Advanced nitrogen removal from wastewater by combining anammox with partial denitrification

Feeding schemes and C/N ratio of a laboratory-scale step-fed sequencing batch reactor for liquid swine manure treatment

This study was undertaken to investigate the effect of two split feeding schemes (600 mL/200 mL and 400 mL/400 mL, designated as FS1 and FS2, respectively) on the performance of a step-fed sequencing batch reactor (SBR) in treating liquid swine manure for nutrient removal. The SBR was run on an 8-h cycle with a repeated pattern of anaerobic/anoxic/aerobic phases in each cycle and the two feedings always occurred at the beginning of each anaerobic phase. A low-level aeration was used (1.0 L/m³.sec) for the anoxic/aerobic phase to facilitate nitrification and phosphorus uptake while reducing the energy consumption. The results showed that FS1 reduced NH₄⁺-N by 98.7% and FS2 by 98.3%. FS1 had 12.3 mg/L NO₃-N left in the effluent, while FS2 had 4.51 mg/L. For soluble phosphorus removal, FS1 achieved 95.2%, while FS2 reached only 68.5%. Both feeding schemes achieved ≥ 95% removal of COD. A good power regression was observed between total nitrogen (sum of all three nitrogen species) and the carbon to nitrogen (C/N) ratio, with the correlation coefficients of 0.9729 and 0.9542 for FS1 and FS2, respectively, based on which it was concluded that higher C/N ratios were required to achieve higher nitrogen removal efficiencies.

Evaluating the potential for dissimilatory nitrate reduction by anammox bacteria for municipal wastewater treatment

Anammox bacteria can perform dissimilatory nitrate reduction to ammonium (DNRA) with nitrite as intermediate coupled to the oxidation of volatile fatty acids (VFA). Batch tests with enriched anammox and a co-culture of anammox and heterotrophic bacteria showed the capacity of Candidatus 'Brocadia fulgida' to perform the DNRA coupled to the anammox reaction (DNRA-anammox) at a high rate although the culture was not previously adapted to VFA. From thermodynamic calculations it could be stated that low COD/N influent ratios favour the DNRA-anammox transformation over heterotrophic conversions since more free energy is gained. A process scheme is proposed for an innovative nitrogen removal system in which the nitrate produced by nitrite oxidizing bacteria and/or anammox bacteria is converted during DNRA-anammox pathway, resulting in a sustainable nitrogen removal from municipal wastewater while circumventing the troublesome out-selection of nitrite oxidizing bacteria encountered in mainstream applications.

Simultaneous domestic wastewater and nitrate sewage treatment by DEnitrifying AMmonium OXidation (DEAMOX) in sequencing batch reactor

A novel DEAMOX system was developed for nitrogen removal from domestic wastewater and nitrate (NO₃^--N) sewage in sequencing batch reactor (SBR). High nitrite (NO₂^--N) was produced from NO₃^--N reduction in partial-denitrification process, which served as electron acceptor for anammox and was removed with ammonia (NH₄⁺-N) in domestic wastewater simultaneously. A 500-days operation demonstrated that the efficient and stable nitrogen removal performance could be achieved by DEAMOX. The total nitrogen (TN) removal efficiency was as high as 95.8% with influent NH₄⁺-N of 63.58 mg L^-1 and NO₃^--N of 69.24 mg L^-1. The maximum NH₄⁺-N removal efficiency reached up to 94.7%, corresponding to the NO₃^--N removal efficiency of 97.8%. The biomass of partial-denitrification and anammox bacteria was observed to be wall-growth. The deteriorated nitrogen removal performance occurred due to excess denitrifying microbial growth in the outer layer of sludge consortium, which prevented the substrate transfer for anammox inside. However, an excellent nitrogen removal could be guaranteed by scrapping the superficial denitrifying biomass at regular intervals. Furthermore, the high-throughput sequencing analysis revealed that the Thauera genera (26.33%) was possibly responsible for the high NO₂^--N accumulation in partial-denitrification and Candidatus Brocadia (1.7%) was the major anammox species.

