Mitsubishi Heavy Industries Technical Review Vol. 59 No. 4 (December 2022)
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Development of High Efficiency Biomass Recovery andRecycling System for Municipal Waste
KEIJI FUJIKAWA*1NOBUYUKI UKAI*1

KEI-ICHI NAKAGAWA*2

TAKASHI IKE*3

SUSUMU OKINO*4

Toward the establishment of a resource recycling society, there is a growing need in thewaste treatment sector for separately collecting, to the extent possible, biomass such as kitchen
waste (food waste) and paper from waste and recycling it. However, it is not easy to separately
collect biomass from waste containing plastics, metals, etc., and it has become a challenge in thepromotion of recycling. Mitsubishi Heavy Industries, Ltd. (MHI) Group is advancing thedevelopment of technologies for facilitating the separate collection of biomass resources fromwaste that had to be incinerated due to the difficulty in separate collection and converting theminto recyclable materials. The overview and features of this system are introduced in this report.

|1. Introduction
The amount of municipal solid waste generated in Japan in 2020 was 41.67
million tons, the breakdown of which is 11.65 million tons of domestic waste such as
household waste and 30.02 million tons of commercial waste from supermarkets,convenience stores, restaurants, etc.(1). About 60% of municipal solid waste (dry weightbasis) is biomass resources such as kitchen waste and paper, but since municipal solid
waste contains plastics, metals, etc., biomass resources are not separately collected
and recycled but are mostly incinerated at present(2). In addition, there is an issue that
although power generation with boiler and heat utilization are conducted in many
waste incineration plants in Japan, the energy recovery rate is low because kitchen
waste contains a lot of water. In the light of such situations, in 2019, the Ministry of
the Environment referred to the importance of developing “the function as a regionalenergy center by efficiently recovering waste energy” and producing methane gas
through “promotion of the recycling of waste and the utilization of biomass”(3).
Looking at the world, the EU plans to substantially increase biomethane
production to 35 billion m3 in 2030 in the Fit for 55 package and the REPowerEU,
which is a plan to respond to the Russia-Ukraine crisis, and the State of California in
the United States has also set the biomethane procurement target for utilities to beabout 2 billion m3 by 2030(4). Thus, with the risks involved in energy security and theprice increase of natural gas in addition to the increasing requirements for
decarbonization of energy, there has been a rapidly growing interest in utilizing
biomethane that can be domestically procured. In Japan as well, which depends onimports for its energy, the expansion of utilization of biomethane will be a significant
challenge in the achievement of carbon neutrality in 2050.
Against such a backdrop, the MHI Group is advancing the development of a high-efficiency
biomass recovery/recycling system that facilitates the easy separate collection of highly
contaminated biomass resources from municipal solid waste containing various materials such asplastics and metal and converts them into materials having properties suited to produce methane*1

Chef Staff Researcher, Chemical Research Department, Research & Innovation Center, Mitsubishi Heavy Industries, Ltd.

*2

Chemical Research Department, Research & Innovation Center, Mitsubishi Heavy Industries, Ltd.

*3

Chef Staff Manager, Business Intelligence & Innovation Department, Technology Strategy Office, Mitsubishi Heavy Industries, Ltd.

*4Senior Manager, MHI Solution Technologies, Ltd.

Mitsubishi Heavy Industries Technical Review Vol. 59 No. 4 (December 2022)
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|2. Overview of high-efficiency biomass recovery system
The basic configuration of this system is shown in Figure 1.

Figure 1 Basic system configuration

This system consists of a reactor for hydrothermally processing waste at a constanttemperature and pressure and a separation equipment for separating reaction products into biomass
resources such as kitchen waste and paper and materials such as plastics and metal that areunsuitable for recycling.
The reactor has a function of processing waste under appropriate reaction conditions (i.e.,temperature, pressure and reaction time) set up for finely granulating only biomass resources while
maintaining the original shapes of unsuitable materials so that waste can be easily separated into
biomass resources (i.e., kitchen waste and paper) and unsuitable materials.
One example of treated products from a simulated waste (domestic waste) is shown inFigure 2. As seen in the figure, plastics such as garbage bags have their original shapes, whilebiomass resources such as kitchen waste are broken into small pieces like sawdust. These reaction
products are separated by a general separation equipment, so a high recovery of biomass resources
can be easily collected.

Figure 2 Treated products from simulated waste sample(one example)

This system adopts batch-type processing in which feeding to the reactor, treatment anddischarge are repeated. When the system is automatized by being interlocked with a waste
charging/discharging conveyor and a separation equipment for treated materials, labor saving in theoperation can be realized.

|3. Effects on energy recovery when combined with methane
fermentation process
The system previously introduced in Chapter 2 can achieve the following effects whencombined with methane fermentation process.

