A rapid removal of Phaeocystis globosa from seawater by peroxymonosulfate enhanced cellulose nanocrystals coagulation

Cellulose nanocrystals (CNC) are recognized as promising bio-based flocculants for controlling harmful algal blooms (HABs). Due to the charge shielding effect in seawater and the strong mobility of algae cells, CNC can't effectively remove Phaeocystis globosa from seawater. To solve this problem, peroxymonosulfate (PMS) was used to enhance the coagulation of CNC for rapidly removal of P. globosa. The results showed that 91.7% of Chl-a, 95.2% of OD680, and 97.2% of turbidity of P. globosa were reduced within 3 h with the use of 200 mg L-1 of CNC and 20 mg L-1 of PMS. The removal of P. globosa was consisted of inactivation and flocculation. Notably, electron paramagnetic resonance (EPR) spectrums and quenching experiments revealed that the inactivation of P. globosa was dominated by PMS oxidation and 1O2. Subsequently, CNC entrained inactivated algal cells to settle to the bottom to achieve efficient removal of P. globosa. The content of total organic carbon (TOC) and chemical oxygen demand (COD) decreased significantly, indicating that a low emission risk of algal cell effluent was produced in the CNC-PMS system. In view of the excellent performance on P. globosa removal, we believe that the CNC-PMS system has great potential for HABs treatments.

Abatement of NO/SO2/Hg0 from flue gas by advanced oxidation processes (AOPs): Tech-category, status quo and prospects

This review article provides a state-of-art insight into the removal of NO, SO₂ and elemental mercury (Hg⁰) from flue gas by using advanced oxidation processes (AOPs) method. Firstly, the main flue gas purification strategies based on AOPs would be classified as gas-gas, gas-liquid and gas-solid systems preliminarily, and the primary chemistry/mechanism of the above homogeneous/heterogeneous reaction systems were presented as the oxidation of NO, SO₂ and Hg⁰ by the oxidative free radicals (OH, O₂ and SO₄^-etc.). Secondly, the research progress and reaction pathways for separately or simultaneously removing NO, SO₂ and Hg⁰ from flue gas by AOPs has been reviewed elaborated and analyzed in more details. Notably, the wet/dry oxidation coupled with efficient absorption process would be a promising method of efficient removal of above gaseous pollutants. Subsequently, four types of assumed layout modes were described graphically. The application prospects of AOPs for the purification of flue gas from coal-fired boiler or industrial furnace were evaluated and found that the operation cost and utilization of oxidants must be reduced and improved respectively. Finally, the limitations in the current removal technologies based on AOPs are highlighted, meanwhile the future research directions are suggested, such as cut down the cost of oxidants and catalysts, improve the yield and valid utilization of highly reactive radicals and enhance the reactivity, resistance and stability of catalysts. Significantly, it is also envisaged that the review could enrich the knowledge repository to function as a scientific reference for the sustainable development of economical, effective and environment-friendly technologies for the abatement of a wide variety of emissions from flue gas, and further improve the feasibility and reliability of the strategies for moving from laboratory studies to large-scale development and industrial application.

A Critical Review on Removal of Gaseous Pollutants Using Sulfate Radical-based Advanced Oxidation Technologies

