Simultaneous nitrification and denitrification in membrane bioreactor: Effect of dissolved oxygen

Nutrient removal performance and microbial composition analysis in hybrid membrane bioreactor for municipal wastewater treatment

The removal of nutrients from wastewater to reduce the toxicity of these compounds to the environment requires more space in wastewater treatment plants to establish anaerobic, anoxic and aerobic treatment stages. To address this limitation, researchers have developed practical, intensive hybrid treatment systems that enhance nutrient removal performance while requiring less space. However, the implementation of hybrid systems within a reactor introduces the interaction between the attached and suspended growth that can influence the microbial community structure and the performance of the system, so it is crucial to understand the composition of the microbial communities involved in hybrid growth to optimize control strategies in these systems. This study investigated the microbial community structure of the integrated moving bed membrane bioreactor (IMBMBR) system and its impact on nutrient removal in municipal wastewater. The findings demonstrated that the effluent quality was improved with the IMBMBR. The efficiency of removing COD, BOD5,NH 4 + -N andPO 4 3 - -P in the IMBMBR were 91 ± 4.0%, 95 ± 4.0%, 99 ± 0.2% and 24 ± 3.0%, respectively. The IMBMBR had better nitrite oxidation and complete nitrification by increasing the diversity and abundance of effective bacteria. The abundance of Proteobacteria, Bacteroidetes and Nitrospira was enhanced in IMBMBR. Coexistence of ammonia-oxidizing bacteria (AOB) and nitrite-oxidizing bacteria (NOB) in IMBMBR led to increased nutrient removal. The study results suggest that IMBMBR can be an effective process for nutrient removal, achieving quality standards that comply with legal requirements for wastewater in municipal and industries with limited space for establishing treatment facilities. Additionally, this process can be quickly implemented as an upgrade to existing wastewater treatment plants, avoiding the need to develop an entirely new system.

Porous polymers embedded with iron carbon enhanced densified activated sludge formation and wastewater treatment

Municipal wastewater treatment plants in China face significant challenges in effectively removing pollutants from low-strength wastewater with a low carbon-to-nitrogen (COD/N) ratio. This study proposes a novel approach incorporating porous polymers embedded with iron-carbon (PP-IC) into an activated sludge system to enhance treatment. The PP-IC accelerated the formation of densified activated sludge (DAS), characterized by small particle sizes (<200 μm), excellent settleability (sludge volume index: 61 mL/g), and improved pollutant removal efficiency, with total nitrogen and total phosphorus removal rates increasing by 14.4 % and 57.4 %, respectively. DAS formation was achieved within 7 days and stabilized after 42 days. The enrichment of microorganisms, including unclassified_f_Caldilineaceae, Dechloromonas, and Candidatus Accumulibacter, further enhanced pollutant removal. Additionally, Fe2+, Fe3+ and hydroxyl radical (·OH) produced by iron-carbon micro-electrolysis supported DAS formation. Microbial interactions with the iron shavings sustained the long-term stability of the micro-electrolysis process. This synergistic mechanism significantly improved pollutant removal in wastewater treatment.

Laccase-loaded CaCO3 sustained-release microspheres modified SBES anode for enhance performance in the remediation of soil contaminated with phenanthrene and pyrene

This study aimed to enhance the efficiency of SBES in remediating polycyclic aromatic hydrocarbon (PAH)-contaminated soils by modifying the anode with laccase. The experiment involved four SBES anodes: a carbon nanotube-modified anode (CNT), a free laccase-modified anode (Lac), a gelatin-encapsulated laccase-modified anode (Lac-Gel), and a CaCO3 sustained-release microsphere-loaded laccase-modified (CaCO3-SMs@Laccase) anode (Lac-SMs). The CaCO3-SMs@Laccase notably extended the active period of laccase, with laccase activity in the Lac-SMs measured at 1.646 U/g after 16 days, which was significantly higher than the 0.813 U/g observed in the Lac-Gel group and the 0.206 U/g in the Lac group. The superior electricity generation and degradation efficiency observed in the Lac-SMs group were due to the sustained enzymatic activity provided by the CaCO3-SMs@Laccase. The prevention of anode acidification through CaCO3 decomposition, and promote the forward progress of electrochemical reactions. The phenanthrene (Phe) and pyrene (Pyr) removal efficiency in the soil of the Lac-SMs reached 90.78 % and 84.72 %, surpassing those of the Lac-Gel (80.36 % and 79.14 %), Lac (79.38 % and 69.31 %), and CNT (63.22 % and 56.98 %). The degradation pathway from Pyr to Phe was possible started with hydroxylation. In addition, the laccase also transformed the predominant microbial communities and metabolism pathways.

