Characterization of sulfate-reducing bacteria dominated surface communities during start-up of a down-flow fluidized bed reactor

Abstract

An anaerobic down-flow fluidized bed reactor was inoculated with granular sludge and started-up with sulfate containing synthetic wastewater to promote the formation of a biofilm enriched in sulfate-reducing bacteria (SRB), to produce biogenic sulfide. The start-up was done in two stages operating the reactor in batch for 45 days followed by 85 days of continuous operation. Low-density polyethylene was used as support. The biofilm formation was followed up by biochemical and electron microscopy analyses and the composition of the community was examined by 16S rDNA sequence analysis. Maximum immobilized volatile solids (1.2 g IVS/L(support)) were obtained after 14 days in batch regime. During the 85 days of continuous operation, the reactor removed up to 80% of chemical oxygen demand (COD), up to 28% of the supplied sulfate and acetate was present in the effluent. Sulfate-reducing activity determined in the biofilm with ethanol or lactate as substrate was 11.7 and 15.3 g COD/g IVS per day, respectively. These results suggested the immobilization of sulfate reducers that incompletely oxidize the substrate to acetate; the phylogenetic analysis of the cloned 16S rDNA gene sequences showed high identity to the genus Desulfovibrio that oxidizes the substrates incompletely. In contrast, in the granular sludge used as inoculum a considerable number of clones showed homology to Methanobacterium and just few clones were close to SRB. The starting-up approach allowed the enrichment of SRB within the diverse community developed over the polyethylene support.

Bacterial community diversity in paper mills processing recycled paper

“…Almost half of the unique clones from this site were similar to Acholeplasma spp., which are distinguished by their lack of a cell wall and a particularly small and simple genome [43]. Other members of this class, i.e., some mycoplasmas, have the ability to form biofilms [28], and sequences similar to Acholeplasma have also been retrieved from a biofilm from a down-flow fluidized bed reactor [4]. The fact that distinct communities evolve in certain biofilms but not in others may be due to differences in adsorption material [40].…”

Effect of sulfide concentration on the location of the metal precipitates in inversed fluidized bed reactors

“…A similar time was necessary in the study of Celis et al [6], who used a lactate:ethanol mixture, a COD/SO 4 2− ratio of 0.6 and operated in batch mode for 45 days.…”

“…However, metal recovery cannot always be achieved in these reactors, since metals precipitate partly in the biomass, which hamper their recovery. A promising reactor configuration for metal sulfate reduction and metal removal in a single unit is the inversed fluidized bed (IFB) reactor [6]. This configuration is based on a floatable carrier material (on which the sulfate reducing bacteria biofilm is formed) which is fluidized downwards, whereas the metal sulfide precipitates settle and thus can be recovered at the bottom of the IFB [7].…”

Bioprecipitation - A Promising Technique for Heavy Metal Removal and Recovery from Contaminated Wastewater Streams

“…Thus, considering the practicality of applying an appropriate bioreactor configuration to treat metal contaminated waste streams, the foremost question in one's mind should be: should metal containing wastewater be treated in-situ or ex-situ?. Celis et al [9] & Janyasuthiwong et al [10] have tested a ''proof-of-concept'' of applying a down flow or inverse fluidized bed (IFB) reactor configuration for the treatment of low pH, sulfate rich wastewater supplied with an external carbon source, in order to produce sulfide and facilitate metal precipitation within the same unit. Similarly, for the sake of convenience and to avoid process disturbances, a two-step process can also be used to recover metals in the form of metal precipitates in bioreactors operating in sequencing batch mode (Figure 1).…”