Achievement of high nitrite accumulation via endogenous partial denitrification (EPD)

This study proposed a novel strategy for achievement of partial denitrification driven by endogenous carbon sources in an anaerobic/anoxic/aerobic activated sludge system. Results showed that in the steady-stage, the nitrate-to-nitrite transformation ratio (NTR) was kept at around 87% without nitrate in the effluent. During the anaerobic period, exogenous carbon sources was completely taken up, accompanied by the consumption of glycogen and production of polyhydroxyalkanoates (PHAs). During the anoxic period, nitrate was reduced to nitrite by using PHAs as carbon sources, followed by the replenishment of glycogen. Thus, the phenotype of denitrifying GAOs was clearly observed and endogenous partial denitrification (EPD) occurred. Furthermore, results showed the nitrate reduction was prior to the nitrite reduction in the presence of nitrate, which led to the high nitrite accumulation.

Integrated anaerobic ammonium oxidization with partial denitrification process for advanced nitrogen removal from high-strength wastewater

In this study, a novel integrated anaerobic ammonium oxidization with partial denitrification process (termed as ANAMMOX-PD) was developed for advanced nitrogen removal from high-strength wastewater, which excess NO₃^--N produced by ANAMMOX was fed into PD reactor for NO₂^--N production and then refluxing to ANAMMOX reactor for further removal. Results showed that total nitrogen (TN) removal efficiency as high as 97.8% was achieved and effluent TN-N was below 20mg/L at influent TN-N of 820mg/L. Furthermore, the feasibility of simultaneously treating domestic wastewater was demonstrated in ANAMMOX-PD process, and NH₄⁺-N removal efficiency of 96.7% was obtained. The nitrogen removal was mainly carried out through ANAMMOX pathway, and high-throughput sequencing revealed that Candidatus_Brocadia was the major ANAMMOX species. The presented process could effectively solve the problem of excess nitrate residual in ANAMMOX effluent, which hold a great potential in application of currently ANAMMOX treating high-strength wastewater (e.g. sludge digestion supernatant).

A novel process combining simultaneous partial nitrification, anammox and denitrification (SNAD) with denitrifying phosphorus removal (DPR) to treat sewage

In this study, a novel process combined simultaneous partial nitrification, anammox and denitrification (SNAD) with denitrifying phosphorus removal (DPR) was proposed for advanced nitrogen removal. Firstly simulating sewage was introduced to a sequencing batch reactor (SBR) for organic matter removal and anaerobic phosphorus release (stage 1). Then effluent of stage 1 with low COD was discharged to a sequencing biofilm batch reactor (SBBR) for partial nitrification, anammox and partial denitrification (stage 2). The nitrate produced in SBBR was fed into SBR again, in which the nitrate was removed by DPR process (stage 3). The performance of the SNAD-DPR process was investigated. And effects of carbon source addition during start-up period on microbial community were discussed based on 16S rRNA amplicon pyrosequencing.

Performance of partial denitrification (PD)-ANAMMOX process in simultaneously treating nitrate and low C/N domestic wastewater at low temperature

The simultaneous treatment of nitrate (NO3(-)-N∼50mgL(-1)) and domestic wastewater (ammonia (NH4(+)-N)∼60.6mgL(-1), COD∼166.3mgL(-1)) via a novel partial denitrification (PD)-ANaerobic AMMonium OXidation (ANAMMOX) process was investigated at low temperature (12.9∼15.1°C). Results showed that desirable performance was achieved with average NO3(-)-N, NH4(+)-N and COD removal efficiencies of 89.5%, 97.6% and 78.7%, respectively. However, deteriorated sludge settleability in PD reactor was observed during operation, which bulked with serious sludge wash-out, leading to excess NO3(-)-N remaining in PD effluent. Fortunately, a satisfactory nitrogen removal was still achieved due to the occurrence of partial denitrification in ANAMMOX reactor. This was demonstrated by high-throughput sequencing, which revealed that the high nitrite (NO2(-)-N) production denitrifying bacteria of Thauera was detected (6.1%). ANAMMOX (above 70%) maintained the dominant pathway for nitrogen removal, and Candidatus Jettenia was identified as the major ANAMMOX species accounted for 2.7%.

