PAHs remediation from hazardous waste landfill leachate using fenton, photo - fenton and electro - fenton oxidation processes - performance evaluation under optimized conditions using RSM and ANN

Polycyclic aromatic hydrocharbons (PAHs) are a class of highly toxic pollutants that are highly detrimental to the ecosystem. Landfill leechate emanated from municipal solid waste are reported to constitute significant PAHs. In the present investigation, three Fenton proceses, namely conventional Fenton, photo-fenton and electro-fenton methods have been employed to treat landfill leehcate for removing PAHs from a waste dumpig yard. Response surface methodology (RSM) and artificial neural network (ANN) methodologies were adopted to optimize and validate the conditions for optimum oxidative removal of COD and PAHs. The statistical analysis results showed that all independent variables chosen in the study are reported to have significant influence of the removal effects with P-values <0.05. Sensitivity analysis by the developed ANN model showed that the pH had the highest significance of 1.89 in PAH removal when compared to the other parameters. However for COD removal, H2O2 had the highest relative importance of 1.15, followed by Fe2+ and pH. Under optimal treatment conditions, the photo-fenton and electro-fenton processes showed better removal of COD and PAH compared to the Fenton process. The photo-fenton and electro-fenton treatment processes removed 85.32% and 74.64% of COD and 93.25% and 81.65% of PAHs, respectively. Also the investigations revelaed the presence of 16 distinct PAH compunds and the removal percentage of each of these PAHs are also reported. The PAH treatment research studies are generally limited to the assay of removal of PAH and COD levels. In the present investigation, in addition to the treatment of landfill leachate, particle size distribution analysis and elemental characterization of the resultant iron sludge by FESEM and EDX are reported. It was revealed that elemental oxygen is present in highest percentage, followed by iron, sulphur, sodium, chlorine, carbon and potassium. However, iron percentage can be reduced by treating the Fenton-treated sample with NaOH.

Coagulation-flocculation treatment for batik effluent as a baseline study for the upcoming application of green coagulants/flocculants towards sustainable batik industry

The batik industry has been one of the main family businesses in most of the east-coast region of the Malaysian peninsula for many years. However, appropriate water treatment is still a major challenge for this industry. Stringent laws introduced by the Malaysian authorities and the intention to protect the environment are factors that drive researchers to search for suitable, appropriate, affordable and efficient treatment of batik wastewater. Treatment research on batik wastewater is still lacking and coagulation-flocculation treatment using alum was introduced and chosen as a stepping stone toward the selection of green coagulants. This study aimed to determine the best conditions for alum flocculation-coagulation using a standard jar test method. Four main factors were investigated: alum dosage (0.1-3.5 g/L), pH (4-11), settling time (0.5-24 h) and rapid mixing rate (100-300 rpm). Results obtained were further analysed statistically using SPSS software prior to determining the significant effect of variable changes. From this study, the best conditions for batik wastewater treatment using the flocculation-coagulation process were found to be at alum dosage of 1.5 g/L, pH 8, 4 h settling time and a rapid mixing rate of 100 rpm. Chemical oxygen demand (COD), turbidity, colour and total suspended solids (TSS) were removed by 70.7, 92.2, 88.4 and 100%, respectively, under these conditions. This study showed that batik wastewater can be treated by the coagulation-flocculation process using chemical means of alum. This indicates the need for forthcoming developments in natural-based-coagulant-flocculants toward the sustainability of the batik industry.

Management of Agricultural Water Containing Acetimidothioic Acid Pesticide through Catalytic Oxidation to Facilitate Reclaimed Water Recycling for Sustainable Food Production

Agro-industrial discharge contains acetimidothioic acid, which is commercially named “Lanox 90” and is a widely applied insecticide in greenhouses, and the result is wastewater loaded with this insecticide. Treating such wastewater is a must to reduce the environmental impact as well as to facilitate the opportunity for water recycling. Thus, the present work introduced Montmorillonite (MMT) clay as a novel Fenton reaction source to treat wastewater loaded with Lanox 90 insecticide as a benign sustainable strategy. Scanning electron microscopy (SEM) supported with energy-dispersive X-ray spectroscopy (EDX) and Fourier-transform infrared spectroscopy (FTIR) were used to characterize the MMT sample. Response surface methodology based on Box–Behnken analysis was selected to optimize the parametric circumstances. The optimized parameters of the proposed technique were obtained at a pH of 2.6 with the addition of 0.8 and 854 mg/L of MMT and H2O2, respectively, to attain the highest predicted Lanox 90 removal rate of 97%. Analysis of variance (ANOVA) was used to examine the statistical data and displayed a significant quadratic model. Ultimately, the results reveal that the oxidation system is exothermic and has a non-spontaneous nature, and the reaction kinetics are categorized according to the second-order reaction kinetic rate. The results of the current study indicate the importance of MMT for treating wastewater. These results confirm the possibility of using oxidation technique as a suitable candidate for greenhouse effluent management to enhance the efficiency of water recycling for smart irrigation.

