Comparative study of zinc oxide nanocomposites with different noble metals synthesized by biological method for photocatalytic disinfection of Escherichia coli present in hospital wastewater

Binary zinc oxide (ZnO) nanocomposites with different noble metals, silver (Ag) and ruthenium (Ru), were prepared from an aqueous leaf extract of Callistemon viminalis. The biosynthesized photocatalysts were characterized and examined for their photocatalytic disinfection against Escherichia coli isolated from hospital wastewater. The influence of the different noble metals showed a difference in physicochemical characteristics and photocatalytic efficiency between Ag–ZnO and Ru–ZnO. The photocatalytic degradation of methylene blue and photocatalytic disinfection were found to be in the order Ag–ZnO > Ru–ZnO > ZnO. The photocatalytic disinfection of Ag–ZnO reached a 75% reduction in 60 min, compared to 34 and 9% reductions of Ru–ZnO and ZnO, respectively. The kinetic reaction rate for the photocatalytic disinfection of Ag–ZnO was found to be 2.8 times higher than that of Ru–ZnO. The outstanding photocatalytic activity of Ag–ZnO over Ru–ZnO was attributed to higher crystallinity, greater UVA adsorption capacity, smaller particle size, and the additional antimicrobial effect of Ag itself. The C. viminalis-mediated Ag–ZnO nanocomposites can be a potential candidate for photocatalytic disinfection of drug-resistant E. coli in hospital wastewater. HIGHLIGHTS Biosynthesis and characterization of two zinc oxide-based nanocomposites with silver and ruthenium were presented.; Photocatalytic disinfection of Escherichia coli present in hospital wastewater was demonstrated.; The influence of different noble metals (silver and ruthenium) on the characteristics and photocatalytic efficiency were discussed.

Free and Encapsulated Phosphate-Solubilizing Bacteria for the Enhanced Dissolution of Swine Wastewater-Derived Struvite—An Attractive Approach for Green Phosphorus Fertilizer

Struvite and hydroxyapatite are byproducts of phosphorus removal from wastewater that can be used as phosphate fertilizers. Due to their low water solubility, especially in alkaline soils, their use is currently limited. The use of phosphate-solubilizing bacteria to enhance the dissolution of struvite and hydroxyapatite could be an attractive solution for expanding their use, but literature reports on this are limited. In this study, Arthrobacter sp. (TBRC 5201), Azotobacter vinelandii (TBRC 7231), and Bacillus megaterium (TBRC 1396) were evaluated for their ability to dissolve struvite and hydroxyapatite on agar media with struvite or hydroxyapatite as the sole source of phosphorus. Only B. megaterium (TBRC 1396) was able to use struvite and hydroxyapatite for growth. After 14 d of incubation in liquid medium, B. megaterium (TBRC 1396) dissolved phosphorus from struvite up to 835.45 ± 11.76 mg P/l compared with 196.08 ± 3.92 mg P/l in a control without cells, whereas the dissolution of hydroxyapatite by B. megaterium was minimal. B. megaterium (TBRC 1396) was also capable of dissolving phosphorus from swine wastewater-derived struvite. Both free cells and alginate-encapsulated cells of B. megaterium (TBRC 1396) were able to rapidly dissolve phosphorus from swine wastewater-derived struvite, resulting in soluble phosphorus concentrations that reached 400 mg P/l within 2 days, compared with those without cells that required 12 days. In conclusion, the application of struvite with phosphate-solubilizing bacteria is a promising tool for green sustainable agriculture

Free and Encapsulated Phosphate-Solubilizing Bacteria for the Enhanced Dissolution of Swine Wastewater-Derived Struvite—An Attractive Approach for Green Phosphorus Fertilizer

Struvite and hydroxyapatite are byproducts of phosphorus removal from wastewater that can be used as phosphate fertilizers. Due to their low water solubility, especially in alkaline soils, their use is currently limited. The use of phosphate-solubilizing bacteria to enhance the dissolution of struvite and hydroxyapatite could be an attractive solution for expanding their use, but literature reports on this are limited. In this study, Arthrobacter sp. (TBRC 5201), Azotobacter vinelandii (TBRC 7231), and Bacillus megaterium (TBRC 1396) were evaluated for their ability to dissolve struvite and hydroxyapatite on agar media with struvite or hydroxyapatite as the sole source of phosphorus. Only B. megaterium (TBRC 1396) was able to use struvite and hydroxyapatite for growth. After 14 d of incubation in liquid medium, B. megaterium (TBRC 1396) dissolved phosphorus from struvite up to 835.45 ± 11.76 mg P/l compared with 196.08 ± 3.92 mg P/l in a control without cells, whereas the dissolution of hydroxyapatite by B. megaterium was minimal. B. megaterium (TBRC 1396) was also capable of dissolving phosphorus from swine wastewater-derived struvite. Both free cells and alginate-encapsulated cells of B. megaterium (TBRC 1396) were able to rapidly dissolve phosphorus from swine wastewater-derived struvite, resulting in soluble phosphorus concentrations that reached 400 mg P/l within 2 days, compared with those without cells that required 12 days. In conclusion, the application of struvite with phosphate-solubilizing bacteria is a promising tool for green sustainable agriculture