The Gates Foundation’s approach has both advantages and limits

THE JANICKI OMNI PROCESSOR, a $2m machine paid for by the Bill & Melinda Gates Foundation, turns human waste into water and electricity. In poor cities such as Dakar in Senegal, where it has been piloted, the hope is that people will send sewage to sanitation plants to be processed, rather than chucking it into the streets.

The Omni Processor exemplifies the Gates Foundation’s approach to philanthropy. Mr Gates likes to apply business principles to doing good, which means focusing on innovative, often technological, solutions with quantifiable results. The processor’s inputs and outputs can be counted. The first version, which arrived in Senegal in 2015, was not designed to deal with sewage filled with sand and rocks as it is in Dakar. It was made of materials that corroded quickly in the city’s sea air. These glitches have been fixed in the “OP 2.0”, which arrived in Dakar this year.

Mr Gates has championed the foundation’s data-driven style of philanthropy. But his ex-wife, now known as Melinda French Gates, is thought to have tempered his relentless focus on efficiency, arguing that number-crunching methods cannot resolve the complex causes of poverty on their own. That difference in emphasis, in turn, raises questions about whether the couple’s divorce, announced this year, will set the world’s most powerful...