UV photolysis for accelerating pyridine biodegradation

Treatment options of nitrogen heterocyclic compounds in industrial wastewater: From fundamental technologies to energy valorization applications and future process design strategies

Nitrogen heterocyclic compounds (NHCs) widely exist in industrial wastewater and presented significant environmental and health risks due to their toxicity and persistence. This review addressed the challenges in treating NHCs in industrial wastewater, focusing on developing sustainable and efficient treatment processes. While various technologies, including adsorption, advanced oxidation/reduction processes (AOPs/ARPs), and microbial treatments, have been studied at the experimental stage of treating synthetic wastewater, scale-up for industrial applications is imperative. After analyzing the characteristics of NHCs and evaluating different treatment methods with the aid of efficiency and cost-benefit analysis, efficient detoxification while maximizing energy recovery constitutes a critical requirement in treating NHC-containing wastewater. Hence, we proposed a comprehensive strategy combining hydrolysis-acidification pretreatment enhanced by electro-assisted micro-aeration with methanogenic anaerobic digestion as core treatment units. The process design for NHC-containing wastewater treatment should consider the dynamic balance between removal efficiency, energy consumption, and ammonia recovery, incorporating environmental and economic impacts through life cycle assessment and technical-economic analysis. The potential of machine learning in optimizing operational parameters, predicting effluent quality, and supporting process design decisions is promising. To develop interpretable and practical solutions, the integration of data-driven approaches with mechanistic understanding and prior knowledge is indispensable. This review provided novel insights into sustainable NHC treatment strategies in the context of energy valorization and artificial intelligence advancement, offering guidance for future research and industrial applications.

How Rhodococcus ruber accelerated biodegradation of benzophenone-3

Benzophenone-3 (2-hydroxy-4-methoxybenzophenone, BP-3) poses risks to human health and natural ecosystems, and means to improve its biodegradation are necessary. When a small mass of Rhodococcus ruber, isolated from BP-3-acclimated biomass, was bioaugmented into the acclimated biomass, BP-3 removal was accelerated by 120 %. The first step of BP-3 biodegradation generates either 2,5-dihydroxy-4-methoxybenzophenone (5-OH-BP-3) or benzophenone-1 (2,4-dihydoxybenzophenone, BP-1). BP-1 is generated by sequential demethylation, hydroxylation, and dehydrogenation reactions, while 5-OH-BP-3 is generated by one mono-oxygenation reaction. Of the two intermediates, 5-OH-BP-3 exhibited stronger inhibition than BP-1 or the original BP-3. Gene-completion mapping showed that R. ruber contains genes for demethylase, hydrolase, dehydrogenase, and mono-oxygenase reaction, which means that R. ruber could generate the less-toxic BP-1. Thus, bioaugmentation of R. ruber into BP-3-acclimated biomass eliminated the accumulation of 5-OH-BP-3 and, consequently, accelerated of BP-3 biodegradation via BP-1.

Two types of microorganisms isolated from petroleum hydrocarbon pollutants: Degradation characteristics and metabolic pathways analysis of petroleum hydrocarbons

The petroleum hydrocarbons in seawater have been worldwide concern contaminants. Biological method, with the advantages of low cost, minimal environmental impact, and no secondary pollution, is a promising method for petroleum hydrocarbon treatment. In this study, two strains, identified as Stenotrophomonas acidaminiphila and Ochrobactrum, were demonstrated to possess the ability to degrade petroleum hydrocarbons. The mixed culture composed of Stenotrophomonas acidaminiphila and Ochrobactrum at a 2:1 ratio was able to achieve 79.41% degradation of the total petroleum hydrocarbons after 5 days. Besides, the average removal efficiencies of C10-C30 components in petroleum hydrocarbons by Stenotrophomonas acidaminiphila, Ochrobactrum, and mixed culture were 62.98%, 59.14% and 73.30%, respectively. The possible degradation pathways of petroleum hydrocarbons had been speculated through gas chromatography-mass spectrometry (GC-MS) and differential gene expression metabolomics analyses. The toxicity of products from the biodegradation of petroleum hydrocarbons was greatly reduced.

Two-way role of iron-carbon in biochemical reactions: Microelectrolysis and enhanced activity of aerobic granular sludge for efficient refractory wastewater treatment

Industrial wastewater contained a large amount of refractory organics, and single treatment processes had limitations. This study investigated the mechanism of refractory organics removal using iron-carbon built-in coupled activated sludge (ICAS) and explored the role and function of iron-carbon (IC) within the ICAS system. The aerobic granular sludge (AGS) cultivated with IC exhibited a loose surface and a tight interior structure. Iron in the AGS concentrated near the outer layer to form a crust, which protected the inner microorganisms. IC promoted EPS secretion and regulated the abundance of positive and negative signaling molecules to maintain AGS stability. Experiments using quinoline as a model refractory organic showed that both physical adsorption by IC and biological adsorption by sludge rapidly fixed a large amount of pollutants, providing a buffer capacity for the system. The iron mineral crust on the AGS surface enhanced quinoline adsorption. Hydroxylation was the first step in quinoline degradation, with IC upregulating the genes iorA/B, qorB, and wrbA involved in this process, and the relative abundances of quinoline-degrading bacteria. Both pyridine ring opening and benzene ring cleavage occurred in the single IC system, and the microelectrolysis process produced •OH and [H], which made degradation pathway for quinoline through IC more complex than microbial degradation. Although the IC-mediated pathway accounted for only a small part of overall quinoline removal in the ICAS system, the ICAS system not only preserved the microelectrolysis process but also enhanced microbial metabolic activity. This work provided insights into the synergistic removal of pollutants and maintenance of AGS stability by the ICAS process, ensuring efficient treatment of refractory organic wastewater.

