Total Nitrogen Removal Rate Research Articles

Insights into nitrogen removal and microbial response of marine anammox bacteria-based consortia treating saline wastewater: From high to moderate and low salinities

Marine anammox bacteria (MAB) have promising nitrogen removal performance in high saline wastewater treatment. Nevertheless, the impact resulting from moderate and low salinities on MAB is still unclear. Herein, MAB were applied to treat saline wastewater from high to moderate and low salinities for the first time. Independent of salinities (35–3.5 g/L), MAB consistently exhibited good nitrogen removal performance, and maximum total nitrogen removal rate (0.97 kg/(m3·d)) occurred at 10.5 g/L salts. More extracellular polymeric substances (EPSs) were secreted by MAB-based consortia to resist hypotonic surroundings. However, a sharp EPS decrease was accompanied by the collapse of MAB-driven anammox process, and MAB granules disintegrated due to long-term exposure to salt-free environment. The relative abundance of MAB varied from 10.7% to 15.9% and 3.8% as salinity decreased from 35 to 10.5 and 0 g/L salts. These findings will provide practical implementation of MAB-driven anammox process treating wastewater with different salinities.

Iron-loaded sludge biochar alleviates the inhibitory effect of tetracycline on anammox bacteria: Performance and mechanism

The anaerobic ammonia oxidation (anammox) process is sensitive to environmental pollutants, such as antibiotics. In this study, the harmful effect of tetracycline (TC) on the performance of an anammox reactor and the mitigation of TC inhibition by iron-loaded sludge biochar (Fe-BC) were studied by analyzing extracellular polymeric substances (EPS), microbial community structure and functional genes. The total inorganic nitrogen (TIN) removal rate of the TC reactor was reduced by 5.86% compared to that of the control group, while that of the TC + Fe-BC reactor improved by 10.19% compared to that of the TC reactor. Adding Fe-BC increased the activity of anammox sludge by promoting the secretion of EPS (including protein, humic acids and c-Cyts). The results of the enzymolysis experiment showed that protein can improve the activity of anammox sludge, while the ability of polysaccharide to improve the activity of anammox was related to the treated enzymes. In addition, Fe-BC alleviated the inhibitory effect of TC by mediating the anammox electron transfer process. Furthermore, Fe-BC increased the absolute abundance of hdh and hzsB by 2.77 and 1.18 times compared to the TC reactor and improved the relative abundance of Candidatus Brocadia in the absence of TC. The addition of Fe-BC is an effective way to alleviate the inhibitory effect of TC on the anammox process.

A syphon-downflow hanging sponge (DHS) reactor for improving the denitrification efficiency of sewage water treatment

The study focused on developing a low-cost down-flow hanging sponge (DHS) to enhance denitrification. The DHS reactor was modified by connecting with a syphon tube to maintain aerobic and anaerobic conditions. This method can simultaneously achieve nitrification and denitrification, requiring no extra energy for pumping. The study had two phases to evaluate the denitrification efficiency of the syphoned reactor at different reactor configurations. In the first phase, the syphon height was equal to the reactor height, and a water column was developed inside the DHS to create an anaerobic zone. The sCOD removal rates of syphon–DHS and conventional-DHS (control) were 75 ± 20% and 73 ± 19%, respectively, and the removal rates were almost similar in both reactors. However, the total nitrogen (TN) removal rate of syphon–DHS was 19 ± 3%, six folds greater than that of the conventional-reactor. In phase II, the syphon height of the developed DHS was changed to 3/5 of the DHS height. The sCOD and NH4+-N removal of syphon–DHS in the second phase were 62 ± 33% and 62 ± 31%, respectively, and approximately similar to the convectional DHSs’ performance. The anaerobic zone of the reactor facilitated enhancing the TN removal two folds than the conventional-reactor and was measured as 18 ± 16%. Nitrifiers, denitrifiers and anammox bacteria were present in the sludge samples of syphon–DHS as nitrogen-removing bacteria. The developed anaerobic conditions in the syphon–DHS enhanced denitrification without using extra energy for operation.

