Mean Total Nitrogen Removal Research Articles

Insights into the rapid start-up of an inoculated municipal sludge system: A high-height-to-diameter-ratio airlift inner-circulation partition bioreactor based on CFD analysis

The utilization of municipal sludge as a seed sludge for initiating the autotrophic nitrogen removal (ANR) process presents a challenge due to the negligible abundance of anaerobic ammonia-oxidizing bacteria (AnAOB). Here, a computational fluid dynamics model was used to simulate sludge volume fraction and sludge particle velocity. A high-height-to-diameter-ratio airlift inner-circulation partition bioreactor (HHAIPBR) was operated for 175 d to enrich AnAOB from municipal sludge, and the performance of the ANR process was investigated. The start-up period of HHAIPBR inoculated with municipal sludge required approximately 69 d. A high nitrogen removal performance, with a mean total nitrogen removal efficiency of 82.1%, was obtained for 1 month. The simulation results validated the presence of sludge circulation and revealed the distribution characteristics of dissolved oxygen inside the reactor, further supporting the promotion of sludge granulation via the high height-to-diameter ratio. Nitrosomonas (3.31%) of Proteobacteria and Candidatus Brocadia (6.56%) of Planctomycetota were dominant in the HHAIPBR. This study presents a viable approach for the industrial cultivation of anammox sludge and the rapid start-up of the partial nitritation-anammox system.

Partial S(0)-driven autotrophic denitrification process facilitated the quick natural enrichment of anammox bacteria at room temperature

Anaerobic ammonium oxidation (anammox) is well-known to be an environmental and promising biotechnology. However, the natural enrichment of anammox bacteria is still a challenging topic. In this study, partial S(0)-driven autotrophic denitrification (PSAD) was developed to stably supply nitrite, and natural enrichment of anammox bacteria was rapidly realized in a single sequencing moving bed biofilm reactor at room temperature. With the initiation of PSAD, anammox bacteria spontaneously emerged within 12 days, and PSAD-anammox coupling system was realized successfully. And then, the influent concentration of ammonium continuously increased to the same concentration as the nitrate, and the mean total nitrogen removal efficiency reached 92.77 %, which was mainly contributed by anammox. Moreover, the coupling of PSAD and anammox reduced the risk of sulfate emissions. cDNA high throughput sequencing revealed that the relative abundance of Candidatus Brocadia and Thiobacillus reached 39.03 % and 13.48 % at the 88th day. Oligotyping analysis illustrated that GATTTAAT and GTCCCA were the dominant Ca. Brocadia and Thiobacillus oligotypes in PSAD-anammox coupling system, respectively. DNA-based stable isotope probing further deciphered that Thiobacillus was the actual performer of PSAD and supported the nitrite for anammox bacteria in PSAD-anammox coupling system. Overall, this work provided a new strategy to naturally enrich anammox bacteria.

Exerting applied voltage promotes microbial activity of marine anammox bacteria for nitrogen removal in saline wastewater treatment

To date, the application of marine anammox bacteria (MAB) is still a challenge in saline wastewater treatment due to the low growth rate and high sensitivity. Herein, bioelectrochemical system with applied voltage was exerted for the first time to promote the activity of MAB for removing nitrogen from saline wastewater. At the optimal voltage of 1.5 V, the mean total nitrogen removal rate (TNRR) reached the maximum of 0.65 kg/m3•d, which was 27.45% higher than that without applied voltage. Besides, applied voltage reduced the microbial diversity of MAB-based consortia, but the relative abundance of Candidatus Scalindua increased by 4.63% at 1.5 V compared with that without applied voltage. Also, proper applied voltage promoted the secretion of EPS and heme c, which resulted in the enhancement of MAB activity. Based on the remodified Logistic model analysis, the lag time of the nitrogen removal process was shortened by 0.72 h at the voltage of 1.5 V. Furthermore, it was found that higher voltage (> 2.0 V) had a negative effect on the MAB activity for low TNRR of 0.33 kg/m3•d (2.5 V). However, TNRR increased back to 0.61 kg/m3•d after removing the high applied voltage, which implied that the bioactivity was recoverable after being inhibited. These findings demonstrated that external electrical stimulation is an effective strategy to promote nitrogen removal and MAB activity for treating saline wastewater.

Applicability of two-stage anoxic/oxic shortcut nitrogen removal via partial nitrification and partial denitrification for municipal wastewater by adding sludge fermentation products continuously

Partial nitrification and partial denitrification combined with anammox is a promising process for sewage treatment. In this study, real municipal wastewater was treated in a continuous two-stage anoxic/oxic (A/O) reactor. External mixed sludge fermentation products were added in the anoxic zone, simultaneously achieving partial nitrification and partial denitrification and achieving a high and relatively stable accumulation of nitrite. The maximum accumulation rates of NO2−-N in A1.2 and A2.1-A2.4 zones of the reactor reached 70% and 61%–37%, respectively, which improved denitrification efficiency and created conditions that supported the coupling of subsequent anammox. The influent nitrogen load of the system was 0.078 kg/(m3•d), and the mean influent and effluent total nitrogen were 51 and 12 mg/L, respectively. The mean total nitrogen removal rate reached 76%. Further analysis revealed that Hyphomicrobium (incomplete denitrifiers) and Nitrosomonas (ammonia oxidizing bacteria) were enriched, which may have facilitated the high nitrite accumulation. Moreover, the batch test showed that adding sludge fermentation during denitrification significantly suppressed nitrite reduction, resulting in the nitrite accumulation.