Excessive emissions of gaseous pollutants such as SO₂, NO_x, heavy metals (Hg, As, etc.), H₂S, VOCs, etc. have triggered a series of environmental pollution incidents. Sulfate radical (SO₄•^-)-based advanced oxidation technologies (AOTs) are one of the most promising gaseous pollutants removal technologies because they can not only produce active free radicals with strong oxidation ability to simultaneously degrade most of gaseous pollutants, but also their reaction processes are environmentally friendly. However, so far, the special review focusing on gaseous pollutants removal using SO₄•^--based AOTs is not reported. This review reports the latest advances in removal of gaseous pollutants (e.g., SO₂, NO_x, Hg, As, H₂S, and VOCs) using SO₄•^--based AOTs. The performance, mechanism, active species identification and advantages/disadvantages of these removal technologies using SO₄•^--based AOTs are reviewed. The existing challenges and further research suggestions are also commented. Results show that SO₄•^--based AOTs possess good development potential in gaseous pollutant control field due to simple reagent transportation and storage, low product post-treatment requirements and strong degradation ability of refractory pollutants. Each SO₄•^--based AOT possesses its own advantages and disadvantages in terms of removal performance, cost, reliability, and product post-treatment. Low free radical yield, poor removal capacity, unclear removal mechanism/contribution of active species, unreliable technology and high cost are still the main problems in this field. The combined use of multiactivation technologies is one of the promising strategies to overcome these defects since it may make up for the shortcomings of independent technology. In order to improve free radical yield and pollutant removal capacity, enhancement of mass transfer and optimization design of reactor are critical issues. Comprehensive consideration of catalytic materials, removal chemistry, mass transfer and reactor is the promising route to solve these problems. In order to clarify removal mechanism, it is essential to select suitable free radical sacrificial agents, probes and spin trapping agents, which possess high selectivity for target specie, high solubility in water, and little effect on activity of catalyst itself and mass transfer/diffusion parameters. In order to further reduce investment and operating costs, it is necessary to carry out the related studies on simultaneous removal of more gaseous pollutants.

Anaerobically-digested sludge disintegration by transition metal ions-activated peroxymonosulfate (PMS): Comparison between Co2+, Cu2+, Fe2+ and Mn2

This study investigates anaerobically-digested sludge (ADS) disintegration by activated peroxymonosulfate (PMS) with transition metal ions of Co²⁺, Cu²⁺, Fe²⁺, and Mn²⁺ (PMS-Me²⁺). The activating performances of Me²⁺ are quantitatively compared by capillary suction time (CST), extracellular polymeric substances (EPS), bound water content (BWC), particle size distribution, and metal speciation. At Me²⁺ dose of 1.2 mmol/g VSS, PMS-Fe²⁺ and PMS-Cu²⁺ achieve the lowest normalized CST, i.e., CST/CST₀, of 0.47, and the higher normalized CST values of 0.71 and 0.74 are observed for PMS-Mn²⁺ and PMS-Co²⁺, respectively. BWC shows little extent of decrease upon PMS-Me²⁺ oxidation, and the most significant decrease from 89.5% to 88.3% is observed for PMS-Mn²⁺. PMS-Co²⁺ contributes to the decrease of DOC in total EPS fractions (DOC_tot) from 698.0 mg/L to 496.6 mg/L, whereas the increased DOC_tot to 713.6, 734.4, and 755.0 mg/L is observed with the introduction of Cu²⁺, Fe²⁺, and Mn²⁺, respectively. Fe²⁺ tends to transform to Fe³⁺ and the coagulation effect increases the median particle diameter (D₅₀) from 15.8 μm to 91.1 μm. Comparatively, much lower D₅₀ values of below 20.0 μm are observed for other divalent ions. The European Community Bureau of Reference (BCR) sequential extraction method is used to analyze the metal speciation in ADS sediment after PMS-Me²⁺ disintegration. The dominant species of Co and Mn are acid extractable fractions with the ratios of 91.0% and 87.3%, whereas the main Fe and Cu species are observed to be residual and oxidizable fractions. The pre-captured Me²⁺ ions with 50-days aging interestingly exhibit activating efficacy towards PMS, and CST values were observed to decrease by 11.5%, 30.5%, 11.8%, and 27.3% with the presence of pre-captured Co²⁺, Cu²⁺, Fe²⁺, and Mn²⁺ at 1.2 mmol/g VSS. This study proposes the potentially valuable strategy for the disintegration and dewatering of sludge with high contents of transition metal ions.

