Optimization of Simultaneous Nitrification Denitrification Performance in Different ENR Process Configurations

Effect of PHB and oxygen uptake rate on nitrous oxide emission during simultaneous nitrification denitrification process

For economic and efficient nitrogen removal from wastewater treatment plants via simultaneous nitrification and denitrification the nitrification process should stop at the level of nitrite such that nitrite rather than nitrate becomes the substrate for denitrification. This study aims to contribute to the understanding of the conditions that are necessary to improve nitrite reduction over nitrite oxidation. Laboratory sequencing batch reactors (SBRs) were operated with synthetic wastewater containing acetate as COD and ammonium as the nitrogen source. Computer controlled operation of the reactors allowed reproducible simultaneous nitrification and denitrification (SND). The oxygen supply was kept precisely at a low level of 0.5 mgL(-1) and bacterial PHB was the only electron donor available for denitrification. During SND little nitrite or nitrate accumulated (< 20% total N), indicating that the reducing processes were almost as fast as the production of nitrite and nitrate from nitrification. Nitrite spiking tests were performed to investigate the fate of nitrite under different oxidation (0.1-1.5 mgL(-1) of dissolved oxygen) and reduction conditions. High levels of reducing power were provided by allowing the cells to build up to 2.5 mM of PHB. Nitrite added was preferentially oxidised to nitrate rather than reduced even when dissolved oxygen was low and reducing power (PHB) was excessively high. However, the presence of ammonium enabled significant reduction of nitrite under low oxygen conditions. This is consistent with previous observations in SBR where aerobic nitrite and nitrate reduction occurred only as long as ammonium was present. As soon as ammonium was depleted, the rate of denitrification decreased significantly. The significance of the observed strongly stimulating effect of ammonium on nitrite reduction under SND conditions is discussed and potential consequences for SBR operation are suggested.

Improved step-feed de-nitrification progress combined with biological fluidized bed was introduced in this study. The progress had good performance and capacity of de-nitrification and organic matter. The experiment result showed that the de-nitrification efficiency of the improved biological fluidized bed with step-feed process was higher than the fluidized bed A/O process under the same water quality and the operating conditions. When the influent proportion of each segment was equal, the system showed good nitrogen removal efficiency with the change of influent C/N ratio, HRT and sludge return ratio. The removal rate of TN reached up to 88.2%. It showed that the simultaneous nitrification and de-nitrification phenomenon happened in the aerobic zone. The nitrogen removal mechanism was also studied.

In this study, nitrous oxide (N(2)O) emission was compared between the operations of two different sequencing batch reactors, conventional sequencing batch reactor (CNVSBR) and simultaneous nitrification and denitrification sequencing batch reactor (SND-SBR), using synthetic wastewater. The CNV-SBR consisted of anoxic (denitrification) and aerobic phases, whereas the SND-SBR consisted of a microaerobic (low dissolved oxygen concentration) phase, which was achieved by intermittent aeration for simultaneous nitrification and denitrification. The CNV-SBR emitted 3.9 mg of N(2)O-N in the denitrification phase and 1.6 mg of N2O-N in the nitrification phase, resulting in a total emission of 5.5 mg from 432 mg of NH(4)(+)-N input. In contrast, the SND-SBR emitted 26.2 mg of N(2)O-N under the microaerobic condition, which was about 5 times higher than the emission obtained with the CNV-SBR at the same NH(4)(+)-N input. From the N(2)O yield based on NH(4)(+)-N input, the microaerobic condition produced the highest yield (6.1%), followed by the anoxic (0.9%) and aerobic (0.4%) conditions. It is thought that an appropriate dissolved oxygen level is critical for reducing N(2)O emission during nitrification and denitrification at wastewater treatment plants.

A laboratory-scale intermittently aerate membrane was applied to treat domestic sewage. At hydraulic retention tims (HRT)of 6h and dissolved oxygen of 1∼2mg/L in aeration, three aeration/non-aeration cycles including 60min/60min, 60min/90min and 90min/60min were experimented separately, which form microenvironment of aerobic/anoxia to reach simultaneous nitrification and denitrification. At a result, more than 90% of COD and NH 4 +-N was removed, among which average 74% of TN was removed in aeration/non-aeration cycles of 60min/60min. at the same time, membrane flux could be renewed in initial level approximately by chemical cleaning.

