Effect of sulfate on low-temperature anaerobic digestion.

Pã¡Dhraig Madden,Gavin Collins,Vincent O'Flaherty,Fabio A Chinalia,Dirk De Beer,Abdul M Al-Raei,Anne M Enright

doi:10.3389/fmicb.2014.00376

Abstract

The effect of sulfate addition on the stability of, and microbial community behavior in, low-temperature anaerobic expanded granular sludge bed-based bioreactors was investigated at 15°C. Efficient bioreactor performance was observed, with chemical oxygen demand (COD) removal efficiencies of >90%, and a mean SO2−4 removal rate of 98.3%. In situ methanogensis appeared unaffected at a COD: SO2−4 influent ratio of 8:1, and subsequently of 3:1, and was impacted marginally only when the COD: SO2−4 ratio was 1:2. Specific methanogenic activity assays indicated a complex set of interactions between sulfate-reducing bacteria (SRB), methanogens and homoacetogenic bacteria. SO2−4 addition resulted in predominantly acetoclastic, rather than hydrogenotrophic, methanogenesis until >600 days of SO2−4-influenced bioreactor operation. Temporal microbial community development was monitored by denaturation gradient gel electrophoresis (DGGE) of 16S rRNA genes. Fluorescence in situ hybridizations (FISH), qPCR and microsensor analysis were combined to investigate the distribution of microbial groups, and particularly SRB and methanogens, along the structure of granular biofilms. qPCR data indicated that sulfidogenic genes were present in methanogenic and sulfidogenic biofilms, indicating the potential for sulfate reduction even in bioreactors not exposed to SO2−4. Although the architecture of methanogenic and sulfidogenic granules was similar, indicating the presence of SRB even in methanogenic systems, FISH with rRNA targets found that the SRB were more abundant in the sulfidogenic biofilms. Methanosaeta species were the predominant, keystone members of the archaeal community, with the complete absence of the Methanosarcina species in the experimental bioreactor by trial conclusion. Microsensor data suggested the ordered distribution of sulfate reduction and sulfide accumulation, even in methanogenic granules.

Highlights

The application of anaerobic digestion (AD) is an efficient approach for the treatment of high-strength organic wastewater (Yu et al, 2005a)
BIOREACTOR PERFORMANCE Low-temperature AD trials have previously demonstrated the potential of cold bioreactors for waste conversion (Collins et al, 2003; Enright et al, 2009; McKeown et al, 2012), including for the treatment of acidified, industrial wastewater similar to the feedstock used for this study (Nedwell and Reynolds, 1996; O’Flaherty and Colleran, 1999; O’Flaherty et al, 1999; Fukui www.frontiersin.org et al, 2000)
We do not present volumetric in situ methane yield data, and it is possible that methane production was depressed, the biogas quality data shown (Figure 1) indicate that methane concentrations were not diluted by sulfidogenic activity

Summary

Introduction

The application of anaerobic digestion (AD) is an efficient approach for the treatment of high-strength organic wastewater (Yu et al, 2005a). Low-temperature (>20◦C) AD (LtAD) has been demonstrated as a feasible approach for wastewater treatment (e.g., Connaughton et al, 2006; Akila and Chandra, 2007; Enright et al, 2009), allowing for further efficiencies by eliminating the need to heat AD bioreactors, and opening AD to new areas of environmental management, including for the digestion of raw sewage in temperate climates (Lew et al, 2004). Many industrial processes that use sulfuric acid (e.g., fermentation or seafood processing); or reduced sulfur compounds i.e., sulfide (e.g., in tanneries, kraft pulping), sulfite (e.g., sulfite pulping), thiosulfate (e.g., fixing of photographs) or dithionite (e.g., pulp bleaching) generate sulfate-contaminated wastewaters (Hulshoff Pol et al, 1998)

Methods

Results

Discussion

Conclusion