Simultaneous Nitrification, Denitrification And Phosphorus Removal Research Articles

Research on the aerobic granular sludge under alkalinity in sequencing batch reactors: Removal efficiency, metagenomic and key microbes

Effects of additional alkalinity on the performance of aerobic granular sludge (AGS) in sequencing batch reactors (SBR) performing simultaneous nitrification, denitrification, and phosphorus removal (SNDPR) were evaluated. Results showed that COD and ammonia-N (NH4+-N) were slightly stimulated and remained high and stable with the increase of alkalinity up to 750 mg/L, while denitrification was boosted and total inorganic nitrogen (TIN) removal efficiency increased from 60.46% to 98.62% with an additional alkalinity of 750 mg/L. However, total phosphorus (TP) removal stayed unaffected and efficient. Illumina MiSeq sequencing revealed that microbial diversity and richness shifted mostly with 500 mg/L exterior alkalinity addition. Additional alkalinity altered the bacterial compositions within aerobic granules at various levels and the enrichment of Thiothrix and Acinetobacter was accounted for the promotion of COD and TIN removal.

Effect of aeration modes on simultaneous nitrogen and phosphorus removal and microbial community in a continuous flow reactor with granules

In this study, a continuous flow reactor with simultaneous nitrification, denitrification and phosphorus removal (SNDPR) granular sludge was operated in the continuous aeration (CA) and intermittent aeration (IA) modes to examine the effect of aeration on the performance of continuous-flow system. Then the experimental results showed that the IA1 mode (4 h aeration and 1 h non-aeration) could improve the simultaneous nitrogen and phosphorus removal and the settleability of granules in continuous flow system. Results of high-throughput pyrosequencing illustrated that the methanogens, AOA, ANAMMOX, DNB, denitrifying polyphosphate-accumulating organisms (DPAOs) were the important participant of simultaneous biological nutrients removal (SBNR), meanwhile, the IA1 mode could effectively inhibit the growth of filamentous microorganisms (Thiothrix and Acinetobacter). Finally, a conceptual model of the SNDPR granular microbial ecosystem under IA1 mode was proposed as a base for analyzing the mechanism of simultaneous nutrient removal in continuous flow system.

Removal of nutrients and emission of nitrous oxide during simultaneous nitrification, denitrification and phosphorus removal process with metal ions addition

The impacts of metal ions (Cu2+ and Fe3+) on nutrients removal and nitrous oxide (N2O) emission during the simultaneous nitrification, denitrification and phosphorus removal (SNDPR) process were evaluated and the mechanism was further investigated. Results showed that both Cu2+ and Fe3+ addition at moderate concentrations enhanced nitrogen removal by reinforcing the denitrification process. The long-term addition of Fe3+ weakened the removal of phosphorus by 2.3%–11.7%, due to the suppression of polyphosphate-accumulating organisms (PAOs) growth and activity. N2O production and emission factor decreased greatly by the addition of Cu2+. This decrease was caused by the enhancement of nitrite reductase and N2O reductase (N2OR) activities. On the contrary, Fe3+ addition at moderate concentrations stimulated the N2O production. Fe3+ enhanced the nitric oxide reductase (NOR) and increased the NOR/N2OR ratio, leading to the accumulation of N2O. Moreover, addition of Fe3+ caused a reduction in polyhydroxyalkanoates synthesis at the anaerobic stage and renforced glycogen-accumulating organisms (GAOs) activity instead of PAOs activity, resulting in increased N2O accumulation. Addition of high concentrations of metal ions (5 mg/L Cu2+ and 60 mg/L Fe3+ in this study) suppressed the nutrients removal and stimulated the N2O production, partly due to the inhibition of the bacterial activity.