Influence of water matrix on the degradation of organic micropollutants by ozone based processes: A review on oxidant scavenging mechanism

The prevalence of organic micropollutants (OMPs) in aquatic environment has expedited scientific and regulatory efforts to retrofit existing wastewater treatment plants (WWTPs). The current strategy involves WWTPs upgrading with post-ozonation i.e., ozone (O₃) and/or peroxone process (O₃ +H₂O₂). Still, ozone-based degradation of OMPs faces several challenges. For example, the degradation mechanism and kinetics of OMPs could largely be affected by water matrix compounds which include inorganic ions and natural organic matter (NOM). pH also plays a decisive role in determining the reactivity of the oxidants (O₃, H₂O₂, andHO^•), stability and speciation of matrix constituents and OMPs and thus susceptibility of OMPs to the reactions with oxidants. There have been reviews discussing the impact of matrix components on the degradation of OMPs by advanced oxidation processes (AOPs). Nevertheless, a review focusing on scavenging mechanisms, formation of secondary oxidants and their scavenging effects with a particular focus on ozonation and peroxone process is lacking. Therefore, in order to broaden the knowledge on this subject, the database 'Web of Science' was searched for the studies related to the 'matrix effect on the degradation of organic micropollutants by ozone based processes' over the time period of 2004-2021. The relevant literature was thoroughly reviewed and following conclusions were made: i) chloride has inhibitory effects if it exits at higher concentrations or as free chlorine i.e. HOCl/ClO^-. ii) The inhibitory effects of chloride, bromide, HOBr/OBr^- and HOCl/ClO^- are dominant in neutral and alkaline conditions and may result in the formation of secondary oxidants (e.g., chlorine atoms or free bromine), which in turn contribute to pollutant degradation or form undesired oxidation by-products such as BrO₃^-, ClO₃^- and halogenated organic products. ii) NOM may induce inhibitory or synergetic effects depending on the type, chemical properties and concentration of NOM. Therefore, more efforts are required to understand the importance of pH variation as well as the effects of water matrix on the reactivity of oxidants and subsequent degradation of OMPs.

Attenuation of organics contamination in polymers processing effluent using iron-based sludge: process optimization and oxidation mechanism

The feasibility of using iron extracted from acid mine drainage (AMD) as Fenton's reagent for removal of organics pollutants from polymer and plastics manufacturing effluent was investigated in this study. AMD iron dose, H₂O₂ concentration and pH were evaluated as the treatment factors for their effects on organics oxidation. Optimum treatment conditions were identified using response surface methodological analysis (RSM), and of the ranges of the treatment factors examined, an optimal treatment combination was found to be AMD iron concentration: 40 mg/L and H₂O₂: 500 mg/L at pH 2.2, organics removal efficiency as high as 98% for TOC removal was achieved. The removal efficiency increased with temperature up to 40°C and further temperature increases resulted in lower removal efficiencies. The organics oxidation was characterized well by investigating the kinetic order and the process is following the second-order reaction kinetics. The thermodynamic parameters showed that the oxidation reaction was endothermic and non-spontaneous in nature.