Identification, degradation characteristics, and application of a newly isolated pyridine-degrading Paracidovorax sp. BN6-4

The Paracidovorax sp. BN6-4 capable of degrading high concentrations of pyridine was isolated from the coking sludge. The removal rate of BN6-4 to 1,000 mg/L pyridine during 48 h was 97.49 ±1.59%. The primary intermediate metabolites of pyridine degradation by strain BN6-4 were identified by gas chromatography-mass spectrometry (GC-MS), including N-Ethylurea, acetamidoacetaldehyde, and N-Hydroxymethylacetamide, etc. Subsequently, two different biodegradation pathways of pyridine were proposed. First, the hydroxylation of pyridine to form the intermediates pyridin-2(1H)-one and 5,6-dihydropyridine-2,5-diol, the former undergoing oxidative ring opening and the latter oxidative ring opening via N-C2 and C2-C3 ring opening to ammonia and carbon dioxide. Furthermore, the organic matter was greatly degraded by the bioremediation of real coking wastewater using BN6-4. This study enriched the microbial resource for pyridine degradation and provided new insights about the biodegradation pathway of pyridine, which is of great significance for the pyridine pollution control and coking wastewater treatment.

Deciphering the synergistic effects of photolysis and biofiltration to actuate elimination of estrogens in natural water matrix

The presence of estrogens in water environments has raised concerns for human health and ecosystems balance. These substances possess potent estrogenic properties, causing severe disruptions in endocrine systems and leading to reproductive and developmental problems. Unfortunately, conventional treatment methods struggle to effectively remove estrogens and mitigate their effects, necessitating technological innovation. This study investigates the effectiveness of a novel sequential photolysis-granular activated carbon (GAC) sandwich biofiltration (GSBF) system in removing estrogens (E1, E2, E3, and EE2) and improving general water quality parameters. The results indicate that combining photolysis pre-treatment with GSBF consistently achieved satisfactory performance in terms of turbidity, dissolved organic carbon (DOC), UV254, and microbial reduction, with over 77.5 %, 80.2 %, 89.7 %, and 92 % reduction, respectively. Furthermore, this approach effectively controlled the growth of microbial biomass under UV irradiation, preventing excessive head loss. To assess estrogen removal, liquid chromatography-tandem mass spectrometry (LC-MS) measured their concentrations, while bioassays determined estrogenicity. The findings demonstrate that GSBF systems, with and without photolysis installation, achieved over 96.2 % removal for estrogens when the spike concentration of each targeted compound was 10 µg L-1, successfully reducing estrogenicity (EA/EA0) to levels below 0.05. Additionally, the study evaluated the impact of different thicknesses of GAC layer filling (8 cm, 16 cm, and 24 cm) and found no significant difference (p>0.05) in estrogen and estrogenicity removal among them.

Efficient utilization of photoelectron-hole at semiconductor-microbe interface for pyridine degradation with assistance of external electric field

In this study, enhanced pyridine bio-photodegradation with assistance of electricity was achieved. Meanwhile, photoelectron-hole played a vital role in accelerating pyridine biomineralization. The significant separation of photoelectron-hole was achieved with an external electric field, which provided sufficient electron donors and acceptors for pyridine biodegradation. The enhanced electron transport system activity also revealed the full utilization of photoelectron-hole by microbes at semiconductor-microbe interface with assistance of electricity. Microbial community analysis confirmed the enrichment of functional species related to pyridine biodegradation and electron transfer. Microbial function analysis and microbial co-occurrence networks analysis indicated that upregulated functional genes and positive interactions of different species were the important reasons for enhanced pyridine bio-photodegradation with external electric field. A possible mechanism of enhanced pyridine biodegradation was proposed, i.e., more photoelectrons and holes of semiconductors were utilized by microbes to accelerate reduction and oxidation of pyridine with the assistance of electrical stimulation. The excellent performance of the photoelectrical biodegradation system showed a potential alternative for recalcitrant organic wastewater treatment.

Mixed valence copper oxide composites derived from metal-organic frameworks for efficient visible light fuel denitrification

The construction of heterojunctions has been used to optimize photocatalyst fuel denitrification. In this work, HKUST-1(Cu) was used as a sacrificial template to synthesize a composite material CuxO (CuO/Cu2O) that retains the original MOF framework for photocatalytic fuel denitrification by calcination at different temperatures. By adjusting the temperature, the content of CuO/Cu2O can be changed to control the performance and structure of CuxO-T effectively. The results show that CuxO-300 has the best photocatalytic performance, and its denitrification rate reaches 81% after 4 hours of visible light (≥420 nm) irradiation. Through the experimental analysis of pyridine's infrared and XPS spectra, we found that calcination produces CuxO-T mixed-valence metal oxide, which can create more exposed Lewis acid sites in the HKUST-1(Cu) framework. This leads to improved pyridine adsorption capabilities. The mixed-valence metal oxide forms a type II semiconductor heterojunction, which accelerates carrier separation and promotes photocatalytic activity for pyridine denitrification.

Efficient pyridine biodegradation by Stenotrophomonas maltophilia J2: Degradation performance, mechanism, and immobilized application for wastewater

Stenotrophomonas maltophilia J2, a highly efficient pyridine-degrading bacterium, was isolated from the aerobic tank of a pesticide-contaminated wastewater treatment plant. The strain J2 demonstrated an impressive pyridine degradation rate of 98.34% ± 0.49% within 72 h, at a pyridine concentration of 1100 mg·L-1, a temperature of 30 °C, a pH of 8.0, and a NaCl concentration of 0.5%. Notably, two new pyridine metabolic intermediates, 1,3-dihydroxyacetone and butyric acid, were discovered, indicating that J2 may degrade pyridine through two distinct metabolic pathways. Furthermore, the immobilized strain J2 was obtained by immobilizing J2 with biochar derived from the stem of Solidago canadensis L. In the pyridine-contaminated wastewater bioremediation experiment, the immobilized strain J2 was able to remove 2000 mg·L-1 pyridine with a 98.66% ± 0.47% degradation rate in 24 h, which was significantly higher than that of the control group (3.17% ± 1.24%), and remained above 90% in subsequent cycles until the 27th cycle. High-throughput sequencing analysis indicated that the J2 +B group had an elevated relative abundance of bacteria and functional genes that could be associated with the degradation of pyridine. The results offer a foundation for the effective use of immobilized strain in the treatment of recalcitrant pyridine-contaminated wastewater.