Simultaneous nitrification, denitrification and phosphorus removal in a sequencing batch reactor (SBR) under low temperature

Simultaneous nitrogen and phosphorus removal in winter is one of the great challenges in wastewater treatment processes due to the poor bioactivity of microbial communities. In this study, excellent performance of simultaneous nitrification, denitrification and phosphorus removal (SNDPR) was achieved at low temperature of 10 °C and COD/N ratio of 6 in a lab-scale sequencing batch reactor. Total nitrogen (TN) and phosphorus (TP) removal efficiency reached 89.6% and 97.5%, respectively, accompanied with N2O emission of 7.46% TN due to the primary contribution (70%) of nitrifier denitrification. It was further confirmed that polyphosphate accumulating organisms (PAOs) were dominant in microbial communities revealed by fluorescence in situ hybridization and 16S rRNA amplicon sequencing. Moreover, denitrifying phosphorus removal by PAOs through nitrite pathway was found to be the main reason for the high efficiency of this SNDPR process. Denitrifying PAOs, especially the subgroup PAOII capable of utilizing nitrite to take up phosphorus, played a significant role in highly efficient TN and TP removal at low temperature. Furthermore, genus Propionivibrio was enriched (48.9%) in the bacterial community based on the 16S rRNA analysis, which was proposed to be a crucial member involved in the nitrogen and phosphorus removal simultaneously at low temperature in this system.

Simultaneous nitrification, denitrification and phosphorus recovery (SNDPr) - An opportunity to facilitate full-scale recovery of phosphorus from municipal wastewater

Sewage treatment plants are a potential point source for recycling of phosphorus (P). Several technologies have been proposed to biologically recover P from wastewater. The majority of these technologies are side-stream processes and rely on an external source of soluble organic carbon to facilitate P recovery. To date, no studies have demonstrated the potential to facilitate main-stream recovery of P, using carbon that is naturally present in wastewater. Simultaneous nitrification, denitrification and phosphorus removal (SNDPR) is an elegant process that can uptake influent carbon and effectively remove both nitrogen (N) and P from wastewater. SNDPR studies to date, however, have failed to facilitate an end-of-anaerobic-phase P rich liquor, that enables economies of scale to recover influent P. Therefore, this study examined the feasibility of achieving a P rich liquor (e.g. > 70 mg-P/L) in a granular SNDPR process. A synthetic influent that replicated the nutrient and carbon concentrations of municipal wastewater was used to investigate whether carbon in the influent wastewater could enable both nutrient removal and P recovery from wastewater. Our granular SNDPR process was able to facilitate an end-of-anaerobic-phase liquor with P enriched to approximately 100 mg-P/L. A dissolved oxygen (DO) concentration of 0.5 mg/L in a sequencing batch reactor (SBR) was found to be essential to achieve complete nutrient removal and a high P concentration at the end of the anaerobic phase. At this steady state of reactor operation, the abundance of polyphosphate accumulating organisms (PAOs) was 2.6 times the abundance of glycogen accumulating organisms (GAOs). The study also demonstrated the importance of denitrifying polyphosphate accumulating organisms (DPAOs) and glycogen accumulating organisms (DGAOs) to achieve complete removal of N from the effluent. Compared to nitrifying bacteria, the polyphosphate accumulating organisms (PAOs) had a higher affinity towards DO. This study, for the first time, showed that the mainstream recovery of P is feasible using a SNDPR process.

Simultaneous nitrification, denitrification and phosphorus removal in an aerobic granular sludge sequencing batch reactor with high dissolved oxygen: Effects of carbon to nitrogen ratios

Simultaneous nitrification, denitrification and phosphorus removal (SNDPR) using aerobic granules is a promising approach in water treatment. The present work investigated the effects of influent carbon to nitrogen (N) ratios (20, 10, and 4) on the SNDPR performance in aerobic granular sequencing batch reactors (AGSBR) under high aeration rate. Results revealed that granules remained long-term stability when the DO concentration was 7–8 mg/L. With the decline of COD/N ratios, the denitrification efficiency was reduced due to the accumulation of nitrate, although the removal of COD and TP remained stable with good efficiency. Rising concentration of ammonia N led to the increase of PN/PS ratio of EPS as well as the protein types according to the results of 3D-EEM fluorescence spectroscopy. MiSeq pyrosequencing technology indicated that the decreasing ratio of COD/N under high DO concentration contributed to accumulation of GAOs and DNPAOs rather than PAOs.

