Recovery strategies and mechanisms of anammox reaction following inhibition by environmental factors: A review.

Anaerobic ammonium oxidation (anammox) is a promising biological method for treating nitrogen-rich, low-carbon wastewater. However, the application of anammox technology in actual engineering is easily limited by environmental factors. Considerable progress has been investigated in recent years in anammox restoration strategies, significantly addressing the challenge of poor reaction performance following inhibition. This review systematically outlines the strategies employed to recover anammox performance following inhibition by conventional environmental factors and emerging pollutants. Additionally, comprehensive summaries of strategies aimed at promoting anammox activity and enhancing nitrogen removal performance provide valuable insights into the current research landscape in this field. The review contributes to a comprehensive understanding of restoration strategies of anammox-based technologies.

A review of anammox metabolic response to environmental factors: Characteristics and mechanisms.

Anaerobic ammonium oxidation (anammox) is a promising low carbon and economic biological nitrogen removal technology. Considering the anammox technology has been easily restricted by environmental factors in practical engineering applications, therefore, it is necessary to understand the metabolic response characteristics of anammox bacteria to different environmental factors, and then guide the application of the anammox process. This review presented the latest advances of the research progress of the effects of different environmental factors on the metabolic pathway of anammox bacteria. The effects as well as mechanisms of conventional environmental factors and emerging pollutants on the anammox metabolic processes were summarized. Also, the role of quorum sensing (QS) mediating the bacteria growth, gene expression and other metabolic process in the anammox system were also reviewed. Finally, interaction and cross-feeding mechanisms of microbial communities in the anammox system were discussed. This review systematically summarized the variations of metabolic mechanism response to the external environment and cross-feeding interactions in the anammox process, which would provide an in-depth understanding for the anammox metabolic process and a comprehensive guidance for future anammox-related metabolic studies and engineering applications.

From waste-activated sludge to algae: a self-reliant cultivation process in photoreactors using saline conditions.

In this study, microalgae-bacteria (MB) systems using saline conditions (3 and 5% salinity) were built in order to use waste-activated sludge (AS) as raw material for cultivating lipid-rich microalgae. Algae were observed to be flourishing in 60 days of operation, which totally used the N and P released from the sludge biomass. A prominent improvement of lipid content in MB consortia was obtained under algae growth and salinity stimulation, which occupied 119-136 mg/g-SS rather than a low content of 12.1 mg/g-SS in AS. Lipid enrichment also brought a 3.1-3.3 times total heat release (THR) in the MB biomass. The marine spherical algae Porphyridium, as well as filamentous Geitlerinema, Nodularia, Leptolyngbya were found to be the main lipid producers and self-flocculated to 23.0% (R1) and 33.5% (R2) volume under the effect of residue EPS. This study had a big meaning in not only waste sludge reduction but also in manufacturing useful bioenergy products.

Microbial population changes and metabolic shift of candidatus accumulibacter under low temperature and limiting polyphosphate.

This study explored the microbial population dynamics of Accumulibacter (Acc) at low temperature and metabolic shift to limiting polyphosphate (Poly-P) in enhanced biological phosphorus removal (EBPR) system. The Accumulibacter-enriched EBPR systems, fed with acetate (HAc) and propionate (HPr) at 10 ± 1 °C respectively, were operated for 60 days in two identical SBR reactors (SBR-1 and SBR-2). The phosphorus removal performance in two systems was stable at 10 ± 1 °C, while the microbial community structure changed. Compared with the population structure in seed sludge, Accumulibacter clades reduced in the HAc system, while Acc I increased significantly in the HPr system. Low temperature was beneficial to the formation of granular sludge in the EBPR system, and the sludge granulation in the HAc system was more homogeneous than that in the HPr system. Accumulibacter in the HPr system can get ATP through glycogen accumulating metabolism (GAM) under limiting Poly-P condition at 10 ± 1 °C, while that in the HAc system cannot. This work suggests that poly-P levels can affect the metabolic pathway of Accumulibacter in EBPR systems under low temperature.

Fate of phthalates in a river receiving wastewater treatment plant effluent based on a multimedia model.

