How the water you flush becomes the water you drink - Francis de los Reyes

譯者: 穎君 紀 審譯者: Helen Chang

In 2003, Singapore’s national water agency launched an unprecedented program.

2003 年，新加坡國家水利署 啟動了前所未見的計畫。

Using two new facilities,

他們使用這兩座新設施

they planned to provide more than 50% of their nation’s water supply

回收污水後淨化成飲用水， 試圖把再生水的供水比例提高到

by recycling wastewater.

全國供水量裡的一半以上。

And yes, we do mean that wastewater.

對，你沒聽錯，就是 馬桶沖下去的廢水。

While this might seem like a desperate decision,

乍看之下還以為國家缺水缺到 無可奈何，才動用這個方案，

this program had been planned for decades

其實這個計畫已經策劃許久，

to ensure the island nation never ran out of clean water.

為了讓這小小的島國有 源源不絕的新鮮水可供使用。

And today, as climate change increases the frequency and duration

而且現在氣候變遷肆虐全球， 異常降雨和乾涸越來越頻常發生，

of droughts worldwide,

more and more regions are facing this problem.

越來越多國家面臨這問題。

But is it really safe to reuse anything we flush down the toilet?

可是，回收馬桶水真的衛生嗎？

To answer this,

回答這個問題之前，

we have to understand exactly what’s inside this cloudy cocktail.

我們要先了解廢水裡究竟有些什麼。

Wastewater is classified into several types,

污水可以分成很多種，

but the primary three are:

其中最主要的三種是：

gray water used in sinks, bathing, and laundry;

來自洗手台、淋浴和洗衣服等 日常活動的「灰水」，

yellow water containing just urine;

「黃水」，就只是人的尿液，

and black water which has come into contact with feces.

以及含有排遺物的「黑水」。

Globally, we generate enough wastewater

一天內全球共可以產生出

to fill about 400,000 Olympic-sized swimming pools every day.

四十萬座奧賽規格游泳池之多的廢水。

In cities and towns with sewage systems,

有污水處理系統的城鎮裡，

this wastewater combines in underground pipes,

污水在地下水管匯集，

which actually aren’t filled with feces.

水管裡並沒有塞滿排遺物。

The average 4,000 liters of sewage

平均四千公升的廢水裡

contains only a single liter of solid fecal material.

只有一公升的固體排遺。

But sewage is still rife with dangerous contaminants,

但污水仍藏有許多危害健康的物質，

including billions of pathogens and microorganisms,

像是幾十億種病原體和微生物，

trace chemicals, and excess inorganic nutrients

微量殘留的化學物質 和過量的無機營養素，

that can pollute rivers and lakes.

都會污染河川和湖泊。

So even if we aren’t planning to drink this concoction,

所以，就算我們不打算喝下這些廢水，

we still need to clean it;

也還是要想辦法處理，

which is why sewer systems typically run to wastewater treatment plants.

也因此下水道大多都是接往淨水設施。

Most plants remove major contaminants

淨水設施大都可以從水體裡

such as feces, pathogens, and excess nitrogen

移除糞便、病原體和過量的 含氮物質等常見污染物。

from all the water they process.

And this involves a ton of biological, chemical, and physical interventions.

淨化污水有很多步驟，會用到 微生物、化學物質和物理法則。

Some of the most important include settling tanks to remove large particles,

其中最重要的包括 在沈澱池裡沉降大顆粒，

biological reaction tanks where microbes eat unwanted materials,

讓微生物分解有害物質，

and chemical disinfection processes that kill pathogens.

以及利用化合物消毒， 去除污水中的病原體。

After these procedures, typical treated wastewater in the US

經過這些手續後， 以美國來說，處理過的污水

is already cleaner than most natural bodies of water,

已經比大部分自然水體還要乾淨，

making it safe to discharge into rivers and lakes.

