Removal of Pb2+ and Ni2+ by bio-sludge in sequencing batch reactor (SBR) and granular activated carbon-SBR (GAC-SBR) systems

Living bio-sludge from domestic wastewater treatment plant was used as adsorbent of heavy metals (Pb2+, Ni2+) and its adsorption capacity was about 10–30% reduced by autoclaving at 110 °C for 10 min. The living bio-sludge acclimatized in synthetic industrial estate wastewater (SIEWW) without heavy metals showed the highest Pb2+ and Ni2+ adsorption capacities at 840 ± 20 and 720 ± 10 mg/g bio-sludge, respectively. The adsorbed Pb2+ and Ni2+ were easily eluted (70–77%) from bio-sludge by washing with 0.1 mol/l HNO3 solution. The heavy metals (Pb2+, Ni2+) removal efficiency of both SBR and GAC-SBR systems were increased with the increase of hydraulic retention time (HRT), or the decrease of organic loading. The SBR system showed higher heavy metals removal efficiency than GAC-SBR system at the same organic loading or HRT. The Pb2+, Ni2+, BOD5, COD and TKN removal efficiencies of GAC-SBR system were 88.6 ± 0.9%, 94.6 ± 0.1%, 91.3 ± 1.0%, 81.9 ± 1.0% and 62.9 ± 0.5%, respectively with industrial estate wastewater (IEWW) with 410 mg/l glucose, 5 mg/l Pb2+ and 5 mg/l Ni2+under organic loading of 1.25 kg BOD5/m3 d (HRT of 3 days). The bio-sludge quality (sludge volume index: SVI) of the system was less than 80 ml/g. The excess sludge from both SBR and GAC-SBR systems with SIEWW under the organic loading of 1.25–2.50 kg BOD5/m3 d contained Pb2+ and Ni2+ at concentrations of 240–250 mg Pb2+/g bio-sludge and 180–210 mg Ni2+/g bio-sludge, respectively.