Masataka Hanashima

Behavior of stabilized fly ashes in solid waste landfills

Abstract In Japan, the fly ash generated by incineration of municipal solid waste has come to be handled as general waste under special management in recent years. At the same time, direct landfilling or ocean dumping of fly ash is legally prohibited. To avoid the possibility of causing damages affecting human health or life environment, fly ash must be subjected to intermediate treatment, and must stabilized, encapsulated and made hygienic by removing pollutants. Four methods can be given for fly ash intermediate treatment; (1) cement solidification, (2) treatment by chemicals, (3) acid and other solvents and (4) melting and solidification. On the other hand, various phenomena affecting fly ash occur on the landfilled waste layer, such as generation of organic acid and carbon dioxide gas due to decomposition of solid waste. Fly ash solidified by cement is deteriorated by water-soluble sulfate and organic acid and carbon dioxide gas produced by decomposition of organic substances in the municipal solid waste. This may result in a reduced strength of hazardous substances and re-melting of fly ash solidified by cement. Furthermore, encapsulated hazardous heavy metals may be eluted from fly ash treated by chemicals due to the change in chemical environments (pH, ORP, etc.) in the landfilled solid waste layer according to stabilization of the landfilled solid waste. However, not much is known about the physical and chemical properties of the fly ash after it has been disposed of with the general solid waste at the landfill site. Thus, in this present study, the large-sized landfill model lysimeter is filled with cement-solidified fly ash or chemically treated fly ash treated together with municipal solid waste (bottom ash and shredded solid waste) to obtain correct information on the changes in the physical and chemical properties of the cement-solidified fly ash, and temporal concentration of hazardous substances (Pb, Cd, Cr6+) contained in seepage leachate or leachate in the landfilled solid waste layer, thereby clarifying the long-term stability of the disposed fly ash. This study has revealed that the pH value of the cement-solidified fly ash tends to be neutralized with the process of time, although the compression strength of the cement-solidified fly ash left to stay in the landfilled solid waste for three years is not reduced much below that at the time of experiment start-up. This trend of neutralization has been found to be conspicuous in the vicinity of the leachate collection pipe at the bottom landfill layer. Furthermore, the pH values of seepage leachate and leachate have been observed to be reduced by the disposal of the fly ash chemically treated with municipal solid waste. This indicates that the concentration of the heavy metal such as Pb and Cd is severely affected by pH values. Namely, the pH value of the leachate from the large-sized landfill model lysimeter filled with chemically treated fly ash is close to neutral value, and concentrations of the Pb and Cd tend to be greater than those of the leachate from the large-sized landfill model lysimeter not filled with chemically treated fly ash. This suggests that the chemical properties of the treated fly ash and the solid waste disposed of with it determines the pH value of the seepage leachate and leachate and, at the same time, greatly affects the concentration of the heavy metal.

Generation of greenhouse effect gases from different landfill types

Abstract Recently much attention is focussed on the problems of global warming due to greenhouse effect gases, notably carbon dioxide and methane. Because these gases cause important problems to the global environment, their generation from landfill sites containing solid wastes has drawn attention and their environmental impact is causing concern. Generally, the gases associated with a greenhouse effect include carbon dioxide, methane and nitrous oxide. However, there are no general basic data available concerning gases generated from biodegradation of solid wastes in landfill sites. Specifically, no assessment has been made concerning greenhouse effect gases from different landfill types. This paper proposes a quantitative model for estimating the gasification rate by different landfill types. The model is based on measurement data for a long-term material balance for an aerobic landfill and an anaerobic landfill, obtained with two types of large-scale lysimeters. This paper will also give an estimate for the amount of greenhouse effect gases by for different types of landfill and propose countermeasures for their reduction.

