayo	1,354,512.56	107,293,000.00	8,715,000.00	-	117,362,512.560
Meath	1,828,922.95	379,478,400.00	15,106,000.00	-	396,413,322.950
Monaghan	302,256.28	216,280,100.00	-	-	216,582,356.280
Offaly	1,302,256.28	201,597,900.00	18,876,300.99	-	221,776,457.270
Roscommon	302,256.28	50,258,300.00	-	-	50,560,556.280
Sligo	654,512.56	446,870,100.00	581,000.00	1,724,684,363.03	2,172,789,975.590
Tipperary	251,339,340.14	1,418,718,800.00	581,000.00	1,724,684,363.03	3,395,323,503.170
Waterford	2,206,768.84	507,665,300.00	15,106,000.00	-	524,978,068.840
Westmeath	952,256.28	177,880,500.00	7,553,000.00	-	186,385,756.280
Wexford	8,463,175.82	472,653,900.00	-	-	481,117,075.820
Wicklow	3,226,871.01	150,210,200.00	15,106,000.00	-	168,543,071.010

), Co. Cork, Kilkenny, Cavan Tipperary, Kerry and Limerick were identified as having high quantity of PF- liquid with approx. 4, 3, 2, 1.6, 1.5, 1.2 thousand million m³, respectively. Seven counties were identified as having intermediate quantity of PF- liquid: counties Waterford, Wexford, Sligo, Meath, Laois, Dublin and Galway with approx. 509, 481, 447, 381, 284, 243, 224 million m³, respectively. The remaining 13 counties were identified as low quantity of PF- liquid with Co. Longford, Roscommon, and Leitrim with less than 70 million m³.

Categories of Primary Feedstocks at County Level

Details on the estimated quantification of PF—solid per categories in tDM of each county can be found in Appendix E, Table A22; for PF—liquid in Appendix E, Table A24 (details on the materials per category in Appendix A,

Table A1. Materials classified by category and type of feedstock.

