Denitrification Of Wastewater Research Articles

Autotrophic denitrification of nitrate rich wastewater in fluidized bed reactors using pyrite and elemental sulfur as electron donors

This study compared denitrification performances and microbial communities in fluidized bed reactors (FBRs) carrying out autotrophic denitrification using elemental sulfur (S 0 ) and pyrite (FeS 2 ) as electron donors. The reactors were operated for 220 days with nitrate loading rates varying between 23 and 200 mg N-NO 3 − /L ⋅ d and HRT between 48 and 4 h. The highest denitrification rates achieved were 142.2 and 184.4 mg N-NO 3 − /L ⋅ d in pyrite and sulfur FBRs, respectively. Pyrite-driven denitrification produced less SO 4 2 − and no buffer addition was needed to regulate the pH. The sulfur FBR needed instead CaCO 3 to maintain the pH neutral and consequentially more sludge was produced (CaSO 4 precipitation). The active community of pyrite-based systems was investigated and Azospira sp ., Ferruginibacter sp. , Rhodococcus sp. and Pseudomonas sp. were the predominant genera, while Thiobacillus sp. and Sulfurovum sp. dominated the active community in the sulfur FBR. However, Thiobacillus sp. became more dominant when operating at elevated nitrogen loading rate. Patterns of diversity and microbial community assembly were assessed and revealed three distinct stages of microbial community succession which corresponded with the operation of a period of high influent nitrate concentration (135 mg N-NO 3 − /L). It is proposed that a high degree of functional redundancy in the initial microbial communities may have helped both reactors to respond better to such high influent nitrate concentration. • Max denitrification rates were 142.2 and 184.4 mgN-NO 3 − / L ⋅ d in the FeS 2 and S 0 FBRs. • FeS 2 -driven denitrification produced low SO 4 2 − and no buffer addition was needed. • Microbial community succession was observed in response to NLR increased. • Functional redundancy in the AD microbiome resulted in resilience to increased NLRs. • The active community of FeS 2 FBR had Azospira and Pseudomonas as dominant genera.

Biofilm-based simultaneous nitrification, denitrification, and phosphorous uptake in wastewater by Neurospora discreta

Biological removal of nitrogen and phosphorous from wastewater conventionally involves multiple processing steps to satisfy the differing oxygen requirements of the microbial species involved. In this work, simultaneous nitrification, denitrification, and phosphorous removal from synthetic wastewater were achieved by the fungus Neurospora discreta in a single-step, biofilm-based, aerobic process. The concentrations of carbon, nitrogen, and phosphorous in the synthetic wastewater were systematically varied to investigate their effects on nutrient removal rates and biofilm properties. Biofilm growth was significantly (p < 0.05) affected by carbon and nitrogen, but not by phosphorous concentration. Scanning electron microscopy revealed the effects of nutrients on biofilm microstructure, which in turn correlated with nutrient removal efficiencies. The carbohydrate and protein content in the biofilm matrix decreased with increasing carbon and nitrogen concentrations but increased with increasing phosphorous concentration in the wastewater. High removal efficiencies of carbon (96%), ammonium (86%), nitrate (100%), and phosphorus (82%) were achieved under varying nutrient conditions. Interestingly, decreasing the phosphorus concentration increased the nitrification and denitrification rates, and decreasing the nitrogen concentration increased the phosphorus removal rates significantly (p < 0.05). Correlations between biofilm properties and nutrient removal rates were also evaluated in this study.

Extracellular DNA plays a key role in the structural stability of sulfide-based denitrifying biofilms.

Sulfide-based biofilm processes are increasingly used for wastewater denitrification, yet little is known about the extracellular polymeric substance (EPS) composition of sulfide-oxidizing biofilms. This can have an important impact on biofilm mechanical strength and stability. In this research, the properties and roles of EPS components in biofilm stability were investigated. Weak biofilm stability characterized by high roughness and numerous "needle" structures was visualized by optical coherence tomography (OCT) and microscopy. A high abundance of extracellular DNA (eDNA) and a low protein to polysaccharide ratio were found in the biofilm. The roles of eDNA, protein and polysaccharide in biofilm cohesion and adhesion were identified through enzyme treatment and atomic force microscopy (AFM). The enzymatic hydrolysis of eDNA increased the elastic modulus of biofilms by 57 times and reduced the adhesion energy by 96%. The hydrolysis of proteins led to an increase of elastic modulus by 27 times and a loss of adhesion energy by 95.5%. The enzymatic hydrolysis of polysaccharides caused minimal changes in elastic modulus and adhesion energy. These results suggest that eDNA was the key EPS component for biofilm cohesion and adhesion, possibly because it provided special binding sites and can form strong cross-linking with magnesium or other multivalent cations. This study provided new insights into the role of eDNA in biofilm stability and shed light on the development of sulfide-based denitrifying biofilms.

