報告書番号

U98057

タイトル（和文）

電気化学的手法によるヘドロ中の重金属除去 -異種汚泥からの重金属除去及び効率的中和操作の検討-

タイトル（英文）

Heavy metal removal from sludge using electrochemical method . -Estimation of effects of heavy metal removal to various types of sludge and examination of effective neutralization for the sludge after the electrolysis

概要 （図表や脚注は「報告書全文」に掲載しております）

当所で開発した電気化学的重金属除去法は、湖沼ヘドロに含まれる、環境基準値を上回る重金属除去に有効であることが示されているが、今回新たに3種類の組成の異なる汚泥からの重金属除去を試みた。湖沼ヘドロのほかに、下水汚泥、し尿汚泥、さらに貝の内臓からの重金属除去実験を実施した結果、湖沼ヘドロの場合と遜色のない除去結果を得ることができた。さらに、従来の電気化学的処理の際に問題であった、処理後汚泥の酸性化について、電気化学的重金属除去の際に生じるアルカリ性の陰極水により、処理後のヘドロの中和操作を試みた。72時間分の陰極水をすべて混合した時点でヘドロのｐHは7.0に到達し、電解処理前の値に戻すことができた。この際、陰極水についても同時に中和することができ、処分が容易になると考えられる。

概要 （英文）

Recently, large amount of sludge is abandoned and the volume is increasing year by year. Many types of sludge occur from the different kinds of origins, ex., construction, sewage and food manufacture. In spite that these sludge contain useful organic and inorganic materials, the existence of serious amount of heavy metal prohibits them from the utilization. Several kinds of heavy metal removal methods have been proposed so far, however, almost all the practical case needs acid or special reagents. In these operations, the sludge would be contaminated by high concentration of salt due to their neutralization, or mixed reagent itself. In addition, these reagents are usually expensive. We have developed an electrochemical heavy metal removal method from sludge deposited bottom of lakes. In this method, heavy metals are electrochemically removed from sludge without any addition of reagents. We also have estimated that the cost of electric power for the electrochemical method was not so expensive. If this method can apply to the remediation of variable types of sludge, we can show a possibility of sludge utilization. In this study, the electrochemical heavy metal removal method were applied to four different types of sludge. A 150 ml of each sample was set into the anode and electrolysis was performed for 72 hours at 400 mA of current stat condition. For all of the samples, concentrations of heavy metal such as cadmium, and zinc were reduced after the electrochemical treatment. The electrochemical heavy metal removal system shown in the last report had a problem that the treated sludge showed low pH because of an accumulation of H+ ion. In contrast, cathodic water, which is used in the electrolysis, became high pH because of a generation of OH-. We tried to develop an economical sludge neutralization method using high pH of cathodic water. During the electrolysis, the cathodic water was over flowed at a rate of 1.5 l/h, and the spilt water was stocked each 12 hour. The cathodic water was poured to the sludge after electrolysis. Although pH for the sludge just after the electrolysis showed 1.5, it increased by the addition of cathodic water. Finally, the sludge’s pH reached 7.0 after when 72 hours of cathodic water was poured. The neutralization method is not only economical, but also both sludge and cathodic water can be nutralized simultaneously.We are confident that those techniques proposed here will give a driving force for build up the recycle society.

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