Category	Material	Type of Feedstock
Dairy Industry	Milk processed (intake)	Primary feedstock
Dairy Industry	Raw milk to product	Primary feedstock
Dairy Industry	Wastewater from dairies	Secondary feedstock
Drink Industry	Beer	Primary feedstock
Drink Industry	Cider	Primary feedstock
Drink Industry	Spirits (grain distillation)	Primary feedstock
Drink Industry	Spirits (pot/malt distillation)	Primary feedstock
Drink Industry	Apples to cider production	Secondary feedstock
Drink Industry	Barley Spent Grain	Secondary feedstock
Drink Industry	Concentrate/thin stillage (grain distillation)	Secondary feedstock
Drink Industry	Draff (grain distillation)	Secondary feedstock
Drink Industry	Dry fibre/pulp from cider production	Secondary feedstock
Drink Industry	Pot ale (pot/malt distillation)	Secondary feedstock
Drink Industry	Spent Grains (pot/malt distillation)	Secondary feedstock
Drink Industry	Spent Lees (grain distillation)	Secondary feedstock
Drink Industry	Spent lees (pot/malt distillation)	Secondary feedstock
Drink Industry	Spent wash/thick stillage (grain distillation)	Secondary feedstock
Energy crops and plants	Hemp oil	Primary feedstock
Energy crops and plants	Hemp seed	Primary feedstock
Energy crops and plants	Miscanthus	Primary feedstock
Energy crops and plants	Rushes	Primary feedstock
Energy crops and plants	Willow Woody stems (including bark)	Primary feedstock
Energy crops and plants	Straw from hemp straw production	Secondary feedstock
Energy crops and plants	Straw from seed production	Secondary feedstock
Energy crops and plants	Willow bark	Secondary feedstock
Energy crops and plants	Willow leaves	Secondary feedstock
Energy crops and plants	Willow Stool/root system	Secondary feedstock
Forestry	Alder	Primary feedstock
Forestry	Ash	Primary feedstock
Forestry	Beech	Primary feedstock
Forestry	Birch spp.	Primary feedstock
Forestry	Douglas fir (aboveground)	Primary feedstock
Forestry	Larch spp.	Primary feedstock
Forestry	Norway spruce (aboveground)	Primary feedstock
Forestry	OLL Broadleaves	Primary feedstock
Forestry	OSL Broadleaves (aboveground)	Primary feedstock
Forestry	Other conifers	Primary feedstock
Forestry	Other Pine spp. (aboveground)	Primary feedstock
Forestry	Scots pine (aboveground)	Primary feedstock
Forestry	Ses. & ped. oak	Primary feedstock
Forestry	Sitka spruce (aboveground)	Primary feedstock
Forestry	Sycamore	Primary feedstock
Forestry	Birch spp. bark	Secondary feedstock
Forestry	Birch spp. branches	Secondary feedstock
Forestry	Birch spp. leaves	Secondary feedstock
Forestry	Birch spp. roots	Secondary feedstock
Forestry	Douglas fir bark	Secondary feedstock
Forestry	Douglas fir branches	Secondary feedstock
Forestry	Douglas fir needles	Secondary feedstock
Forestry	Norway spruce bark	Secondary feedstock
Forestry	Norway spruce branches	Secondary feedstock
Forestry	Norway spruce needles	Secondary feedstock
Forestry	Norway spruce roots	Secondary feedstock
Forestry	OSL Broadleaves leaves	Secondary feedstock
Forestry	OSL Broadleaves roots	Secondary feedstock
Forestry	Other Pine spp. bark	Secondary feedstock
Forestry	Other Pine spp. branches	Secondary feedstock
Forestry	Other Pine spp. needles	Secondary feedstock
Forestry	Other Pine spp. roots	Secondary feedstock
Forestry	Sitka spruce bark	Secondary feedstock
Forestry	Sitka spruce branches	Secondary feedstock
Forestry	Sitka spruce needles	Secondary feedstock
Forestry	Sitka spruce roots	Secondary feedstock
Grass	Grass from grasslands which purpose is intensive farming only (Season yield methodology)	Primary feedstock
Grass	Grass from grasslands which purpose is silage only	Primary feedstock
Horticulture	Apple production	Primary feedstock
Horticulture	Brussels sprouts	Primary feedstock
Horticulture	Carrot	Primary feedstock
Horticulture	Fodder beet	Primary feedstock
Horticulture	Fodder rape leaves	Primary feedstock
Horticulture	Kale leaves	Primary feedstock
Horticulture	Mushrooms	Primary feedstock
Horticulture	Potatoes	Primary feedstock
Horticulture	Spring Broccoli	Primary feedstock
Horticulture	Spring Cabbage	Primary feedstock
Horticulture	Spring Cauliflower	Primary feedstock
Horticulture	Sugar beet	Primary feedstock
Horticulture	Swedes	Primary feedstock
Horticulture	Turnip	Primary feedstock
Horticulture	Winter Broccoli leaves	Primary feedstock
Horticulture	Winter Cabbage	Primary feedstock
Horticulture	Winter Cauliflower	Primary feedstock
Horticulture	Apple pruning residues	Secondary feedstock
Horticulture	Fodder beet leaves	Secondary feedstock
Horticulture	Fodder rape stems	Secondary feedstock
Horticulture	Kale stems	Secondary feedstock
Horticulture	Mushroom offcuts	Secondary feedstock
Horticulture	Potato leaves	Secondary feedstock
Horticulture	Spent Mushroom compost	Secondary feedstock
Horticulture	Spring Broccoli leaves	Secondary feedstock
Horticulture	Spring Broccoli stalks	Secondary feedstock
Horticulture	Spring cabbage leaves	Secondary feedstock
Horticulture	Spring Cauliflower leaves	Secondary feedstock
Horticulture	Sugar beet Leaves	Secondary feedstock
Horticulture	Swedes leaves	Secondary feedstock
Horticulture	Turnip leaves and stems	Secondary feedstock
Horticulture	Winter Broccoli	Secondary feedstock
Horticulture	Winter Broccoli stalks	Secondary feedstock
Horticulture	Winter cabbage leaves	Secondary feedstock
Horticulture	Winter Cauliflower leaves	Secondary feedstock
Livestock	Beef	Primary feedstock
Livestock	Chicken meat	Primary feedstock
Livestock	Milk-derived products	Primary feedstock
