Read this: The Reinvent the Toilet Challenge is a long-term research and development effort to develop a hygienic, stand-alone toilet. This challenge is being complemented by another investment program to develop new technologies for improved pit latrine emptying (called by the foundation the "Omni-Ingestor") and fecal sludge processing (called "Omni-Processor"). The aim of the "Omni Processor" is to convert excreta (for example fecal sludge) into beneficial products such as energy and soil nutrients with the potential to develop local business and revenue.

What does another investment program use to convert sludge?
What is the answer? (If it cannot be answered, return "unanswerable")
unanswerable