Modeling the partial nitrification in sequencing batch reactor for biomass adapted to high ammonia concentrations

Partial nitrification has proven to be an economic way for treatment of industrial N-rich effluent, reducing oxygen and external COD requirements during nitrification/denitrification process. One of the key issues of this system is the intermediate nitrite accumulation stability. This work presents a control strategy and a modeling tool for maintaining nitrite build-up. Partial nitrification process has been carried out in a sequencing batch reactor at 30 degrees C, maintaining strong changing ammonia concentration in the reactor (sequencing feed). Stable nitrite accumulation has been obtained with the help of an on-line oxygen uptake rate (OUR)-based control system, with removal rate of 2 kg NH4 (+)-N x m(-3)/day and 90%-95% of conversion of ammonium into nitrite. A mathematical model, identified through the occurring biological reactions, is proposed to optimize the process (preventing nitrate production). Most of the kinetic parameters have been estimated from specific respirometric tests on biomass and validated on pilot-scale experiments of one-cycle duration. Comparison of dynamic data at different pH confirms that NH3 and NO2- should be considered as the true substrate of nitritation and nitratation, respectively. The proposed model represents major features: the inhibition of ammonia-oxidizing bacteria by its substrate (NH3) and product (HNO2), the inhibition of nitrite-oxidizing bacteria by free ammonia (NH3), the INFluence of pH. It appears that the model correctly describes the short-term dynamics of nitrogenous compounds in SBR, when both ammonia oxidizers and nitrite oxidizers are present and active in the reactor. The model proposed represents a useful tool for process design and optimization.     

Nitrification inhibition in landfill leachate treatment and impact of activated carbon addition

Leachate from a municipal landfill was combined with domestic wastewater and treated in batch, semi-continuously fed-batch (SCFB) and continuous-flow (CF) activated sludge systems with and without powdered activated carbon (PAC) addition. In the absence of PAC, nitrification was severely inhibited and nitrite accumulated to about 85–100% of the total NO_x-N. Addition of PAC to activated sludge reactors enhanced nitrification. In continuous-flow operation, nitrite accumulation could be completely prevented by PAC addition.     

水体中亚硝酸盐积累的生物过程及影响因素研究进展

亚硝酸盐是氮循环过程的中间产物,其积累超过一定量则会抑制微生物的生长与代谢,也会给人与水生生物带来健康风险。而在高氮污水生物脱氮工艺中,持续维持亚硝酸盐的积累能实现短程硝化过程,降低生物脱氮的能耗进而降低运营成本。本文综述了在水环境中亚硝酸盐积累的生物过程与积累原因,并对影响亚硝酸盐积累的因素进行了总结,旨在为提高污水处理过程中氮的去除效率,降低运营成本,减少排放污水及自然水体中亚硝态氮含量提供参考。     

Nitrification-denitrification via nitrite accumulation for nitrogen removal from wastewaters

The biological nitrification-denitrification process is used extensively for removal of ammonia nitrogen from wastewaters. Saves in aeration, organic matter (for denitrification) and surplus sludge are achievable if nitrite accumulation is possible in the nitrification step. In this paper, operational parameters were studied for each process for maximum nitrite accumulation in the nitrification step and nitrite adaptation in the denitrification step. Nitrite accumulation during nitrification can be controlled by the dissolved oxygen (DO) concentration, presenting a maximum of 65% at around 0.7 mg DO/L. Denitrification can be adapted to nitrite and the process is stable if nitrite in the reactor is keep low. The performance of a continuous stirred tank reactor (CSTR) and an up flow sludge blanket reactor (USB) were compared. Once the operational parameters were established, a CSTR for nitrification and an USB reactor for denitrification were operated in series for 25 days. The process was stable and a steady state was maintained for 20 days, and 93.5% of overall nitrogen removal was achieved in the nitrification-denitrification via the nitrite process.     

