Abstract
The effect of copper, zinc, chromium, and lead on the anaerobic co-digestion of waste activated sludge and septic tank sludge in Hanoi was studied in the fermentation tests by investigating the substrate degradation, biogas production, and process stability at the mesophilic fermentation. The tested heavy metals were in a range of concentrations between 19 and 80 ppm. After the anaerobic tests, the TS, VS, and COD removal efficiency was 4.12%, 9.01%, and 23.78% for the Cu(II) added sample. Similarly, the efficiencies of the Zn(II) sample were 1.71%, 13.87%, and 16.1% and Cr(VI) efficiencies were 15.28%, 6.6%, and 18.65%, while the TS, VS, and COD removal efficiency of the Pb(II) added sample was recorded at 16.1%, 17.66%, and 16.03% at the concentration of 80 ppm, respectively. Therefore, the biogas yield also decreased by 36.33%, 31.64%, 31.64%, and 30.60% for Cu(II), Zn(II), Cr(VI), and Pb(II) at the concentration of 80 ppm, compared to the raw sample, respectively. These results indicated that Cu(II) had more inhibiting effect on the anaerobic digestion of the sludge mixture than Zn(II), Cr(VI), and Pb(II). The relative toxicity of these heavy metals to the co-digestion process was as follows: Cu (the most toxic) > Zn > Cr > Pb (the least toxic). The anaerobic co-digestion process was inhibited at high heavy metal concentration, which resulted in decreased removal of organic substances and produced biogas.
Highlights
Anaerobic process of waste activated sludge and septic tank sludge is a complex microbiological process involving various types of anaerobic and facultative bacteria. is way of sludge treatment involves degradation and stabilization of organic matter. e microorganisms are susceptible to heavy metals due to some specific physicochemical parameters, including the electronegativity, Pearson’s softness index, the standard reduction potential, the solubility product of the metal-sulfide complex, the electron density, and the covalent index [1, 2].e heavy metals accumulated in municipal sludge from various sources such as the use of metallic chemicals, pipeline corrosion, the washing machine equipment process, bleaching, and neutralization [3, 4]
Other studies revealed that the inhibition effect of toxic was quite different with the pattern of Zn > Cr > Ni≈Cd [10] or Cu > Ni∼Zn > Pb [11] or Hg > Cd > Cr (III) [12]
There are no reports that have been performed to assess the effect of four metals (Cu, Zn, Cr, and Pb) on coanaerobic processes of waste activated sludge and septic tank sludge. is study aims to investigate the effects of metals on co-anaerobic processes of waste activated sludge and septic tank sludge; this eventually specifies the inhibitory effect of these metals on the anaerobic stabilization of sludge
Summary
E tested heavy metals were in a range of concentrations between 19 and 80 ppm. The TS, VS, and COD removal efficiency was 4.12%, 9.01%, and 23.78% for the Cu(II) added sample. The efficiencies of the Zn(II) sample were 1.71%, 13.87%, and 16.1% and Cr(VI) efficiencies were 15.28%, 6.6%, and 18.65%, while the TS, VS, and COD removal efficiency of the Pb(II) added sample was recorded at 16.1%, 17.66%, and 16.03% at the concentration of 80 ppm, respectively. Erefore, the biogas yield decreased by 36.33%, 31.64%, 31.64%, and 30.60% for Cu(II), Zn(II), Cr(VI), and Pb(II) at the concentration of 80 ppm, compared to the raw sample, respectively. E anaerobic codigestion process was inhibited at high heavy metal concentration, which resulted in decreased removal of organic substances and produced biogas The efficiencies of the Zn(II) sample were 1.71%, 13.87%, and 16.1% and Cr(VI) efficiencies were 15.28%, 6.6%, and 18.65%, while the TS, VS, and COD removal efficiency of the Pb(II) added sample was recorded at 16.1%, 17.66%, and 16.03% at the concentration of 80 ppm, respectively. erefore, the biogas yield decreased by 36.33%, 31.64%, 31.64%, and 30.60% for Cu(II), Zn(II), Cr(VI), and Pb(II) at the concentration of 80 ppm, compared to the raw sample, respectively. ese results indicated that Cu(II) had more inhibiting effect on the anaerobic digestion of the sludge mixture than Zn(II), Cr(VI), and Pb(II). e relative toxicity of these heavy metals to the co-digestion process was as follows: Cu (the most toxic) > Zn > Cr > Pb (the least toxic). e anaerobic codigestion process was inhibited at high heavy metal concentration, which resulted in decreased removal of organic substances and produced biogas
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