The characteristics of various sulfate-rich wastewaters, including pH, temperature, and salinity, are typically determined by domestic activities and industrial processes from which they originate; these can be far from the physiological optima of anaerobic microorganisms. Sulfate conversion biotechnologies (SCBs) have been developed for treating various sulfate-laden domestic and industrial wastewaters. For anaerobic treatment, the concentration of biomass and contact between pollutants and bacteria are considered the main factors dictating overall treatment capacity. Internal hydrodynamic properties can be adjusted via reactor configuration to improve the contact, but any high concentration of biomass cannot be reached easily through physiochemical means. The efficiency of th...[ Read more ]

The characteristics of various sulfate-rich wastewaters, including pH, temperature, and salinity, are typically determined by domestic activities and industrial processes from which they originate; these can be far from the physiological optima of anaerobic microorganisms. Sulfate conversion biotechnologies (SCBs) have been developed for treating various sulfate-laden domestic and industrial wastewaters. For anaerobic treatment, the concentration of biomass and contact between pollutants and bacteria are considered the main factors dictating overall treatment capacity. Internal hydrodynamic properties can be adjusted via reactor configuration to improve the contact, but any high concentration of biomass cannot be reached easily through physiochemical means. The efficiency of the bioreactor is also highly dependent on ambient conditions and fluctuant characteristics of the influent. Compact and resilient sulfate-converting granular sludge systems may offer a promising solution to overcoming these constraints in the implementation of SCB biotechnology. Previous researchers Hao et al. (2013) developed sulfate reducing granular (SRG) sludge with synthetic sewage. A real-world sewage trial is essential to scale up this new technology, as real sewage not only contains complex pollutants but also fluctuates in its characteristics, representing a significant challenge as far as successful research and development of SRG.

This study attempted to apply sulfate reducing granular (SRG) sludge to real saline sewage. Two reactors, a sulfate-reducing up-flow sludge blanket (SRUSB) and a continuous stirred tank reactor (CSTR), were adopted for comparison purposes. Granular sludge was successfully developed in both reactors with average diameter of SRG of 200-300 μm, settling velocity of 7-19 m/h, porosity of 0.01 ml/g, and specific area of 18.8-24 m²/g. The hydraulic retention time (HRT) decreased to 2.2 and 2.8 h in the SRUSB and CSTR, respectively, corresponding to respective organic loading rates of 3.8 and 3 kg COD/m³. Regarding the COD removal efficiency, CSTR achieved 5% greater than that of SRUSB (~75%). CSRT also showed advantages of faster startup, less accumulation of inert matter, and simpler operation than SRSUB during the development of SRG. The sulfate reducing bacteria (SRB) abundance in the granular sludge of SRUSB reached 29.3% of the total sequences, while the SRG in the CSTR showed higher SRB abundance (45%), most likely owing to different substrate distribution patterns. The SRG developed in the CSTR one month earlier than the SRUSB due to implementation of dual selection forces mixing and upflow velocity.

Sulfide oxidation bacteria (SOB) and acidogens dominated the mature/stable SRB granules, and the related microbial pattern was proven independent of substrate (synthetic or real sewage) or reactor type (SRUSB or CSTR). The particular microflora were found to be controlled by the reactor type, however. Reactor type dictates the substrates and internal flow pattern, thus influencing the microbial structure of the granules. The dominant SRB genus (Desulfobacter, 25%) in the SRUSB granules belongs to the complete organic oxidation group, while the non-complete organic oxidation SRB genus was detected in the CSTR.