In light of recent events in Wichita Falls, TX, where the city council is asking water regulation agencies to have the ability to treat wastewater for use as regular tap water, the idea of recycling water has many citizens concerned. The small Northwest Texas town has been under severe drought conditions and is to the point of enacting rare water restrictions.
The process of recycling water is not a new idea. In fact, all wastewater gets reused to an extent. Once it is initially treated to remove waste, most of it is used for irrigation, landscaping, and industrial applications. In certain situations, it is used to support fragile water-based eco-systems and aquifers to prevent saltwater intrusion. What the city of Wichita Falls is proposing goes a step further, and reintroduces purified wastewater back into the tap water cycle.
The process for wastewater treatment has been deemed safe by the World Health Organization as well as several other organizations and is already happening in some parts of the world where clean water is extremely scarce. The science behind the process and the results are time-tested, so before I go into the ins and outs of water purification, if you’d like to know how I really feel, please click here; otherwise, please read on.
The Process
First, wastewater is collected in large open-air tanks where the process of sedimentation takes place. Sedimentation is where all of the heavy waste settles to the bottom of the tank and microbes are added to consume the particulates that are suspended. The top layer of the treated water is then run through a microfiltration process. Pipes are full of straw-like filters that have pores 500 times smaller than the width of a human hair and will catch any remaining solid waste as it moves on to the next stage in the process.
Once the water is filtered it goes through a process called reverse osmosis. Filtered water is forced through a plastic membrane that has pores so small that not even dissolved salts can make it through. This process removes any remaining solid wastes. After the reverse osmosis procedure, the water is exposed to intense ultraviolet light to kill any remaining microbes, and certain chemicals are added to the water (depending on the treatment facility). Once the wastewater has made it through that cycle, it is often added directly to groundwater stores for further purification.
Wastewater Treatment Technologies
There are even new technologies emerging in the treatment of wastewater that are even more beneficial. For instance:
Researchers at the J. Craig Venter Institute in San Diego are working on microbial fuel cells. Through the process of bacteria breaking down sewage, electricity is generated. A microbial fuel cell consists of two tanks of water separated by a membrane. Two electrodes (one in each chamber) are connected by one wire. In one tank, anaerobic bacteria feed on sewage. As they digest the sewage, they produce electrons and positively charged hydrogen atoms called protons. The electrons flow to the electrode in the tank and across the wire that joins the two tanks and an electrical current is generated. While that is happening, the protons pass back through the membrane and into the other tank where they combine with the electrons flowing into that electrode. Oxygen is then added to the solution to make pure water.
The Institute of Environmental Science and Engineering, based in Singapore, has found that something known as an anaerobic membrane bioreactor could reduce the cost of wastewater treatment and its environmental impact. Membrane bioreactors are already in place in many modern wastewater treatment plants, because they shorten the conventional sewage treatment process by adding a membrane to the aeration step. Aerobic bacteria (oxygen respiring) break down the organic sewage. Because of this process of sending the water through a membrane, follow-up settling and filtration steps are not necessary. After passing through a membrane bioreactor, water is clean enough to be discharged or can be used for irrigation. In contrast, an anaerobic membrane bioreactor uses bacteria that don’t need oxygen to breathe. Therefore, oxygen is not bubbled through the reactors. That reduces treatment costs. These bacteria can also consume more solid waste, which reduces the amount of waste requiring costly disposal. In the right configuration, they also release less methane than conventional membrane bioreactors.
The Scarcity of Clean Water
No matter the process of cleaning wastewater, clean water is said to be the oil of the 21st century, as it is becoming a scarce commodity. As unpopular as recycling wastewater may be in principle, unless stricter water regulations are established, we may not have any other options.