The basic waste disposal process in Japan consists of volume reduction for municipal solid waste, carried out through incineration and crushing, detoxification and landfilling of incineration residues. Incineration residues therefore account for more than 75% of the wastes destined for landfills. Against such a background, the authors identified challenges associated with landfilling of incineration residues including inorganic salt control, recycling by-product salt, controlling leachate treatment inhibition by organic chelating agents and early stabilization of landfill sites. We also examined methods for solving such challenges.

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Kagoshima Prefecture constructs a closed system industrial waste control type landfill site based on public involvement : Japan′s largest such facility to date. The concept expects success within a limited time period through integration of reclamation pre-treatment (air injection and watering), reclamation management (early stabilized-type reclamation and monitoring) and reclamation after-treatment (air injection and oxidizer pouring). The site is based on the new multi-barrier concept.

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In Japan, controlled-type solid waste landfills are usually controlled under semi-aerobic conditions, however, an impermeable layer has been made in most of them. Therefore, parts of the waste layer in such landfills tend to be under anaerobic conditions. This paper investigates characteristics of the leachate from the mixture of organic and inorganic waste under the anaerobic state. Factors that could reduce COD and heavy metals in the internal water after it passes through the intermediate cover soil are also explained. Furthermore, the authors clarify the phenomenon whereby Ca²⁺ in the incineration ash is dissolved in leachate and trapped by the intermediate cover soil. This causes the incineration ash to solidify. In addition, the paper mentions how to keep the permeability of waste and intermediate cover soil in landfills in order to induce faster stabilization.
　 In conclusion, for maintenance of a landfill site, it is important to take three factors into careful consideration: incompatibility of waste, permeability of landfill site and quality of intermediate cover soils.

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Leachate treatment in Japan has made significant advancements, especially in the use of trickling filter, rotating disc and contact aeration as well as in calcium removal, desalting processes, dioxin separation and decomposition and also 1,4 dioxane processing. Due to the fact that the quality and composition of pollutants being removed from each landfill for transport to their final disposal site will vary to a great degree, we show here which leachate treatment technology is applicable for each pollutant. In addition, we describe the historical changes that have taken place in water treatment technology with regard to final disposal sites. We also discuss the questions that need to be asked concerning the future of leachate treatment technologies.

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The flow for leachate treatment method commonly used in controlled final landfill sites is as follows : First stage of Chemical Clarification → Biological Treatment → Second stage of Chemical Clarification → Advanced Wastewater Treatment. Recently, however, property changes in landfill waste have caused reductions in organic pollutant loads such as BOD and COD, which conversely increases the salinity level. This is causing a growing impact on living organisms. In addition, the density of persistent COD components rises with the passage of time in a landfill, making it difficult for conventional processes to properly treat T-N and COD. In response to this situation, we studied a treatment method that uses a combination of electrolytic denitrification and catalyzed oxidative decomposition. Our results confirm the possibility of treating T-N and COD in a stable, low cost way.

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While the municipal government is promoting the adoption of incineration for treatment of MSW, those in the landfill industry are facing the problem of calcium scale adhesion onto water pipes during the process of leachate treatment. Although a method that uses lime soda has generally been adopted in order to remove calcium scale its massive use of chemicals spells high running costs for the landfills.
　Taiheiyo Cement Corp. has already developed a new method for removing calcium scale and we can now apply this method for leachate treatment as well. The new method uses no chemicals but instead utilizes an ion exchange resin. Moreover, this method does not generate calcium sludge, successfully assisting in the mitigation of a decreased landfill capacity and in preventing the re-elution of calcium caused by reclamation.
　We have already finished pilot-scale testing of this leachate treatment and are currently looking for people in the landfill industry willing to adopt the technology.

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In Matsuyama City, we are currently working on extending the life of a general waste MSW landfill site that has been in service since 2003. Up to now, through recycling landfill waste and bringing in strict criteria for what is accepted, the site was expected to have a significantly long service life. However, now due to an increase in the proportion of incinerated ash found in the landfill waste, calcium and salt of leachate is eluting at higher concentrations than originally planned. The result of this is that the desalting capacity in the leachate desalting facility has been significantly impaired. In response, we plan to renew the leachate desalting facility, change the disposal process and introduce equipment that produces sodium hypochlorite in order to increase the efficiency of salt concentration and enhance the processing capacity of the facility. In addition, we are planning to use the sodium hypochlorite that is produced as a sterilizing agent at the sewer terminal treatment plant.

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