Phthalic acid esters (PAEs) can enter environment media by secondary effluent discharge from wastewater treatment plants (WWTP) into receiving rivers, thus posing a threat to ecosystem health. A level III fugacity model was established to simulate the fate and transfer of four PAEs in a study area in Tianjin, China, and to evaluate the influence of WWTP discharge on PAEs levels in the receiving river. The results show that the logarithmic residuals of most simulated and measured values of PAEs are within one order of magnitude with a good agreement. PAEs in the study area were mainly distributed in soil and sediment phases, which accounted for 84.66%, 50.26%, 71.96% and 99.09% for dimethyl phthalate (DMP), diethyl phthalate (DEP), dibutyl phthalate (DBP) and di-(2-ethylhexyl) phthalate (DEHP), respectively. The upstream advection accounted for 77.90%, 93.20%, 90.21% and 90.93% of the total source of DMP, DEP, DBP and DEHP in the river water, respectively, while the contribution of secondary effluent discharge was much lower. Sensitivity analysis shows that emission and inflow parameters have greater influences on the multimedia distributions of PAEs than physicochemical and environmental parameters. Monte Carlo analysis quantifies the uncertainties and verifies the reliability of the simulation results.

Effect of organic loading on phosphorus forms transformation and microbial community in continuous-flow A2/O process.

A continuous-flow Anaerobic/Anoxic/Oxic (A2/O) system was operated at different organic concentrations to systematically investigate the effect on the nutrient removal, secretion characteristics of extracellular polymer, phosphorus forms transformation and changes in functional flora in this system. The results showed that high organic loading was more conducive to promote the secretion of extracellular polymeric substance (EPS), the increase of polysaccharide content was more obvious compared with protein, the impact of organic loading on the components of loosely bound EPS (LB-EPS) was higher than that of tight-bound EPS (TB-EPS). Phosphorus in sludge floc mainly existed in the form of inorganic phosphorus (IP), and IP mainly existed in the form of apatite inorganic phosphorus (AP). High organic load showed higher phosphorus storage in EPS, and the phosphorus content in EPS was positively correlated with the content of EPS. Non-apatite phosphorus (NAIP) content played an important role in the extracellular dephosphorization. The abundance of Nitrosomonas and Nitrospira responsible for nitrification decreased with the increase in organic loading. The group of denitrifiers was large, and Azospira was the most abundant genus among them. Dechloromonas, Acinetobacter, Povalibacter, Chryseolinea and Pirellula were the functional genera closely associated with phosphorus removal.

Chemical speciation and risk assessment of heavy metals in biochars derived from sewage sludge and anaerobically digested sludge.

Dewatered sewage sludge (DSS) and anaerobically digested sludge (ADS) were pyrolyzed at 550 °C to investigate the characteristics of derived biochar and evaluate the risk of heavy metals (Cr, Ni, Cu, As, Cd, and Pb). The results showed that the pH value of the biochar derived from DSS (DSS-C) was slightly lower than that of the biochar derived from ADS (ADS-C), while DSS-C presented relatively higher specific surface area and total pore volume. DSS-C also showed higher H/C and lower O/C ratios than ADS-C, indicating a higher aromatic condensation and a lower polarity. Total concentrations of Cr, Ni, Cu, As, Cd, and Pb in DSS and ADS increased significantly after pyrolysis owing to the thermal decomposition of organic matter in the sludge, with corresponding rise of the Nemerow pollution index (NPI) of the biochars compared with the raw sludge. In addition, the sequential extraction procedure (BCR) analysis revealed that the pyrolysis process promoted the transformation of heavy metals from bio-available fractions to stable fractions. The potential environmental risk of heavy metals decreased from moderate and extremely high levels in the DSS and ADS to low risk and moderate levels in DSS-C and ADS-C after pyrolysis, respectively.

Influence of thermal hydrolysis treatment on chemical speciation and bioleaching behavior of heavy metals in the sewage sludge.

