There has been a steady increase in the number of biogas energy plants available worldwide, especially in regions with high animal density [1
]. If a biogas plant has been installed properly, anaerobic digestion of animal wastes and residues produces biogas and digestate. Biogas can be used to produce heat and electricity. It can also be used to fuel vehicles after upgrading the quality of natural synthesis gas or biomethane [3
]. This renewable energy can replace fossil fuels and can provide a more self-sufficient energy supply. Moreover, in comparison with traditional manure storage, anaerobic digestion of animal manure avoids large greenhouse gas (GHG) emissions [4
]. The digestate, which is the end-product of anaerobic digestion, can be used as an alternative to chemical fertilizers [5
]. Therefore, biogas systems, which have low input costs, can lead to efficient organic waste recycling [1
], giving them a high potential to fulfill multiple environmental and socioeconomic goals that contribute to a more bio-based circular economy [6
A number of studies have assessed the constraints and actions for the uptake of agricultural biogas systems in different parts of the world [8
]. For instance, Tranter et al. [10
], based on a survey with 381 farmers as “possible adopters” of on-farm biogas plant in England, found that the critical barriers include high capital costs of installing plant and doubts about the economic returns being high enough. Similar results were reported by Brudermann et al. [12
] from Switzerland with the analysis of the strengths, weakness, opportunities, and threats (SWOT analysis) of agricultural biogas production. They conclude that such plants will only succeed in contributing to sustainable energy supply goals when economic and political conditions are favorable over the long term. Beside the economic issues, Rupf et al. [13
] found that limited training for biogas users and insufficient follow-up services were the key barriers in Sub-Saharan Africa; therefore, the sharing of knowledge and technical improvement to suit the needs of the intended user may promote further up-take of biogas systems. Furthermore, Qu et al. [11
], based on a survey with 1227 households in China, revealed that agro-climatic conditions can be decisive factors in farmers’ biogas use. Technical solutions, for instance, to tackle the low productivity of biogas digesters in cold regions, thus need to be further considered. Literature reviews show that there are wide ranges of factors impacting the widespread adoption of biogas systems. However, we found that two scopes of studies for sustainable development of biogas systems are still missing.
First, we suggest that more attention needs to be paid to how various types of local biogas stakeholders perceive and understand biogas systems. Compared to other renewable energy systems, biogas systems are more complex and involve many stakeholders with different values and priorities, including local municipalities, dairy and arable farmers, engineers, and energy companies [15
]. Thus, management is deeply embedded in rural institutional structure and social practices [16
], giving rise to different perceptions of what constitutes the proper use of biogas and digestate. These different values and perspectives, along with power struggles, institutional barriers, a lack of participation, and uncertainty, are major sources of conflict and failure [17
], which may prevent the widespread use of biogas systems. These challenges can be addressed by analyzing “mental models” of biogas systems among its stakeholders.
Second, although many studies have focused on the input side of livestock sectors, concentrating their resources on biogas energy production, the digestate side of biogas production has been largely neglected. Its high potential as a fertilizer seems to be well-perceived among scientists and engineers in the biogas sector [19
], but its disadvantages for practical use are not paid much attention. Only a few authors have reported that farmers are reluctant to use digestate due to its nutrient variability and effects on soil compaction when applied with a spreader [15
]. Despite the fact that a well-functioning biogas system depends on how to handle the large amount of digestate produced [15
], the perception of practical digestate users, i.e., arable farmers, towards digestate values and their acceptance as a fertilizer remain largely unknown.
Through the application of mental model approaches, this study aims to analyze similarities and differences in the perception among local biogas stakeholders including arable farmers. If there were any differences in perception of biogas systems, it can be potential constraints for the further expansion of systems and thus any support for this purpose needs to be considered. We focus on a local community in Hokkaido in Japan, where on-farm biogas plants have been installed over the last decade. This Japanese case study is of general interest, because a wide expansion of biogas systems is needed to make a transition to a bio-based circular economy. This requires that local users and stakeholders accept and support these projects. Since Hokkaido is the most intensive area for dairy farming in Japan, findings from this study may be useful for other livestock-intensive areas of Japan and other countries. We first introduce our case study and methodology, and we then elicit and compare mental models regarding the motivations and constraints associated with biogas implementation and actions necessary for further expansion. Finally, we discuss the policy implications for sustainable development of the biogas system.