Simultaneous nitrification, denitrification and phosphorus removal in aerobic granular sequencing batch reactors with high aeration intensity: Impact of aeration time

A new operating approach by reducing the aeration time while keeping high intensity was evaluated for enhanced nutrients removal and maintenance of granular stability. Three aerobic granular sequencing batch reactors (SBR) performing simultaneous nitrification, denitrification and phosphorus removal (SNDPR) were run at different aeration time (120, 90, and 60 min). Aerobic granules could remain their integrity and stability over long-term operation under high aeration intensity and different time, and shorter aeration time favored the retention of biomass, better settleability, and more production of extracellular polymeric substances (EPS). Besides, efficient and stable reactor performance for carbon and phosphorus were achieved, especially, enhanced nitrogen removal was obtained due to reduction of aeration time. Further exploration revealed that the aeration time shaped the bacterial community in terms of diversity, composition, as well as the distribution of functional groups involving carbon, nitrogen and phosphorus removal.

Simultaneous nitrification, denitrification and phosphorus removal in an aerobic granular sequencing batch reactor with mixed carbon sources: reactor performance, extracellular polymeric substances and microbial successions

Development of simultaneous nitrification, denitrification and phosphorus removal (SNDPR) is a promising approach for domestic wastewater treatment. Mixed carbon sources by sodium acetate and glucose at various ratios (3:1, 1:1, and 1:3) were investigated to evaluate the effects on the sequencing batch reactors (SBR) based on aerobic granules. Results revealed that the mixed carbon did not change the settleability of aerobic granules, while glucose was more favorable for biomass retention induced by heterotrophs. Both carbon and ammonia nitrogen removal remained unaffected, while increased residual nitrate and phosphorus were detected with higher glucose ratios. Growing percentages of glucose led to more production of extracellular polymeric substances (EPS), especially polysaccharides (PS). Shifts of compositions of EPS were observed by the three-dimensional exaction and emission matrix (3D-EEM) fluorescence spectroscopy. MiSeq pyrosequencing technology demonstrated that the increasing ratios of glucose reduced the diversity of microbial community, though the dominant microbes remained unchanged. Phylogenetic classification of key groups involved in carbon, nitrogen and phosphorus removal suggested that mixed carbon source decidedly shaped the bacterial community.

Elucidation of microbial characterization of aerobic granules in a sequencing batch reactor performing simultaneous nitrification, denitrification and phosphorus removal at varying carbon to phosphorus ratios

An aerobic granules simultaneous nitrification, denitrification and phosphorus removal (SNDPR) system was evaluated in terms of the reactor performance and microbial population dynamics with decreasing C/P ratios from 50 to 16. The effects of C/P ratios on organic carbon and nutrients removal were investigated, as well as the alpha diversity of the bacterial community and bacterial compositions by using Illumina MiSeq pyrosequencing technology. Finally, the relative abundances and distribution patterns were identified and assessed given the key functional groups involved in biological nutrients removals to reveal the effects of C/P ratios to aerobic granules in the SNDPR from the molecular level.

Unraveling characteristics of simultaneous nitrification, denitrification and phosphorus removal (SNDPR) in an aerobic granular sequencing batch reactor

An aerobic granular sequencing batch reactor (SBR) on an aerobic/oxic/anoxic (AOA) mode was operated for 50days with acetate sodium as the sole carbon source for simultaneous carbon, nitrogen and phosphorus removal. Excellent removal efficiencies for chemical oxygen demand (COD) (94.46±3.59%), nitrogen (96.56±3.44% for ammonia nitrogen (NH4+-N) and 93.88±6.78% for total inorganic nitrogen (TIN)) and phosphorus (97.71±3.63%) were obtained over operation. Mechanisms for simultaneous nutrients removal were explored and the results indicated that simultaneous nitrification, denitrification and phosphorus removal (SNDPR) under aerobic conditions was mainly responsible for most of nitrogen and phosphorus removal. Identification and quantification of the granular AOA SBR revealed that higher rates of nutrients removal and more potentials were to be exploited by optimizing the operating conditions including time durations for AOA mode and the feeding compositions.

