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.

Effect and mechanism of coexistence of microplastics on arsenate adsorption capacity in water.

Arsenic pollution control technology in water was important to ensure environmental health and quality safety of agricultural products. Therefore, the adsorption performance of three adsorbents for chitosan, sepiolite, and Zeolitic Imidazolate Framework-8 (ZIF-8) were investigated in arsenate contaminated water. The results revealed that the adsorption capacity of ZIF-8 was higher than that of chitosan and sepiolite. The analysis of adsorption isotherm models showed that the behavior of ZIF-8 was more consistent with the Langmuir model. Furthermore, the adsorption mechanisms of three adsorbents for arsenate were investigated by Fourier-transform infrared spectroscopy (FTIR) and X-ray photoelectron spectroscopy (XPS). The analysis of FTIR showed that ZIF-8 maintained the stability of the interaction with arsenate by forming As-O chemical bonds. However, the effect of chitosan and sepiolite with arsenate was mainly physical adsorption. The analysis of XPS showed that the absorption of ZIF-8 with arsenate involved metal sites and nitrogen through the characteristic peak and the change of the binding energy. Furthermore, the impact of microplastics as a widespread coexistence pollutant in the water on adsorbent performance was investigated. The results indicated that the adsorption capacity of ZIF-8 was almost not affected by microplastics. The maximum adsorption amount of arsenate was changed from 73.45 mg/g to 81.89 mg/g. However, the maximum adsorption amount of chitosan and sepiolite decreased by 31.4 % and 11.6 %, respectively. The analysis of FTIR and XPS revealed that ZIF-8 enhances arsenate adsorption by forming N-O-As bonds in the presence of microplastics. This study provides scientific evidence for the management of arsenate pollution in water bodies, especially in complex water bodies containing microplastics.

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.

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.

Arsenate phytotoxicity regulation by humic acid and related metabolic mechanisms.

The use of irrigation water containing arsenic (As) had led to large areas of As-contaminated farmland, and as a result, plants and food have become severely poisoned. Humic acid (HA) can be complexed with metals, which in turn affects the metals' behavior. Herein, we explored the accumulation of arsenate in lettuce treated with different concentrations of arsenate and studied the effects of HA on the accumulation and toxicity of arsenate. The addition of HA did not cause significant changes in the arsenate content in lettuce but had a significant effect on the activity of antioxidant enzymes, which improved the antioxidant capability of the lettuce plants. Furthermore, HA promoted the accumulation of nutrients, such as magnesium (Mg), calcium (Ca), molybdenum (Mo) and manganese (Mn), in the leaves. Arsenate disrupted metabolic pathways, such as amino acid metabolism, carbohydrate metabolism, and aminoacyl-tRNA biosynthesis. The addition of HA increased the contents of amino acids and sugars, thereby improving lettuce growth. The present study explored the effects of HA on As accumulation and related physiological changes (antioxidant enzyme activities, absorption of nutrients and metabolic mechanisms) and provided insights into the regulation of As contamination by HA, which is relatively inexpensive.

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.

Stability of pure oxygen aeration-activated sludge system under non-steady food-to-microorganism ratio conditions during petrochemical wastewater treatment.

This study investigates the stability of a pure oxygen aeration-activated sludge system for petrochemical wastewater treatment under high organic concentration and non-steady food-to-microorganism (F/M) ratio conditions. Sludge settling characteristics maintained relatively stable conditions with an F/M ratio variation from 0.15 ± 0.04 to 0.33 ± 0.07 kg COD/kg MLSS⋅d, while the excess F/M ratio (0.44 ± 0.16 kg COD/kg MLSS⋅d) resulted in deterioration of the organic removal and sludge-water separation performances. Loosely bound extracellular polymeric substances (EPS) showed more significant effect on sludge settleability than the tightly bound EPS. The genus Hydrogenophaga was related to organic removal performance, while Zoogloea and Chitinophaga were related to the effluent quality of suspended solids. The excess F/M ratio also caused an increase in Zoogloea and Chitinophaga, whereas the toxicity of petrochemical wastewater resulted in decreased abundance of Hydrogenophaga. These changes caused deterioration of the organic removal and sludge-water separation performances.

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.

