Counteracting ammonia inhibition in anaerobic digestion by removal with a hollow fiber membrane contactor

• Published in: Water research (Oxford) 2012-10, Vol.46 (15), p.4861-4869
• Main Authors: Lauterböck, B., Ortner, M., Haider, R., Fuchs, W.
• Format: Article
• Language: English
• Subjects: adsorbents; ammonia; Ammonia - isolation & purification; Ammonia inhibition; Ammonia removal; ammonium nitrogen; anaerobic digesters; anaerobic digestion; Anaerobiosis; Applied sciences; Exact sciences and technology; fatty acid composition; Membrane contactor; Membranes, Artificial; Particle rich substrate; Pollution; slaughterhouse wastes; Submerged hollow fibers; sulfuric acid; volatile fatty acids; Water treatment and pollution
• ISSN: 0043-1354; 1879-2448
• DOI: 10.1016/j.watres.2012.05.022

The aim of the current study was to investigate the feasibility of membrane contactors for continuous ammonia (NH3–N) removal in an anaerobic digestion process and to counteract ammonia inhibition. Two laboratory anaerobic digesters were fed slaughterhouse wastes with ammonium (NH4+) concentrations ranging from 6 to 7.4 g/L. One reactor was used as reference reactor without any ammonia removal. In the second reactor, a hollow fiber membrane contactor module was used for continuous ammonia removal. The hollow fiber membranes were directly submerged into the digestate of the anaerobic reactor. Sulfuric acid was circulated in the lumen as an adsorbent solution. Using this set up, the NH4+–N concentration in the membrane reactor was significantly reduced. Moreover the extraction of ammonia lowered the pH by 0.2 units. In combination that led to a lowering of the free NH3–N concentration by about 70%. Ammonia inhibition in the reference reactor was observed when the concentration exceeded 6 g/L NH4+–N or 1–1.2 g/L NH3–N. In contrast, in the membrane reactor the volatile fatty acid concentration, an indicator for process stability, was much lower and a higher gas yield and better degradation was observed. The chosen approach offers an appealing technology to remove ammonia directly from media having high concentrations of solids and it can help to improve process efficiency in anaerobic digestion of ammonia rich substrates. ► Submerged membrane contactor for N removal in ammonia and particle rich substrates. ► Method limits ammonia inhibition and leads to better reactor performance. ► Nitrogen recovery in the form of an ammonium sulfate solution.