Simultaneous nitrification, denitrification and phosphorus removal (SNDPR) in a full-scale water reclamation plant located in warm climate.

The combination of simultaneous nitrification-denitrification (SND) with enhanced biological phosphorus removal (EBPR) provides a more efficient and economically viable option for nutrient removal from municipal wastewater compared to conventional two-step nitrification-denitrification. This study analyzed the nutrients (N and P) profiles in a full-scale municipal wastewater reclamation plant (WRP) located in the tropical region, in which more than 90% of nitrogen was removed. Interestingly, average SND efficiency in aerobic zones was found to be up to 50%, whereas phosphorus profile displayed a clear cyclic release and uptake pattern with a phosphorus removal efficiency of up to 76%. The capability of sludge to perform SND and EBPR was further confirmed through a series of batch experiments. Microbial analysis revealed the presence of Accumulibacter and Tetrasphaera phosphate accumulating organisms in the plant, while few glycogen accumulating organisms (GAO) was observed. This study showed the significant occurrence of combined SND and EBPR, known as simultaneous nitrification, denitrification and phosphorus removal (SNDPR), in the studied WRP under warm climate. The possible causes behind the observed SNDPR were also discussed.

Nutrients removal and nitrous oxide emission during simultaneous nitrification, denitrification, and phosphorus removal process: impact of temperature

Simultaneous nitrification, denitrification, and phosphorus removal (SNDPR) process was achieved in a SBR system operated in anaerobic–aerobic (low dissolved oxygen (DO)) mode. The contaminant removal and nitrous oxide (N2O) emission characteristics in the reactor at two different temperatures (25 and 10°C) were investigated to evaluate the impacts of low temperature on SNDPR process. The results showed that TP and TN removal efficiencies of the reactor were 95.6 and 77%, respectively at 25°C indicating that simultaneous nitrogen and phosphorus removal were successfully achieved in the reactor. However, the removal of TN and ammonium was weakened significantly by the low temperature. The low temperature has little impact on phosphorus removal, mainly due to the enrichment of PAOs at low temperature. The N2O emission mainly occurred during the low DO aerobic period. N2O emission amount at 10°C was calculated as 648.8 μg N/g MLSS, which was about 43.3% higher than that at 25°C, and 10.11% of nitrogen removed was converted to N2O at low temperature, showing that low temperature stimulated the emission of N2O during SNDPR process.

Determination of optimum conditions for dairy wastewater treatment in UAASB reactor for removal of nutrients

In this study, the granular sludge was generated for simultaneous nitrification, denitrification and phosphorus removal (SNDPR) and studied on a laboratory scale. Analyzing the nutrients removal percentages from wastewater were scrutinized by using an optimization of the variables, i.e., COD:N:P ratio, OLR, aeration time, MLSS, F:M and HRT. These 6 interrelated parameters were evaluated as the process response. Microscopic observations of the performance of the SNDPR process revealed that the granules included Bacillus sp. in the bacterial community. According to these results, the UAASB system produced an effluent that lends dairy wastewater suitable for land irrigation and that this an attractive process of using granular sludge is appropriate for achieving carbon, nitrogen and phosphorus removal from nutrient-rich wastewater by a biological method.

