Biological nitrogen removal with nitrification and denitrification via nitrite pathway

Presently, the wastewater treatment practices can be significantly improved through the introduction of new microbial treatment technologies. To meet increasingly stringent discharge standards, new applications and control strategies for the sustainable removal of ammonium from wastewater have to be implemented. Partial nitrification to nitrite was reported to be technically feasible and economically favorable, especially when wastewater with high ammonium concentrations or low C/N ratios is treated. For successful implementation of the technology, the critical point is how to maintain partial nitrification of ammonium to nitrite. Partial nitrification can be obtained by selectively inhibiting nitrite oxidizing bacteria through appropriate regulation of the system’s DO concentration, microbial SRT, pH, temperature, substrate concentration and load, operational and aeration pattern, and inhibitor. The review addressed the microbiology, its consequences for their application, the current status regarding application, and the future developments.     

Characteristics of bacteria showing high denitrification activity in saline wastewater

AIMS: Denitrification efficiency at 10% salinity was compared with that at 2% salinity. The characteristics of bacterial strains isolated from the denitrification system, where an improvement of denitrification efficiency was observed at a high salinity were investigated. METHODS AND RESULTS: Two continuous feeding denitrification systems for saline solutions of 2% and 10% salinity, were operated. Denitrification efficiency at 10% salinity was higher than that at 2% salinity. The bacterial strains were isolated using the trypticase soy agar (TSA) medium at 30 degrees C. The phylogenetic analysis of 16S rRNA gene sequences of isolates indicated that halophilic species were predominant at 10% salinity. CONCLUSIONS: The improvement of denitrification efficiency at a high salinity was demonstrated. The strains isolated from the denitrifying system with 10% salinity were halophilic bacteria, Halomonas sp. and Marinobacter sp., suggesting that these bacteria show a high denitrifying activity at 10% salinity. SIGNIFICANCE AND IMPACT OF THE STUDY: The long-term acclimated sludge used in this study resulted in high denitrification performance at a high salinity, indicating that the design of a high-performance denitrification system for saline wastewater will be possible.     

Characterization and in situ monitoring of atrazine-transforming bacteria

The possible application of the in situ hybridization method to detect soil microflora able to transform the herbicide atrazine was investigated. Digoxigenin-labeled probes were shown to provide sufficient resolution when used either for hybridization on colonies or for in situ detection of bacteria in soil.Translated from Mikrobiologiya, Vol. 73, No. 6, 2004, pp. 763–767.Original Russian Text Copyright © 2004 by Koneva.     

Inhibition of denitrification activity but not of mRNA induction in Paracoccus denitrificans by nitrite at a suboptimal pH

The influence of pH on the denitrification activity of a continuous culture of Paracoccus denitrificans was studied in relation to the presence of nitrite. After a transition from aerobic to anaerobic conditions at the suboptimal pH of 6.8, P. denitrificans was not able to build up a functional denitrification pathway. Nitrite accumulated in the medium as the predominant denitrification product. Although the nitrite reductase gene was induced properly, the enzyme could not be detected at sufficient amounts in the culture. These observations indicate that either translation was somehow inhibited, or once synthesized nitrite reductase was inactivated, possibly by the high concentrations of nitrous acid (HNO₂. Interestingly, when a P. denitrificans culture which was grown to steady-state under anaerobic conditions was then exposed to suboptimal pHs, cells exhibited a reduced overall denitrification activity, but neither nitrite nor any other denitrification intermediate accumulated.     

Stoichiometry and kinetics of microbial toluene degradation under denitrifying conditions

Batch experiments were carried out to investigate the stoichiometry and kinetics of microbial degradation of toluene under denitrifying conditions. The inoculum originated from a mixture of sludges from sewage treatment plants with alternating nitrification and denitrification. The culture was able to degrade toluene under anaerobic conditions in the presence of nitrate, nitrite, nitric oxide, or nitrous oxide. No degradation occurred in the absence of Noxides. The culture was also able to use oxygen, but ferric iron could not be used as an electron acceptor. In experiments with¹⁴C-labeled toluene, 34%±8% of the carbon was incorporated into the biomass, while 53%±10% was recovered as¹⁴CO₂, and 6%±2% remained in the medium as nonvolatile water soluble products. The average consumption of nitrate in experiments, where all the reduced nitrate was recovered as nitrite, was 1.3±0.2 mg of nitrate-N per mg of toluene. This nitrate reduction accounted for 70% of the electrons donated during the oxidation of toluene. When nitrate was reduced to nitrogen gas, the consumption was 0.7±0.2 mg per mg of toluene, accounting for 97% of the donated electrons. Since the ammonia concentration decreased during degradation, dissimilatory reduction of nitrate to ammonia was not the reductive process. The degradation of toluene was modelled by classical Monod kinetics. The maximum specific rate of degradation, k, was estimated to be 0.71 mg toluene per mg of protein per hour, and the Monod saturation constant, K _s , to be 0.2 mg toluene/l. The maximum specific growth rate, _max , was estimated to be 0.1 per hour, and the yield coefficient, Y, was 0.14 mg protein per mg toluene.Abbreviations NVWP Non Volatile Water-soluble Products     