Effective and robust partial nitrification to nitrite by real-time aeration duration control in an SBR treating domestic wastewater

Achieving sustainable partial nitrification to nitrite has been proven difficult in treating low strength nitrogenous wastewater. Real-time aeration duration control was used to achieve efficient partial nitrification to nitrite in a sequencing batch reactor (SBR) to treat low strength domestic wastewater. Above 90% nitrite accumulation ratio was maintained for long-term operation at normal condition, or even lower water temperature in winter. Partial nitrification established by controlling aeration duration showed good performance and robustness even though encountering long-term extended aeration and starvation period. Process control enhanced the successful accumulation of ammonia oxidizing bacteria (AOB) and washout of nitrite oxidizing bacteria (NOB). Scanning electron microscope observations indicated that the microbial morphology showed a shift towards small rod-shaped clusters. Fluorescence in situ hybridization (FISH) results demonstrated AOB were the dominant nitrifying bacteria, up to 8.3 ± 1.1% of the total bacteria; on the contrary, the density of NOB decreased to be negligible after 135 days operation since adopting process control.     

Denitrification in lucerne nodules is not involved in nitrite detoxification

Dissimilatory reduction of ionic nitrogen oxides to gaseous forms such as nitrous oxide or nitrogen can be carried out by free living or symbiotic forms of some strains of Rhizobium meliloti. In this paper we investigate whether bacteroid denitrification plays a role in the alleviation of the inhibitory effects of nitrate on nitrogen fixation both in bacteroid incubations as in whole nodules. The presence of a constitutive nitrate reductase (NR) activity in isolated bacteroids caused nitrite accumulation in the incubation medium, and acetylene reduction activity in these bacteroids was progressively inhibited, since nitrite reductase (NiR) activity was unable to reduce all the nitrite produced by NR and denitrification occurred slowly. Even nodules infiltrated with nitrate and nitrite failed to increase gaseous forms of nitrogen substantially, indicating that nitrite availability was not limiting denitrification by bacteroids. In spite of the low rates of bacteroidal denitrification, the effect of nodule denitrification on the inhibition of nitrogen fixation by nitrate in whole plants was tested. For that purpose, lucerne plants (Medicago sativa L. cv. Aragon) were inoculated with two Rhizobium meliloti strains: 102-F-65 (non denitrifying) and 102-F-51 (a highly denitrifying strain). After a seven days nitrate treatment, both strains showed the same pattern of inhibition, and it occurred before any nitrate or nitrite accumulation within the nodules could be detected. This observation, together with the lack of alleviation of the ARA inhibition in the denitrifying strain, and the limited activity of dissimilatory nitrogen reduction present in these bacteroids, indicate a role other than nitrite detoxification for denitrification in nodules under natural conditions.     

Nitrite effect on ammonium and nitrite oxidizing processes in a nitrifying sludge

Nitrite accumulation can be undesirable in nitrifying reactors used for the biological elimination of nitrogen from wastewaters because the ammonium oxidation process was seen to be inhibited. There is a need to better understand the effects of nitrite on both ammonium and nitrite oxidizing processes. In this paper, the effect of nitrite on the nitrifying activity of a sludge produced in steady-state nitrification was evaluated in batch cultures. At 25 mg N/l of added nitrite, nitrification was successfully carried out. Addition of higher nitrite concentrations to nitrifying cultures (100 and 200 mg N/l) provoked inhibitory effects on the nitrification respiratory process. Nitrite at 100 and 200 mg N/l induced a significant decrease in the values for nitrate yield (−20% and −34%, respectively) and specific rate of nitrate formation (−26% and −67%, respectively), while the ammonium consumption efficiency kept high and the specific rate of ammonium oxidation did not significantly change. This showed that the nitrite oxidizing process was more sensitive to the presence of nitrite than the ammonium oxidizing process. These results showed that as a consequence of nitrite accumulation in nitrification systems, the activity of the nitrite oxidizing bacteria could be more inhibited than that of the ammonium oxidizing bacteria, provoking a higher accumulation of nitrite in the medium.     

