By Jonny Lupsha, Wondrium Staff Writer
An Iowa family’s basement has flooded with animal blood, CBS affiliate WKYT reported. The fluid came from a meat locker plant next door due to interconnected drainage pipes between the two buildings. An investigation is ongoing, though waste disposal is rarely so troublesome.
According to the WKYT article, the basement of the Des Moines house flooded nearly five inches with the blood, fat, and bones of multiple species of animals due to the runoff from a meat locker plant that occupies the building adjacent to their home. The family then vacated the premises while the house gets cleaned after the Iowa Department of Natural Resources recommended that they do so due to potential biohazards of the wastewater. While sewage is an unpleasant business in most people’s minds, it’s usually carried out in a far less gruesome capacity.
The Long Road Ahead
Provided your meat locker doesn’t somehow end up dumping its drainage into your neighbor’s basement, all wastewater leaves your bathroom sink, toilet, shower, and garbage disposal either on its way to a municipal sanitary sewer system or an onsite septic system.
“The sanitary sewer begins with a lateral pipe where it connects to a larger pipe called a branch,” said Dr. Stephen Ressler, Professor Emeritus from the United States Military Academy at West Point. “Branches feed into progressively larger pipes—typically called trunks and interceptors—in a tree-like topology. In large, municipal wastewater systems, the interceptors can be huge: a 48-inch diameter concrete pipe is fairly typical.”
These pipes are either made of concrete, iron, vitrified clay, or PVC plastic, Dr. Ressler said. They follow public streets and progress downhill at a precise angle that keeps the wastewater moving, but not moving quickly enough to damage the pipes. So what happens when the city is built in such a manner that the pipes can’t go downhill to the sewage treatment plant?
“In cases where topography prevents a continuous downhill gradient, a sewage lift station is installed to pump the wastewater stream to a higher elevation, at which point it resumes its gravity-driven downhill flow,” Dr. Ressler said.
What Happens at the Plant: Primary Treatment
Few of us know what happens at the wastewater treatment plant and are hesitant to ask. However, the answer is far cleaner of a discussion than we would imagine.
“Treatment begins as the wastewater stream enters through a series of trash racks—metal grills that filter out large pieces of debris and foreign objects,” Dr. Ressler said. “From here, the flow enters a grit chamber, which is designed to settle out the larger suspended particles like sand, coffee grounds, and watermelon seeds to keep them from damaging pumps and other equipment at later stages of treatment.”
Next, according to Dr. Ressler, the stream enters a sedimentation tank, also called a clarifier, where floating contaminants rise to the top and are removed from the surface by a skimmer. At the same time, heavier materials settle in at the bottom and are mechanically raked out away from the water. Finally, after about two hours, the water is collected in a separate trough, clear of solid detritus.
This process completes the primary treatment of wastewater. Before modern, federal law requirements of water quality standards, that used to be the point in time when the wastewater was released back into rivers and streams. Thankfully, in the present day, secondary treatment is mandated.
What Happens at the Plant: Secondary Treatment
After the suspended solids and other unpleasantness have been separated from wastewater, the biggest remaining task involves dissolved oxygen.
“The fundamental challenge in secondary treatment is a phenomenon called biochemical oxygen demand, abbreviated BOD,” Dr. Ressler said. “Water naturally contains dissolved oxygen, which it acquires through contact with the air and from the photosynthesis of algae and aquatic plants. Dissolved oxygen is critical for the health of an aquatic ecosystem because fish and other aquatic animals need it to breathe.”
Dr. Ressler said that most water also contains organic compounds like dead algae, which microorganisms like aquatic bacteria consume as food. However, the decomposition of these organic compounds that comes from the microorganisms eating it also consumes the dissolved oxygen in the wastewater at dangerously high rates, which can harm the overall ecosystem on a larger scale.
“The most common technology for reducing BOD to safe environmental levels is the rather colorfully named ‘activated sludge process,'” Dr. Ressler said. “In this process, the wastewater stream is directed into a series of deep vats called bioreactors, where it’s combined with carefully managed populations of bacteria, protozoa, worms, and microscopic animals called rotifers.”
Rest assured, the microorganisms consume a safe amount of organic compounds in the water and are then gently and completely removed from the wastewater via a second clarifier tank to be returned for their next meal.
“The water is now clean and quite safe for discharge into the local stream,” Dr. Ressler said.
Dr. Stephen Ressler contributed to this article. Dr. Ressler is Professor Emeritus from the United States Military Academy at West Point. He earned a B.S. from West Point and an M.S. and a Ph.D. in Civil Engineering from Lehigh University, as well as a Master of Strategic Studies from the U.S. Army War College.