Reduction of heavy metals from waste activated sludge via anaerobic fermentation and chemical post treatment for land application


MOLAEY R., YEŞİL H. , ÇALLI B. , TUĞTAŞ KARNABAT A. E.

2020 11th International Conference on Environmental Science and Development, Barcelona, İspanya, 10 - 12 Şubat 2020

  • Basıldığı Şehir: Barcelona
  • Basıldığı Ülke: İspanya

Özet

Heavy metal (HM) content of waste activated sludge (WAS) rises concerns regarding the application of WAS on the agricultural lands. Therefore, in this study bioleaching of heavy metals from WAS has been investigated first through gradual increase of organic loading rate (OLR) and then through increase of carbon to nitrogen (C/N) ratio via co-digestion of sludge with sugar. Two anaerobic fermenters (control and test) with volumes of five liters were operated at 37oC for 190 days. In the first part of the assay, OLR of control and test reactors was increased gradually from 3.81 to 16.70 g VS/L.d. Increasing OLR to 16.70 g VS/L.d resulted in increase of volatile fatty acid (VFA) concentration to 7170 mg COD/L. In the second part of the assay, to decrease the activity of methanogens, 25 mM of 2-Bromoethanesulfonate and then 2 mg/L of sugar was added daily to the test reactor. Increase of C/N ratio through the addition of sugar resulted in decrease of pH to 4.5 in the test reactor, which did not improve the bioleaching efficiency of metals. Soluble fraction of Ni, declined gradually to levels lower than 5% in both reactors. The solubility of Cr, Cu and Zn did not exceed 3.4% of the total HMs concentration. To enhance the HMs removal efficiency from the solid state of the digestate, post treatment was applied. Chemical reagents such as H2O2 and Fe2+ were applied at neutral and low pH to the digestate. After acidic post-treatment, 77% of Ni, 92.6% of Cu and 43% of Zn were leached from the WAS. However, only 23% of the Cr migrated to the soluble fraction. Results show that only anaerobic bioleaching is not enough to remove HMs from WAS, post treatment of WAS following an anaerobic fermentation process increases solubilization efficiency of HMs.