Inhibition of mesophilic solid-substrate anaerobic digestion by ammonia nitrogen |
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Authors: | H M Poggi-Varaldo R Rodríguez-Vázquez G Fernández-Villagómez F Esparza-García |
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Institution: | (1) P3 Consulting Engineers, P.O. Box 75–202, Mexico DF, 07300, Mexico, MX;(2) CINVESTAV, Department of Biotechnology and Bioengineering, Mexico City, Mexico, MX;(3) National University of Mexico (UNAM) and Centre for Disaster and Hazards Prevention (CENAPRED), Mexico City, Mexico, MX |
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Abstract: | This work focused on determining the effects of ammonia-nitrogen supplementation on the mesophilic solid-substrate anaerobic
digestion of municipal wastes and waste activated sludge (biosolids). Bench-scale, semi-continuous, mesophilic reactors were
operated with a 21-day mass-retention time and dosed with NH4Cl, such that the corresponding chemical O2 demand (COD)/N ratios in their feeds were 90, 80, 65 and 50 (reactors R1 or control, R2, R3 and R4 respectively). Reactor
performance was evaluated in terms of the efficiency of volatile solid removal (efficiency for short), biogas productivity,
methane content in the biogas, pH and volatile organic acid contents, among other monitoring and analytical parameters. The
feedstock was a mixture of urban wastes with biosolids. It was found that the process performance deteriorated at increasing
dosages of ammonia N, the process practically ceasing at COD/N = 50 (R4). Inhibition was characterized by efficiency and biogas
productivity decreases and a more sudden drop of methane content in biogas and pH. A significant rise of propionic, butyric
and valeric acid was found in reactors receiving the highest doses of ammonia N (R3 and R4). This suggested that inhibition
of the syntrophic bacteria present in the anaerobic consortia also occurred. Luong and Pearson inhibition models were fitted
to the data. Both models represented very well the acute effects of N supplementation on solid-substrate anaerobic digestion.
However, the Luong model could also represent the process ceasing at a critical ammonia N concentration of 2800 mg/kg mixed
solids.
Received: 12 April 1996 / Received revision: 23 July 1996 / Accepted: 5 August 1996 |
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