The dataset contains the chemical compositional changes occurred in anaerobic digestate, with and without biomass ash, simulating storage conditions during 128 days. Additionally, Sulphuric Acid (H2SO4) was added to these materials to test the effectivity on preventing nitrogen loss via acidification. Experiments were carried out in the laboratory during 2016, being measured via a combination of internal and external laboratories. The dataset provides data on chemical changes, namely: dry solids, pH, Kjeldahl nitrogen and total sulphur.