Mechanisms for the Aging-Induced Reduction of Lead Solubility in Scrubber Residues from Municipal Solid Waste Combustion

This manuscript elucidates the mechanisms responsible for aging-induced reduction in lead leaching from scrubber residues. Leaching tests (JLT13) were conducted on 48 types of scrubber residues and lead solubility was found to be significantly reduced independent of incinerator type or type of gas treatment method. Reaction kinetics that result in lead solubility reduction were shown to be proportional to carbon dioxide partial pressure and in many cases were limited by mass transfer to the residue. With forced gas convection through the residue and a CO2 partial pressure of 0.3%, the concentration of lead in leachate was reduced from 84 mg L-1 to < 0.5 mg L-1 in two days. Ettringite analogs (Ca6Al2(SO4)3(OH)2•26H2O) were identified by X-Ray Diffraction in the wetted scrubber residues early in the aging process; these appear to have been converted into gypsum (CaSO4•2H2O) and vaterite (CaCO3) in the aged material. All of these solid phases are believed to substitute lead into their crystal structure and evidence for this attenuation mechanism is presented.

Toxicological evaluation of the chemical oxidation methods for landfill stabilization

As the stabilization criteria for landfill sites, only chemical criteria for the leachate discharges from the landfill sites have been used in Japan and many other countries. Recently, chemical oxidation has been developed as a method for the early-stabilization of landfills. However, by-products that are difficult to detect by chemical analysis can be produced by this method. Therefore, toxicity tests are useful tools for detecting the changes of leachate quality after application of this method. The heat source in the A landfill was analyzed by organic position inquiry technology, and ozone-treated leachate was sprayed back to the heat source in the landfill. Toxicity changes of the leachate after the spray were monitored using Microtoxtrade mark, ToxScreen-II, and DaphTox tests. The hardly-degradable organic matter was efficiently removed and toxicities of the leachate in the heat source decreased after the application. These toxicity results were significantly related to chemical oxygen demand (COD) changes. Thus, it was concluded that the toxicity tests were effective for monitoring the leachate quality after applying the chemical oxidation method for landfill stabilization, and its incorporation to establish the criteria for early-stabilization of landfill sites needs to be considered.

Evaluation of Four Methods for Concentrating Mutagens in Ames Salmonella/Microsome Assays on Leachate Collected from a Municipal Solid Waste Landfill.

Four concentration methods ; XAD resin adsorption, CSP/CHPA resin adsorption, dichloromethane solvent extraction, and blue rayon adsorption were compared for their abilities to concentrate mutagens from leachate samples obtained from a municipal solid waste landfill. The Ames Salmonella/microsome assay was used to evaluate the four methods. The XAD resin adsorption, the CSP/CHPA resin adsorption, and the solvent extraction well recovered mutagens from leachate samples, while the blue rayon adsorption could scarcely recover mutagens, suggesting that polyaromatic hydrocarbons having 3 or more fused aromatic rings in their structures less contribute to the mutagenic activity of landfill leachate. Mutagens were well recovered only after leachate samples were acidified. Therefore, it is likely that predominant mutagens in landfill leachate are acidic compounds. TA98 detected mutagenicity of concentrates better than TA100 and the addition of S9 did not increase the number of revertants.Judging from these results, the XAD resin adsorption, the CSP/CHPA resin adsorption, and the solvent extraction are suitable for concentrating mutagens from landfill leachate.

Pollutant transformations in landfill layers

Abstract The behaviour of pollutants, in particular organic carbon and nitrogen, in solid waste landfill layers and factors affecting their decomposition have been studied using four large scale simulated lysimeters in four landfill thicknesses, and operated under semi-aerobic conditions. This paper presents about 800 days of data through November 1991. Data in this study indicate that the thicker solid waste layer has lower production rates of Total Organic Carbon (TOC) and Total Nitrogen (T-N) than does the thinner layer. If the layer, however, becomes too thick, no significant increase in the removal rate of T-N is observed, as nitrogen is leached out in the form of NO 3 − -N without being demitrified at the bottom of the landfill layer. It is also assumed that temperature and pH in the landfill layer play important roles not only in microbial degradation, but also in dissolution of organic carbon and nitrogen.

