Mechanism of arsenic release in sulfate rich sediment during microbial sulfate reduction

Arsenic contamination of drinking water is a major problem in An Giang, one of the Southwestern Vietnamese provinces. To simulate the natural redox cycles to which natural sediments are subjected, batch redox oscillation bioreactor experiments were conducted on arsenic and sulfate doped natural sediments. Eh oscillation in the range between - 300 mV and + 500 mV was implemented by modulating the influx gas mixture between N2/CO2 and compressed air automatically. Cellobiose was added at the beginning of reducing cycles to stimulate metabolism of a natively present microbial community. Results showed that repetitive redox cycling could decrease arsenic mobility significantly during reducing conditions up to 92%. Phylogenetic and functional analyses of 16S rRNA genes from metagenomic sequencing revealed the dominance of sulfur-cycling and iron-cycling bacteria, indicating that sulfate and iron reducing is a key driver of As immobilization during the reducing cycles.