Selective reduction of nitrite to nitrogen by polyaniline-carbon nanotubes composite at neutral pH

The selective reduction of nitrite (NO2−) to nitrogen by chemical reductant is a desirable strategy to remove NO2− from polluted water and wastewater. However, the residue and reuse of chemical reductant are two main issues to be addressed. Herein, a novel polyaniline-carbon nanotubes composite (PANI-CNTs) was developed by in-situ polymerization to selectively reduce NO2− to nitrogen gas (N2). The used PANI-CNTs could be reused after regeneration with NaBH4. The PANI-CNTs could reduce NO2− with 93.9% N2 selectivity at initial pH of 6.8. The NO2− removal efficiency only decreased by 12.08% after five cycles of reduction/regeneration. The interconversion between imine nitrogen (–N) and amine nitrogen (–NH–) groups induced the chemical reduction of NO2− and regeneration of PANI-CNTs. PANI-CNTs exhibited an excellent performance for the removal of NO2− in the presence of competitive ions and in actual water and wastewater samples. This new PANI-CNTs composite may have great potential for water purification and wastewater denitrification.

Effect of feeding gas type and nitrogen: Sulfur ratio on a novel sulfide-driven denitrification methane oxidation (SDMO) system

To save treatment costs of nitrogen-polluted water, a novel sulfide-driven denitrification methane oxidation (SDMO) system, which integrated autotrophic denitrification (AD) and denitrification anaerobic methane oxidation (DAMO) to simultaneously realize wastewater denitrification and biogas utilization in situ, has been operated. In this work, nine groups V0—V8 were derived from a mature SDMO reactor which already enriched AD and DAMO microorganisms. Batch tests about them were proceeded to investigate the effect of feeding gas type and N/S ratio on kinetic performance, microorganism community structure, and functional genes. Results showed as N/S rising up from 2.3 to 23.3, the nitrate removal efficiency decreased from 100 % to 15.4 % but its contribution by DAMO/AD ratio increased from 0.5 to 2.2. Biogas serving as feeding gas enhanced nitrate removal efficiency to 100 % at most in group V3 (N/S = 2.3, H2S = 1.5 %) whereas DAMO and AD contribution for nitrate removal was 33.1 % and 65.6 % respectively. Low H2S content gave little effect on microorganism community structure but high hydrogen sulfide content decreased the abundance of DAMO bacteria Candidatus Methylomirabilis to ∼ 4 % and increase abundance of AD bacteria Thiobacillus to > 20 %. Comparing with V1 feeding with methane, nitrate reduction genes napA, narG, nirK, nirS, cnorB and sulfide oxidation gene soxB up-regulated to > 3.0 × 109 copies/g in HS groups (biogas with high H2S content > 1 %) while gene pmoA up-regulated to ∼ 1.0 × 109 copies/g in LS groups (biogas with low H2S content < 1 %). This study provided more comprehensive understanding for the effect of feeding gas type and N/S ratio on SDMO system.

Treatment of DEHP-rich PVC waste in subcritical urine wastewater: Efficient dechlorination, denitrification, plasticizer decomposition, and preparation of high-purity phthalic acid crystals