Strategic analysis on development of simultaneous adsorption and catalytic biodegradation over advanced bio-carriers for zero-liquid discharge of industrial wastewater

With rapid industrial development, millions of tons of industrial wastewater are produced that contain highly toxic, carcinogenic, mutagenic compounds. These compounds may consist of high concentration of refractory organics with plentiful carbon and nitrogen. To date, a substantial proportion of industrial wastewater is discharged directly to precious water bodies due to the high operational costs associated with selective treatment methods. For example, many existing treatment processes rely on activated sludge-based treatments that only target readily available carbon using conventional microbes, with limited capacity for nitrogen and other nutrient removal. Therefore, an additional set-up is often required in the treatment chain to address residual nitrogen, but even after treatment, refractory organics persist in the effluents due to their low biodegradability. With the advancements in nanotechnology and biotechnology, novel processes such as adsorption and biodegradation have been developed, and one promising approach is integration of adsorption and biodegradation over porous substrates (bio-carriers). Regardless of recent focus in a few applied researches, the process assessment and critical analysis of this approach is still missing, and it highlights the urgency and importance of this review. This review paper discussed the development of the simultaneous adsorption and catalytic biodegradation (SACB) over a bio-carrier for the sustainable treatment of refractory organics. It provides insights into the physico-chemical characteristics of the bio-carrier, the development mechanism of SACB, stabilization techniques, and process optimization strategies. Furthermore, the most efficient treatment chain is proposed, and its technical aspects are critically analysed based on updated research. It is anticipated that this review will contribute to the knowledge of academia and industrialist for sustainable upgradation of existing industrial wastewater treatment plants.

Selective photoelectrocatalytic oxidation of 3-methylpyridine to vitamin B3 by WO3 decorated nanotube-structured TiO2

Nanotube-structured TiO₂ electrodes on Ti plates were formed in ethylene glycol solution by the anodic oxidation method applied for different times and calcined at 500 °C. Different amounts of WO₃ were decorated on the nanotube surfaces electrochemically. The electrodes were characterized, and the effects of the nanotube length on the Ti plate, decorated WO₃ amount, electrolyte concentration, applied potential, and type of radiation source on the oxidation of 3-methylpyridine were investigated, together with the product distribution/selectivity. In a photoelectrocatalytic system, the vitamin B₃ yield increased significantly (ca. 17 fold) under UVA by decorating nanotube-structured TiO₂ with WO₃, whilst low reaction rates and no products were found under Vis irradiation, as only unselective photolytic reactions occurred. This unexpected result was clarified for the first time in the literature.

Surface Coordination of Pd/ZnIn2S4 toward Enhanced Photocatalytic Activity for Pyridine Denitrification

New surface coordination photocatalytic systems that are inspired by natural photosynthesis have significant potential to boost fuel denitrification. Despite this, the direct synthesis of efficient surface coordination photocatalysts remains a major challenge. Herein, it is verified that a coordination photocatalyst can be constructed by coupling Pd and CTAB-modified ZnIn₂S₄ semiconductors. The optimized Pd/ZnIn₂S₄ showed a superior degradation rate of 81% for fuel denitrification within 240 min, which was 2.25 times higher than that of ZnIn₂S₄. From the in situ FTIR and XPS spectra of 1% Pd/ZnIn₂S₄ before and after pyridine adsorption, we find that pyridine can be selectively adsorbed and form Zn⋅⋅⋅C-N or In⋅⋅⋅C-N on the surface of Pd/ZnIn₂S₄. Meanwhile, the superior electrical conductivity of Pd can be combined with ZnIn₂S₄ to promote photocatalytic denitrification. This work also explains the surface/interface coordination effect of metal/nanosheets at the molecular level, playing an important role in photocatalytic fuel denitrification.

Treatment of pyridine in industrial liquid waste by atmospheric DC water plasma

Pyridine is a basic heterocyclic compound with high toxicity, widely found in liquid waste from industrial processes. The treatment of highly-concentrated pyridine was demonstrated using a novel mist-type water thermal plasma torch. Decomposition rate and TOC removal rate were more than 94% in all conditions, while the max energy efficiency reached about 23 g/kWh. With a high temperature of 5500-7500 K, more than 95% of carbon content in pyridine was converted into valuable gas products, while a little amount of formic acid and acetic acid were observed as liquid by-products. The production of hydrogen cyanide (HCN) during the thermal decomposition of pyridine was observed, which can be inhibited by increasing the input power. Based on the experimental results, detailed decomposition mechanisms in the high-temperature and the downstream region were discussed respectively. Water plasma shows significant potential in the treatment of non-biodegradable industrial liquid waste.

Nitrogen-Doped Carbon Nanodots Produced by Femtosecond Laser Synthesis for Effective Fluorophores

Understanding the effect of heteroatom doping is crucial for the design of carbon nanodots (CNDs) with enhanced luminescent properties for fluorescence imaging and light-emitting devices. Here, we study the effect and mechanisms of luminescence enhancement through nitrogen doping in nanodots synthesized by the bottom-up route in an intense femtosecond laser field using the comparative analysis of CNDs obtained from benzene and pyridine. We demonstrate that laser irradiation of aromatic compounds produces hybrid nanoparticles consisting of a nanocrystalline core with a shell of surface-bonded aromatic rings. These nanoparticles exhibit excitation-dependent visible photoluminescence typical for CNDs. Incorporation of nitrogen into pyridine-derived CNDs enhances their luminescence characteristics through the formation of small pyridine-based fluorophores peripherally bonded to the nanoparticles. We identify oxidation of surface pyridine rings as a mechanism of formation of several distinct blue- and green-emitting fluorophores in nanodots, containing pyridine moieties. These findings shed additional light on the nature and formation mechanism of effective fluorophores in nitrogen-doped carbon nanodots produced by the bottom-up route.

