Managing the interactions between sulfate- and perchlorate-reducing bacteria when using hydrogen-fed biofilms to treat a groundwater with a high perchlorate concentration

摘要

A groundwater containing an unusually high concentration (～4000 ng/L) of perchlorate (ClO_4~-) and significant (～60 mg/L) sulfate (SO_4~2 ) was treated with hydrogen (H2_)-fed biofilms. The objective was to manage the interactions between sulfate-reducing bacteria (SRB) and perchlorate-reducing bacteria (PRB) by controlling the H_2-delivery capacity to achieve ClO_4~- reduction to below the detection limit (4 μg/L). Complete ClO_4~- reduction with minimized SO_4~(2-) reduction was achieved by using two membrane biofilm reactors (MBfRs) in series. The lead MBfR removed ＞96% ClOJ, and the lag MBfR further reduced ClOJ to below the detection limit. SO_4~(2-) reduction ranged from 10 to 60%, and lower SO_4~(2-) reduction corresponded to lower H_2 availability (i.e., lower H_2 pressure or membranes with lower H_2-delivery capacity). Minimizing SO_4~(2-) reduction improved ClO_4~- removal by increasing the fraction of PRB in the biofilm. High SO_4~(2-) flux correlated with enrichment of Desulfovi-brionales, autotrophic SRB that can compete strongly with denitrifying bacteria (DB) and PRB. Increased SO_4~(2-) reduction also led to enrichment of: 1) Ignauibacteriales and Thio-bacteriales, sulfide-oxidizing bacteria that allow sulfur cycling in the biofilm; 2) Bacteroidales, heterotrophic microorganisms likely using organic sources of carbon (e.g., acetate); and 3) Spirochaetales, which potentially utilize soluble microbial products (SMPs) from autotrophic SRB to produce acetate.