It is difficult to dispose diethylhexyl phthalate-rich polyvinyl chloride (DEHP-rich PVC) waste due to the high level of chlorine and plasticizer. On the other hand, the denitrification of urine wastewater with high nitrogen content also faces great challenges. In this study, a synergistic treatment strategy was developed for the DEHP-rich PVC waste and urine wastewater by a subcritical water process. Subcritical urine wastewater (SUW) was used as a reaction medium in the synergistic treatment. PVC dechlorination, DEHP decomposition, and denitrification of urine wastewater were synchronously achieved in the one pot SUW. Under the optimal conditions (300 °C, 15 min, 1:5 g/mL), the PVC dechlorination ratio, urine wastewater denitrification ratio and DEHP decomposition ratio could reach 98.4%, 64.9%, and 99.2%, respectively. The decomposition of DEHP mainly included hydrolysis, nucleophilic substitution, and acylation. DEHP could be converted into phthalic acid crystal at 220 °C with a yield of 66.25% due to the efficient hydrolysis action of SUW. All the removed Cl was transferred from PVC matrix to aqueous phase. Hydroxyl nucleophilic substitution is the principal dechlorination path of PVC. The reactions between N-containing species and DEHP in SUW resulted in the high-efficiency denitrification of urine wastewater, and the N element was fixed in solid residue or transferred to oil phase as amides compounds. It is believed that the proposed SUW process is a promising technology for the synergistic treatment of DEHP-rich PVC waste and urine wastewater.

Dissolved organic nitrogen derived from wastewater denitrification: Composition and nitrogenous disinfection byproduct formation

Microbially derived dissolved organic nitrogen (mDON) is a major fraction of effluent total nitrogen at wastewater treatment plants with enhanced nutrient removal, which stimulates phytoplankton blooms and formation of toxic nitrogenous disinfection by-products (N-DBPs). This study identified denitrifiers as major contributors to mDON synthesis, and further revealed the molecular composition, influential factors and synthetic microorganisms of denitrification-derived mDON compounds leading to N-DBP formation. The maximum mDON accumulated during denitrification was 8.92% of converted inorganic nitrogen, higher than that of anammox (4.24%) and nitrification (2.76%). Sodium acetate addition at relatively high C/N ratio (5−7) favored mDON formation, compared with methanol and low C/N (1−3). Different from acetate, methanol-facilitated denitrification produced 13–69% more lignin-like compounds than proteins using Orbitrap LC-MS. The most abundant N-DBPs formed from denitrification-derived mDON were N-nitrosodibutylamine and dichloroacetonitrile (13.32 μg/mg mDON and 12.21 μg/mg mDON, respectively). Major amino acids, aspartate, glycine, and alanine were positively correlated with typical N-DBPs. Biosynthesis and degradation pathways of these N-DBP precursors were enriched in denitrifiers belonging to Rhodocyclaceae, Mycobacteriaceae and Hyphomicrobiaceae. As intensive disinfection is applied at worldwide wastewater treatment plants during COVID-19, carbon source facilitated denitrification should be better managed to reduce both effluent inorganic nitrogen and DON, mitigating DON and N-DBP associated ecological risks in receiving waters.

Treatment Effect of Corncob and Rice Straw Enhanced Subsurface Flow Constructed Wetland on Low C/N Ratio Wastewater

The lack of carbon sources severely inhibits denitrification in wastewater with a low C/N ratio. Corncob and rice straw were chosen as supplementary carbon sources to bring into the wetland system to supplement the carbon sources needed for denitrification, and the enhancing effects of the two carbon sources on nitrogen removal from the wetland were studied. The cumulative release of carbon was in the order of rice straw[(145.17±9.44) mg·g-1]>corncob[(57.41±5.04) mg·g-1] based on the 11-day pure water extraction and release experiment, whereas the cumulative release of nitrogen was in the order of rice straw[(2.31±0.09) mg·g-1]>corncob[(0.66±0.08) mg·g-1]. The average carbon/nitrogen ratios released and accumulated by corncob and rice straw during the observation period were 94.78 and 63.64, respectively. Corncob was more suited as an additional carbon source than rice straw. COD concentrations in the effluent from the corncob and straw constructed wetlands were found to be below 50 mg·L-1 for the 58-day pilot test of subsurface flow constructed wetlands, except on days 8 to 12. The NO3--N removal rates of the corncob-added built wetlands were 93%-99% over the observation period, with good denitrification performance. In comparison, the lowest NO3--N removal rate of the constructed wetland with the addition of rice straw was only 76.8% at the late stage of operation, and the denitrification rate dropped dramatically. The control group removal rates of NO3--N were only 76.2%-77.7%, indicating a clear lack of carbon sources. The accumulation of NO2--N was also induced by a lack of carbon supply. NO2--N effluent concentrations were 2.5-6 times and 6-26 times higher in the constructed wetlands with rice straw and the control groups, respectively, than those in the wetlands constructed with corncob. The addition of corncob resulted in a more substantial reduction in NO2--N content in the constructed wetland than the addition of rice straw (P<0.05). The TN removal rates of wetlands constructed with corncob and rice straw and the control group were 83.75%-93.49%, 76.59%-78.85%, and 67.85%-72.56%, respectively, with significant differences among the three (P<0.01). Finally, pretreatment with dilute alkali heating raised the cumulative carbon release of corncob to (93.73±17.49) mg·g-1 and the carbon/nitrogen ratio to 175.8, significantly improving the carbon release performance of corncob and demonstrating that it is a suitable source of extra carbon.

