The Effect of Bacillus Globigii Spores on the Activity and Performance of Activated Sludge

Matthew D. Smith


This research investigated the effect of a biological warfare surrogate (Bacillus globigii) on activated sludge through respirometry at concentrations from 2x101 CFU/ml to 2x107 CFU/ml. No concentrations caused statistically significant effects on peak (p-values, 0.11 - 0.32) or cumulative O2 (p-values, 0.21 - 0.62) consumption. Molar O2/CO2 ratios were also not impacted. Shape factors were impacted by the introduction of spores (p-values, 8.53 E-06 0.95) but these factors proved a poor indicator of biological inhibition when considered in light of other factors. B. globigii did not inhibit COD or N removal. When spores of the same concentrations in their 40% ethanol storage solution were tested, the results at 2x107 CFU/ml were significantly inhibited. Initial peak O2 consumption was 34% to 44% less. Final effluent COD increased to 136.3 mg/l, while NO3-N was reduced. Biological treatment was inhibited by ethanol, not B. globigii. Spore germination was observed at 0.88% to 1.7%. Spores preferentially adhered to the floc (81%) verse bulk liquid (19%). These results illustrate that B. globigii is unlikely to cause short-term interference with biological treatment at an activated sludge plant, but organic co-contaminants may cause inhibition. Spore germination may cause the WWTP to become a longer-term source of biocontamination.