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.