Enhancement of microbial resistance to toxic wastewater by granulation in upflow anaerobic sludge blanket reactor

Abstract

To investigate the effect of granular structure on resistance to toxic chemicals in upflow anaerobic sludge blanket (UASB) reactors, normal and broken granules were examined for their ability to degrade acetate with and without the addition of toluene or trichloroethylene as a toxic chemical. Without toxic chemical, both normal and broken granules degraded the acetate at the same volumetric degradation rate $(3.21 mM·h^{-1}). However, When 500 $μl·l^{-1}$ of toluene or trichloroethylene was added, the acetate-degradation rate of the broken granules was about a third of the rate with normal granules. Therefore, the layered structure of the UASB granules seems to give microbial populations the ability to resist toxic chemicals. Effect of the granulation in the UASB reactor was studied in order to select the most optimal anaerobic microbial population to resistant toxic materials. Metal ions $(Cd^{2+}, Cu^{2+}, Ni^{2+}, Zn^{2+} and Cr^{3+})$ on anaerobic digestion with intact and disintegrated granules from a UASB reactor did not affect glucose degradation or the production of methane. However, when $Cu^{2+} was at 500 mg/g-VSS (volatile suspended solids) in the media, the glucose degradation rates and methane production rates decreased by 14% and 32% in disintegrated granules, respectively, whereas, in intact granules, decreases were 3% and 14%, respectively. When various electroplating metal ions were tested, 50% inhibition of acetate degradation and methane production were produced by 210 - 770 mg/g-VSS and 120 - 630 mg/g-VSS, respectively. The relative toxicity of the electroplating metals on methane production was in the order of $Zn^{2+}$ (most toxic) ＞ $Ni^{2+} ＞ Cu^{2+} ＞ Cr^{3+} ＞ Cd^{2+}% (least toxic). In the acetate degradations test of UASB granules with $Cu^{2+}$, all of the acetate disappeared was not converted to methane, stoichiometrically. To study how much acetate was used by the other microorganisms except methanogens, reduction of nitrate and...