1 Introduction: In recent years, regulations on waste incineration have become increasingly stringent, including amendments to the Special Measures Law Concerning Dioxin Countermeasures and the Waste Management and Public Cleansing Act. Concurrently, various recycling laws have been enacted to realize a resource-recycling society. Furthermore, the shortage of final disposal sites has led to soaring waste treatment costs. There is a strong demand for shifting waste treatment from incineration and landfill to resource recovery.

1 Introduction: In recent years, regulations on waste incineration have become increasingly stringent, including amendments to the Special Measures Law Concerning Dioxin Countermeasures and the Waste Management and Public Cleansing Act. Concurrently, various recycling laws have been enacted to realize a resource-recycling society. Furthermore, the shortage of final disposal sites has led to soaring waste treatment costs. There is a strong demand for shifting waste treatment from incineration and landfill to resource recovery.
Consequently, there is a growing need for recycling methods to replace simple incineration, even for organic waste (such as construction waste wood, food waste, sewage sludge, and livestock manure) that would typically undergo intermediate treatment like dewatering, drying, and incineration before being landfilled. Among these alternatives, "carbonization" is suddenly gaining attention.

Current Status and Direction of Carbonization Furnace Development: A prime example of carbonization is charcoal production. Currently, traditional charcoal-making techniques (such as kilns and block furnaces) are used for this purpose, alongside industrial-scale mass production methods like flat furnaces, screw furnaces, rotary kilns, and fluidized bed furnaces. However, for materials with well-defined properties, such as thinned timber or sawmill waste, the need for dioxin countermeasures is low, and conventional techniques suffice. Yet, when considering carbonization equipment as an alternative to waste incineration or as a resource recovery device, the dioxin issue cannot be avoided.
The key requirements for carbonization equipment aimed at recycling boil down to producing high-quality carbonized material at low cost without generating dioxins. This means the furnace must be sealed to suppress dioxin formation by operating under oxygen-free (or low-oxygen) conditions while enabling high-temperature steaming. Additionally, the contents must be agitated to ensure uniform carbonization.
Currently, rotary kiln-based systems are relatively well-regarded as carbonization equipment meeting these conditions. The rotary kiln method involves placing raw materials into a rotating cylindrical furnace and carbonizing them using internal or external heat. A drawback of rotary kiln incinerators was the need for a stoker to completely burn residual carbonized material into ash. In carbonization, this becomes an advantage.
Other reasons for its promise as a carbonization device include: ① It can carbonize any material containing organic matter, converting the organic content into combustible pyrolysis gas. This gas provides the heat needed for carbonization, saving fuel. ② Its simple structure, lacking mechanical parts inside the furnace, results in fewer breakdowns.
③ Although advanced sealing technology is required for furnace containment, the absence of dioxin removal equipment and a stoker offers advantages in installation space and equipment cost. Compared to gasification-melting furnaces—considered next-generation incinerators by municipalities and costing around ¥50 million per ton—this technology can be introduced at roughly one-third to one-half the cost.
④ Raw materials are continuously rotated by the kiln, preventing uneven burning. As the underlying technology is well-established, numerous players—from major machinery manufacturers to small-to-medium enterprises and startups—have entered the carbonization equipment market. Equipment ranging from small-scale units processing about 1,000 kg per day to large-scale units handling tens of tons has been developed. Let's examine carbonization processing cases for various organic wastes, the specific carbonization furnaces used for each, and their market potential.

