Retrospect and prospect of aerobic biodegradation of aniline: Overcome existing bottlenecks and follow future trends

Function of N-acetyltransferase in the biotransformation of aniline in the green alga Chlamydomonas reinhardtii

Phytoplankton plays a crucial role in the fate of pollutants in aquatic ecosystems by biotransformation and bioaccumulation. Aniline was listed in priority pollutants due to its toxicity and widespread distribution in the aquatic environment. This study focused on investigating the capacity and mechanism of eukaryotic alga Chlamydomonas reinhardtii in transforming aniline. Results showed that the total removal percentage of aniline was 56% within 8 days at an initial concentration of 10 mg · L-1. The percentage of the biotransformation by C. reinhardtii was 23.4%. The biotransformation product was identified as acetanilide, indicating that acetylation was the primary biotransformation pathway. To reveal the key enzyme of the biotransformation process, the N-acetyltransferase (NAT) gene was cloned from the C. reinhardtii genome, and the NAT protein was obtained through heterologous expression. Aniline was significantly transformed by the purified NAT protein in vitro, and the product was also acetanilide. The characteristics of C. reinhardtii NAT in biotransformation of aniline was analyzed by bioinformatics methods. The binding sites in C. reinhardtii NAT for ligands (aniline and acetyl-CoA) were identified. Three highly reserved valine residues (Glu85-Asp86-Val87-Val88-Val89) as well as GLU131 and Cys122 were the indispensable amino acid residues for the catalysis from aniline to acetanilide. These results demonstrated the capacity of C. reinhardtii in the biotransformation of aniline, and the transformation process was primarily through N-acetylation of aniline to acetanilide catalyzed by NAT enzyme. This study provides novel insights into the biotransformation mechanism of aniline in eukaryotic green alga C. reinhardtii, facilitating the evaluation of the fate of aniline within aquatic ecosystems.

Redundancy and resilience of microbial community under aniline stress during wastewater treatment

Aniline is one of the most toxic and widespread organic pollutants. Although biological treatment is cost-effective and generates minimal secondary pollution, microbial communities are significantly affected by high aniline concentrations, which result in low degradation efficiency. However, a comprehensive understanding of the microbial community response to aniline stress is lacking. Here, we performed a cyclic experiment with aniline concentrations (200, 600, 1200, 600, and 200 mg/L) to investigate the ability of microbial communities to recover their performance after exposure to high aniline concentrations. At aniline concentrations up to 600 mg/L, the bioreactor exhibited high aniline removal efficiency (almost 100 %). Comamonas, Zoogloea, and Delftia played crucial roles in removing aniline and microbial beta diversity changed. Additionally, alpha diversity and network complexity decreased with increasing aniline concentration, but these metrics recovered to their original levels when the aniline concentration was returned to 200 mg/L. Homogeneous and heterogeneous selection dominated microbial community assembly. Therefore, according to the observed variations in community structure and the recovery of keystones after aniline stress, microbial community redundancy and resilience are pivotal for ensuring system stability. Overall, this study provides valuable insights into the redundancy and resilience of microbial communities under aniline stress and establishes a scientific basis for managing and evaluating wastewater treatment plants.

Biodegradation of Crude Oil and Aniline by Heavy Metal-Tolerant Strain Rhodococcus sp. DH-2

Aniline and crude oil are common environmental pollutants that present a significant risk to both the ecological and human health environments. The implementation of efficacious bioremediation strategies is imperative for the elimination of these contaminants. In this study, a bacterial strain designated DH-2 was isolated from soil contaminated with aniline. The strain was identified as belonging to the genus Rhodococcus. The optimal conditions for the growth and aniline degradation by strain DH-2 were determined to be pH 8.0 and 35 °C, respectively. Under these conditions, the degradation rate of aniline at a concentration of 1000 mg/L exceeded 90% within 36 h. Even in the presence of 4% NaCl, the degradation rate remained above 60%. HPLC-MS analysis revealed that the aniline degradation pathway of strain DH-2 follows the catechol pathway. Additionally, strain DH-2 is capable of utilizing crude oil as the sole carbon source, achieving a degradation rate of 91.0% for 2% crude oil concentration within 4 days. In soil modeling experiments, strain DH-2 was observed to degrade aniline and crude oil under triple stress conditions, including 1000 mg/L aniline, 2% crude oil, and 20 mg/L Fe(II) or Pb(II). Complete degradation of aniline and crude oil was achieved after 3 days and 12 days, respectively. The addition of Fe(II) or Pb(II) ions was found to enhance the degradation ability of DH-2. These results demonstrate that strain DH-2 is an extremely effective biodegradable strain, with potential applications in the remediation of environments contaminated with aniline and crude oil, even in the presence of heavy metals.