Livestock	Sheep meat	Primary feedstock
Livestock	Chicken—Blood	Secondary feedstock
Livestock	Chicken—Bones	Secondary feedstock
Livestock	Chicken—Brain	Secondary feedstock
Livestock	Chicken—Feathers	Secondary feedstock
Livestock	Chicken—Heart	Secondary feedstock
Livestock	Chicken—Liver	Secondary feedstock
Livestock	Chicken—Lung	Secondary feedstock
Livestock	Chicken—Skin	Secondary feedstock
Livestock	Chicken—Spleen	Secondary feedstock
Livestock	Pig—Blood	Secondary feedstock
Livestock	Pig—Bones	Secondary feedstock
Livestock	Pig—Heart	Secondary feedstock
Livestock	Pig—Intestines	Secondary feedstock
Livestock	Pig—Lung	Secondary feedstock
Livestock	Pig—Spleen	Secondary feedstock
Livestock	Pig—Tongue	Secondary feedstock
Livestock	Sheep—Bones	Secondary feedstock
Livestock	Sheep—Brain	Secondary feedstock
Livestock	Sheep—Heart	Secondary feedstock
Livestock	Sheep—Kidney	Secondary feedstock
Livestock	Sheep—Liver	Secondary feedstock
Livestock	Sheep—Tongue	Secondary feedstock
Livestock	Slaughtered total cattle—Blood	Secondary feedstock
Livestock	Slaughtered total cattle—Bones	Secondary feedstock
Livestock	Slaughtered total cattle—Brain	Secondary feedstock
Livestock	Slaughtered total cattle—Heart	Secondary feedstock
Livestock	Slaughtered total cattle—Kidney	Secondary feedstock
Livestock	Slaughtered total cattle—Liver	Secondary feedstock
Livestock	Slaughtered total cattle—Lung lobes	Secondary feedstock
Livestock	Total Slaughtered cattle—Tongue	Secondary feedstock
Manure	Chicken manure	Secondary feedstock
Manure	Manure—Sheep	Secondary feedstock
Manure	Slurry—Bulls	Secondary feedstock
Manure	Slurry—Cattle rearing/dry stock (0–3 years)	Secondary feedstock
Manure	Slurry—Dairy Cattle	Secondary feedstock
Manure	Slurry—Other cows/sucklers	Secondary feedstock
Manure	Slurry—Pigs	Secondary feedstock
Marine	Aquaculture Alaria esculenta	Primary feedstock
Marine	Aquaculture all red seaweeds	Primary feedstock
Marine	Aquaculture Laminaria	Primary feedstock
Marine	Aquaculture Saccharina	Primary feedstock
Marine	Atlantic Herring	Primary feedstock
Marine	Atlantic Mackerel	Primary feedstock
Marine	Atlantic salmon	Primary feedstock
Marine	Blue mussel (suspended and seabed cultured)	Primary feedstock
Marine	Blue Whiting	Primary feedstock
Marine	Cod Atlantic	Primary feedstock
Marine	Crab	Primary feedstock
Marine	Haddock	Primary feedstock
Marine	Hake European	Primary feedstock
Marine	Horse Mackerel	Primary feedstock
Marine	Lobster Norway	Primary feedstock
Marine	Megrim	Primary feedstock
Marine	Monkfish Angler nei	Primary feedstock
Marine	Oyster Pacific + European flat oyster	Primary feedstock
Marine	Prawns and shrimps	Primary feedstock
Marine	Sole Black	Primary feedstock
Marine	Thornback Ray	Primary feedstock
Marine	Trout	Primary feedstock
Marine	Backbone	Secondary feedstock
Marine	Crustacean meat	Secondary feedstock
Marine	Crustacean shell	Secondary feedstock
Marine	Fins	Secondary feedstock
Marine	Guts	Secondary feedstock
Marine	Heads	Secondary feedstock
Marine	Meat	Secondary feedstock
Marine	Shellfish meat	Secondary feedstock
Marine	Shellfish Shell	Secondary feedstock
Marine	Skin	Secondary feedstock
Pulses	Peas	Primary feedstock
Pulses	Spring beans	Primary feedstock
Pulses	Winter beans	Primary feedstock
Pulses	Heavy rainfalls destroy plants	Secondary feedstock
Pulses	Pea pods	Secondary feedstock
Pulses	Pea stems and leaves	Secondary feedstock
Pulses	Spring beans pods	Secondary feedstock
Pulses	Spring beans stems and leaves	Secondary feedstock
Pulses	Winter beans pods	Secondary feedstock
Pulses	Winter beans stems and leaves	Secondary feedstock
Straw	Maize stems and leaves	Secondary feedstock
Straw	Spring barley straw	Secondary feedstock
Straw	Spring oat straw	Secondary feedstock
Straw	Spring Oil rapeseed straw	Secondary feedstock
Straw	Spring wheat straw	Secondary feedstock
Straw	Winter barley straw	Secondary feedstock
Straw	Winter oat straw	Secondary feedstock
Straw	Winter oil rapeseed straw	Secondary feedstock
Straw	Winter wheat straw	Secondary feedstock
Tillage	Maize silage	Primary feedstock
Tillage	Spring barley grain	Primary feedstock
Tillage	Spring oat grains	Primary feedstock
Tillage	Spring rape seeds	Primary feedstock
Tillage	Spring rape seeds Rape oil	Primary feedstock
Tillage	Spring wheat Grain	Primary feedstock
Tillage	Winter barley grain	Primary feedstock
Tillage	Winter oat grains	Primary feedstock
Tillage	Winter rape seeds	Primary feedstock
Tillage	Winter rape seeds Rape oil	Primary feedstock
Tillage	Winter Wheat Grain	Primary feedstock
Tillage	Spring barley Lodging	Secondary feedstock
Tillage	Spring barley Machine setting errors	Secondary feedstock
Tillage	Spring oats hull	Secondary feedstock
Tillage	Spring oats husk	Secondary feedstock
Tillage	Spring rape seeds Cake meal	Secondary feedstock
Tillage	Spring rape seeds Damaged rapeseed	Secondary feedstock
Tillage	Spring rape seeds Shelling before harvest	Secondary feedstock
Tillage	Spring wheat Bran	Secondary feedstock
Tillage	Spring wheat Husk	Secondary feedstock
Tillage	Winter barley Lodging	Secondary feedstock
Tillage	Winter barley Machine setting errors	Secondary feedstock
Tillage	Winter oats hull	Secondary feedstock
Tillage	Winter oats husk	Secondary feedstock
Tillage	Winter rape seeds Cake meal	Secondary feedstock
Tillage	Winter rape seeds Damaged rapeseed	Secondary feedstock
Tillage	Winter rape seeds Shelling before harvest	Secondary feedstock
Tillage	Winter Wheat Bran	Secondary feedstock
Tillage	Winter Wheat Husk	Secondary feedstock

