Removal of refractory organics in wastewater by coagulation/flocculation with green chlorine-free coagulants

Enhanced removal of nano-oil droplets utilizing polysilicate aluminum ferric (PSAF): Leveraging bridging and non-polar surface advantages

Hydraulic oil leaks during mechanical maintenance, resulting in flushing wastewater contaminated with dispersed nano-oil droplets. In this study, 75 mg L-1 of polysilicate aluminum ferric (PSAF) was stirred at 350 rpm and the optimal chemical oxygen demand (COD) removal was 71%. The increase of PSAF led to more hydrolysis of Fe, and 1,175 cm-1 hydroxyl bridged with negative oil droplets. At the same molar concentration, PSAF hydrolyzes cationic metals more rapidly than polymeric aluminum chloride (PAC). PSAF forms flocs of smaller complex structures with greater bridging. The Al-O and Si-O peaks occurred at 611 and 1,138 cm-1, indicating the formation of Si-O-Fe and Si-O-Al bonds on the flocs surface. Higher stirring speeds did not change the free energy of the flocs surface γTot, mainly because the decrease in the van der Waals force (γLW) offset the increase of Lewis acid-base force (γAB). Preserving the non-polar surface, in summary, owing to its bridging abilities and affinity for non-polar surfaces, PSAF demonstrates superior efficiency over PAC in capturing and removing oil droplets.

Preparation and Application of Polyaluminum Ferric Sulfate from Red Mud: Behaviors of Leaching, Polymerizing, and Coagulation

Red mud is a solid waste containing valuable components, such as aluminum and iron. This paper aims to recover aluminum and iron from red mud by acid leaching and prepare polyaluminum ferric sulfate (PAFS) to apply for the turbidity reduction treatment of coal slurry water. The behaviors of leaching, polymerizing, and coagulation were analyzed by leaching thermodynamics and advanced micro-detection methods. More than 90% of aluminum and 60% of iron in red mud were dissolved into the leaching solution by using 50% sulfuric acid (v/v) with 7 mL/g at 100 °C for 2 h, where the crystal lattice of cancrinite was significantly destroyed to promote the dissolution of aluminum. The low polymerization (Al + Fe)a, medium polymerization (Al + Fe)b, and high polymerization (Al + Fe)c could be generated in PAFS by adjusting the basicity of the leaching solution with 0.7-0.9. The removal efficiency of turbidity of wastewater could reach more than 95% by using PAFS at 25 mg/L in the pH range of 6.0-7.0. The turbidity reduction mechanism included not only the electric neutralization of (Al + Fe)a but also the adsorption of (Al + Fe)b and the entrapment effect of (Al + Fe)c. This current study contributes to the future development of red mud based on flocculants containing aluminum and iron for wastewater treatment.

A Comprehensive Review on the Excitation-Emission Matrix Fluorescence Spectroscopic Characterization of Petroleum-Containing Substances: Principles, Methods, and Applications

Petroleum-containing substance (PCS) is a general term used for petroleum and its derivatives. A comprehensive characterization of PCSs is crucial for resource exploitation, economic development and environmental protection. Fluorescence spectroscopy, especially excitation-emission matrix fluorescence (EEMF) spectroscopy, has been proved to be a powerful tool to characterize PCSs since its remarkable sensitivity, selectivity, simplicity and high efficiency. However, there is a lack of systematic review focusing on this field in the literature. This paper reviews the fundamental principles and measurements of EEMF for characterizing PCSs, and makes a systematic introduction to various information mining methods including basic peak information extraction, spectral parameterization and some commonly used chemometric methods. In addition, recent advances in applying EEMF to characterize PCSs during the whole life-cycle process of petroleum are also revisited. Furthermore, the current limitations of EEMF in the measurement and characterization of PCSs are discussed and corresponding solutions are provided. For promoting the future development of this field, the urgent need to build a relatively complete EEMF fingerprint library to trace PCSs, not only pollutants but also crude oil and petroleum products, is proposed. Finally, the extensions of EEMF to high-dimensional chemometrics and deep learning are prospected, with the expectation of solving more complex systems and problems.

Synthesis and characterization of a novel N-rich porous organic polymer and its application as an efficient porous adsorbent for the removal of Pb(II) and Cd(II) ions from aqueous solutions

In this study, a novel N-rich triazine-based porous organic polymer (NR-POP) was synthesized via Schiff-base condensation. The structure of the synthesized porous polymer was identified using FT-IR, XRD, SEM, EDS, TEM, TGA, and BET analyses. The adsorption efficiency of this polymer was investigated for the removal of lead and cadmium ions pollutants. The adsorption processes of Pb(II) and Cd(II) metal ions by this polymer adsorbent were exothermic and matched by the Langmuir isotherm with a high correlation coefficient (R² = 0.9904, 0.9778), the maximum adsorption capacity (833.33, 178.57 mg g^-1), and the pseudo-second-order kinetic model. Furthermore, NR-POP showed an excellent adsorption selectivity for Pb(II) compared to Cd(II).