The mechanism of lead (Pb) leaching from incinerator fly ash in monodisposal landfill

This study considers the leaching behaviour of heavy metals from Municipal Solid Waste Incinerator (MSWI) fly ash contained in a landfill dedicated solely to fly ash disposal. Large scale lysimeters were used to study four materials: untreated fly ash; two types of chemically treated fly ash; and a molten fly ash slag. The study also considers the effect of highly saline solutions to accelerate the leaching of lead and concludes that the concentration of calcium ions influences the leaching process.

Degradation of Biodegradable Plastics in Incineration Ash

生分解性プラスチックの一般土壌中における分解については研究報告がなされているが, 焼却灰主体の埋立廃棄物中に埋設された場合の分解特性と微生物活性に関する知見はこれまでにない。本研究では, PLA, PBSA, PHB/V, PBS, PCLの5種類の生分解性プラスチック素材を, 焼却灰主体の埋立廃棄物 (A: 焼却灰+不燃破砕ごみ, B: A+コンポスト) 中に埋設した場合の分解の様子, 面積消失率, SEM観察など物理的側面からの観察を行い, その分解要因を調査した。その結果, 焼却灰中での分解特性として, 以下の点が明らかとなった。 (1) 焼却灰主体の埋立廃棄物中における分解型は, 微生物関与で生じている孔拡大型と, 焼却灰中のアルカリ成分による加水分解で生じるクラック発生型の2タイプみられた。 (2) 焼却灰主体の埋立廃棄物中において, 有機物の添加や温度上昇など, 微生物活性を高める操作を行うことによってBPの生分解が促進された。 (3) 有機物含有量の少ない焼却灰中においては, 一般土壌と同程度の分解速度を示すことがわかった。 (4) 生分解を受けたBPは, PBSA>PHB/V>PCL>PBSの順で分解が速かった。 (5) BPが生分解を受けない場合は, 焼却灰中のアルカリ成分によってクラックが生じた。 (6) 焼却灰主体の埋立廃棄物は, PBSAとPCLによって微生物活性が高められたと推察された。

Production Process of Mutagens in Landfill Site received Incineration Residue

筆者らは有害化学物質による埋立地のリスクを軽減することを目的として, バイオアッセイ, 特に変異原性試験による有害性の評価に注目し, 埋立廃棄物および浸出水の変異原性の調査を行っている。これまでに, 埋立地浸出水を用いて最適な変異原物質の濃縮・変異原性試験の方法について検討した。また, 実埋立地浸出水の調査を通して, 浸出水の生物的酸化処理によって変異原物質が生成されることを明らかにした。そこで本研究では, 埋立模型槽を用いて廃棄物の種類および埋立条件と変異原性の関係を調査し, 浸出水中に主に検出されるフレームシフト型の直接変異原物質の生成機構とその要因について検討した。さらに, この結果を基に, 変異原物質の生成実験を行い, 生成機構の検証を行った。その結果, (1) 好気的な埋立構造ほど変異原性の出現が早いこと, (2) 焼却灰と窒素化合物を含む廃棄物を埋め立てた場合, 生物的硝化過程および硝酸塩の化学的還元過程におけるNO-2およびN2Oの生成初期に変異原物質が生成されること, (3) 硝酸塩の還元過程において検出される変異原物質に多環芳香族炭化水素のニトロ誘導体や芳香族アミンが含まれていること等が明らかになった。

Heavy metal elution characteristics from municipal solid waste scrubber residue by a centrifugation method

The objective of this study is to clarify the elution characteristics of heavy metals into scrubber residue solution such as bound water and pore water. The L/S ratio of wet scrubber residue is smaller than that the L/S ratios used in elution tests such as: the one based on Notification No. 13 of the Japanese Environment Agency (Japanese official method, JLT13), the Toxicity Characteristics Leaching Procedure (U.S.A. official method) and the Availability test (Dutch official method). A centrifugation method employed to sample soil solution was adopted for use to sample two types of scrubber residue solutions, and to compare the concentrations of heavy metals in the leachates with that obtained from the JLT13 and the Availability test as well as the pH dependency test.