Effects of combined 4-chlorophenol and Cu2+ on functional genes for nitrogen and phosphorus removal and heavy metal resistance genes in sequencing batch bioreactors

Nano-biochar reduces sustainable remediation of cadmium-contaminated soil more than micro-biochar: Evidence from cadmium removal and Eisenia foetida toxicity

Micro- (M-BC) and nano-biochar (N-BC) particles are ready to be disintegrated from biochar (BC), which is extensively applied to remediate heavy metal-contaminated soil. Still, its effects on the remediation efficiency remain poorly understood. This study investigated the interactions between the BC particles (M-BC and N-BC) and Eisenia foetida (E. foetida) in cadmium (Cd)-contaminated soils. Results indicated that M-BC has weak negative effect on E. foetida with survival rates of ≥85% as it is failed to be internalized. The interactive effects between M-BC/N-BC and Cd reduced the mobility of Cd, leading to low avoidance behavior of E. foetida. The synergistic effect of 0.1% M-BC and E. foetida caused pH regulation, BC diffusion and alternation of soil microbial community in the soil. This favored the remediation of Cd-contaminated soils with 56.2% Cd fixation efficiency identified. Conversely, internalization of Cd-loaded N-BC by E. foetida was recorded when 0.1% N-BC was amended in the soil. This triggered DNA damage, antioxidant suppression, antiapoptotic inhibition, digestion impairment, reproductive decline, and survival rates reduction (55%) in E. foetida, indicating the essential role of E. foetida in the soil is likely to be depressed. These findings are helpful to understand the potential negative effects of BC application in soil remediation.

Potential effects of Cu2+ stress on nitrogen removal performance, microbial characteristics, and metabolism pathways of biofilm reactor

Sequencing batch biofilm reactors (SBBR) were utilized to investigate the impact of Cu2+ on nitrogen (N) removal and microbial characteristics. The result indicated that the low concentration of Cu2+ (0.5 mg L-1) facilitated the removal of ammonia nitrogen (NH4+-N), total nitrogen (TN), nitrate nitrogen (NO3--N), and chemical oxygen demand (COD). In comparison to the average effluent concentration of the control group, the average effluent concentrations of NH4+-N, NO3--N, COD, and TN were found to decrease by 40.53%, 17.02%, 10.73%, and 15.86%, respectively. Conversely, the high concentration of Cu2+ (5 mg L-1) resulted in an increase of 94.27%, 55.47%, 22.22%, and 14.23% in the aforementioned parameters, compared to the control group. Low concentrations of Cu2+ increased the abundance of nitrifying bacteria (Rhodanobacter, unclassified-o-Sacharimonadales), denitrifying bacteria (Thermomonas, Comamonas), denitrification-associated genes (hao, nosZ, norC, nffA, nirB, nick, and nifD), and heavy-metal-resistant genes related to Cu2+ (pcoB, cutM, cutC, pcoA, copZ) to promote nitrification and denitrification. Conversely, high concentration Cu2+ hindered the interspecies relationship among denitrifying bacteria genera, nitrifying bacteria genera, and other genera, reducing denitrification and nitrification efficiency. Cu2+ involved in the N and tricarboxylic acid (TCA) cycles, as evidenced by changes in the abundance of key enzymes, such as (EC:1.7.99.1), (EC:1.7.2.4), and (EC:1.1.1.42), which initially increased and then decreased with varying concentrations of Cu2+. Conversely, the abundance of EC1.7.2.1, associated with the accumulation of nitrite nitrogen (NO2--N), gradually declined. These findings provided insights into the impact of Cu2+ on biological N removal.

Contaminant removal performance and lipid productivity of a cyanobacteria-bacteria consortium containing exogenous phytohormones during the treatment of antibiotic-polluted wastewater