所以可以放心地排放。

If we plan on reusing the water for non-potable purposes,

如果計劃將水重新用於非飲用目的，

such as irrigation or washing cars,

如灌溉或洗車，

it gets even further disinfected to prevent bacteria from growing

那污水就要再進一步淨化，

以防止儲存時細菌大爆發。

during storage.

But if we want it clean enough to drink,

如果要把再生水拿來煮飯或飲用，

there's much more treatment to be done.

那就要再經過幾道處理過程。

One common process includes microfiltration,

其中一種常見的處理方式 叫做「微過濾」，

where membranes with pores one millionth of a meter across

利用微濾膜上無數個直徑一微米的孔洞

filter out small particles and larger microorganisms.

過濾掉微小的粒子和較大的微生物。

Next, the water passes through an even finer reverse osmosis membrane,

接下來，污水經過更細密的逆滲透膜，

which can remove particles as small as a tenth of a billionth of a meter.

去除直徑 0.1 奈米以上的雜質。

This membrane is semi-permeable, allowing water to pass through,

逆滲透膜具選擇滲透性， 它可以讓水通過，

but stopping things like salt, viruses, or unwanted chemicals.

但不讓鹽份、病毒 或人類不需要的化學物質通過。

After this stage, UV lamps are plunged into the water,

過濾程序完成後，紫外線燈管進入水中

emitting radiation that permanently damages

放出紫外線，永久性消滅

the genetic material of any lingering life forms.

殘餘的生物身體組織。

Sometimes UV disinfection is then combined with further disinfection processes

有時候除了紫外線消毒以外，

還會用過氧化氫再做一道消毒工程，

that use chemicals like hydrogen peroxide

to handle a wide range of microorganisms and micropollutants.

來消滅更多之前沒除掉的 微生物和微小污染物質。

At this point, the treated wastewater is tested rigorously.

結束這些步驟後， 水會經過嚴格的水質檢測，

And if it passes, it can safely enter the typical pipeline for drinking water,

通過水質檢測後， 水就進入供飲用水的管線，

going through the standard treatment procedures

再經過一些處理程序，

before joining the municipal supply.

才進入地方配水管線。

This approach is called direct potable reuse,

這個處理污水的方法叫做 「可直飲水再生法」，

but even though it’s perfectly healthy,

但即使再生水完全對人體無害，

there’s still some concern with such a direct system.

這個方式還是有些衛生上的疑慮。

Instead, most places opt for indirect potable reuse,

取而代之，大多地區使用 「不直接飲用水再生法」，

where the treated wastewater is discharged to an environmental buffer,

處理過的污水先暫時匯集到

such as a reservoir, lake, wetland, or groundwater aquifer.

水庫、湖泊、濕地， 或地下水層等緩衝地區。

After some time in this environment,

在緩衝地區停留一陣子之後，

any lingering chemicals from the treatment process

在污水處理過程中殘留的化學物質

will diffuse and degrade.

會被稀釋、分解。

Then, the water can be extracted and enter the drinking water pipeline.

經過這個步驟，才被送到飲用水管線。

Indirect potable reuse is the process used in Singapore,

新加坡使用「不直接飲用水再生法」

and it's become an increasingly common lifeline for arid regions in the US.

這個處理方法在美國也越來越普遍。

But this system is only feasible in places with centralized sewer systems

但這種方法只適用在有 集中的污水處理系統，

and infrastructure for pumping water into people's homes.

以及有設施能把水 直接送入住家的地區。

This means it can’t help communities

換句話說，這個處理系統

dealing with the most serious sanitation issues,

沒辦法幫到面臨飲水衛生疑慮，

where access to clean water is a daily struggle.

取得乾淨飲用水比登天還難的地區。

Researchers are investigating smaller scale technologies to recycle sewage

研究人員目前還在研發 小規模的污水淨化器材，

into potable water on site.

讓污水當場變成飲用水。

But helping these communities in the long term

然而從長遠來看，幫助這些社區

will require us to take a closer look at all the water we’ve been wasting.

則需要我們更仔細地審視 我們一直在浪費的所有水資源。