I’m a sucker for a plant tour. Such a sucker, in fact, that a mild day in March had me suiting up in reflective vest, safety goggles, and a hardhat for an hour-and-a-half tromp around Arlington County’s sewage treatment facility, the Water Pollution Control Plant (WPCP). (Also, I am the mother of a potty-training three-year-old boy. This is familiar territory.) My guide was Frank Corsoro, Operations Specialist. His job involves monitoring and controlling the processes that turn all the stuff that people flush down their toilets into clear water that is pretty darn clean. (Cleaner, in fact, than what much of the world is drinking.) Mr. Corsoro conducts tours of the plant to help educate the public about this facility that is so important to the health of Virginia waterways, including Four Mile Run, the Potomac River, and the Chesapeake Bay. If you like to eat crab cakes, you should care deeply about what goes on at the WPCP and places like it throughout the Ches Bay watershed.
Mr. Corsoro is a longtime sewage treatment process control guy. When he says he could talk about this stuff all day, I believe him. There is a lot to know. Raw sewage undergoes physical, chemical, and biological treatment processes. All the inputs and outputs of each process are constantly measured and monitored, to make sure the right levels of nutrients, oxygen, coagulants, bacteria, and minerals are present. Computers in the Operations Control Building keep all the systems running smoothly. Recent upgrades to the plant included a massive generator to allow business to continue as usual in case of power outages.
The tour provides an overview of the WPCP processes: input, output, and how we get from one to the other. It won‘t make you an expert at wastewater treatment, but it will give you plenty of cocktail party conversation starters.
Input: what you expect. Raw sewage enters the premises through two HUGE pipes. If you are between five and six feet tall, you could walk upright through at least one of these pipes, although you surely would not find it pleasant.
Output: water. Mr. Corsoro describes the shock and horror of a visiting foreign delegation when they discovered that the County, after expending much energy and money on treating the effluent until it has no measurable regulated contaminants, simply dumps the water into a stream. Once you’ve bothered to treat it that much, said the group, you should be drinking this water. An interesting perspective, but no thank you (speaking of shock and horror).
Wastewater is processed in four stages, with a set of steps on the side for handling the solids that are collected throughout the treatment cycle. The basic goal of each of the steps is to separate solids from liquids and then remove contaminants and excess nutrients from the liquids. A delightful discovery: most of the tour is not nasally offensive.
Step 1 (Smelly): Preliminary Treatment. In this initial step, non-organic matter – your paper towels, your Q-tips, your stray action figure – is removed from the influent. The large solids (or “rag,” things that should never have been flushed in the first place) and gritty stuff like sand and eggshells are screened and settled out. The sand and grit can damage pumps in downstream processes, and the other stuff can clog valves. Kids’ TV icon Mr. Rogers says in his potty-training book that the toilet is only for things our bodies don’t need. The WPCP staff would concur: the only non-organic item that should get flushed is toilet paper.
Step 2 (A little smelly, but not bad): Primary Treatment. After all the inappropriate objects have been fished out of the wastewater stream, the slow-moving influent is directed into open channels where fats, oils, and grease (FOG in plant parlance – they are not talking about the weather) are floated and collected, and suspended solids have time to settle.
Step 3 (Not smelly): Secondary Treatment. The output from primary treatment is a smooth brown slurry. This stuff is sent through an aeration tank where bacteria eat up the organic matter and other nutrients before the solids are again settled out. This is an oxygen-intensive process, and it is critical that it be done here at the plant instead of out in the Bay. There are plenty of micro-organisms in our waterways that would be happy to dine on our effluent, but when they do, they use up all the dissolved oxygen in the water and create zones where fish and other marine life can’t survive. It’s the aquatic version of getting locked in the bank vault: when the air is gone, so are you. Better that this digestion happen at the WPCP, where air is pumped into the tank to help the bacteria do their work. The surface of the tank foams and froths pleasantly, like a roux bubbling on the stove.
Step 4 (Not Smelly): Tertiary Treatment. In the last step, the secondary effluent is filtered to remove the last nutrients and itty-bitty suspended solids. I imagine workers coming here at the end of a stressful shift to listen to the soothing sound of trickling water in the filtration basins. If not for the noise of Route 1, the Metro trains, and the airport, I could close my eyes and imagine myself out in the country beside a babbling brook. The final output – clear wastewater – is disinfected and neutralized and released into Four Mile Run. It’s WAY cleaner than when it came in, and it’s also cleaner than the water that is already in the stream. Would I wade in the stream below the outfall? Yes, I would.
Arlington’s WPCP processes an average of 30 million gallons a day of wastewater. What does that look like? Our tour paused by a giant equalization tank, at least two stories tall and as big around as a baseball infield. It’s for special occasions – rainstorms, Thanksgiving, Super Bowl Sunday – when the sewage flows in faster than the plant can handle it. (The preliminary and primary treatment processes can take whatever comes; but the microbes in the secondary treatment process will get overwhelmed and stop working unless conditions, especially input rate, are just right.) Excess flow is stored in the equalization tank until the processes are ready for it. And this massive tank is only five million gallons – one sixth of an average day’s input. The plant now has three tanks this size or larger, and so the WPCP will be ready if the Super Bowl ever moves to a doubleheader format.
Special treat: while we are making our way to visit the “rag and grit removal” area, an Arlington County sewer vac truck arrives to disgorge its contents for treatment. When sewer lines back up because tree roots intrude or something really wrong goes down the drain, this truck comes in to vacuum out the clog. This is how I learn that not all the treatment processes are automated and controlled by sterile computers. The back of the truck opens, and black glop spews and sloshes out onto a concrete pad that is canted ever so slightly toward a drain. The liquids go down the drain to join the treatment process; the solids left on the pad are shoveled off to the side by human workers and are later added to the solids processing.
After we watch this little show, our tour continues past a wide brown puddle alongside the roadway. Mr. Corsoro sees me eyeing it and comments, “that’s just rainwater.” The reassurance is unnecessary. The WPCP is clean, bright, well-kept, well-marked. There is no possibility of a chance encounter with untreated waste.
Mr. Corsoro describes, but does not make me visit, the smelliest parts of the plant. These are the buildings on the north side of the plant, where the solids are managed. In the dewatering process, sludge is spun in centrifuges to extract some of the liquid. The sludge eventually gets trucked out of town, so to minimize transportation costs it needs to be as dry as possible. It’s the same principle as buying cleaning products in concentrated form – why pay for water?
The WPCP takes pains to be a good neighbor. White pipes labeled “FOUL AIR” snake in and out of buildings, capturing as much of the stink as possible. These pipes converge at a massive scrubbing stack, where the odor-causing compounds are neutralized through strategic application of chemicals.
As I head back to my car after reluctantly relinquishing my hardhat, a couple operations employees greet me with smiles and ask if I’ve enjoyed my tour. They seem gratified to hear that I have learned a lot and had a marvelous time. The staff at the plant are rightly proud of the work they do. They may not have the most glamorous jobs in Our Nation‘s Capital, but I have no desire to experience life without them.
Many thanks to Arlington Kids Resident Blogger, Katherine Bahnsen Stikkers for writing this post. Find Katherine’s occasional blog at www.runrunleap.com.
Arlington County Department of Environmental Services. Saving the Bay, Every Day: Arlington County’s Water Pollution Control Plant & Master Plan. Arlington, VA.
Corsoro, Frank. 2011. Interview/tour at Water Pollution Control Plant. March 17, 2011.
Click here to view more photos of the tour.