A sustainable energy system requires, according to energy policies, reduced emissions of greenhouse gases, increased ratio of renewable sources of energy and more efficient use of energy. Horse manure could be regarded as waste, but also as a resource for renewable energy and plant nutrients. This thesis explores the potential of horse manure as a renewable energy source, and its possibilities to support and contribute to energy and environmental objectives. To do this, data was collected from literature, simulations, study visits and interviews.

A number of horse keeping activities were identified in the assessment of horse manure as a feedstock for energy and as a plant resource: feeding, indoor housing, outdoor keeping, manure storage, fertilizing and transport, all with effect on amount and content of horse manure. Results indicated that choice and amount of bedding are important for both energy performance and plant nutrient content in the biofertilizer. Operational conditions such as long hydraulic retention time and high temperature had less impact for horse manure as a biogas feedstock. Anaerobic digestion resulted in the lowest global warming potential compared to incineration and composting, while large-scale incineration reduced primary energy demand, acidification potential and eutrophication potential. In a subsequent simulation, anaerobic digestion had lower potential environmental impact than unmanaged composting, regarding all chosen environmental impact categories in the study. Experiences from energy companies suggest that horse manure can be used in small quantities in co-incineration, with suitable incineration technology, but odor was mentioned as a problem. Farm-scale incineration required continuous maintenance and monitoring and mixing with pellets. As a feedstock for anaerobic digestion horse manure was regarded as suitable for plug-flow processes while stirred processes experienced more technical problems leading to increased cost for plants. With adaption of horse manure to the energy recovery technology to be used, and adaption at energy conversion plants to homogenous materials, this not yet fully utilized bioenergy resource has potential to contribute with renewable energy to the energy system, and thereby also reduce environmental impact from horse manure treatment

A transition to renewable energy sources and a circular economy has increased interest in renewable resources not usually considered as energy sources or plant nutrient resources. Horse manure exemplifies this, as it is sometimes recycled but not often used for energy purposes. The purpose of this study was to explore horse manure management in a Swedish municipality and prospects for energy recovery. The case study includes a survey of horse manure practices, environmental assessment of horse manure treatment in a biogas plant, including associated transport, compared to on-site unmanaged composting, and finally a simplified economic analysis. It was found that horse manure management was characterized by indoor collection of manure most of the year and storage on concrete slabs or in containers, followed by direct application on arable land. Softwood was predominantly used as bedding, and bedding accounted for a relatively small proportion (13%) of the total mix. Anaerobic digestion was indicated to reduce potential environmental impact in comparison to unmanaged composting, mainly due to biogas substituting use of fossil fuels. The relative environmental impact from transport of manure from horse facilities to anaerobic digestion plant was small. Results also indicate a relatively high cost for horse keepers to change from composting on site to anaerobic digestion in a centralized plant.

Keeping horses causes environmental impacts through the whole chain from feed production to manure. According to national statistics, the number of horses in Sweden is currently 360,000 and is continuing to increase. This result in increasing amounts of horse manure that has to be managed and treated, which is currently done using practices that cause local, regional, and global environmental impacts. However, horse manure and its content of nutrients and organic material could be a useful fertiliser for arable land and a substrate for renewable energy production as biogas. The aim of the paper is to identify and describe potentially critical factors in horse keeping determining the amount (total mass) and characteristics (nutrient content and biodegradability) of horse manure, and thus the potential for anaerobic digestion. A systematic combining approach is used as a structural framework for reviewed relevant literature. All factors identified are expressed as discrete choices available to the horse keeper. In all, 12 different factors were identified: type and amount of feed, type and amount of bedding, mucking out regime, residence time outdoors, storage type and residence time of manure in storage, spreading and soil conditions, and transport distance and type of vehicle fuel used. Managing horses in terms of these factors is of vital importance in reducing the direct environmental impacts from horse keeping and in making horse manure attractive as a substrate for anaerobic digestion. The results are also relevant to environmental systems analysis, where numerical calculations are employed and different biogas system set-ups are compared to current and other treatments. In such assessments, the relevance and importance of the critical factors identified here and corresponding conditions can be examined and the most promising system set-up can be devised.