Preparation of magnetic Co-Fe modified porous carbon from agricultural wastes by microwave and steam activation for mercury removal

In this article, a magnetic cobalt-iron modified porous carbon derived from agricultural wastes by microwave and steam activation was developed to remove elemental mercury in coal-fired flue gas. The effects of operating parameters on Hg⁰ capture were discussed. Reaction mechanism and regeneration performance were also studied. Results show that the activation of microwave and steam significantly improves the pore structure of the porous carbon. The ultrasound-assisted impregnation promotes the dispersion of cobalt oxides and iron oxides on the samples. The Co_0.4Fe₁₂/RSWU(500) sorbent exhibits highest Hg⁰ removal efficiency at 130 °C. The characterization analysis shows that cobalt oxides and iron oxides are the main active components for Hg⁰ removal. The XPS analysis suggests that the chemisorption oxygen and the lattice oxygen (derived from Co³⁺/Co²⁺ and Fe³⁺/Fe²⁺) participate in the Hg⁰ capture process. Moreover, the cobalt-iron mixed oxide modified porous carbon has a good regeneration performance, which is conductive to reduce the costs in the future application.

Preparation of microwave-activated magnetic bio-char adsorbent and study on removal of elemental mercury from flue gas

In this study, novel activated magnetic bio-char adsorbents were proposed to remove the element mercury (Hg⁰) from flue gas. Microwave activation and Mn-Fe mixed oxides impregnation assisted by ultrasound treatment were applied on the modification of renewable cotton straw chars. The influence of different preparation methods, loading value of Mn-Fe, molar ratio of Mn/Fe, calcining temperature, reaction temperature and individual flue gas ingredients (O₂, NO, SO₂ and H₂O) on removal of Hg⁰ was investigated in a fixed bed system. The characterization results reveal that microwave activation is advantageous for the development of the pore structure, and ultrasound treatment can optimize the dispersion of Mn and Fe active ingredients. MnFe4%(3/10)/CSWU700 adsorbent exhibits the optimal Hg⁰ removing performance. O₂, NO, low concentration of SO₂ (<600 ppm) and low concentration of H₂O (<2%) are found to be favourable for the capture of Hg⁰, while high concentrations of SO₂ and H₂O inhibit the removal of Hg⁰. Chemical adsorption acts a pivotal part in the process of Hg⁰ removal. Mn and Fe active ingredients are consumed in large quantities during the Hg⁰ capture. In addition, chemisorbed oxygen (O_β) also plays an indispensable in the oxidation process of Hg⁰. Furthermore, the magnetic adsorbent MnFe4%(3/10)/CSWU700 presents a good regeneration performance and adsorption capacity.

Removal of Carbon Monoxide from Simulated Flue Gas Using Two New Fenton Systems: Mechanism and Kinetics

Two novel removal processes of carbon monoxide using two new Fenton systems (i.e., Cu²⁺/Fe²⁺ and Mn²⁺/Fe²⁺ coactivated H₂O₂ systems) were developed. The effect of several process parameters (concentrations of H₂O₂, Fe²⁺, Cu²⁺, and Mn²⁺, reagent pH value, solution temperature, and simulated flue gas components) on CO removal was studied in a bubbling reactor. The mechanism and kinetics of CO removal were also revealed. Results show that adding Cu²⁺ or Mn²⁺ obviously enhances the removal process of CO in new Fenton systems. The measured results of free radical yield demonstrate that the enhancing role is derived from producing more ·OH (they are produced due to the synergistic activation role of Cu²⁺/Fe²⁺ or Mn²⁺/Fe²⁺ in new Fenton systems. The removal efficiency of CO is raised by increasing concentrations of Fe²⁺, Cu²⁺, and Mn²⁺ and is reduced by raising concentrations of CO, NO, and SO₂. Increasing H₂O₂ concentration, reagent pH, and solution temperature demonstrates a dual impact on CO absorption. Three oxidation pathways are found to be responsible for CO removal in new Fenton systems. Results of mass-transfer reaction kinetics reveal that CO removal processes are located in a fast-speed reaction kinetics region (the CO removal process is controlled by the mass transfer rate).