In this study, the transformation of chemical speciation of Cr, Mn, As and Cd in the sewage sludge before and after thermal hydrolysis treatment was investigated using modified BCR method. The effect of thermal hydrolysis treatment and chemical speciation change on the subsequent bioleaching behavior was also researched. The results showed that the concentrations of Cr, Mn, As and Cd in oxidizable fraction decreased in the sludge treated by thermal hydrolysis. Meanwhile, the proportions of Cr, Mn and As in the mobile fractions (acid-soluble/exchangeable and reducible fraction) all decreased, while Cd was concentrated in the sludge treated by thermal hydrolysis. The final pH value of bioleached sludge treated by thermal hydrolysis was lower than that in the bioleached raw sewage sludge. And faster increase of oxidation-reduction potential (ORP) was also found in the bioleaching process of the sludge treated by thermal hydrolysis. The removal percentage of Mn and Cd increased in the bioleached sludge treated by thermal hydrolysis. Thermal hydrolysis treatment can promote the bioleaching to some extent. Furthermore, the environmental risk of Cr, Mn, As and Cd in the bioleached sludge treated by thermal hydrolysis was all alleviated according to risk assessment analysis compared with the bioleached raw sewage sludge.

Start-up of single-stage partial nitritation-anammox micro-granules system: Performance and microbial community dynamics.

By manipulating influent nitrogen load and DO concentration in bulk liquid, the start-up and performance of a new micro-granule based partial nitritation-anammox process was investigated in a continuous stirred tank reactor (CSTR). Under the condition of nitrogen loadings from 0.3 to 1.4 kgN /m³/d and DO <0.21mg/L, the single-stage partial nitritation-anammox (SPNA) system was successfully started, with a nitrogen removal of 76.2%. Meanwhile, the oxygen utilization efficiency by ammonium oxidizing bacteria (AOB) increased in the system with the increase of influent ammonia loading rate. Micro-granules with an average diameter of 0.25 mm were formed. Sludge granulation was promoted by increasing influent nitrogen load, and there was a positive correlation between nitrogen load, extracellular polymeric substances (EPS) content and sludge particle size. Ca. Kuenenia became the dominant anaerobic ammonium oxidizing bacteria (AnAOB) in the SPNA system. As the dominant AOB genera, Nitrosomonas coexist with Ca. Kuenenia in the micro-granules.

Effect of biochar on the SPNA system at ambient temperatures.

Biochar has been extensively studied in wastewater treatment systems. However, the role of biochar in the single-stage partial nitritation anammox (SPNA) system remains not fully understood. This study explored the impact of biochar on the SPNA at ambient temperatures (20 °C and 15 °C). The nitrogen removal rate of the system raised from 0.43 to 0.50 g N/(L·d) as the biochar addition was raised from 2 to 4 g/L. Metagenomic analysis revealed that gene abundances of amino sugar metabolism and nucleotide sugar metabolism, amino acid metabolism, and quorum sensing were decreased after the addition of biochar. However, the gene abundance of enzymes synthesizing NADH and trehalose increased, indicating that biochar could stimulate electron transfer reactions in microbial metabolism and assist microorganisms in maintaining a steady state at lower temperatures. The findings of this study provide valuable insights into the mechanism behind the improved nitrogen removal facilitated by biochar in the single-stage partial nitritation anammox system.

A review of distribution and functions of extracellular DNA in the environment and wastewater treatment systems.

Extracellular DNA refers to DNA fragments existing outside the cell, originating from various cell release mechanisms, including active secretion, cell lysis, and phage-mediated processes. Extracellular DNA serves as a vital environmental biomarker, playing crucial ecological and environmental roles in water bodies. This review is summarized the mechanisms of extracellular DNA release, including pathways involving cell lysis, extracellular vesicles, and type IV secretion systems. Then, the extraction and detection methods of extracellular DNA from water, soil, and biofilm are described and analyzed. Finally, we emphasize the role of extracellular DNA in microbial community systems, including its significant contributions to biofilm formation, biodiversity through horizontal gene transfer, and electron transfer processes. This review offers a comprehensive insight into the sources, distribution, functions, and impacts of extracellular DNA within aquatic environments, aiming to foster further exploration and understanding of extracellular DNA dynamics in aquatic environments as well as other environments.

Transformation and environmental risk of heavy metals in sewage sludge during the combined thermal hydrolysis, anaerobic digestion and heat drying treatment process.