).

Grass, livestock (meat and milk-derived products), energy crops and plants, forestry and tillage are estimated to be the predominant categories of PF—solid identified as high quantities, and dairy industry for PF—liquid (Figure 2,

Table 8. National sum of estimated solid primary feedstocks per category (tDM).

Category	National Sum of Solid Primary Feedstocks (tDM)
Grass	27,051,322
Livestock (meat and milk-derived products)	6,224,152
Energy crops and plants	3,837,687
Forestry	3,669,809
Tillage	2,517,547
Horticulture	244,103
Pulses	64,013
Marine	63,078
Total	43,671,711

and

Table 9. National sum of estimated liquid primary feedstocks per category (m³).

Category	National Sum of Liquid Primary Feedstocks (m3)
Drink Industry	850,060,000
Dairy Industry	17,652,833,200
Total	18,502,893,200

).

Counties with the highest quantity of PF—solid per category were identified from Table A22. Figure 3 visualises 19 counties identified as having at least one high quantity category of solid (Figure 3A) and liquid (Figure 3B) PF in the county, whilst Figure 4 shows the cumulative sum of the highest quantities of solid (Figure 4A) and liquid (Figure 4B) PF per county and category.

Co. Cork was identified as having all eight categories of PF—solid in large quantities, and as a high aggregate total. Figure 2 shows the proportion of categories per counties, with grass in Co. Cork at 63%, livestock (meat and milk-derived products) at 16%, energy crops and plants at 7% and forestry at 7%.

Co. Meath is the next county in number of high quantity categories of PF—solid; however, Meath is the fifth in the list when sum of highest quantities are considered. Figure 2 shows that category grass in Meath is at 71%, forestry at 15%, and energy crops and plants at 11% energy crops.

Co. Kilkenny, on the other hand, has the second place at sum of highest quantities (Figure 3A) with only two categories identified as high quantity (Figure 4A): livestock (meat and milk-derived products) at 56% and grass at 35% (Figure 2). Co. Limerick has been identified with having only 3 high quantity PF—solid, nonetheless, is listed the third when the sum of high quantity PF—solid is considered: grass at 49%, livestock (meat and milk-derived products) at 38%, and energy crops and plants at 9%.

Dairy industry is estimated to be the predominant category of the studied PF—liquid (Figure 2, Table 9). Co. Cork as also identified as having both categories of PF—liquid as high quantity and at the top of the list of sums of the highest quantities (92% dairy, 8% drink industry, Figure 2). Counties Kerry, Tipperary and Wexford were identified as having also the two categories of PF—liquid, however, Kerry is the 7th in sum of the highest quantities (99% dairy, 1% drink industry), Tipperary the 4th (dairy 85%, drink industry 15%) and Wexford the 5th (dairy 98%, drink industry 2%). The sum highest quantities of dairy industry PF—liquid appear to be in counties Kilkenny and Cavan.

Estimation of the Potential Surplus of Grass in the Livestock System

This study also estimated the potential surplus of grass in the RoI for the year 2020 based on the usage of grass from different types of cattle that year (dairy cows, other cows, male 2 years and older, heifers, 2 years and older, over 1 but less than 2 years, and under 1 year old cattle) to identify a potentially important pool of feedstock for the circular bioeconomy. It is worth highlighting that an accurate representation of the potential surplus of grass in Ireland is a complex task as several variables need to be considered to accurately estimate grass production (e.g., soil fertility, management systems, stocking rate and grazing management practices [75]). The methodology followed is detailed in Appendix B.2.

Table 10. Estimated surplus of pasture grass (PG) and silage grass (SG) by livestock system in tDM. Req.: Requirement.

System	PG Intake	SG Intake	PG Req.	SG Req.	PG Surplus	SG Surplus
Other cows	2,089,938	1,248,062	3,047,867	1,733,911	957,929	485,849
Male, 2 years old and over	569,344	42,189	830,464	57,754	261,120	15,565
Dairy cows	4,604,041	1,710,252	6,714,031	2,343,562	2,109,990	633,310
Heifers, 2 years old and over	474,603	222,725	692,080	305,130	217,478	82,404
1 but less than 2 years old	2,484,351	1,349,469	3,623,274	1,848,673	1,138,923	499,205
Under 1 year old	1,152,707	1,028,862	1,680,898	1,408,864	528,192	380,002
Total	11,374,983	5,601,558	16,588,613	7,697,892	5,213,630	2,096,335
Total estimated surplus (PG + SG) (tDM)					7,309,965

represents the estimated national pasture and silage intake (estimated proportion used by cattle) and requirement (current grass production on pasture and silage land) across different types of cattle, estimating national about 7 million tonnes (DM) of pasture and silage surplus.

3.1.4. Secondary Feedstocks at County Level

Four out of six counties were identified as having high quantity of SF—solid in the southeast and west. Eight out of 14 counties in the midland and west regions were identified as having intermediate quantity of SF—solid; and the east coast and the northwest were identified as having low quantity of these. In parallel, five out of seven counties in the southwest and southeast regions were identified as having high quantity of SF—liquid. Three out of six counties in the east were identified as having intermediate quantity of SF—liquid, whereas nine out of 13 counties the midlands and west counties were identified as having the lowest quantity of SF—liquid (

Table 11. Regional distribution of secondary solid and liquid feedstock quantities in the Republic of Ireland.

Feedstock Type	Feedstock Quantity	Regions
Secondary Solids	High quantity	Southeast and west
Secondary Solids	Intermediate quantity	Midlands and west
Secondary Solids	Low quantity	East coast and northwest
Secondary Liquids	High quantity	Southeast and southwest
Secondary Liquids	Intermediate quantity	East coast
Secondary Liquids	Low quantity	Midlands and west

).

In other words, counties Cork, Tipperary, Wexford, Galway, Mayo and Meath were identified as having highest quantities of SF—solid, with approx. 817, 468, 369, 350, 296 and 294 thousand tDM, respectively. Fourteen counties were identified as having intermediate quantities of SF—solid, with Co. Kerry at the top of that list with 283 thousand tDM and Co. Monaghan at the bottom with 142 thousand tDM. Six counties were identified as having low quantities of SF—solid, Co. Westmeath, Louth, Sligo, Leitrim, Dublin and Longford, with 130, 126, 125, 123, 112 and 69 thousand tDM, respectively (Figure 5). In Appendix E,

Table A23. Quantification of secondary feedstocks (SFs) in tonnes dry matter (tDM) by county and category. No data: “- “.

