Performance of photo-catalytic oxidation for degradation of chlorophenols: Optimization of reaction parameters and quantification of transformed oxidized products

A comprehensive review of chlorophenols: Fate, toxicology and its treatment

Chlorophenols represent one of the most abundant families of toxic pollutants emerging from various industrial manufacturing units. The toxicity of these chloroderivatives is proportional to the number and position of chlorine atoms on the benzene ring. In the aquatic environment, these pollutants accumulate in the tissues of living organisms, primarily in fishes, inducing mortality at an early embryonic stage. Contemplating the behaviour of such xenobiotics and their prevalence in different environmental components, it is crucial to understand the methods used to remove/degrade the chlorophenol from contaminated environment. The current review describes the different treatment methods and their mechanism towards the degradation of these pollutants. Both abiotic and biotic methods are investigated for the removal of chlorophenols. Chlorophenols are either degraded through photochemical reactions in the natural environment, or microbes, the most diverse communities on earth, perform various metabolic functions to detoxify the environment. Biological treatment is a slow process because of the more complex and stable structure of pollutants. Advanced Oxidation Processes are effective in degrading such organics with enhanced rate and efficiency. Based on their ability to generate hydroxyl radicals, source of energy, catalyst type, etc., different processes such as sonication, ozonation, photocatalysis, and Fenton's process are discussed for the treatment or remediation efficiency towards the degradation of chlorophenols. The review entails both advantages and limitations of treatment methods. The study also focuses on reclamation of chlorophenol-contaminated sites. Different remediation methods are discussed to restore the degraded ecosystem back in its natural condition.

Analysis of the chloride ion removal mechanism from simulated wastewater by discarded vitamin tablets

Vitamin (VM) tablets are often discarded or incinerated as medical waste, and untreated highly chlorinated wastewater is discharged, polluting the environment. In this study, Cu²⁺ was reduced by vitamin C (VC, a component of VM), and the precipitate formed by the reaction of its product with Cl^- in water was used to remove Cl^- from simulated wastewater. This allows for the resourceful use of waste VM, while also achieving the goal of dechlorinating wastewater. Meanwhile, the effect of various parameters on dechlorination was studied, and the dechlorination mechanism was analyzed. According to the results, the removal rate of Cl^- increased first and then decreased with pH, removal time and reaction temperature. Using VC in VM to dechlorinate simulated wastewater, the removal rate of Cl^- was 94.31% under optimum conditions: pH 2.5, temperature 30 °C and reaction time 10 minutes. According to the dechlorination process, it can be inferred that Cu²⁺ is reduced to Cu⁺ by VC, and Cu⁺ and Cl^- coprecipitate to remove Cl^-. Therefore, it is feasible to use discarded VM to treat high concentration chlorine-containing wastewater.

Challenges and opportunities for the biodegradation of chlorophenols: Aerobic, anaerobic and bioelectrochemical processes

Chlorophenols (CPs) are highly toxic and refractory contaminants which widely exist in various environments and cause serious harm to human and environment health and safety. This review provides comprehensive information on typical CPs biodegradation technologies, the most green and benign ones for CPs removal. The known aerobic and anaerobic degradative bacteria, functional enzymes, and metabolic pathways of CPs as well as several improving methods and critical parameters affecting the overall degradation efficiency are systematically summarized and clarified. The challenges for CPs mineralization are also discussed, mainly including the dechlorination of polychlorophenols (poly-CPs) under aerobic condition and the ring-cleavage of monochlorophenols (MCPs) under anaerobic condition. The coupling of functional materials and degraders as well as the operation of sequential anaerobic-aerobic bioreactors and bioelectrochemical system (BES) are promising strategies to overcome some current limitations. Future perspective and research gaps in this field are also proposed, including the further understanding of microbial information and the specific role of materials in CPs biodegradation, the potential application of innovative biotechnologies and new operating modes to optimize and maximize the function of the system, and the scale-up of bioreactors towards the efficient biodegradation of CPs.

Effluents detoxification from pulp and paper industry using microbial engineering and advanced oxidation techniques

Due to the high demand of paper and related items, pulp and paper industry is flourishing day by day. With increased production, come the hazards associated with the toxic elements present in the effluents. Various microorganisms are currently employed in the remediation of these toxic effluents. In addition, various techniques like ozonation, electrocoagulation, UV treatment, Fenton's reagent, and photo-Fenton based techniques are used in advanced oxidation processes to reduce these toxins from effluents. This review highlights various above mentioned advanced techniques and innovative processes along with the biological remediation of these toxic effluents with the help of some potential microbial consortia or their combinatory effects. Moreover, the present review will also disclose the ideas on utilizing the tools of metabolic engineering, systems biology, and artificial intelligence towards microbial engineering for relatively better bioremediation processes. In the future, these techniques might be helpful in increasing the capability of microbial consortia towards detoxification of effluents to make them environmentally safe. Finally, this review gives well-synchronized approaches to get more insights into these innovative methodologies and techniques and their use for various industrial applications.

