Wastewater Nitrogen Removal Research Articles

Enhancing biological dissolved organic nitrogen removal in landfill leachate wastewater: The role of sodium acetate co-metabolism

Dissolved organic nitrogen (DON) comprises approximately 25% of dissolved nitrogen in landfill leachate wastewater (LLW), posing potential risks such as stimulating algal growth and forming disinfection by-products if not treated properly. While DON characterization and removal by physicochemical methods in wastewater treatment systems have been examined, biological strategies for effective DON removal remain less developed. This study explores the influence of sodium acetate addition during denitrification process on LLW DON removal. With sodium acetate addition (Stage I), we achieved 99% ammonia removal, 94% total inorganic nitrogen (TIN) removal, and 45% DON removal. Fourier-transform ion cyclotron resonance mass spectrometry (FTICR-MS) results suggested the majority of sulfur-containing DON molecules were eliminated in Stage I. Conversely, in the absence of sodium acetate (Stage II), while 99% ammonia removal was maintained, TIN removal dropped to around 10%, and DON concentrations (largely sulfur-containing DON) increased by approximately 22%. Cycle tests revealed similar DON reductions in the aerobic phase across both stages, whereas in the anoxic phase, DON concentrations decreased in Stage I but increased in Stage II. Functional gene prediction indicated higher expression of decarboxylase and deaminase genes in Stage I compared to Stage II. Consequently, this study posits that sodium acetate addition enhances DON removal, potentially via co-metabolism.

Enhanced biodegradability and ammonia nitrogen removal of high-salinity pharmaceutical wastewater by ozonation with iron-based monolithic catalyst packing

High-salinity pharmaceutical wastewater has gained much attention due to its refractory organic contaminants which are difficult to be effectively removed by traditional treatment methods, catalytic ozonation as an effective method for advanced treatment is expected to solve this problem. In this research, the treatment efficiency of ozonation with iron (Fe)-based monolithic catalyst packing for high-salinity pharmaceutical wastewater advanced treatment was evaluated, and a combination of catalytic ozonation-anoxic oxic (CO-AO) process has been applied to improve the existing wastewater treatment system. The influence of the ratio of O3 dose to influent COD (O/C) on COD, BOD5/COD, NH4+-N and NO3−-N was systematically investigated by regression analysis. Results showed that Fe-based monolithic catalyst packing could effectively remove COD (163.5 mg/L to 118.2 mg/L on average) and NH4+-N (70.3 % on average) from wastewater and improve the biodegradability of wastewater (the average BOD5/COD increased from 0.065 to 0.165). Regression analysis showed that the biodegradability of high-salinity pharmaceutical wastewater improved with the increase of O/C in the range of 0.1–1.3. The operation data of 588 days showed that the catalytic ozonation-anoxic oxic process could greatly reduce the effluent COD and NH4+-N concentration. The Cl− was the key factor associated with a large amount of NO3−-N in effluent. The long-term deposition of CaCO3 has a negative effect on the treatment effect, but it can improve the corrosion resistance of the catalyst. The findings of this study clearly demonstrate the significant potential and feasibility of Fe-based monolithic catalyst packing, also promote the application of the catalytic ozonation-anoxic oxic in high-salinity actual wastewater treatment.

Sustainable mainstream deammonification by ion exchange and bioregeneration via partial nitritation/anammox

The partial nitritation and anammox (PN/A) process has gained popularity for the treatment of nitrogen removal in wastewater due to significant energy savings and its potentially much lower CO2 footprint. However, the treatment of mainstream municipal wastewater by PN/A has been limited mainly due to its unsuitable composition. In this research, we apply ion exchange using a zeolite column to selectively remove and concentrate ammonium from mainstream municipal wastewater. After an absorption phase, the ion exchange column is regenerated using a brine solution. The ammonium rich brine is “bioregenerated” in a PN/A reactor where ammonium is converted to nitrogen gas allowing the brine to be reused in another cycle of ion exchange regeneration. To successfully remove ammonium from the spent brine, anammox and ammonia oxidizing bacteria (AOB) were first cultivated in separate reactors under hypersaline conditions (4.0 %) and later combined in a single PN/A reactor. After continuous operation with sea water, the PN/A reactor treated recirculating brine from the ion exchange column for 48 cycles of ammonium absorption and bioregeneration with minimal blowdown. The various cations of the regenerant solution were stable except for calcium that reached very high values upwards of 3000 mg/L as Ca2+ and finally caused PN/A reactor failure due to mineral precipitation. The buildup of high concentrations of calcium in the regenerant was addressed in two ways: 1) 20 % regenerant replacement per cycle, and 2) precipitation of CaCO3 via the addition of sodium carbonate. Both methods were applied to 30 absorption and bioregeneration cycles each and shown to be effective in keeping calcium concentrations from accumulating in the regenerant allowing for stable PN/A reactor operation.

