Combining gamma-radiation and bioaugmentation enhances wastewater's quality for its reuse in agricultural purposes

Abstract

The reuse of wastewater in agriculture can be environmentally beneficial due to its abundance of nutrients that promote plant growth and soil fertility. However, wastewater effluents (WWE) are often considered sources of dissemination of bacteria, antibiotics, heavy metal resistance genes, and pathogens. In this study, we employed a combination of gamma irradiation and bioaugmentation as a strategy for WWE treatment. Gamma irradiation facilitates the elimination of pathogens and the degradation of complex organic matter, while bioaugmentation utilises a consortium of microorganisms specialised in metal sorption. Bacterial strains were isolated from soils irrigated with WWE and selected based on their tolerance to Cd (0.2 g L^-1), Pb (1 g L^-1) and Cu (1.5 g L^-1). A consortium composed of Bacillus selenatarsenatis S53, Bacillus thuringiensis S15, and Staphylococcus edaphicus S107 was selected for their metal biosorption capacity, which was evaluated after 24 h of incubation in gamma-irradiated WWE (WWEI). The treated WWE was then used for pea (Pisum sativum L.) seeds germination over a 9 days' period. The bacterial consortium successfully biosorbed 180, 8085, and 125 µg g^-1 dry weight of Cd, Pb, and Cu, respectively, when incubated in WWEI. Seed imbibition with bioaugmented WWEI (WWEIB) resulted in significant increases in radicle and epicotyl elongation compared to germination in WWE (+91.6% and +123.7%, respectively). Additionally, there was an improvement in fresh biomass production for seedlings hydrated with WWEIB compared to WWE. Overall, this strategy appears highly promising for the safe reuse of WWE and enhancing crop productivity by mitigating contaminant-induced plant stress.

Keywords: Bioaugmentation; Gamma-radiation; Wastewater reuse; heavy metals biosorption; plant metal stress alleviation.