Effect of sulfate on low-temperature anaerobic digestion

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.

Methanogens, sulphate and heavy metals: a complex system

“…Another factor that can influence the competition is temperature because methanogens and SRB have different optimal temperature ranges (O'Flaherty et al 1998a, b). Madden et al (2014) investigated the effect of sulphate in lowtemperature (15°C) anaerobic expanded granular sludge bed (EGSB) bioreactors. At this lower temperature, methanogenesis seems to be affected only at COD:SO 4 2-ratios B1:2.…”

De NovoGrowth of Methanogenic Granules Indicates a Biofilm Life-Cycle with Complex Ecology

“…The biomass was allowed a 48-h acclimatisation period at 37ºC, regulated using built-in water jackets and recirculating water baths (Grant Optima, T100-ST12), before feeding and recirculation were commenced, which were controlled using peristaltic pumps (Watson and Marlow 2058 and 300 series, respectively). Influent was introduced at the base of each bioreactor, and bioreactor liquor was recirculated through the system to achieve the superficial upflow velocity required (Table 1), according to the same set-up, and approach, as described previously (38, 39).…”

Biological treatment of organic sulfate-rich wastewaters

“…Anaerobic treatment of sulfate-rich organic wastewater has focused on overcoming inhibition of methanogenesis. However, sulfate-reducers are versatile organisms, which can be applied in a wide range of temperature (Gil-Garcia et al, 2018;Lopes et al, 2007;Madden et al, 2014), pH (Sánchez-Andrea et al, 2015;Sousa et al, 2015), or salinity (Wei et al, 2018) conditions, enabling sulfate bio-based processes to be engineered for several purposes. This idea contributed to further research on the linkage of sulfur based biotechnologies with other biogeochemical cycles (Bhattarai et al, 2019;Hao et al, 2014;Qian et al, 2019).…”