Effects of temperature on simultaneous nitrification and denitrification via nitrite in a sequencing batch biofilm reactor

A laboratory scale experiment was described in this paper to enhance biological nitrogen removal by simultaneous nitrification and denitrification (SND) via nitrite with a sequencing batch biofilm reactor (SBBR). Under conditions of total nitrogen (TN) about 30 mg/L and pH ranged 7.15–7.62, synthetic wastewater was cyclically operated within the reactor for 110 days. Optimal operation conditions were established to obtain consistently high TN removal rate and nitrite accumulation ratio, which included an optimal temperature of 31 °C and an aeration time of 5 h under the air flow of 50 L/h. Stable nitrite accumulation could be realized under different temperatures and the nitrite accumulation ratio increased with an increase of temperature from 15 to 35 °C. The highest TN removal rate (91.9%) was at 31 °C with DO ranged 3–4 mg/L. Process control could be achieved by observing changes in DO and pH to judge the end-point of oxidation of ammonia and SND.     

New pathways for ammonia conversion in soil and aquatic systems

Ammonia conversion processes are essential for most soil and aquatic systems. Under natural conditions, the many possible reactions are difficult to analyze. For example, nitrification and denitrification have long been regarded as separate phenomena performed by different groups of bacteria in segregated areas of soils, sediments or aquatic systems sequentially in time. It has now been established that strict segregation in place and time of the two processes is not necessary and that both denitrifiers and nitrifiers have versatile metabolisms. However, the rates described for aerobic denitrifiers are very low compared to the rates observed under anoxic conditions. Also the rates of nitrifier denitrification are quite low, indicating that these conversions may not play an important role under natural conditions. In addition, these processes often result in the emission of quite large amounts of undesirable products, NO and N₂O. Heterotrophic nitrification might be of relevance for systems, that contain a high carbon to nitrogen ratio. Recently, a novel process (Anammox) has been discovered in which ammonium serves as the electron donor for denitrification of nitrite into dinitrogen gas. ¹⁵N labeling studies showed that hydrazine and hydroxylamine were important intermediates in this process. Enrichment cultures on ammonium, nitrite and bicarbonate resulted in the dominance of one morphotypical microorganism. The growth rate of the cultures is extremely low (doubling time 11 days), but the affinity for ammonium and nitrite and the conversion rates (9.2 10^–4 mol kg^–1 s^–1) are quite high. Some of the reported high nitrogen losses in soil and aquatic systems might be attributed to anaerobic ammonium oxidation. In addition, this conversion offers new opportunities for nitrogen removal, when it is combined with recently developed processes for partial nitrification.     

盐分对生物脱氮工艺中硝化反应的影响与机理

高盐废水来源广泛,在利用生物脱氮法处理高盐含氮废水时,盐分会对生物脱氮产生抑制作用.硝化反应是生物脱氮工艺中的关键过程,研究盐分对硝化反应的影响机理具有重要意义.本文概述了盐分对废水生物脱氮过程中硝化反应影响的研究进展,总结了盐胁迫对好氧氨氧化过程、亚硝酸盐氧化过程中硝化效率和反应特性的影响规律,并分析了盐分对硝化微生物细胞形态、生物絮体结构和胞外聚合物特性变化以及菌群结构的影响,系统阐述了盐胁迫下的硝化反应机理,为高盐分高铵氮废水生物脱氮工艺设计提供理论指导.
     

