Effects of reactor geometry and electron donor on performance of the hybrid linear flow channel reactor

Abstract

Semi-passive sulphate reducing bioreactors show potential to play an important role in remediation of persistent, low volume acid or neutral rock drainage, characterised by high sulphate concentration. The hybrid linear flow channel reactor (LFCR) integrates biological sulphate reduction and partial sulphide oxidation within a single operating unit, allowing elemental sulphur recovery. Here, the impact of reactor geometry and scale-up of the hybrid LFCR was evaluated. In addition, the use of acetate as an alternative carbon source and electron donor to lactate was investigated. Scale up from 2 to 8 L did not significantly affect process performance over the range of hydraulic residence times tested. A decrease in HRT from 4 to 2 days resulted in an increase in VSRR (2 L: 0.068 to 0.113 mmol/L/h; 8 L: 0.070–0.132 mmol/L/h), coupled with a small decrease in sulphate conversion (2 L: 63–52%; 8 L: 65–61%) in the lactate-fed reactors. This confirmed the consistency of performance across the reactor configurations. On using acetate as a carbon source and electron donor, under optimal conditions, a sulphate conversion efficiency of 64% and a VSRR of 0.069 mmol/L/h was comparable to its lactate-fed equivalent. Unlike the lactate-fed system, disruption or harvesting of the biofilm resulted in a significant decrease in sulphate reduction performance in the acetate system and an extended recovery time.