Algal-bacterial bioremediation of cyanide-containing wastewater in a continuous stirred photobioreactor

This study reports the isolation and characterization of highly resistant bacterial and microalgal strains from an Egyptian wastewater treatment station to cyanide-containing compounds. The bacterial strain was identified as Bacillus licheniformis by 16S rRNA gene sequencing. The isolate removed up to 1 g L^-1 potassium cyanide, 3 g L^-1 benzonitrile, and 1 g L^-1 sodium salicylate when incubated as 10% v/v in MSM at 30 ℃. However, it failed to degrade potassium thiocyanate at all tested concentrations. The microalgal isolate was identified by electron microscopy as a strain of Chlorella spp.. Algal toxicity was tested by incubating the microalgae as 6% v/v in MSM containing 2 g L^- 1 NaHCO₃ with increasing concentrations of the pollutants. Results showed that 0.05 g L^-1 KCN, 1.5 g L^-1 benzonitrile, 5 g L ^-1 KSCN, and 5 g L^-1 sodium salicylate inhibited 93%, 96%, 75%, and 21% of algal growth, respectively. In a continuous stirred photobioreactor, the bacterial-microalgal microcosm detoxified synthetic wastewater containing 0.2 g L^-1 KCN, 0.1 g L^-1 benzonitrile, and 0.5 g L^-1 sodium salicylate in 3.5 days of hydraulic retention time. System failure was recorded when the KCN concentration was increased to 0.25 g L^-1. The effluent had no inhibitory effect on the germination of Lepidium sativum seeds in phytotoxicity testing. Temperature, pH, and chitosan effects were assessed on the algal/bacterial settleability. Statistical analysis showed no significant difference between the tested parameters. The microcosm represents a potential candidate for the treatment of industrial wastewater containing cyanide compounds.