Introduction
Water is the most essential substance for all life on earth and a
precious resource for human civilization. Reliable access to
clean and affordable water is considered one of the most basic
humanitarian goals, and remains a major global challenge for
the 21st century.
Our current water supply faces enormous challenges, both
old and new. Worldwide, some 780 million people still lack
access to improved drinking water sources (WHO, 2012). It is
urgent to implement basic water treatment in the affected
areas (mainly in developing countries) where water and
wastewater infrastructure are often non-existent. In both
developing and industrialized countries, human activities
play an ever-greater role in exacerbating water scarcity by
contaminating natural water sources. The increasingly stringent
water quality standards, compounded by emerging contaminants,
have brought new scrutiny to the existing water
treatment and distribution systems widely established in
developed countries. The rapidly growing global population
and the improvement of living standard continuously drive up
the demand. Moreover, global climate change accentuates the
already uneven distribution of fresh water, destabilizing the
supply. Growing pressure on water supplies makes using
* Corresponding author. Tel.: þ1 713 348 2046; fax: þ1 713 348 5268.
E-mail address: qilin.li@rice.edu (Q. Li).
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