The city of O’Fallon, IL, provides around 13,000 residents with fresh water from a variety of sources each day. The local sewer system collects waste from close to 16,000 locations nearby, treats it, and then safely discharges what remains into the environment. This system is an open loop, in which fresh water enters at one end and wastewater exits at the other. Not all wastewater is equal, however. These are the three types of wastewater the city of O’Fallon has to deal with, and how it does that.
Black wastewater is not good stuff. This is the flow from toilets and food-preparation sinks, as well as dishwashers and other organic-material sources. Black water means highly contaminated, hot with disease-causing germs and possibly chemically active. This waste almost always has to pass through an industrial treatment process before it’s safe to release as gray water.
Gray water is the product of clothes washers, bathroom sinks, some industrial processes and miscellaneous applications, such as irrigation and lawn care. While not fit for human consumption, gray water proves much safer than black water. Gray water may have dissolved fertilizer and fluoride in it, as well as laundry detergent, liquid fabric softener, some biological material (think shaving and brushing teeth over the sink) and the occasional small solids.
Gray wastewater is most often treated by being sprayed onto constructed wetlands (CW). These serve as artificial wetlands with plants and microbes to soak up and process gray water. Runoff from these sites is typically safe for everything except drinking. With reverse-osmosis treatment, the CW water can safely go back into O’Fallon’s water supply through recharge pumps that send fresh water down into the aquifer.
Yellow wastewater is in a class by itself, and it represents a unique. . . stream of wastewater collection. Furthermore, yellow water is almost exclusively urine, and it comes from stand-up urinals and some portable toilets. This waste has to be specially collected and kept separate from other types of wastewater, especially black water.
Urine contains a lot of nitrogen, and other chemicals that are good for plants. Left alone, these chemicals usually precipitate out of urine as crystals within about 6 months, though the process accelerates when adding magnesium oxide. The resulting white powder makes a powerful fertilizer additive, and it often turns up in soil rechargers sold commercially.