Biodegradation characteristics of p-Chloroaniline and the mechanism of co-metabolism with aniline by Pseudomonas sp. CA-1

Co-metabolism is a promising method to optimize the biodegradation of p-Chloroaniline (PCA). In this study, Pseudomonas sp. CA-1 could reduce 76.57 % of PCA (pH = 8, 70 mg/L), and 20 mg/L aniline as the co-substrate improved the degradation efficiency by 12.50 %. Further, the response and co-metabolism mechanism of CA-1 to PCA were elucidated. The results revealed that PCA caused deformation and damage on the surface of CA-1, and the -OH belonging to polysaccharides and proteins offered adsorption sites for the contact between CA-1 and PCA. Subsequently, PCA entered the cell through transporters and was degraded by various oxidoreductases accompanied by deamination, hydroxylation, and ring-cleavage reactions. Thus, the key metabolite 4-chlorocatechol was identified and two PCA degradation pathways were proposed. Besides, aniline further enhanced the antioxidant capacity of CA-1, stimulated the expression of catechol 2,3-dioxygenase and promoted meta-cleavage efficiency of PCA. The findings provide new insights into the treatment of PCA-aniline co-pollution.

Regulating microbial redox reactions towards enhanced removal of refractory organic nitrogen from wastewater

Biotechnology for wastewater treatment is mainstream and effective depending upon microbial redox reactions to eliminate diverse contaminants and ensure aquatic ecological health. However, refractory organic nitrogen compounds (RONCs, e.g., nitro-, azo-, amide-, and N-heterocyclic compounds) with complex structures and high toxicity inhibit microbial metabolic activity and limit the transformation of organic nitrogen to inorganic nitrogen. This will eventually result in non-compliance with nitrogen discharge standards. Numerous efforts suggested that applying exogenous electron donors or acceptors, such as solid electrodes (electrostimulation) and limited oxygen (micro-aeration), could potentially regulate microbial redox reactions and catabolic pathways, and facilitate the biotransformation of RONCs. This review provides comprehensive insights into the microbial regulation mechanisms and applications of electrostimulation and micro-aeration strategies to accelerate the biotransformation of RONCs to organic amine (amination) and inorganic ammonia (ammonification), respectively. Furthermore, a promising approach involving in-situ hybrid anaerobic biological units, coupled with electrostimulation and micro-aeration, is proposed towards engineering applications. Finally, employing cutting-edge methods including multi-omics analysis, data science driven machine learning, technology-economic analysis, and life-cycle assessment would contribute to optimizing the process design and engineering implementation. This review offers a fundamental understanding and inspiration for novel research in the enhanced biotechnology towards RONCs elimination.

Tire materials disturb transformations of nitrogen compounds and affect the structure of biomass in aerobic granular sludge reactors

Tire materials (TMs) present a notable hazard due to their potential to release harmful chemicals and microplastics into the environment. They can infiltrate wastewater treatment plants, where their effects remain inadequately understood, raising concerns regarding their influence on treatment procedures. Thus, this study investigated the impact of TMs in wastewater (10, 25, 50 mg/L) on wastewater treatment efficiency, biomass morphology, and microbial composition in aerobic granular sludge (AGS) reactors. TM dosage negatively correlated with nitrification and denitrification efficiencies, reducing overall nitrogen removal, but did not affect the efficiency of chemical-oxygen-demand removal. The presence of TMs increased the diameter of the granules due to TM incorporation into the biomass. The most frequently leached additives from TMs were N-(1,3-dimethylbutyl)-N'-phenyl-1,4-phenylenediamine, benzothiazole (BTH), and 2-hydroxybenzothiazole. In the treated wastewater, only BTH and aniline were detected in higher concentrations, which indicates that tire additives were biodegraded by AGS. The microbial community within the AGS adapted to TMs and their chemicals, highlighting the potential for efficient degradation of tire additives by bacteria belonging to the genera Rubrivivax, Ferruginibacter, and Xanthomonas. Additionally, our research underscores AGS's ability to incorporate TMs into biomass and effectively biodegrade tire additives, offering a promising solution for addressing environmental concerns related to TMs.