In this study, a cyanobacteria-bacteria consortium containing native wastewater bacteria and immobilized Synechococcus sp. was constructed. The cyanobacterial cellular responses (including growth, biomass and lipid productivity) and contaminant removal ability (for TN, TP, COD and antibiotics) in the consortium were evaluated during the advanced treatment of wastewater containing 10-50 μg/L of mixed antibiotics (amoxicillin, tetracycline, erythromycin, sulfadiazine and ciprofloxacin) with the addition of a certain phytohormone (indole-3-acetic acid, gibberellin A3 or 6-benzylaminopurine) at trace level within a period of four days. Each phytohormone promoted the growth of Synechococcus sp. and increased the tolerance of Synechococcus sp. to mixed antibiotics. Indole-3-acetic acid coupled to moderate antibiotic stress could elevate lipid productivity and lipid content of Synechococcus sp. to 33.50 mg/L/day and 43.75%, respectively. Phytohormones increased the pollutant removal performance of the cyanobacteria-bacteria consortium through the stimulation of cyanobacterial growth and the regulation of cyanobacteria-bacteria interaction, which increased the abundances of microalgae-associated bacteria including Flavobacterium, Allorhizobium-Neorhizobium-Pararhizobium-Rhizobium, Bosea, Sphingomonas and Emticicia. Up to 80.83%, 98.06%, 83.26%, 99.84%, 99.50%, 89.41%, 65.61% and 60.65% of TN, TP, COD, amoxicillin, tetracycline, erythromycin, sulfadiazine and ciprofloxacin were removed by the consortium with the addition of phytohormones. In general, indole-3-acetic acid was the optimal phytohormone for enhancing lipid production and contaminant removal performance of the cyanobacteria-bacteria consortium.

Influence and mechanism of typical transition metal ions on the denitrification performance of heterotrophic nitrification-aerobic denitrification bacteria

To investigate the inhibitory effects of various transition metal ions on nitrogen removal and their underlying mechanisms, the single and combined effects of Cu2+ Ni2+ and Zn2+ on Heterotrophic nitrification-aerobic denitrification (HN-AD) bacteria Acinetobacter sp. TAC-1 were studied in a batch experiment system. The results revealed that increasing concentrations of Cu2+ and Ni2+ had a detrimental effect on the removal of ammonium nitrogen (NH4+-N) and total nitrogen (TN). Specifically, Cu2+ concentration of 10 mg/L, the TN degradation rate was 55.09%, compared to 77.60% in the control group. Cu2+ exhibited a pronounced inhibitory effect. In contrast, Zn2+ showed no apparent inhibitory effect on NH4+-N removal and even enhanced TN removal at lower concentrations. However, when the mixed ion concentration of Zn2++Ni2+ exceeded 5 mg/L, the removal rates of NH4+-N and TN were significantly reduced. Moreover, transition metal ions did not significantly impact the removal rates of chemical oxygen demand (COD). The inhibition model fitting results indicated that the inhibition sequence was Cu2+ > Zn2+ > Ni2+. Transcriptome analysis demonstrated that metal ions influence TAC-1 activity by modulating the expression of pivotal genes, including zinc ABC transporter substrate binding protein (znuA), ribosomal protein (rpsM), and chromosome replication initiation protein (dnaA) and DNA replication of TAC-1 under metal ion stress, leading to disruptions in transcription, translation, and cell membrane structure. Finally, a conceptual model was proposed by us to summarize the inhibition mechanism and possible response strategies of TAC-1 bacteria under metal ion stress, and to address the lack of understanding regarding the influence mechanism of TAC-1 on nitrogen removal in wastewater co-polluted by metal and ammonia nitrogen. The results provided practical guidance for the management of transition metal and ammonia nitrogen co-polluted water bodies, as well as the removal of high nitrogen.

Performance evaluation and metagenomic analysis of sequencing batch reactor under transient 2,4,6-trichlorophenol shock

The transient chlorophenol shock under some emergency conditions might directly affect the pollutant removal of bioreactor. Therefore, the recovery of bioreactor performance after transient chlorophenol shock is a noteworthy issue. In the present research, the performance, antioxidant response, microbial succession and functional genes of sequencing batch reactor (SBR) were evaluated under transient 2,4,6-trichlorophenol (2,4,6-TCP) shock. The chemical oxygen demand (COD) and ammonia nitrogen (NH4+-N) removal efficiencies decreased sharply in the first 4 days after 60 mg/L 2,4,6-TCP shock for 24 h and gradually recovered to normal in the subsequent 8 days. The nitrogen removal rates and their corresponding enzymatic activities rapidly decreased after transient 2,4,6-TCP shock and then gradually increased to normal. The increase of antioxidant enzymatic activity, Cu-Zn SOD genes and Fe-Mn SOD genes contributed to the recovery of SBR performance. The abundance of genes encoding ammonia monooxygenase and hydroxylamine dehydrogenase decreased after transient 2,4,6-TCP shock, including amoA, amoC and nxrA. Thauera, Dechloromonas and Candidatus_Competibacter played key roles in the restorative process, which provided stable abundances of narG, norB , norC and nosZ. The results will deeply understand into the effect of transient 2,4,6-TCP shock on bioreactor performance and provide theoretical basis to build promising recoveries strategy of bioreactor performance.

