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Effect of ammoniacal nitrogen on one-stage and two-stage anaerobic digestion of food waste
- Ariunbaatar, Javkhlan, Scotto Di Perta, Ester, Panico, Antonio, Frunzo, Luigi, Esposito, Giovanni, Lens, Piet N.L., Pirozzi, Francesco
- Waste management 2015 v.38 pp. 388-398
- alkalinity, ammonia, ammonium nitrogen, anaerobic digestion, biogas, biohydrogen, food waste, inhibitory concentration 50, inoculum, methanogens, pH, propionic acid, volatile fatty acids, waste management
- This research compares the operation of one-stage and two-stage anaerobic continuously stirred tank reactor (CSTR) systems fed semi-continuously with food waste. The main purpose was to investigate the effects of ammoniacal nitrogen on the anaerobic digestion process. The two-stage system gave more reliable operation compared to one-stage due to: (i) a better pH self-adjusting capacity; (ii) a higher resistance to organic loading shocks; and (iii) a higher conversion rate of organic substrate to biomethane. Also a small amount of biohydrogen was detected from the first stage of the two-stage reactor making this system attractive for biohythane production. As the digestate contains ammoniacal nitrogen, re-circulating it provided the necessary alkalinity in the systems, thus preventing an eventual failure by volatile fatty acids (VFA) accumulation. However, re-circulation also resulted in an ammonium accumulation, yielding a lower biomethane production. Based on the batch experimental results the 50% inhibitory concentration of total ammoniacal nitrogen on the methanogenic activities was calculated as 3.8g/L, corresponding to 146mg/L free ammonia for the inoculum used for this research. The two-stage system was affected by the inhibition more than the one-stage system, as it requires less alkalinity and the physically separated methanogens are more sensitive to inhibitory factors, such as ammonium and propionic acid.