Insights into current bio-processes and future perspectives of carbon-neutral treatment of industrial organic wastewater: A critical review

With the rise of the concept of carbon neutrality, the current wastewater treatment process of industrial organic wastewater is moving towards the goal of energy conservation and carbon emission reduction. The advantages of anaerobic digestion (AD) processes in industrial organic wastewater treatment for bio-energy recovery, which is in line with the concept of carbon neutrality. This study summarized the significance and advantages of the state-of-the-art AD processes were reviewed in detail. The application of expanded granular sludge bed (EGSB) reactors and anaerobic membrane bioreactor (AnMBR) were particularly introduced for the effective treatment of industrial organic wastewater treatment due to its remarkable prospect of engineering application for the high-strength wastewater. This study also looks forward to the optimization of the AD processes through the enhancement strategies of micro-aeration pretreatment, acidic-alkaline pretreatment, co-digestion, and biochar addition to improve the stability of the AD system and energy recovery from of industrial organic wastewater. The integration of anaerobic ammonia oxidation (Anammox) with the AD processes for the post-treatment of nitrogenous pollutants for the industrial organic wastewater is also introduced as a feasible carbon-neutral process. The combination of AnMBR and Anammox is highly recommended as a promising carbon-neutral process for the removal of both organic and inorganic pollutants from the industrial organic wastewater for future perspective. It is also suggested that the AD processes combined with biological hydrogen production, microalgae culture, bioelectrochemical technology and other bio-processes are suitable for the low-carbon treatment of industrial organic wastewater with the concept of carbon neutrality in future.

Vanadium nitride decorated carbon cloth anode promotes aniline degradation and electricity generation of MFCs by efficiently enriching electroactive bacteria and promoting extracellular electron transfer

To increase the colonization of electroactive bacteria and accelerate the rate of extracellular electron transfer, a simple coated anode of microbial fuel cell was designed. Here, we took advantage of vanadium nitride (VN) particles to modify the carbon cloth (VN@CC). Compared with bare carbon cloth, the designed VN@CC bioanodes exhibited a larger electrochemically active area, better biocompatibility, and smaller charge transfer impedance. The MFC with VN@CC bioanodes achieved the maximum power density of 3.89 W m-2 and chemical oxygen demand removal rate of 84% when 1000 mg L-1 aniline was degraded, which were about 1.88 and 2.8 times that of CC. The morphology of biofilm and 16s rRNA gene sequence analysis proved that the VN@CC bioanodes facilitated the enrichment of electroactive bacteria (99.02%) and increased the ratio of fast electron transfer in the extracellular electron transfer, thus enhancing the MFC performance of aniline degradation and power output. This work disclosed that it was feasible to increase the overall performance of MFC by enhancing the EET efficiency and presented valuable insights for future work.

Treatment of aniline-containing wastewater by electrochemical oxidation using Ti/RuO2 anode: the influence of process parameters and reaction mechanism

Aniline detected in many industrial wastewater is a refractive organic pollutant with strong biological toxicity to aquatic organisms and humans. In this research, electrochemical oxidation process with Ti/RuO2 as the anode has been used to degrade aniline-containing wastewater on a laboratory scale. The influence of anode materials, electrolyte, NaCl concentration, current density, and aniline initial concentration on COD removal, ICE, and Ep were studied. The results showed that Cl- addition in the electrolyte is essential to promote aniline degradation efficiency and avoid the anode being passivated. Furthermore, decreasing the current density, increasing Cl- concentration, and initial aniline concentration are beneficial to increase current efficiency and reduce energy consumption. Although the addition of SO42- has a restriction on the active chlorine evolution process, the conductivity increased, which resulted in the reduction of energy consumption. At last, the aniline degradation mechanism in the presence of chloride ions was summed up and proposed based on the literature.