“…The physics is described by the Langmuir adsorption model with where D is the concentration of dissolved arsenate and A the concentration of arsenate adsorbed at the pipe wall. We adopt realistic parameter values from and consider the system on the approximately positively invariant Ω given by D ∈[0,1]mg/l and A ∈[0,100]mg/m 2 . To discretize time and space, we decouple the advection and the reaction step with the Trotter formula .…”