Elucidating the impacts of cobalt (II) ions on extracellular electron transfer and pollutant degradation by anodic biofilms in bioelectrochemical systems during industrial wastewater treatment

Electrogenic biofilms in bioelectrochemical systems (BES) are critical in wastewater treatment. Industrial effluents often contain cobalt (Co2+); however, its impact on biofilms is unknown. This study investigated how increasing Co2+ concentrations (0-30 mg/L) affect BES biofilm community dynamics, extracellular polymeric substances, microbial metabolism, electron transfer gene expression, and electrochemical performance. The research revealed that as Co2+ concentrations increased, power generation progressively declined, from 345.43 ± 4.07 mW/m2 at 0 mg/L to 160.51 ± 0.86 mW/m2 at 30 mg/L Co2+. However, 5 mg/L Co2+ had less effect. The Co2+ removal efficiency in the reactors fed with 5 and 10 mg/L concentrations exceeded 99% and 94%, respectively. However, at 20 and 30 mg/L, the removal efficiency decreased substantially, likely because of reduced biofilm viability. FTIR indicated the participation of biofilm functional groups in Co2+ uptake. XPS revealed Co2+ presence in biofilms as CoO and Co(OH)2, indicating precipitation also aided removal. Cyclic voltammetry and electrochemical impedance spectroscopy tests revealed that 5 mg/L Co2+ had little impact on the electrocatalytic activity, while higher concentrations impaired it. Furthermore, at a concentration of 5 mg/L Co2+, there was an increase in the proportion of the genus Anaeromusa-Anaeroarcus, while the genus Geobacter declined at all tested Co2+ concentrations. Additionally, higher concentrations of Co2+ suppressed the expression of extracellular electron transfer genes but increased the expression of Co2+-resistance genes. Overall, this study establishes how Co2+ impacts electrogenic biofilm composition, function, and treatment efficacy, laying the groundwork for the optimized application of BES in remediating Co2+-contaminated wastewater.

Photochemical-promoted ZVI reduction for highly efficient removal of 4-chlorophenol and Cr(VI): Catalytic activity, performance and electron transfer mechanisms

Zero-valent iron (ZVI) reduction represents a promising methodology for water remediation, but its broad application is limited by two critical challenges (i.e., aggregation and passivation). Here, we report a hybrid strategy of photochemical-promoted ZVI reduction with high efficiency and reduction capacity for removing coexisting refractory pollutants in water. A composite material with Pd/Fe bimetallic nanoparticles supported onto semiconducting metal oxide (Pd/Fe@WO3-GO) was prepared and subsequently used as the model catalyst. By using the developed strategy with visible light as light source, this catalyst showed a remarkable catalytic performance for simultaneously eliminating 4-chlorophenol (4-CP) and Cr(VI), with dehalogenation rate as high as 0.43 min-1, outperforming the reported ZVI-based catalysts. A synergistic interaction of photocatalysis and ZVI reduction occurred in this strategy, where the interfacial electron transfer on particles surface were greatly strengthened with light irradiation. The activation was attributed to the dual functions of semiconducting material as support to disperse Pd/Fe nanoparticles and as (photoexcited) electron donor to directly trigger reduction reactions and/or indirectly inhibit the formation of oxides passivation layer. Both direct electron transfer and H*-mediated indirect electron transfer mechanisms were confirmed to participate in the reduction of pollutants, while the later was quantitatively demonstrated as the predominant reaction route. Importantly, this strategy showed a wide pH applicability, long-term durability and excellent catalytic performance in different real-water systems. This work provides new insights into ZVI reduction and advances its applications for the removal of combined organic and inorganic pollutants. The developed photochemical-promoted ZVI reduction strategy holds a great potential for practical applications.

The impact of alloying element Cu on corrosion and biofilms of 316L stainless steel exposed to seawater

Copper-containing stainless steel (SS) has been reported to mitigate biofilms in industrial and clinical environments. However, the impact of copper released from copper-containing SS in natural seawater on biofilms and corrosion is still unclear. In this study, three kinds of 316L SS were immersed in natural seawater for 6 months, and the pitting depth decreased in the order: 316L-Cu SS (annealed) > 316L SS > 316L-Cu SS (aged). The biofilm thickness and number of sessile cells on the surface of 316L-Cu SS (annealed) and 316L SS were similar but notably greater than those of 316L-Cu SS (aged). Furthermore, the results of the community analysis indicated that the addition of copper in 316L-Cu SS (aged) reduced the diversity and richness of the microbial community, resulting in a significant reduction in the number of genera constituting the biofilms. Copper ions exhibit a broad-spectrum bactericidal effect, effectively reducing the abundance of dominant populations and microbial genera in the biofilms, thereby mitigating pitting corrosion induced by microorganisms. In addition, the PCoA scatter plot showed that time also played an important role in the regulation of microbial community structure.