Impact of wastewater treatment upgrade and nitrogen removal on bacterial communities and their interactions in eutrophic prairie streams.

Eutrophication can impact bacteria by altering fluxes and processing of nutrients and organic matter. However, relatively little is known of how bacterial communities, diversity, and interactions with phytoplankton might respond to nutrient management. We used 16S rRNA amplicon sequencing to compare bacterial assemblages in the water column upstream (control) and downstream (impact) of a wastewater treatment plant (WWTP) located on a eutrophic prairie stream. Sampling occurred before (2012) and after (2018) the 2016 biological nutrient removal (BNR) upgrade that removed >90% of nitrogen (N, mainly NH4+). Multivariate ordination suggested that effluent-impacted bacterial communities were associated mainly with elevated NH4+ concentrations before the upgrade, whereas those after BNR were characteristic of reference systems (low NO3-, diverse regulation). Genera such as Betaproteobacteria and Rhodocyclacea were abundant at impacted sites in 2012, whereas Flavobacterium and a potential pathogen (Legionella) were common at impacted sites in 2018. Nitrifier bacteria (Nitrospira and Nitrosomonas) were present but rare at all sites in 2012, but recorded only downstream of the WWTP in 2018. Generalized additive models showed that BNR reduced bacterial diversity, with ∼70% of the deviance in diversity explained by hydrology, pH, nutrients, and phytoplankton abundance. Overall, NH4+ removal reduced symptoms of cultural eutrophication in microbe assemblages.

Nitrification of an anaerobic filter effluent in a flat sheet membrane aerated biofilm reactor

Compared with activated sludge intensification by integrating membrane aerated biofilm reactors (MABRs) to promote sustainable nitrogen removal, treatment of anaerobic reactors effluents with MABRs is scarcely studied. Here the capability of a flat sheet MABR for nitrogen removal and nitrification of real wastewater previously treated in an anaerobic filter was analyzed. Removal of 71–81 % of ammonia with 54–72 % conversion to nitrate, while eliminating 13–28 % of total inorganic nitrogen in water containing 38–80 mg ammonia-N/L and 25–78 mg COD/L was achieved with aeration at atmospheric pressure. Experimental data in combination with stoichiometry and sequencing suggested a combination of autotrophic and heterotrophic bacteria associated to the nitrogen cycle was present in the biofilm. Nitrogen and ammonia removal rates up to 117 mg N/L-d and 258 mg N/L-d, respectively evidenced a competitive nitrogen conversion capability of the flat sheet MABR attained with non-pressurized aeration involving potential energy savings. Effluent content (mg/L) of ammonia 10–17, nitrite 13–23, nitrate 21–37 and phosphate 21–45, is suitable for further nitrogen removal or nutrient recovery as dissolved fertilizer for irrigation.

Nitrogen removal performance of aerobic denitrifying bacteria enhanced by an iron-anode pulsed electric field.

Pulsed electric field (PEF) technology has attracted considerable attention because it can efficiently treat pollutants that are difficult to degrade. In this study, a PEF system using iron as the electrode was constructed to investigate the effect of PEF-Fe on the growth and metabolism of aerobic denitrifying bacteria and the effectiveness of wastewater nitrogen removal. The chemical oxygen demand, NO3--N and nitrate removal rates were 98.93%, 97.60% and 24.40 mg·L-1·h-1, respectively, under optimal conditions. As confirmed in this study, PEF-Fe could improve the key enzyme activities of W207-14. Scanning electron microscopy revealed that the surface of PEF-Fe-treated W207-14 was intact and smooth without any irreversible deformation. Flow cytometry combined with fluorescence staining analysis also confirmed reversible electroporation on the cell membrane surface of PEF-Fe-treated W207-14. Differentially expressed gene enrichment analysis showed that PEF-Fe activated the transmembrane transport function of ATP-binding cassette transporte (ABC) transport proteins and enhanced the cell membrane permeability of aerobic denitrifying bacteria. The significant differential expression of iron-sulphur cluster proteins facilitated the regulation of electron transport and maintenance of the dynamic balance of iron ions within the PEF-Fe system.

