This review is intended to evaluate the use of ferrate (Fe(VI)), being a green coagulant, sustainable and reactive oxidant, to remove micro pollutants especially pharmaceutical pollutants in contaminated water. After a brief description of advanced oxidation processes, fundamental dimensions regarding the nature, reactivity, and chemistry of this oxidant are summarized. The degradation of contaminants by Fe(VI) involves several mechanisms and reactive agents which are critically evaluated. The efficiency and chemistry of Fe(VI) oxidation differs according to the reaction conditions and activation agent, such as soluble Fe(VI) processes, which involve Fe(VI), UV light, and electro-Fe(VI) oxidation. Fe(VI) application methods (including single dose, multiple doses, chitosan coating etc), and Fe(VI) with activating agents (including sulfite, thiosulfate, and UV) are also described to degrade the micro pollutants. Besides, application of Fe(VI) to remove pharmaceuticals in wastewater are intensely studied. Electrochemical prepared Fe(VI) has more wide application than wet oxidation method. Meanwhile, we elaborated Fe(VI) performance, limitations, and proposed innovative aspects to improve its stability, such as the generation of Fe(III), synergetic effects, nanopores entrapment, and nanopores capsules. This study provides conclusive direction for synergetic oxidative technique to degrade the micro pollutants.

The reactivity characteristics of humic acid (HA) with aluminium coagulants at different pH values was investigated. It revealed that the linear complexation reaction occurred between aluminum and humic acid at pH < 7, and the reaction rate increased as the pH increased from 2 to 6. While at pH = 7, most of the dosed aluminum existed in the form of free aluminum and remained unreacted in the presence of HA until the concentration reached to trigger Al(OH)₃₍ₛ₎ formation. Differentiating the change of functional groups of HA by ¹H nuclear magnetic resonance spectroscopy and X-ray photoelectron spectra analysis, it elucidated that there was a selective complexation between HA and Al with lower Al dosage at pH 5, which was probably due to coordination of the activated functional groups onto aluminium. While almost all components were removed proportionally by sweep adsorption without selectivity at pH 7, as well as that with higher Al dosage at pH 5. This study provided a promising pathway to analyse the mechanism of the interaction between HA and metal coagulants in future.

In the present work, low-cost and efficient iron oxide nanoparticle incorporated on mesoporous biochar was prepared from effluent treatment plant (ETP) sludge collected from the textile industry. This sludge contains a higher amount of Fe due to the use of ferric chloride as a coagulant in the treatment of wastewater generated during the process. The raw sludge and prepared biochar was extensively examined by various sophisticated techniques like XRF, XRD, BET, TGA, XPS, RAMAN, FTIR, FESEM, TEM, and VSM. TEM and XRD analysis confirms the presence of iron oxide nanoparticles on mesoporous biochar. The prepared biochar was found to possess BET surface area of 91 m² g⁻¹. Several parameters like pH, dose, initial concentration, temperature and time were optimized for the adsorptive removal of ofloxacin (OFL) from aqueous solution. Biochar (named as BTSFe) achieved ≈96% removal efficiency of OFL with a maximum adsorption capacity (qₘ) of 19.74 mg g⁻¹ at optimum condition. π-π electron–donor-acceptor and H bonding were the major mechanisms responsible for the OFL adsorption. Kinetic and equilibrium thermodynamic study of showed that the adsorption of OFL was represented by the pseudo-second-order kinetics model, and the process was exothermic and spontaneous. Additionally, Redlich-Peterson and Freundlich isotherms best fitted the experimental data indicating multilayer adsorption phenomenon. Biochar was magnetically separated and thermally regenerated after each cycle for five times with a nominal overall decrease of ≈8% in removal efficiency. Leaching of iron during the adsorption process was also checked and found to be within the permissible limit. This study provides an alternative application of the textile industry sludge as an efficient, low-cost biochar for the removal of emerging pharmaceutical compounds.

With the development and application of graphene oxides (GO), the potential toxicity and environmental behavior of GO has become one of the most forefront environmental problems. Herein, a novel nanoscale layered double hydroxides (glycerinum-modified nanocrystallined Mg/Al layered double hydroxides, LDH-Gl), layered double oxides (calcined LDH-Gl, LDO-Gl) and metallic oxide (TiO2) were synthesized and applied as superior coagulants for the efficient removal of GO from aqueous solutions. Coagulation of GO as a function of coagulant contents, pH, ionic strength, GO contents, temperature and co-existing ions were studied and compared, and the results showed that the maximum coagulation capacities of GO were LDO-Gl (448.3 mg g−1) > TiO2 (365.7 mg g−1) > LDH-Gl (339.1 mg g−1) at pH 5.5, which were significantly higher than those of bentonite, Al2O3, CaCl2 or other natural materials due to their stronger reaction active and interfacial effect. The presence of SO32− and HCO3− inhibited the coagulation of GO on LDH-Gl and LDO-Gl significantly, while other cations (K+, Mg2+, Ca2+, Ni2+, Al3+) or anion (Cl−) had slightly effect on GO coagulation. The interaction mechanism of GO coagulation on LDO-Gl and TiO2 might due to the electrostatic interactions and strong surface complexation, while the main driving force of GO coagulation on LDH-Gl might be attributed to electrostatic interaction and hydrogen bond, which were further evidenced by TEM, SEM, FT-IR and XRD analysis. The results of natural environmental simulation showed that LDO-Gl, TiO2 or other kinds of natural metallic oxides could be superior coagulants for the efficient elimination of GO or other toxic nanomaterials from aqueous solutions in real environmental pollution cleanup.