County	SFtDM_Grass	SFtDM_Livestock	SFtDM_Energy	SFtDM_Forestry	SFtDM_Tillage	SFtDM_Horti	SFtDM_Pulses	SFtDM_Marine	Total
Carlow	433,710.65	3064.70	131,291.49	33,983.24	140,963.76	17,063.43	4333.40	-	151,510.66
Cavan	1,048,713.65	429,434.84	253,796.34	75,712.07	311.94	1047.89	89.07	-	159,487.76
Clare	979,093.20	2480.67	173,255.61	258,387.59	798.20	217.92	-	26.72	240,744.55
Cork	3,987,713.02	1,049,632.02	467,550.00	450,791.55	352,138.01	43,103.24	5420.79	6968.24	817,113.51
Donegal	726,994.92	5420.36	172,384.52	228,107.39	36,762.16	6259.80	-	46,710.95	261,994.88
Dublin	89,008.63	673.30	111,196.31	35,670.84	108,693.39	14,594.12	6263.41	951.35	112,716.64
Galway	1,589,450.85	7189.34	52,243.79	308,478.79	23,295.17	5240.35	42.49	1437.89	350,494.88
Kerry	1,182,301.65	692,990.99	324,632.69	243,121.63	17,396.43	1633.43	23.74	2589.43	283,826.38
Kildare	453,129.35	5191.51	76,985.52	24,751.03	255,808.64	9201.73	6858.62	-	227,364.02
Kilkenny	1,275,571.13	2,073,924.48	120,133.92	92,849.39	125,432.41	13,951.58	2112.51	8.31	230,288.36
Laois	886,728.08	6427.32	60,950.87	145,340.28	127,457.04	16,618.96	2078.81	-	238,440.32
Leitrim	316,214.30	979.48	172,572.70	154,860.60	-	6.83	-	-	123,056.58
Limerick	1,722,490.92	1,308,827.86	308,499.25	136,548.57	8462.12	441.32	63.92	-	212,050.87
Longford	377,694.45	2162.02	138,996.32	46,704.90	3130.33	44.74	6.06	-	69,954.51
Louth	345,847.56	3865.02	19,998.61	3654.37	159,042.04	10,954.69	3477.11	441.77	126,498.68
Mayo	1,222,403.79	5227.83	166,137.74	301,156.54	1360.24	927.56	-	1499.61	296,310.35
Meath	1,367,341.55	8951.95	207,636.53	23,108.84	298,037.67	22,887.16	8488.44	-	294,498.79
Monaghan	819,964.00	23,676.80	96,970.06	13,256.87	3812.24	2990.50	0.71	-	142,733.32
Offaly	960,866.67	5514.27	18,709.54	100,701.62	75,874.84	9309.46	1508.47	35.70	181,165.92
Roscommon	814,274.94	4533.27	70,435.65	161,610.56	3013.62	1279.05	50.29	-	174,247.81
Sligo	426,908.90	277,320.96	95,791.15	137,007.50	495.04	181.76	-	6.69	125,243.07
Tipperary	2,523,579.59	288,611.56	145,781.91	227,459.99	179,414.30	14,658.50	3305.51	11.04	468,289.59
Waterford	970,836.47	5298.31	137,683.13	119,081.50	73,033.89	8158.08	788.71	1154.29	193,043.30
Westmeath	1,001,974.25	4664.55	23,848.08	48,263.15	43,640.82	2786.95	2155.51	-	130,511.17
Wexford	1,078,971.59	5426.61	139,570.19	78,859.15	375,230.27	33,556.91	14,740.47	1202.42	369,225.08
Wicklow	449,537.55	2661.77	150,635.09	220,341.20	103,942.46	6987.41	2204.82	33.52	238,409.93

displays estimated quantities of SF—solid.

Seven counties were identified as having high quantity of SF—liquid (Appendix E, Table A24), counties Kilkenny, Cavan, Cork, Kerry, Limerick, Sligo and Tipperary with approx. 12, 8, 7, 4, 2, 1.7 and 1.7 thousand million m³, respectively. Six counties were identified as having intermediate quantity, Co. Louth, Dublin, Offaly, Meath, Waterford, Wicklow with approx. 234, 23, 18, 15, 15 and 15 million m³, respectively. The remaining 13 counties were identified as having low quantity of SF—liquid, with Co. Donegal, Galway and Longford at the bottom of the list with approx. 1.7, 1.1 and 581 million m³, respectively. Co. Kildare, Laois, Monaghan, Roscommon and Wexford did not estimate any SF—liquid arisings due to a shortage of data on micro distilleries and micro dairy producers. Not all counties were projected to generate SF—liquid at the time of this study.

Categories of Secondary Feedstocks at County Level

Details on the estimated quantification of SF—solid per categories in tDM of each county can be found in Appendix E, Table A23; for SF—liquid in Table A24.

Forestry, manure and straw from tillage, are the predominant categories identified as highest quantities of SF—solid, and dairy industry for SF—liquid (Figure 5,

Table 12. National sum of estimated solid secondary feedstocks per category (tDM).

Category	National Sum of Solid Secondary Feedstocks (tDM)
Forestry	2,212,663
Manure	2,153,065
Straw from tillage	1,162,242
Other secondary feedstocks from tillage	250,955
Slaughterhouse arisings from livestock	177,794
Horticulture	163,036
Drink industry and organic waste	45,903
Pulses	32,152
Marine	16,815
Energy crops and plants	4590
Total	6,219,220

and

Table 13. National sum of estimated liquid secondary feedstocks per category (m³).

Category	National Sum of Liquid Secondary Feedstocks (m3)
Dairy Industry	37,945,625,766
Drink Industry	1,725,926,982
Total	39,671,552,749

).