Performance and microbial community of simultaneous anammox and denitrification (SAD) process in a sequencing batch reactor

A sequencing batch reactor (SBR) was used to test the simultaneous anammox and denitrification process. Optimal nitrogen removal was achieved with chemical oxygen demand (COD) of 150mg/L, during which almost all of ammonia, nitrite and nitrate could be removed. Organic matter was a key factor to regulate the synergy of anammox and denitrification. Both experimental ΔNO2(-)-N/ΔNH4(+)-N and ΔNO3(-)-N/ΔNH4(+)-N values deviated from their theoretical values with increasing COD. Denitrifying bacteria exhibited good diversity and abundance, but the diversity of anammox bacteria was less abundant. Brocadia sinica was able to grow in the presence of organic matter and tolerate high nitrite concentration. Anammox bacteria were predominant at low COD contents, while denitrifying bacteria dominated the microbial community at high COD contents. Anammox and denitrifying bacteria could coexist in one reactor to achieve the simultaneous carbon and nitrogen removal through the synergy of anammox and denitrification.

Nitrogen removal from wastewater and external waste activated sludge reutilization/reduction by simultaneous sludge fermentation, denitrification and anammox (SFDA)

This work demonstrates the feasibility of simultaneous nitrogen removal and external waste activated sludge (WAS) reutilization/reduction by using the synergy of sludge fermentation, denitrification and anammox processes in up-flow reactors (SFDA). Pre-treated domestic wastewater and synthetic wastewater (containing nitrite ∼20mg/L, ammonium ∼10mg/L in both) were fed to 1# and 2# SFDA, respectively. Long-term operation of 1# SFDA was investigated with achieving the peak ammonium removal rate of 0.021 and nitrite removal rate of 0.081kgN/(m(3)d) as nitrogen loading rate elevated from 0.075 to 0.106kgN/(m(3)d). Negative effect of dissolved oxygen on anammox or fermentation in the 2# SFDA was demonstrated negligible due to rapid depletion by microorganisms. Furthermore, a "net" sludge reduction of 38.8% was obtained due to sludge decay and organics consumption by denitrification. The SFDA process was expected to potentially be used for nitrogen removal and WAS reutilization/reduction in full-scale application.

Characteristic of nitrous oxide production in partial denitrification process with high nitrite accumulation

Nitrous oxide (N2O) production during the partial denitrification process with nitrate (NO3(-)-N) to nitrite (NO2(-)-N) transformation ratio of 80% was investigated in this study. Results showed that N2O was seldom observed before complete depletion of NO3(-)-N, but it was closely related to the reduction of NO2(-)-N rather than NO3(-)-N. High COD/NO3(-)-N was in favor of N2O production in partial denitrification with high NO2(-)-N accumulation. It was seriously enhanced at constant acidic pH due to the free nitrous acid (FNA) inhibition. However, the N2O production was much lower at initial pH of 5.5 and 6.5 due to the pH increase during denitrification process. Significantly, the pH turning point could be chosen as a controlled parameter to denote the end of NO3(-)-N reduction, which could not only achieve high NO2(-)-N accumulation but also decrease the N2O production significantly for practical application.

Nitrite production in a partial denitrifying upflow sludge bed (USB) reactor equipped with gas automatic circulation (GAC)