With the extensive application of graphene oxide (GO), it is noticeable that part of GO is directly/indirectly released into the environment and widespread research indicated that it had adverse influences on human health and ecological balance. In this work, a novel nanobelt-like Ca/Al layered double hydroxides (CA-LDH) was synthesized and applied as efficient coagulant for the removal of GO from aqueous solutions. The results indicated that neutral pH, co-existing cations and higher temperature were beneficial to the coagulation of GO. The sequence of cation effect for promoting of GO coagulation was Ca2+ > Mg2+ > K+ > Na+, whereas the effect of anions on GO coagulation was PO43− > CO32− > SO42− > Cl−. Comparing with anions, the cations showed more dominate effect for GO coagulation than anions. Hydrogen bonds and electrostatic interaction were the main coagulation mechanisms for GO coagulation, which were evidenced by FT-IR and XPS analysis. Specifically, for the first time, the reclaimed product of CA-LDH after GO coagulation (CA-LDH + GO) was applied as adsorbents for the secondary application in the removal of heavy metal ions from aqueous solutions. Interestingly, the CA-LDH + GO still had high adsorption capacities, i.e., the maximum adsorption capacities (qmax) for Cu(II), Pb(II), and Cr(VI) were 122.7 mg/g, 221.2 mg/g and 64.4 mg/g, respectively, higher than other similar materials. This paper highlighted the LDH-based nanomaterials are promising materials for the elimination of environmental pollutants and the migration and transformation of carbon nanomaterials in the natural environment.

PURPOSE OF REVIEW: The use of conventional chemical coagulant in treatment of wastewater is gaining great attention. Drawbacks related to the prolonged effects on human health and environment due to the generation of by-product non-biodegradable sludge are becoming the latest topics. Transition from chemical to natural coagulant can be a good strategy to reduce the aforementioned drawbacks. Therefore, this review aims to provide critical discussions on the use of natural coagulant along with the comparative evaluation over the chemical coagulant. RECENT FINDINGS: Treatment performances by chemical and natural coagulant have been reviewed on various types of wastewater with different success rates. Based on this review, a transition from the use of chemical to natural coagulant is highly suggested as the performance of the natural coagulant is comparable to that of the chemical coagulant and in some cases even better. The comparative advantages and disadvantages also convinced that the natural coagulant stands a great chance to be used as an alternative over the chemical coagulant. Though the current utilization of natural coagulant is encouraging, three main aspects were overlooked by researchers: active coagulant agent, extraction, and optimization due to different wastewater characteristics. Furthermore, delving into these aspects could clarify the uncertainties on the natural coagulant. Hence, it makes this transition a prospect of green technology with sustainable application towards wastewater treatment.

The indigo blue dye is widely used in the textile industry, specifically in jeans dyeing, the effluents of which, rich in organic pollutants with recalcitrant characteristics, end up causing several environmental impacts, requiring efficient treatments. Several pieces of research have been conducted in search of effective treatment methods, among which is electrocoagulation. This treatment consists of an electrochemical process that generates its own coagulant by applying an electric current on metallic electrodes, bypassing the use of other chemical products. The purpose of this study was to evaluate the potential use of iron slag in the electrocoagulation of a synthetic effluent containing commercial indigo blue dye and the effluent from a textile factory. The quantified parameters were color, turbidity, pH, electrical conductivity, sludge generation, phenol removal, chemical oxygen demand (COD), and total organic carbon (TOC). The electrocoagulation treatment presented a good efficiency in removing the analyzed parameters, obtaining average removal in the synthetic effluent of 85% of color and 100% of phenol after 25 min of electrolysis. For the effluent from the textile factory, average reductions of 80% of color reaching 177.54 mg Pt CoL⁻¹, 91% of turbidity reaching 93.83 NTU (nephelometric turbidity unit), 100% of phenol, 55% of COD with a final concentration of 298.8 mg O₂ L⁻¹, and 73% of TOC with a final concentration of 56.21 mg L⁻¹, in 60 min of electrolysis. The reduced time for removal of color and phenolic compounds in synthetic effluent demonstrates the complexity of treating the real effluent since to obtain removals of the same order a 60-min period of electrolysis was necessary. The results obtained demonstrate the potential of using iron slag as an electrode in the electrocoagulation process in order to reuse industrial waste and reduce costs in the treatment and disposal of solid waste. Thus, the slag can be seen as an alternative material to be used in electrocoagulation processes for the treatment of effluents from the textile industry under the experimental conditions presented, its only limitation being the fact that it is a waste and therefore does not have a standardization in the amounts of iron present in the alternative electrodes.