In horse keeping horse manure is produced, which can be utilized as a fertilizer or considered a waste. Horse manure constitutes a resource in terms of both plant nutrients and energy. In addition energy policies and objectives aim at replacing fossil fuels with renewable energy sources. The interest to improve resource recovery of horse manure increases due various incentives for renewable vehicle fuels, legal requirements on management of manure, and environmental impact from current horse manure management.

This thesis aims at describing horse manure management in a life cycle perspective. This is made by (1) identifying factors in horse keeping affect­ing the possibility to use horse manure as a biogas feedstock and to recycle plant nutrients, (2) analysing factors in anaerobic digestion with influence on methane potential and biofertilizer nutrient content and (3) comparing the environmental impact from different horse manure treatment methods. Literature reviews, systematic combining, and simulations have been used as research methods.

The results show that horse keeping activities such as feeding, indoor keeping, outdoor keeping and manure storage affect the amount and charac­teristics of horse manure and thereby also the possibilities for anaerobic digestion horse manure. Transport affects the collected amount and spread­ing affects loss of nutrients and nutrient recycling. Simulation results in­dicate the highest methane yield and energy balance from paper bedding, while straw and peat gave a higher nutrient content of the biofertilizer. The highest methane yield was achieved with a low rate of bedding, which in the cases of woodchips and paper is also preferable for plant nutrient recycling. Still, results indicate the best energy balance from anaerobic digestion with a high ratio of bedding. The environmental impact assessment indicates a reduction in global warming potential for anaerobic digestion compared to incineration or composting.

Vid hästhållning alstras hästgödsel som kan användas som växtnäring eller anses vara ett avfall. Hästgödsel utgör både en växtnäringsresurs och en energi resurs. Dessutom styr uppsatta energimål mot att förnybar energi ska ersätta fossila bränslen. Intresset för att öka resursutnyttjandet av hästgödsel ökar på grund av olika incitament för förnybara drivmedel, lagstiftning om gödselhantering och miljöpåverkan från dagens hantering av hästgödsel.

I den här avhandlingen beskrivs hästgödselhantering i ett livscykel­perspektiv genom att (1) identifiera olika faktorer vid hästhållningen som påverkar möjligheten att utvinna biogas ur hästgödsel och återföra näringen till jordbruksmark, (2) analysera faktorer i biogasprocessen som påverkar den specifika metanmängden och innehållet av växtnäring i gödseln och (3) jämföra olika gödselhanteringsmetoders miljöpåverkan. Metoderna i avhan­dlingen har varit litteraturstudier, systematisk kombination av teori och em­piri samt simulering. Resultaten visar att utfodringen, om och hur hästarna hålls inomhus och utomhus och hur hästgödsel lagras påverkar mängden hästgödsel och dess egenskaper, och därmed också hur den fungerar som ett biogassubstrat. Trans­porterna har betydelse för hur mycket gödsel som kan samlas in och spridas, medan gödselspridningen påverkar näringsförluster och närings återföring.

Resultaten från simuleringarna indikerar högst metanutbyte och bäst energi­balans från papper som strömaterial, medan halm och torv gav högre växt­näringsinnehåll i biogödseln. De högsta resultaten på specifik metanmängd nåddes med låg andel strö, vilket också var positivt för växtnäringsinnehållet vid scenarierna med spån och papper. Samtidigt indikerar resultaten att en hög andel strömaterial ger den bästa energibalansen. Miljöpåverkansbedöm­ningen indikerar att potentialen för klimatpåverkan minskar om hästgödsel behandlas i en biogasprocess jämfört med förbränning eller kompostering.