Advanced reduction process to achieve efficient degradation of pyridine

Pyridine and its derivatives are widely consumed and detected in the environment persistently, which can cause potential adverse impacts on environment and human health. Considering the fact that pyridine could absorb UV light at 254 nm to generate excited one, which could react with reductive radicals, promoting its structural changes, we proposed that one typical efficient advanced reduction process (ARP) which combines UV irradiation with sulfite could be used to eliminate pyridine quickly. Sulfite/UV process showed a higher pyridine removal rate with a pseudo-first-order reaction rate constant of 0.1439 min^-1, which was 3 times of that in UV irradiation and 1.3 times in UV/H₂O₂ process. This was primarily due to reductive radicals (e_aq^-, H^• and SO₃^•-) produced by UV irradiation. The removal rate of pyridine was highest in slightly alkaline environment. And the presence of oxygen, as well as certain concentration of humid acid just showed slight inhibition, indicating the possibility of application in practical environment. A positive impact was observed with increasing sulfite dosage, but it was gradually inhabited when the dosage was over 5 mM. The present study may provide an alternative efficient technology for the degradation of pyridine ring-containing substances.

Selective acceleration of 2-hydroxyl pyridine mono-oxygenation using specially acclimated biomass

Biodegradation of pyridine starts with two mono-oxygenation reactions, and 2-hydroxyl pyridine (2-HP) accumulates as pyridine is mono-oxygenated in the first reaction. The accumulation of 2-HP inhibits both initial reactions. Therefore, selective acceleration of the second mono-oxygenation reaction should significantly enhance pyridine transformation and mineralization. Activated-sludge biomass was separately acclimated with pyridine or 2-HP to produce pyridine- and 2-HP-acclimated biomasses. The pyridine-acclimated biomass was superior for pyridine biodegradation, but the 2-HP-acclimated biomass was superior for 2-HP biodegradation. As a consequence, the pyridine-acclimated biomass by itself achieved faster mono-oxygenation of pyridine to 2-HP, but 2-HP accumulated, which limited mineralization to 60%. In contrast, mineralization reached 90% when one-third of the pyridine-acclimated was replaced with 2-HP-acclimated biomass, because 2-HP did not accumulate during pyridine biodegradation. The lack of 2-HP accumulation relieved its inhibition: e.g., the pyridine removal rates, normalized to the mass of pyridine-acclimated biomass, increased from 0.52 to 0.57 mM^0.5⋅h^-1 when one-third of the pyridine-acclimated biomass was replaced by 2-HP-acclimated biomass. Phylogenetic analysis showed that microbiological communities of pyridine-acclimated biomass and 2-HP-acclimated biomass differed in important ways. On the one hand, the 2-HP-acclimated biomass was richer and dominated by a rare biosphere, or genera having <0.1% of total reads. On the other hand, the most-enriched genus in the pyridine-acclimated community (Methylibium) is associated with the first mono-oxygenation of pyridine, while enriched genera in the 2-HP-acclimated community (Sediminibacterium and Dokdonella) are associated with the second mono-oxygenation of pyridine.

Characterization of pyridine biodegradation by two Enterobacter sp. strains immobilized on Solidago canadensis L. stem derived biochar

In this study, two pyridine-degrading strains namely Enterobacter cloacae complex sp. BD17 and Enterobacter sp.BD19 were isolated from the aerobic tank of a pesticide wastewater treatment plant. The mixed bacteria H4 composed of BD17 and BD19 at a ratio of 1:1 was immobilized by Solidago canadensis L. stem biochar with a dosage of 2 g·L^-1. The highest pyridine removal rate of 91.70% was achieved by the immobilized H4 at an initial pyridine concentration of 200 mg·L^-1, pH of 7.0, temperature of 28 °C and salinity of 3.0% within 36 h. The main intermediates of pyridine degradation by BD17 were pyridine-2-carboxamide, 2-aminopropanediamide, and 2-aminoacetamide, while 2-picolinic acid, isopropyl acetate, isopropyl alcohol, and acetaldehyde were identified with BD19 by adopting GC-MS technique. Interestingly, there was a possibility of totally mineralization of pyridine and the corresponding degradation pathways of BD17 and BD19 were revealed for the first time.

Synergy of strains that accelerate biodegradation of pyridine and quinoline

Three bacterial strains were isolated from activated sludge acclimated to biodegrade pyridine and quinoline simultaneously. The strains were identified as Bacillus tropicus, Bacillus aquimaris, and Rhodococcus ruber. When the isolated bacteria were used for pyridine and quinoline biodegradation in separate or combined modes, R. ruber had much faster kinetics, and combining R. ruber with one or both of the Bacillus strains increased further the biodegradation kinetics. For example, the time needed for complete biodegradation of 1 mM quinoline and pyridine decreased to 20 h and 6 h, respectively, with the three strains combined, compared to 26 h and 7 h with R. ruber alone. Whereas quinoline was completely mineralized by all three strains, 10-14% of the pyridine persisted as a dead-end product, 2-hydroxypyridine (2HP). The acclimated sludge from which the three bacterial species were isolated was able to transform 2HP, and adding the bacterial strains (especially R. ruber) to the acclimated sludge accelerated the rate of 2HP removal and mineralization through a form of synergy.