Effects of pH and substrate concentrations on dark fermentative biohydrogen production from xylose by extreme thermophilic mixed culture.

Biohydrogen is considered as one of the most promising energy alternatives considering the climate and energy crisis. The dark fermentative hydrogen production from xylose at extreme thermophilic condition (70 °C) using mixed culture was conducted in this study. The effects of initial pH values (ranged from 5.0 to 10.0) and substrate concentrations (ranged from 2.5 to 15.0 g/L) on the hydrogen production, substrate degradation and metabolite distributions were investigated using batch-mode operations. Results showed that initial substrate pH values in the neutral region (6.0-7.0) were beneficial for hydrogen production. The fermentation at initial pH 7.0 and 7.5 g/L xylose reached an optimal hydrogen yield of 1.29 mol-H2/mol-xyloseconsumed. Ethanol, butyrate, and propionate were the major liquid metabolites. The xylose biodegradation efficiency of the mixed culture decreased sharply at high initial culture pH values. The increase of xylose concentration resulted in the accumulation of propionate and an obvious decrease in the final pH value, as well as a low hydrogen yield. Polymerase chain reaction-denaturing gradient gel electrophoresis analysis indicated that hydrogen producing bacteria were enriched by repeated culture under extreme thermophilic conditions. Also, the mixed culture was dominated with bacterial species related to Clostridium and Thermoanaerobacterium.

Purification of high ammonia wastewater in a biofilm airlift loop bioreactor with microbial communities analysis.

A 70 m(3) gas-liquid-solid three-phase flow airlift loop bioreactor, in which biofilm attached on granular active carbon carriers, was used for purification of the high ammonia wastewater from bioethanol production. Under the optimum operating conditions, COD and NH4 (+)-N average removal rate of 89.0 and 98.6 % were obtained at hydraulic retention time of 10 h. Scanning electron microscopy was applied for observation of the biofilm formation. High contaminants removal efficiency was achieved by holding high biomass concentration in the reactor due to the attached biofilm over the carriers. The 16S rRNA gene clone library analysis indicated that 68.6 % of the clones were affiliated with the two phyla Bacteroidetes and Proteobacteria, and residual clones clustered with various sequences from uncultured bacteria. The presence of various anoxic/anaerobic bacteria indicated that the oxygen gradient inside the biofilm could provide appropriate micro-environment for nitrogen removal through simultaneous nitrification and denitrification.

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.

A method for simulating spatial fates of chemicals in flowing lake systems: Application to phthalates in a lake.

In order to describe spatio-temporal distribution of chemicals in flowing lake systems, a dynamic multimedia fate model of chemicals with spatial differentiation was constructed by coupling the level IV fugacity model with lake hydrodynamics. It was successfully applied to four phthalates (PAEs) in a lake recharged by reclaimed water and its accuracy was verified. Results show that under the long-term influence of flow field, the distributions of PAEs in both lake water and sediment have significant spatial heterogeneity of 2∼5 orders of magnitude, but present different distribution rules, which was explained by analysis of PAE transfer fluxes. The spatial distribution of PAEs in the water column depends on hydrodynamic conditions and whether the primary source is reclaimed water or atmospheric input. Slow water exchange and flow speed promote the migration of PAEs from water to sediment, causing them to always accumulate in sediments far away from the recharging inlet. Uncertainty and sensitivity analysis show that the PAE concentrations in water phase are mainly affected by emission and physicochemical parameters, while those in sediment phase are also sensitive to environmental parameters. The model can provide important information and accurate data support for the scientific management of chemicals in flowing lake systems.

[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.

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.

Effect of mixed petrochemical wastewater with different effluent sources on anaerobic treatment: organic removal behaviors and microbial community.

Petrochemical industrial effluent contains industrial wastewater from various manufacturing processes. The mixed treatment of these different petrochemical wastewater effluents may influence the organic removal performance of the anaerobic processes. In this study, three typical petrochemical effluents, including polyester (PE), polyethylene terephthalate, and purified terephthalic acid wastewater, were collected. The effect of the mixed petrochemical wastewater on the organic removal and microbial community structure was investigated in the anaerobic batch assays via spectroscopy and high-throughput sequencing. The organic removal efficiencies were similar (71-85%) in all the batch assays for 90 h acclimation. The mixture of wastewater, especially the addition of PE wastewater, significantly prolonged organic removal process. It was related to the aromatic removal performance and microbial community structure during the mixed wastewater treatment. The microbial community structure in the mixed wastewater batch assay showed high similarity with that in the PE wastewater batch assay. Ignavibacterium, Syntrophus, and Pelotomaculum were crucial to the degradation of aromatic compounds together with Methanosaeta. The mixture of wastewater, especially the addition of PE wastewater, caused the decay of these functional microbes and resulted in the inefficient removal of the aromatic compounds.