Catalytic supercritical water oxidation of o-chloroaniline over Ru/rGO: Reaction variables, conversion pathways and nitrogen distribution

To ascertain the reaction variables on o-chloroaniline (o-ClA) mineralization, total nitrogen (TN) removal rate, and N-species distribution, o-ClA was subjected to catalytic supercritical water oxidation (CSCWO) in a fused quartz tube reactor (FQTR). The findings demonstrated that when the temperature, reaction time, and excess oxidant were 400 °C, 90 min, and 150%, respectively, the mineralization rate of o-ClA could reach more than 95%. Moreover, potential degradation pathways of o-ClA in supercritical water oxidation (SCWO) was proposed according to the GC-MS results. TN removal rate is significantly impacted by Ru/rGO, despite the fact that its catalytic effect on the mineralization of o-ClA was not particularly noteworthy. Compared with no catalyst, the TN removal rate of o-ClA obviously increased from 44.1% to 90.3% at 400 °C, 10 wt% Ru loading, 90 min and 200% excess oxidant. In addition, N-species distribution in SCWO and CSCWO were also investigated. Results indicated that the Ru/rGO catalyst could accelerate the oxidation of ammonia-N and convert it to nitrate-N, promoting N2 generation. Finally, the possible N transformation pathway in CSCWO of o-ClA was proposed. As a result, this work offers fundamental information about o-ClA catalytic oxidation removal in the SCWO process.

Root vertical spatial stress: A method for enhancing rhizosphere effect of plants in subsurface flow constructed wetland

The depth of the substrate of subsurface flow (SSF) constructed wetlands (CWs) is closely related to their cost and operation stability. To explore the physiological regulation mechanism of wetland plants and pollutant removal potential of SSF CWs under “vertical spatial stress of roots” (by greatly reducing the depth of the substrate in SSF CWs to limit the vertical growth space of roots, VSSR), the physiological response and wetland purification effect of a 0.1 m Canna indica L. CW under VSSR were studied compared with conventional SSF CWs (0.6 m, 1.2 m). The results demonstrated that VSSR significantly enhanced the dissolved oxygen (DO) concentration (p < 0.05) within the SSF CWs, with the DO in 0.1 m CW remaining stable at over 3 mg/L. Under the same hydraulic retention time (HRT), VSSR significantly improved the removal effect of pollutants (p < 0.05). The removal rates of COD, NH4+-N, and total phosphorus (TP) remained above 87%, and the mean removal rates of total nitrogen (TN) reached 91.71%. VSSR promoted the morphological adaptation mechanisms of plants, such as significantly increased root-shoot ratio (p < 0.05), changed biomass allocation. Plants could maintain the stability of the photosynthetic mechanism by changing the distribution of light energy. The results of microbial community function prediction demonstrated that aerobic denitrification was the main mechanism of N transformation in the 0.1 m CW under VSSR. VSSR could induce the high root activity of plants, augment the concentration of root exudates, enhance the redox environment of the plant rhizosphere, further foster the enrichment of aerobic denitrifying bacteria, and strengthen the absorption efficiency of wetland plants and substrate, thus achieving an efficient pollutant removal capacity. Studies showed that VSSR was an effective means to enhance the rhizosphere effect of plants and pollutant removal in SSF CWs.

Enhancement of nitrogen removal in coupling Anammox and DAMO via Fe-modified granular activated carbon