2. Carbonization Gains Attention from Both Expanding Charcoal Markets and New Applications for Organic Waste A major reason carbonization is gaining attention is the expanding applications for charcoal. While many recycling businesses struggle with distributing their products, carbonized materials have relatively bright prospects. Charcoal, which was produced at over 2.7 million tons annually in the 1930s and used as a major fuel alongside coal, has seen steadily declining production. However, in recent years, new demand beyond fuel has emerged, leading to increased production. Currently, charcoal sold domestically for non-fuel applications totals 58,350 tons annually (1999 figures).
This growth stems from the charcoal's excellent material properties: its ability to adsorb odor substances from air and water, as well as pollutants from water, due to its surface covered in countless microscopic pores; and its soil improvement capabilities, such as promoting soil microorganism growth and enhancing aeration and permeability (designated as a soil improvement material under the Soil Fertility Improvement Act established in 1984). Recently, its adsorption effectiveness for volatile organic compounds (VOCs) such as toluene, xylene, and formaldehyde—factors linked to sick building syndrome—has also been proven. Consequently, the use of charcoal from wood-based waste, including thinned timber, pruned branches, and sawdust and offcuts from sawmills, is expanding. Such carbonized materials are expected to find widespread, high-value-added applications as alternatives to traditional charcoal products. For example, applications include drinking water purification,
bedding and pillows, deodorizers, and bath products. Additionally, soil conditioners and residential humidity control materials (regulating subfloor humidity to prevent mold and termite infestations) are gaining attention.
Furthermore, they show promise as activated carbon for more advanced applications such as adsorbing dioxins, purifying industrial water, and solvent recovery. Activated carbon is produced by reacting carbonized materials with oxidizing gases at high temperatures (gas activation method) or by impregnating uncarbonized raw materials with dehydrating/oxidizing chemicals and carbonizing them in an oxygen-free environment (chemical activation method), thereby enhancing porosity.
Generally, materials with a surface area per gram below 800 square meters are classified as charcoal, while those above are considered activated carbon. However, some carbonized materials produced at high temperatures (800°C or higher) possess equivalent surface areas, offering higher added value as recycled products. While efforts to carbonize wood-based waste are advancing, the development of applications for organic waste, including food waste, as carbon feedstock is also beginning. The current state of resource recovery for organic waste primarily involves composting or converting it into slag for subsequent commercialization. However, composting faces challenges, including an anticipated future oversupply of the resulting product. Additionally, incineration ash and molten slag (slag) have limited applications, such as roadbed materials or construction aggregates. This backdrop has drawn attention to charcoal as a new potential use. Incidentally, the current market price
s for charcoal made from waste materials are as follows: coffee grounds charcoal (for soil conditioners) at ¥30 per kg, okara charcoal (for fertilizers) at ¥80 per kg, and tire charcoal (for deodorizers) at ¥30 per kg.

3 Construction Waste Wood: Construction waste wood represents the largest business opportunity in the carbonization market. It is the closest to charcoal's original raw material and has largely untapped recycling potential. The full enforcement of the Construction Materials Recycling Act in May 2002 will provide a significant tailwind.
According to the Ministry of Land, Infrastructure, Transport and Tourism's "Survey on the Actual Status of Recycling Construction By-products, Fiscal Year 2000," while the reuse of asphalt concrete and concrete blocks as recycled aggregate and road subgrade material significantly increased to 98% (85% in FY95) and 96% (65% in FY95), respectively, the rate for wood deteriorated to 38% (40% in FY95). Demand for fuel chips, which had been the main use for construction-generated wood, has decreased due to factors like the aging of wood chip boilers and the successive closures of public bathhouses. Recycled chips are now in surplus, and prices for chips used in paper and pulp production have fallen across the board. For fuel chips, cases of so-called reverse payments—where companies pay transportation fees to have chips delivered to sites—are increasing, making the development of new uses an urgent priority.
Under the Construction Recycling Law, wood may be incinerated as a special exception only when costs become prohibitively high, such as when no recycling facility exists within a certain radius (25 kilometers) of the construction site. However, simply burning it yields zero added value as a resource. Considering the growing societal opposition to incineration, combined with the cost benefits of recycling, the long-term trend is expected to shift toward recycling.
Kumagaya Carbon in Kumagaya City, Saitama Prefecture, is a pioneer in this field. Established in October 1998 as a subsidiary of Kamei Sangyo—a company licensed for industrial waste collection, transportation, and disposal—it began as a carbonization business for wood chips, a product facing sluggish demand.
The reason for establishing it as a separate entity was that if Kamei Sangyo, an industrial waste processor, performed the carbonization itself, it would be classified as incineration under current laws. The resulting carbonized material would then be categorized as "ash residue," making it unsellable as a commercial product. Therefore, Kamei Sangyo handles the chipping process up to that point, selling the chips as a valuable material. Kumagaya Carbon then purchases these chips as raw material and processes them at its factory.
The company's carbonization system first removes coatings, termite preventatives, and preservatives during the chipping process. This is because these substances could leach out if the carbonized material were used as a soil conditioner. The selected waste wood is then chipped using a crusher. Paint fragments and metals are thoroughly removed using screens, magnetic separators, and metal detectors before the raw material chips are finally produced.
The carbonization equipment adopted by the company is a type called the reciprocating swing kiln, jointly developed by Kyoko Giken and Chiyoda Engineering. While fundamentally similar to the rotary kiln type in performing dry distillation gasification under low-oxygen conditions, the furnace swings like a cradle instead of rotating. This design ensures the charcoal is formed uniformly and finely without deformation. Only a small amount of fuel (kerosene or A-grade heavy oil) is used as an ignition aid during raw material loading. After that, the material is self-ignited and steamed at temperatures exceeding 1000°C for approximately 40 minutes. The dry distillation gas produced during carbonization is not used for carbonization itself. Instead, it is mixed with air in a dry distillation gas calcination furnace and re-burned. This exhaust gas also exceeds 1000°C and is used for drying when high-moisture-content raw materials are used. Even then, significant excess heat remain
s, making it possible to utilize this heat as an energy source for other equipment. The plant produces 2,000 liters of charcoal per hour from 2,500 kilograms of wood chips. In addition to shipping the charcoal as soil conditioners and de-icing agents, the company also markets its own bagged products: the subfloor humidity control material "Sukoyaka Mokkun" and the soil conditioner "Irodori".