Organic Material for Clean Production in the Batik Industry: A Case Study of Natural Batik Semarang, Indonesia

Batik has become more desirable in the current fashion mode within the global market, but the environmental damage induced by this fabric’s synthetic dye practices is a matter of concern. This study aimed to discuss the application of organic materials as natural dyes in the clean production of textiles to maintain the environment. The research was a case study from the community services program in Kampung Malon, Gunungpati, Semarang City, Indonesia, focused on the batik home industry of the Zie Batik fabric. Furthermore, natural pigments from various plant organs (stem, leaves, wood, bark, and fruit) of diverse species, including Caesalpinia sappan, Ceriops candolleana, Maclura cochinchinensis, Indigofera tinctorial, I. arrecta, Rhizopora spp., Strobilantes cusia, and Terminalia bellirica were used for this type of material. These pigments are more biodegradable, relatively safe, and easily obtained with zero liquid waste compared to the synthetic variants. The leftover wastewater from the coloring stages was further utilized for other processes. Subsequently, the remaining organic waste from the whole procedure was employed as compost and/or timber for batik production, although a large amount of the wastewater containing sodium carbonate (Na2CO3), alum (KAl(SO4)2·12H2O), and fixatives (Ca(OH)2 and FeSO4) were discharged into the environment during the process of mordanting and fixating, with the requirement of additional treatment.

Facile one-pot synthesis of heterostructure SnO2/ZnO photocatalyst for enhanced photocatalytic degradation of organic dye

In this work, heterostructure SnO₂/ZnO nanocomposite photocatalyst was prepared by a straightforward one step polyol method.

Efficient treatment of saline recalcitrant petrochemical wastewater using heterogeneous UV-assisted sono-Fenton process

An effective hybrid system was applied as a first report for successful treatment of recalcitrant petrochemical wastewater (PCW). In this regards, magnetic powdered activated carbon (MPAC), as a heterogeneous catalyst, was coupled with ultrasound (US) and UV irradiations for activation of H₂O₂ (marked as MPAC/US/UV/H₂O₂). Chemical oxygen demand (COD) removal ratio was evaluated with various influencing operating factors including solution pH, MPAC and H₂O₂ concentrations, US power and quenchers. A possible mechanism for catalytic degradation and generation of reactive species was proposed. To evaluate the biodegradability of both raw and treated PCWs, the activated sludge inhibition experiments were performed based on Zahn-Wellens test. MPAC indicated high catalytic activity, reusability and stability in the studied system. Over 87% of COD was removed under optimum conditions within 80 min treatment and the residual COD concentration reached 82.9 mg/L, which was permissible to discharge surface water sources based on the environmental standards. Leaching of transition metals from catalyst textural was negligible. Compared to homogeneous system (Fe²⁺/US/UV/H₂O₂), heterogeneous system (MPAC/US/UV/H₂O₂) represented a better performance in COD removal. Identification of intermediates by GC-MS showed that a wide range of recalcitrant compounds was removed and/or degraded into small molecular compounds effectively after treatment. A biodegradability ratio of 64% and the residual COD of 28 mg/L for treated PCW, indicating that the biodegradability was improved and refractory organic matters removed effectively. As conclusion, MPAC/US/UV/H₂O₂ hybrid system can be introduced as a successful advanced treatment process for efficient remediation of refractory PCWs.

Synthesis and application of pillared clay heterogeneous catalysts for wastewater treatment: a review

The use of pillared interlayered clays (PILCs) as heterogenous catalysts in wastewater treatment technologies, particularly advanced oxidation processes (AOPs), is gaining popularity for the treatment of refractory wastewater effluents. The recent literature involving these solid materials is reviewed, with more focus on studies that aim at reducing the synthesis costs and escalating the synthesis process to industrial scale. Their role as active solid materials in the AOPs such as photocatalysis, catalytic wet peroxide oxidation (CWPO), the Fenton process and catalytic wet air oxidation (CWAO) of refractory organic compounds in polluted aqueous streams is also reviewed. These processes are evaluated to evidence their main direction for future research, particularly with reference to possible industrial use of these technologies to treat refractory organic wastewater using pillared clay-based catalysts. The pillared clay catalysts demonstrate good application prospects for the removal of refractory wastewater effluents using AOP technology. The reviewed studies suggest that the photocatalytic process is useful in low concentrations of these compounds, while CWPO, the Fenton process and CWAO are recommended for higher concentrations. However, catalyst development to reduce the severity of oxidation reaction conditions, with focus on the low cost, catalyst stability, reusability and environmental friendliness are the key aspects to be addressed by future research work.

Heterogeneous Fenton-like oxidation of petrochemical wastewater using a magnetically separable catalyst (MNPs@C): process optimization, reaction kinetics and degradation mechanisms

MNPs@C magnetic composite was synthesized and applied as a heterogeneous catalyst in the Fenton oxidation for PCW treatment. The organic compounds were degraded by the ˙OH radicals released from decomposition of H₂O₂ in the presence of MNPs@C.