Anaerobic ammonium oxidation (Anammox) coupled with Denitrifying anaerobic methane oxidation (DAMO) is an attractive technology to simultaneously remove nitrogen and mitigate methane emissions from wastewater. However, its nitrogen removal rate is usually limited due to the low methane mass transfer efficiency, low metabolic activity and slow growth rate of functional microorganisms. In this study, GAC and Fe-modified GAC (Fe-GAC) were added into Anammox-DAMO process to investigate their effects on nitrogen removal rates and then reveal the mechanism. The results showed that after 80-day experiments, the total nitrogen removal rate was slightly improved in the presence of GAC (3.94 mg L−1·d−1), while it reached high as 16.66 mg L−1·d−1 in the presence of Fe-GAC, which was ca.17 times that of non-amended control group (0.96 mg L−1·d−1). The addition of Fe-GAC stimulated the secretion of extracellular polymeric substance (EPS), improved the electron transfer capability and promoted the production of Cytochrome C. Besides, the key functional enzyme activities (HZS, HDH and NAR) were highest in the Fe-GAC group, which were approximately 1.06–1.56 times higher than those of GAC-amended and blank control groups. Microbial community analysis showed that the abundance of the DAMO archaea (Candidatus Methanoperedens) and Anammox bacteria (Candidatus Brocadia) were remarkably increased with the addition of Fe-GAC. Functional genes associated with nitrogen removal and methane oxidation in Fe-GAC system were up-regulated. This study provides a promising strategy for achieving high rate of nitrogen removal upon Anammox-DAMO process.

Simultaneous partial nitrification, Anammox and nitrate-dependent Fe(II) oxidation (NDFO) for total nitrogen removal under limited dissolved oxygen and completely autotrophic conditions

Sustainable nitrogen removal from wastewater at reduced energy and/or chemical consumptions is challenging. This paper investigated, for the first time, the feasibility of coupled partial nitrification, Anammox and nitrate-dependent Fe(II) oxidation (NDFO) for sustainable autotrophic nitrogen removal. With NH4+-N as the only nitrogen-containing compound in the influent, near-complete nitrogen removal (a total of 97.5 % with a maximal total nitrogen removal rate of 6.64 ± 2.68 mgN/L/d) was achieved in a sequencing batch reactor for a 203-d operation without organic carbon source addition and forced aeration. Anammox (predominated by Candidatus Brocadia) and NDFO bacteria (such as Denitratisoma) were successfully enriched, with total relative abundances up to 11.54 % and 10.19 %, respectively. Dissolved oxygen (DO) concentration was a key factor affecting the coupling of multi (ammonia oxidization, Anammox, NDFO, iron-reduction, etc.) bacterial communities, resulting in different total nitrogen removal efficiencies and rates. In batch tests, the optimal DO concentration was 0.50–0.68 mg/L with a maximal total nitrogen removal efficiency of 98.7 %. Fe(II) in the sludge not only competed with nitrite oxidizing bacteria for DO to prevent complete nitrification, but promoted the transcription of NarG and NirK genes (10.5 and 3.5 times higher than the group without Fe(II) addition) as indicated by the reverse transcription quantitative polymerase chain reaction (RT-qPCR), resulting in increased NDFO rate (by 2.7 times) and promoted NO2−-N generated from NO3−-N, which back fed the Anammox process, achieving near-complete nitrogen removal. The reduction of Fe(III) by iron-reducing bacteria (IRB) and hydrolytic and fermentative anaerobes enabled a sustainable Fe(II)/Fe(III) recycling, avoiding the need in continuous Fe(II) or Fe (III) dosage. The coupled system is expected to benefit the development of novel autotrophic nitrogen removal processes with neglectable energy and material consumptions for the treatment of wastewater with low organic carbon and NH4+-N contents in underdeveloped regions, such as decentralized rural wastewaters.

Experimental investigation on decomposition characteristics of doxycycline in wastewater using hydrothermal treatment: Exploring the way to complete decomposition