An aerobic denitrifier Pseudomonas stutzeri Y23 from an oil reservoir and its heterotrophic denitrification performance in laboratory-scale sequencing batch reactors

Biological nitrogen removal from wastewater is considered to be more economical and efficient than physicochemical methods. Furthermore, denitrifying strains with complete denitrifying capacity play crucial roles in biological denitrification of wastewater. In this study, a heterotrophic bacterium Y23 with high denitrifying efficiency was isolated from production brine of an oilfield, which was flooded by microbial-enhanced oil recovery technique through injecting carbohydrate and nitrate into oil-bearing strata. Strain Y23 identified as Pseudomonas stutzeri contains denitrifying genes that are responsible for converting NO3− to NO2− and sequentially to NO, N2O, and N2. Y23 with secreted extracellular polymeric substances formed flocs and biofilm and showed good sedimentation and immobilization properties. Strain Y23 grew well with NaNO3, NaNO2, and (NH4)2SO4 as nitrogen sources, and showed excellent denitrification performance under high dissolved oxygen (DO) concentration, which benefited nitrite reduction. The removal efficiencies of nitrogen and chemical oxygen demand were enhanced by the augmentation of strain Y23 back into a laboratory-scale sequencing batch reactor. The reactor with Y23 also showed stronger impact resistance. Further investigation of microbial communities within the sequencing batch reactor showed that Y23 coexisted with other denitrifiers during operation. Overall, this study isolated a promising denitrifier that performs complete denitrification at high DO condition, and found that the accumulation or reduction of nitrite can be achieved by regulating hydraulic retention time or increasing DO, respectively.

Nitrogen removal intensification of aerobic granular sludge through bioaugmentation with “heterotrophic nitrification-aerobic denitrification” consortium during petroleum wastewater treatment

The bioaugmentation potential of aerobic granular sludge (AGS) was investigated using heterotrophic nitrification-aerobic denitrification (HN-AD) bacterial consortium to improve nitrogen removal during petroleum wastewater treatment. An efficient HN-AD consortium was constructed by mixing Pseudomonas mendocina K0, Brucella sp. K1, Pseudomonas putida T4 and Paracoccus sp. T9. AGS bioaugmented by immobilized HN-AD consortium enhanced nitrogen removal, which showed NH4+-N and TN removal efficiency of 92.4% and 79.8%, respectively. The immobilized consortium addition facilitated larger AGS formation, while granules > 2.0 mm accounted for 16.7% higher than that of control (6.7%). Further, the abundance of napA gene was 4-times higher in the bioaugmented AGS as compared to the control, which demonstrated the long-term stability of HN-AD consortium in the bioreactor. The bioaugmented AGS also showed a higher abundance of xenobiotics biodegradation and nitrogen metabolism. These results highlight that bioaugmentation of AGS technology could be effectively used for enhanced denitrification of petroleum wastewater.

Regulation, quantification and application of the effect of functional groups on anion selectivity in capacitive deionization

Capacitive deionization (CDI) has been widely studied as a highly efficient method for the removal of charged pollutants in sewage. However, the control of ion selectivity has always been challenging, limiting the application of this approach. In this article, the regulation of different acid/base functional group distributions on the selectivity of four anions are comprehensively discussed. The effects are quantified through simulations and statistical analysis. Finally, optimized CDI is used for the simultaneous denitrification and dephosphorization of municipal wastewater. The results show that carboxyl groups significantly promote the selectivity of dihydrogen phosphate and that amino groups promote the selectivity of sulfate and dihydrogen phosphate. Density functional theory is used to calculate the influence of the functional groups on the anion adsorption energy. Compared with other anions, the energy released is improved when carboxyl groups are included in the adsorption of dihydrogen phosphate. The increase in the released energy is highest when amino groups participate in the adsorption of sulfate and is second-highest when they participate in the adsorption of dihydrogen phosphate. Statistical analysis shows that the valence and hydration energy of the anion and the effect of the functional groups on anion adsorption are significantly related to anion adsorption (P < 0.05), and the correlation coefficient of the model is 0.7253. A CDI stack for the removal of phosphorus and nitrogen under high background ion concentrations is constructed and applied, and it is shown that the treated wastewater meets higher discharge standards. Moreover, the method reaches nearly 80% water production under optimized operating modes. This study reveals the importance of functional groups in ion-selective regulation and provides a potential method for high-standard wastewater treatment.

