Combined iron and sulfate reduction biostimulation as a novel approach to enhance BTEX and PAH source-zone biodegradation in biodiesel blend-contaminated groundwater.

•Two long-term controlled biodiesel blend field experiments were monitored.•Combined iron and sulfate reduction processes were stimulated in one experiment.•BTEX and PAH source-zone degradation was enhanced relative to natural attenuation.•Geobacter spp. and GOUTA19 spp. played a key role in B20 source-zone biodegradation.•Biostimulation with AMD-derived product can cleanup B20-contaminated groundwater.