Doxycycline is widely found in medical and aquaculture wastewater, posing a great threat to the ecological environment. In this study, the doxycycline was decomposed by hydrothermal method, and its decomposition properties and paths were analyzed. By using univariate experimental method, the influence of hydrothermal temperature (100–340 °C), hydrothermal time (30–120 min) and mass concentration (1–4 wt%) on the decomposition rate of doxycycline, chemical oxygen demand and nitrogen distribution in the product were studied, and the Pearson correlation coefficient of chemical oxygen demand, Total nitrogen and doxycycline removal rate was obtained. The results showed that the removal rate of doxycycline increased with the hydrothermal temperature, decreased with the reactant concentration, and increased first and then decreased with the hydrothermal time. The quantitative relation between the removal rate of doxycycline and operation conditions (temperature, time, and concentration) was obtained by using the response surface method, and the optimization conditions of the hydrothermal decomposition of doxycycline were gotten. The averaged removal rate of doxycycline reached 99.5% at temperature of 260 °C, reaction time of 102.2 min, and mass concentration of 1.4 wt%. Finally, the liquid chromatography and mass spectrometry were used for quantitative and qualitative analysis of liquid products, and three potential hydrothermal decomposition routes of doxycycline were proposed. This study will lay the foundation for the hydrothermal treatment of medical and aquaculture wastewater containing antibiotics.

Distribution and dynamics of antibiotic resistance genes in a three-dimensional multifunctional biofilm during greywater treatment

Antibiotic resistance genes (ARGs) have been identified as serious threats to public health. Despite the widespread in various systems, dynamics of ARGs in three-dimensional multifunctional biofilm (3D-MFB) treating greywater are largely undefined. This work tracked the distributions and dynamics of eight target genes (intI1, korB, sul1, sul2, tetM, ermB, blaCTX-M and qnrS) in a 3D-MFB during greywater treatment. Results showed that hydraulic retention times at 9.0 h achieved the highest linear alkylbenzene sulfonate (LAS) and total nitrogen removal rates at 99.4% and 79.6%, respectively. ARGs presented significant liquid-solid distribution feature, but non-significant with biofilm position. Intracellular ARGs (predominant by intI1, korB, sul1 and sul2) at bottom biofilm were 210- to 4.2 × 104- fold higher than that in cell-free liquid. Extracellular polymeric substances (EPS)-attached LAS showed linear relationship with most of ARGs (R2 > 0.90, P < 0.05). Sphingobacteriales, Chlamydiales, Microthrixaceae, SB-1, Cryomorphaceae, Chitinophagaceae, Leadbetterella and Niabella were tightly bound up with target ARGs. Key is that EPS-attached LAS considerably determines the occurrence of ARGs, and microbial taxa play an important role in the dissemination of ARGs in the 3D-MFB.

Formation of microbial products by activated sludge in the presence of sulfamethoxazole (SMZ) and zinc oxide nanoparticles (ZnO NPs) in long-term operated sequencing batch reactors

Emerging contaminants, sulfamethoxazole (SMZ) and zinc oxide nanoparticles (ZnO NPs), were selected as the target pollutants for this study and using a sequencing batch reactor (SBR), the coexistence effect of antibiotics and nanomaterials on the activated sludge system was investigated. The results showed that the average total nitrogen (TN) removal rates during long-term operation (60 days) for the blank group, the reactor with SMZ, ZnO NPs, and SMZ combined with ZnO NPs were 80.47 %, 78.22 %, 73.77 %, and 72.52 %, respectively, and the average total phosphorous (TP) removal rates were 84.17 %, 82.48 %, 74.69 %, and 76.20 %, respectively. This indicates that ZnO NPs, rather than SMZ, have a negative effect on the treatment efficiency of the system, whereas the coexistence of the two has not yet had a higher effect. Both SMZ and ZnO NPs caused an increase in soluble microbial products (SMP) and extracellular polymers (EPS). High-throughput sequencing results showed that the relative abundance of nitrifying, denitrifying, and phosphorus-polymerizing bacteria was the highest in reactor R1, and the long-term stress of either SMZ or ZnO NPs caused a decrease in these functional bacteria. Finally, the comprehensive mechanism of SMZ and ZnO NPs in activated sludge is discussed.

