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A three phase (aqueous/solid/gas) mixed weak acid/base kinetic model is developed to simulate the physical and chemical processes that occur on aeration of anaerobic digester supernatant. Included in the model are the kinetic reactions for (i) weak acid/base dissociations (water, carbonate, ammonium, phosphate, and short-chain fatty acids), (ii) precipitation of struvite, newberyite, amorphous calcium phosphate, calcium and magnesium carbonate and (iii) stripping of CO₂ and NH₃ gasses. A preliminary validation of the model is done using data available in the literature. The model was then applied to simulate batch aeration tests on two anaerobic digester supernatants from (i) a spent wine upflow anaerobic sludge bed digester and (ii) a sewage sludge anaerobic digester. In the batch tests pH, Ca, Mg, PO₄-P, free and saline ammonia (FSA) and H₂CO₃^∗ Alkalinity (from which inorganic carbon is calculated …