The ashes of the revered anti-apartheid leader Desmond Tutu were interred Sunday in a private ceremony in St. George’s Cathedral in Cape Town, South Africa.

       The Anglican archbishop and Nobel Peace Prize laureate, who died Dec. 26 at age 90, had requested that his funeral not be ostentatious and that his body not be cremated by flame. Instead, Tutu reportedly requested aquamation, or alkaline hydrolysis, a water-based process considered an eco-friendly alternative to traditional cremation.

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       So after Tutu’s remains lay in a simple pine casket during his funeral at St. George’s Cathedral on Saturday, his body was liquefied under pressure and his bones then dried to dusty ashes in an oven.

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       Aquamation is part of a growing “green burial” movement that avoids non-biodegradable materials and promotes natural decomposition. Advocates say it’s an environmentally friendly alternative to ornate caskets and cremation by fire, which emits greenhouse gases.

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       South Africa has no legislation specifically covering aquamation. About 20 U.S. states have legalized the process, most over the past decade.

       The practice has been little studied outside the funeral industry and environmental groups.

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       Resomation, a British manufacturer of machinery used in water cremation, estimates that substituting aquamation for fire-based cremation cuts a funeral’s greenhouse gas emissions by 35 percent. Bio-Response Solutions, an Indiana-based manufacturer, estimates that its technology cuts energy use by 90 percent compared with cremation by flame.

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       Some faith traditions, such as Judaism and Islam, forbid the use of cremation and require bodies to be buried in shrouds — and, for the former, in caskets made only of wood, which allows for natural decomposition. Other traditions and rituals involve burials at sea.

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       In aquamation, a machine uses “a heated (sometimes pressurized) solution of water and strong alkali to dissolve tissues, yielding an effluent that can be disposed through municipal sewer systems, and brittle bone matter that can be dried, crushed, and returned to the decedent’s family,” Philip Olson, a technology ethicist at Virginia Tech, wrote in a 2014 paper.

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       The process takes three to four hours at a temperature of around 300 degrees Fahrenheit, though it can be longer if lower temperatures are used, according to Olson. By comparison, fire-based cremation takes around two hours at a temperature of 1,400 to 1,800 degrees.

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       In the United States, aquamation was first adopted in the 1990s by researchers looking for an inexpensive and safe way to discard the remains of animals used in experiments. Around that time, scientists in Japan and Scotland began studying its use for disposing of the carcasses of animals sickened by illnesses such as mad cow diseases, according to Olson.

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       By the early 2000s, the practice was gaining popularity among veterinarians in the United States. By the following decade, it was being marketed to funeral homes as the technologies improved and interest widened.

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       Tutu, along with defending human rights, was a champion of the environment and spoke frequently of the perils of climate change, which he once called among the “greatest moral challenges of our time.”

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       He advocated for boycotts of oil and fossil fuel-producing firms and called for greater investment in clean energy and low-carbon products. He also sought to amplify the voices of young climate activists.

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