Effect of salinity stress on nitrogen and sulfur removal performance of short-cut sulfur autotrophic denitrification and anammox coupling system

The effects of salinity on anaerobic nitrogen and sulfide removal were investigated in a coupled anammox and short-cut sulfur autotrophic denitrification (SSADN) system. The results revealed that salinity had significant nonlinear effects on the nitrogen and sulfur transformations in the coupled system. When the salinity was <2 %, the anammox and SSADN activities increased with increasing salinity, and the total nitrogen removal rate, S0 production rate, and nitrite production rate were 0.41 kg/(m3·d), 0.37 kg/(m3·d), and 0.28 kg/(m3·d), respectively. With continuous increase of salinity, the performances of the anammox and SSADN gradually decreased, and the three indicators decreased to 0.14 kg/(m3·d), 0.22 kg/(m3·d), and 0.14 kg/(m3·d) at 5 % salinity, respectively. When the salinity reached 5 %, the nitrogen removal contribution of anammox decreased to 68.4 %, while the contribution of the sulfur autotrophic denitrification increased to 31.6 %. The coupled system recovered in a short time after alleviation of the salinity stress, and the SSADN activity recovery was faster than anammox. The microbial community structure and functional microbial abundance in the coupled system changed significantly with increasing salinity, and the functional microbial abundance after recovery was considerably different from the initial state.

New insights into the microalgal culture using kitchen waste: Enzyme pretreatment and mixed microalgae self-flocculation

With the development of the catering industry, the output of kitchen waste increases significantly. To respond to the carbon neutral policy, this study proposed the technology of combining kitchen waste treatment and microalgae culture. The kitchen waste was pretreated by enzymatic hydrolysis, and the optimal composition and proportion of compound enzymes were investigated. The results showed that acid protease: α-amylase: glucoamylase: cellulase = 50:1:10:1 (enzyme activity ratio) was chosen as the most suitable compound enzymes according to the growth and water purification effect of Scenedesmus obliquus in the hydrolysate. To optimize the microalgae biomass accumulation especially high-value substances, microalgae harvesting, and water purification effects, mixed culture of microalgae was performed. Chlorella sp. HQ and Scenedesmus sp. LX1 were the best combination, in which the contents of lipid, polysaccharide, and protein were 8.78 ± 4.48%, 2.11 ± 0.14%, and 8.38 ± 0.12%, respectively. After combination, the flocculation rate reached up to 63.75 ± 1.08%, and the removal rates of chemical oxygen demand, total nitrogen, and total phosphorus were 88.54 ± 0.58%, 90.97 ± 4.73%, and 88.81 ± 4.75%, respectively. The above results indicated that the enzymatic hydrolysate of kitchen waste had a promising application prospect in microalgae culture, and self-flocculation of mixed microalgae had the potential to recover biomass.

Eutrophic water remediation efficiency of algicidal bacteria, Cellvibrio sp. G1 and Chitinimonas sp. G2, and their influence on microbial community structure

Algal blooms that occur periodically in rivers, lakes, and reservoirs are associated with the cumulative effects of excess nutrients from industrial and agricultural development. Algicidal bacteria can be used as environmentally friendly biocontrol agents to manage harmful algal blooms in eutrophic water. However, there is still a dearth of studies on the effects of mixed algicidal agents, the persistence of algae removal efficiency, and the impacts on native aquatic microbial communities. Two strains of algicidal bacteria, Cellvibrio sp. G1 and Chitinimonas sp. G2, were previously isolated and purified from reservoir sediment. Herein, G1 and G2 broth cultures, alone and in combination (1:1, V/V), were added to eutrophic water collected from a park at the volume ratio of 5 %. Eutrophic water remediation efficiency under different treatments was monitored for 30 days, and microbial community dynamics in water were analyzed by full-length sequencing of the 16S rRNA genes. The best algae removal efficiency was observed in the water treated with G1 alone, as indicated by the highest algae removal rate of 41.3 %. The total nitrogen removal rates of G1, G2, and their combination were 33.47 %, 23.65 %, and 28.88 %, respectively; ammonia‑nitrogen removal rates were 24.11 %, 25.02 %, and 19.63 %, respectively; total phosphorus removal rates were 24.11 %, 25.02 %, and 19.63 %, respectively; and orthophosphate removal rates were 46.11 %, 44.37 %, and 27.92 %, respectively. In the water treated with G1 and/or G2, the major genera with algicidal capacity (i.e., Cellvibrio and Chitinimonas) were outcompeted by the well adapted genera (e.g., Pseudomonas). At the late stages of treatment, the algicidal genera decreased in relative abundance, leading to decline in algae removal efficiency and increase in chlorophyll concentration. Based on both eutrophic water remediation efficiency and environmental adaptability, G1 alone was superior to G2 alone or in combination with G1, thus having potential practical implications.