The design of this study was to investigate the solid-aqueous migration and chemical speciation transformation of heavy metals (HMs) in the sewage sludge during the combined process of thermal hydrolysis, anaerobic digestion and heat-drying. The results showed that most of the HMs were still accumulated in the solid phase of various sludge samples after treatment. After thermal hydrolysis, the concentrations of Cr, Cu and Cd increased slightly. All the HMs measured after anaerobic digestion were concentrated obviously. While the concentrations of all HMs decreased slightly after heat-drying. The stability of HMs in the sludge samples was enhanced after treatment. The environmental risks of various HMs were also relieved in the final dried sludge samples.

[Properties of Biochars Prepared from Different Crop Straws and Leaching Behavior of Heavy Metals].

In this study, rice straw, soybean straw, wheat straw, and corn straw were chosen as raw materials, and biochars were prepared through the pyrolysis method at 550℃ under oxygen-limited conditions to investigate the physicochemical properties of biochars derived from the straws, the migration and transformation characteristics of heavy metals (HMs) (Cr, Ni, Cu, As, Cd, and Pb) after pyrolysis, and their leaching behaviors in different leaching solutions. The results showed that the physicochemical properties and elemental composition of the biochars were basically consistent. However, compared with that of biochars derived from other straws, biochar derived from wheat straw had a higher ash content (22.48%) and H/C radio (0.06). Meanwhile, biochar derived from corn straw had a smaller micropore volume (0.006 cm3·g-1) and a correspondingly smaller specific surface area (110.120 m2·g-1), which was consistent with the SEM image. After pyrolysis, the content of HMs (except Cd) increased by 14.04% to 410.81%, especially that of Cu and As. However, the content of Cd in soybean straw and corn straw decreased by 20.49% and 8.20% after pyrolysis, respectively, due to the low boiling point of Cd. Furthermore, most of the HMs (except Cd and Pb) tended to transform from unstable (acid-soluble/exchangeable and reducible forms) to stable forms (oxidizable and residual forms), implying that pyrolysis facilitated the stabilization of the HMs. The HMs in biochar were not leached or were leached in small amounts in ultra-pure water and buffered salt solutions, as opposed to leaching in relatively larger amounts in acetic acid solution and humic acid solution. Cr and Ni showed low leaching capacity in all leaching solutions. Cu showed relatively high leaching capacity in acetic acid solution, with the leaching amount ranging from 2.601 mg·kg-1 to 4.224 mg·kg-1, and As showed a relatively high leaching capacity in humic acid solution, with the leaching amount ranging from 0.074 mg·kg-1to 0.166 mg·kg-1. After pyrolysis, the environmental quality index (PIi) and the Nemerow pollution index (NPI) values of various HMs increased by different degrees. However, the pollution of single HMs remained at a safe level, and the integrated pollution of biochars was at the level of "clean". Due to the significant increase in potential ecological risk factors (Er) of Ni, Cd, and Pb after pyrolysis, the potential ecological risk index (RI) of biochar derived from the rice straw increased slightly. However, the potential ecological risk indexes of biochars derived from other straws significantly decreased after pyrolysis, owing to the stabilization of HMs.

Extracellular polymeric substances and microbial community shift during the start-up of a single-stage partial nitritation/anammox process.

A sequencing batch reactor (SBR) was operated to investigate variations of extracellular polymeric substances (EPS) and microbial community during the start-up of the single-stage partial nitritation/anammox (SPN/A) process at intermittent aeration mode. The SPN/A system was successfully started on day 34, and the nitrogen removal efficiency and total nitrogen loading rate were 82.29% and 0.31 kg N/(m3 ·day), respectively. Furthermore, the relationship between the protein secondary structures and microbial aggregation was strongly related. The α-helix/ (ß-sheet + random coil) ratios increased obviously from 0.20 ± 0.03 to 0.23 ± 0.01, with the sludge aggregation mean size increased from 56 to 107 µm during the start-up of SPN/A. During the start-up of SPN/A, Candidatus Kuenenia was the primary anammox bacteria, whereas Nitrospira was the main functional bacteria of nitrite-oxidizing bacteria. Correlation between the microbial community and EPS components was performed. The EPS and microbial community played important roles in keeping stable nitrogen removal and the formation of sludge granules. PRACTITIONER POINTS: Intermittent aeration strategy promoted SPN/A system start-up. EPS composition and protein secondary structure were related with the sludge disintegration and aggregation. Microbial community shift existed and promoted the stability of sludge and reactor performance during SPN/A start-up.