Excavated soils from construction activities contaminated with geogenic arsenic (As) are increasing concerns owing to after disposal impact on ecosystem and human health. Washing remediation with chelators, e.g., ethylenediaminetetraacetic acid (EDTA), has been evaluated widely to treat contaminated soil. However, prolonged persistence and noxiousness of EDTA and its homologs evoke eco-concerns. Herein, the efficiency of ethylenediamine N,N'-disuccinic acid (EDDS) and 3-hydroxy-2,2'-imino disuccinic acid (HIDS) was evaluated to treat As-contaminated excavated soil as eco-compliant alternatives to EDTA. Besides, the post-treatment preferences for the chelator-washed suspension and soil residue were also assessed to immobilize eluted-As and suppress subsequent As-leaching, respectively. The efficiency of chelators toward the extraction of As was positively correlated with washing variables (e.g., washing time, solution pH, chelator concentration, liquid-to-soil ratio, and shaking speed) and optimized for maximum As-removal. Biodegradable chelator, HIDS (10 mmol L–¹, pH 11) showed better washing effectiveness among the tested chelators (duration, 12 h). The eluted-As in chelator-washed suspension was better immobilized with combined Feᴵᴵᴵ and Caᴵᴵ salt application blended with organic coagulant and polymer flocculant. Stabilization/solidification (S/S) of As-content in soil residues with cement-based binders was examined with or without the addition of Feᴵᴵᴵ. The cement amendments, except the ordinary Portland cement, Tuff-rock ace, and GS225, showed superior As-stabilization capability without Feᴵᴵᴵ-additives. The proposed combined remediation approach can be a green solution to recycle As-contaminated surplus soils for extensive geotechnical applications.

It was aimed to precisely investigate the coagulation properties of graphene oxide (GO) as a novel coagulant for turbidity removal from water. For this purpose, the process was simulated through response surface methodology (RSM) to determine the effect of the preselected independent factors (pH, GO dosage, and initial turbidity) and their interaction effects on the process. Based on the results, increased turbidity removal efficiencies were obtained as pH decreased from 10 to 3. Besides, increase of GO dosage within the test range (2.5–30 mg/L) was highly beneficial for enhancing the process performance. However, a slight overdosing of GO was observed for dosages of more than 20 mg/L under pH values of less than about 4. For initial turbidity with test range of 25–300 NTU, there was an optimum range (approximately 120–200 NTU) out of which the removal efficiency declined. According to the results of the analysis of variance (ANOVA), pH and GO dosage, orderly, had the strongest individual effect on the process performance. The most significant interaction effect was also observed between pH and GO dosage. The optimal coagulation conditions with GO dosage of 4.0 mg/L, pH of 3.0, and initial turbidity of 193.34 NTU led to a turbidity removal efficiency of about 98.3%, which was in good agreement with RSM results. Under basic pH levels, the sweeping effect was recognized as the main coagulation mechanism occurred between the negatively surface charged particles of GO and soil. However, according to zeta potential (ZP) analysis results, under acidic pH conditions in addition to the sweep coagulation, the electric double layer compression, and the subsequent ZP reduction also contributed significantly to the process. Scanning electron microscopy (SEM) images showed that the layered structure of GO particles provided an appropriate platform on which the flocs were formed.

The world needs to adapt to recycling and reusing water due to limited resources. So, decision-makers and policy leaders should use sustainable practices to improve protection and pollution remediation. Aluminum sulfate is used for surface water treatment, which leads to waste sludge being disposed into water bodies, causing environmental pollution. Coagulants’ regeneration from sludge improves water quality and reuse options. Organics accumulation is the primary concern regarding coagulant regeneration, using acidification. Our study investigated the raw water quality, aluminum sulfate, and sludge and evaluated its influence on coagulant recovery, using acidification, from eight water treatment plants (WTPs) in Cairo, Egypt. The significant elements in the tested sludge were aluminum with a concentration range of 86.65–688.85 mg/g sludge in El-Rawda and Embaba and iron with a concentration range of 9.45–7.45 mg/g in Shamal Helwan and El-Fostat. Recovery percentages of aluminum, iron, manganese, and strontium recorded the highest values 97%, 89%, 89%, and 92% for Embaba, Rod El-Farag, Embaba, El-Rawda, respectively. The correlation between metal concentration and recovery was insignificant in the studied matrix and conditions for the four metals. Total organic carbon (TOC) transfer into recovered solutions was maximum in El-Fostat (82.6%) and minimum in Embaba (36.7%). The TOC transfer percentage depends on the matrix of the sludge. The best location for coagulant recovery is at the Embaba WTP, where there were minimum organics transfer and maximum Al recovery.