Purification efficiency of Pyropia-processing wastewater and microalgal biomass production by the combination of Chlorella sp. C2 cultivated at different culture temperatures and chitosan

To elucidate the impacts of culture temperature on nutrient removal efficiency of Pyropia-processing wastewater (PPW) and microalgal biomass production, Chlorella sp. C2 was employed and cultivated in raw PPW under different temperatures. Results showed that, after incubating for 7 days, higher biomass (0.50 g/L) and total lipids (21.84 %) were attained at 35 °C. The maximal chemical oxygen demand (COD), phycobiliprotein, total nitrogen and total phosphorus removal rates were observed at 30–35 °C and separately reached 62.41 %, 92.61 %, 92.19 % and 98.33 %. Interestingly, COD removal efficiencies of Chlorella cells, cultivated for 3, 5 and 7 days at 30–35 °C, 15–25 °C and 10 °C respectively, could reach >75 % with assistance from 60–80 mg/L chitosan. Meanwhile, the clarification efficiency of chitosan on algal cells reached >95 %. It suggests that Chlorella strain cultured at altered temperatures could efficiently remove PPW nutrients assisted by moderate chitosan, simultaneously achieving the rapid harvest of microalgae.

Decontamination and Ecological Restoration Performance of a Bioretention Cell-Microbial Fuel Cell under Multiple-Antibiotics Stress

Antibiotics are refractory pollutants that have been widely found in various environmental media such as soil and surface water. Existing sewage treatments perform poorly at preventing antibiotics in urban sewage from polluting natural environments. In this study, we designed a bioelectrically enhanced bioretention cell system (bioretention cell-microbial fuel cell, BRC-MFC) that utilizes the unique structure of the BRC system to improve the removal of sewage antibiotics. This new system can efficiently remove antibiotics by using a synergy of plant absorption, filler adsorption, filler filtration and microbial degradation. To study the influences of multiple-antibiotics stress on the decontamination performance of BRC-MFC, ofloxacin (OFLX) and tetracycline (TC) were selected as target antibiotics, and five BRC-MFCs were built to treat sewage containing antibiotics of different concentrations. The concentrations of pollutant in the influent and effluent were measured and the pollutant removal performance of BRC-MFC was studied. The diversity of rhizosphere microorganisms and the abundance of denitrifying functional genes were analyzed. Experimental results showed that over 90% of OFLX and TC in each BRC-MFC were removed, with the removal rates positively correlating with the concentration of antibiotics. In addition, the removal rates of chemical oxygen demand (COD) in BRC-MFC were both over 90%, while the removal rate of total nitrogen (TN) was around 70%. Meanwhile, antibiotics could significantly improve the removal of ammonia nitrogen (NH4+-N, p &lt; 0.01). The microbial richness decreased, and we found that combined antibiotic stress on microorganisms was stronger than single antibiotic stress. The abundance of denitrifying functional genes was reduced by antibiotic stress. The results of this study provide reference values for other projects focusing on removing various antibiotics from domestic sewage using BRC-MFC.

