When water runs down the drain or we flush it down the toilet, we usually don't care where it ends up. This is because with adequate basic sanitation, wastewater shouldn't be a concern. Yet, although humanity has already taken man to space and plans to colonize Mars, it continues to fail to provide basic living conditions for a large part of its population. A comprehensive study estimates that 48% of global wastewater production is released into the environment untreated. The UN, in turn, presents a much less encouraging figure, citing that 80% of the world's sewage is released without treatment. But returning to the question of the title, there are basically two destinations for sewage if it is not being released directly into the natural environment: it can be treated locally through septic tanks, or connected to a sewage treatment plant through the sewage network, eventually returning to nature after a series of treatment processes.
Sewage has been a problem for humanity since we first ceased to be nomadic and cities began to form. It is estimated that the first sewage installations appeared about 6,000 years ago, in Babylon. They used a simple ditch to concentrate the excrement. But soon even the Babylonians developed hydraulic systems to transport water through clay pipes. The history of sanitation systems is rich and, until the mid-20th century, sewage from virtually all urban centers was discharged untreated into a body of water, such as a stream, river, lake, bay, or ocean. That was the rule, not the exception. But this remains the reality for many, triggering huge public health problems. The issue is so critical that the Bill & Melinda Gates Foundation, a philanthropic institution, devotes much of its effort to “enable widespread use of sustainable and safely managed sanitation services that contribute to positive health outcomes, economy, and gender equality for the poorest people in the world.”
Sanitation systems aim to protect human health, providing a clean environment that can prevent the transmission of diseases, especially through the fecal-oral route. Waste water, or sewage, means used water, which includes feces, food waste, cleaning products, soap, grease, and even industrial sewage. The treatment aims to remove contaminants from wastewater and convert it into an effluent that can be returned to the water cycle.
If the location does not have a public sewage system, the most common way to treat it is through septic tanks. The septic tank is a reservoir built to store wastewater for a certain period of time, so that the solids settle to the bottom and the fat is retained on the surface. The water that remains in the middle is usually directed to a second tank, called an anaerobic filter. This consists of a closed container, containing a filling material (such as gravel). There, the fixation and development of microorganisms takes place, which will help in the cleaning of liquids and provide greater efficiency in filtering the sewage, which should leave it a satisfactory quality to be returned to the environment through a sink, infiltrating the soil. In order for the pit to operate properly, it is important to clean it daily and see if it is working normally.
When the owners' concern is to return the cleanest possible water to nature, an extremely efficient natural method is to use the root zone. Basically, when the root zone receives the water drained from the septic tank, the water will pass through a path containing different species of macrophyte plants, which will filter impurities through their roots. In other words, this method uses nature's incredible ability to clean itself. Another option is to use the biodigester, which is also a closed tank that works in the absence of oxygen to accelerate the decomposition process of organic matter. Generally, the biodigester will only receive so-called black water (which contains fecal matter and urine). In this case, the bacteria present in the container will do a kind of digestion, and the decomposition product can be used as biofertilizers and biogas.
But if the city has a sewer system, the building owner will have to connect his plumbing to it. Several branches of streets and neighborhoods are usually attached to the same system, which will terminates at a treatment plant. These are a set of large, (usually) circular tanks, each performing a function. Commonly, the process is divided into 3 main steps for sewage treatment.
The primary treatment starts with grids to filter solid components that cannot enter the system, such as kindling, solid waste, debris, and others, which are separated and sent to the landfill. The sewage is then directed to settling tanks, where the sludge settles to the bottom and a foam is formed on the surface. Only the water that remains in the middle goes to the next stage, the secondary.
Secondary wastewater treatment uses bacteria to digest the remaining pollutants. The water is then taken to other decantation tanks, by the end of which the water is about 95% clean. Many systems finish there and return the water to nature. There are other more complete systems in which the water will still go through a sand filter to remove additional pollutants.
Tertiary treatment, which is not always used, removes specific pollutants through physical-chemical or biological techniques. The water is disinfected with chlorine, ozone, or ultraviolet light to remove pathogens, ensuring that the water is safe to return to the system of supply.
Wastewater treatment facilities are often uninviting, yet they play a vital role for cities. But there are some examples of architecture that reverse this undesirability. At PUBLIC, Canada's Sechelt Water Resource Centre, “instead of encapsulating this essential service behind a wire fence, the installation reveals mechanical and biological systems that clean wastewater, encouraging the public to witness their role in the hydrological cycle. The Center captures resources (biosolids, heat and water) for industry, parks and agriculture.”
In the LOTT Clean Water Alliance Regional Services Center project, developed by Miller Hull Partnership, the approach is similar. “LOTT actively engages the audience. Recovered water is water that has already been sewered and then cleaned with high quality standards so that it could be returned to the community for irrigation, toilet flushing, industry and many other uses. Benefits include wastewater management, water supply and environmental improvement, as well as the use of reclaimed water for wetland restoration and increased river flow.” "The new facility is a tangible example of the sustainable principles that guide the LOTT organization and fuel its efficient operations and education programs," said Scott Wolf, partner at Miller Hull.
We already have several technologies available to improve our relationship with sewage and basic sanitation. By being aware of the processes of the systems around us, we can also understand the possibilities and are able to envision improvements.
Check out some more good examples of infrastructure equipment architectures in this My ArchDaily folder.
