Elimination of hazardous Se(IV) through adsorption-coupled reduction by iron nanoparticles embedded on mesopores of chitin obtained from waste shrimp shells.

Selenium is an essential nutrient for biological function. However, there is a detrimental effect on the aquatic environment associated with higher concentrations of > 40 µg/L. The utilization of waste shrimp shells for the removal of high-concentrated selenium from wastewater is a commendable strategy in both the pollution control and waste management sectors. In the present study, a chitin-iron polymer complex hybrid material (Fe@SHC) was prepared from shrimp shell-derived hydrochar (SHC), and the synthesized composite was successfully employed to uptake selenium from wastewater. The highest removal performance of 79.18 mg/g was attained by Fe@SHC, whereas the capacity of SHC was 15.30 mg/g. It was found that the calcium content of Fe@SHC (1.98%) was lower than that of SHC (25.20%) and pHzpc of Fe@SHC was extended to 7.78 compared with that of SHC (2.00). The abundance of protonated hydroxyl (-OH2+) and amine (-NH3+) functional groups that developed through the iron co-precipitations resulted in the improved adsorption performance of Fe@SHC. XPS analysis demonstrated that the captured Se(IV) species were converted into less hazardous Se(0), which is accompanied by the electron transfer with both N-C = O (acetyl amine) and -NH2 (amine) functional groups. Adsorption kinetics disclosed that the adsorption process was governed by chemical sorption, and the Sips isotherm model provided the most accurate description of the isotherm equilibrium. This study proposed an inexpensive and environmentally friendly method for effective decontamination of Se from wastewater.

Nitrogen-rich carbon composite fabricated from waste shrimp shells for highly efficient oxo-vanadate adsorption-coupled reduction.

Protein, calcium carbonate, and chitin are abundant in shrimp shells. In this study, chemical treatment followed by hydrothermal carbonization was used to synthesize the nitrogen-rich hydrochar (HSHC) from shrimp shells. The untreated hydrochar exhibited a higher amount of calcium (25.37%) and less amount of nitrogen (2.68%) with alkaline pH (9.1). Interestingly chemical pre-treatment on shrimp shells boosted the nitrogen content to 6.81% and eliminated the calcium while controlling the pH to 6.4, which was beneficial for oxo-vanadate removal. The HSHC achieved vanadium(V) adsorption capacity of 21.20 mg/g at an optimal solution pH of 3.0, whereas the pristine hydrochar performed poorly (0.66 mg/g). The abundance of oxygen and nitrogen-based functional groups that developed through the chemical treatment resulted in improved adsorption coupled reduction performance of HSHC. This study proposed an inexpensive and environmentally friendly method for converting waste shrimp shells into value-added adsorbent.

Lanthanum hydroxide engineered sewage sludge biochar for efficient phosphate elimination: Mechanism interpretation using physical modelling.

In the present study, lanthanum hydroxide (La OH)-engineered sewage sludge biochar (La-SSBC) was utilized for efficient phosphate elimination from an aqueous medium. A high adsorption capacity of 312.55 mg P/g was achieved using La-SSBC at 20 °C, which was an excellent adsorbent performance in comparison to other biochar-based adsorbents. Additionally, the performance of La-SSBC was stable even at wider range of pH level, the existence of abundant active anions, and recycling experiments. Statistical physics modeling with the fitting method based on the Levenberg-Marquardt iterating algorithm, as well as various chemical characterizations, suggested the unique double-layered mechanism of phosphate capturing: one functional group of La-SSBC adsorbent describing a prone direction of the PO4 ions on the stabilize surface in a multi-ionic process, forming the first layer adsorption. Additionally, SSBC played an important role by releasing positively charged cations in solution, overcoming the electronic repulsion to form a second layer, and achieving excellent adsorption capacity. The calculation of multiple physicochemical parameters including adsorption energy further evidenced the process. This two-layered mechanism sheds light on the complex interaction between phosphate and biochar. Moreover, the management of sewage sludge associated with the requirement of cost-effectively and environmentally acceptable mode. Therefore, the present investigation demonstrated an efficient approach of the simultaneous sewage sludge utilization and phosphate removal.

Phosphate-lanthanum coated sewage sludge biochar improved the soil properties and growth of ryegrass in an alkaline soil.

The reclamation of alkaline soils remains challenging while the application of biochar has been proposed as a viable measure to rehabilitate soil fertility. The objective of the current pot study was to evaluate the efficacy of various P-La modified sewage sludge biochars (SSBC, La-SSBC, SSBC-P, La-SSBC-P) on soil phosphate-retention and ryegrass (Lolium perenne L.) growth in an alkaline soil (excess CaCO3). The results revealed that germination percentage, plant dry biomass, plant height, and the total amount of P in the ryegrass leaves were significantly (P < 0.05) improved under La-SSBC-P treatment as compared to other treatments. La-SSBC-P treatment significantly altered the chemical characteristics of post-harvest alkaline soil, such as pH, electrical conductivity (EC), cation exchange capacity (CEC), soil organic matter (SOM), limestone (CaCO3), phosphate, and lanthanum contents. In comparison to the SSBC treatment, soil available phosphorous (AP) contents under La-SSBC-P were enhanced by 6.7 times after loading biochar with P and La (La-SSBC-P). After the plantation of ryegrass, concentration of lanthanum in the soil was negligible. The contents of CaCO3 reduced by 76.2% after La-SSBC-P biochar treatment, compared to the cultivated control. This phenomenon clearly indicated that lanthanum was reduced due to the precipitation with limestone, which was proposed based on the data of X-ray diffraction (XRD) analysis. Overall, results showed that the P-loaded lanthanum decorated biochar (La-SSBC-P) could be used as a potential substitute for P-fertilizer under the experimental conditions. However, field experiments are required to confer the efficiency of La-SSBC-P as P fertilizer in different soils.

Regulating the redox centers of Fe through the enrichment of Mo moiety for persulfate activation: A new strategy to achieve maximum persulfate utilization efficiency.

Persulfate Fe-based catalytic oxidation is considered as one of the most attractive strategy for the growing concerns of water pollution. However, the undesirable FeIII/FeII redox cycle restrict them from attending the sustainable activity during practical applications. This study was intended to develop a new strategy to regulate the redox cycles of FeIII/FeII by introducing the second redox center of MoS42- in the interlayers of Fe-based layered double hydroxide (FeMgAl-MoS4 LDH). Based on the first-order kinetic model, the fabricated FeMgAl-MoS4 catalyst was 10-100 fold more reactive than the bench marked peroxymonosulfate (PMS) activators including FeMgAl LDHs and other widely reported nano-catalysts such as Co3O4, Fe3O4, α-MnO2, CuO-Fe3O4 and Fe3O4. The enhanced catalytic activity of FeMgAl-MoS4 LDH was related to the continuous regeneration of active sites (FeII/MoIV), excellent PMS utilization efficiency and generation of abundant free radicals. Moreover, the FeMgAl-MoS4/PMS system shows an effective pH range from 3.0 to 7.0 and the degradation kinetics of parahydroxy benzoic acid (PHB) were not effected in the presence of huge amount of background electrolytes and natural organic matters. Based on the in-situ electron paramagnetic resonance spectroscopy (EPR), chemical scavengers, XPS analysis and gas chromatography couple with mass spectrometer (GC-MS), a degradation pathway based on dominant free radicals (•SO4- and •OH), passing through the redox cycles of FeIII/FeII and MoVI/MoIV was proposed for PMS activation. We believe that this strategy of regulating the redox center through MoS42- not only provides a base to prepare new materials with stable catalytic activity but also broaden the scope of Fe-based material for real application of contaminated water.