We propose a Lagrangian solid mechanics framework for the simulation of salt tectonics and other large-deformation geomechanics problems at the basin scale. Our approach relies on general elastic-viscoplastic constitutive models to characterize the deformation of geologic strata, in contrast with the majority of published works on the subject, which utilize nonlinear Stokes flow models. By means of multiscale asymptotics, we also show that the inertia term in the momentum balance equation can be safely neglected, if the goal is to track the Earth's crust deformation over long periods of time. Our time integration strategy is a blended transient/quasistatic approach, in that it consists of a constitutive stress update, subject to the constraint that the stresses must satisfy static equilibrium. In addition, we use stabilized finite element methods specifically built for triangular and tetrahedral grids, which can also perform well under incompressibility constraints. Our approach offers computational geologists the following advantages: (1) improved flexibility in the choice of subsurface constitutive models with respect to the nonlinear Stokes flow; (2) improved efficiency over transient dynamics algorithms used in this context in the past, which are forced to resolve seismic events over geologic time scales; and (3) improved robustness in large strain computations over quadrilateral/hexahedral finite elements. We demonstrate the performance of the proposed approach with simulations of passive diapirism.

Anaerobic ammonia oxidation (anammox) is a well-developed biotechnology for treating high-strength ammonium wastewaters. Recently, partial denitrification has been considered as an alternative to supply anammox with the required nitrite. In this study, a process of sulfide-driven partial denitrification and anammox (SPDA) was developed and operated continuously in an upflow anaerobic sludge blanket (UASB) reactor for 392 days. This reactor was fed with synthetic wastewater containing 100 mgN/L nitrate, 80 mgN/L ammonium and 20–80 mgS/L sulfide. After 160 days of operation, the reactor reached stable performance, and the nitrogen removal efficiency and rate were maintained at 80% and 0.29 kgN/(m³•d), respectively. The estimated nitrogen removal via anammox and sulfide-driven denitrification were 87.2% and 12.8%. Additional batch experiments were conducted to investigate the effects of sulfide on anammox and the mechanisms of nitrogen removal in the SPDA system. The following results were obtained: (1) sulfide had an inhibitory effect on the specific anammox activity with IC₅₀ of 9.7 mgS-H₂S/L. (2) The rapid oxidation of sulfide by sulfur-oxidizing bacteria (SOB) could relieve the toxic effects of sulfide on the anammox in the SPDA system. (3) Sulfide bio-oxidation was a two-step reaction with biologically produced elemental sulfur (BPS⁰) as the intermediate, and the second step using BPS⁰ as the electron donor, can efficiently produce nitrite via partial denitrification (NO₃⁻ → NO₂⁻) as a supply for anammox. Finally, a high-throughput sequencing analysis identified Thiobacillus and Sulfurimonas as the dominant genera of SOB in the SPDA system, and Candidatus Kuenenia as the dominant anammox bacteria. Overall, this research gives the foundation for the practical application of sulfide-driven partial denitrification and anammox process in the future.