Horse keeping is of great economic, social and environmental benefit for society, but causes environmental impacts throughout the whole chain from feed production to manure treatment. According to national statistics, the number of horses in Sweden is continually increasing and is currently approximately 360,000. This in turn leads to increasing amounts of horse manure that have to be managed and treated. Current practices could cause local and global environmental impacts due to poor performance or lack of proper management. Horse manure with its content of nutrients and organic material can however contribute to fertilisation of arable land and recovery of renewable energy following anaerobic digestion. At present anaerobic digestion of horse manure is not a common treatment. In this paper the potential for producing biogas and biofertiliser from horse manure is analysed based on a thorough literature review in combination with mathematical modelling and simulations. Anaerobic digestion was chosen as it has a high degree of resource conservation, both in terms of energy (biogas) and nutrients (digestate). Important factors regarding manure characteristics and operating factors in the biogas plant are identified. Two crucial factors are the type and amount of bedding material used, which has strong implications for feedstock characteristics, and the type of digestion method applied (dry or wet process). Straw and waste paper are identified as the best materials in an energy point of view. While the specific methane yield decreases with a high amount of bedding, the bedding material still makes a positive contribution to the energy balance. Thermophilic digestion increases the methane generation rate and yield, compared with mesophilic digestion, but the total effect is negligible.

Horse manure consists of feces, urine, and varying amounts of various bedding materials. The management of horse manure causes environmental problems when emissions occur during the decomposition of organic material, in addition to nutrients not being recycled. The interest in horse manure undergoing anaerobic digestion and thereby producing biogas has increased with an increasing interest in biogas as a renewable fuel. This study aims to highlight the environmental impact of different treatment options for horse manure from a system perspective. The treatment methods investigated are: (1) unmanaged composting; (2) managed composting; (3) large-scale incineration in a waste-fired combined heat and power (CHP) plant; (4) drying and small-scale combustion; and (5) liquid anaerobic digestion with thermal pre-treatment. Following significant data uncertainty in the survey, the results are only indicative. No clear conclusions can be drawn regarding any preference in treatment methods, with the exception of their climate impact, for which anaerobic digestion is preferred. The overall conclusion is that more research is needed to ensure the quality of future surveys, thus an overall research effort from horse management to waste management.

Antalet hästar i samhället ökar och idag finns det enligt Jordbruksverket drygt 360 000 hästar i Sverige, där tre fjärdedelar återfinns inom tätorter eller i tätortsnära miljöer. Alla dessa hästar skall enligt beräkningar ge upphov till en total gödselmängd på uppemot 1,4 miljoner ton per år. Om denna gödsel rötas effektivt motsvarar detta en årlig biogaspro­duktion på 641 GWh, vilket är knappt hälften av all biogas som producerades i Sverige 2010. Även om det föreligger en del praktiska begränsningar i hur mycket av potentialen som kan utnyttjas så finns här trots allt en betydande potential till ökad användning av förnybar energi. Genom att samla in gödseln och röta den uppnås tre miljövinster:

1. Utsläppen från konventionell hantering där gödseln ligger kvar eller komposteras upphör.
2. Rötning av gödseln ger upphov till biogas som kan användas för att generera el och värme eller, efter rening, som fordonsbränsle; därigenom kan utsläpp från fossila bränslen reduceras.
3. Den efter processen uppkomna biogödseln kan användas inom jordbruket och däri­genom ersätta konstgödsel varigenom ytterligare miljövinster uppstår.

Trots alla dessa möjligheter finns det dock en del hinder och kunskapsluckor. I denna rapport görs en systematisk genomgång av kunskapsläget angående hästgödselhantering, förbehandlingsmetoder, rötningsmetoder för hästgödsel samt aspekter på spridning av biogödsel från hästgödsel. I denna del görs i huvudsak kvalitativa beskrivningar medan kommande rapporter redovisar indikativa beräkningar av miljövinsterna med olika sätt att ställa om hanteringen.