化感物质对枯草芽孢杆菌(Bacillus subtilis)在厌氧条件下的生长及反硝化作用的影响

研究由秸秆腐解产生的化感物质 :阿魏酸 ( t-FA)、对羟基苯甲酸 ( p-HA)和苯甲酸 ( BA)在不同浓度下对厌氧培养的枯草芽孢杆菌 ( Bacillussubtilis)的生长及其反硝化活性的影响。结果表明 ,3种浓度的阿魏酸 ( 5.1 5、2 .58、0 .2 6mmol/L)均表现出对枯草芽孢杆菌的生长有抑制作用。对羟基苯甲酸 ( 0 .3 6、3 .62、7.2 4 mmol/L )对生长影响不明显。 8.1 9mmol/L和 4 .0 9mmol/L的苯甲酸有一定的刺激作用 ,而 0 .4 1 mmol/L的苯甲酸与对照无差别。实验表明枯草芽孢秆菌不仅能转化 NO- 3生成 NO- 2 ,而且还能转化 NO- 2 生成 N2 O。 3种化感物质对 NO- 3的转化均表现抑制作用 ,其抑制作用强弱依次为阿魏酸 >对羟基苯甲酸 >苯甲酸。高浓度的抑制作用强于低浓度。阿魏酸在 5.1 5mmol/L和 2 .58mmol/L浓度下 ,其抑制作用的差异显著性分别为 P<0 .0 1 ,P<0 .0 5。 NO- 2 的生成与 NO- 3的减少相互有关联 ,第 3天测定时 ,各处理中NO- 3急剧减少 ,而 NO- 2 急剧增加。在阿魏酸、苯甲酸处理中的 NO- 2 积累高峰在第 3天、第 4天 ,然后下降。而在对羟基苯甲酸的处理中 NO- 2 的积累一直上升 ,在第 6天的观察中仍未出现下降趋势。 3种化感物质均能抑制 N2 O的生成 ,至于在田间的抑制效果尚需进一步试验     

The denitrification potential and density of denitrifying bacteria in the bottom sediments of Matupi Harbor (Papua New Guinea)

The denitrification potential and density of denitrifying bacteria were determined in suboxidized sediments of Matupi Harbor (Papua New Guinea). The sediments were characterized by low denitrification potentials, not exceeding 0.8 nM/(g h). The maximum density of denitrifying bacteria was recorded in the upper sediment horizons and was 10⁴ cells/g of wet ground.     

Grass species and soil type effects on microbial biomass and activity

We evaluated plant versus soil type controls on microbial biomass and activity by comparing microbial biomass C, soil respiration, denitrification potential, potential net N mineralization and nitrification in different soils supporting four grass species, and by growing a group of 10 different grass species on the same soil, in two experiments respectively. In the first experiment, none of the microbial variables showed significant variation with grass species while all variables showed significant variation with soil type, likely due to variation in soil texture. In the second experiment, there were few significant differences in microbial biomass C among the 10 grasses but there were significant relationships between variation in microbial biomass C and potential net N mineralization (negative), soil respiration (positive) and denitrification (positive). There was no relationship between microbial biomass C and either plant yield or plant N concentration. The results suggest that 1) soil type is a more important controller of microbial biomass and activity than grass species, 2) that different grass species can create significant, but small and infrequent, differences in microbial biomass and activity in soil, and 3) that plant-induced variation in microbial biomass and activity is caused by variation in labile C input to soil.     

Estimating denitrification rates in estuarine sediments: A comparison of stoichiometric and acetylene based methods

We compared denitrification rates obtained using an adaptation of the acetylene block technique to rates estimated from benthic flux nutrient stoichiometry in the subtidal sediments of Tomales Bay, California (USA). By amending whole cores with acetylene and saturating nitrate concentrations, we obtained potential denitrification rates, which ranged between 4 and 30 mmol N m^–2 d^–1. We determined the apparent Michaelis constant (K_app) and the maximum potential rate (V_mp) of the denitrifying community and used these constants in a rectangular hyperbola to estimatein situ denitrification rates. Both the K_app and V_mp of the denitrifying community exhibited significant variation over both depth in the sediment column and time of sampling.Estimates ofin situ denitrification obtained using our kinetic-fix adaptation of the acetylene block ranged between 1.8 (March) and 9 (Sept.) mmol N m^–1 d^–1. Denitrification rates obtained using benthic flux stoichiometry ranged between 0.7 and 4.1 mmol N m^–2 d^–1. Average denitrification rates obtained using the kinetic-fix acetylene block approach exceeded those obtained from net benthic flux stoichiometry; however, these differences were not significant. We conclude that our kinetic-fix adaptation of the acetylene block technique provides realistic estimates of denitrification in sediments, even when pore water nitrate concentrations are low and nitrification and denitrification are closely coupled.