Tomoo Sekito

Phosphate recovery from phosphorus-rich solution obtained from chicken manure incineration ash.

The recovery of phosphorus from waste is very important for Japan because Japan has no natural phosphorus resources. In order to recover phosphorus from incineration ash of chicken manure, an acid dissolution-alkali precipitation method was investigated. Phosphorus content in the ash was 8%. The ash was treated with hydrochloric acid to obtain phosphorus-rich solution. Phosphorus could then be recovered as a precipitant by adding sodium hydroxide solution into the phosphorus-rich solution and gradually changing the pH in the solution to 3, 4, and 8. At pH3, a small amount of phosphorus was precipitated to remove iron, which would cause coloring of subsequent precipitants. At pH4, 84% of the phosphorus in the original solution could be recovered as CaHPO4 x 2H2O with a purity of 92%. At pH8, 8% of the phosphorus in the phosphorus-rich solution could be recovered as identified hydroxyapatite. A recovery rate of 92% phosphorus as CaHPO4 x 2H2O and identified as hydroxyapatite was achieved.

Study on composition and particle characteristics of shredded municipal waste for the improvement of separation efficiency in a municipal bulky waste processing facility

In order to propose a new and more efficient method of separation for shredded municipal bulky waste (SBW), particle characteristics (namely shape, density and terminal settling velocity) were investigated. It was found that particles of the combustibles such as wood, paper and plastics were included in the fraction smaller than 50 mm. Consequently, separation of SBW into combustibles and non-combustibles by particle size is difficult. Since the particles of the various materials are of all shapes, it is difficult to sort them by shape discrimination. The overall separation efficiencies using air flow and density for SBW separation were estimated and the maximum values are as high as approximately 90% and 99% respectively. However, because of the overlapping ranges of the terminal settling velocities in air for glass, metals, rubber, and plastics, the overall efficiency will become smaller if those materials are major components of the feed. It is concluded that density separation is more suitable for the separation of combustibles and non-combustibles in SBW than air separation.

Characteristics of element distributions in an MSW ash melting treatment system

Thermal treatment of municipal solid waste (MSW) has become a common practice in waste volume reduction and resource recovery. For the utilization of molten slag for construction materials and metal recovery, it is important to understand the behavior of heavy metals in the melting process. In this study, the correlation between the contents of elements in feed materials and MSW molten slag and their distributions in the ash melting process, including metal residues, are investigated. The hazardous metal contents in the molten slag were significantly related to the contents of metals in the feed materials. Therefore, the separation of products containing these metals in waste materials could be an effective means of producing environmentally safe molten slag with a low hazardous metals content. The distribution ratios of elements in the ash melting process were also determined. The elements Zn and Pb were found to have a distribution ratio of over 60% in fly ash from the melting furnace and the contents of these metals were also high; therefore, Zn and Pb could be potential target metals for recycling from fly ash from the melting furnace. Meanwhile, Cu, Ni, Mo, Sn, and Sb were found to have distribution ratios of over 60% in the metal residue. Therefore, metal residue could be a good resource for these metals, as the contents of Cu, Ni, Mo, Sn, and Sb in metal residue are higher than those in other output materials.

Resource Recycling Society Indicators on Solid Waste Management and Questionnaire Surveys in Metropolitan Cities in Japan

資源循環型社会の実現が, 社会の共通目標になっている。しかし, その具体的な目標について定まったものはなく, 各自治体は独自に設定しているのが現状である。本論文は自治体のごみ処理を対象とし, 施策の目標を明確にし, 達成度を評価するための指標提案を目的とした。まず, 市民の意識・行動, 自治体の施策に対する協力, 理解などによって資源循環型社会度を測ることができると考え, 指標項目を設定し, 各指標ごとに一般性の高い質問群を選んだ。このアンケートを13大都市の市民に送付し, 各都市の指標得点を求めたところ, 都市ごとの特徴が明らかとなった。さらに, 指標間の関係を解析することにより自治体のごみ処理施策がどのように指標得点に反映されているかを考察した。

Estimation of the avoidable lead in MSW by inverse manufacturing system

Under the inverse manufacturing system, it is important not only to minimize the amount of solid waste but also the environmental impact of hazardous materials found in municipal solid waste (MSW). In this present study, we examined which products contribute to the lead content in MSW by examining the literature on this subject and by measuring the lead content in waste products. We also estimated the amount of avoidable lead from MSW fly ash and bottom ash using the inverse manufacturing system. We found that 411 mg/kg (dry MSW) of lead was discharged with MSW from households, and we discovered that 80% of the lead in MSW originates from TV sets. If the inverse manufacturing system is applied to TV sets, the lead content in the incineration residue decreases by about 85%.