Excellent treatment effect of actual wastewater from a pesticide plant using electro-Fenton process catalyzed by natural pyrite

The experiment used natural pyrite as catalyst for electro-Fenton process to treat actual wastewater containing high concentrations of chlorine salts from a pesticide factory in Guangdong province, China. It revealed that under the optimized conditions of initial pH of 3, electrode spacing of 4 cm, and current density of 40 mA/cm2, excellent treatment effect was achieved using 3 g/L pyrite as catalyst with graphite cathode and Ti/RuO2-IrO2-SnO2 anode after a duration of 3 h. Specifically, the removal efficiencies of chemical oxygen demand (COD), absorbance at 478 nm (I478), ammonia nitrogen (AN) and total nitrogen (TN) reached 99.1 %, 99.8 %, 98.9 % and 46.0 % respectively, and instantaneous current efficiency (ICE) at 3 h and energy consumption (EC) were 48.16 % and 97 kWh/kgCOD. Pyrite exhibited good reusability, mainly due to its proper dissolution capacity to renew surface active sites. It was speculated that the nitrogen removal of pesticide wastewater might mainly owe to the oxidation of NH4+ by chlorine/hypochlorite which were based on anode discharge reaction of contained Cl−. The electro-Fenton process catalyzed by natural pyrite showed good potential for efficiently treating the actual pesticide processing plant wastewater with high contents of chlorine salts.

Iron-sulfur mediated antibiotic resistance genes attenuation and autotrophic denitrification mechanisms in bioelectrochemical systems

Aiming at the problems of antibiotic resistance genes (ARGs) transfer, mobile gene elements (MGEs) and nitrogen removal in livestock wastewater, pyrite was introduced into the bioelectrochemical constructed wetland, mainly focusing on the mechanism of ARGs transfer and autotrophic denitrification in bioelectrochemical system. The results indicated that pyrite promoted the degradation of antibiotics while inhibiting the efflux of ARGs and MGEs in effluent. The removal rate of antibiotics in pyrite-mediated constructed wetland coupled with microbial fuel cell (PCW-MFC) was 26.84 % and 21.20 % higher than constructed wetland-microbial fuel cell (CW-MFC) and pyrite-mediated constructed wetland (PCW). Metagenomic analysis revealed that the abundance of ARGs in effluent and anodic microorganism in PCW-MFC was effectively controlled by inhibiting the expression of genes encoding antibiotic efflux (macB, tetA, smeS). The expression levels of periplasmic nitrate reduction genes (napA, napB) and encoding cytochrome c nitrite reductase small subunit genes (nrfH) in PCW-MFC were much higher than CW-MFC. The total expression of ARGs in CW-MFC anode biofilms was 35.77 % higher than PCW-MFC, indicating that the system can effectively reduce the spread of ARGs and abate environmental risks. The findings can provide theoretical reference for the control of ARGs and efficient nitrogen removal in livestock wastewater.

Effect of hydraulic retention time on the performance of sequencing batch reactor under combined stress of ibuprofen and ciprofloxacin

The impacts of changes in hydraulic retention time (HRT) on nitrogen elimination, the activity of sludge and the structure of microbial communities in a sequencing batch reactor under the joint stress of ibuprofen (IBP) and ciprofloxacin (CIP) were investigated. Under the combined stress of IBP (belonged to nonsteroidal anti-inflammatory drugs) and CIP (belonged to antibiotics), the elimination level of ammonia nitrogen, chemical oxygen demand, and the rate of specific ammonia oxidation, specific nitrite oxidation, specific nitrate reduction in activated sludge declined with the shortening of HRT. Under the joint stress of IBP and CIP, the content of polysaccharide (PS) and protein (PN) together with the ratio of PN to PS in the extracellular polymeric substances grew with the shortening of HRT, and the content of aromatic proteins increased significantly, which indicated that aromatic proteins were the major protective response substances to the shortening of HRT. Under the joint stress of IBP and CIP, with the reduction of HRT, and the reduction rate of relative abundance of nitrifying bacteria was more evident than that of denitrifying bacteria. This exploration gives novel thoughts for understanding the impacts of HRT on biological nitrogen removal of wastewater under combined stress of IBP and CIP.

