Page 236 - Microbial methane cycling in a warming world From biosphere to atmosphere Michiel H in t Zandt

Chapter 10. Co-culturing methanogens and methanotrophs in an MBR
Figure 3. Total methane consumption in mmol/day as measured by reactor inflow and outflow gas methane concentrations. Gray areas indicate co-cultivation periods. At t = 92, methanogens were added. The first co-cultivation lasted until t = 155 days. At t = 252, a second batch of M. barkeri was added. The second co-cultivation lasted until t = 317. Right top graph shows zoom-in from t = 200 to t = 350 days.
Ammonium and nitrite concentrations were measured weekly within the co-cultivation periods from t = 83 to t = 315 days to monitor nitrogen availability, consumption, and nitrite toxicity risk (data not shown). Total available ammonium ranged between 2.3 and 4.7 mM with an average of 3.3 mM ± 0.5 (standard deviation, SD).
Monitoring showed constant availability and consumption of acetate
Five millimolars of acetate was added to the medium as methanogenic substrate. Acetate concentrations were monitored weekly (Fig. 4). These data indicated acetate consumption during the pre-cultivation period and thus suggested that the methanotrophic bacteria assimilated some of the acetate into biomass. M. barkeri Ks for acetate is 3-5 mM, and the threshold is 0.2-1.2 mM (Daniels 1993). Acetate concentrations were increased to 10 mM after 92 days to reduce acetate limitation risks for the methanogens. Further measurements indicated that acetate was not limiting during the entire co-cultivation periods.
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