High-Rate Nitrification at Low pH in Suspended- and Attached-Biomass Reactors

Abstract

This article reports on high-rate nitrification at low pH in biofilm and suspended-biomass reactors by known chemolithotrophic bacteria. In the biofilm reactor, at low pH (4.3 ؎ 0.1) and low bulk ammonium concentrations (9.3 ؎ 3.3 mg ⅐ liter ؊1 ), a very high nitrification rate of 5.6 g of N oxidized ⅐ liter ؊1 ⅐ day ؊1 was achieved. The specific nitrification rate (0.55 g of N ⅐ g of biomass ؊1 ⅐ day ؊1 ) was similar to values reported for nitrifying reactors at optimal pH. In the suspended-biomass reactor, the average pH was significantly lower than that in the biofilm reactor (pH 3.8 ؎ 0.3), and values as low as pH 3.2 were found. In addition, measurements in the suspended-biomass reactor, using isotope-labeled ammonium ( 15 N), showed that in spite of the very low pH, biomass growth occurred with a yield of 0.1 g of biomass ⅐ g of N oxidized ؊1 . Fluorescence in situ hybridization using existing rRNA-targeted oligonucleotide probes showed that the nitrifying bacteria were from the monophyletic genus Nitrosomonas, suggesting that autotrophic nitrification at low pH is more widespread than previously thought. The results presented in this paper clearly show that autotrophic nitrifying bacteria have the ability to nitrify at a high rate at low pH and in the presence of only a negligible free ammonia concentration, suggesting the presence of an efficient ammonium uptake system and the means to cope with low pH.

Nitrification in a Biofilm at Low pH Values: Role of In Situ Microenvironments and Acid Tolerance

“…In contrast to bare chalk, we measured an even lower pH close to the chalk surface when the surface was covered with a biofilm relative to the bulk pH. Interestingly, the lowest local pH found in all experiments was around 3.9, which is close to what is reported to be the lower limit for nitrification (50) and reactor performance (60). Future studies of the phys- iological mechanisms of adaptation might help to find additional evidence and explanations for this empirical limit.…”

“…In biofilm-based systems, stable but low rates of nitrification could be achieved at pH 5 or below (2,17,33). More recently, a high rate of nitrification using chalk particles as the biofilm carrier was demonstrated with an average pH of 5 (24) or even as low as pH 3.8 using sintered glass particles as the carrier and in suspended systems (60).…”

“…A fluidized-bed reactor system with chalk as a carrier material was shown earlier to provide conditions leading to reliable and high nitrification rates at pHs as low as 3.8 (24,60) and, therefore, was chosen as a model system for appropriate sample material. Besides the fact that similar system performance is obtained when urea is provided as a substrate in this reactor, its use was excluded under the operation conditions applied here.…”

“…The maintenance of a low-pH steady state with high activity was also demonstrated in a system using nonbuffering carrier material, i.e., sintered glass beads. The system was supplied with bicarbonate in stoichiometric amounts to the nitrification rate (60). No difference in pH or oxygen microprofiles or in local conversion rates was found between biofilms grown on both materials.…”

Influence of Inorganic Nitrogen Management Regime on the Diversity of Nitrite-Oxidizing Bacteria in Agricultural Grassland Soils

“…The successful amplification of Nitrospira-like sequences from soil indicates a sufficient degree of specificity of the PCR assay, while amplification of non-Nitrospira sequences suggests inclusion of currently closely related uncharacterized groups. Nitrospiralike sequences have been documented in numerous clone surveys generated with general bacterial PCR primers (5,8,10,29,35,42,65,72). This may result from a bias of bacterial primers toward the phylum Nitrospira but also suggests the ubiquity and high relative abundance of these organisms in natural communities, indicating a role in other ecosystem processes, in addition to nitrite oxidation, which may not be sufficient to support such high population levels.…”