Demonstration of simultaneous biological sulphate reduction and partial sulphide oxidation in a hybrid linear flow channel reactor

Abstract

Semi-passive remediation systems have the potential to treat low-volume, sulphate-rich, mining impacted waters in a cost-effective and sustainable way. This paper describes the “proof of concept” evaluation of a hybrid linear flow channel reactor, capable of sustaining efficient biological sulphate reduction and partial oxidation of the sulphide product to elemental sulphur. Key elements include the presence of a sulphate-reducing microbial community, immobilised onto carbon fibres and the rapid development of a floating biofilm at the air-liquid interface. The biofilm consists of heterotrophic species and autotrophic sulphide oxidisers. It impedes oxygen mass transfer into the bulk volume and creates a suitable pH-redox microenvironment for partial sulphide oxidation. Demonstration of the concept was successful, with near 20 complete reduction of the sulphate in the feed (1 g/l), effective management of the sulphide generated (95-100% removal) and recovery of a portion of the sulphur by harvesting the elemental-sulphur-rich biofilm. The biofilm re-formed within 24 hours of harvesting, with no decrease in volumetric sulphate reduction rate during this period. Colonisation of the carbon microfibers by sulphate reducing bacteria ensured biomass retention, suggesting the reactor could remain effective at high volumetric flow rates.