The inhibitory effect of antimicrobial zeolite on the biofilm of Acidithiobacillus thiooxidans.

The inhibitory effect of antimicrobial zeolite coated concrete specimens (Z2) against Acidithiobacillus thiooxidans was studied by measuring biomass dry cell weight (DCW), biological sulphate generation, and oxygen uptake rates (OURs). Uncoated (UC), and blank zeolite coated without antimicrobial agent (ZC) concrete specimens were used as controls. The study was undertaken by exposing inoculated basal nutrient medium (BNM) to the various specimens. The coating material was prepared by mixing zeolite, epoxy and cure with ratios, by weight of 2:2:1. Concrete specimens were characterized before and after exposure to inoculated or sterile BNM by field emission-scanning electron microscopy (FE-SEM). Gypsum, which was absent in the other test concrete specimens, was detected in uncoated specimens exposed to the bacterium. In UC and ZC, the growth of the bacteria increased throughout the duration of the experiment. However, significant biomass inhibition was observed in experiments where Z2 was used. The overall biomass growth rate in suspension before the specimens were placed ranged from 3.18 to 3.5 mg DCW day(-1). After the bacterium was exposed to UC and ZC, growth continued with a corresponding value of 4 + or - 0.4 and 5.5 + or - 0.6 mg DCW day(-1), respectively. No biomass growth was observed upon exposure of the bacterium to Z2. Similarly, while biological sulphur oxidation rates in UC and ZC were 88 + or - 13 and 238 + or - 25 mg SO(4)(2-) day(-1), respectively, no sulphate production was observed in experiments where Z2 concrete specimens were used. Peak OURs for UC and ZC ranged from 2.6 to 5.2 mg l(-1) h(-1), and there was no oxygen uptake in those experiments where Z2 was used. The present study revealed that the antimicrobial zeolite inhibits the growth of both planktonic as well as biofilm populations of Acidithiobacillus thiooxidans.

Inhibition of microbial concrete corrosion by Acidithiobacillus thiooxidans with functionalised zeolite-A coating.

The inhibition of the corrosive action of Acidithiobacillus thiooxidans on concrete specimens coated by functionalised zeolite-A containing 14% zinc and 5% silver by weight was studied. Uncoated concrete specimens, epoxy-coated concrete specimens (EP), and functionalised zeolite-A coated concrete specimens with epoxy to zeolite weight ratios of 3:1 (Z1), 2:2 (Z2) and 1:3 (Z3) were studied. Specimens were characterised by x-ray powder diffraction and field emission scanning electron microscopy for the identification of corrosion products and morphological changes. Biomass growth at the conclusion of the 32-day experiments was 4, 179 and 193 mg volatile suspended solids g(-1) sulphur for the uncoated, EP and Z1 specimens, whereas that of Z2 and Z3 were negligible. In the uncoated, EP and Z1 specimens, sulphate production rates were 0.83, 9.1 and 8.8 mM SO(4)(2-) day(-1) and the specific growth rates, mu, were 0.14, 0.57 and 0.47 day(-1), respectively. The corresponding values for Z2 and Z3 were negligible due to their bacterial inhibition characteristics.