Rapid Start-Up Characteristics of Anammox under Different Inoculation Conditions

The long multiplication time and extremely demanding enrichment environment requirements of Anammox bacteria (AAOB) have led to difficult reactor start-ups and hindered its practical dissemination. Few feasibility studies have been reported on the recovery of AAOB activity initiation after inlet substrate disconnection caused by an unfavorable condition, and few factors, such as indicators of the recovery process, have been explored. Therefore, in this experiment, two modified expanded granular sludge bed reactors (EGSB) were inoculated with 1.5 L anaerobic granular sludge (AGS) + 1 L Anammox sludge (AMS) (R1) and 2.5 L anaerobic granular sludge (AGS) (R2), respectively. After a long-term (140 days) starvation shock at a high temperature (38 °C), the bacteria population activity recovery experiments were conducted. After 160 days, both reactors were successfully started up, and the total nitrogen removal rates exceeded 87%. Due to the experimental period, the total nitrogen removal rate of R2 was slightly higher than that of R1 in the final stage. However, it is undeniable that R2 had a relatively long activity delay during startup, while R1 had no significant activity delay during startup. The sludge obtained from R1 had a higher specific anammox activity (SAA). Analysis of the extracellular polymer substances (EPS) results showed that the extracellular polymer content in R1 was higher than that in R2 throughout the recovery process, indicating that R1 had higher sludge stability and denitrification performance. Scanning electron microscopy (SEM) analysis showed that more extracellular filamentous bacteria could be seen in the R1 reactor with better morphology of Anammox bacteria. In contrast, the R2 reactor had fewer extracellular hyphae and micropores as a percentage and higher filamentous bacteria content. The results of microbial 16SrDNA analysis showed that R1 used AAOB as inoculum to initiate Anammox, and the reactor was enriched with Anammox bacteria earlier and in much greater abundance than R2. The experimental results indicated that inoculating mixed anaerobic granular sludge and Anammox sludge to initiate an anammox reactor was more effective.

Assembled denitrifying consortia for efficient nitrate removal under low-COD/N conditions

The low denitrification efficiency of wastewater under a low COD/N ratio is an intractable barrier in the nitrate contamination remediation field. In response to this predicament, the present study enriched a high-efficiency denitrification community with the selection pressure of gradually shifting the COD/N ratio from 8.0 to 3.2 and then assembled a simplified denitrification microbial consortium based on representative species isolated from this community. The continuous culture resulted in a novel consortium consisting of Acinetobacter sp., Pseudomonas stutzeri, Paracoccus sp. and Comamonas nitrativorans, which achieved a 98.4% total nitrogen (TN) removal rate at a COD/N ratio of 3.2. Selectively culturing three of the four species indicated that delicate interspecies cooperation occurred among the four species. P. stutzeri and Paracoccus sp. were found to be the key to NOx reduction. Acinetobacter sp. could drive the co-aggregating of other species, and C. nitrativorans provided the other three microorganisms with electron donors (3-hydroxybutyric acid and succinic acid) after the depletion of acetate at COD/N 3.2. Further bioaugmentation studies showed that the assembled consortium could effectively enhance the denitrification performance of simulated nitrate-contaminated groundwater under low COD/N ratios. Overall, this study not only assembled an excellent four-species denitrifying consortium for nitrate removal and explored the interspecies cooperation in detail but also provided a novel approach to develop bioaugmentation technology in the future.

Efficient nitrogen removal through coupling biochar with zero-valent iron by different packing modes in bioretention system

Three kinds of bioretention were designed to explore the effects of zero-valent iron (ZVI) and biochar on the nitrogen removal performance and to seek a more reasonable packing method in this study. The results showed that the effluent removal rates of nitrate, ammonium and total nitrogen were 53.30 ± 12.68%, 98.41 ± 0.38% and 64.03 ± 8.72% respectively in Bioretention-3 during the rainfall events, while the nitrate concentration decreased gradually with the increase of drying time. According to the batch experiment, it was found that zero-valent iron could release continuously and stably in Bioretention-3 and Bioretention-1 due to the interception effect of biochar on dissolved oxygen. In addition, biochar in soil layer could protect zero-valent iron from excessive oxidation while biochar in the substrate layer could release organic matter to promote heterotrophic denitrification. Microbial community analysis showed that the dominant phyla were Proteobacteria (20.92–40.81%) and Actinobacteriota (9.89–24.54%). The dominant nitrifying genera was Nitrospira while there were also aerobic denitrifying bacteria (Sphingomonas, Bradyrhizobium and Chryseolinea, etc.) in soil layer. In the substrate layer, there was more ferrous iron-mediated autotrophic denitrification process (Thiobacillus, Geobacter and Denitratisoma, etc.) in Bioretention-1 and Bioretention-3 while a larger proportion of Dissimilatory Nitrate Reduction to Ammonium process (DNRA) (Bacillus, Desulfovibrio and Pseudomonas, etc.) in Bioretention-2. In general, this study showed that biochar addition in soil coupled with mixing zero-valent iron and biochar as substrate layer was a more stable and efficient design through various aspects of evidence. It provides a new way for how to use zero-valent iron and biochar to improve nitrogen removal capacity in stormwater management.