The cultivation of aerobic granular sludge in Sequencing Batch Airlift Reactor (SBAR) was investigated. The results showed that the aerobic granular sludge could be formed in short time (35 d) owing to better shear force and selective pressure in SBAR. Meanwhile, aerobic granulation was clearly accelerated when the external carbon source was intermittently added at one-cycle intervals. The mean diameter of the granules formed in this research was around 1.0 mm, MLSS 7 g/L, SVI 30. The analysis of nitrite-nitrogen and nitrate-nitrogen, in typical cycle clarified the Simultaneous Nitrification and Denitrification (SND) process in SBAR with the aerobic granular sludge.

The role of nitrate and nitrite in a granular sludge process treating low-strength wastewater

Simultaneous denitrification and denitrifying phosphorus removal in a full-scale anoxic–oxic process without internal recycle treating low strength wastewater

A pilot-scale primary maturation pond was spiked with (15)N-labelled ammonia ((15)NH(4)Cl) and (15)N-labelled nitrite (Na(15)NO(2)), in order to improve current understanding of the dynamics of inorganic nitrogen transformations and removal in WSP systems. Stable isotope analysis of delta(15)N showed that nitrification could be considered as an intermediate step in WSP, which is masked by simultaneous denitrification, under conditions of low algal activity. Molecular microbiology analysis showed that denitrification can be considered a feasible mechanism for permanent nitrogen removal in WSP, which may be supported either by ammonia-oxidising bacteria (AOB) or by methanotrophs, in addition to nitrite-oxidising bacteria (NOB). However, the relative supremacy of the denitrification process over other nitrogen removal mechanisms (e.g., biological uptake) depends upon phytoplanktonic activity.

To improve the efficiency of simultaneous heterotrophic nitrification and aerobic denitrification (SND) at high concentrations of NaCl and ammonia nitrogen (NH4+-N), we investigated the SND characteristics of Halomonas bacteria with the ability to synthesize the compatible solute ectoine. Halomonas sp. strain B01, which was isolated, screened and identified in this study, could simultaneously remove nitrogen (N) by SND and synthesize ectoine under high NaCl conditions. Gene cloning and sequencing analysis indicated that this bacterial genome contains ammonia monooxygenase (amoA) and nitrate reductase (narH) genes. Optimal conditions for N removal in a solution containing 600 mg/L NH4+-N were as follows: sodium succinate supplied as organic carbon (C) source at a C/N ratio of 5, pH 8 and shaking culture at 90 rpm. The N removal rate was 96.0% under these conditions. The SND by Halomonas sp. strain B01 was performed in N removal medium containing 60 g/L NaCl and 4,000 mg/L NH4+-N; after 180 h the residual total inorganic N concentration was 21.7 mg/L and the N removal rate was 99.2%. Halomonas sp. strain B01, with the ability to synthesize the compatible solute ectoine, could simultaneously tolerate high concentrations of NaCl and NH4+-N and efficiently perform N removal by SND.

Free cyanide (CN&lt;sup&gt;-&lt;/sup&gt;) is a threat to metabolic functions of the microbial population used for the treatment of wastewater, particularly, total nitrogen removal (TN) consortia which gets inhibited by CN&lt;sup&gt;-&lt;/sup&gt; in wastewater treatment plants (WWTPs). Many other methods are used to treat CN&lt;sup&gt;-&lt;/sup&gt; prior to the TN removal stages; however, these methods increase the operational cost of the WWTPs. The capability of a microbial population to use multiple substrates is critical in WWTP and in eliminating inhibition associated with CN&lt;sup&gt;-&lt;/sup&gt;. Previously, cyanide resistant bacteria were used to eliminate the inhibitory effect of CN&lt;sup&gt;-&lt;/sup&gt; towards simultaneous nitrification and aerobic denitrification (SNaD). However, a study to predict the degradation efficiency of the microorganism was required. In this study, response surface methodology (RSM) and cybernetic models were used to predict and optimize SNaD performance for TN removal under CN&lt;sup&gt;-&lt;/sup&gt; conditions. Physiological parameters influencing the SNaD were pH 6.5 and 36.5&lt;sup&gt;o&lt;/sup&gt;C, with TN and CN&lt;sup&gt;-&lt;/sup&gt; degradation efficiency of 78.6 and 80.2%, respectively. These results show a complete elimination of the CNinhibitory effect towards SNaD and show the prediction ability of both RSM and the cybernetic models used. These results exhibited a promising solution in the control, management, and optimization of SNaD.