4 Municipal Waste: Approximately 51 million tons of general waste is generated annually. While the proportion recycled has increased recently due to expanded sorting and collection by municipalities, the current reality is that about 39 million tons still relies on direct incineration. Against this backdrop, municipalities required to strengthen dioxin countermeasures when renewing incinerators are beginning to consider introducing new carbonization furnaces.
Due to the potential for various substances to be mixed in and the large volume generated at once, the uses for the products of municipal waste are limited to thermal recycling extensions such as fuel, cement kiln feed, or raw materials for steelmaking. However, the aim is to enhance the quality as fuel through carbonization and achieve high added value. The Itoigawa Regional Administrative Association (Itoigawa City, Niigata Prefecture), which decided to introduce carbonization furnaces as a municipal waste recycling method for the first time nationwide, adopted a carbonization furnace technology introduced by Hitachi Ltd. from France's Tido. This process recovers metals contained in the waste and carbonizes the remaining organic matter. With a processing capacity of 70 tons per day in continuous 24-hour operation, completion is scheduled for March this year. The resulting carbonized material has a high calorific value of 4,000 to 5,000 kilocalories per kilogram, making it s
uitable as a substitute fuel for coal. Kurimoto Iron Works has also received an order from Ena City, Gifu Prefecture, for a waste-to-solid fuel (RDF) facility equipped with carbonization equipment. This facility dries combustible municipal waste, converts it into RDF, and then carbonizes it through dry distillation, also targeting fuel applications. Using this carbonized material in waste-to-energy plants that drive steam turbines with heat from municipal waste incineration could more than double the energy recovery efficiency compared to directly burning the waste. Considering this, recycling as an energy source becomes a viable path. Sewage Sludge: Japan's sewer coverage rate was 62% at the end of 2000. Sewage sludge generated at treatment plants nationwide totals approximately 1.86 million tons (based on dry weight at generation). With a high moisture content of 75-80%, this sludge is prone to decay, making recycling difficult. Its utilization as cement or solidified cons
truction materials is advancing, achieving a resource recovery rate of 57% when combined with return to green agricultural land. Additionally, 3% is effectively utilized for energy and other purposes.
However, aiming for higher value-added utilization, cases of introducing carbonization plants are actually increasing. The Lake Biwa South Central Purification Center (Kusatsu City, Shiga Prefecture) has been operating a sewage sludge carbonization facility since April 2001. This system, developed by Daido Steel in collaboration with the Japan Sewage Works Agency, is called the "External Combustion Rotary Kiln with Dry Distillation Gas Blowing Pipe." It comprises a complete system including a sludge hopper, dryer/carbonization furnace, and carbonized sludge storage and transport equipment.
It processes 20 tons of dewatered sludge daily, producing approximately 1.7 tons of carbonized material. This carbonized material is effectively utilized within the center as a dewatering aid and deodorizer, and is also returned to the surrounding area as soil conditioner and snow melting agent.