Characteristics variations of size-fractionated anammox granules and identification of the potential effects on these evolutions

Anaerobic ammonium oxidation (anammox) granulation which contributed to system stabilization and performance improvement has great potential in the field of wastewater nitrogen removal. The researchers fractionated anammox granules into small-size (0.5–0.9 mm), medium-size (1.8–2.2 mm), and large-size (2.8–3.5 mm) categories to examine their properties and mechanisms. Various analyses, including high-throughput sequencing, determination of inorganic elements and extracellular polymeric substances (EPS), and microbial function prediction, were conducted to characterize these granules and understand their impact. The results revealed distinct characteristics among the different-sized granules. Medium-size granules exhibited the highest sphericity, EPS content, and anammox abundance. In contrast, large-size granules had the highest specific surface area, heme c content, specific anammox activity, biodiversity, and abundance of filamentous bacteria. Furthermore, the precipitates within the granules were identified as CaCO3 and MgCO3, with the highest inorganic element content found in the large-size granules. Microbial community and function annotation also varied with granule size. Based on systematic analysis, the researchers concluded that cell growth, chemical precipitation, EPS secretion, and interspecies interaction all played a role in granulation. Small-size granules were primarily formed through cell growth and biofilm formation. As granule size increased, EPS secretion and chemical precipitation became more influential in the granulation process. In the large-size granules, chemical precipitation and interspecies interaction, including synergistic effects with nitrifying, denitrifying, and filamentous bacteria, as well as metabolic cross-feeding, played significant roles in aggregation. This interplay ultimately contributed to higher anammox activity in the large-size granules. By fully understanding the mechanisms involved in granulation, this study provides valuable insights for the acclimation of anammox granules with optimal sizes under different operational conditions.

Study on adsorption of ammonia nitrogen by sodium-modified kaolin at calcination temperature.

Natural kaolin (NK) is not used as a material for removal of ammonia nitrogen in wastewater because of its low ammonia adsorption capacity. In this study, sodium-modified kaolin adsorbent (NaCK) with high ammonia nitrogen adsorption capacity was prepared by NaOH modification of calcined NK, which was developed to address this problem. The adsorption properties were evaluated by batch static adsorption test. The results showed that when the initial concentration of ammonia nitrogen was 10 mg/L, pH = 8, and dosage of adsorbent was 1 g/L, the adsorption capacity of NaCK-600 for ammonia nitrogen was the best, reaching 6.23 mg/g, which was 34.6 times higher than that of NK (0.18 mg/g). Batch static adsorption test combined with adsorption kinetics, adsorption isothermal, and characteristic data showed that NaCK prepared at different temperatures had different adsorption mechanisms. Batch static adsorption test data of NaCK-600 was in good agreement with the pseudo-second-order model and Langmuir model, and the main mechanism of its adsorption of ammonia nitrogen was the ion exchange of NH4+ and Na+ in NaCK. After the third cycle, the removal rate of NaCK-600 was still up to 76.44%, which indicates that NaCK-600 has considerable potential for removal of ammonia nitrogen in wastewater and provides a new way for the application of kaolin in removal of ammonia nitrogen.

