Agricultural waste materials for adsorptive removal of phenols, chromium (VI) and cadmium (II) from wastewater: A review.

Management of basic natural resources and the spent industrial and domestic streams to provide a sustainable safe environment for healthy living is a magnum challenge to scientists and environmentalists. The present remedial approach to the wastewater focuses on recovering pure water for reuse and converting the contaminants into a solid matrix for permanent land disposal. However, the ground water aquifers, over a long period slowly leach the contaminants consequently polluting the ground water. Synthetic adsorbents, mainly consisting of polymeric resins, chelating agents, etc. are efficient and have high specificity, but ultimate disposal is a challenge as most of these materials are non-biodegradable. In this context, it is felt appropriate to review the utility of adsorbents based on natural green materials such as agricultural waste and restricted to few model contaminants: phenols, and heavy metals chromium(VI), and cadmium(II) in view of the vast amount of literature available. The article discusses the features of the agricultural waste material-based adsorbents including the mechanism. It is inferred that agricultural waste materials are some of the common renewable sources available across the globe and can be used as sustainable adsorbents. A discussion on challenges for industrial scale implementation and integration with advanced technologies like magnetic-based approaches and nanotechnology to improve the removal efficiency is included for future prospects.

Green route for recycling of low-cost waste resources for the biosynthesis of nanoparticles (NPs) and nanomaterials (NMs)-A review.

Nowadays, nanoparticles (NPs) and nanomaterials (NMs) are used extensively in various streams such as medical science, solar energy, drug delivery, water treatment, and detection of persistent pollutants. Intensive synthesis of NPs/NMs carried out via physico-chemical technologies is deteriorating the environment globally. Therefore, an urgent need to adopt cost-effective and green technologies to synthesize NPs/NMs by recycling of secondary waste resources is highly required. Environmental wastes such as metallurgical slag, electronics (e-waste), and acid mine drainage (AMD) are rich sources of metals to produce NPs. This concept can remediate the environment on the one hand and the other hand, it can provide a future roadmap for economic benefits at industrial scale operations. The waste-derived NPs will reduce the industrial consumption of limited primary resources. In this review article, green emerging technologies involving lignocellulosic waste to synthesize the NPs from the waste streams and the role of potential microorganisms such as microalgae, fungi, yeast, bacteria for the synthesis of NPs have been discussed. A critical insight is also given on use of recycling technologies and the incorporation of NMs in the membrane bioreactors (MBRs) to improve membrane functioning and process performance. Finally, this study aims to mitigate various persisting scientific and technological challenges for the safe disposal and recycling of organic and inorganic waste for future use in the circular economy.

A comprehensive review on green perspectives of electrocoagulation integrated with advanced processes for effective pollutants removal from water environment.

The rapidly expanding global energy demand is forcing a release of regulated pollutants into water that is threatening human health. Among various wastewater remediating processes, electrocoagulation (EC) has scored a monumental success over conventional processes because it combines coagulation, sedimentation, floatation and electrochemical oxidation processes that can effectively decimate numerous stubborn pollutants. The EC processes have gained some attention through various academic and industrial publications, however critical evaluation of EC processes, choices of EC processes for various pollutants, process parameters, mechanisms, commercial EC technologies and performance enhancement via other degradation processes (DPs) integration have not been comprehensively covered to date. Therefore, the major objective of this paper is to provide a comprehensive review of 20 years of literature covering EC fundamentals, key process factors for a reactor design, process implementation, current challenges and performance enhancement by coupling EC with pivotal pollutant DPs including, electro/photo-Fenton (E/P-F), photocatalysis, sono-chemical treatment, ozonation, indirect electrochemical/advanced oxidation (AO), and biosorption that have substantially reduced metals, pathogens, toxic compound BOD, COD, colors in wastewater. The results suggest that the optimum treatment time, current density, pulse frequency, shaking speed and spaced electrode improve the pollutants removal efficiency. An elegant process design can prevent electrode passivation which is a critical limitation of EC technology. EC coupling (up or downstream) with other DPs has resulted in the removal of organic pollutants and heavy metals with a 20% improved efficiency by EC-EF, removal of 85.5% suspended solid, 76.2% turbidity, 88.9% BOD, 79.7% COD and 93% color by EC-electroflotation, 100% decolorization by EC-electrochemical-AO, reduction of 78% COD, 81% BOD, 97% color by EC-ozonation and removal of 94% ammonia, 94% BOD, 95% turbidity, >98% phosphorus by aerated EC and peroxicoagulation. The major wastewater purification achievements, future potential and challenges are described to model the future EC integrated systems.

Tetracycline removal from aqueous solution by electrooxidation using ruthenium-coated graphite anode.

This paper reports the electrochemical oxidation treatment of 80 mL of acidic aqueous solutions with 0.2 mM of the drug tetracycline in 25 mM Na2SO4 using a lab-scale electrochemical cell. The performance of tetracycline removal with Ru-coated graphite by the chemical bath deposition (CBD) and raw graphite anode has been demonstrated. The effects of operating parameters were tested such as pH, applied current, supporting electrolyte concentration, and initial tetracycline concentration. The best tetracycline degradation was obtained with Ru-coated graphite anode due to its higher oxidation power, which allowed the complete degradation of refractory compounds. The modified surface structure of the Ru-coated graphite anode was characterized by scanning electron microscopy (SEM), atomic force microscopy (AFM), and energy-dispersive X-ray (EDX). The EO process with Ru-coated graphite anode allowed 93.8% tetracycline abatement after 100 min of electrolysis at an applied current of 100 mA. In all cases, tetracycline decay obeyed pseudo-first-order kinetics. The tetracycline removal performance of graphite electrodes with nano coating on graphite has offered a performing alternative. A Comparative study revealed that electrolysis with Ru-coated graphite acted as a better electrode material than raw graphite for the catalytic reaction.