2. Overview of the Biogas System in Hokkaido, Japan
Hokkaido is the northern most island of Japan (Figure 1
) and contains the most intensive dairy production [22
]. Due to its high livestock density, the majority of agricultural biogas plants are concentrated in Hokkaido, followed by Honshu (the main island) and then Kyushu (the southwest island). The number of biogas plants has increased over the last two decades. The first construction boom was triggered by the Kyoto Protocol in 1997 when more public attention was given to biogas technology to reduce GHG emissions. Furthermore, dairy farmers became more aware of its application as an appropriate manure treatment in response to the Manure Management Act implemented in 1999 [23
]. In the early 2000s, new plants were constructed under the “Biomass Nippon Strategy,” which was approved by the cabinet in 2002 to promote the use of biomass for energy and material production [24
]. However, implementation of biogas systems began to fade out in the mid-2000s, because biogas technology was immature, and the purchase price for the biomass-generated electricity was low. As a consequence, many biogas plants were not profitable [23
]. Biogas production remained stagnant until 2011, at which point public concerns over renewable energy increased due to the disaster at the Fukushima nuclear energy plant. Furthermore, the introduction of Feed in Tariff (FIT) in 2012 provided incentives to various actors to start up new biogas projects. In 2016, a partial amendment of FIT was adopted by the National Diet that ensured a fixed purchase price for 20 years for biogas-generated electricity (39 JPY/kWh, before tax) [27
]. In addition, various subsidies were available for plant construction. For instance, a subsidy from the Ministry of Agriculture, Forestry, and Fisheries (MAFF) could cover 50% of construction costs [28
As of 2016, 69 agricultural biogas plans run in Hoikaido, with a total power capacity of 8202 kW, which is nearly five times greater than in 2011 [26
]. About 90% of these plants digest cattle manure as a main feedstock for biogas production. Although most biogas plants are on-farm plants, the number of centralized biogas plants also is increasing. Indeed, an additional 10 biogas plants are under construction in Hokkaido, and half of all biogas-based electricity currently is generated by centralized biogas plants [26
Despite the rapid spread of biogas systems in Hokkaido, biogas production is far from reaching its full potential of producing 20 times more than the level of 2016 by utilizing all manure available [29
]. The primary reason continues to be the relatively high cost for plant construction and maintenance [26
], as well as required expenditures for coordinating technical and institutional settings with electricity companies [30
]. Furthermore, arable farmers’ perception and willingness to use digestate as a fertilizer remain unknown.
displays the motivation variables that the stakeholders presented. The most frequently mentioned benefit of biogas installation for all stakeholders was the additional source of income generated from electricity sales. Seven of the stakeholders also mentioned that plant installation would be essential for dairy farmers who intend to increase the number of dairy cattle (farm enlargement). This is because biogas plants are believed to be an appropriate means of handling large amounts of slurry manure, which reduces workload for manure handling. In addition, biogas plants were seen by all groups as an effective way of reducing energy costs through self-provision. In particular, dairy farmers appreciated the use of co-generated heat for processing raw milk.
Regarding the benefits of digestate use, the main motivation for all three groups was the reduction in odor from spreading digestate compared to conventional composts. Half of the stakeholders expected reduced fertilizer costs by substituting commercial fertilizers for digestate. Some stakeholders saw digestate as a quick-release nitrogen fertilizer that would be valuable in grasslands. In addition, anaerobic digestion of manure was perceived to be effective for inactivating weed seeds mixed in manure.
At the local community level, 12 stakeholders from all three groups considered that biogas systems had environmental benefits, such as reduced nitrogen leaching, odors, and GHG emissions. Nearly half of the non-farmers believed that wide implementation of biogas systems can lead to energy self-sufficiency and a ripple effect on the local economy (e.g., creation of new jobs). Compared to non-farmers, dairy and arable farmers tended to be less motivated by these benefits to the local community. However, dairy farmers believed that wide implementation of biogas systems, including improvement of barn environments (e.g., less disposal of manure within a farm) and reduction of manure odor, would lead to an improved image of dairy farming in general.
displays stakeholders’ cognitive constraint variables. Financial issues were the most frequently mentioned constraints related to biogas plants. In particular, 15 stakeholders, including all dairy farmers, pointed out the high costs of plant construction. Eight of them also mentioned that this is the critical barrier preventing small- and medium-sized dairy producers from setting up a biogas plant.
Among non-farmers, more than half of them were unsatisfied with the current situation of electric power sale (i.e., limited grid access due to a monopoly of Japan’s electric power system and competition with other renewable energy companies, such as solar). Three out of four dairy farmers without the plant noted risks of future policy changes around renewable energy production support (e.g., reduction of FIT), and they thought this lack of long-term stability would be a potential barrier to install biogas plant on their farms.
More than 70% of dairy farmers were concerned about handling such large amounts of digestate if more biogas plants would be installed in the town. The main future threat they perceived was potentially higher competition for gaining access to fields as the number of biogas plants increased in the neighborhood. Three arable farmers also mentioned the same concern.
Most arable farmers were not inclined to use digestate as a substitute for chemical fertilizer regardless of their previous digestate use. The top six mentioned constraints included: (1) distance and costs for digestate transportation; (2) limited timing and conditions for application, because liquid digestate cannot be spread on rainy and windy days or on sloping fields; (3) unclear impacts on yield; (4) risk of soil compaction by heavy digestate spreaders; (5) preference of solid composted manure over liquid digestate; and (6) high variability of nutrient contents and dry matter contents. Conventional compost can be stored on a shelf, but liquid digestate requires a storage tank and re-application of composted manure as a soil amendment, causing extra application costs. In contrast to the major cognitive motivation of reducing odor (Table 2
), two arable farmers still perceived that digestate has an unpleasant odor.