Counties with the highest quantity of SF—solid per category were identified from Table A23. Figure 6 shows 21 counties identified as having at least one high quantity category of solid (Figure 6A) and liquid (Figure 6B) SF in the county, whilst Figure 7 shows the cumulative sum of the highest quantities of solid (Figure 7A) and liquid (Figure 7B) SF per county and category.

Again, Co. Cork was identified as having all ten categories of SF—solid, as well as being at the top of the list for the sum of high quantities categories of SF—solid. Figure 5 shows the proportion of categories per counties, with manure, forestry and straw from tillage at 37%, 34%, and 18%, respectively.

Co. Tipperary ranks second in both number of categories and summed quantity of SF—solid. Figure 5 shows in Tipperary manure, forestry and straw from tillage at 40%, 28% and 18%, respectively.

Meanwhile, Co. Meath ranks third in number of categories of SF—solid with large quantities available (Figure 6A), and ranks seventh in terms of sum of high quantity SF—solid (Figure 7A). Figure 5 shows in Meath straw from tillage, manure and other secondary feedstocks from tillage at 47%, 31% and 11%, respectively.

In comparison, Co. Galway ranks third nationally for sum of SF—solid while being identified as having only three categories of large quantity SF—solid. Figure 5 shows the biomass breakdown in Galway as forestry, manure and straw from tillage at 54%, 39% and 3%, respectively.

Dairy is estimated to be the predominant category of the studied SF—liquid (Figure 5, Table 13). Due to lack of information at the time of this study, SF—liquid quantities could not be reliably quantified for all counties, however, Co. Kilkenny is at the top of the list of sums of highest quantities of SF—liquid (100% dairy industry, Figure 5), followed by Cavan (100% dairy industry, Figure 5), Cork (83% dairy industry, 17% drink industry Figure 5) and Kerry (100% dairy industry, Figure 5).

3.2. Fate of Studied Irish Feedstocks

The typical fate or use found for most of the PF—solid is animal bedding and feed, ~61%, (from grass, tillage, straw, horticulture, and drink industry SF such as BSG and dry fibre/pulp from cider production), the second one is leaving it on the land or bringing it back to land, ~14.5%, (from energy crops and plants such as rushes and hemp and from horticulture) and the third one is dairy industry, ~9.8%, (milk-derived products such as butter, cheese, whey-powder products, etc.) (Figure 8).

Looking into the fates of the SF—solid, the most common fate is sending the feedstocks back to land, ~73%, mostly coming from forestry, manure, straw from tillage, and other SF from tillage and horticulture. The other main SF fate is animal bedding and feed, ~17%, mostly from straw from tillage, drink industry and horticulture (Figure 9).

As for PF- liquid, these arise from and go to the dairy industry (raw milk intake, 14%), for human consumption (18%), to other streams (recovery of wastewater from dairies, 65%) and exports (>1%). The fate of drink industry feedstocks is primarily human consumption as well as animal bedding and feed (1%) and a small portion for energy production (>1%) (Figure 10). Further details on the fate of the SF—liquid are in Figure 11, which shows again the recovery of wastewater from dairies (~96%), and also, the different SF from the drink industry, going either back to the drink industry (3%) or to energy production (~0%) and animal bedding and feed (~1%).

4. Discussion

In this study, the systematic classification of 221 liquid and solid PFs and SFs, the customised quantification and mapping at count-level, the fate information and the tailored development of proportions and estimation methods for the quantification of SF was supported by numerous databases, peer-reviewed articles and expert interviews. This can offer guidance to future studies and other EU member states to develop their own mapping, and quantification of feedstocks; particularly these results can offer guidance to stakeholders to identify raw materials for BBVCs, such as Tsakalova, et al. [169] who discuss that availability of SF such as wood composites value chains, is as important as innovative processing technologies or the economic benefit of the raw materials for the development BBVCs; or Hand, et al. [170] who identifies through Irish stakeholder engagement that new processing sites should be set up near the feedstock source, amongst other important variables. Other authors also recognise that knowing the quantities and locations of these feedstocks can identify opportunities for bioenergy production and BBVC development [26,171].

It was found heterogeneity in the RoI regarding the geographical distribution of feedstock quantities and typologies, yet counties Cork and Tipperary were identified as having high quantity of solid and liquid PF and SF. Counties Kerry, Kilkenny and Limerick were associated with high quantities of PF—solid, PF—liquid, and SF—liquid; Galway and Meath with high quantities of PF—solid and SF—liquid; and Wexford and Mayo with high quantities of SF—solid, while Sligo with high quantities of SF—liquid only. Moreover, many counties such as Dublin, Longford, Roscommon, Louth, and Leitrim were identified as having low quantities of these, yet these still have a considerable amount of feedstocks (e.g., the lowest quantity identified of SF—solid is 69 thousand tDM and of SF—liquid is 15 million m³).

In other words, counties in regions such as the southwest and southeast tend to have high amounts of liquid and solid PF and SF, being locations to consider for development of processing plants of SF and development of BBVCs, such as the dairy biorefinery, in Lisheen, Co. Tipperary, it is being developed for conversion of whey permeate and delactosed whey permeate into lactic acid [172,173]. The northwest and east coast tend to have the lowest amounts of these. The west and midlands counties are the most heterogeneous in terms of quantity and type of feedstock, however these are under the Plan and Programme ‘Ireland’s Territorial Just Transition Plan’, a scheme to help implement bottom-up local and regional economic strategies, including circular economy and bioeconomy ones [174].