Potential plant leaves as sustainable green coagulant for turbidity removal

Chemical coagulation-flocculation has been used widely in water and wastewater treatment. In the present study, green coagulant was investigated. The role of Iraqi plants was examined to remove turbidity by using kaolin synthetic water. Thirteen selected plants were prepared as powdered coagulant. The experiment was run based on coagulant mass varied from 0 to 10,000 mg/L for each plant with a rapid mixing speed of 180 rpm for 5 min, slow mixing speed at 50 rpm for 15 min and settling time for 30 min. The seven best green coagulants are Albizia lebbeck (L.), Clerodendrum inerme (10,000 mg/L), Azadirachta indica, Conocarpus lancifolius, Phoenix dactylifera (5000 mg/L), Dianthus caryophyllus (3000 mg/L) and Nerium oleander (1000 mg/L) with turbidity removal rates of 39.3%, 51.9%, 67.2%, 75.5%, 51.0%, 52.6% and 57.2%, respectively. The selected seven plants that were used as green coagulants are economically feasible to achieve the highest turbidity and removal of other compounds.

Response Surface Optimization on Ferrate-Assisted Coagulation Pretreatment of SDBS-Containing Strengthened Organic Wastewater

Sodium dodecylbenzene sulfonate (SDBS), an anionic surfactant, has both hydrophilic and lipophilic properties and is widely used in daily production and life. The SDBS-containing organic wastewater is considered difficult to be degraded, which is harmful to the water environment and human health. In this study, ferrate-assisted coagulation was applied to treat SDBS wastewater. Firstly, a single-factor experiment was conducted to investigate the effect of the Na2FeO4 dosage, polyaluminum chloride (PAC) dosage, pH and temperature on the treatment efficiency of SDBS wastewater; then, a response surface optimization experiment was further applied to obtain the optimized conditions for the SDBS treatment. According to the experimental results, the optimal treatment conditions were shown as follows: the Na2FeO4 dosage was 57 mg/L, the PAC dosage was 5 g/L and pH was 8, under which the chemical oxygen demand (COD) removal rate was 90%. Adsorption bridging and entrapment in the floc structure were the main mechanisms of pollution removal. The ferrate-assisted coagulation treatment of strengthened SDBS wastewater was verified by a response surface experiment to provide fundamental understandings for the treatment of the surfactant.

Magnetic Field Effect on Coagulation Treatment of Wastewater Using Magnetite Rice Starch and Aluminium Sulfate

The use of synthetic coagulants to reduce suspended particles from drinkable water and wastewater is prompting new issues because it poses many health and environmental risks. Hence, improving the coagulation process using sophisticated nanotechnology with a magnetic field (MF) for quick recoverability emerges as being useful. In this study, the effects of magnetite rice starch (MS) and aluminum sulfate (alum) were investigated at a constant dose (3 g or 3000 mg/L) using a Jar test (six beakers) as potential low-cost coagulants for industrial wastewater treatment. At a high magnification of 1000× and a surface pore size of 298 µm, scanning electron microscopy and energy dispersive X-ray (SEM/EDX) analyses were utilized to elucidate the morphology of the coagulants. Coagulation was performed at 150 rpm (quick mixing) for 2 min, and 30 rpm (slow mixing) for 15 min. Thereafter, samples were allowed to settle (10-60 min) with and without MF. The findings showed more than 65% contaminants removal (turbidity and TSS) and 30% chemical oxygen demand (COD) removal using alum while MS showed 80% contaminants removal (turbidity and TSS) and 50% COD removal. MS showed an increase of more than 3% in contaminants removal (COD, turbidity, and TSS) when exposed to MF. As a result, the use of MS together with MF in water and wastewater treatment is anticipated as an environmentally benign and effective coagulant.

