Anaerobic Co-digestion efficiency under the stress exerted by different heavy metals concentration: An energy nexus analysis

Abstract

The effects of heavy metals (HMs) on the anaerobic co-digestion (AD) process of activated sludge and olive mill wastewater of 50% v/v were investigated. At varying doses (15–60 ppm), the inhibiting and toxicity effects of HMs on the digestive process were determined. In terms of biogas generation, CH4 content, degradation of the organic load, removal efficiency of TCODr-eff, and hydrogenotrophic-methanogenic bacteria inhibition, a high concentration of HMs has resulted in a considerable decline in AD performance. The HMs toxicity can be Arranged in ascending order with respect to the removal of TS: Pb < Cr≈ Zn < Cu, the TCODr-eff: Pb<Zn<Cr<Cu, biogas yield: Cu > Zn ≈ Cr > Pb, and methane content: Pb<Cr<Zn<Cu. The results also demonstrated that the methanogenic generation was adversely affected more than the acetogenic generation. Pb concentrations below 30 ppm had a lower influence as an inhibitor on AD. Meanwhile, the lowest Cu concentration caused a considerable inhibitor effect on the diges. The TCODr-eff was 20.53%, 19.13%, 17.07% and 15.64%, the removal of VS was 5.17%, 7.94%, 20.53% and 19.13% and biogas production decreased by 73.91%, 68.1%, 51.55% and 66.46% at 60 ppm concentration of Cu, Cr, Pb and Zn, respectively.