2 Biogasification of Biogenous Waste using Dry Anaerobic Fermentation System

Corporate Planning Dept.Corporate Planning &
Administration Division
Takuma Co., Ltd.

 We are reporting about the verification test of “biodegradable fish trays” and the succeeding use of treated waste products as a core technology based on methane fermentation. Further, the CAMPO RECYCLE PLAZA, which can be a reference example of “Biomass-town Concept”, is described. The basic technology is to ferment anaerobically 15% - 40% of highly concentrated solid using the dry type by continuous plug-floe. This technique is called the Kompogas process.

1. Anaerobic degradation test of biodegradable plastic
 Biodegradable fish trays composed of polylactate materials were crushed into smaller pieces and mixed with kitchen garbage and newspaper. Subsequently, the highly concentrated mixture was fermented anaerobically at 55 degrees C in the fermentation tank with effective capacity of 100m3 for 60 days detention time. Typical material balance after acclimation is shown in Fig. 1. As a presumed result of the decomposition rate of biodegradable fish trays, biogasification was 99.7%-VS while residual solid ratio was 0.3%-VS.

Fig-1 Mean material balance for 34 days after acclimation
Fig-1 Mean material balance for 34 days after acclimation

 The result of the verification test indicated that biodegradable plastics consisting of polylactate could be fermented anaerobically and conversion to further useful products could be performed. In the dry type of anaerobic fermentation, bulky wastes like fish trays were rough-crushed to about 20-40mm in size and were fed into the tank. The pretreatment process was easy. In addition, the system was deemed practical from the economical point of view.

  Approximately 140t/day of general and industrial wastes is incinerated in the rotary kiln and stoker incinerator of the CAMPO RECYCLE PLAZA (Sonobe city, Kyoto). There are three plants which operate in the site. The heat recovery plant 1 effectively processes the wastes and salvages the heat as steam from the exhaust. The recovered heat is then utilized to drive an induced draft fan and to provide warmth for greenhouses of adjoining farms. The waste appliance recycle plant receives 70t/day of general and industrial wastes and performs crushing, selection, and retrieval of resources. Lastly, the biogas plant, which adopted the Kompogas process in April 2004, is transformed into a biotechnology recycle plant.
  The wastes treated in the plant include kitchen garbage, general wastes from pruning wood and food wastes, and industrial wastes, such as wood waste and sludge. The fermentation tank has a disposal capacity of 50t/day (fermentation tank: 25t x two units).
  The flow of the recycling procedure is shown in Fig. 2. The biogenous wastes brought in the plant are rough-crushed to about 20-40mm in size. Subsequently, they are fed into a mixer with a crane and mixed with diluted water. Small scale plants are able to treat wastewater with a solid concentration of 15 -40% using the dry type of anaerobic fermentation. After moisture is adjusted, the garbage is heated to 55 degrees C, which is the temperature suitable for anaerobic fermentation; and is fed into the anaerobic fermentation tank. The fermentation tank is an oblong tank with 6.8m in diameter and 39m in length per unit, which is considered the world's largest class. The biogas produced is used as power to operate the gas engine (310kw x 2 units) and as fuel for automobiles in the facilities. Residues are converted to compost after aerobic fermentation, while the waste not suited for compost is incinerated by the existing heat recovery plant.

Fig-2 CAMPO RECYCKE PLAZA/The treatment flow
Fig-2 CAMPO RECYCKE PLAZA/The treatment flow

 After the residual dehydrator effluent is treated with carrier-added anaerobic-aerobic activated sludge process, it is utilized as dilution water for the said mixer. In addition, the remaining treated water is concentrated and allowed to precipitate as gas coolant water for the existing heat recovery plant. Thus, no wastewater is disposed into the rivers.
  The results after a commercial operation are revealed as follows: 1) The biogas generation is an average of 205 m3 N/ton per refuse2) Approximately 26.8%-wet of refuse is collected as biogas and approximately 20%-wet is dehydro-residue. 3) The power consumption at the time of constant load operation is approximately 40% of the total power generation.4) The power consumption per refuse is 114 KW-h/ton.
  The material balance of the present three plants is shown in Fig. 3.

Fig-3 CAMPO RECYCLE PLAZA, Waste Recycle System

Fig-3 CAMPO RECYCLE PLAZA, Waste Recycle System

 Therefore, we can conclude as follows: 1) Waste, which previously cannot be recycled, is finally treated. 2) The wastewater from the plant can reduce drainage processing expense and cost of water supply by undergoing treatment within the system. 3) Fermentation residues are converted to compost and are utilized in farmland. Otherwise, fermentation residues are transformed into auxiliary fuel in the heat recovery plant. 4) Treatment of general and industrial wastes enables the establishment of "biomass town", which is the foundation of the plants.
  In the future, there is a design to adopt biodegradable plastic products to collect kitchen garbage brought in the biorecycle plants. Subsequent conversion into useful products from the recycled kitchen garbage is put into practice, as well.

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