The sticky problem of sludge

Sewage treatment plants do a fine job of cleaning up our shit, preventing it from mucking up our treasured rivers, lakes and, beaches. But the stuff that gets filtered out of the sewage stream has to go somewhere. The solid residue from wastewater treatment is known as sludge.

Dealing with sludge is a problem. You can mix it with oil and burn it, but that’s dirty and expensive. You can put in in landfill, but that uses land. You can ship it somewhere else, but that’s not very nice.

Or you can spread it on land to fertilize crops. Boom!

Not so fast.

Sewage streams are often contaminated with some nasty, persistent chemicals collectively known as PFAS.

Per- and polyfluoroalkyl substances (PFAS) are a group of man-made chemicals that includes PFOA, PFOS, GenX, and many other chemicals… [PFOA and PFOS] are very persistent in the environment and in the human body – meaning they don’t break down and they can accumulate over time. There is evidence that exposure to PFAS can lead to adverse human health effects.

That’s from the Environmental Protection Agency.

The problem is that sludge is often rich in these chemicals. When spread on land, they end up in the groundwater. Then you risk getting PFAS in the public water supply.

The long-standing practice of spreading treated sewage sludge and septage on farm fields has contaminated groundwater in some areas with PFAS, recent sampling shows. The discovery has prompted a state agriculture official to say that a prohibition on harvesting feed and crops from those fields may be needed.

This refers to recent testing in the state of Vermont (article here in the VT Digger).

An insightful reader comment:

One centrally located wastewater sludge incinerator facility could handle the entire State of VT. Incineration sounds terrible until you look at the alternatives. Landfills ? Limited space, no news ones being built, leachate issues, odors. Land application? Who wants PFAS contaminated sludge applied on their land. Digestion ? Reduces volume but there is still 50-60% of sludge volume to deal with. Split the cost among all treatment facilities to gain the economies of scale to make the project viable. States have to take the lead on this issue. Every city or town for themselves is not going to work.

One way of dealing with the problem would be to legislate against the use of PFAS in manufactures (although presumably these chemicals are quite useful). A bill is in the state legislature: https://legislature.vermont.gov/bill/status/2020/S.295