Continuous-mode acclimation and operation of lignocellulosic sulfate-reducing bioreactors for enhanced metal immobilization from acidic mining-influenced water

Lignocellulosic sulfate-reducing bioreactors are an inexpensive passive approach for treatment of mininginfluenced water (MIW). Typically, microbial community acclimation to MIW involves bioreactor batch-mode operation to initiate lignocellulose hydrolysis and fermentation and provide electron donors for sulfatereducing bacteria. However, batch-mode operation could significantly prolong bioreactor start-up times (up to several months) and select for slow-growing microorganisms. In this study we assessed the feasibility of bioreactor continuous-mode acclimation to MIW (pH 2.5, 6.5 mM SO42-, 18 metal(loid)s) as an alternate start-up method. Results showed that bioreactors with spent brewing grains and sugarcane bagasse achieved acclimation in continuous mode at hydraulic retention times (HRTs) of 7-12-d within 16-22 days. During continuousmode acclimation, extensive SO42- reduction (80 +/- 20% -91 +/- 3%) and > 98% metal(loid) removal was observed. Operation at a 3-d HRT further yielded a metal(loid) removal of 97.5 +/- 1.3 -98.8 +/- 0.9% until the end of operation. Sulfate-reducing microorganisms were detected closer to the influent in the spent brewing grains bioreactors, and closer to the effluent in the sugarcane bagasse bioreactors, giving insight as to where SO(4)(2- )reduction was occurring. Results strongly support that a careful selection of lignocellulose and bioreactor operating parameters can bypass typical batch-mode acclimation, shortening bioreactor start-up times and promoting effective MIW metal(loid) immobilization and treatment.

Automated summary

The study found that lignocellulosic sulfate-reducing bioreactors acclimated to mining-influenced water in continuous mode have good feasibility for efficient metal(loid) removal within a short period of time. The bioreactor microbial communities varied between spent brewing grains and sugarcane bagasse reactors, affecting the location of sulfate-reducing microorganisms and SO42- reduction efficiency.