High Performance of Commercial PAC on the Simultaneous Desulfurization and Denitrification of Wastewater From a Coal-Fired Heating Plant.

The flue gas desulfurization wastewater is highly saline and has too many refractory pollutants to be recycled during the desulfurization process of the coal-fired heating plant. Given that waste heat is abundant in coal-fired heating plants, a thermal treatment method was developed to simultaneously remove sulfates and nitrates from the wastewater, with the production of chemical-grade natroalunite and recycled water. The results showed that sulfates and nitrates were 50.3 and 10 g/L in the wastewater, respectively, and only 2.8% and 9.1% were removed after direct treatment at 270°C for 7 h; but these rates increased to 99.3% and 99.9%, respectively, with the addition of commercial poly aluminum chloride. Mass balance summarized that the treatment of 1 ton wastewater needed 0.1 ton PAC and produced 0.11 ton natroalunite and 0.92 ton recycle water. The removal of sulfates and nitrates was mainly done by the precipitation reaction of sulfates such as natroalunite and the redox reaction between nitrates and organics, respectively. Thermodynamic analysis demonstrated that the precipitate reaction occurred at 45°C and accelerated in the temperature range of 45–270°C, but became slow with the decrease of sulfate and Al concentrations in wastewater. Four other reagents were also used for wastewater treatment in comparison with PAC and showed the following order of performance: PAC > citrate calcium > limestone > subacetate aluminum > citrate ferric. This method provided a practical route to treat wastewater from flue gas desulfurization without generating secondary waste.

Enhanced denitrification of dispersed swine wastewater using Ca(OH)2-pretreated rice straw as a solid carbon source

In a pilot-scale packed bed reactor, the denitrification performance and microbial community structure of the dispersed swine wastewater treatment using calcium hydroxide (Ca(OH)2) pretreated rice straw as a carbon source were investigated. In a Ca(OH)2-pretreated rice straw supported denitrification system (Ca(OH)2-RS), the removal efficiency of NO3−-N was 96.39% at an influent NO3−-N load of 0.04 kg/(m3•d). Meanwhile, there was no obvious accumulation of NO2−-N or chemical oxygen demand (COD) in the effluent of Ca(OH)2-RS. The contents of soluble microbial byproduct-like substances and tryptophan-like substances in the effluent of Ca(OH)2-RS were reduced by 46.2% and 43.4%, respectively, compared with the influent. Overall, the Ca(OH)2-pretreated rice straw system had a strong resistance to fluctuations in water quality conditions, such as influent NO3−-N and COD concentrations. According to the microbial assay results, the Ca(OH)2 pretreatment enriched more denitrifying bacteria. Among them, Proteobacteria (42.33%) and Bacteroidetes (35.28%) were the dominant bacteria. Moreover, the main denitrifying functional bacteria, generanorank_f_Saprospiraceae (13.32%), norank_f_Porphyromonadaceae (4.22%), and Flavobacterium (3.25%), were enriched in Ca(OH)2-RS. This suggested that using Ca(OH)2-pretreated rice straw as a carbon source was a stable and efficient technology to enhance the denitrification performance of dispersed swine wastewater.

A new LDH based sustained-release carbon source filter media to achieve advanced denitrogenation of low C/N wastewater at low temperature

Advanced denitrogenation of wastewater is now facing major challenges brought by low C/N ratio and low temperature. The development of sustained-release materials with good and stable carbon release properties was an effective countermeasure. FeNi-Layered double-metal hydroxides (LDH)- sodium carboxymethyl cellulose (CMC) filter media and its potential use in heterotrophic and sulfur-based mixotrophic denitrification biological filter (DNBF), was firstly reported. It demonstrated stable structure and good carbon release performance with a mass transfer coefficient (K) of 4.40 mg·L−1·s−1. When the influent NO3−-N of 50 mg/L with the C/N ratio of 3 at 10 °C, the maximum nitrogen loading rate of 0.22 kg·N/(m3·d) and effluent TN close to 5 mg/L (nitrogen removal of almost 90 %) could be achieved. The slowly released carbon source and the leached iron increased the abundance of denitrifying bacteria and functional genes, and the augmentation of Sulfuritalea and the secretion of biofilm protein stimulated by sulfur also played a synergistic role. This study provided a new potentially effective strategy to enhance advanced denitrification of wastewater of low C/N wastewater at low temperature.