Nitrite reduction: a ubiquitous function from a pre‐aerobic past

In eukaryotes, small amounts of nitrite confer cytoprotection against ischemia/reperfusion‐related tissue damage in vivo, possibly via reduction to nitric oxide (NO) and inhibition of mitochondrial function. Several hemeproteins are involved in this protective mechanism, starting with deoxyhemoglobin, which is capable of reducing nitrite. In facultative aerobic bacteria, such as Pseudomonas aeruginosa, nitrite is reduced to NO by specialized heme‐containing enzymes called cd₁ nitrite reductases. The details of their catalytic mechanism are summarized below, together with a hypothesis on the biological role of the unusual d₁‐heme, which, in the reduced state, shows unique properties (very high affinity for nitrite and exceptionally fast dissociation of NO). Our results support the idea that the nitrite‐based reactions of contemporary eukaryotes are a vestige of earlier bacterial biochemical pathways. The evidence that nitrite reductase activities of enzymes with different cellular roles and biochemical features still exist today highlights the importance of nitrite in cellular homeostasis.     

Nitrite inhibition of denitrification by Pseudomonas fluorescens

Using a pure culture of Pseudomonas fluorescens as a model system nitrite inhibition of denitrification was studies. A mineral media with acetate and nitrate as sole electron donor and acceptor, respectively, was used. Results obtained in continuous stirred-tank reactors (CSTR) operated at pH values between 6.6 and 7.8 showed that growth inhibition depended only on the nitrite undissociated fraction concentration (nitrous acid). A mathematical model to describe this dependence is put forward. The maximum nitrous acid concentration compatible with cell growth and denitrification activity was found to be 66 mug N/L. Denitrification activity was partially associated with growth, as described by the Luedeking-Piret equation. However, when the freshly inoculated reactor was operated discontinuosly, nitrite accumulation caused growth uncoupling from denitrification activity. The authors suggest that these results can be interpreted considering that (a) nitrous acid acts as a proton uncoupler; and (b) cultures continuoulsy exposed to nitrous acid prevent the uncoupling effect but not the growth inhibition. Examination of the growth dependence on nitrite concentration at pH 7.0 showed that adapted cultures (grown on CSTR) are less sensitive to nitrous acid inhibition than the ones cultivated in batch. (c) 1995 John Wiley & Sons, Inc.     

Induced cooperation between marine nitrifiers and anaerobic ammonium-oxidizing bacteria by incremental exposure to oxygen

In oxygen-limited marine ecosystems cooperation between marine nitrifiers and anaerobic ammonium-oxidizing (anammox) bacteria is of importance to nitrogen cycling. Strong evidence for cooperation between anammox bacteria and nitrifiers has been provided by environmental studies but little is known about the development of such communities, the effects of environmental parameters and the physiological traits of their constituents. In this study, a marine laboratory model system was developed. Cooperation between marine nitrifiers and anammox bacteria was induced by incremental exposure of a marine anammox community dominated by Scalindua species to oxygen in a bioreactor set-up under high ammonium (40 mM influent) conditions. Changes in the activities of the relevant functional groups (anammox bacteria, aerobic ammonia oxidizers and nitrite oxidizers) were monitored by batch tests. Changes in community composition were followed by Fluorescence in situ Hybridization (FISH) and by amplification and sequencing of 16S rRNA and amoA genes. A co-culture of Scalindua sp., an aerobic ammonia-oxidizing Nitrosomonas-like species, and an aerobic (most likely Nitrospira sp.) nitrite oxidizer was obtained. Aerobic ammonia oxidizers became active immediately upon exposure to oxygen and their numbers increased 60-fold. Crenarchaea closely related to the ammonia-oxidizer Candidatus 'Nitrosopumilus maritimus' were detected in very low numbers and their contribution to nitrification was assumed negligible. Activity of anammox bacteria was not inhibited by the increased oxygen availability. The developed marine model system proved an effective tool to study the interactions between marine anammox bacteria and nitrifiers and their responses to changes in environmentally relevant conditions.     

