Abstract:

This paper  investigated  the affect of gypsum on methane emission and organic matter mineralization  in anaerobic
biochemical system by using beef extract peptone as  the nutrient source. To explore  the effect and mechanism of gypsum on
suppressing the activity of methane-producing bacteria (MPB), three kinds of chemical and physical indexes were tested: 1) TOC,
TIC, SO4^2-, sulfide and pH values of the aqueous phase; 2) volume of CO2, CH4 and H2S emissions in the gas phase, and 3) SEM,
EDS and XRD analyses of the solid phase. Our results showed that addition of gypsum could effectively reduce methane emission
by more than 40 %. However, no apparent impact on the release of CO2 was observed during this process. Furthermore, the content
of carbonate minerals in solid phase increased dramatically compared with the control group. These data further suggested that the
major role of gypsum in this anaerobic system is represented in the following aspects: 1) the continuous dissolution of gypsum, one
of the slightly soluble minerals, played an important role in controlled release of SO4^2-during its sustained reduction; 2) sulfate-reducing bacteria  (SRB)   were promoted  to be  the dominant microorganism under  the conditions of stable SO4^2-concentration and sufficient electron acceptors generated by slow dissolution of gypsum, and its competition of substrates and electrons further suppressed the methane production of MPB; 3) the consumption of organic carbon by SRB accelerated mineralization of organic matter, by which the carbonate generated could combine with Ca2+ in gypsum to form CaCO3. In this way, gypsum plays a crucial role in carbon sequestration by efficiently improving the rate of organic carbon mineralization.

Key words: gypsum, sulfate-reducing bacteria, methane-producing bacteria, methane, carbon sequestration