Effectiveness of agricultural waste in the enhancement of biological denitrification of aquaculture wastewater.

Nitrogen pollution in aquaculture wastewater can pose a significant health and environmental risk if not removed before wastewater is discharged. Biological denitrification uses external carbon sources to remove nitrogen from wastewater; however, these carbon sources are often expensive and require significant energy. In this study, we investigated how six types of agricultural waste can be used as solid carbon sources in biological denitrification. Banana stalk (BS), loofah sponge (LS), sorghum stalk (SS), sweet potato stalk (SPS), watermelon skins (WS) and wheat husk (WH) were studied to determine their capacity to release carbon and improve denitrification efficiency. The results of batch experiments showed that all six agricultural wastes had excellent carbon release capacities, with cumulative chemical oxygen demands of 37.74–535.68 mg/g. During the 168-h reaction, the carbon release process followed the second-order kinetic equation and Ritger-Peppas equation, while carbon release occurred via diffusion. The kinetic equation fitting, scanning electron microscopy, and Fourier transform infrared spectroscopy results showed that LS had the lowest cm and the maximum t1/2 values and only suffered a moderate degree of hydrolysis. It also had the lowest pollutant release rate and cumulative chemical oxygen demand, as well as the most efficient removal of total phosphorous (TP) and total nitrogen (TN). Therefore, we concluded that LS has the lowest potential risk of excess carbon release and capacity for long-lasting and stable carbon release. The WS leachate had the highest TN contents, while the SPS leachate had the highest TP content. In the 181-h denitrification reaction, all six agricultural wastes completely removed nitrate and nitrite; however, SS had the highest denitrification rate, followed by LS, WH, BS, SPS, and WS (2.16, 1.35, 1.35, 1.34, 1.34, and 1.01 mg/(L·h), respectively). The denitrification process followed a zero-order and first-order kinetic equation. These results provide theoretical guidance for effectively selecting agricultural waste as a solid carbon source and improving the denitrification efficiency of aquaculture wastewater treatment.

Microbial community structure analyses and cultivable denitrifier isolation of Myriophyllum aquaticum constructed wetland under low C/N ratio

With the rapid expansion of livestock production, the amount of livestock wastewater accumulated rapidly. Lack of biodegradable organic matter makes denitrification of livestock wastewater after anaerobic digestion more difficult. In this study, Myriophyllum aquaticum constructed wetlands (CWs) with efficient nitrogen removal performance were established under different carbon/nitrogen (C/N) ratios. Analysis of community composition reveals the change of M. aquaticum CWs in microbial community structure with C/N ratios. The proportion of Proteobacteria which is one of the dominant phyla among denitrifier communities increased significantly under low C/N ratio conditions. Besides, to obtain cultivable denitrifier that could be added into CWs in situ, 33 strains belonging to phylum Proteobacteria were isolated from efficient M. aquaticum CWs, while the best-performing denitrification strain M3-1 was identified as Bacillus velezensis JT3-1 (GenBank No. CP032506.1). Redundancy analysis and quadratic models showed that C/N ratio had significant effects on disposal of nitrate (NO3−-N) and the strains isolated could perform well in denitrification when C/N ratio is relatively low. In addition, they have relatively wide ranges of carbon sources, temperature and a high NO3− removal rate of 9.12 mg/(L·hr) at elevated concentrations of 800 mg/L nitrate. Thus, strains isolated from M. aquaticum CWs with low C/N ratio have a practical application value in the treatment of nitrate-containing wastewater. These denitrifying bacteria could be added to CWs to enhance nitrogen removal efficiency of CWs for livestock wastewater with low C/N ratio in the future.