Although a higher number of SF—solid were mapped in the RoI, the quantity of these is only a fraction of the feedstocks of precedence or PFs. For instance, the average proportion of SF—solid to PF—solid studied is estimated to be 0.17 ± 0.06 tDM, i.e., on average, 1 t of PF—solid generates approximately 170 ± 60 kg of SF—solid. On the other hand, the drink and dairy industry feedstocks produce vast amounts of SF—liquid as they consume large amounts of water or milk as raw materials, producing significant amounts of SF—liquid and SF—solid; e.g., dairy industry produces an average of 9 L of whey to create 1 kg of cheese [175]. The proportion of SF—liquid originating from PF—liquid inputs is estimated to be 0.85 ± 1.30 m³, reflecting extremely high variability, but also indicating that approx. 1 m³ of the PF—liquid can generate more than 2 m³ of SF—liquid depending on the feedstock. However, the potential of the SF—liquid is as great as SF—solid for BBCVs and biorefineries as these are rich in proteins, minerals, vitamins, nitrogen, and enzymes [175,176,177,178,179].

Moreover, these outputs can be a key resource for the development of environmentally sustainable BBVCs within the circular bioeconomy [169,180,181]. In particular, the utilisation of SF as raw materials in value chains has been shown to reduce the upstream environmental burden compared to the utilisation of PF [180,181]. Other authors also highlight that understanding the proportion of SF generated from primary processing similarly becomes paramount for the development of green markets, BBVCs and reduction of greenhouse gas (GHG) emissions [180,182]. The abovementioned geographical location of SF infers that whilst a specific BBVC could be stablished anywhere a feedstock arises, building environmentally sustainable BBVCs in Ireland that demands high quantity of solid or liquid SF should consider establishing the processing sites (biorefineries, demonstration plants, pilot plants, etc.) near the source of high quantity SF, i.e., the southeast and southwest as well as in some counties on the west and midlands of the RoI.

In terms of which feedstocks could potentially be used by environmentally sustainable BBVCs, it is clear that abundance of feedstocks does not imply variability of these, except for Co. Cork, as it is the county estimated to have the highest quantity of PF—solid, PF—liquid and SF—solid and all categories studied are available there. Cork is the largest county in Ireland and has the highest agriculture area utilised including commonage, permanent pasture and rough grazing area of the RoI, in addition to having the highest number of farm types and being the largest milk producer and second to largest cattle producers [183,184]. Cattle generate high volume secondary feedstocks directly such as slurry, and indirectly such as whey, dairy wastewaters, meat-derived secondary feedstocks from slaughterhouses, etc. [123,170,185,186,187].

On the other hand, grass from grasslands is a PF—solid that emerges as predominant in nearly all counties, with the exception of Co. Dublin, Limerick, and Kilkenny. It is assumed to be fully utilized as animal feed [30]. However, a potential surplus of approx. 7 million tonnes of DM of grass production has been estimated for the year of study, 2020, potentially fuelled by overproduction (fertiliser overuse) in some farms as mentioned by the Grass10 report for 2017 to 2020 [188]. It mentions that there was significant potential to grow more grass on the average dairy farm, as well as showing differences between grass growth and grass-used yields; specifically, it indicated that for 2019, dairy farms grew 10.7 tonnes of DM/ha; however, only 8 tonnes of DM were used. A similar case was observed with cattle rearing, where 7.9 tonnes of DM/ha was grown and only 5.9 tonnes of DM were used. On the other hand, Teagasc [189] have indicated that grass production for 2023 was below its potential, estimating a loss of approx. 7 tonnes DM/ha of grass per stocking rate. Continuous monitoring and mapping of grass growth is crucial for identifying surplus zones that can be strategically used in the circular bioeconomy, such as for developing and optimizing scalable, sustainable grass biorefineries [170].

The category SF—solid that has been estimated as predominant are arisings from forestry. As explained, this category includes forest biomass generated naturally (e.g., needles/leaves, branches, bark, stumps, roots, cones, etc., as opposed to the timber itself, which is considered PF) and wood processing feedstocks (SF arising from the wood industry, e.g., bark, sawdust and woodchip). This adds up to approx. 2.2 million tonnes (DM), and it is estimated to be distributed mostly between Co. Cork, Galway, Mayo, Clare, Kerry and Donegal. At the time of this study, it was found that approx. 95% of the forestry SF stays on the land, with a 4% of this only being used for energy and 1% for wood industry (bark mulch). However, these biomass such as bark or pine needles, although being a minor part in a volume/mass ratio, have high economical value in biorefinery applications. They contain lipophilic and phenolic extractives, as well as tannins, terpenes, resin acids, flavonoids, stilbenes and stilbene glucosides, lignin and holocellulose, etc., i.e., compounds of high economic value for pharma and green chemical industries. Traditionally, extracting these valuable compounds was environmentally harmful. However, technological advancements have led to less impacting methods, such as supercritical carbon dioxide extraction, which reduce environmental impact while generating high-value products from the forestry SF, thereby the potential to create economic and environmentally [190,191,192].

It is imperative to highlight that to support the growth of circular bioeconomy in Ireland through the generation of forestry SF value chains, a sustainable forest management system is needed, i.e., ensuring forests remain resilient and that their productive capacity is respected for generations to come. In this sense, surveying the bioeconomy potential of the forests is crucial, to understand the type and quantity of biomass arisings from the forests that can be retrieved for the creation of valuable bio-based products, while sustainably valuing the forest ecosystems [193,194,195].