Assessing the effect of multiple variables on the production of bioflocculant by Serratia marcescens: Flocculating activity, kinetics, toxicity, and flocculation mechanism

Bioflocculants gain attention as alternatives to chemical flocculants because they are more environmentally friendly and highly biodegradable. This study aims to improve the bioflocculant production by Serratia marcescens using one-variable-at-a-time (OVAT) analysis and analyze its flocculating activity performance, toxicity, and the flocculation mechanism. The effect of multiple variables including initial inoculum size, pH, mixing speed, temperature, growth medium, and incubation period was assessed through OVAT. Flocculating activity was then determined via jar test analysis, and toxicity test was performed using Daphnia magna and Daphnia pulex. The flocculation mechanism was determined via particle size distribution and zeta potential analysis. The optimum conditions for the improved bioflocculant production were as follows: 10% v/v initial inoculum size, pH 7, mixing speed of 150 rpm, room temperature, nutrient broth medium, and 72 h of incubation period. Scanning electron microscopy showed flake-like intact structure with coarse surface. The produced bioflocculant showed flocculating activity of 48% in 5227 ± 580 NTU initial kaolin turbidity with 1 mg/L concentration and 5% v/v dosage of bioflocculant, following the second-order kinetics. Toxicity test to D. magna and D. pulex showed the 48 h LC₅₀ values of 8.06 and 6.42 g/L, respectively; these values are greatly higher than the fabricated chemical flocculants. The flocculation process using bioflocculant produced by S. marcescens was suggested to occur via bridging mechanism because it greatly affected the particle size distribution. Results indicated that bioflocculant produced by S. marcescens is much environmentally friendly and has great potential for turbidity removal in water/wastewater.

Characterization and flocculation performance of a newly green flocculant derived from natural bagasse cellulose

A newly green natural polymer bagasse cellulose based flocculant (PBCF) was synthesized utilizing a grafting copolymerization method for effectively enhancing humic acid (HA) removal from natural water. This work aims to investigate flocculation behavior of PBCF in synthetic water containing HA, and the effects of flocculant dose and initial solution pH on flocculation performance. Results showed that PBCF functioned well at a flocculant dose of 60 mg/L and pH ranging from 6.0 to 9.0. The organic removal efficiency in synthetic water in terms of HA (UV₂₅₄) and chemical oxygen demand (COD _Mn) were up to 90.6% and 91.3%, respectively. Furthermore, the charge neutralization and adsorption bridging played important roles in HA removal. When applied for lake water, PBCF removed 91.6% turbidity and 50.0% dissolved organic matter, respectively. In short, PBCF demonstrates great potential in water treatment in a safe and environmentally friendly or 'green' way.

Preparation, characterization, and applications of Fe-based catalysts in advanced oxidation processes for organics removal: A review

Fe-based catalysts as low-cost, high-efficiency, and non-toxic materials display superior catalytic performances in activating hydrogen peroxide, persulfate (PS), peracetic acid (PAA), percarbonate (PC), and ozone to degrade organic contaminants in aqueous solutions. They mainly include ferrous salts, zero-valent iron, iron-metal composites, iron sulfides, iron oxyhydroxides, iron oxides, and supported iron-based catalysts, which have been widely applied in advanced oxidation processes (AOPs). However, there is lack of a comprehensive review systematically reporting their synthesis, characterization, and applications. It is imperative to evaluate the catalytic performances of various Fe-based catalysts in diverse AOPs systems and reveal the activation mechanisms of different oxidants by Fe-based catalysts. This work detailedly summarizes the synthesis methods and characterization technologies of Fe-based catalysts. This paper critically evaluates the catalytic performances of Fe-based catalysts in diverse AOPs systems. The effects of solution pH, reaction temperature, coexisting ions, oxidant concentration, catalyst dosage, and external energy on the degradation of organic contaminants in the Fe-based catalyst/oxidant systems and the stability of Fe-based catalysts are also discussed. The activation mechanisms of various oxidants and the degradation pathways of organic contaminants in the Fe-based catalyst/oxidant systems are revealed by a series of novel detection methods and characterization technologies. Future research prospects on the potential preparation means of Fe-based catalysts, practical applications, assistive technologies, and impact in AOPs are proposed.

Monitoring particulate composition changes during the flocculation process using polarized light scattering

Monitoring the particulate composition changes during the flocculation process is still challenging for the research community. We use an experimental setup based on polarized light scattering to measure the polarization states of the scattered light of the individual particles. We build a classifier based on the support vector machine and feed it with the measured parameters. Results show that the classifier can effectively classify the particulate compositions, such as the sediment particles, flocculants, and flocs, which can be used to monitor the particulate composition changes during the flocculation process. Discussions on the intensity and polarization parameters find that the polarization parameters play a vital role in the classification of the particulate compositions in the flocculation suspensions. Additionally, the further analysis of the experimental data and the related simulations show that the degree of polarization can be an indicator of the flocculation process. We prove that the method based on polarized light scattering may be a potential in situ monitoring tool in the future for the study of the flocculation process.