In addition to these difficulties for the actual usage of digestate, non-technical constraints also were identified. Some arable farmers were afraid to use it because none of their neighboring farmers used it, while they also felt that there were poor linkages and communication with the dairy farmers who supplied the digestate. In addition, the characteristics of suppliers matter. Some arable farmers, in particular non-digestate users, believed that suppliers were careless about the demand-side wishes (i.e., spreading digestate with proper timing and amount) and instead put greater priority on their disposal of digestate.
Furthermore, insufficient knowledge of digestate among farmers was regarded as a barrier for successful digestate use. This was mainly due to the limited access of gaining information and meeting experts. It should be noted that most of these technical and non-technical constraints to digestate use were mentioned by arable farmers, while only a few variables were raised by the other two groups.
A few comments on community challenges were found in the mental models of arable and non-farmers. One from each group considered that local people had insufficient knowledge of biogas systems, while one arable farmer felt that only dairy farmers received the benefits of biogas systems, and there were low returns to the whole community.
The actions that the stakeholders think would be necessary to take for wide implementation and maintenance of biogas system are shown in Table 3
. The most frequently mentioned action was to start a new project of joint biogas plants. The joint biogas plant includes co-digestion of cattle manure collected from multiple small- and mid-sized dairy farmers. This action, as a way of sharing various costs, was suggested by eight stakeholders, including all dairy farmers who had no experience with biogas plants. Continuation of or increases in the level of current public support (FIT and construction subsidies) was recommended by dairy and non-farmers.
The majority of non-farmers thought that more technical development is needed to produce biogas at lower costs and with more efficiency for further promotion of biogas plant installation. Government financial support for engineers and researchers was recommended. Simplification of the technology, leading to more user-friendly operation systems, also was suggested.
Regarding the actions for stimulating digestate use, the most common suggestion (from seven of the dairy and arable farmers) was increased financial support to purchase new equipment, such as spreaders, and the use of contractors who can handle digestate collection and spreading on behalf of plant operators. On the contrary, more than 40% of arable farmers believed that plant operators (i.e., dairy farmers) should spread digestate free of charge and with proper timing and amounts.
When looking at suggestions raised by arable farmers, the most popular action was to clarify the actual merits of digestate as a fertilizer. This includes chemical analysis of nutrient contents and field experiments of digestate application. The second most frequent suggestion was to upgrade digestate to be more user-friendly. For example, this includes (1) treating digestate to homogenize nutrient contents, (2) upgrading digestate to a solid or concentrated product, (3) downsizing digestate spreaders to avoid soil compaction, and (4) providing sub-tanks for digestate storage near the fields to avoid frequent round trips between a plant and the fields.
The stakeholders, mainly arable farmers, mentioned that more action would be needed to overcome non-technical constraints on digestate use. These actions include organizing a study group to learn how to use digestate, setting up a place where digestate suppliers and receivers can be matched up, and developing a decision support system through which arable farmers can be supported to make a crop nutrient plan for digestate use. Some farmers expect that JA Shihoro may play a significant role in coordinating a study group and matching.
In order to take advantage of the benefits or to overcome the barriers to biogas systems at the community level, some stakeholders, in particular non-farmers, noted several actions. The most frequent suggestion was to expand the energy use system outside of dairy farms. This includes application of co-generated heat to greenhouse farming and public buildings.
Biogas systems are local and complex systems, involving many stakeholders affecting input (manure and residues) and output (biogas, digestate, energy, and heat) use within a community. Once the systems are managed properly, there is a high potential to provide multiple environmental and socioeconomic benefits to the community. However, implementation and widespread adoption of biogas systems are challenging because of differences in values and perspectives of biogas systems among the diverse set of stakeholders. Thus, this study aimed to understand similarities and differences in the views of biogas systems among its stakeholders by creating mental models among stakeholders in Shihoro, Japan.
Our results show that stakeholders in Shihoro shared the same motivations toward accepting biogas systems, including expected environmental benefits. This finding indicates that there is a high potential for further expansion. However, differences were also found: arable farmers were not attracted to digestate use due to several technical and non-technical constraints, while dairy farmers and non-farmers were ambivalent about these demand-side constraints. From both economic and environmental points of view, this difference in perception may lead to future conflict regarding digestate disposal that represents a potential obstacle for further expansion. Therefore, biogas energy policy must be implemented in cooperation with agri-environmental policies related to digestate use. Implementation of mandatory planning of digestate use when planning a new biogas plant is one option, and policies could be developed to improve the attractiveness of digestate for farmers. The findings and suggestions from this study should be useful for other livestock-intensive areas of Japan and other countries, in particular where the number of biogas plants is rapidly increasing but the management system of the digestate produced has yet to be organized.
Several studies have indicated that, if a biogas system brings about localized benefits, it is likely to be sustained over the long term [16
]. The localized benefits do not have to refer only to energy supply [16
]. Our approach, using mental models to understand various stakeholders’ perceptions, motivations, constraints, and actions related to biogas systems, explored a possible roadmap to achieve localized benefits. The next step is to share mental models obtained among various stakeholders in a workshop. This can improve understanding and social learning, and thus better support the establishment of sustainable biogas systems.