Wastewater management facilities are like a “black box” for many people. They know the wastewater feed enters the plant and that the outflow from the plant is different from the feed, but they know little or nothing about what happens in the plant. If you’d like to know something about the process, this article is for you.We’ll discuss a little of the history of wastewater treatment plants (WWTPs), describe in simple terms what systems are used and some unusual plant configurations.This will help you understand some of the processes used in wastewater treatment. We recommend that, if you’d like to see a plant in action, you contact the wastewater treatment authorities in your community. Most such authorities are happy to demonstrate the plants to citizens showing interest, and it’s to their benefit, as well as yours, for you to understand their operation.
A Little History
Water is essential to all life. With that as a premise, it’s not surprising that water distribution systems date from the beginning of man’s history. The relationship between diseases and pathogens in water began to be better understood in the mid-19th century. Before that, there was little effort to treat wastewater before releasing it into the environment.
In the 20th century, wastewater management gained serious attention, and the wastewater treatment processes in use today were gradually discovered. As with all science and technology, new advances come much more quickly now than 100 years ago.
Wastewater treatment plants have become continually more sophisticated and automated, and produce cleaner effluent every year.
What are the Processes Used in WWTPs?
Here are some of the processes most commonly employed to treat wastewater are conventional activated sludge (AS, CAS), membrane bioreactor (MBR), Moving bed biofilm reactor (MBBR). Integrated fixed-film activated sludge (MBBR IFAS, IFAS), and sequencing batch reactor (SBR).
CAS was the first effective wastewater treatment process. It was discovered by scientists in England in the early 20th century, while MBR is one of the newer processes. It uses membranes that allow water to pass through but trap many undesirable contaminants.
MBBR was discovered in the 1980s and has become an increasingly popular choice. It employs small plastic carriers that present a large contact area to the liquid they float in, collect biomass and can be easily screened out as the clarified liquor leaves the tank. IFAS removes nitrogen very effectively.
A sequencing batch reactor (SBR) is an activated sludge system. As the name suggests, the reactor is filled with feedwater, and then the treatment takes place on that batch without further inflow. After the batch is treated and discharged, a new batch enters the system.
Many process choices are available to a wastewater treatment process designer. There’s much more information on those we’ve mentioned and other processes here.
Wastewater management is important everywhere there are people. The greatest challenge, and of course the greatest need, in providing wastewater treatment are where population density is highest.
Other potential challenges to the plant designer are:
- Extreme weather – unusual high or low temperatures, and heavy rain or snow.
- Physical limitations of the site – total space available, terrain, elevations, etc.
- Unusual feedwater characteristics – volume, unusual contamination elements, etc.
Considering all these factors, here are a few unique plants that have been built
- The Jean R. Marcotte wastewater treatment plant in Montreal, Quebec, Canada, is the world’s largest. Its treatment capacity is up to 7.6 million m³/day (2 billion gal./day.)
- The Huaifang Water Reclamation Plant in China is Asia’s largest underground advanced wastewater management arrangement. Building it underground had the benefits of saving space on the surface and eliminating any visual impact. The plant operates on three levels, limiting the area taken up.
- Sometimes, a package wastewater management system is the answer in communities where the feed water volumes are small. Such a plant can be shipped in on trucks and installed faster than a built-on-site plant. Such plants are typically limited to serving about 5000 people.
As the world population increases, wastewater management becomes increasingly important. People are generally trending more toward urban lifestyles, so small package systems or rural single-home systems contribute less to the overall picture.
Additionally, when communities face the fact that wastewater treatment is important to them, they may have delayed that decision to the point where time is critical. Designing a treatment plant with old-fashioned manual calculations can take weeks, delaying the project further.
Transcend Water’s design generator (TDG) shortens this phase by creating a preliminary plant and process design in as little as 8 hours. Check out their website.