UV photolysis for accelerated quinoline biodegradation and mineralization

Enhanced nitrate reduction in hypotrophic waters with integrated photocatalysis and biodegradation

Addressing nitrate contamination in water bodies is a critical environmental challenge, and Intimately Coupling Photocatalysis and Biodegradation (ICPB) presents a promising solution. However, there is still debate about the effectiveness of ICPB in reducing nitrate under hypotrophic conditions. Further research is needed to understand its microbial metabolic mechanism and the functional changes in bacterial structure. Here we explored microbial metabolic mechanisms and changes in bacterial structure in ICPB reactors integrating a meticulously screened TiO2/g-C3N4 photocatalyst with biofilm. We achieved a 26.3% increase in nitrate reduction using 12.2% less organic carbon compared to traditional biodegradation methods. Metagenomic analysis of the microbial communities in ICPB reactors revealed evolving metabolic pathways conducive to nitrate reduction. This research not only elucidates the photocatalytic mechanism behind nitrate reduction in hypotrophic conditions but also provides genomic insights that pave the way for alternative approaches in water remediation technologies.

Historical development and prospect of intimately coupling photocatalysis and biological technology for pollutant treatment in sewage: A review

Through the synergistic effect of photocatalysis and biodegradation, intimately coupling photocatalysis and biological (ICPB) technology could improve the removal rate and mineralization rate of refractory pollutants and reduce the toxicity of intermediate products. ICPB system was characterized with the advantages of simple operation, low energy consumption and high treatment efficiency. As a new sewage treatment technology, ICPB system has shown great potential in the treatment of refractory pollutants, and has been widely concerned. In this study, the research progress of photocatalyst, carrier and biofilm in ICPB system were discussed, and the degradation mechanism was introduced. The shortcomings of the current ICPB system were pointed out, and the possible research directions of ICPB in the future were proposed. This review aimed to deepen the understanding of ICPB technology and promoted the further development of ICPB technology in the treatment of refractory pollutants.

Degradation of organic pollutants by intimately coupling photocatalytic materials with microbes: a review

With the rapid development of industry and agriculture, large amounts of organic pollutants have been released into the environment. Consequently, the degradation of refractory organic pollutants has become one of the toughest challenges in remediation. To solve this problem, intimate coupling of photocatalysis and biodegradation (ICPB) technology, which allows the simultaneous action of photocatalysis and biodegradation and thus integrates the advantages of photocatalytic reactions and biological treatments, was developed recently. ICPB consists mainly of porous carriers, photocatalysts, biofilms, and an illuminated reactor. Under illumination, photocatalysts on the surface of the carriers convert refractory pollutants into biodegradable products through photocatalytic reactions, after which these products are completely degraded by the biofilms cultivated in the carriers. Additionally, the biofilms are protected by the carriers from the harmful light and free radicals generated by the photocatalyst. Compared with traditional technologies, ICPB remarkably improves the degradation efficiency and reduces the cost of bioremediation. In this review, we introduce the origin and mechanisms of ICPB, discuss the development of reactors, carriers, photocatalysts, and biofilms used in ICPB, and summarize the applications of ICPB to treat organic pollutants. Finally, gaps in this research as well as future perspectives are discussed.

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.

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.

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.

Removal of selected nitrogenous heterocyclic compounds in biologically pretreated coal gasification wastewater (BPCGW) using the catalytic ozonation process combined with the two-stage membrane bioreactor (MBR)

Three identical anoxic-aerobic membrane bioreactors (MBRs) were operated in parallel for 300 consecutive days for raw (R₁), ozonated (R₂) and catalytic ozonated (R₃) biologically pretreated coal gasification wastewater (BPCGW) treatment. The results demonstrated that catalytic ozonation process (COP) applied asa pretreatment remarkably improved the performance of the unsatisfactory single MBR. The overall removal efficiencies of COD, NH₃-N and TN in R₃ were 92.7%, 95.6% and 80.6%, respectively. In addition, typical nitrogenous heterocyclic compounds (NHCs) of quinoline, pyridine and indole were completely removed in the integrated process. Moreover, COP could alter sludge properties and reshape microbial community structure, thus delaying the occurrence of membrane fouling. Finally, the total cost for this integrated process was estimated to be lower than that of single MBR. The results of this study suggest that COP is a good option to enhance pollutants removal and alleviate membrane fouling in the MBR for BPCGW treatment.

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.

Transformation of acesulfame in water under natural sunlight: joint effect of photolysis and biodegradation

The transformation of acesulfame in water under environmentally relevant conditions, including direct and indirect photolysis, biodegradation, and hydrolysis, was systematically evaluated. Under natural sunlight, both direct and indirect photolysis of acesulfame were negligible in sterilized systems at neutral or alkaline pH, whereas direct photolysis occurred at pH of 4 with a rate constant of 0.0355 d(-1) in deionized water. No significant reduction in acesulfame contents was found in the dark controls or in the incubation experiments, indicating acesulfame was resistant to hydrolysis and biodegradation. In unsterilized systems, photolysis was substantially enhanced, implying that there was a joint effect of photolysis and biodegradation or that the sterilization process had the secondary effect of inactivating some photosensitizers. The near-surface summer half-life of acesulfame in the water from the Haihe River was 9 d. Specific experiments revealed the involvement of (1)O2/(3)DOM* in acesulfame photolysis, whereas OH exhibited only a slight contribution in the presence of DOM or bicarbonate. As indicated by the total organic carbon data, no significant mineralization occurred in both sterilized and unsterilized systems after acesulfame was irradiated under simulated sunlight for 7 d, suggesting the generation of persistent intermediates. Finally, major degradation intermediates were analyzed, and the degradation pathways of acesulfame under environmentally relevant conditions were proposed for the first time.