The amount of sewage sludge produced from municipal wastewater treatment plants in Japan is increasing every year. This sewage sludge has to be condensed, dewatered, incinerated and then landfilled. However, because landfill capacity is decreasing in Japan, effective treatment methods and disposal technologies for sewage sludge are urgently needed. Usually, sewage sludge has been used as compost and construction materials, but the amount of sewage sludge is not reduced effectively through these uses. Recently, the solubilization process has become the focus of attention as a means by which sewage sludge can be reduced effectively.
In this review, we introduce an overview of solubilization processes using chemical, biological and physical technologies while referring to previous sludge treatment methods. Additionally, we provide details about the performance and efficacy of each solubilization process.

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In bio-diesel production, waste glycerin liquid containing methanol and potassium is produced as a byproduct. At present, this waste liquid is treated by burning. In consideration of the effective use of degradable organic substances such as glycerin and methanol, the possibility of applying waste glycerin liquid to methane fermentation was studied. In the experiments for this study, the decomposition rate of COD_cr was more than 80% and fermentation obstruction did not occur. The methane gas production rate per 1 g of COD_cr decomposition was 0.51 Nl-dry. This rate nearly coincides with the theoretical rate. It is also necessary to keep nutrients such as nitrogen and phosphate and solids at suitable concentrations for successful methane fermentation. However, since waste glycerin liquid contains no solids and less nitrogen and phosphate, kitchen waste was mixed with waste glycerin liquid to compensate for the lack of nutrients and solids.

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Basicity (mainly CaO/SiO₂) is often used to describe the melting characteristics of wastes, which are comprised of multiple components. Although basicity shows certain tendencies related to the melting characteristics of individual types of waste, it lacks versatility.
Diagrams with SiO₂, CaO, and FeO at the vertexes were depicted by slicing 14 existing types of quaternary phase diagrams with SiO₂, Al₂O₃, CaO, and FeO on a plane at a fixed amount of Al₂O₃. Compared with basicity-based indications, the quaternary phase diagrams are found to be able to describe more precisely the relationships between components and melting (flowing) temperatures. Melting temperature data obtained from Russian research on the viscosity of blast-furnace slag were plotted on the diagram, indicating that their distribution patterns closely resemble those of our data. It can be said that these results confirm the effectiveness of the diagram in describing the melting characteristics of wastes.

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Some of the most important questions for managing Japan’s recycling system include how much should recycling costs be set at and who should bare them. This paper estimates recycling costs on a volume basis by using inverse density of the waste. After this theory was proposed and measured by the authors, comparisons were made between the types of waste, between the municipalities, and by volume-basis and weight-basis. A questionnaire survey was conducted in 13 municipalities revealing the recycling costs for aluminum cans, steel cans, PET bottles, and glass bottles, on both a weight-basis and a volume-basis. The results are discussed here.

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Fuel oil production is expected to become a typical method for waste plastic recycling, due to increasing demands for inexpensive fuels and the fact that it gives a higher energy recovery rate when compared to the other methods.
Technical requirements and the economic conditions behind this type of fuel production were investigated with the aim of promoting the recycling business. Poor performance and the high facility costs of tank reactors spoiled the economic feasibility: small sized plants of 1-1.5 ton/day capacity could not give business profits. Other typical problems were low thermal conductivity of the thick reactor wall and serious coke formation. Large sized plants of over 20 ton/day require huge investments, and do not fit into the treatment scale, typically 3-7 ton/day of waste management companies. In the current business of fuel oil production, collecting enough waste and reducing the recycling costs are obstacles that need to be looked at in a practical way.
To promote fuel oil production, a typical estimation suggests a business model that uses an oil production plant with a treatment capacity of at least 6 tons per day, a plant cost of 50000000 yen under the conditions where the selling price for oil produced is at 40 yen/kg, and a disposal charge of 30 yen/kg.

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The Law for the Recycling of Specified Home Appliances has been reinforced in Japan in order to promote the recycling of end-of-life home appliances. The number of product types to be covered under this law is expected to increase as a result. While elaborate dismantling of end-of-life products will increase the reuse of parts and the recycling of materials, it may at the same time increase the time and cost required for dismantling. Monitoring how dismantling levels for end-of-life products will need to be set for each individual product will be of great interest.
Hitachi, Ltd. has developed the Recyclability Evaluation Method, known as REM, which allows an estimation of the recycling rate for end-of-life products to be made based on the time and costs required for dismantling. In this paper, REM has been applied to a PDP-TV (plasma display panel television) to investigate the relationship between recycling costs and recycling rates at each level of dismantling, with a comparison made for the same on a CRT-TV. The reliability of the results and the difficulties in covering a PDP-TV under the recycling law are also discussed.

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The effect of the combination of hyperthermophilic hydrolysis and ammonia stripping on thermophilic anaerobic digestion was evaluated by a continuous experiment using a 2-litter reactor system. As a result, methane yield was increased by 20% and digestion residue was reduced by 50%. Ammonia stripping conditions in the hyperthermophilic hydrolysis reactor at 80°C and pH 7.5 was shown to keep ammonia concentration in the digester at 1000mg/L or less. The low concentration of ammonia allows the digester effluent to be used as a substitution for dilution water. Improved gasification efficiency also reduces the organic load on the subsequent effluent treatment process by 50%.

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This paper presents some of the primary factors involved in introducing garbage fees by local governments in Japan, and explains how the price per bag of garbage is set. Whether a local government introduces a garbage fee or not does not strongly depend on the cost of managing wastes. Instead, it depends more heavily on the financial situation of that particular government. The price level for a garbage bag is affected by income levels and the number of explanation sessions in the community. In addition to these endogenous factors, exogenous factors such as decision-making regarding garbage fees by adjacent communities also play a significant role in the decision process-both in introducing garbage fees and setting prices.

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We propose a self-restoring liner system that uses colloidal solution for landfill sites. The colloidal solution is filled in a pressurized state between a double liner. This prevents the leak of exudation water and immediately forms new liner around a damaged area when liner damage occurs. As a result, the function of the system is restored naturally.
We carried out some basic experiments with colloidal solution of about 3-5% weight ratio. As a result of these experiments, we were able to confirm that mud cake and a penetration deposition layer were formed around a liner damage area by the colloidal solution and that the function of the system was restored.
In addition, we confirmed the long-term continuity of colloidal particle dispersion in the colloidal solution and the fluidity performance of the colloidal solution in the double liner.
From these experimental results, we were able to confirm the possibility of practical application of this liner system that uses colloidal solution.

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