Many of us get accused of having our minds in the gutter. I say, why stop there. My mind is in the sewer.
Haven’t you always wondered what happened to the dishwater that went down the drain or what happened when you flushed the toilet? Well if you are in Hopewell Borough, it flows to the sewer facility on Aunt Molly Road, where it is elaborately treated and discharged into Bedens Brook.
If you live in Pennington Borough, it gets treated at the Rocky Hill-Pennington Road facility and discharges into Stony Brook.
Both plants are operated by the Stony Brook Regional Sewerage Authority, a public agency serving six municipalities and established in 1971.
Of course, if you are in the township, you undoubtedly have a septic system that gets pumped out regularly and transported by truck to appropriately equipped plants for processing.
According to Kyle Stewart, assistant plant manager, who gave me a tour of the Hopewell facility, the local system does not take septic tank goop because it contains anaerobic bacteria, while the Stony Brook facilities use aerobic bacteria to break down sewage.
Incidentally, Mr. Stewart noted that 99.9% of waste going into the sewer system is water. The remaining solids comprise primarily of human waste and toilet paper.
The flow rate to the Hopewell plant ranges from 50 gallons per minute to over 170 gallons per minute, depending upon time of day. According to Toni Shurott-Pchola, executive director of the SBRSA, it’s rated for an average flow rate of 300,000 gallons per day.
* * *
So let’s dive in, so to speak. When you run water in the sink or flush toilets, everything goes into a pipe in your yard which connects to a large main.
The effluent is moved by gravity through those mains, sometimes needing pumps to lift the liquid to a height where it can once again use gravity to continue its journey.
Once the waste reaches the treatment plant, increasingly finer screens filter out “rags”: materials that won’t break down. Real people with rakes scoop out the rags.
Waste liquid then enters a primary rectangular sedimentation tank, which separates out heavier solids.
The remaining effluent flows into “oxidation ditches”: concentric circles of liquid where “stabilizing organics” convert ammonia to nitrites to nitrates. Giant spinning disks keep the mixture aerobic, and the processing removes phosphorus and nitrogen. Buoys with sensors measure the dissolved oxygen in liquid.
The liquid next moves to “secondary clarifiers”: smaller circular tanks where remaining solids sink to the bottom. Remarkably, these two tanks are home to approximately 100 enormous goldfish that were introduced to eat water fleas that had infested the surface of the treated water.
These fish, some of which measure 8 inches or more, thrive in the wastewater. The possibility of holding a fishing derby on site has not been broached — yet.
Rotating “plows” send solids back to the aeration tank.
Bacteria do all the work, continuously breaking down solid substances in the wastewater. Lab samples are taken regularly to ensure that phosphorus, nitrogen and total dissolved solids are in compliance with effluent permits. Monthly reports are sent to the state.
Toward the end of the process, a spillway containing fully treated water flows into filters of sand and anthracite that remove fine particles. A 15% chlorine solution in a contact tank kills any dangerous organisms. Sodium bisulfite in the penultimate tank neutralizes the chlorine.
Finally, a last aeration tank makes sure that water is well oxygenated, resulting, in Kyle Stewart’s words, in “crystal clear effluent” which flows into Bedens Brook, then into the Millstone River and, ultimately, to the Raritan River, Raritan Bay and the Atlantic.
* * *
Well may you ask, what happens to the filtered-out solids? That sludge gets trucked to SBRSA’s main facility on River Road in Princeton. There, polymers are added to stick the solids together which, along with compression, create “sludge cakes.”
These cakes are incinerated, and the resulting ash is transported to a landfill in Warren County.
Tours are available at the facilities for residents and school groups, including Princeton engineering students interested in the design of sewer plants. Little kids are also given tours and tend to respond with “stinky.”
Incidentally, during my tour, the Hopewell site was fragrance free.
Mr. Stewart said that the enemy of a functioning sewer system is grease, which clogs pipes. Clogging calls for the use of fearsome Jet Vac trucks that employ high-pressure water and rotating blades to scour pipes, cut roots, and vacuum out the debris.
(So, maybe you can stop pouring bacon fat down the drain.)
Seven manholes on Aunt Molly Road provide access to those pipes. When my incredibly astute granddaughter, age five, heard the word “manholes,” she wanted to know why there weren’t any for girls.
Please, should the occasion arise, show your gender sensitivity and descend into “personholes.”
,