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

Granular sludge has recently come under study as an efficient technology in wastewater treatment. Different microorganisms coexisting within the granules allow simultaneous nitrification, denitrification and phosphorus removal (SNDPR). However, the behaviour of the process varies when nitrogen and phosphorus removal are coupled. The purpose of this paper is to study the SNDPR process in granular sludge with low-strength wastewater, focusing on the effect of nitrification products such as nitrite and nitrate on phosphorus removal. Results showed that aerobic granules allowed anoxic phosphorus uptake using either nitrite or nitrate as an electron acceptor. Phosphorus uptake rates had similar values using either product of nitrification (13.64 mg P g −1 VSS h −1 in the presence of nitrate and 12.20 mg P g −1 VSS h −1 in the presence of nitrite) without any observed nitrite inhibition of phosphorus uptake. However, different P uptake-N removal ratios were found in simultaneous denitrification and phosphorus removal. Nitrate was the best option for phosphorus-rich wastewater treatment (3.04 mg P mg −1N), while nitrite was more beneficial with the SNDPR of nitrogen-rich influents (1.68 mg P mg −1N).

Microbial distribution of Accumulibacter spp. and Competibacter spp. in aerobic granules from a lab‐scale biological nutrient removal system

Granular sludge for simultaneous nitrification, denitrification and phosphorus removal (SNDPR) was generated and studied in a lab-scale sequencing batch reactor (SBR). The SBR was monitored for 450 days during which the biomass was transformed from flocs to granules, which persisted for the last 130 days of operation. Short sludge settling time was employed to successfully generate the granules, with the 10th and 90th percentiles of diameter being 0.7 and 1.6 mm respectively. Good phosphorus removal and nitrification occurred throughout the SBR operation but only when granules were generated were denitrification and full nutrient removal complete. Fluorescence in situ hybridization and oxygen microsensors were used to study the granules at a microscale. Accumulibacter spp. (a polyphosphate-accumulating organism, PAO) and Competibacter spp. (a glycogen non-polyphosphate-accumulating organism, GAO) were the most abundant microbial community members (together 74% of all Bacteria) and both are capable of denitrification. In the aerobic period of the SBR operation, the oxygen penetrated 250 microm into the granules leaving large anoxic zones in the centre part where denitrification can occur. In granules > 500 microm in diameter, Accumulibacter spp. was dominant in the outermost 200 microm region of the granule while Competibacter spp. dominated in the granule central zone. The stratification of these two populations between the outer aerobic and inner anoxic part of the granule was highly significant (P < 0.003). We concluded that the GAO Competibacter spp., and not the PAO Accumulibacter spp., was responsible for denitrification in this SBR. This is undesirable for SNDPR as savings in carbon demand cannot be fulfilled with phosphorus removal and denitrification being achieved by different groups of bacteria.

Identifying causes for N 2O accumulation in a lab-scale sequencing batch reactor performing simultaneous nitrification, denitrification and phosphorus removal

The recently described process of simultaneous nitrification, denitrification and phosphorus removal (SNDPR) has a great potential to save capital and operating costs for wastewater treatment plants. However, the presence of glycogen-accumulating organisms (GAOs) and the accumulation of nitrous oxide (N 2O) can severely compromise the advantages of this process. In this study, these two issues were investigated using a lab-scale sequencing batch reactor performing SNDPR over a 5-month period. The reactor was highly enriched in polyphosphate-accumulating organisms (PAOs) and GAOs representing around 70% of the total microbial community. PAOs were the dominant population at all times and their abundance increased, while GAOs population decreased over the study period. Anoxic batch tests demonstrated that GAOs rather than denitrifying PAOs were responsible for denitrification. N 2O accumulated from denitrification and more than half of the nitrogen supplied in a reactor cycle was released into the atmosphere as N 2O. After mixing SNDPR sludge with other denitrifying sludge, N 2O present in the bulk liquid was reduced immediately if external carbon was added. We therefore suggest that the N 2O accumulation observed in the SNDPR reactor is an artefact of the low microbial diversity facilitated by the use of synthetic wastewater with only a single carbon source.