Exploring interactions between quorum sensing communication and microbial development in anammox membrane bioreactor

The long duration required to enrich bacteria that perform anaerobic ammonium oxidation (anammox) limits their wide application in wastewater treatments. Anammox enrichment requires extensive microbial development, but the mechanisms involved are still being studied. Here, a total nitrogen removal rate of 1.22 kg N/m3/day was obtained over 280 days when anammox was enriched in a membrane bioreactor (MBR). Interactions between quorum sensing (QS) and microbial community development were investigated. Acyl-homoserine lactones (AHLs) were detected in the MBR effluent, with C8-HSL having the highest concentration (2.05 ng/L). The specific anammox activity (SAA) of the biomass increased from 335.8 (± 16.4) mg NH4+-N/g VSS/day to 382.9 (± 19.6) mg NH4+-N/g VSS/day with 0.1 μM C8-HSL addition. Anammox bacteria from the genus Candidatus Brocadia were enriched in the MBR. Metagenomic analysis suggested quorum sensing dependent on AHL and c-di-GMP (bis-[3′−5′]-cyclic dimeric guanosine monophosphate) contributed to microbial development. C-di-GMP-dependent quorum sensing may impact the formation of extracellular polymeric substances (EPS) and cell motility of biomass.

Evaluation of the Combined C/N ratio, DO Set Point, and HRT Influence on Nitrogen Removal Rate in One-Stage Reactor Through Partial Nitrification Anammox Process During Treatment of Synthetic Digestate of Poultry Litter Wastewater

Highlights A one-stage reactor PN/A process was developed and evaluated. The highest TN removal rate was 87.3% for the PN/A process to treat synthetic wastewater containing poultry litter at room temperature. Bacterial composition of mature sludge community of wastewater was investigated in this study. Adjusted parameters controlled the growth of AOB and NOB. Abstract. Anammox is an increasingly common process used for the treatment of municipally rejected water and even mainstream wastewater due to its low oxygen demand. However, anammox is not commonly utilized in the treatment of poultry litter because of its high organic content, which would inhibit the anammox process. One-stage partial nitrification and anammox (PN/A) process was developed and evaluated for removing total nitrogen (TN) content from synthetic digestate of poultry litter using a sequencing batch biofilm reactor (SBBR). Independent variables including carbon to nitrogen ratio (C/N) at 1, 2, and 3, dissolved oxygen level (DO, mg/L) at 0.2, 0.35, and 0.5, and hydraulic retention time (HRT, h) at 24, 48, and 72 were examined using Central Composite Design (CCD) coupled with Response Surface Methodology (RSM) to optimize the TN removal rate. Results showed that the one-stage PN/A process achieved an optimal TN removal rate of 87.3% and an optimal NH4+-N removal rate of 100% when C/N, DO, and HRT were 1, 0.5 mg/L, and 72 h, respectively. The quadratic regression model developed (p = 0.0018) perfectly fitted the nitrogen removal efficiency of the SBBR. The uncertainty analysis showed an error range of 0.12% to 0.96% for the model's accuracy within the DO, C/N ratio, and HRT ranges tested. The bacterial consortium analysis suggested that the control of the growth of ammonium oxidizing bacteria (AOB) and nitrite-oxidizing bacteria (NOB) was achieved. Keywords: Anammox, Comammox, Nitrospira, Partial nitrification, Poultry litter wastewater.