A divided flow aerobic-anoxic baffled reactor for simultaneous nitrification-denitrification of domestic wastewater

A novel aerobic-anoxic baffled reactor is designed for the effective denitrification of real domestic wastewater without an external carbon source. The flow is divided between two inlets at the beginning of each zone to provide a carbon source for the denitrifying bacteria. The effects of operating parameters such as the ratio of chemical oxygen demand to nitrogen (COD/N), flow division ratio, and hydraulic retention time (HRT) on the nitrogen removal were investigated. The optimum values of COD/N and HRT were estimated using response surface methodology (RSM) coupled with a central composite experimental design. The addition of porous biomass support media considerably improved the denitrification and removal of COD. Furthermore, the aerobic-anoxic system showed high stability against sudden HRT and COD/N ratio changes. The microbial analysis showed that Alcaligenes, Achromobacter, and Bordetella were the dominant denitrifying bacteria in the anoxic zone, whereas other species coexisted in the aerobic zone.

Formation of disinfection byproducts from chlorinated soluble microbial products: Effect of carbon sources in wastewater denitrification processes

Carbon sources are crucial for biological denitrification in wastewater treatment that significantly affects the production of soluble microbial products (SMPs), thereby affecting the formation of disinfection byproducts (DBPs) during subsequent chlorination. However, the effect of carbon sources on DBPs formation has not been studied. In this work, sodium acetate, sodium lactate, and glucose were used as carbon sources, and denitrifying SMPs derived from different carbon sources were used as DBPs precursors to investigate the formation potential (FP) of 16 carbonaceous DBPs and 19 nitrogenous DBPs. Results showed that the carbonaceous DBPs FP of SMPs derived from acetate, lactate, and glucose were 502.1–584.3, 250.3–288.9, and 374.7–439.1 μg/L, respectively, and the nitrogenous DBPs FP were 19.1–45.6, 12.8–21.9, and 7.9–9.0 μg/L, respectively. After chlorination, the genotoxicity of SMPs measured by the SOS/umu test was also evaluated with 364 ng 4-NQO/L for acetate, 212 ng 4-NQO/L for lactate, and 138 ng 4-NQO/L for glucose. Based on X-ray photoelectron spectroscopy, chemical structures of SMPs were characterized, and their relationship with DBPs FP was investigated to explain the mechanism of DBPs formation. Aromatic C and C-O were found to be the major precursor structures to form carbonaceous DBPs, and their lowest proportions in lactate-derived SMPs caused the lowest carbonaceous DBPs FP. Organic nitrogen, including aromatic N, amide/peptide N, and primary amine N, was the precursor of nitrogenous DBPs. The lowest concentration of dissolved organic nitrogen for glucose-derived SMPs caused the lowest nitrogenous DBPs FP and genotoxicity. Glucose may be a better choice among the three carbon sources in terms of reducing genotoxicity.

Selective photo-reduction of NO2− to N2 in the presence of Fe2+ and citric acid

The photo-reduction of NO2− has received increasing attention due to its high photo-activity. However, the intermediate products of NO2− photo-reduction might contain NOx, which are also toxic pollutants. Herein, a novel strategy to selectively photo-reduce NO2− to N2 was proposed using Fe2+ and citric acid (H3Cit) as assistant to eliminate the formation of NOx. In this strategy, NO2− was firstly reduced to NO by the combination of photon, Fe2+ and H3Cit; the generated NO was then immediately captured by Fe2+-H3Cit to form Fe2+-H3Cit-NO complex; finally, H3Cit was activated by Fe3+ and •OH in Fe2+/H3Cit/UV/NO2− system to produce carbon dioxide anion radical (CO2•−), which could reduce the NO in Fe2+-H3Cit-NO complex to N2 with high efficiency and selectivity. The removal efficiencies of NO2− and TN were 98.6% and 87.5%, respectively, and the selectivity of N2 was 81.6% in Fe2+/H3Cit/UV/NO2− system after 60-min reaction at initial pH of 2.2, Fe2+ dosage of 3.0 mmol·L−1 and H3Cit dosage of 3.0 mmol·L−1. Based on the experimental results and spectral analysis, the mechanism of NO2− selective reduction in Fe2+/H3Cit/UV/NO2− system was proposed. Our finding provides a new way for wastewater denitrification and water purification.

Effect of Polypropylene Microplastics Concentration on Wastewater Denitrification

Effect of Polypropylene Microplastics Concentration on Wastewater Denitrification