From the digesters we drive to the dewatering building--just as at the water treatment plant, the wastewater plant uses belt presses to squeeze the water out of the last, bug-eat-bug stage of the sludge. Enormous screw conveyors grind big pieces of the dewatered stuff along like the mixers in an industrial bakery. Lynch hands me a piece of what they call cake. It has no odor at all and feels a lot like inch-thick rubber, the kind used under playground equipment. Polymers are introduced to help coagulation and add to the rubbery feel. "Don't forget to wash your hands," Lynch says.
We leave the sludge and return to the water. Primary treatment is mechanical--settling; secondary treatment is biochemical--activated sludge digestion. Tertiary treatment combines mechanical and photochemical: The water flows to a dozen deep sand filters, which remove the remaining fine particles. The final hurdle the water clears is ultraviolet treatment. We walk over to a small, low concrete building, in front of which Lynch pulls up a flat piece of aluminum to reveal a 4- or 5-foot-wide channel of water flowing smoothly past banks of green-glowing UV lamps. They look much like fluorescent lights, though they have a self-wiping mechanism to keep them clean. "It doesn't kill [pathogens]," he says of the light. "It just scrambles their RNA. Sterilizes 'em." He mentions in passing an open concrete channel between the filters and the UV treatment, in which tilapia swim. "It keeps the duckweed down," he says. Once fish are swimming in your treated sewage, you've got to feel like you're getting the job done.
Out behind the UV building we finally reach the finished product: the effluent, flowing out in strong wide arcs into a canal from a dozen UV channels. The water seems to have a greenish tinge, but when Lynch fills a little water bottle and holds it up it looks utterly clear. Then we drive down toward the end of the line, where the effluent enters the Neuse River. There, in a tiny green glade at the bottom of the hill, the river bends into a cove, near the bank of which a few surface bubbles give away the presence of the underground pipe. Lynch says if you didn't know where the pipe was you could follow shad upstream to find it: "The water's warm and highly oxygenated," so the fish love it.
Lynch says the river is the natural place for the water anyhow. Every drop of Raleigh water comes from the Neuse watershed and ought to return there. "All we're doing," he says, "is what a river would do." That is, rivers are naturally self-cleaning, and the Neuse would absorb waste, given time and distance. Waste on the ground would be dispersed by rain and the water would be filtered through the earth, entering the groundwater system clean; matter that made it to the stream would become waterlogged and sink. "On the rocky bottom, bacteria live," he says, that feed off the nutrients in waste. "What happens in our plant is the exact same thing that happens in a stream. That's exactly where the process came from. We've just concentrated it," Lynch says. "It might take the river a couple hundred miles to accomplish what we do in a couple days." We've been talking about sewage treatment for 2 hours--about dewatered cake and grit screens and activated sludge and UV filters--and suddenly I understand.
What the river does is exactly what a sewage plant does, and until around World War I most people didn't really think plants were needed at all. It was understood that watercourses were to some degree self-cleaning, that "the solution to pollution is dilution." But as populations increased, especially downstream, dilution stopped offering much of a solution. Chicagoans felt great about their famous flow-reversal of the Chicago River, sending their sewage into the Mississippi instead of into their own water supply of Lake Michigan. Predictably, the people of St. Louis were not as delighted. Their expression of dissatisfaction eventually landed them in front of the Supreme Court. Raleigh itself was sued in the late 1940s by downstream neighbor Smithfield. Smithfield won, and in 1956 Raleigh's first sewage treatment plant opened, treating 12 million gallons per day. The current plant replaced it in 1977; it's expanded since, and now it's expanding again.