The performance and microbial communities of an anaerobic membrane bioreactor for treating fluctuating 2-chlorophenol wastewater

Long-term stable and efficient degradation of ornidazole with minimized by-product formation by a biological sulfidogenic process based on elemental sulfur

Conventional biological treatment processes cannot efficiently and completely degrade nitroimidazole antibiotics, due to the formation of highly antibacterial and carcinogenic nitroreduction by-products. This study investigated the removal of a typical nitroimidazole antibiotic (ornidazole) during wastewater treatment by a biological sulfidogenic process based on elemental sulfur (S0-BSP). Efficient and stable ornidazole degradation and organic carbon mineralization were simultaneously achieved by the S0-BSP in a 798-day bench-scale trial. Over 99.8 % of ornidazole (200‒500 μg/L) was removed with the removal rates of up to 0.59 g/(m3·d). Meanwhile, the efficiencies of organic carbon mineralization and sulfide production were hardly impacted by the dosed ornidazole, and their rates were maintained at 0.15 kg C/(m3·d) and 0.49 kg S/(m3·d), respectively. The genera associated with ornidazole degradation were identified (e.g., Sedimentibacter, Trichococcus, and Longilinea), and their abundances increased significantly. Microbial degradation of ornidazole proceeded by several functional genes, such as dehalogenases, cysteine synthase, and dioxygenases, mainly through dechlorination, denitration, N-heterocyclic ring cleavage, and oxidation. More importantly, the nucleophilic substitution of nitro group mediated by in-situ formed reducing sulfur species (e.g., sulfide, polysulfides, and cysteine hydropolysulfides), instead of nitroreduction, enhanced the complete ornidazole degradation and minimized the formation of carcinogenic and antibacterial nitroreduction by-products. The findings suggest that S0-BSP can be a promising approach to treat wastewater containing multiple contaminants, such as emerging organic pollutants, organic carbon, nitrate, and heavy metals.

Phenol Degradation Performance in Batch and Continuous Reactors with Immobilized Cells of Pseudomonas putida

Phenol is a highly persistent environmental pollutant and is toxic to living organisms. The main objective of this study is to observe the phenol degradation performance by free and immobilized Pseudomonas putida (P. putida) in batch and continuous reactors, respectively. Batch experiments were evaluated to determine the maximum specific growth rate, saturation constant, inhibition constant, and cell yield. These kinetic parameters were used as the input values for the continuous-flow immobilized cells model. The immobilized cells model was validated by experimental results obtained from an immobilized cells continuous reactor. The model-predicted and experimental results showed good agreement for phenol effluent concentration in the continuous mode. In the steady-state condition, high phenol removal was achieved under various hydraulic retention times. The corresponding removal of phenol ranged from 93.3 to 95.9%, while the hydraulic retention times were maintained at 3.1–10.5 h. Furthermore, polyvinyl alcohol-immobilized cells with nanoscale particles were also prepared. The polyvinyl alcohol-immobilized P. putida cells with nanoscale Fe3O4 enhanced the ability of phenol degradation. The experimental results revealed that immobilized cells with nano-Fe3O4 had the highest phenol degradation performance at a low salinity of 1%. However, the advantage of the addition of nano-Fe3O4 was insignificant for phenol degradation at a higher salinity of 5%. The approaches of the batch and continuous column tests were practical in the treatment of actual phenol-containing wastewater.

Fate, toxicity and effect of triclocarban on the microbial community in wastewater treatment systems

Triclocarban (TCC), one of the typical antimicrobial agents, is a contaminant of emerging concern commonly found in high concentration in water environments. However, the fate and toxicity of TCC in wastewater treatment systems remain poorly understood. Here, we investigated how TCC impacts chemical oxygen demand and inorganic nitrogen transformation in a hydrolytic anaerobic-anoxic/oxic process. In the anaerobic section, the transformation of TCC was dominated by reductive dechlorination and supplemented by two amid bonds hydrolysis. In the anoxic and oxic sections, the hydrolysis of amid bonds dominated. The toxicity was reduced after the treatment (IC₅₀ from 0.09 to 0.54). TCC inhibited NH₄⁺-N removal in the anaerobic section and led to the NO₃^--N accumulation (2.84-4.13 mg/L) after treatment, with the abundance of N-removal bacteria decreased by 6%. Furthermore, the original ecological niche was gradually replaced by TCC-resistant/degradative bacteria, formating new microbial modules to resist the TCC stress. Importantly, fourteen genera including Methanosaeta, Longilinea, Dokdonella and Mycobacterium as potential bioindicators warning TCC and its intermediates were proposed. Overall, this study provides new insights into the fate of TCC in biological wastewater treatment systems and suggests a great importance for TCC control to ensure the health and resilience of ecosystems.

Fabrication of ZnAl-LDH mixed metal-oxide composites for photocatalytic degradation of 4-chlorophenol

In this work, two different types of ZnAl-layered double hydroxide (LDH) mixed metal-oxide composites (CeO₂ and SnO₂) were synthesized and applied for the photodegradation of 4-chlorophenol (4-CP) in wastewater. The fabricated CeO₂/ZnAl-LDH and SnO₂/ZnAl-LDH were characterized by X-ray diffraction (XRD), Fourier transform infrared (FTIR) spectroscopy, UV-visible diffuse reflectance spectroscopy (UV-vis DRS), and theoretical density functional theory (DFT) calculations, suggesting that the band gaps of the synthesized hybrid composites were much lower than those of traditional ZnAl-LDH. In addition, the photocatalytic activity for 4-CP degradation and reaction kinetics were investigated to evaluate the catalytic behavior of the prepared composites. The results indicated that the photocatalytic process in this case followed a pseudo-first-order kinetic model, and SnO₂/ZnAl-LDH illustrated the optimum performance for 4-CP degradation with an efficiency of 95.2% due to its stability and recyclability. Additionally, the reaction mechanism of 4-CP photodegradation was studied over SnO₂/ZnAl-LDH; it presented that 4-CP could be oxidized by hydroxyl radicals, holes, and superoxide radicals, where hydroxyl radicals were identified as the dominant active species during the degradation process. Finally, decomposition intermediates were measured to deduce the reaction pathway of 4-CP, and three tentative pathways were proposed and discussed.