The effects of combined different strains on a simultaneous denitrification and biomineralization process were examined. The influence of sodium succinate concentration, pH, and hydraulic retention time on nitrate and hardness removal was evaluated in bioreactors. Experimental results indicated that high nitrate and hardness removal efficiencies were obtained under optimum conditions. The community diversity was markedly influenced by the concentration of sodium succinate. The findings proved that Pseudomonas sp. H117 and Pseudomonas sp. H2 played a key role in the process of nitrate and hardness removal. The main component of sedimentation generated from the bioreactor was detected as calcium ion precipitation by scanning electron microscopy and X‐ray diffraction.

SIMULTANIOUS NITRIFICATION AND DENITRIFICATION IN ONE-STAGE ACTIVATED SLUDGE SYSTEMSA structured model of suspended-growth biological processes is used to identify the conditions under which simultaneous denitrification and nitrification occur reliably at steady state for a single-reactor system. Systematic variation of the dissolved oxygen concentration demonstrates that a D.O. “window” for major denitrification with nitrification occurs for approximately 0.1-0.75 mg...Author(s)D.G. VIRAJ DE SILVABRUCE E. RITTMANNSourceProceedings of the Water Environment FederationSubjectSession 1 - Research Symposium: Biological Nutrient Removal with AEESP LectureDocument typeConference PaperPublisherWater Environment FederationPrint publication date Jan, 2001ISSN1938-6478SICI1938-6478(20010101)2001:16L.77;1-DOI10.2175/193864701790901834Volume / Issue2001 / 16Content sourceWEFTECFirst / last page(s)77 - 83Copyright2001Word count156

Despite the fact that heterotrophic nitrification was identified more than 100 years ago, the biochemistry of heterotrophic nitrifiers is poorly known and their contribution to nitrification in soil is still speculative. Heterotrophic nitrifiers need organic compounds as their energy source in contrast to the chemolithotrophic nitrifiers. Most of the potential pathways for nitrite/nitrate production by heterotrophs can be considered as secondary metabolism. Only nitrification and simultaneous denitrification by some heterotrophic bacteria is known to have connection to the energy metabolism. Evidently, the nitrification pathways of bacteria and fungi differ. Some heterotrophic bacteria oxidizing ammonia have ammonia monooxygenase (AMO), but there are also heterotrophic bacteria oxidizing ammonia without AMO. The structure of AMO of chemolithotrophic ammonia oxidizers and heterotrophs differs. AMO has not been found in nitrifying fungi. The conditions for heterotrophic nitrification in soil highly differ from those in waste waters where heterotrophic nitrification activity can be high. Heterotrophic nitrification in soil is limited by the low availability of easily decomposable organic substrates. Possible nitrification by heterotrophs in the rhizosphere and endophytic root microbes gaining a good supply of substrates from plants is not known. Fungi are of special interest in heterotrophic nitrification in soil because fungi can evidently nitrify not only easily decomposable substrates but also when decomposing recalcitrant organic compounds (like lignin) which are abundant in soil. Nitrite/nitrate production from easily decomposable nitrogenous organic compounds, such as amino acids, is common among heterotrophic bacteria and fungi. The general conclusion that heterotrophs use solely an “organic pathway” in their nitrification is, however, not valid because also ammonia can be oxidized. Owing to the diverse, poorly known biochemistry of heterotrophic nitrification and methodological difficulties to differentiate heterotrophic and chemolithotrophic nitrification in soil, the role of heterotrophic nitrification in soil nitrogen cycle remains uncertain.

Simultaneous nitrification denitrification (SND) is a well-established phenomenon in biological nutrient removal activated sludge systems. Study at a municipal wastewater treatment facility sought to determine nitrogen removal effectiveness within a full-scale sequential batch reactor (SBR) system utilizing SND in conjunction with traditional nitrogen removal. In addition to characterizing extent of SND, the research examined the ability of SND to meet state-based effluent water quality standards. At the selected facility, the average SND efficiency during a two-month sampling period was 52.8%, paralleling results from similar SBR municipal wastewater systems. The observed SBR system had removal efficiencies > 99% for the influent to effluent -N concentrations. The SND process also resulted in average NO3-NO2-N concentration that was 82% lower than the theoretical concentration under comparable circumstances. Overall, nitrogen removal for this SBR system was >99% which typified results in other SND systems, but at a higher Total Nitrogen removal rate.