Start‐up and operation of anammox biofilter in treating low‐strength ammonia wastewater prepared by tail water from a municipal wastewater treatment plant

AbstractBACKGROUNDEconomic technology of advanced nitrogen removal of municipal wastewater is urgently needed. In this study, anammox biofilter (A‐BF) as a carbon‐ and energy‐saving advanced nitrogen removal process was tested under the conditions of sewage secondary effluent.RESULTSThe results showed that A‐BF could be successfully started up under total nitrogen (TN) of both 25 and 75 mg L−1 within 30 days at 25 °C. It achieved a nitrogen removal rate of 0.62 ± 0.08 kg‐N m−3 d−1 with nitrogen loading rate of 1.35 kg‐N m−3 d−1 at TN of 17 mg L−1. The ceramsite bed was conducive to the formation of biofilm and enrichment of functional microorganisms. The volatile suspended solid reached 1.39–7.33 g L−1, in which the abundance of the typical anammox bacteria Candidatus_Brocadia and Candidatus_Kuenenia occupied 0.96–1.35% and 0.29–0.92%, respectively.CONCLUSIONSOverall, under low TN concentration and high nitrogen load, A‐BF could be a candidate technique for advanced nitrogen removal of municipal sewage. © 2023 Society of Chemical Industry.

Advanced synergetic nitrogen removal of municipal wastewater using oxidation products of refractory organic matters in secondary effluent by biogenic manganese oxides as carbon source.

Due to the high operational cost and secondary pollution of the conventional advanced nitrogen removal of municipal wastewater, a novel concept and technique of advanced synergetic nitrogen removal of partial-denitrification anammox and denitrification was proposed, which used the oxidation products of refractory organic matters in the secondary effluent of municipal wastewater treatment plant (MWWTP) by biogenic manganese oxides (BMOs) as carbon source. When the influent NH4+-N in the denitrifying filter was about 1.0, 2.0, 3.0, 4.0, 5.0 and 7.0mg/L, total nitrogen (TN) in the effluent decreased from about 22mg/L to 11.00, 7.85, 6.85, 5.20, 4.15 and 2.09mg/L, and the corresponding removal rate was 49.15, 64.82, 69.40, 76.70, 81.36 and 90.58%, respectively. The proportional contribution of the partial-denitrification anammox pathway to the TN removal was 12.00, 26.45, 39.70, 46.04, 54.97 and 64.01%, and the actual CODcr consumption of removing 1mg TN was 0.75, 1.43, 1.26, 1.17, 1.08 and 0.99mg, respectively, which was much lower than the theoretical CODcr consumption of denitrification. Furthermore, CODcr in the effluent decreased to 8.12mg/L with a removal rate of 72.40%, and the removed organic matters were mainly non-fluorescent organic matters. Kinds of denitrifying bacteria, anammox bacteria, hydrolytic bacteria and manganese oxidizing bacteria (MnOB) were identified in the denitrifying filter, which demonstrated that the advanced synergetic nitrogen removal was achieved. This novel technology presented the advantages of high efficiency of TN and CODcr removal, low operational cost and no secondary pollution.

Long-term effect of acetate and biochar addition on enrichment and activity of denitrifying anaerobic methane oxidation microbes

The denitrifying anaerobic methane oxidation (DAMO) process plays a crucial role in the global carbon/nitrogen cycles and methane emission control, and also has application potential in biological wastewater treatment. However, given that DAMO microbes are susceptible to external conditions such as additional carbon source in the system, it is essential to evaluate the effect of alternative carbon substance on the enrichment efficiency and metabolic activity of DAMO microbes. To this end, this study investigated the effect of acetate (0.1 mmol/L-R2, 0.5 mmol/L-R3) and biochar addition (R4) on the enrichment and activity of DAMO microbes. The long-term operation showed that the NO2−-N and CH4 consumption rates in the reactors almost presented the sequence of R4>R2>R3>R1. However, the short-term activity test with isotope labelling showed the sequence of R2>R4>R1>R3. Furthermore, the addition of acetate and biochar improved the electrochemical activity and extracellular polymeric substance (EPS) secretion in the systems. In R4 reactor, the proportion of DAMO bacteria was the highest (7.20%), indicating that the addition of biochar could promote the enrichment of DAMO bacteria, and Thauera was co-enriched with the proportion increasing from 0.26% to 6.73%. While in R1, R2 and R3 reactors, DAMO bacteria were enriched with relatively low abundances (0.10%, 0.23%, 0.15%, respectively), together with methanogens and denitrifiers. This study showed that biochar and acetate with appropriate concentration could enhance the enrichment and activity of DAMO bacteria, the results can provide reference for the enrichment of DAMO microbes and its application in the biological nitrogen removal of wastewater.

