Fig. 2. Mass balance and electron balance batch tests.

a Typical biochemical profile of the systems (started on Day 1050) showing simultaneous nitrate and propane consumption with transitory formation of nitrite, and production of dinitrogen gas and ammonium. Nitrate reduction appeared to occur in two distinct phases. In Stage 1, nitrate was converted to nitrite and dinitrogen gas with negligible ammonium production; while in Stage 2, both dinitrogen gas and ammonium were generated from accumulated nitrite. b Average nitrogen- and electron balances were calculated from the three batch tests (for complete data and calculation see Supplementary Table 1). Error bars represent standard errors. Source data are provided as a Source Data file.