Pure cleanliness! Water treatment in Memphis
In Memphis, Tennessee, much of the waters of the Mississippi river are brown in color and carry high levels of organics from agricultural uses. This makes wastewater treatment in these areas a particular challenge, and conventional disinfection plants are not up to the task. To this end, the city of Memphis chose to deploy an alternative technology based on peracetic acid several years ago. Evonik Active Oxygens’ process not only kills the pathogens in the water, but is also sustainable in many regards.
What do you think of when you hear “Memphis”? Elvis Presley or Johnny Cash? Pleasant-tasting tap water is probably not one of the first things you associate with the city on the Mississippi in south-west Tennessee. However, Memphis’ drinking water is of particularly high quality. This is due to the natural reservoirs located hundreds of meters below the Earth’s surface, sandwiched between layers of clay and sand. This sand acts as a natural filter and helps remove contaminations.
However, the water quality in the nearby Mississippi river is far lower. Industrial wastewater generated during agricultural processes and cotton processing is fed into the river, thus posing a big challenge for the Memphis wastewater treatment plant. This wastewater contains large quantities of organic waste that is discharged into the river and turns it a cloudy broth of coffee-brown color.
As such, conventional treatment technologies cannot simply be deployed for this water. For example, the water color is too dark for UV technology to be used to disinfect it. Chemicals containing chlorine or ozone are also unsuitable for disinfecting this water, as the organic compounds simply absorb large quantities of these chemicals – meaning that extreme concentrations would have to be used in order to achieve the desired results. In addition, chemical agents containing chlorine would react with the organic waste and form carcinogenic compounds and therefore cannot be used in the requisite concentrations.
The city of Memphis therefore began looking for a different solution and invited tenders from providers of alternative disinfection technologies around ten years ago.
Disinfection with peracetic acid – an impressive solution
Amongst the applicants was PeroxyChem – in 2020 acquired by Evonik and now integrated into Evonik Active Oxygens business line – with a suggestion that impressed the decision-makers in Memphis. The key part of the process was the construction of a production plant for peracetic acid (PAA) on leased land next to the wastewater treatment plant. This enables the disinfectant agent to be manufactured in direct proximity to the wastewater treatment plant and fed into it via a special dosing system.
Compared to conventional disinfection methods, using a peracetic acid solution has many advantages. For example, the fact that PAA decomposes into oxygen, water and vinegar when used and thus does not represent a hazard to human health or the environment – unlike agents containing chlorine. And it is also cost-efficient in deployment.
“The benefit of peracetic acid compared to other conventional methods is that a significantly smaller amount is required to disinfect the water,” explains Philip Block, Technology Director Specialty Market and Water Treatment at Evonik Active Oxygens. “As a result, we only need around one sixth of the amount of peracetic acid compared to agents containing chlorine for this wastewater.”
The PAA plant in Memphis uses the VIGOROX® WWT II product line from Evonik Active Oxygens. “The fact we were able to convince the city of our product and all the associated services is a huge success for us as a producer of PAA with sustainability in mind,” says Block. “Although we only use PAA in small and environmentally compatible concentrations, we still need around 30 million pounds (just less than 14,000 metric tons) of the product each year to supply the treatment plant in Memphis.”
Ecologically and economically sustainable
Memphis is also benefiting from the sustainable nature of the cooperation, both from an ecological and an economic standpoint.
The PAA dosing system …
- … is integrated into the Memphis wastewater treatment process and contributes to cleaning the wastewater.
- … provides reliable disinfection and is effective against E. coli and other fecal bacteria, even in low doses.
- … is more cost-efficient than conventional technologies (e.g., UV or chlorine-based procedures).
- … has very short transportation routes due to the direct proximity of the PAA production plant and the wastewater treatment plant.
- … creates new jobs in Memphis, as staff are required to operate the PAA production plant.
- … is an additional source of income for Memphis from the lease and commissions.
Following a development and construction phase lasting nine years, including comprehensive laboratory and field tests, the plant has been up and running as a fully commercial operation since the end of 2019. Evonik Active Oxygens is supplying not only the Memphis wastewater treatment plant, but also other customers in the south-east USA with peracetic acid from the new production plant.