3.1

Increased biogas generation by improvement of recovery and decomposition
rate of biomass resources
When this system is applied, a high recovery rate of biomass resources can be achieved as

Mitsubishi Heavy Industries Technical Review Vol. 59 No. 4 (December 2022)
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described above. In addition, the decomposition rate of paper, trees, plants and crop residue, whichwere considered to have a slow reaction rate in producing methane gas, is increased, resulting in an
increase in biogas generation. From laboratory test results, it is estimated that for municipal solid
waste containing about 60% biomass resources (dry weight basis), when the high-efficiency
biomass recovery system and wet fermentation are applied in combination, the biogas generation
will be 1.2 to 1.3 times larger than that of the conventional method which consists of crusher,separator and dry fermentation (Figure 3).

Figure 3 Comparison of biogas generation between methane fermentation process methods(one example)

3.2

Contribution to stable operation of methane fermentation process and small
footprint

When waste having a large variety of properties and shapes is supplied, methane
fermentation sometimes becomes unstable due to fluctuations in the input load and changes in thereaction rate. There is an issue in the methane fermentation process that it is difficult to keep stable
operation. The biomass resources treated by this system are broken into small pieces and havehomogenized properties and shapes. Therefore, the input load into a fermenter and the reaction rate
are stabilized and the operation management of methane fermentation can be simplified.
Furthermore, as the operation of methane fermentation is stabilized, a thermophilic(high-temperature) fermentation method can be applied. In thermophilic fermentation where thetemperature is around 55℃, the reaction rate is higher than that in mesophilic fermentation around37℃ and the retention time in a methane fermenter can be reduced by half. Therefore, the capacityof the fermenter can be reduced by half and can be made compact.

3.3

Rationalization of wide-area waste management by reducing waste in volume
and rendering waste harmless and odorlessBiomass resources treated and collected by this system are broken into small pieces, thereby
being reduced in volume as well as being rendered harmless and odorless through heat treatment
and sterilization. For example, in the wide-area and intensive management of municipal solid(household) waste treatment which has been recommended by the government, there may be a casewhere a transfer station to a waste incineration plant is required. When this system is applied, (1)production of methane gas from biomass resources can be completed at a transfer station and thewaste transportation load is substantially reduced and (2) separated unsuitable materials such as
plastics and metal are rendered harmless and odorless by heat treatment and can be transported to awaste incineration plant in a relatively hygienic state (Figure 4).

Mitsubishi Heavy Industries Technical Review Vol. 59 No. 4 (December 2022)
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Figure 4 Image of application of this system in wide-area management ofmunicipal solid waste

3.4

Increase in energy recovery and reduction of CO2 emissions by 20% by hybrid
treatment with waste incineration

This system can be also applied to hybrid treatment with incineration and methane
fermentation combined, as shown in Figure 5, which is being introduced as a new municipal solid
waste treatment method. With the energy recovery through methane production from biomass
resources and power generation by gas engine as well as the power generation efficiency being
improved by the increased heating value of waste through incineration of plastics separated as
unsuitable materials, the increased energy is obtained even after the energy required for this system
is deducted.
The CO2 emissions reduction effects for municipal solid waste were compared
between (1) the incineration treatment (conventional method) and (2) the hybrid
treatment with incineration by application of this system. The respective net CO2
emissions in (1) and (2) were calculated as follows: obtaining the total of the CO2
emissions derived from plastics in waste and the CO2 emissions to which the electric
power consumption at a plant was converted with the assumed CO2 emission factor of
the electric power system; converting the electric power obtained from powergeneration to the amount of CO2 emissions reduced; and subtracting the amount ofCO2 emissions reduced from the obtained total CO2 emissions to calculate the net CO2emissions for each of (1) and (2). The calculation result is shown in Figure 6. (2) Hybrid
treatment is expected to reduce CO2 emissions by about 20% due to an increase inenergy recovery compared to (1) incineration treatment.

Figure 5 System flow of hybrid treatment with this system applied (oneexample)

Mitsubishi Heavy Industries Technical Review Vol. 59 No. 4 (December 2022)
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CO2 emissions calculation result|4. Conclusion
We devised a treatment system that can easily collect biomass resources such as kitchen
waste and paper from waste containing plastics, metal, etc., and convert them to materials having
properties suitable for recycling. In combination with methane fermentation process, this system
can increase the collection rate and decomposition rate of biomass resources from waste, producing
an effect of increasing the biogas generation amount. Going forward, we will contribute to solving
global environmental issues and realizing a resource recycling society by providing this systemwidely to domestic and overseas private companies and local governments.

References(1)

Technical information on waste disposal, (2022), Ministry of the Environment Government of Japan,
https://www.env.go.jp/recycle/waste_tech/index.html (in Japanese)(2) Municipal solid waste generation and disposal in FY2020, (2022)，Ministry of the Environment
Government of Japan, https://www.env.go.jp/content/900518688.pdf (in Japanese)(3) Wide-area waste management and concentration for securing sustainable and adequate treatment(Notification), Ministry of the Environment Government of Japan,
https://www.env.go.jp/hourei/11/000652.html (in Japanese)(4) Expanding use of biomethane in Europe and the United States (2022), Agency for Natural Resources
and Energy, https://www.meti.go.jp/shingikai/energy_environment/methanation_suishin/pdf/007 (inJapanese)