The Purpose Prize, now in its fourth year, provides five $100,000 and five $50,000 awards to social innovators over the age of 60 who, rather than retire quietly into their latter years, combine their creativity and experience toward addressing the world's big social problems. It is the nation's only large-scale investment in social innovators for the second half of life, and each year's winners are shining, inspirational examples that inventiveness is not the sole province of the young.

One of this year's winners is engineer, professor, inventor and entrepreneur Henry Liu, who is best known for having developed an environmentally safe brick made from the waste produced by coal-fired power plants.

The importance of the technology he pioneered cannot be understated. Each year, nearly 45 million tons of leftover fly ash — toxic byproduct from burning coal — is recklessly disposed of in landfills and ash ponds, contaminating the environment and putting people's health at risk. The problem can be particularly bad in countries with developing industries. In India alone, fly ash landfill covers an area of 40,000 acres.

But where others saw pollution, Liu saw possibility. He invented a commercially viable, green manufacturing process by which the fly ash could be turned into bricks. Liu's bricks look, feel, and function exactly like standard clay bricks often used on houses, banks, or other buildings, with one exception — fly ash bricks actually conserve energy, cost less to manufacture, and don't contribute to air pollution or global warming like the manufacturing of clay bricks can.

In other words, not only did Liu find a use for what was otherwise hazardous waste, he transformed that waste into a building material that was beneficial to the environment.

The green bricks have already been licensed for production in 11 countries, including the world's biggest coal polluters: China, India and the United States. Furthermore, Liu predicted that in 10 years, half of the all bricks manufactured and used each year will be fly ash bricks.

For most people, patenting and developing one revolutionary technology to solve the world's environmental problems is more than exemplary, but fly ash bricks were only one of Liu's several big projects.

For instance, in 2001 he set up his own business called the Freight Pipeline Company. With the aim of lessening noise and air pollution, decongesting highways, and reducing accidents, the company has developed what it calls capsule pipeline technology. The visionary project seeks to reshape how freight is transported around the country. Instead of using trucks or trains or ocean freighters, Lui promoted moving it through large underground pipelines powered by an electromagnetic pump.

Lui's accomplishments after the age of 60 could fill the ambitions of people half his age, and his legacy, company and drive continue to be an inspiration to his family, colleagues and community. Tragically, shortly after being nominated for his Purpose Prize, Henry Lui passed away in 2009 just as his latest ideas were coming to fruition.

"Most other men of my age are enjoying their retirement lives," said Liu before his death. "I enjoy, on the other hand, continued work. Both kinds of life bring enjoyment, but I believe that my encore career life is more fulfilling."

"He's always wanted to change the world. Success to my dad isn't about making money. It's about leaving the world a better place," said Lui's son Jeffrey, who plans to honor his father's legacy by continuing his important work.

Nominations are currently open for the 2010 Purpose Prizes. If you know someone who might qualify, you can nominate them at encore.org using their Application & Nomination form.