亚硝酸盐影响Lactobacillus brevis 4903发酵的研究

通过研究可知,亚硝酸盐对Lactobacillusbrevis4903发酵有抑制作用,环境中亚硝酸盐一旦分解掉,这种抑制作用就会被解除。分析其原因:①亚硝酸盐抑制了乳酸菌生长,从而抑制了乳酸发酵;②在发酵初期可能因亚硝酸盐还原酶的作用,使亚硝酸盐酶解生成NH3,NH3中和了乳酸菌生成的酸(H ),从而使环境pH值的下降和酸的积累变得缓慢。     

Nitrite-oxidizing bacteria guild ecology associated with nitrification failure in a continuous-flow reactor

Nitrification is an important process for nitrogen removal in many wastewater treatment plants, which requires the mutualistic oxidation of ammonia to nitrate by ammonia-oxidizing bacteria (AOB) and nitrite-oxidizing bacteria (NOB). However, this process can be quite unpredictable because both guilds are conditionally sensitive to small changes in operating conditions. Here, dynamics are examined within the NOB guild in two parallel chemostats operated at low and high dilution rates (0.10 and 0.83 day(-1), respectively) during periods of varying nitrification performance. NOB and AOB guild abundances and nitrogen-oxidation efficiency were relatively constant over time in the 0.10 day(-1) reactor; however, the 0.83 day(-1) reactor had two major disturbance episodes that caused destabilization of the NOB guild, which ultimately led to nitrification failure. The first episode caused the extinction of Nitrospira spp. from the system, resulting in chronic incomplete ammonia oxidation and nitrite accumulation. The second episode caused complete loss of nitrification activity, likely resulting from metal toxicity and the previous extinction of Nitrospira spp. from the system. These results exemplify the types of changes that can occur within the NOB guild that result in process impairment or failure, and provide one possible explanation for why nitrification is often unstable at higher dilution rates.     

Development and application of a PCR-denaturing gradient gel electrophoresis tool to study the diversity of Nitrobacter-like nxrA sequences in soil

A new PCR-denaturing gel gradient electrophoresis (DGGE) tool based on the functional gene nxrA encoding the catalytic subunit of the nitrite oxidoreductase in nitrite-oxidizing bacteria (NOB) has been developed. The first aim was to determine if the primers could target representatives of NOB genera: Nitrococcus and Nitrospira. The primers successfully amplified nxrA gene sequences from Nitrococcus mobilis, but not from Nitrospira marina. The second aim was to develop a PCR-DGGE tool to characterize NOB community structure on the basis of Nitrobacter-like partial nrxA gene sequences (Nb-nxrA). We tested (1) the ability of this tool to discriminate between Nitrobacter strains, and (2) its ability to reveal changes in the community structure of NOB harbouring Nb-nrxA sequences induced by light grazing or intensive grazing in grassland soils. The DGGE profiles clearly differed between the four Nitrobacter strains tested. Differences in the structure of NOB community were revealed between grazing regimes. Phylogenetic analysis of the sequences corresponding to different DGGE bands showed that Nb-nxrA sequences did not group in management-specific clusters. Most of the nxrA sequences obtained from soils differed from nxrA sequences of NOB strains. Along with existing tools for characterizing the community structure of nitrifiers, this new approach is a significant step forward to performing comprehensive studies on nitrification.     

Improved nitrogen removal by application of new nitrogen-cycle bacteria

In order to meet increasingly stringentEuropean discharge standards, new applicationsand control strategies for the sustainableremoval of ammonia from wastewater have to beimplemented. In this paper we discuss anitrogen removal system based on the processesof partial nitrification and anoxic ammoniaoxidation (anammox). The anammox process offersgreat opportunities to remove ammonia in fullyautotrophic systems with biomass retention. Noorganic carbon is needed in such nitrogenremoval system, since ammonia is used aselectron donor for nitrite reduction. Thenitrite can be produced from ammonia inoxygen-limited biofilm systems or in continuousprocesses without biomass retention. Forsuccessful implementation of the combinedprocesses, accurate biosensors for measuringammonia and nitrite concentrations, insight inthe complex microbial communities involved, andnew control strategies have to be developed andevaluated.     

