The city of Concord is looking at building an anerobic digester one day to better process its sewage. I’ll have a column about that next week – but while reporting for it, I came across this intriguing back-of-the-envelope calculation:
Each week the city’s sewage treatment plant produces about 100 tons of biosolids, a.k.a. sludge – the solids that are left after they have squeezed as much water as possible out of the mess we send them through pipes. About half of that is lime that is added to kill pathogens, so let’s say Concord sewer customers generate 50 tons, or 100,000 pounds, of solid matter each week.
The system serves roughly 50,000 people (it extends beyond the city limits). That means each person in the Concord area excretes 2 pounds of solid matter a week, or 104 pounds a year. That’s about the size of a fifth-grader, or a Newfoundland dog.
Think about that. Concord is a pretty small city, yet year after year after year we poop out 50,000 Newfoundlands worth of solid matter that has to go somewhere. It gets spread on fields as fertilizer, but that’s still a lot of … stuff … to be distributed around the environment. Think about how many Newfoundlands are produced in Boston, or New York, or Tokyo, or Mumbai and Lagos and Mexico City.
The mind boggles.