Intermittent operating characteristics of an ecological soil system with two-stage water distribution for wastewater treatment

Ecological soil systems (ESSs) are usually used to remove nitrogen from wastewater. Due to the poor denitrification performance of traditional ecological soil systems (ESSs), this study proposes a two-stage water distribution system to improve the nitrogen removal. The effects of different distribution ratios on the system treatment effect were studied in an intermittent operation mode. After determining the optimal distribution ratio and intermittent operation conditions, the dynamics of system inflow, outflow, and nitrogen removal were monitored. Theoretical analysis of the denitrification mechanism was carried out. The results showed that the optimum water distribution ratio was 2: 1, and a mean total nitrogen removal rate of 60.42% was achieved, which is 23.09% greater than that is typically achieved by the single-section ecological system. Under optimum distribution ratio conditions, the system also demonstrated effective removal of chemical oxygen demand (COD), total phosphorus (TP) and ammonia nitrogen (NH4+-N), allowing the effluent to satisfy China's urban sewage treatment plant level B emission standards.

New nitrogen removal pathways in a full-scale hybrid constructed wetland proposed from high-throughput sequencing and isotopic tracing results

Constructed Wetlands (CWs), which usually feature limited supply of electron acceptors, possess complex microbial nitrogen removal pathways. Based on Illumina high-throughput sequencer, 15N isotopic tracer, and three years of physicochemical analysis, in this study, we report on a complex microbial consortium responsible for the nitrogen removal in a full-scale hybrid CW, consisted of vertical-baffled flow wetland (VBFW, first stage) and horizontal subsurface flow wetland (HSFW, second stage), receiving municipal sewage. Two organotrophic anaerobic ammonium oxidation (anammox) bacteria, Candidatus ‘Anammoxoglobus propionicus’ and ‘Brocadia fulgida’, chemolitho-autotrophic denitrifiers mainly Thiobacillus denitrificans, heterotrophic denitrifiers, ammonia oxidizers, and nitrite oxidizers were found in the HSFW, which achieved a mean total nitrogen removal load of 3.7gNm−2 d−1 in the summer season. A phylogenetic analysis and isotopic incubation experiment revealed that simultaneous autotrophic denitrification, heterotrophic denitrification and anammox processes contributed to the nitrogen loss from the system, which composed of a complex nitrogen removal scheme in a full-scale CW for low-strength municipal sewage treatment. Sulphur-oxidizing Thiobacillus denitrificans, the most abundant bacterial species in HSFW sediments, can convert nitrate to nitrite and support anammox bacteria with the necessary substrate to complete nitrogen removal. The present study confirmed the presence of anammox process in a full-scale CW and indicated that the nitrogen removal pathways in CWs are much more complex than we previous thought.

Seasonal nutrient uptake of plant biomass in a constructed wetland treating piggery wastewater effluent

The surface-flow constructed wetland (CW) located in Nonsan City, South Korea, and constructed as the final stage of a piggery wastewater treatment plant that aims to treat high nutrient content effluent during dry days and stormwater runoff during wet days was monitored from October 2008 to November 2011. This research investigated the seasonal nutrient uptake of plant biomass in the CW and nutrient concentration changes in each treatment region under monsoon and temperate climate conditions. Results showed that the mean total nitrogen removal during summer (June to August) was higher by 13% than in spring (March to May), while total phosphorus removal was higher by 22% in fall (September to November) than in winter (December to February). All plants in the CW reached their maximum biomass coverage and weight in summer and minimum growth in winter. The highest N and P content in plants occurred in September with 583.2 g/m(2) and August with 62.0 g/m(2), respectively. Based on the results, it is recommended that the harvesting of plants should be conducted during the time of the peak nutrient uptake and before the plants release the nutrient content back to the CW. The dependence of nutrient removal efficiency on plants is not so significant. In order to increase the nutrient removal rate by plant uptake, it is suggested that the treatment regions in the CW be covered by plants.