Slutsatserna är att det finns många faktorer som talar för att utvinna energi från häst­gödsel som t.ex. att det finns betydande gödselmängder relativt nära tätorter, att halm som strömaterial ger ett tillskott i biogasproduktionen, att det finns gott om mark för spridning av biogödsel och att en förbättrad hästgödselhantering även är en bra vattenskyddsåtgärd. På den negativa sidan finns att rötning av hästgödsel är relativt oprövat och att det är svårt att bedöma hur ökade kostnader för avfallshantering påverkar hästnäringen. En annan slutsats är att det överlag saknas kunskap om hästgödsel ur ett miljöperspektiv på en sådan nivå som krävs för tillförlitliga miljöbedömningar. Vi hoppas trots detta kunna föreslå systemlösningar som i högre utsträckning än tidigare ska kunna visa sig fungera tekniskt och vara genomförbara ekonomiskt. Om dessa systemlösningar omsätts i praktisk verklighet kan miljövinster göras genom minskad klimatpåverkan, minskad övergödning, ökad biologisk mångfald och minskad användning av ändliga resurser.

The number of horses in society is increasing and today, according to Swedish Board of Agriculture, there are approximately 360,000 horses in Sweden, where three-quarters are found in urban or near-urban environments. All these horses will, according to calcula­tions, give rise to a total amount of manure of up to 1.4 million tons per year. If this manure is digested efficiently, this corresponds to an annual biogas production of 641 GWh, which is almost half of all biogas produced in Sweden in 2010. Although there are some practical limitations on how much of the potential that can be exploited, there is nevertheless a significant potential for increased use of renewable energy. By collecting manure and digesting it, three environmental benefits can be achieved:

1. Emissions from conventional management where the manure is piled and stored, or spontaneously composted, are avoided
2. Anaerobic digestion of manure produces biogas that can be used to generate elec­tricity and heat and, after upgrading (purification and pressure increase), as vehicle fuel; thereby fossil fuel emissions are reduced
3. The resulting digestate can be used in agriculture, thereby replacing chemical ferti­lizer which provides additional environmental benefits

Despite all these possibilities there are some obstacles and gaps in knowledge. This report is a systematic review of the state of knowledge about horse manure management, pre­treatment methods, digestion methods of horse manure, as well as aspects of the prolifer­ation of bio-fertilizer from horse manure. This part is mainly qualitative descriptions while subsequent reports present indicative calculations of the environmental benefits of different ways to design the management.

The conclusions are that there are many factors that point to extract energy from horse manure, e.g. there are significant amounts of manure relatively close to urban areas, the straw bedding materials provide a supplement in biogas production, there is plenty of land for spreading digestate, and an improved horse manure management is also a good water protection measure. Drawbacks are that the digestion of horse manure is relatively untested and it is difficult to assess how increased waste management costs affect the horse industry. Another conclusion is the general lack of knowledge of horse manure from an environmental perspective at a level required for reliable environmental assess­ments. Nevertheless we hope to be able to propose system solutions which to a greater extent than previously should prove to work technically and be economically feasible. If these systems are translated into practical reality, environmental gains can be made through reduced environmental impact, reduced eutrophication, increased biodiversity and reduced use of finite resources.

Antalet hästar i Sverige ökar och enligt beräknad statistik från Jordbruksverket finns det uppskattningsvis 360 000 hästar i landet. Dessa hästar återfinns i olika typer av verksam­heter (jordbruk, turridning, trav och galopp med mera) och ger upphov till stora mängder hästgödsel. Hästgödsel består av fekalier, urin och strömaterial där olika strömaterial används olika mycket. Hanteringen av hästgödseln medför miljöproblem då miljöstö­rande ämnen avges vid nedbrytning av det organiska materialet, samtidigt som växtnä­ringsämnen inte återförs till kretsloppet. Intresset för att kunna röta hästgödseln och till­verka biogas har ökat i och med ett ökat intresse för biogas som förnybart drivmedel.