The response of nitrifying activated sludge to chlorophenols: Insights from metabolism and redox homeostasis

The specialized wastewater treatment plants for the chemical industry are rapidly developed in China and many other countries. But there is a common bottleneck in that the toxic pollutants in chemical wastewater often cause shock impacts on biological nitrogen removal systems, which directly affects the stability and cost of operation. As the research on nitrification inhibition characteristics is not sufficient till now, there is a great lack of theoretical guidance on the control of the inhibition. This study investigated the response of nitrifying activated sludge to chlorophenols (CPs) inhibition in terms of metabolism disorder and oxidative stress. At the initial stage of reaction (i.e., 1 h), reactive oxygen species (ROS)-induced membrane damage which might account for declining nitrification performance. Simultaneously excessive extracellular polymeric substances (EPS) were secreted to alleviate oxidative stress injury and protected microorganisms to some extent. In particular tyrosine-like substances in LB-EPS with a Fmax increase of 242.30% were confirmed to efficiently resist phenols inhibition. Thus, as the inhibition proceeded, metabolism disorder replaced oxidative stress as the main cause of nitrification inhibition. The affected metabolic processes include weakened enzyme catalysis, restricted electron transport and lessened energy generation. At 4 h, nitrifying production of sludge amended with 5 mg/L chlorophenols was 89.27 ± 9.51%-98.15 ± 9.60% lower than blank, the inhibition could be attributed to comprehensively affected metabolism. The structural equation modeling indicated that phenols restricted nitrification enzymes and bacterial electron transport efficiency which was critical to nitrification performance. Moreover, the lessened energy generation weakens enzyme activity to further suppress nitrification. These findings enriched our knowledge of nitrifiers' responses to CPs inhibition and provided the basis for addressing nitrification inhibition.

Effects of salinity on the performance, microbial community, and functional genes among 4-chlorophenol wastewater treatment

Chlorophenols frequently occur alongside salinity in industrial wastewater; thus, the effects of low concentrations of salinity (NaCl, 100 mg/L) on sludge performance, microbial community, and functional genes were deeply analyzed among 4-chlorophenol (4-CP, 2.4-4.0 mg/L) wastewater treatment. The influent 4-CP was effectively degraded, but the efficiencies for PO₄^3--P, NH₄⁺-N, and organics reduction were slightly inhibited by NaCl stress. Long-term NaCl and 4-CP stress significantly stimulated the secretion of extracellular polymeric substances (EPS). The abundances of predominant microbes at different taxonomic levels were affected by NaCl, and the increased relative abundances of functional genes encoding proteins contributed to resist NaCl and 4-CP stress. The functional genes associated with phosphorus metabolism and nitrogen metabolism in nitrification were unaffected, but the functional genes in denitrification increased in diversity under NaCl stress in 4-CP wastewater treatment. This finding acquires useful insight into the wastewater treatment with low chlorophenols and low salinity.

Trace phenolic acids simultaneously enhance degradation of chlorophenol and biofuel production by Chlorella regularis

Coupling the cultivation of microalgae with wastewater treatment is a promising technology to recover bioresources from wastewater. However, toxic pollutants in wastewater seriously inhibit the growth of microalgae and the removal of pollutants. Phenolic acids are similar to phytohormones, could potentially relieve the toxicity to microalgae and simultaneously promote pollutant degradation and lipid accumulation. Chlorella and 4-chlorophenol (4-CP) were utilized to simulate the toxic wastewater treatment, and the roles of two typical phenolic acids, such as p-hydroxybenzoic acid (p-HBA) and caffeic acid (CA), were explored. The 0.2 μM concentration of p-HBA or CA improved the specific growth rate by 7.6% by enhancing photosynthesis and DNA replication. The oxidative damage caused by 4-CP was reduced by 30.3-49.7% via the synthesis of more antioxidant enzymes and the direct scavenging of free radicals by phenolic acids. Furthermore, the 4-CP removal rate increased by 27.0%, and toxic 4-CP was degraded into non-toxic compounds. The phenolic acids did not change the 4-CP degradation pathway but accelerated its removal and detoxification by enhancing the expression of 4-CP degradation enzymes. Simultaneously, lipid production increased by 20.5-23.1% due to the upregulation of enzymes related to fatty acid and triacylglycerol synthesis. Trace phenolic acids stimulated the mitogen-activated protein kinase signaling cascade and the calcium signaling pathway to regulate the physiology of the microalgae and protect cells from toxic stress. This study provides a promising new strategy for toxic wastewater treatment and bioresource recovery.