Akademik Veri Yönetim Sistemi
2020 11th International Conference on Environmental Science and Development, Barcelona, İspanya, 10 - 12 Şubat 2020
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.