Hybrid biofilm system based on corncob coupling with scrap iron for synergistic nitrogen removal and phosphorus recovery in low-carbon source wastewater

Low-carbon source wastewater (LCSW) challenged the nutrients removal capability of traditional wastewater treatment techniques, becoming a hidden problem of eutrophic waters. Thus, a hybrid biofilm system (HBS) was developed based on corncob coupled with scrap iron for synergistic nitrogen removal and phosphorus recovery in LCSW. Corncob provided the sustainable carbon source by hydrolyzing and fermenting coupling with dissimilatory iron reduction (DIR) process, resulting in a maximum release of over 191.2 mg/L COD and supporting nitrogen removal of 83.5 % in HBS with HRT at 6 h. Meanwhile, scrap iron supported the DIR process and chemical precipitation by Fe3+ release, generating vivianite with Fe2+ for phosphate recovery (97.1 %) in HBS. By microbial community analysis, heterotrophic denitrification was the primary process for nitrogen removal, which benefitted from hydrolyzing and fermenting bacteria. After chemical precipitation, phosphorus recovery was realized by biological solubilization and DIR process, which were functioned by Acinetobacter calcoaceticus, Bacillus aryabhattai and Bacillus sp. X12014, etc. The DIR process was the critical driving force that coupled organics degradation with synergistic removal of N and P.

Enhanced nitrogen removal in low-carbon saline wastewater by adding functional bacteria into Sesuvium portulacastrum constructed wetlands

Functional bacterial communities (FBC) have members of different taxonomic biochemical groups, such as N2-fixation, nitrification and denitrification. This study explored the mechanism of the FBC from an upflow three-dimensional biofilm electrode reactor on enhancing the nitrogen removal efficiencies in a Sesuvium potulacastum (S. potulacastum) constructed wetland. There were high abundances of denitrifying bacteria detected in the FBC, and they had potential metabolic processes for nitrogen reduction. In the constructed wetland, cellular nitrogen compounds of S. potulacastum were enriched by overexpressed differentially expressed genes (DEGs), and the napA, narG, nirK, nirS, qnorB, and NosZ genes related to the denitrification process had more copies under FBC treatment. Nitrogen metabolism in root bacterial communities (RBCs) was activated in the FBC group compared with the control group without FBC. Finally, these FBCs improved the removal efficiencies of DTN (dissolved total nitrogen), NO3¯­N, NO2¯­N, and NH4+-N by 84.37 %, 87.42 %, 67.51 %, and 92.57 %, respectively, and their final concentrations met the emission standards of China. These findings indicate that adding FBC into S. potulacastum-constructed wetlands would result in high nitrogen removal efficiencies from wastewater and have large potential applications in further water treatment technology.

Pangenome-driven insights into nitrogen metabolic characteristics of Citrobacter portucalensis strain AAK_AS5 associated with wastewater nitrogen removal.

Nitrogen metabolism in the genus Citrobacter is very poorly studied despite its several implications in wastewater treatment. In the current study, Citrobacter portucalensis strain AAK_AS5 was assessed for remediation of simulated wastewater supplemented with different inorganic nitrogen sources. Combination of (NH4)2SO4 with KNO3 was the most preferred for achieving high growth density followed by (NH4)2SO4 and KNO3 alone. This was in agreement with highest ammonical nitrogen removal of 92.9% in the presence of combined nitrogen sources and the corresponding nitrate nitrogen removal of 93% in the presence of KNO3. Furthermore, these removal capacities were validated by investigating the uniqueness and the spread of metabolic features through pan-genomic approach that revealed the largest number of unique genes (2097) and accessory genes (705) in strain AAK_AS5. Of the total 44 different types of nitrogen metabolism-related genes, 39 genes were associated with the core genome, while 5 genes such asgltI,nasA,nasR,nrtA,and ntrCuniquely belonged to the accessory genome. Strain AAK_AS5 possessed three major nitrate removal pathwaysviz., assimilatory and dissimilatory nitrate reduction to ammonia (ANRA & DNRA), and denitrification; however, the absence of nitrification was compensated by ammonia assimilation catalyzed by gene products of the GDH and GS-GOGAT pathways. narGHIJ encoding the respiratory nitrate reductase was commonly identified in all the studied genomes, while genes such as nirK, norB, and nosZ were uniquely present in the strain AAK_AS5 only. A markedly different genetic content and metabolic diversity between the strains reflected their adaptive evolution in the environment thus highlighting the significance of C. portucalensis AAK_AS5 for potential application in nitrogen removal from wastewater.