Pre-anoxic electro-stimulation enhanced simultaneous nitrification-denitrification in single-stage electrolysis-integrated sequencing batch biofilm reactor

Simultaneous nitrification-denitrification (SND) is a promising nitrogen removal process. However, total nitrogen (TN) removal is limited due to unsatisfactory denitrification. This study demonstrated that short-time (1 h) pre-anoxic electro-stimulation significantly enhanced SND efficiency in the aerobic phase by promoting the proliferation of mixotrophic and heterotrophic denitrifiers. SND and TN removal efficiencies at the optimal electric current (EC) (0.02 A) were 85.6 % and 93.9 %, which were 39.1 % and 17.2 % higher than control. Microbial community analysis indicated that the abundance of mixotrophic and heterotrophic denitrifiers significantly increased. H2 generated in the electro-stimulation process induced the proliferation of mixotrophic denitrifiers. The weak EC (0.02 A) promoted the activity and growth of heterotrophic denitrifiers by accelerating electron transfer. They concurrently mediated heterotrophic denitrification to enhance SND efficiency. PICRUSt2 analysis revealed that the abundance of denitrifying genes dramatically surged. This study provides new insights into applying electrolysis to achieve advanced SND while minimizing electricity consumption.

Dissolved oxygen drives heterotrophic microorganism succession to regulate low carbon source wastewater treatment enhanced by slurry

The limited availability of carbon sources in low carbon source wastewater has always hindered nitrogen removal efficiency. The residual slurry liquid after anaerobic digestion has the potential to be used as a carbon source. This study investigated the optimal parameters of dissolved oxygen (DO) for enhancing the treatment of low carbon source wastewater using slurry, and revealed the characteristics of carbon metabolism gene enrichment and carbon fixation potential driven by DO. The results indicated that treating wastewater under high DO concentrations (3-4 mg/L) conditions could meet the emission standards set by wastewater treatment plants in China. However, the lower-cost DO concentration of 3 mg/L is considered a more cost-effective parameter, effectively removing 85.68% of chemical oxygen demand and 91.56% of total nitrogen. Mechanistic analysis suggested that reducing DO concentration increased the diversity of microbial communities. Regulating DO concentration reshaped the co-metabolic network of microorganisms with different DO sensitivities by influencing Hydrogenophaga and Chlorobium. This ultimately led to the reconstruction of heterotrophic microbial communities dominated by Sphaerotilus and Acidovorax under high DO conditions, and heterotrophic-autotrophic co-enriched microbial communities dominated by Chlorobium under low DO conditions (1-2 mg/L). Additionally, under high DO conditions, high microbial mass transfer efficiency and the enrichment of functional genes were crucial for achieving high nitrogen removal performance. Further, the microbial carbon fixation potential was relatively high under the DO 3 mg/L condition, helping to reduce the consumption of additional carbon sources. This study provided innovative ideas for the sustainable and low-carbon development of wastewater treatment technology.