How bioaugmentation with Comamonas testosteroni accelerates pyridine mono-oxygenation and mineralization

Pyridine is a common heterocycle found in industrial wastewaters. Its biodegradation begins with a mono-oxygenation reaction, and bioaugmentation with bacteria able to carry out this mono-oxygenation is one strategy to improve pyridine removal and mineralization. Although bioaugmentation has been used to enhance the biodegradation of recalcitrant organic compounds, the specific role played by the bioaugmented bacteria usually has not been addressed. We acclimated activated-sludge biomass for pyridine biodegradation and then isolated a strain -- Comamonas testosteroni -- based on its ability to biodegrade and grow on pyridine alone. Pyridine was removed faster by C. testosteroni, compared to pyridine-acclimated biomass, but pyridine mineralization was slower. Pyridine biodegradation and mineralization rates were accelerated when C. testosteroni was bioaugmented into the acclimated biomass, which increased the amount of C. testosteroni, but otherwise had minimal effects on the microbial community. The key role of C. testosteroni was to accelerate the first step of pyridine biodegradation, mono-oxygenation to 2-hydroxylpyridine (2HP), and the acclimated biomass was better able to complete downstream reactions leading to mineralization. Thus, bioaugmentation increased the rates of pyridine mono-oxygenation and subsequent mineralization through the synergistic roles of C. testosteroni and the main community in the acclimated biomass.

Effective removal of odor substances using intimately coupled photocatalysis and biodegradation system prepared with the silane coupling agent (SCA)-enhanced TiO2 coating method

Intimately coupled photocatalysis and biodegradation (ICPB) combining photocatalysis with microbial degradation is an attractive wastewater treatment technology. However, when prepared in conventional ways, the supported-photocatalysts aggregate frequently, detach easily from carriers, and prohibit the colonization of microorganisms inside the carriers. To overcome these challenges, silane coupling agent (SCA)-enhanced TiO₂ coating method is developed in this study. The coupling agent γ-glycidoxypropyltrimethoxysilane (KH560) greatly enhanced the adhesion between photocatalysts and the carrier through ether and Ti-O-Si linkages. The dense TiO₂ layer was firmly adhered to the carrier outer surface, and the loading amount reached 351.8±8.2 mg/g, over ten times higher than using the powder sintering method (31.5±2.4 mg/g). In the ICPB system constructed with the KH560-enhanced TiO₂-supported polyurethane sponge (KH560-TiO₂-PU) carriers, removal efficiencies of two model odor substances, 2-methylisoborneol (2-MIB) and geosmin (GSM), reached 88.9±0.3% and 85.0±1.0% in 12 h at an initial concentration of 500 ng/L respectively, which were 17.7±0.6% and 19.4±0.4% greater than those of the ICPB system prepared with the powder sintering method. After 5 operating cycles, the novel ICPB system remained stable with high 2-MIB and GSM removal efficiencies, reaching 89.9±0.8% and 86.1±0.2% respectively after 12h, while TiO₂ peeling ratio was as low as 5.0±2.8%. Biofilms attached onto the carrier inner surface were resilient over the operating cycles with the increase of both richness and diversity of microbial communities. Analysis of biofilm microbial community and pollutant degradation pathways revealed the enhanced removal of 2-MIB and GSM in the novel ICPB system might be attributed to multiple factors. First, the alleviated aggregation and increased adhesion of photocatalysts onto carriers improved the overall photocatalysis efficiency. Second, biofilm inside of the carrier was protected and the microbial activity was well remained. Third, photocatalytic intermediate products were efficiently biodegraded by the enriched functional microbial populations, such as Thauera and Flavobacterium, with little concern of excessive oxidation. Collectively, this research provides a new technological solution that synergizes photocatalysis and biodegradation for effective removal of odorous substances in polluted natural water.

Pre-electrochemical treatment combined with fixed bed biofilm reactor for pyridine wastewater treatment: From performance to microbial community analysis

To overcome the high biotoxicity and poor biodegradability of pyridine and its derivatives, a pre-electrochemical treatment combined with fixed bed biofilm reactor (EC-FBBR) was designed for multi-component stream including pyridine (Pyr), 3-cyanopyridine (3-CNPyr), and 3-chloropyridine (3-ClPyr). The EC-FBBR system could simultaneously degrade these pollutants with a mineralization efficiency of 90%, especially for the persistent 3-ClPyr. Specifically, the EC could partially degrade all pollutants, and allow them to be completely destructed in FBBR. With EC off, Rhodococcus (35.5%) became the most abundant genus in biofilm, probably due to its high tolerance to 3-ClPyr. With EC on, 3-ClPyr was reduced to an acceptable level, thus Paracoccus (21.1%) outcompeted among interspecies competition with Rhodococcus and became the dominant genus. Paracoccus was considered to participate in the subsequent degradation for the residual 3-ClPyr, and led to the complete destruction for all pollutants. This study proposed promising combination for effective treatment of multi-component pyridine wastewater.

BiVO4/FeOOH semiconductor-microbe interface for enhanced visible-light-driven biodegradation of pyridine

Pyridine, a highly toxic nitrogen-containing heterocyclic compound, is recalcitrant in the conventional biodegradation process. In this study, BiVO₄/FeOOH semiconductor-microbe interface was developed for enhanced visible-light-driven biodegradation of pyridine, where the efficiencies of pyridine removal (100%), total organic carbon (TOC) removal (88.06±3.76%) and NH₄⁺-N formation (84.51±8.95%) were remarkably improved, compared to the biodegradation system and photodegradation system. The electron transport system activity and photoelectrochemical analysis implied the significant improvement of photogenerated carriers transfer between microbes and semiconductors. High-throughput sequencing analysis suggested functional species related to pyridine biodegradation (Shewanella, Bacillus and Lysinibacillus) and electron transfer (Shewanella and Tissierella) were enriched at the semiconductor-microbe interface. The light-excited holes played a crucial role in promoting pyridine mineralization. This study demonstrated that this bio-photodegradation system would be a potential alternative for the efficient treatment of wastewater containing recalcitrant pollutant such as pyridine.