Occurrence, migration and health risk of phthalates in tap water, barreled water and bottled water in Tianjin, China.

This study was to investigate the occurrence, migration and health risk of phthalic acid esters (PAEs) in tap water, barreled water and bottled water in Tianjin, China. Six priority controlled PAEs were measured, among which the detection frequency of butyl benzyl phthalate (BBP), dibutyl phthalate (DBP) and di(2-ethylhexyl) phthalate (DEHP) was 100%, while the others were not detected. The concentration of DEHP was higher than BBP and DBP in all the samples. The initial ∑3PAEs concentrations in tap water, barreled water and bottled water were 2.409 ± 0.391 µg/L, 1.495 ± 0.213 µg/L and 1.963 ± 0.160 µg/L, respectively. Boiling tap water could reduce the PAEs content to an extent, but they increased significantly in hot tap water contacting with disposable plastic cups. The migration of PAEs in barreled water and bottled water were positively correlated with storage time and temperature, which could be described by exponential models. The hazard indexes of PAEs in different types of drinking water were very low. However, the human carcinogenic risks of DEHP will reach the maximum acceptable risk level of 10-6 when bottled water is stored for 8.8 days at 40 °C, 7.7 days at 50 °C, or 6.1 days at 60 °C.

Effect of ozonation treatment on the chemical speciation distributions of heavy metals in sewage sludge and subsequent bioleaching process.

Effect of ozonation treatment on the chemical form distributions of heavy metals (Cr, Mn, Ni, Cu, Zn, As, Cd, and Pb) in sewage sludge (SS) and bioleaching efficiency was investigated. The results showed that the portions of heavy metals present in the oxidizable fraction decreased in the ozonized sewage sludge (OSS). Meanwhile, the proportions of most heavy metals in the reducible fraction were increased (Cr, Ni, Cu, As, and Pb) or remained constant (Mn and Cd) after ozonation treatment. Slight increase of the heavy metals (except As) in the residual fraction was also found. The OSS showed lower final pH value after bioleaching and faster increase of oxidation-reduction potential (ORP) during bioleaching process. As a result, the bioleaching rate of all the heavy metals was improved, and the solubilization efficiency of Cr, Ni, Zn, As, and Pb was increased in OSS. The comparisons of the chemical fractions in the bioleached SS and OSS indicated that the higher solubilization in OSS might be mainly due to the decrease of the oxidizable fraction and increase of the unstable fraction of these heavy metals after ozonation treatment.

Biodegradation of phenol and m-cresol by Candida albicans PDY-07 under anaerobic condition.

Strain Candida albicans PDY-07 was used to study the anaerobic biodegradation of phenol and m-cresol as single and dual substrates in batch cultures. The strain had a higher potential to degrade phenol than m-cresol. The cell growth kinetics of batch cultures with various initial m-cresol concentrations was investigated, and the Haldane kinetic model adequately described the dynamic behavior of cell growth on m-cresol. When cells grew on the mixture of phenol and m-cresol, substrate interactions were observed. Phenol inhibited the utilization of m-cresol; on the other hand, m-cresol also inhibited the degradation of phenol. However, the presence of low-concentration phenol enhanced m-cresol biodegradation; 100 mg/l m-cresol could be completely degraded within a shorter period of time than m-cresol alone in the presence of 150-300 mg/l phenol. The maximum m-cresol biodegradation rate was obtained at the existence of 200 mg/l phenol. Phenol was preferably utilized by the strain as a carbon and energy source. In addition, a sum kinetics model was used to describe the cell growth behavior in binary mixture of phenol and m-cresol, and the interaction parameters were determined. The model adequately predicted the growth kinetics and the interaction between the substrates.