5 Food Waste: The Food Recycling Law, enacted in April 2001, mandated that food-related businesses generating 100 tons or more of food waste annually must reduce their discharge by 20% by 2006 through measures such as source reduction, minimization, and recycling. Annual food waste generated domestically totals 19.4 million tons (1996 Ministry of Health survey). Of this, the law targets 3.4 million tons of industrial waste from food manufacturing and 6 million tons of commercial waste from food distribution and the restaurant industry, totaling 9.4 million tons. Currently, only 1.65 million tons (17%) of this commercial food waste is recycled; the remaining 7.75 million tons is incinerated or landfilled, making improving the recycling rate an urgent priority. However, food waste generated by food distribution and the restaurant industry requires secondary processing even when converted into fertilizer or feed, as its effective components are low relative to its volume. Furthe
rmore, salt incorporated during food processing and cooking becomes concentrated through composting. Concerns about salt damage have been raised, potentially reducing its commercial value as fertilizer or feed. On the other hand, large corporations generating substantial organic waste, particularly the beer industry, are advancing efforts to repurpose waste or utilize it as biomass energy through methane fermentation as part of achieving zero emissions at their factories. However, much of the food manufacturing industry is concentrated in rural and fishing villages, the source regions for raw materials, and is primarily carried out by small and medium-sized enterprises (SMEs). For these businesses, whose emissions are limited and who lack the economic capacity for large-scale equipment, small-scale carbonization units present a viable option. Regarding the concern of salt residue in carbonization, Yasuhara Chemical (Fuchu City, Hiroshima Prefecture) and VID (Shinjuku Ward, T
okyo) resolved this by using limonene extracted from citrus fruits as a pretreatment. Limonene has the property of dissolving and removing salts and oils.
The jointly developed "V-BOX J" first adds limonene to food waste at a weight ratio of 1%, stirs it at 50°C for 24 hours, then dehydrates it. This removes salt and oil while reducing volume to about 10% of the original. Steaming this material at 300-400°C produces activated carbon. One hundred units have been delivered to onion farmers on Awaji Island, Hyogo Prefecture, for processing waste such as stems and peels. The resulting activated carbon is planned to be mixed into non-woven fabric for use as substrate in rooftop greening.

6 Livestock Manure: Animal manure (livestock waste) amounts to 91.52 million tons annually. It is said that 96% is recycled as compost, etc., with only 1% disposed of directly. However, management before transport to composting facilities is often lax. Many facilities lack adequate odor control measures or prevent leakage into the environment, such as using composting beds (natural fermentation on concrete floors). This has led to cases of water pollution in rivers and groundwater due to nitrate nitrogen.
In response to this situation, the Livestock Waste Act, effective November 2004, mandates proper treatment and storage of livestock waste by livestock farmers. This requirement applies to the majority of small-scale, individually operated livestock farms (those with 10 or more cattle, 100 or more pigs, 2,000 or more chickens, or 10 or more horses). At one poultry farm in Hokkaido, chicken manure is typically used as fertilizer, but they were incinerating it on-site in their own incinerator.
However, due to difficulties in renewing the incinerator because of dioxin concerns, they decided to introduce a carbonization unit. For every 100 kg of chicken manure, 30 kg of granular charcoal was produced. Analysis showed it contained the three major elements essential for crop growth: nitrogen, phosphorus, and potassium. They mix this charcoal back into the chicken manure to create a value-added fertilizer for sale. The revenue from this fertilizer is then reinvested into grain production for poultry feed, creating a circular system.
Summary: For food waste, sludge, and livestock manure—materials with high moisture content that were difficult to dispose of even as waste—carbonization processing offers clear benefits. It reduces input waste to 1/5 to 1/20 of its original weight (by mass), making it valuable even as a simple volume reduction device. Furthermore, the resulting charcoal itself has higher commercial value compared to products like compost or molten slag, making it easier to establish as a viable recycling business.
However, current charcoal production is only about 50,000 tons. Even if half of this could be replaced by charcoal made from organic waste, the reduction in processing volume would be negligible. Without further development of applications, oversupply is inevitable, similar to compost. Fortunately, however, utilization is beginning to advance in areas such as building materials (subfloor and wall materials) driven by the greenhouse effect problem, as well as for slopes, expanding greening projects, and gardening. Demand expansion is still anticipated.

Moving forward, carbonization furnaces will require more specific performance tailored to how various organic wastes are collected, their resulting characteristics, and the intended uses of the final product. Consequently, while carbonization furnaces certainly process waste, they should be positioned not as an extension of the all-purpose incinerators of the past, but rather as industrial "calcination furnaces" specifically designed to produce charcoal. This shift in positioning is expected to expand the market.