Treatment of Domestic Sewage in an Anaerobic–Aerobic Fixed‐bed Reactor with Recirculation of the Liquid Phase

AbstractThis study reports the performance of a combined anaerobic–aerobic packed‐bed reactor that can be used to treat domestic sewage. Initially, a bench‐scale reactor was operated in three experimental phases. In the first phase, the anaerobic reactor was operated with an average organic matter removal efficiency of 77% for a hydraulic retention time (HRT) of 10 h. In the second phase, the reactor was operated with an anaerobic stage followed by an aerobic zone, resulting in a mean value of 91% efficiency. In the third and final phase, the anaerobic–aerobic reactor was operated with recirculation of the effluent of the reactor through the anaerobic zone. The system yielded mean total nitrogen removal percentages of 65 and 75% for recycle ratios (r) of 0.5 and 1.5, respectively, and the chemical oxygen demand (COD) removal efficiencies were higher than 90%. When the pilot‐scale reactor was operated with an HRT of 12 h and r values of 1.5 and 3.0, its performance was similar to that observed in the bench‐scale unit (92% COD removal for r = 3.0). However, the nitrogen removal was lower (55% N removal for r = 3.0) due to problems with the hydrodynamics in the aerobic zone. The anaerobic–aerobic fixed‐bed reactor with recirculation of the liquid phase allows for concomitant carbon and nitrogen removal without adding an exogenous source of electron donors and without requiring any additional alkalinity supplementation.

Biosolubilization of heavy metals from biosolids

Constructed Wetlands (CWs), which usually feature limited supply of electron acceptors, possess complex microbial nitrogen removal pathways. Based on Illumina high-throughput sequencer, 15N isotopic tracer, and three years of physicochemical analysis, in this study, we report on a complex microbial consortium responsible for the nitrogen removal in a full-scale hybrid CW, consisted of vertical-baffled flow wetland (VBFW, first stage) and horizontal subsurface flow wetland (HSFW, second stage), receiving municipal sewage. Two organotrophic anaerobic ammonium oxidation (anammox) bacteria, Candidatus ‘Anammoxoglobus propionicus’ and ‘Brocadia fulgida’, chemolitho-autotrophic denitrifiers mainly Thiobacillus denitrificans, heterotrophic denitrifiers, ammonia oxidizers, and nitrite oxidizers were found in the HSFW, which achieved a mean total nitrogen removal load of 3.7 g N m−2 d−1 in the summer season. A phylogenetic analysis and isotopic incubation experiment revealed that simultaneous autotrophic denitrification, heterotrophic denitrification and anammox processes contributed to the nitrogen loss from the system, which composed of a complex nitrogen removal scheme in a full-scale CW for low-strength municipal sewage treatment. Sulphur-oxidizing Thiobacillus denitrificans, the most abundant bacterial species in HSFW sediments, can convert nitrate to nitrite and support anammox bacteria with the necessary substrate to complete nitrogen removal. The present study confirmed the presence of anammox process in a full-scale CW and indicated that the nitrogen removal pathways in CWs are much more complex than we previous thought.

NITROGEN REMOVAL FOR ON-SITE SEWAGE DISPOSAL: A RECIRCULATING SAND FILTER/ROCK TANK DESIGN

ABSTRACT The nitrogen removal abilities of recirculating sand filter/rock tank (RSF) systems and conventional septic tank/soil absorption trench systems were compared in a field laboratory. The degree of total nitrogen removal was a function of both nitrification and denitrification. Nitrification was the limiting step for nitrogen removal in the RSF system. In the RSF systems, nitrification was achieved in recirculating sand filters, with an average of 66% for the two-year study period. Denitrification was achieved in buried rock tanks using three different carbon sources. With raw septic tank effluent as the carbon source, an average of only 25% denitrification was observed, while with methanol and ethanol as the carbon sources, mean denitrification was 99%. Relative to the conventional systems, the RSF systems achieved a mean total nitrogen removal of 36% with septic tank effluent as the carbon source and 78-82% with methanol and ethanol as the carbon sources.

Nitrogen removal in artificial wetlands

This report describes investigations which have demonstrated the exceptional utility of artificial wetlands for the removal of nitrate from secondary wastewater effluents at relatively high application rates. The artificial wetlands (14 in number) were plastic-lined excavations containing emergent vegetation growing in gravel. Without supplemental additions of carbon, total nitrogen removal efficiency was low (∼ 25%) in both vegetated and unvegetated beds. When methanol was added to supplement the carbon supply and stimulate bacterial denitrification, the removal efficiency was extremely high (95% removal of total nitrogen at a wastewater application rate of 16.8 cm day −1). Since methanol is a relatively expensive form of carbon, we tested the feasibility of using plant biomass, mulched and applied to the surface of marsh beds, as an alternate source of carbon. At a wastewater application rate of 8.4 cm day −1, the mean total nitrogen removal efficiency for the mulch-amended beds was 86%. When the application rate was higher (16.8 cm day −1) the mean total nitrogen removal efficiency was lower, 60% in the mulch-amended beds. By using plant biomass as a substitute for methanol, the energy savings for a treatment facility serving a small community (3785 m 3 day −1 or 1 mgd) would amount to the equivalent of 731 day −1 of methanol. As the cost of fossil fuel increases, energy cost will become a predominant factor in the selection of small (0.5–5 mgd) wastewater treatment systems. However, in many cases where natural wetlands are either geographically unavailable or protected from wastewater discharge by environmental, legal, or aesthetic restraints, artificial wetlands offer a viable alternative for energy-effective treatment of municipal and agricultural wastewater effluents.