UV activation of the pi bond in pyridine for efficient pyridine degradation and mineralization by UV/H2O2 treatment

Pyridine and organics containing pyridine rings are widely used but persist in the environment and cause toxic pollution. Due to the attraction of the nitrogen atoms to the electrons in the pi bond, the pyridine ring is difficult to oxidize by oxidant. Here, we propose that ultraviolet (UV) irradiation activates the electrons in the pi bond and enables combination with the hydroxyl radical (OH) originating from hydrogen peroxide (H₂O₂) to eliminate pyridine quickly and mineralize the byproducts. The removal rates of pyridine and total organic carbon (TOC) were compared in different treatments: UV irradiation, UV/H₂O₂ treatment and Fenton oxidation with different initial pyridine concentrations, pH values and H₂O₂ concentrations. The UV/H₂O₂ treatment yielded a higher pyridine removal rate and greater mineralization than the other treatments. The removal rate of pyridine was highest in neutral aqueous solution and H₂O₂ concentration of 10 mM. At an initial H₂O₂ concentration of 10 mM, more than 90% of the pyridine was degraded in 10 min, and approximately 70% of the TOC was removed in 60 min. The absorption of UV light at 254 nm by the pi bond of pyridine can accelerate the damage to the stable pyridine structure, especially in the presence of OH. This study provides a promising alternative for the removal and mineralization of pyridine ring-containing materials.

Highly efficient, reversible iodine capture and exceptional uptake of amines in viologen-based porous organic polymers

A viologen-based porous organic polymer, POP-V-VI, was designed and synthesized by a facile nucleophilic substitution between cyanuric chloride and 1,2-bis(4-pyridinium) ethylene. Together with the reported POP-V-BPY with a similar structure, these viologen-based porous organic polymers bear high charge density, phenyl ring and nitrogenous affinity sites, which endow them with excellent iodine vapor uptake capacity (4860 mg g-1 for POP-V-VI and 4200 mg g-1 for POP-V-BPY) and remarkably high adsorption capacity for pyridine (4470 mg g-1 for POP-V-VI and 8880 mg g-1 for POP-V-BPY) and other aliphatic amines. POP-V-VI and POP-V-BPY could be efficiently recycled and reused three times without significant loss of iodine vapor uptake. All these results demonstrate that POP-V-VI and POP-V-BPY are promising adsorbents for practical applications in portable devices such as gas masks.

Intimate coupling of photocatalysis and biodegradation for wastewater treatment: Mechanisms, recent advances and environmental applications

Due to the increase of emerging contaminants in water, how to use new treatment technology to make up for the defects of traditional wastewater treatment method has become one of the research hotspots at present. Intimate coupling of photocatalysis and biodegradation (ICPB) as a novel wastewater treatment method, which combines the advantages of biological treatment and photocatalytic reactions, has shown a great potential as a low-cost, environmental friendly and sustainable treatment technology. The system mainly consists of photocatalytic materials, porous carriers and biofilm. The key principle of ICPB is to transform bio-recalcitrant pollutants into biodegradable products by photocatalysis on the surface of porous carriers. The biodegradable products were mineralized simultaneously through the biofilm inside the carriers. Because of the protection of the carriers, the microorganism can remain active even under the UV-light, the mechanical force of water flow or the attack of free radicals. ICPB breaks the traditional concept that photocatalytic reaction and biodegradation must be separated in different reactors, improves the purification capacity of sewage and saves the cost. This review summarizes the recent advances of ICPB photocatalysts, carriers and biofilm being applied, and focuses on the mechanisms and reactor configurations which is particularly novel. Furthermore, the possible ongoing researches on ICPB are also put forward. This review will provide a valuable insight into the design and application of ICPB in environment and energy field.

New insights into clopyralid degradation by sulfate radical: Pyridine ring cleavage pathways

Contamination by herbicides such as clopyralid (CLP) poses a significant threat to human health and ecological systems. In the present study, efficient removal of CLP was achieved by thermo activated persulfate, among which sulfate radical was identified as the predominant oxidizing species responsible for the decontamination. Based on high resolution LC-MS, derivatization method and density functional theory (DFT) computation, the detailed oxidation pathways and mechanisms were proposed. The primary oxidation pathways included dechlorination-hydroxylation, decarboxylation and the formation of quinone-like moieties. Afterwards, numerous intermediate byproducts ranging from high molecular to very small ones were identified, suggesting the pyridine ring was damaged during the thermo activated persulfate process. The detected products containing six and five carbons indicated the pyridine ring cleavage would take place on the quinone-structure intermediate. Further oxidation could continue by breaking each bond on the ring-cleavage product, yielding a series of short-chain carbonyl chemicals, carboxylic acids and inorganic ions. In addition, the presence of dissolved oxygen (DO) was favorable to CLP degradation, indicating DO played an important role in applying such technology. The degradation rate constants of CLP increased appreciably with increasing temperature, and acidic pH facilitated the CLP degradation. The results obtained in this work would increase our understanding on the environmental fates of nitrogen heterocyclic compounds during sulfate radical (SO₄^•-)-based advanced oxidation processes (SR-AOPs).