A novel isophorone wastewater treatment technology-wet electrocatalytic oxidation and its degradation mechanism study

How to solve the poisoning and loss of catalysts in catalytic wet air oxidation (CWAO) process remains a great challenge. In this work, an electric field was introduced into wet air oxidation (WAO) process for the efficient degradation of isophorone (IP) wastewater for the first time, named as wet electrocatalytic oxidation (WEO) process. Different composite electrodes including Ti/PbO₂, Ti/Pt, Ti/Ru-Ir and Ti/Ir-Ta electrode were selected as the anodes of WEO technique and the results showed that the total organic carbon (TOC) removal via WEO process with PbO₂ anode (89.56 %) was much higher than CWAO equipped with noble metal catalyst (Ru/TiZrO₄, 75.0 %). Additionally, the current efficiency of WEO process was 85.6 %, which was significantly better than that of EO process (12.1 %). A response surface methodology was applied to elucidate the effects of reaction conditions on IP degradation. Analysis of response surface model showed TOC removal were markedly affected (p ≤ 0.01) by the reaction time (t), temperature (T), current density (I_D), T² and I_D², and also determined (p ≤ 0.05) by the interactions of T with t and I_D respectively. In addition, a synergistic effect was proved to take place in WEO process with synergistic effect factor f of 1.2 at optimized conditions. As an advanced wastewater treatment technology, WEO integrates the advantages of both electro-catalytic oxidation (EO) and WAO.

Ortho and para oxydehalogenation of dihalophenols catalyzed by the monooxygenase TcpA and NAD(P)H:FAD reductase Fre

Dihalophenols such as dichlorophenols (DCPs) are important industrial chemical intermediates, but also persistent pollutants in the environment. Oxidative dehalogenation by microbes is an efficient biological method to degrade halophenols, but the mechanism is unclear yet. Cupriavidus nantongensis X1^T was a type strain of genus Cupriavidus, and could degrade 2,4-dichlorophenol of 50 mg/L within 12 h. The degradation rate constant was approximately 84 fold greater than that by Bacillus endophyticus CP1R43, a well-studied 2,4-DCP-degrading bacterial strain. The genes encoding 2,4,6-trichlorophenol monooxygenase (TcpA) and NAD(P)H:FAD reductase (Fre) from strain X1^T were cloned and expressed. The expressed TcpA Fre were purified. The molecular docking of TcpA with DCPs and point mutation experiments showed that the degradation activity of TcpA was associated with the length of the hydrogen bond between the substrates and the amino acids in the active pocket. DCPs were degraded via a stepwise oxidative dechlorination in a positive relationship between the oxidation ability and the electron-withdrawing potential of the p-position group. In addition, TcpA has dual dehalogenation and denitration functions. The results demonstrate that either strain X1^T or TcpA and Fre can effectively dehalogenate dihalophenols, which can be useful for the treatment of dihalophenols in wastewaters and remediation of DCP-contaminated environments.

Characterisation and utilization of steel industry waste sludge as heterogeneous catalyst for the abatement of chlorinated organics by advanced oxidation processes

Catalytic advanced oxidation processes (AOPs) utilising UV irradiation have been reported to be highly efficient for the degradation of recalcitrant compounds. The focus of present study was to evaluate the potential of steel industry waste as an alternative to homogenous iron salts often used in AOPs. Iron rich sludge from effluent treatment plant (ETP) of a steel industry was subjected to acid washing and acid washing followed by calcination before using as catalyst for the oxidative removal of chlorinated organics present in synthetic and simulated bleaching effluents. The maximum total organic carbon removals of 64% and 25% from 4-chlorophenol solution and simulated pulp bleaching effluent, respectively were observed during photo-catalytic oxidation with acid washed steel sludge at stoichiometric H₂O₂ dose after 2 h reaction (catalyst dose = 1 g/L, and pH = 4.4). Low iron leaching (<2%) was observed from the catalyst even in acidic conditions and it could be reused twice without significant loss of catalytic activity.