Anthropic methane emissions can largely be prevented or minimized using technologies that are already available. One such technology is anaerobic digestion (AD), which is used commercially around the world, especially in Europe and the United States, where some challenging targets have been set to diversify the energy mix with more renewable energy. This foresight study was designed to identify which technological solutions out of the many options available for biogas production are attracting most interest, for which purpose patent documents and scientific publications were analyzed. The aim is to identify which raw materials are most attractive for AD and biogas production. It was found that the raw materials that have attracted most research and patenting activity are sludge, sewage, and wastewater, livestock waste, and agriculture waste, which together account for 62% of all the patents filed and 74% of all the scientific publications. The countries most engaged in producing biogas from AD plants are China, Germany, and the United States. We also identified a rising trend in the use of biogas around the world, and a steady increase in the number of patents filed on the subject, especially in Japan and South Korea. This growth is driven, amongst other things, by strategic governmental actions, global environmental pacts, and the realization on the part of industry that anaerobic digestion can be used as an efficient method for treating waste and effluents.
The development of sustainable technologies that combine the use of waste materials or byproducts with energy generation is gaining ground, especially since the oil crisis in the 1970s, when heightened interest in energy recovery and reducing environmental pollution was first awakened. Anaerobic digestion (AD) is a useful energy production technique. It is used to break down waste of primarily organic content through the action of microbes, producing biogas and high- quality fertilizer. Other benefits of using AD include: flexibility in the choice of feedstock for the process; reduced dependency on fossil fuels; lower greenhouse gas (GHG) emissions; contribution to rural socioeconomic development; and a feasible means to help countries attain the gas emission and waste treatment targets established in international agreements. The average chemical composition of the biogas produced by anaerobic digestion is: 50% - 85% CH4 (methane), 20% - 35% CO2 (carbon dioxide), and varying quantities of H2, N2, and water vapor [
What really sets AD apart is the fact that it can be used to treat industrial waste, agricultural waste, animal waste, sewage, sludge, and wastewater, since the main prerequisite is that the feedstock used must be primarily organic [
In the early 1990s, co-digestion started to emerge as a new technique for overcoming the limitations of the AD process, whereby different raw materials are processed together [
For many years, anaerobic digestion has been used successfully for treating domestic, industrial, farm, food, and municipal solid waste, as well as other types of waste. It is employed in different parts of the globe and is quite widely used, especially in rural parts, where there is a ready supply of feedstocks with a high organic load [
Many studies have indicated that anaerobic digestion is an environmentally friendly and efficient way of generating energy and producing fertilizer. Indeed, rural communities in particular have much to gain socially and economically from producing and using biogas [
Technology foresight is one of the most widely used methods for investigating the future use of given technologies, mapping out and giving an overview of a production chain or process. In this research, a foresight study of AD was conducted by investigating patenting activity and scientific publications on the subject [
Patent documents were retrieved from the Derwent Innovations Index and imported into VantagePoint®, version 5.0 (2007), a commercial software package for text mining and data organization. The search strategy was based on specific keywords and certain Derwent Manual Codes. These codes are provided by the database and operate in much the same way as the International Patent Classification (IPC), in that the patent documents are read and then assigned to codes according to the scope of protection of the inventions they describe. The search retrieved documents indexed in the database between 2000 and May 2016, and the following Derwent Manual Codes were used: D05-C14 (Methane) and H06-A04 (Biofuel gases e.g. methane production by digestion or fermentation of e.g. waste organic materials). The patents’ titles and abstracts were searched using the keyword “biogas” and its synonyms, like “greengas” and “biomethane”. Keywords were then used to identify which of the retrieved patents referred to some specific feedstock, and these were then sorted into groups (
Group | Keywords |
---|---|
Animal Waste | animal OR swine OR pig OR excrement OR livestock OR manure OR chicken OR dairy OR dung OR poultry OR cattle OR slurry OR urine OR horse OR sheep, duck OR mule OR rabbit OR llama OR bull OR horse OR elephant OR giraffe OR buffalo |
Wastewater | wastewater OR waste water OR sewage OR sludge |
Municipal Solid Waste | garbage OR “solid urban residue” OR OFMSW OR “household” OR “municipalwaste” OR biowaste OR “organic fraction of municipal solid waste” |
Food Waste | “food waste” OR “kitchen waste” OR “vegetable waste” OR “fruit waste” OR “foodstuffs” |
Agricultural Waste | maize OR agriculture OR stalks OR straw OR cotton OR beet OR corn OR rice OR cereal OR agricultural OR silage OR crop OR sorghum |
Lignocellulosic Waste | wood OR cellulose OR cellulosic OR branches OR leave* OR lignocellulosic OR firewood OR grass OR yard OR “sugarcane bagasse” |
Industrial Waste | “paper waste” OR palm oil OR stillage OR brewery OR glycerin OR “textile industry” OR fishery OR “industrial waste” OR “industrial residue” OR “fabric residue” OR tannery OR “winery waste” |
Algae | Algae OR microalgae OR “aquatic plants” |
This search for patent documents yielded 11,625 documents for AD technology and biogas production, but only 21% of these mentioned the use of a specific kind of waste, reducing the total number of patent documents for analysis to 2493.