Enhanced biodegradation of pyridine using sequencing batch biofilm reactor under intermittent micro-aerobic condition

A sequencing batch biofilm reactor under intermittent micro-aerobic or anaerobic conditions was investigated to remove pyridine at various concentrations from synthetic wastewater. The results showed that over 98% of pyridine (influent concentration ≤200 mg L^-1) was degraded under intermittent micro-aerobic condition, while about 21% of pyridine was removed under anaerobic condition. Additionally, at least 60% of nitrogen located in the pyridine ring was transformed to ammonium. At the same time, the sulphate reduction was obviously inhibited under intermittent micro-aerobic conditions. The microscopic observation showed that abundant microorganisms were attached on the surface or inside of porous biocarriers under intermittent micro-aerobic conditions after a short-term period of operation. High-throughput sequencing analysis demonstrated that Azotobacter, Rhodobacteraceae and Tolumonas were the dominant species in the intermittent micro-aerobic system. The kinetic study at steady period showed that pyridine degradation was fitted well with the pseudo-first-order model (R² > 0.96). The two possible intermediate products were identified and the possible biodegradation pathway of pyridine was proposed under micro-aerobic condition.

Facile light-initiated radical generation from 4-substituted pyridine under ambient conditions

A facile photogeneration of a stable radical species from a 4-substituted pyridine derivative under ambient conditions is achieved. The radical generation reaction accompanies visible colour change into green and is repeatable multiple times.

Effects of carbon source, nitrogen source, and natural algal powder-derived carbon source on biodegradation of tetracycline (TEC)

The present study aimed to investigate Klebsiella sp. SQY5-mediated tetracycline (TEC) degradation, nitrogen (N) conversion, and mechanisms underlying this process as influenced by various carbon and N sources under aerobic conditions. Effects of additional organic carbon sources on TEC degradation and N conversion processes were explored, and we found that 34.71% of TEC was degraded at removal rates of 0.97 mg·L^-1·h^-1 for NH₄⁺-N and 1.97 mg·L^-1·h^-1 for NO₃^--N. A study examining powder natural algal powder in aquaculture wastewater as a carbon source for TEC degradation and denitrification process was also discussed. It suggested that 49.95% of TEC and 60.45% of NO₃^--N were removed with a reduction and denitrification rate of 0.11 mg·L^-1·h^-1 and 1.34 mg·L^-1·h^-1, respectively, within 72-108 h. Mechanisms underlying TEC degradation and N conversion processes were also proposed, and analysis indicated that specific functional genes played an important role in this process.

Bioavailable electron donors leached from leaves accelerate biodegradation of pyridine and quinoline

Fallen leaves of Platanus orientalis and Ginkgo biloba linn were separately immersed in water to obtain leachates that were used as exogenous electron donors for accelerating pyridine and quinoline biodegradations. Leachate addition accelerated the pyridine removal rate by up to 4.4% and 3.6% and the quinoline removal rate by 9.5% and 11%. The rates increased further after the leachates were illuminated by UV light: up to 8.5% for pyridine and 12% for quinoline. Succinate and oxalate were separately added into solutions of pyridine and quinoline (respectively) to gauge the acceleration impact of the leaf leachates. Equations describing the relationships between addition of leachate and pyridine or quinoline removal rates were established based on electron-equivalent balances and comparison to the acceleration effects from succinate and oxalate. From 22% to 98% of the COD leached from leaves was available as an electron donor, with the fraction being greater for pyridine and after UV illumination.

The role of ultrasound-treated sludge for accelerating quinoline mono-oxygenation

Activated sludge treated by ultrasound was tested as a source of exogenous electron donor to accelerate quinoline mono-oxygenation, which requires an intracellular electron donor (2H). The quinoline-removal rate was proportional to the amount of treated or untreated sludge added in flask experiments, but the best biodegradation kinetics was obtained with a mixture of 25% untreated sludge plus 75% treated sludge. The treated sludge primarily provided exogenous electron donor, while the untreated sludge provided active biomass. A biofilm system also showed the same beneficial effect of treated sludge, and the soluble fraction of the treated sludge had the greatest impact. Using treated sludge instead of a purchased electron donor provides an economic advantage for accelerating the biodegradation of contaminants whose biodegradation is initiated by an oxygenation reaction, such as quinoline.

Roles of an easily biodegradable co-substrate in enhancing tetracycline treatment in an intimately coupled photocatalytic-biological reactor

Intimately coupled photocatalysis and biodegradation (ICPB) was realized in a macroporous carrier in which a photocatalyst was present on the outer surface, while a biofilm accumulated inside the carrier. In ICPB, photocatalysis products are rapidly biodegraded by a protected biofilm, leading to mineralization of the refractory organics, such as antibiotics. However, mineralization in ICPB could be compromised if the photocatalysis products remain refractory or are inhibitory. To address this, we attempted to increase metabolic activity by providing a readily biodegradable co-substrate (acetate) that could act as a source of energy and electrons to improve biotransformation and mineralization of the refractory antibiotic tetracycline (TCH). When we added acetate during ICPB of TCH, TCH removal increased by ∼5%, mineralization increased by ∼20%, and almost all photocatalysis products disappeared. Acetate addition also led to an increase in active biomass, an increase in the biomass's respiratory activity, and evolution of the microbial community to having more members able to biodegrade photocatalysis and biotransformation intermediates. Thus, providing an easily biodegradable co-substrate was an effective means for enhancing TCH removal and mineralization with the ICPB technology.

Substantial enhancement of anaerobic pyridine bio-mineralization by electrical stimulation

Due to highly recalcitrant and toxicological nature of pyridine, the conventional anaerobic bioprocess is often limited by low removal rate and poor process stability. In this study, an electricity-assisted anaerobic system was developed in order to enhance biodegradation of pyridine from wastewater. The results showed that the performance and stability of the anaerobic reactor was remarkably improved for pyridine biodegradation with the applied direct current of 0.3 mA, where the efficiencies of pyridine and total organic carbon removal as well as NH₄⁺-N formation were as high as 100.0%, 96.1 ± 1.2% and 60.1 ± 2.1% respectively. The compact biofilm due to electrical stimulation as well as the microaerobic environment in the bioanode might promote pyridine bio-mineralization in the anaerobic reactor. Moreover, the species related to pyridine biodegradation (Desulfovibrio, Dokdonella, Hydrogenophaga, and Paracoccus) were enriched in the anodic biofilm, which would be another reason for better reactor performance. This study demonstrated that electrical stimulation would be a potential alternative for the enhancement of pyridine removal from wastewater in anaerobic systems.