Denna studie har haft som mål att belysa miljöpåverkan från olika sätt att hantera häst­gödsel i ett systemperspektiv. Särskild uppmärksamhet har riktats mot inblandningen av olika typer av strömedel och hur det påverkar effektiviteten i olika behandlingsprocesser. Behandlingsmetoderna som undersökts är

1. Okontrollerad kompostering
2. Kontrollerad kompostering
3. Storskalig förbränning i ett avfallskraftvärmeverk
4. Torkning och småskalig förbränning
5. Torrötning
6. Våtrötning med och utan termisk förbehandling

Till följd av betydande dataosäkerhet i undersökningen är resultaten endast indikativa men de pekar ändå på storskalig förbränning som en miljömässigt bra metod. Undantag utgör bidrag till klimatpåverkan där rötning i olika former är att föredra. Utifrån under­sökningen av olika strömaterial framstår pappersströ som ett intressant alternativ att gå vidare med.

Den övergripande slutsatsen är att mer forskning behövs för att säkerställa kvaliteten i kommande undersökningar, det vill säga en samlad forskningsinsats från hästhållning till avfallshantering. 

The number of horses in Sweden is increasing and according to estimated statistics from Swedish Board of Agriculture, there are an estimated amount of 360,000 horses in the country. These horses are found in different types of activities (agriculture, trail riding, trot and canter, etc.) and they generate large quantities of horse manure. Horse manure consists of feces, urine and bedding material which various bedding materials used to various amount. The management of horse manure causes environmental problems when emissions occur during decomposition of organic material, in addition to nutrients not being recycled. The interest for horse manure be subject to anaerobic digestion and thereby produce biogas has increased with the increased interest in biogas as a renewable fuel.

This study has aimed to highlight the environmental impact of different ways to treat horse manure from a system perspective. Special attention has been focused on the involve­ment of different types of litter/bedding material and how it affects the effective­ness of various treatment processes. The treatment methods investigated are

1. Unmanged composting
2. Managed Composting
3. Large-scale incineration in a waste fired CHP plant
4. Drying and small-scale combustion
5. Solid state anaerobic digestion
6. Liquid state anaerobic digestion with and without thermal pre-treatment

Following significant data uncertainty in the survey, the results are only indicative, but they still point to large-scale incineration as an environmentally sound method. An excep­tion is the contribution to climate impact where digestion in different forms are preferred. Based on the study of various bedding materials, paper pellet appear as an interesting alternative to move forward with.

The overall conclusion is that more research is needed to ensure the quality of future surveys, thus an overall research effort from horse management to waste management.

European Union and Swedish national energy policy and energy objectives state an increased interest in transition of energy systems to more efficient use of energy, as well as increased use of renewable sources of energy. Horse manure is a potential resource available for renewable energy. Horse manure is sometimes considered a waste problem, resulting in research of possible energy recovery processes, such as combustion and anaerobic digestion. In this study 13 energy actors’ experiences of horse manure were explored by means of interviews and e-mail. Five related to combustion of horse manure and eight related to anaerobic digestion. The aim was to make a compilation of their knowledge and from the results identify how horse manure could be made more attractive as an energy resource. The challenges the actors face are mainly connected with horse manure being a heterogeneous material, primarily due to its bedding content (straw, wood bedding, etc.), and occasionally to other types of added waste. These unpredictable variations in the substrate as well as impurities like sand make it more difficult for plants to have standard procedures for processing horse manure. The view that bedding material needs to be specifically straw pellets and that all impurities should be kept out of the collected horse manure for anaerobic treatment was also expressed. Horse manure as part of co-combustion processes was perceived as a fuel with capacity to contribute to plant economy as it gives revenue from gate fees and could reduce costs for its NO_x reducing capacity. Another view was that grate furnaces could possibly be more suitable than fluidized beds as incineration technology. However, problems with odour made two plants end their combustion trials. In farm-scale incineration horse manure required a lot of monitoring and co-combustion with pellets in order to maintain an effective process. When compiling all available information this study has a number of suggestions for how horse manure should be treated already at the production stage in order to be a more versatile resource in energy recovery processes. The recommendation is to keep horse manure dry (transports and incineration), avoid initiation of composting processes (AD and incineration), sort the waste = no added other waste (AD), and depending on intended AD-treatment process, use a specific bedding type. Most of these issues may be solved by supplier’s involvement in the supply chains for resource recovery, i.e. closing natural cycles of plant nutrients and energy recovery.