Bio-accessibility and health risk assessment of some selected heavy metals in indoor dust from higher institutions in Ondo State, Nigeria.

Risks of heavy metal exposure from contaminated indoor dust constitute a major threat to human health. In this paper, heavy metals in deposited indoor dust samples from four tertiary institutions in Ondo State, Nigeria-Federal University of Technology, Akure; Federal College of Agriculture, Akure; Ondo State College of Health Science Technology, Akure; and Adeyemi College of Education, Ondo-were examined. The samples were collected from each location by dusting the surfaces of doors, windows, and bookshelves in lecture rooms, hostels, laboratories, and libraries, homogenized into a representative composite, and analyzed for Cr, Pb, Cd, Cu, and Zn using a flame atomic absorption spectrophotometer (FAAS) to assess their potential health risk to humans. Cu had the highest mean metal concentration in the range (0.18-0.31 mg/kg) and Cd had the lowest (ND-0.02 mg/kg) in the study. Samples from Federal College of Agriculture had the highest metal concentration, while those from Ondo State College of Health Science Technology had the lowest. The average daily dose (ADD) through ingestion was determined to be the key exposure pathway in a non-carcinogenic investigation followed by ADD through dermal contact and ADD via inhalation accordingly. Despite this, the hazard quotients (HQ) and hazard indices (HI) were well below the safety limit of one. The study established that carcinogenic effect cannot be experienced with exposure to the studied dust samples. To retain the status, it is suggested that a reasonable level of safety and tight rules be implemented.

Removal of phenol from aqueous solution by coupling alternating current with biosorption.

The present research was devoted to water decontamination through the valorization of cellulosic fibers for the preparation of performing biosorbent, with high pollutant-uptake capacity and low cost. Luffa cylindrica (L.C) and zinc oxide were chosen for the synthesis of hybrid materials by precipitation with and without alternating current (AC). AC was used as a new alternative able to accelerate the reaction kinetics and to enhance the biosorption speed. The potential to remove phenol, from aqueous solution by coupling biosorption and AC, was highlighted. Pure L.C and hybrid materials (L.C + 4% Zn2+) synthesized with and without AC were chosen for the biosorption tests. The effects of pH, initial concentration, frequency, and contact time were studied. The efficiency of the coupling process was evaluated according to the quality of the treated water before and after purification. Results have shown that the percentages of chemical oxygen demand (COD), total organic carbon (TOC), germination indexes, and phenol removals have increased when adopting the coupling process. The maximal uptakes of phenol reached 15.4, 28.07, and 28.9 mg g-1 for a concentration of 30 mg L-1 of phenol, respectively, for raw L.C, L.C + 4% Zn2+ + AC, and L.C + 4% Zn2+ at pH = 2. Quantitative and qualitative characterizations confirmed the efficiency of the synthesized hybrid materials compared with pure L.C. The fractal model of Brouers Sotolongo was chosen for the description of the random distribution of the active sites. The kinetic and isotherm data showed a good correlation with the experimental results.

Coupling anodic oxidation, biosorption and alternating current as alternative for wastewater purification.

Anodic oxidation process is considered as an effective solution for the treatment of refractory effluents. Its performance is strongly depending on the stability of the anodes used during the process. For this reason, we aim to enhance the stability of the SS/PbO2 anodes electrodeposited by pulsed current while studying their performance for the anodic oxidation of methylene blue and industrial textile wastewater. The basic idea deals with the possibility to replace the expensive alternatives used for reinforcing the steadiness of the anodes during the anodic oxidation by a simple method based on coupling electrochemical oxidation with biosorption by vegetable material (Luffa cylindrica). The performance of the coupling process was optimized based on its performance in colored and industrial wastewater depollution. Results confirmed the efficiency of the coupling process where 98.7 and 80.02% of methylene blue were removed, respectively, after 60 and 120 min for alternating and direct current. Otherwise, 62.84 and 46.87% of methylene blue were removed by anodic oxidation, respectively, after 120 and 180 min for alternating and direct current. The % COD obtained for the anodic oxidation and the coupling process reached 57.45, 33.61, 91.32 and 75.48% respectively for alternating and direct current. The use of alternating current for both processes has enhanced the speed and the efficiency. Atomic absorption analysis has confirmed that the rates obtained of Pb2+ complied with those allowed by the Standards. LC/MS analysis allowed the identification of by-products generated and the germination tests proved the reuse of the treated water.

Use of alternating current for colored water purification by anodic oxidation with SS/PbO2 and Pb/PbO2 electrodes.

This paper suggests a new alternative for the acceleration of dye removal by adopting alternating current instead of direct current in the treatment of methylene blue solutions and industrials effluents, using anodic oxidation on Pb/PbO2 and stainless steel (SS)/PbO2 anodes. A comparative study of the influence of electrolyte support (NaCl, NaNO3, and Na2SO4) on the anodic oxidation performance and the anode stability was performed. The best results were obtained in presence of NaCl where the color removal percentage reached about 80.13% and 55.8%, for Pb/PbO2 anodes, and 89.5% and 60.4% for the SS/PbO2 anodes for alternating and direct current, respectively. Treatment in alternating current conditions enhanced the removal speed. Atomic absorption analysis confirmed the decrease of the release of (Pb2+) ions to much lower values compared with direct current and to those allowed by the Standards. LC/MS and phytotoxicity analyses confirmed the non-toxicity of the generated by-products during the anodic oxidation of methylene blue and the possibility of the reuse of the treated water.