Competition for electrons between pyridine and quinoline during their simultaneous biodegradation

Biodegradation of pyridine and quinoline is initiated with mono-oxygenation reactions that require an intracellular electron donor. Simultaneous biodegradation of both substrates should set up competition for the intracellular electron donor that may inhibit one or more of the mono-oxygenation steps. An internal circulation baffled biofilm reactor (ICBBR) was used to evaluate the impacts of competition during pyridine and quinoline biodegradation. Compared with independent biodegradation, pyridine and quinoline removal rates were slowed when biodegraded simultaneously, although the pyridine removal rate decreased more than for quinoline. The first mono-oxygenation of quinoline (to 2-hydroxyquinoline) always was faster than the first mono-oxygenation of pyridine (to 2-hydroxypyridine), and the difference was accentuated with pyridine and quinoline which were biodegraded simultaneously due to the competition for intracellular electron donor. Competition also existed between the second mono-oxygenations, and the removal rate of 2-hydroxypyridine was faster than the rate for 2-hydroxyquinoline, even though the rate was faster for quinoline than pyridine. Adding an exogenous electron donor accelerated all mono-oxygenations in proportion to the amount of donor added, but the increments were greater for quinoline due to its higher affinity for intracellular electron donors than pyridine. When actual coking wastewater was used as the background matrix, removals of pyridine and quinoline exhibited the same competitive trends.

Accelerating biodegradation of a monoazo dye Acid Orange 7 by using its endogenous electron donors

Biodegradation of a monoazo dye - Acid Orange 7 (AO7) was investigated by using an internal circulation baffled biofilm reactor. For accelerating AO7 biodegradation, endogenous electron donors produced from AO7 by UV photolysis were added into the reactor. The result shows that AO7 removal rate can be accelerated by using its endogenous electron donors, such as sulfanilic and aniline. When initial AO7 concentration was 13.6mg/L, electron donors generated by 8h UV photolysis were added into the same system. The biodegradation rate 0.4mg^0.05h^-1 was enhanced 60% than that without adding electron donor. Furthermore, sulfanilic and aniline were found to be the main endogenous electron carriers, which could accelerate the steps of the azo dye biodegradation.

Accelerating Quinoline Biodegradation and Oxidation with Endogenous Electron Donors

Quinoline, a recalcitrant heterocyclic compound, is biodegraded by a series of reactions that begin with mono-oxygenations, which require an intracellular electron donor. Photolysis of quinoline can generate readily biodegradable products, such as oxalate, whose bio-oxidation can generate endogenous electron donors that ought to accelerate quinoline biodegradation and, ultimately, mineralization. To test this hypothesis, we compared three protocols for the biodegradation of quinoline: direct biodegradation (B), biodegradation after photolysis of 1 h (P1h+B) or 2 h (P2h+B), and biodegradation by adding oxalate commensurate to the amount generated from photolysis of 1 h (O1+B) or 2 h (O2+B). The experimental results show that P1h+B and P2h+B accelerated quinoline biodegradation by 19% and 50%, respectively, compared to B. Protocols O1+B and O2+B also gave 19% and 50% increases, respectively. During quinoline biodegradation, its first intermediate, 2-hydroxyquinoline, accumulated gradually in parallel to quinoline loss but declined once quinoline was depleted. Mono-oxygenation of 2-hydroxyquinoline competed with mono-oxygenation of quinoline, but the inhibition was relieved when extra electrons donors were added from oxalate, whether formed by UV photolysis or added exogenously. Rapid oxalate oxidation stimulated both mono-oxygenations, which accelerated the overall quinoline oxidation that provided the bulk of the electron donor.

Intimately coupling of photolysis accelerates nitrobenzene biodegradation, but sequential coupling slows biodegradation

Photo(cata)lysis coupled with biodegradation is superior to photo(cata)lysis or biodegradation alone for removal of recalcitrant organic compounds. The two steps can be carried out sequentially or simultaneously via intimate coupling. We studied nitrobenzene (NB) removal and mineralization to evaluate why intimate coupling of photolysis with biodegradation was superior to sequential coupling. Employing an internal circulation baffled biofilm reactor, we compared direct biodegradation (B), biodegradation after photolysis (P+B), simultaneous photolysis and biodegradation (P&B), and biodegradation with nitrophenol (NP) and oxalic acid (OA) added individually and simultaneously (B+NP, B+OA, and B+NP+OA); NP and OA were NB's main UV-photolysis products. Compared with B, the biodegradation rate P+B was lower by 13-29%, but intimately coupling (P&B) had a removal rate that was 10-13% higher; mineralization showed similar trends. B+OA gave results similar to P&B, B+NP gave results similar to P+B, and B+OA+NP gave results between P+B and P&B, depending on the amount of OA and NP added. The photolysis product OA accelerated NB biodegradation through a co-substrate effect, but NP was inhibitory. Although decreasing the UV photolysis time could minimize the inhibition impact of NP in P+B, P&B gave the fastest removal of NB by accentuating the co-substrate effect of OA.

Nitrogen removal from municipal wastewater by a bioreactor containing ceramic honeycomb

Ceramic honeycombs were used as bio-carriers for removal of nitrogen from municipal wastewater by a bioreactor under aerobic conditions.

An ultraviolet/biological (UV/B) reactor for the removal of nitrogenous compounds from the secondary effluent of wastewater treatment plants (WWTPs)

An ultraviolet/biological (UV/B) reactor was used to treat the secondary effluent of wastewater treatment plants (WWTPs).