Concurrence of Anaerobic Ammonium Oxidation and Organotrophic Denitrification in Presence of p-Cresol
G. González-Blanco1 & F. J. Cervantes2 &
R. Beristain-Cardoso3 & J. Gómez1
Received: 23 January 2015 /Accepted: 1 June 2015 /
Published online: 12 June 2015 # Springer Science+Business Media New York 2015
Abstract This study was carried out to evaluate the capacity of anaerobic granular sludge for oxidizing ammonium and p-cresol with nitrate as terminal electron acceptor. Kinetics for the anaerobic oxidation of ammonium and p-cresol is described in this paper. The phenolic compound was very efficiently consumed, achieving 65 % of mineralization. Ammonium and nitrate were also consumed at 83 and 92 %, respectively, being the main product N2. Anaerobic ammonium oxidation was promoted owing to accumulation of nitrite, and it allowed the synergy of anaerobic ammonium oxidation and organotrophic denitrification for the simultaneous removal of ammonium, nitrate, and p-cresol. A carbonaceous intermediate partially identified was transiently accumulated, and it transitorily truncated the respiratory process of denitrification. These experimental results might be considered for defining strategies in order to remove nitrate, ammonium, and phenolic compounds from wastewaters.
Keywords Denitrification . Anaerobic ammonium oxidation . Nitrite . p-Cresol . Intermediates
Appl Biochem Biotechnol (2015) 176:2120–2130
Electronic supplementary material The online version of this article (doi:10.1007/s12010-015-1702-3) contains supplementary material, which is available to authorized users. * J. Gómez firstname.lastname@example.org 1 Departamento de Biotecnología, Universidad Autónoma Metropolitana-Iztapalapa, Iztapalapa, DF,
Mexico 2 División de Ciencias Ambientales, Instituto Potosino de Investigación Científica y Tecnológica (IPICyT), Camino a la Presa San José 2055, Col. Lomas 4ª. Sección, San Luis Potosí, SLP 78216,
Mexico 3 Departamento de Recursos de la Tierra, División de Ciencias Básicas e Ingeniería, Universidad
Autónoma Metropolitana-Lerma, Lerma de Villada, Edo, Mexico
Cresols and nitrogenous compounds (i.e., ammonia, nitrate) have been discharged into aquatic ecosystems, such as surface or groundwaters, through their use as biocides, fertilizers or generated by the petrochemical or chemical industry [1, 2]. For instance, in sour water from petrochemical industry is common to find p-cresol, ammonium, and nitrate . The US Environmental
Protection Agency has classified cresols as pollutant of group C (possible human carcinogen) . p-Cresol, even at very low concentration, has adverse effects on the central nervous system, cardiovascular system, lungs, and kidneys and can cause central nervous system depression .
On the other hand, ammonia is one of the main nitrogenous compounds that can lead to eutrophication, hypoxia, and loss of biodiversity and habitat in water bodies [6, 7].
Biological removal of these compounds is more environmentally friendly than physicochemical processes . Ammonium is usually oxidized (to nitrate) and then reduced to N2 by sequential nitrification-denitrification or directly through anaerobic oxidation (anammox). The first step in nitrification-denitrification is the aerobic oxidation of ammonium into nitrate. The second stage is denitrification, where nitrate is reduced to N2. Denitrifying microorganisms use nitrate or nitrite as the final electron acceptor [9, 10]. In this step, organic or inorganic compounds are needed as electron donors. Denitrifying sludge has the versatility to oxidize an extensive group of organic compounds, such as methanol, acetate, propionate, ethanol, phenol, and p-cresol. . Likewise, denitrifying consortia can use inorganic energy sources, such as sulfide, which is oxidized to sulfate with elemental sulfur as a possible intermediate product [12, 13]. N2 production from anaerobic ammonia oxidation via anammox is carried out only when nitrite is present, but not with nitrate [14–16]. The presence of organic matter has been seen as inhibitory to this autotrophic process [17, 18]. Therefore, wastewaters containing low levels of organic carbon and high nitrogen concentrations might be treated via anammox process. However, some studies have documented that the coupling between anammox and organotrophic denitrification can contribute to the simultaneous oxidation of ammonium and organic substrates, including phenolic compounds, linked to the reduction of nitrite/nitrate [19, 20]. For instance, Cervantes et al.  evaluated several ammonium loading rates (25–500 mg NH4 +/L day) in a denitrifying continuous UASB reactor using nitrate as electron acceptor. N2 production rates increased, whereas ammonium loading rates were increasing. The authors suggested that overproduction of N2 might have been associated to the coupling between anammox and organotrophic denitrification processes.
It has been observed that nitrite can be accumulated during denitrification when the electron donor is stoichiometrically insufficient, when nitrate reduction proceeds faster than nitrite reduction, or when the nitrite reductase enzyme is inhibited [22, 18]. Meza et al.  observed transient nitrite accumulation when p-cresol was added as reducing source during denitrification. In some cases, this accumulation might negatively affect the respiratory process. However, the promotion of nitrite accumulation might also be a good alternative to achieve anaerobic ammonium oxidation into molecular nitrogen, with the concomitant mineralization of phenolic compounds under denitrifying conditions. Nevertheless, a better understanding about the metabolism and kinetic behavior of the denitrifying sludge is still necessary to overcome this challenge. The aim of this work was to evaluate the metabolic capability of denitrifying sludge to achieve simultaneous removal of ammonium, nitrate, and p-cresol, with the overall goal of obtaining N2 and CO2 as the main products. This research might be crucial because industrial wastewaters are highly heterogeneous and several of them are polluted with these compounds.