Afterwards, in order to identify the research done on each groups of feedstocks identified in the patent documents, a search of scientific publications was conducted. All the publications indexed in the Web of Science between 2000 and June 2016 were retrieved. A different search strategy was used for each group of raw materials identified in the patents, employing the same keywords as used to retrieve the patents (see
Using the strategy described above, 2493 patent documents were retrieved, which were sorted into groups according to the kind of waste material they were for (
In anaerobic digestion, the composition of the feedstock can have a direct impact on the final yield of methanol in the biogas. When fat is degraded, the fatty acid content in the fermentation medium rises, which limits and slows down the overall degradation of the feedstock [
The search for scientific publications was based on the main types of feedstock found in the patents. The breakdown per year is shown in
In addition,
In view of the breadth and diversity of the findings of this study, the decision was taken to discuss only the groups of waste materials that accounted for 12% or more of the patents retrieved. As such, the following groups will be discussed: wastewater, sludge, and sewage (25%), animal waste (23%), and agricultural waste (14%).
Wastewater, sludge, and sewage was the group that accounted for the highest number of patent applications (970) and academic publications 4271. Anaerobic digestion is already widely used in wastewater treatment because of its high organic load. It started being used more widely for this kind of treatment in the 1980s, when the first UASB reactors were developed [
When it comes to the countries with the most interest in developing this technology (countries where the most priority patent applications have been filed), the top five countries account for 82% of all the patents retrieved for this category. China and Japan, with 262 and 253 patent applications respectively, are the leading countries. As for the academic publications, indicators of research activity, the top countries are China (712 publications), the USA (414), Spain (354), India (279), Germany (275), and Italy (260) (
The second biggest group, with 3046 publications and 863 patent applications, has to do with the use of animal waste. The motivation for developing and protecting intellectual property for this kind of waste is certainly associated with the size and importance of livestock farming. Only in 2015, the 28 member countries of the European Union slaughtered 7590.34 thousand tons of beef, with France alone holding some 19.3 million heads of cattle. As for pork production, the leaders in this economic bloc are Germany and Spain, with 28.3 million and 26.6 million pigs, respectively [
For a more detailed analysis, animal waste was further sub-categorized into the animals that produce the waste. Often, the same patent document cited the use of waste from more than one animal or else a combination of different types of animal waste. Fifty-one percent of the patent applications involving animal waste were for waste from cattle, 22% were for waste from pig breeding, 13% for poultry, 11% for other animals (e.g. elephant, horse, rabbit, llama, buffalo), and 3% did not mention the animal, just stating that the claim was for livestock waste.
