水道水から安価に鉛除去　米高校生チームがフィルター開発

【ワシントンＡＦＰ＝時事】新型コロナウイルスのパンデミック（世界的な大流行）により、学校が遠隔授業への切り替えを余儀なくされた際、米首都ワシントン近郊の理科教師、レベッカ・ブッシュウェー氏は生徒たちに難しい課題を与えた──水道水から有害金属の鉛を取り除く、蛇口取り付け型の安価なフィルターの設計と開発だ。（写真は生徒が開発した浄水フィルターの実演の様子。米メリーランド州シルバースプリングにあるバリー中・高等学校で）
　生徒たちのチームは、３Ｄ印刷技術と高校レベルの化学の知識を駆使して課題に取り組み、このほど実用試作品を作り上げた。縦７．５センチの生分解性プラスチック製フィルターケースだ。ゆくゆくは、この鉛フィルターを１個１ドル（約１３０円）で販売したいと考えている。
　メリーランド州郊外にあるバリー中・高等学校でＡＦＰの取材に応じたブッシュウェー氏は、「『ここには３Ｄプリンターが複数ある。（それを使って）こんな物を作ってみたらどうだろう？』と、ふと思った」と説明する。
　米国では、最大１０００万世帯の水道水の供給にいまだ鉛管が使われている。小児期の鉛への暴露は特に有害な影響が懸念される。

■巧妙な仕掛け
　ブッシュウェー氏のアイデアは、汚染土壌修復と同じ化学反応を用いたものだ。水に溶け込んだ鉛とリン酸カルシウムの粉末を反応させ、リン酸鉛と無害な遊離カルシウムに変化させる。このリン酸鉛をフィルターで捕らえる。
　フィルターには他にも巧妙な仕掛けが施されている。リン酸カルシウムの下にヨウ化カリウムを置いたことだ。リン酸カルシウムが使い尽くされると、水に溶けた鉛が下層のヨウ化カリウムと反応し、水が黄色く濁る。これがフィルター交換のサインになる。
　生徒の一人は、数か月かけて３Ｄプリンターでフィルターケースを設計し、何度も試作を重ねた。「パズルのように問題を解く必要があり、やりがいがあった」と話す。
　今回の開発についてブッシュウェー氏は、隙間市場があるとみている。
　同様に鉛を除去する装置として「逆浸透システム」があるが、導入には数万～数十万円の費用がかかる。一方、より安価な炭素ブロックフィルターは２０ドル（約２５００円）程度だが、数か月ごとの交換が必要だ。チームが開発したフィルターはこれよりも交換頻度が低い。
　「生徒たちのことをとても誇りに思っています」と言うブッシュウェー氏。チームは企業と協力して設計を完成させ、大量生産にこぎ着けたいと意気込んでいる。【翻訳編集ＡＦＰＢＢＮｅｗｓ】
〔ＡＦＰ＝時事〕（2022/05/30-13:55）

When the pandemic forced schools into remote learning, Washington-area science teacher Rebecca Bushway set her students an ambitious task: design and build a low-cost lead filter that fixes to faucets and removes the toxic metal.
Using 3D printing and high-school level chemistry, the team now has a working prototype -- a three-inch (7.5 centimeter) tall filter housing made of biodegradable plastic, which they hope to eventually bring to market for $1 apiece.
The science is straightforward, Bushway told AFP on a recent visit to the Barrie Middle and Upper School in suburban Maryland, where she demonstrated the filter in action.
I thought, 'We have these 3D printers. What if we make something like this?'
Bushway has presented the prototype at four conferences, including the prestigious spring meeting of the American Chemistry Society, and plans to move forward with a paper in a peer-reviewed journal.
Up to 10 million US homes still receive water through lead pipes, with exposure particularly harmful during childhood.
The metal, which evades a key defense of the body known as the blood-brain-barrier, can cause permanent loss of cognitive abilities and contribute to psychological problems that aggravate enduring cycles of poverty.
A serious contamination problem uncovered in Flint, Michigan in 2014 is perhaps the most famous recent disaster -- but lead poisoning is widespread and disproportionately impacts African Americans and other minorities, explained Barrie team member Nia Frederick.
And I think that's something we can help with, she said.
The harms of lead poisoning have been known for decades, but lobbying by the lead industry prevented meaningful action until recent decades.
President Joe Biden?s administration has pledged billions of dollars from an infrastructure law to fund the removal of all the nation?s lead pipes over the coming years -- but until that happens, people need solutions now.
- A clever trick -
Bushway's idea was to use the same chemical reaction used to restore contaminated soil: the exposure of dissolved lead to calcium phosphate powder produces a solid lead phosphate that stays inside the filter, along with harmless free calcium.
The filter has a clever trick up its sleeve: under the calcium phosphate, there's a reservoir of a chemical called potassium iodide.
When the calcium phosphate is used up, dissolved lead will react with potassium iodide, turning the water yellow - a sign it is time to replace the filter.
Student Wathon Maung spent months designing the housing on 3D printing software, going through many prototypes.
What's great about it was that it's kind of this little puzzle that I had to figure out, he said.
Calcium phosphate was clumping inside the filter, slowing the reaction. But Maung found that by incorporating hexagonal bevels he could ensure the flow of water and prevent clumping.
The result is a flow rate of two gallons (nine liters) per minute, the normal rate at which water flows out a tap.
Next, the Barrie team would like to incorporate an instrument called a spectrophotometer that will detect the yellowing of the water even before it is visible to the human eye and then turn on a little LED warning light.
Paul Frail, a chemical engineer who was not involved in the work, said the group deserves an incredible amount of credit for its work, combining general chemistry concepts with 3D printing to design a novel product.
He added, however, that the filter would need further testing with ion chromatography instruments that are generally available in universities or research labs -- as well as market research to determine the demand.
Bushway is confident there is a niche. Reverse osmosis systems that fulfill the same role cost hundreds to thousands of dollars, while carbon block filters available for around $20 have to be replaced every few months, which is more often than her group's filter.
I am over-the-Moon proud of these students, Bushway said, adding that the group hoped to work with partners to finalize the design and produce it at scale.