According to Maggie Koerth-Baker, Kate Ascher, author of The Heights: Anatomy of a Skyscraper, explain what happens to sewage from the Burj and Dubai's other tall buildings.
In order for these tall buildings to dispose their waste, the buildings have access to "a municipal system but many of them actually use trucks to take the sewage out of individual buildings and then they wait on a queue to put it into a waste water treatment plant, said Ascher." These trucks, she says can wait up to 24 hours before they get to the head of the queue.
Ascher explains that Dubai emerged in the last 50 years from a sleepy Bedouin town to what it is today and "literally can build anything, including a building of 140 or 150 stories. But designing a municipal network of sewage treatment is in some ways more complex."