The number of publications has grown year on year, with 2015 seeing the highest number: 508 in all. One of the factors behind the growing interest in the use of AD for treating livestock waste is its capacity to help integrate livestock with other farming activities, converting manure, which is normally attributed little or no commercial value, into two products of interest: renewable energy (biogas) and organic fertilizer [
The third biggest group was agricultural waste, with 2879 publications and 540 patent applications. The importance of this kind of waste is linked to the ease with which the agricultural sector can undertake the co-digestion of this material (agricultural waste + livestock waste). Another driver behind the production of renewable energy from this source is the fact that aside from biogas, anaerobic digestion also generates biofertilizer, which can be fed back into the agricultural production chain, contributing to the recycling of nutrients while also reducing greenhouse gas emissions and unpleasant odors [
The importance of this group of waste is justified by the size of the agricultural sector in developing countries. Even so, much of the potential of this kind of waste is best harnessed in conjunction with other feedstocks in co-digestion set-ups, since crop waste is not easily degraded by microbes. However, the combined treatment of crop and livestock waste could potentially account for up to 80% of all biogas generated [
The co-digestion of pig manure with three crop waste products-corn stalks, oat straw, and wheat straw-has been investigated as a way of boosting biogas yields. It was found that for all types of agricultural waste, there was a considerable increase in yields when they were combined with pork waste as compared with when they were treated by AD alone under the same conditions [
Although the composition of crop waste can vary greatly, its water content tends to be low and its volatile solids content tends to be high. This means that the type of AD unit most commonly used to process it is the continuously stirred tank reactor. Around 90% of the biogas plants installed in Germany use this technology [
In this research, it was found that 64% of the patent applications that mentioned the possibility of using agricultural waste in their invention also cited waste from one or more of the other seven categories in this paper. This would indicate that technology is being developed in line with the scientific literature, which stresses that the best methane yields are obtained when agricultural waste is combined with other kinds of waste.
Cellulosic waste accounted for 11% of the patent documents (414) and 1264 scientific publications. The research and patenting of this kind of waste is still growing, especially given the potential need to use multiple types of pre-treat- ments to separate out the fibers before biodegradation.
The number of patent documents for municipal solid waste (MSW) is similar (391%, or 11%), but there are fewer academic publications. The use of AD for treating MSW is one of the biggest breakthroughs of the last decade [
Fewer patents and publications were found for industrial waste: just 4% of the patents (153) and 3% of the publications. However, there is still an upward trend in the use of this kind of waste. The main industries with biogas generation potential are pulp and paper, sugar and ethanol, abattoirs, dairy, breweries, food, and drink, all of which need to reduce the organic load of their effluents to comply with environmental legislation [
Finally, algae and aquatic plants accounted for 2% of the patents (91), constituting an area of potential use that should not be overlooked. There are reports that macroalgae can reach 2 - 20 times the biofuel production potential of conventional terrestrial energy crops. Furthermore, microalgae are capable of doubling their biomass in 24 hours [
The scientific research in this field is wide-ranging and exploratory in nature. Meanwhile, the commercial reality is that the adoption of biogas production technologies is generally driven by economic forces or else by government legislation [
While Germany is the most advanced European country when it comes to the number of AD units-8928 in 2015 [
Two hundred and seventy-five patent applications filed in the United States that mention the use of some kind of waste were retrieved. The patenting in this country has remained fairly stable over the years, suggesting that while biogas production is seen as a mature technology, there is still room for technological innovation. The other countries with the most priority patents for AD and biogas production involving some specific waste as a feedstock between 2000 and 2016 are: South Korea (149 patent applications), Russia (82), France (58), Poland (32), and Brazil (31) (
Five hundred and four patent applications filed in Japan involving claims for biogas production from waste were retrieved. Brazil is in ninth position (not on the chart in
There is no consensus in the literature about which raw materials are best suited for biogas production. A great deal of research is underway and the choice depends on multiple factors. These are generally associated with the geographical location and climate of the place where the biogas will be generated, the local resources, and the investments available. Government stimulus measures, such as policies designed to boost the complete use of biomass, are another driver of academic research. Finally, many of the publications investigated the combined treatment of agricultural and livestock waste. However, when the market reality was assessed, it was found that crop waste receives little attention outside universities, while raw materials from industrial plants and municipal solid waste are the types of waste that attract most commercial interest.
The choice of feedstock is therefore far from straightforward. Practical issues and operational details must be taken into account, as well as the seasonality of some waste materials and logistical considerations.
Grando, R.L., Fonseca, F.V. and Antunes, A.M.S. (2017) Mapping of the Use of Waste as Raw Materials for Biogas Production. Journal of Environmental Protection, 8, 120-130. https://doi.org/10.4236/jep.2017.82010