Applying real-time control for achieving nitrogen removal via nitrite in a lab-scale CAST system.

In this study, a bench-scale Cyclic Activated Sludge Technology (CAST) reactor (72?L), fed with domestic sewage, was operated in alternating anoxi-aerobic operation mode to investigate the feasibility of achieving short-cut nitrification and denitrification with a real-time control strategy. An online system for controlling the length of the aeration and stirring phases was implemented, based on pH and oxidation-reduction potential signals, to switch between aerobic and anoxic sequences. Results show that the real-time control strategy was successful in achieving a stable nitrogen removal performance. Furthermore, short-cut nitrification can be achieved by controlling aeration length under the modified real-time control strategy. Gradually reducing the energy supply for nitrite-oxidizing bacteria caused the limitation of their growth and, finally, their elimination. When short-cut nitrification was obtained, the nitrite pathway became the primary way for nitrogen removal, and aeration duration was reduced by 28.4%.

Control strategy and performance of simultaneous removal of nitrogen and organic matter in treating swine manure digestate using one reactor with airlift and micro-granule.

A simultaneous partial nitritation, anammox, denitrification, and COD oxidation (SNADCO) process was used to evaluate the nitrogen and biodegradable organic matter removal of swine manure digestate based on a nitrite limitation and ammonium surplus strategy. As influent ammonium concentration increased from 500 mg/L to 2100 mg/L, the 5 day biochemical oxygen demand (BOD5) maintained at a high removal efficiency of 95.4%. However, nitrogen removal efficiency (NRE) decreased from 90.9% to 68.2% due to the inhibition of AnAOB caused by an ammonium concentration of 2100 mg/L. The contribution of AnAOB to nitrogen removal was 75.6-86.5%, while that of denitrifying bacteria was 4.6-7.0%. In the case of COD removal, the contributions were from ordinary heterotrophic organisms and denitrifying bacteria, at 27.1-64.9% and 11.2-22.1%, respectively. The results of specific bacteria activity tests and microbial analysis showed that a highly efficient synergism between functional microorganisms is essential for the stability of the SNADCO process.

Effect of filamentous algae in a microalgal-bacterial granular sludge system treating saline wastewater: Assessing stability, lipid production and nutrients removal.

In this study modified microalgal-bacterial granular sludge (MBGS) was constructed and employed to compare the performance for treating 1%-5% saline wastewater with aerobic granular sludge (AGS). Filamentous algae were found to flourish at 1% salinity when nutrients were temporarily restricted to low level (COD 0, N 10 mg/L, P 0.5 mg/L). A significant improvement of granule stability was detected as the integrity coefficients of MBGS was only 0.12-0.24 rather than 0.19-0.48 of AGS under 1%-5% salinities, which reduced the risk of particle disintegration. Filamentous algae including Leptolyngbya and Geitlerinema occupied 91.2% of identified algae, and were beneficial for enhancing the biomass content and lipid production to about 1.27-1.37, 3.1-5.0 times than AGS. The MBGS had best nitrogen and phosphorus removal efficiencies of 93.4% and 64.6% at 1% salinity, and showed higher resistance to 3%-5% salinities. This study could provide meaningful information for using this modified MBGS technology in practice.

Enhancement of thermophilic anaerobic digestion of thickened waste activated sludge by combined microwave and alkaline pretreatment.