Response of 2,4,6-trichlorophenol-reducing biocathode to burial depth in constructed wetland sediments

Biocathode systems could be used for in-situ bioremediation of chlorophenols (CPs) in constructed wetland (CW) sediments. However, little is known regarding whether or how cathode burial depths affect the dechlorination of CPs in sediments. Here, 2,4,6-trichlorophenol (2,4,6-TCP)-dechlorinating biocathode systems were constructed under a cathode potential of - 0.7 V (vs. a saturated calomel electrode, SCE) at three different cathode burial depths (5, 10, and 15 cm). The 2,4,6-TCP removal efficiency and average transformation rate with the biocathode increased by 21.46-36.86% and 14.63-34.88% compared to those in the non-electrode groups. Deeper cathode burial depths enhanced the 2,4,6-TCP dechlorination performance. Furthermore, the oxidation-reduction potential (ORP) of the sediment decreased with sediment depth and the applied potential created a more favorable redox environment for the enrichment of functional bacteria. Deeper cathode burial depths also promoted the selective enrichment of electro-active and dechlorinating bacteria (e.g., Bacillus and Dehalobacter, respectively). The biocathode thus served as the carrier, electron source, and regulator of functional bacteria to accelerate the transformation of 2,4,6-TCP (2,4,6-TCP → 2,4-dichlorophenol → 4-chlorophenol → phenol) in sediments. These results offer insights into the effects of cathode burial depth on 2,4,6-TCP dechlorination in sediments from a redox environment and microbial community structure standpoint.

Anaerobic Membrane Bioreactors for Municipal Wastewater Treatment: A Literature Review

Currently, there is growing scientific interest in the development of more economic, efficient and environmentally friendly municipal wastewater treatment technologies. Laboratory and pilot-scale surveys have revealed that the anaerobic membrane bioreactor (AnMBR) is a promising alternative for municipal wastewater treatment. Anaerobic membrane bioreactor technology combines the advantages of anaerobic processes and membrane technology. Membranes retain colloidal and suspended solids and provide complete solid–liquid separation. The slow-growing anaerobic microorganisms in the bioreactor degrade the soluble organic matter, producing biogas. The low amount of produced sludge and the production of biogas makes AnMBRs favorable over conventional biological treatment technologies. However, the AnMBR is not yet fully mature and challenging issues remain. This work focuses on fundamental aspects of AnMBRs in the treatment of municipal wastewater. The important parameters for AnMBR operation, such as pH, temperature, alkalinity, volatile fatty acids, organic loading rate, hydraulic retention time and solids retention time, are discussed. Moreover, through a comprehensive literature survey of recent applications from 2009 to 2021, the current state of AnMBR technology is assessed and its limitations are highlighted. Finally, the need for further laboratory, pilot- and full-scale research is addressed.

Characteristics of denitrification in a vertical baffled bioreactor

A vertical baffled bioreactor (VBBR) was employed for tertiary denitrification. Its features were designed to minimize the demand for externally supplied electron donor by minimizing net biomass synthesis and oxygen respiration. Over a two-year period, complete denitrification was realized routinely in the VBBR. The nitrate-removal rate was proportion to the influent COD/N ratio, with complete denitrification possible for COD/N ratios >3 gCOD/gN. Batch kinetic tests carried out at the end of years 1 and 2 documented that supplied electron donor was oxidized in the first 1-2 h, but nitrate and nitrite reductions occurred predominantly after 2 h and were driven by internally stored electron donor. Measurements confirmed that the VBBR minimized the demand of added electron donor: The observed yield was only 0.05 mgVSS/mgCOD, and the COD demand for O₂ respiration was only 1-6.7% of the COD demand for N reductions. Biofilm samples taken from the upper and lower ports in cylinder of VBBR had similarly high alpha diversity and dominant genera, but the upper biofilm had a denitrification rate about 70% greater than the lower biofilm. The higher denitrification rate in the upper biofilm correlated its higher content of active biomass.

More rapid dechlorination of 2,4-dichlorophenol using acclimated bacteria

The key step for anaerobic biodegradation of 2,4-dichlorophenol (2,4-DCP) is an initial dechlorination reaction, but Cl in the para-position is more difficult to remove than Cl in the ortho-position using normal 2,4-DCP-acclimated bacteria. In this work, a bacterial community previously acclimated to biodegrading 2,4-DCP slowly dechlorinated 4-chlorophenol (4-CP Cl only in the para-position), which limited mineralization. That community was exposed to the selective pressure of having 4-CP as its only organic substrate in order to generate a 4-CP-dechlorinating community. When the 4-CP-dechlorinating community was challenged with 2,4-DCP, 4-CP hardly accumulated, although the kinetics for 2,4-DCP biodegradation were slower. When the community acclimated to 4-CP was mixed with the community acclimated to 2,4-DCP, the 2,4-DCP removal rate remained high, and 4-CP was more rapidly biodegraded. The genera Treponema, Blvii28, Dechloromonas, Nitrospira, and Thauera were significantly more abundant in the 4-CP-dechlorinating biomass and may have played roles in 2,4-DCP dechlorination and mineralization.