• 08.07.2020
  • WTW and SI Analytics | Lab Segment

Using sludge for Wastewater Treatment plants as Fertilizer?

Using sludge for Wastewater Treatment plants as Fertilizer?

How to eliminate viruses in valuable sewage sludge?

An application story from France

Waste treatment plants in France release about 70 % of the sludge from waste water to agriculture as fertilizer. In the course of the corona pandemic, it was found that traces of the corona virus could be detected in sewage sludge. It was suspected that these viruses could still be active for several days. The French authorities of ANSES did not want to take any risks, but on the other hand did not want to lose these valuable fertilizers and the business model associated with them. Therefore, a way had to be found to treat the sludge in an environmentally friendly way and to eliminate the risk of infection and the health risk posed by the viruses it contains. An additional decisive factor is that this process can also be implemented by the individual wastewater treatment plant operators.

Xylem has a wealth of experience in the field of sludge treatment and can provide customers with optimal support in solving their challenges. To inactivate the bacteria and viruses contained in the sludge, slaked lime is added to the sludge and brought to a pH value of 12. This completely deactivates the viruses, as their protective cover cannot withstand the lye. Most other microorganisms do not survive this treatment either.

To ensure that the sludge is inactivated, the pH value must be reliably and safely verifiable.  This can be done optimally with a WTW ProfiLine pH 3310 pH meter and a BlueLine pH 21 SI Analytics penetration electrode from the Xylem Analytics business unit. Both products are robust and easily allow more than 500 measurements per day.

One challenge is the introduction of slaked lime into the sludge silos. The addition increases the temperature on the one hand and the sludge's flow behaviour towards a higher viscosity on the other hand. However, it must still be ensured that the slaked lime is reliably mixed in. There are different options for this. The powerful silo agitators of the 4600 and 4220 series ensure efficient mixing and have a sufficiently high motor power reserve even under the above conditions. A decrease in power would otherwise endanger the process. Another possibility is the use of centrifugal pumps with N-technology which ensure safe and efficient mixing in pits or basins. The possibility of renting pumps or agitators from Xylem is certainly an interesting option for temporary local use.