NAS: Nitrogen Recovery From Concentrated Nitrogen Stream. Like Reject Water And Digestate
Delgorge, F.H.1, Menkveld, H.W.H.1, Shengyu, M.O.2 and Scheffe, B.3, 1Nijhuis Water Technology, The Netherlands, 2Wageningen University, The Netherlands, 3H20K Systems Ltd, UK
(free)
Abstract Anaerobic digestion is sensitive to high NH3 concentrations, which are inhibiting and at certain levels even toxic. Poisoning is depending on concentration and pH due to the NH3 – NH4 – equilibrium. Bacteria in the thermophilic range (50 – 60 ⁰C) are even more sensitive than the bacteria in the mesophilic (30 – 40 ⁰C) range. Generally the level of N Kjehldahl is toxic at a level of 7,000 mg/l at a pH of 7.2 for mesophilic bacteria. For thermophilic bacteria the level is 4,500 mg/l at pH of 7.2.
During anaerobic digestion of manure, COD and BOD are removed by 70 – 80 %. Nitrogen is hardly removed and the only removal is due to cell synthesis, therefore the effluent of the anaerobic treatment often features a too high COD/N ratio making it difficult to treat by aerobic biological treatment and reach the desired consent on nitrogen.
The Nijhuis Ammonia Recovery unit or NAR, has been developed to remove NH3. This technique is based on stripping of NH3 from liquid. The carrier gas is washed with sulfuric acid in order to form ammonium sulfate, which is accepted as a nutrient and can be used for agricultural purposes. Because NH3 separates easier at high temperature and pH the process is foreseen to run at approximate 80 ⁰C and pH 8.5.
Keywords NAR, Nitrogen recovery, removal, digestate treatment, nutrient production.
