Sustainable conversion of palm juice wastewater into extracellular polysaccharides for absorption of heavy metals from Saudi Arabian wastewater

Abstract

The main aim of the study was to use palm juice wastewater as an alternative feedstock for the production of extracellular polysaccharide and to remove heavy metals from the wastewater. Heavy metal resistant bacteria were screened from soil sediment samples, and metal resistant properties were analysed. A total of five bacterial strains were selected for the analysis of maximum tolerance limit against five toxic heavy metals (Cu2+, Cd2+, Pb2+, Co2+ and Zn2+). Among the five bacterial strains, Pseudomonas aeruginosa Al-Dhabi144 showed resistance against Cu2+, Cd2+, Pb2+, Cu2+ and Zn2+ and maximum tolerance limit was 400, 350, 2000, 100 and 350 mg/L, respectively. Wastewater was used as the feedstock for the production of extracellular polysaccharide in submerged fermentation. Extracellular polysaccharide production was enhanced after 72 h incubation (4.8 ± 0.37 g/L), 1.5% inoculums (4.96 ± 0.15 g/L), 10% date syrup wastewater (8.3 ± 0.041 g/L), pH 7.5 (7.9 ± 0.059 g/L), 0.5% yeast extract (8.1 ± 0.074 g/L) and 0.5% starch (9.74 ± 0.036 g/L). The metal-absorption properties of extracellular polysaccharides revealed that P. aeruginosa Al-Dhabi144 extracellular polysaccharides had the ability to remove Cu2+ (300 ± 5.3 mg/g), Cd2+ (250 ± 10.4 mg/g), Pb2+ (380 ± 5.1 mg/g), Co2+ (225 ± 5.6 mg/g) and Zn2+ (250 ± 10.7 mg/g) from the wastewater.