Nitrite production in a partial denitrifying (NO3(-)-N→NO2(-)-N) upflow sludge bed (USB) reactor equipped with gas automatic circulation (GAC) was investigated at ambient temperature (28.8-14.1 °C). The nitrite production rate (NPR) increased with the nitrate loading rate (NLR). Average NPR of 6.63 kgN m(-3) d(-1) was obtained at 28.0 °C with the organic loading rate (OLR) and NLR of 25.38 KgCOD∙m(-3)∙d(-1) and 10.82 kgN m(-3) d(-1), respectively. However, serious sludge floatation was observed when the NLR increased to 13.18 kgN m(-3) d(-1), which might be attributed to sludge bulking at high NLR. The USB reactor recovered rapidly when seeded with the sludge discharged before the deteriorated period, and a stable NPR of ∼4.35 kgN m(-3) d(-1) was achieved at 14.1-15.7 °C in the following 100-day operation, during which the maximum nitrate-to-nitrite transformation ratio (NTR) of 81.4% was achieved at the GAC rate of 1.08 L h(-1). The application of GAC in the partial denitrifying USB reactor enhanced mass transfer, which effectively avoided the channel and dead space, and improved the nitrate transform to nitrite. Moreover, it was found that the GAC system played an important role in promoting the stability of the USB reactor by preventing the sludge floatation. The Illumina high-throughput sequencing analysis revealed that the genus of Thauera was dominate in the USB reactor (67.2-50.2%), which may be responsible for the high nitrite accumulation. Results in this study have an important application in treating nitrate wastewater with an economic and efficient way by combining with ANAMMOX process.

Start-up performance of Anammox process in a fixed bed reactor (FBR) filled with honeycomb-like polypropylene carriers

Novel honeycomb-like carriers, made of polypropylene, were applied to enhance biomass retention capacity so as to improve Anammox start-up performance in a fixed bed reactor (FBR). The reactor was operated for 3 months. On day 45, Anammox activity appeared. After 61 days' operation, the removal efficiencies of ammonium and nitrite were both over 91% based on 70 mg N L(-1) of the influent ammonium and influent nitrite, indicating that a remarkable Anammox activity was attained. A final specific Anammox activity of 0.12 g NH4(+)-N gVSS(-1) d(-1) was reached (VSS: volatile suspended solids). The FBR showed a good capacity for resisting shock loading and was more able to resist shock loading of nitrogen concentration than resist hydraulic shock loading. Phylogenetic analysis showed that Candidatus Brocadia anammoxidans' and Candidatus Kuenenia stuttgartiensis' were detected in the mature biofilm, and Candidatus Brocadia anammoxidans' was the dominant Anammox strain. Candidatus Kuenenia stuttgartiensis' played a positive role in the reactor performance, as it could consumed nitrite quickly and efficiently so as to avoid an adverse effect of temporary nitrite accumulation. The results showed that the honeycomb-like carriers were suitable for start-up of Anammox.

Biological nitrogen removal from sewage via anammox: Recent advances

Biological nitrogen removal from sewage via anammox is a promising and feasible technology to make sewage treatment energy-neutral or energy-positive. Good retention of anammox bacteria is the premise of achieving sewage treatment via anammox. Therefore the anammox metabolism and its factors were critically reviewed so as to form biofilm/granules for retaining anammox bacteria. A stable supply of nitrite for anammox bacteria is a real bottleneck for applying anammox in sewage treatment. Nitritation and partial-denitrification are two promising methods of offering nitrite. As such, the strategies for achieving nitritation in sewage treatment were summarized by reviewing the factors affecting nitrite oxidation bacteria growth. Meanwhile, the methods of achieving partial-denitrification have been developed through understanding the microorganisms related with nitrite accumulation and their factors. Furthermore, two cases of applying anammox in the mainstream sewage treatment plants were documented.

Metagenomic insights into the effects of volatile fatty acids on microbial community structures and functional genes in organotrophic anammox process

To explore the metabolic versatility of "Candidatus Brocadia sinica" in the presence of VFAs, the impacts of VFAs on anammox activity and nitrogen removal were investigated in this study. Results found that low VFAs concentrations has no affect on anammox activity and the removal efficiencies of NH4(+)-N and NO2(-)-N. However, "Ca. Brocadia sinica" showed higher adaptability to some VFAs stresses. Furthermore, Illumina MiSeq pyrosequencing results indicated that the microbial community structures varied significantly and the phyla Chloroflexi, Proteobacteria, Bacteroidetes and Chlorobi were dominated. Finally, qPCR was performed to validate the growth of anammox bacteria and gain the quantitative insights into the correlation between nitrogen transformation rates and the key functional genes in the organotrophic anammox system. Combined analysis clearly demonstrated that the coupling of the anammox, denitrification and DNRA were the noteworthy pathway for the simultaneous removal of nitrogen and organic carbon.