Sulfate reduction applied to environmental biotechnology using marine and freshwater sediments as inoculum: A review

The present work presents advances made in recent decades on the understanding of the metabolic capabilities of sulfate reducing bacteria (SRB) from marine and other types of sediment (i.e., freshwater, estuarine) for the biotransformation of carbon compounds and sulfate that are present as pollutants in several types of waters and soils. Therefore, this review is about the findings on sulfate reduction in natural scenarios and also in engineered systems and their applications in environmental biotechnology. The bacteria from marine sediments could be the source of microorganisms with an improved capability for adaptation to stressful conditions such as the prevailing in marine environments, for example: abrupt temperature changes, a wide range of pH, salinity and variation of water streams, among others. Thus, it is possible to think that the microorganisms present in marine sediments could be more easily adaptable and resistant to extreme conditions in comparison with microorganisms from other sources. In fact, there are studies on the tolerance of marine microorganisms to acidic environments. Besides, several studies on sulfate reducing conditions showed that microorganisms enriched from sediments can also tolerate high heavy metals concentrations. This is an example of the potential application of biogenic sulfide for the removal of heavy metals in various scenarios such as the treatment of complex industrial wastewaters as well as acid mine and acid rock drainage due to the high efficiencies in metals removal at low pH that these microorganisms can reach. Also, it has been observed that marine sediments are important sinks for recalcitrant or xenobiotic compounds, which often times present low solubility in water and can enter into food chains affecting the health of the living systems and the environment in general. The use of sediments in sulfate reduction has been evaluated by using oil, petroleum derivatives and some halogenated compounds, among others as electron donors to reduce sulfate to sulfide and at the same time to obtain good removal rates of sulfate reduction and high efficiency in the biodegradation of the compounds. There are other possible applications for sulfate reduction performed by enriched sediments, these have been less explored such as the utilization of biogenic sulfide as an electron donor in other biological processes, for example to reduce NO₃^-, NO₂^-, Mn and Fe (hydro) oxides. Along the same lines, the utilization of sediments for biofilm formation in microbial fuel cells has been undervalued, most of the studies have been performed in situ. Furthermore, the sulfate reduction process carried out with inocula derived from marine or freshwater sediments can be an attractive alternative for the treatment of various effluents due to its tolerance to high concentrations of sulfate, organic compounds and heavy metals as well as pH and temperature variations. Also, this process can be an alternative for the development of engineered systems particularly designed for power generation or the development of coupled processes more robust, as for example: biological denitrifying sulfide removal (DSR), sulfate reduction, autotrophic denitrification, nitrification integrated (SANI®) process or the sulfur cycle associated to enhanced biological phosphorous removal (EBPR).