Electrooxidation Treatment for Wastewater Sludge

Sludge produced during wastewater treatment, contain pathogens that increases the risks to human health. In particular, the density of bacteria and helminth eggs in sludge generated in Mexico significantly exceeds the levels reported in developed countries (Jimenez , et al. 2002 ; Jimenez, 2007). These microorganisms enter into the sewage system and due to its physicochemical properties tend to accumulate in the sludge during the wastewater treatment (Diaz Cruz, et al.  2009 ) .

Some studies have reported on the BDD electrooxidation for removal of emerging pollutants in secondary effluents (Frontistis, 2011), however, with respect to sludge, this process has been applied only for stabilization and conditioning (Drogui et al. 2013) but not for the removal of pathogens. This work presents the results obtained when electrooxidation with BDD electrodes was applied to sludge under laboratory conditions.

A batch cylindrical electrochemical reactor containing a pair of BDD electrodes (BDD film supported on a niobium substrate) was used for electrooxidation tests. Each electrode was 20.0 cm by 2.5 cm with a surface area of 50 cm2. Batch volumes of 0.3 L were treated in a 1.0 L glass reactor. A direct-current power source supplied the system with 0.5, 1.0 and 2.0 amperes, corresponding to current densities of 10, 20, and 30 mA/cm². Sludge samples were mixed using a magnetic stirrer to reduce liquid-solid phase separation.

Figure 1 shows the COD removal as a function of the pH. Note that the best conditions are reached under acid pH.

References

 Díaz-Cruz, M.J. García-Galán, P. Guerra, A. Jelic, C. Postigo, E. Eljarrat, M. Farré,  M.J. López d Alda,  M. Petrovic, D. Barceló. 2009. Analysis of selected emerging contaminants in sewage sludge. TrAC Trends in Analytical Chemistry Volume 28, Issue 11, Pages 1263–1275.

Jiménez, B. (2007). Helminth ova control in sludge: a review. Water Science & Technology, Vol. 56, No. 9, pp. 147–155.

Jiménez, B., Maya, C., Sánchez, E., Romero, A., Lira, L. and Barrios, J.A. (2002) Comparison of the quantity and quality of the microbiological content of sludge in countries with low and high content of pathogens. Water Science & Technology, Vol. 46, No. 10, pp. 17–24.