Purification of inorganic nitrogen from the mariculture tail water by anaerobic/anoxic/oxic (A2O) process

This study aims to address the suboptimal performance of conventional denitrifying strains in treating mariculture tail water (MTW) containing inorganic nitrogen (IN). The concentration of inorganic nitrogen in the mariculture tail water is about 5-20 mg·L-1. A biofilm treatment process was developed and evaluated using an anoxic-anoxic-aerobic biofilter composite system inoculated with the denitrifying strain Meyerozyma guilliermondii Y8. The removal effect of total nitrogen (TN), IN, and Chemical Oxygen Demand (CODMn) from MTW was investigated. The results indicate that the A2O composite biological filter has excellent pollutant removal efficiency within 25 days of operation, after the acclimation of the denitrifying microorganisms. The initial concentrations of TN, IN, and CODMn ranged between 10.24 and 12.89 mg·L-1, 7.84-10.49 mg·L-1, and 9.44-11.52 mg·L-1, respectively, and the removal rates of these indexes reached 38-68 %, 45-70 %, and 55-70 %, respectively. The experiments with different hydraulic retention times (HRT = 6 h, 8 h, 10 h) demonstrated that longer HRT was more conducive to the removal of inorganic nitrogen. Moreover, scanning electron microscopy observations revealed that the target strain successfully grew and attached to the filler in large quantities. The findings of this study provide practical guidance for the development of efficient biofilm processes for the treatment of MTW.

Key genes of electron transfer, the nitrogen cycle and tetracycline removal in bioelectrochemical systems

BACKGROUND

Soil microbial fuel cells (MFCs) can remove antibiotics and antibiotic resistance genes (ARGs) simultaneously, but their removal mechanism is unclear. In this study, metagenomic analysis was employed to reveal the functional genes involved in degradation, electron transfer and the nitrogen cycle in the soil MFC.

RESULTS

The results showed that the soil MFC effectively removed tetracycline in the overlapping area of the cathode and anode, which was 64% higher than that of the control. The ARGs abundance increased by 14% after tetracycline was added (54% of the amplified ARGs belonged to efflux pump genes), while the abundance decreased by 17% in the soil MFC. Five potential degraders of tetracycline were identified, especially the species Phenylobacterium zucineum, which could secrete the 4-hydroxyacetophenone monooxygenase encoded by EC 1.14.13.84 to catalyse deacylation or decarboxylation. Bacillus, Geobacter, Anaerolinea, Gemmatirosa kalamazoonesis and Steroidobacter denitrificans since ubiquinone reductase (encoded by EC 1.6.5.3), succinate dehydrogenase (EC 1.3.5.1), Coenzyme Q-cytochrome c reductase (EC 1.10.2.2), cytochrome-c oxidase (EC 1.9.3.1) and electron transfer flavoprotein-ubiquinone oxidoreductase (EC 1.5.5.1) served as complexes I, II, III, IV and ubiquinone, respectively, to accelerate electron transfer. Additionally, nitrogen metabolism-related gene abundance increased by 16% to support the microbial efficacy in the soil MFC, and especially EC 1.7.5.1, and coding the mutual conversion between nitrite and nitrate was obviously improved.

CONCLUSIONS

The soil MFC promoted functional bacterial growth, increased functional gene abundance (including nitrogen cycling, electron transfer, and biodegradation), and facilitated antibiotic and ARG removal. Therefore, soil MFCs have expansive prospects in the remediation of antibiotic-contaminated soil. This study provides insight into the biodegradation mechanism at the gene level in soil bioelectrochemical remediation.

Nitrogen source affects non-aeration microalgal-bacterial biofilm growth progression and metabolic function during greywater treatment

The non-aeration microalgal-bacteria symbiotic system has attracted great attention due to excellent pollutants removal performance and low greenhouse gas emission. This study investigated how nitrogen (N) sources (ammonia, nitrate and urea) impact biofilm formation, pollutants removal and microbial niches in a microalgal-bacterial biofilm. Results showed that functional genus and enzymes contributed to organics biodegradation and carbon fixation, N transformation and assimilation enabled efficient pollutants removal without CO2 emission. Urea achieved the maximum chemical oxygen demand (89.2%) and linear alkylbenzene sulfonates (95.3%) removal. However, Nitrate significantly influenced microbial community structure and enabled the highest removal of total N (89.7%). Multifarious functional groups enabled the fast adsorption of pollutants, which favored the continuous transformation and fixing of carbon and N. But N source significantly affects the carbon and N dissimilation and fixing pathways. This study offers a promising alternative method that achieving low-carbon-footprint and cost-saving greywater treatment.