Modeling kinetics of ammonium oxidation and nitrite oxidation under simultaneous inhibition by free ammonia and free nitrous acid

Inhibition of ammonium oxidation and nitrite oxidation by free ammonia (FA) and free nitrous acid (FNA) was studied using three different sludges. An uncompetitive inhibition model fit the experimental data well when the reactions were under FA inhibition, whereas a noncompetitive model fit well under FNA inhibition. The estimates of the inhibition constant (K_I) of nitrite oxidation were 46 μM for FA and 1.7–6.8 μM for FNA, each of which was significantly smaller than that of ammonium oxidation, which were 290–1600 μM for FA and 12 μM for FNA. The much smaller values of K_I for nitrite oxidation reflected the susceptibility of that reaction to inhibition by FA and FNA, which could lead to accumulation of nitrite during nitrification. A kinetic model for simultaneous inhibition by FA and FNA was derived. The model predicted that nitrite oxidation should be affected more seriously than ammonium oxidation by the simultaneous inhibition, which would accelerate the accumulation of nitrite in a strong nitrogenous wastewater treatment. It also indicated that a complete removal of ammonia could be achieved with high accumulation of nitrite in a sequencing batch reactor, which is impossible in a continuous-flow reactor.     

Activity of nitrifying populations in grassland soil polluted by polychlorinated biphenyls (PCBs)

The activity of nitrification was studied in the period of 1992 – 1994 in two grassland plots from the surroundings of a municipal waste incinerator. The soil parameters were fully comparable in both plots and the soils differed in the level of polychlorinated biphenyls (PCBs). The concentration of PCBs found in Klajdovka-control plot (KL): 4.4 ng g_{dry soil} ^–1 can be regarded as a background value, while the polluted plot, Bílá Hora (BH), contained increased amount of PCBs: 14.0 ng g_{dry soil} ^–1.The following parameters of nitrifying activity were determined: field concentrations of N_inorg species, mineralization potentials, nitrifying activity during long-term laboratory incubations, and the potential activity of both ammonium and nitrite oxidizers in short-term incubations in soil slurries. Simultaneous application of all these methods appeared to be very suitable for reliable assessment of nitrifying activity in the field.In the case of the polluted plot, the abnormal accumulation of nitrite was observed both in the field (e.g. in September 1992: BH-656.8 ng NO _inf2 ^– -N g_{dry soil} ^–1; KL-208.2 ng NO _inf2 ^– -N g_{dry soil} ^–1) and in the laboratory incubations. Furthermore, the capability of the polluted plot to nitrify higher amount of ammonium nitrogen appeared to be significantly reduced due to detrimental changes in the activity of nitrite-oxidizing community. In contrast to the nitrification, the mineralization potential did not differ between the plots throughout the sampling period.     

Nitrite-catalase interaction as an important element of nitrite toxicity

It was established that nitrite in the presence of chloride, bromide, and thiocyanate decreases the rate of hydrogen peroxide decomposition by catalase. The decrease was recorded by the permanganatometric method and by a method of dynamic calorimetry. Nitrite was not destroyed in the course of the reaction and the total value of heat produced in the process was not changed by its presence. These facts suggest that nitrite induces inhibition of catalase with no change in the essence of the enzymatic process. Even micromolar nitrite concentrations induced a considerable decrease in catalase activity. However, in the absence of chloride, bromide, and thiocyanate inhibition was not observed. In contrast, fluoride protected catalase from nitrite inhibition in the presence of the above-mentioned halides and pseudohalide. As hydrogen peroxide is a necessary factor for triggering a number of important toxic effects of nitrite, the latter increases its toxicity by inhibiting catalase. This was shown by the example of nitrite-induced hemoglobin oxidation. The naturally existing gradient of chloride and other anion concentrations between intra- and extracellular media appears to be the most important mechanism of cell protection from inhibition of intracellular catalase by nitrite. Possible mechanisms of this inhibition are discussed.