It is also noteworthy to mention manure as the second most common SF—solid, summing up to ca. 2.1 tonnes (DM). The estimated amount of slurry produced in the cattle, pig and sheep sectors was calculated over housing days using specific references, as explained in the Section 2. The actual volume of manure and slurry from these animals would be much higher if this study would have included non-housing days. However, these details are difficult to collect as measuring cattle manure on grassland requires more resources than anticipated. Regardless, the major use of slurries identified at the time of this study was to bring it back to land (ca. 99%) while less than 1% was used in energy generation. There is valorisation potential of slurry as some studies have indicated that utilisation of cattle slurry and grass silage for Anaerobic Digestion (AD) decreased GHG emissions by 24%, others that the co-digestion of cattle slurry with grass clover silage could create a N-rich digestate to be used as fertilizer [196,197], however high capital investment are usually required for the implementation of AD plants [198].

Another possible SF—solid for less impactful BBVCs, due to its abundance, is straw from tillage with approx. 1.1 million tonnes (DM) in the RoI, and the majority of this being used as animal bedding (ca. 90%), being reapplied to land (ca. 9%) and for mushroom compost (ca. 1%) at the time of this study. Yet, innovations such as mixing wheat straw with BSG creates high quality compost as an alternative to conventional fertilisers, or utilising wheat straw in bio-based packaging materials for increasing the durability of biocomposites [199] have been proposed.

During the study of SF—liquid, it was found that there are little SF in dairy industry that will be considered a waste of biomass, meaning that a high rate of recovery is achieved in this industry. Dairy industry in Ireland produces several types of powder products from skimmed milk, buttermilk and whey generated from milk, butter, cheese and lactic acid processes [128,130,172,173]. For this reason, the majority of the SF—liquid from dairy industry identified (ca. 37 thousand million m³) comes from dairy wastewater. Multiple studies have described new technologies and value chains to grow different microbes in these waters such as microalgae, or duckweed for different purposes, bioelectricity, pollutant detoxification, biofertilisers or exopolysaccharides as thickening agents, stabilizers, gelling agents, and emulsifiers [200,201,202,203]. In fact, Walsh, et al. [204] investigated an innovative cascade system for the valorisation of dairy wastewater in Ireland, grounded in circular economy principles, which effectively created an integrated setup combining microbial-based anaerobic digestion and aerobic dynamic feeding with duckweed cultivation.

Cascade systems are interesting approaches for BBVC development. For instance, Sameti, Dominguez and Gaffey [13] performed analysis at county-level for bioenergy potential utilising PFs and SFs in Ireland revealing a total calculated bioenergy potential across Ireland of 194 TWh, indicating substantial renewable energy capacity distributed nationwide. This allows stakeholders to build cascading sequences to account for bioenergy generation when utilising biomass as feedstocks, as in the framework of the biomass value pyramid in the bioeconomy, using biomass exclusively for energy should be considered a final option to maximise resource efficiency and minimise waste, while generating high-value products and contributing to energy production [205,206].

It is noteworthy that the feedstock availability estimates represent theoretical rather than technically, economically, or legally recoverable feedstock availability. While some methods used (i.e., meat by-products and waste estimations) provide a useful overview of potential resources and their regulatory context, they also introduce uncertainty due to variable conversion factors, limited data availability (e.g., grass data), and gaps in sector-specific information (e.g., drink sector and dairy sector). Thus, the results should be interpreted with caution.

Building on these theoretical estimation methods, the tailored SF generation ratios, and the quantification details (location and fate), this study lays the foundation for future feedstock mapping for those stakeholders willing to develop innovative BBCVs in the RoI and on-site observations. This allows for an increase in the number of feedstocks, and the identified ratios can also be re-applied to revised national statistics to produce updated feedstock mapping. Overall, this work offers the baseline knowledge for multiple future studies in Ireland looking for utilising and optimising the utilisation of bio-based feedstocks in Ireland for the circular bioeconomy.

5. Conclusions

The holistic mapping and quantification of 221 liquid and solid PFs and SFs (85 PFs and 136 SFs) in Ireland at the county level undertaken in this study will allow the government and investors to localise the efforts and resources needed to develop a vibrant bioeconomy. The estimates of potential availability summed up to approximately 49 million tDM of solid feedstocks (ca. 43 million tDM are PF—solid and ca. 6 million tDM of SF—solid) and around 58 billion m³ of liquid feedstocks (ca. 18 billion m³ of PF and ca. 39 billion m³ of SF). These estimates provided for the quantity and distribution of a wide range of PF and SF in the RoI showcasing what a feedstock mapping product may look like. Furthermore, this study provides a detailed overview of the fates of the mapped feedstocks, providing insight into current material flows. Most importantly, this study demonstrates the effort needed to build a comprehensive feedstock inventory by detailing how the PF quantities, SF conversion factors and feedstock fates were obtained.

Outputs such as identifying the southeast and southwest regions of Ireland as the largest quantities of SF and county Cork containing the widest variety of feedstocks, provides a working example of a spatial feedstock inventory which can support the development BBVCs, and the bioeconomy as a whole.

Although a more detailed analysis of feedstock availability must be undertaken when planning BBVC policies and investments, this study provides a useful first reference to pinpoint promising regions. Using SF for BBVCs reduces environmental burdens; therefore, this study will support the development of more environmentally sustainable and circular BBVCs, contributing to Ireland’s goal of climate neutrality for 2050.

In conclusion, this study firstly provides a map of first estimates, a solid basis for future, high spatial and temporal resolution mapping of bioeconomy development potential in the RoI. And secondly, the tools for future continuous mapping, updating, and expansion of existing inventories, both in Ireland and potentially other countries as well.