An innovative bilayer solid carbon source for tertiary denitrification: Synthesis, performance, and microbial diversity analysis

The low C/N ratio poses a constraint on the tertiary nitrogen removal process in domestic sewage. Composite solid carbon sources have recently gained attention in recent years for improving nitrogen removal efficacy. However, little research has focused on the lengthy start-up of denitrification systems caused by composite solid carbon sources. In this study, we employed a biodegradable sodium alginate (SA) and corn cob (CC) mixture, implanted a polycaprolactone (PCL) and corn starch (CS) mixture, and created a new composite solid carbon source polycaprolactone-corn starch‑sodium alginate-corn cob microspheres (PCSC). The early rapid carbon release and late stable carbon release properties of PCSC allow it to rapidly enrich denitrifying bacteria and form biofilms on its surface. It only takes 5 days to start denitrification biological filters utilizing PCSC as a carbon source, with an average nitrogen removal rate of 85 %, which is 60 % and 10 % higher than SA-CC and PCL-CS, respectively. The 16S rRNA gene high-throughput sequencing revealed that the primary denitrifying bacteria on the surface of PCSC were Chitinophagaceae, Comamonadaceae, and Blastocatellaceae. Overall, PCSC can make the denitrification system start up fast, steadily, and efficiently, and it has tremendous application prospects in tertiary nitrogen removal of wastewater.

Acorus calamus recycled as an additional carbon source in a microbial fuel cell-constructed wetland for enhanced nitrogen removal

Acorus calamus was recycled as an additional carbon source in microbial fuel cell-constructed wetlands (MFC-CWs), for efficient nitrogen removal of low carbon wastewater. The pretreatment methods, adding positions, and nitrogen transformations were investigated. Results indicated that alkali-pretreatment cleaved the benzene rings in dominant released organics, producing chemical oxygen demand of 164.5 mg from per gram of A. calamus. Pretreated biomass addition in the anode of MFC-CW attained the maximum total nitrogen removal of 97.6% and power generation of 12.5 mW/m2, which were higher than those with biomass in the cathode (97.6% and 1.6 mW/m2, respectively). However, the duration of a cycle with biomass in the cathode (20–25 days) was longer than that in the anode (10–15 days). Microbial metabolisms related to organics degradation, nitrification, denitrification, and anammox were intensified after biomass recycling. This study provides a promising method to improve nitrogen removal and energy recovery in MFC-CWs.

Feasibility of low-intensity ultrasound treatment with hydroxylamine to accelerate the initiation of partial nitrification and allow operation under intermittent aeration

Partial nitrification is a key aspect of efficient nitrogen removal, although practically it suffers from long start-up cycles and unstable long-term operational performance. To address these drawbacks, this study investigated the effect of low intensity ultrasound treatment combined with hydroxylamine (NH2OH) on the performance of partial nitrification. Results show that compared with the control group, low-intensity ultrasound treatment (0.10 W/mL, 15 min) combined with NH2OH (5 mg/L) reduced the time required for partial nitrification initiation by 6 days, increasing the nitrite accumulation rate (NAR) and ammonia nitrogen removal rate (NRR) by 20.4% and 6.7%, respectively, achieving 96.48% NRR. Mechanistic analysis showed that NH2OH enhanced ammonia oxidation, inhibited nitrite-oxidizing bacteria (NOB) activity and shortened the time required for partial nitrification initiation. Furthermore, ultrasonication combined with NH2OH dosing stimulated EPS (extracellular polymeric substances) secretion, increased carbonyl, hydroxyl and amine functional group abundances and enhanced mass transfer. In addition, 16S rRNA gene sequencing results showed that ultrasonication-sensitive Nitrospira disappeared from the ultrasound + NH2OH system, while Nitrosomonas gradually became the dominant group. Collectively, the results of this study provide valuable insight into the enhancement of partial nitrification start-up during the process of wastewater nitrogen removal.