Saturday, April 5, 2008
photo credit: Andrew Wallace
Its time to move on. Granted we're making a big jump from the basics to the more advanced. But I'll try my best to explain this as simply as possible.
Water (and wastewater/sewage) treatment can be done on an individual basis or en masse. Treatment plants are just mass water decontamination sites. They both use a combination of the processes discussed in "Water 101: Decontamination" to clean water.
Most developed countries (and the urban areas of developing countries) use centralized water distribution and sewer collection systems. Centralizing water and wastewater have their ups and downs, and I don't necessarily think that centralizing everything is the best way for every country, but its the way things are done at the moment.
Schematic Diagram of a Wastewater Treatment Plant (source: Ohio State University)
What's the difference between a water and wastewater treatment plant??
Generally, its the type of water that comes in--a Water Treatment Plant (WTP) generally takes water from ground, surface, or rainwater sources, makes it drinkable and distributes it to water storage tanks or directly to people; a Wastewater Treatment Plant (WWTP) generally collects sewage and other waste water (and in some cases stormwater) from various sites, cleans it and releases it back into the environment at a safe level for humans, fish, and plants to be around. Golf courses or parks that say "watered with reclaimed wastewater" often refer to this water.
WTPs generally are smaller operations than WWTPs, because of the water quality coming in. Generally WTPs just need a bit of cleaning and disinfection (because the water is generally clean already). WWTPs take pretty nasty sewage water (from industries and homes and businesses and schools) and get rid of most of the nastiness. This is why WWTPs are much larger and more elaborate. The solids generally end up going to landfills, the liquid (water) is cleaned and purified until it is safe for humans, animals and plants.
Is reclaimed wastewater potable??
Depends...on how clean they (the WWTPs) make the water before releasing it. It is definitely possible to take wastewater and put it through a series of cleaning steps to make it potable. But it can be expensive, which is why most wastewater treatment plants in the world don't generally do these extra steps. But as clean water resources get scarcer and the human population grows, it will become increasingly likely (and less expensive) to create fully recycled water plants.
Personally, I think the biggest barrier is not the technology or the expense, but rather the human factor. People are just not comfortable drinking water that entered a factory as sewage a few days before.
Reclaimed water: potable or not?? (photo credit: Peyri Leigh)
Howstuffworks.com : Wastewater plants
The USGS site for wastewater Treatment
How Water Treatment Plants work
FAQs about WWTPs
The Water Environment Federation's engaging presentation on WTP and WWTP
Using microorganisms in cleaning up water