Effects of air blower and pump failures on the performance of A2O processes for wastewater treatment

The unexpected failure of equipment such as pumps and fans in wastewater treatment plants can reduce wastewater treatment efficiency, leading to direct leakage of untreated wastewater into the environment. It is hence important to predict the possible consequences of equipment failure to minimize the leakage of harmful substances. This study examines the impacts of equipment shutdown on the performance and recovery time of a laboratory-scale anaerobic/anoxic/aerobic system with regard to reactor conditions and water quality. Two days after the air blowers are stopped, the concentrations of the soluble chemical oxygen demand, NH4-N, and PO4-P in the effluent of the settling tank increase to 122 mg/L, 23.8 mg/L, and 46.6 mg/L, respectively. These concentrations return to their initial values after 12, 24, and 48 h of restarting the air blowers. The concentrations of PO4-P and NO3-N in the effluent increase to 58 mg/L and 20 mg/L, respectively, about 24 h after stopping the return activated sludge and mixed liquor recirculation pumps, owing to the release of phosphates in the settling tank and inhibition of denitrification.

Different in root exudates and rhizosphere microorganisms effect on nitrogen removal between three emergent aquatic plants in surface flow constructed wetlands

Swine wastewater contains high concentration of nitrogen (N), causing pollution of surrounding water bodies. Constructed wetlands (CWs) are considered as an effective ecological treatment measure to remove nitrogen. Some emergent aquatic plants could tolerate high ammonia, and play a crucial part in CWs to treat high concentration N wastewater. However, the mechanism of root exudates and rhizosphere microorganisms of emergent plants on nitrogen removal is still unclear. Effects of organic and amino acids on rhizosphere N cycle microorganisms and environmental factors across three emergent plants were investigated in this study. The highest TN removal efficiency were 81.20% in surface flow constructed wetlands (SFCWs) plant with Pontederia cordata. The root exudation rates results showed that organic and amino acids were higher in 56 d than that in 0 d in SFCWs plants with Iris pseudacorus and P. cordata. The highest ammonia-oxidizing archaea (AOA) and ammonia-oxidizing bacteria (AOB) gene copy numbers were found in I. pseudacorus rhizosphere soil, while the highest nirS, nirK, hzsB and 16S rRNA gene copy numbers were detected in P. cordata rhizosphere soil. Regression analysis results demonstrated that organic and amino acids exudation rates were positive related to rhizosphere microorganisms. These results indicated that organic and amino acids secretion could stimulate growth of emergent plants rhizosphere microorganisms in SFCWs for swine wastewater treatment. In addition, the EC, TN, NH4+-N and NO3--N were negatively correlated with organic and amino acids exudation rates, and abundances of rhizosphere microorganisms via Pearson correlation analysis. These results imply that organic and amino acids, and rhizosphere microorganisms synergically affected on the nitrogen removal in SFCWs.

Recent advances in simultaneous nitrification and denitrification for nitrogen and micropollutant removal: a review

Simultaneous Nitrification and Denitrification (SND) is a promising process for biological nitrogen removal. Compared to conventional nitrogen removal processes, SND is cost-effective due to the decreased structural footprint and low oxygen and energy requirements. This critical review summarizes the current knowledge on SND related to fundamentals, mechanisms, and influence factors. The creation of stable aerobic and anoxic conditions within the flocs, as well as the optimization of dissolved oxygen (DO), are the most significant challenges in SND. Innovative reactor configurations coupled with diversified microbial communities have achieved significant carbon and nitrogen reduction from wastewater. In addition, the review also presents the recent advances in SND for removing micropollutants. The micropollutants are exposed to various enzymes due to the microaerobic and diverse redox conditions present in the SND system, which would eventually enhance biotransformation. This review presents SND as a potential biological treatment process for carbon, nitrogen, and micropollutant removal from wastewater.