Investigations of Nitrogen Removal Pathways in a Biological Packed Bed Reactor Using Elementary Mass Balances

Abstract

Nitrogen (N) cycle involves a complex set of potential biochemical pathways with reactions catalyzed by different microorganisms. Elementary mass balances for COD, DO, NH 4 -N and alkalinity were conducted and stoichiometric relationships were investigated to explain possible pathways of the nitrogen removal mechanisms in a lab-scale submerged down flow biological packed bed (BPB) reactor. Four sets of experiments were performed by modifying the organic loading and C/N ratio in comparison with steady-state conditions. Approximately 90% of COD and NH 4 -N removal occurred in two upper sections occupying 1/5 of the reactor height. The elementary mass balances could not explain all the experimental results with respect to nitrogen removal and oxygen consumption by known mechanisms. The mass balance calculations, excluding the possibility of nitrification, were in general in accordance with the observations indicating no or minimal NO 3 -N production. The theoretical stoichiometric requirements for nitrification reaction were satisfied in 6 experiments and in another 8 experiments nitrification may have occurred, but stoichiometry was not satisfied. Using C/N ratio as the variable, only at C/N ratio = 10, the predictions confirmed the possibility of nitrification in the same 3 (out of 4) assays as observed in practice. The results of this study reveal that the nitrogen transformations occurring in the studied reactor are complex and cannot be explained by simple mechanisms of microbial assimilation and nitrification.

Effect of aeration on steady-state conditions in non- and partially aerated low-loaded biofilter

“…However, these values were measured at the ports and the nitrifiers benefited from the higher DO concentrations coming from the feeding solution (average value of 7.73 mg O 2 L -1 ). These results are worser than the ones obtained in another study (Albuquerque et al 2009a), using a similar not aerated biofilter fed with NH 4 -N concentrations up to 31.2 mg L -1 , where an overall average NH 4 -N removal of 28 % (74 % of which was observed in section TM-P2) was obtained. This higher removal rate is associated with the higher NLR used in that study, since it was also proved that the increase of the nitrogen loads influenced the respective removal rates (for influent concentrations from 5 to 31 mg NH 4 -N L -1 ).…”

“…A bench-scale cylindrical vertical biofilter was used for this study, made in acrylic glass with 7.0 cm 9 40.5 cm size [internal diameter 9 packing height (he)] and filled with natural porous volcanic rock material (puzzolane) with an effective diameter of 4 mm, specific surface area of 1,740 m 2 m -3 and void ratio of 0.52 [a similar device and the same bed media were used in the works of Albuquerque et al (2009a) and to study of nitrogen removal, in a downward flow configuration ( Fig. 1)].…”

“…The biofilter was therefore continuously fed with the synthetic wastewater, which was prepared with tap water by diluting the concentrated solutions in the following proportions: 2 mL L -1 of buffer solution, 0.2 mL L -1 of magnesium sulphate solution, 0.2 mL L -1 of calcium chloride solution, 0.2 mL L -1 of iron chloride solution, 0.2 mL L -1 of trace element solution, 2 mL L -1 of sodium acetate solution, and 0.5 mL L -1 of ammonia chloride solution. The concentrations of TOC and NH 4 -N were obtained by diluting the concentrated solutions of sodium acetate and ammonia chloride and were chosen in order to obtain influent values of 40 mg C L -1 , 10 mg NH 4 -N L -1 and a C/N ratio of 4 (characteristic ratio of secondary effluents, which was also used in previous studies (Albuquerque et al 2009a(Albuquerque et al , b, 2011. The feeding solution was kept in a storage tank (ISCO FTD 220, Italy) at a constant temperature of approximately 4°C and pumped to the biofilter through a peristaltic pump (ISMATEC MCP CA4, Switzerland).…”

Impact of aeration conditions on the removal of low concentrations of nitrogen in a tertiary partially aerated biological filter

“…The feeding solution used for the experiments included a mineral medium (buffer, magnesium sulphate, calcium chloride and iron chloride solutions) and sources of organic carbon (sodium acetate) and ammonia (ammonia chloride), as previously described in Albuquerque et al (2009a). The concentrated sodium acetate solution (113.…”

“…In a previous paper (Albuquerque et al, 2009a) the performance of a non-aerated lab-scale biofilter (filled with 2-4 mm of puzzolane particles) on the removal of organic matter (acetate), ammonia, nitrite and nitrate was analysed. In this study, the same reactor was converted to a partially aerated BAF and long-term operating data were analysed in terms of the removal of low ammonia nitrogen concentrations.…”