Abstract Pretreatment of thickened waste activated sludge (TWAS) by combined microwave and alkaline pretreatment (MAP) was studied to improve thermophilic anaerobic digestion efficiency. Uniform design was applied to determine the combination of target temperature (11 degrees-210 degrees C), microwave holding time (1-51 min), and NaOH dose (0-2.5 g NaOH/g suspended solids (SS)) in terms of their effect on volatile suspended solids (VSS) solubilization. Maximum solubilization ratio (85.1%) of VSS was observed at 210 degrees C with 0.2 g-NaOH/g-SS and 35 min holding time. The effects of 12 different pretreatment methods were investigated in 28 thermophilic batch reactors by monitoring cumulative methane production (CMP). Improvements in methane production in the TWAS were directly related to the microwave and alkaline pretreatment of the sludge. The highest CMP was a 27% improvement over the control. In spite of the increase in soluble chemical oxygen demand concentration and the decrease in dewaterability of digested sludge, a semi-continuous thermophilic reactor fed with pretreated TWAS without neutralization (at 170 degrees C with 1 min holding time and 0.05 g NaOH/g SS) was stable and functioned well, with volatile solid (VS) and total chemical oxygen demand (TCOD) reductions of 28% and 18%, respectively, which were higher than those of the control system. Additionally, methane yields (L@STP/g-CODadded, at standard temperature and pressure (STP) conditions of 0 degree C and 101.325 kPa) and (L@STP/g VSadded) increased by 17% and 13%, respectively, compared to the control reactor.

Efficient degradation of ciprofloxacin by magnetic γ-Fe2O3-MnO2 with oxygen vacancy in visible-light/peroxymonosulfate system.

In this work, the magnetic γ-Fe2O3-MnO2 bifunctional catalyst with oxygen vacancy was synthesized for peroxymonosulfate (PMS) activation under visible light. The activity of γ-Fe2O3-MnO2 was investigated by ciprofloxacin (cipro) degradation. Results showed that 98.3% of cipro (50 µM) was removed within 30 min in visible-light/PMS system mediated by γ-Fe2O3-MnO2 (2:1) with fine-tuned oxygen vacancy. The cipro degradation data fitted well with pseudo-first-order kinetic model with the highest kinetic constant of 0.114 min-1. Besides, the γ-Fe2O3-MnO2 exhibited stability, recyclability and practicability. High selectivity for cipro degradation was observed with coexisting anions in visible-light/γ-Fe2O3-MnO2/PMS system. Furthermore, the enhanced mechanism of PMS activation under visible light with γ-Fe2O3-MnO2 was proposed. The appropriate oxygen vacancy enhanced the separation of photo-induced carriers and Z scheme heterostructure maintained the highest redox potential. Accordingly, the synergistic effect of photocatalysis and PMS activation enhanced cipro degradation. Free radical and non-radical species including , h+, 1O2, •OH and co-existed in the coupled system. Impressively, this study provides a handy approach for oxygen vacancy regulation in metallic oxides composite and an easily recycled catalyst with high-activity in coupled oxidation system towards antibiotic degradation.

Removal behavior and chemical speciation distributions of heavy metals in sewage sludge during bioleaching and combined bioleaching/Fenton-like processes.

The removal and chemical speciation changes of heavy metals in the sewage sludge during the single bioleaching and combined bioleaching/Fenton-like processes were compared in this study. The improvement in the dewaterability of the treated sludge was also investigated. The single bioleaching led to a removal of Zn, Cu, Cd, Cr, Mn, Ni, As and Pb of 67.28%, 50.78%, 64.86%, 6.32%, 56.15%, 49.83%, 20.78% and 10.52% in 10 days, respectively. The chemical speciation analysis showed that the solubilization of heavy metals in mobile forms (exchangeable/acid soluble and reducible forms) and oxidizable form was the main reason for their removal. Subsequent Fenton-like treatment was carried out at different bioleaching stages when the bioleached sludge dropped to certain pH values (4.5, 4.0 and 3.0), by adding H2O2 at different dosages. The highest removal ratio of Zn, Cu, Cd, Cr, Mn and Ni could reach 75.53%, 52.17%, 71.91%, 11.63%, 66.29% and 65.19% after combined bioleaching/Fenton-like process, respectively, with appropriate pH and H2O2 dosages in less than 6 days. The solubilization efficiencies of these heavy metals in mobile forms were further improved by Fenton-like treatment. The removal efficiencies of As and Pb decreased due to their transformation into insoluble forms (mostly residual fraction) after Fenton treatment. The capillary suction times (CST) of the raw sludge (98.7 s) decreased by 79.43% after bioleaching and 87.44% after combined process, respectively.