Qingzhu Li

Formation of abiological granular sludge – A facile and bioinspired proposal for improving sludge settling performance during heavy metal wastewater treatment

Heavy metal contamination in wastewater poses a severe threat to the environment and public health. Chemical precipitation is the most conventional process for heavy metal wastewater treatment. However, the flocculent structure of chemical precipitation sludge raises the problem of poor sludge settling performance that is difficult to overcome. Inspired by the biological granular sludge (BGS) formation process, we report here a facile and effective strategy to produce abiological granular sludge (ABGS) to solve this problem. In this procedure, controlled double-jet precipitation was performed to simulate the cell multiplication process in BGS formation by controlling the solution supersaturation. Meanwhile, ZnO seeds and flocculant polyacrylamide were added to simulate the role of nuclei growth and extracellular polymeric substances in BGS formation process, respectively. This procedure generates ABGS with a dense structure, large size and regular spherical morphology. The settling velocity of ABGS can reach up to 3.0cms(-1), significantly higher than that of flocculent sludge (<1cms(-1)).

Fast esterification of spent grain for enhanced heavy metal ions adsorption.

This work describes a novel method for fast esterification of spent grain to enhance its cationic adsorption capacity. The esterification of spent grain with citric acid was achieved by using sodium hypophosphite monohydrate (NaH(2)PO(2).H(2)O) as a catalyst in N,N-dimethylformamide (DMF). Fourier transform infrared (FTIR) spectroscopic analysis revealed the formation of ester groups after esterification, demonstrating that spent grain was successfully esterified with citric acid. The adsorption capacity of esterified spent grain (ESG) for each metal ion was greatly improved as compared with that of raw spent grain (RSG). Typically, Pb(2+) adsorption capacity increased from 125.84mg g(-1) of RSG to 293.30mg g(-1) of ESG. This increase can be attributed to both the formation of ester linkage and the grafting of carboxyl groups on spent grain. The results suggest that a fast process for esterification of spent grain has been realized and ESG has strong ability to adsorb heavy metal ions.

Synthesis of thiol-functionalized spent grain as a novel adsorbent for divalent metal ions

Spent grain (SG) was functionalized with thioglycolic acid in N,N-dimethylformamide (DMF) medium using sodium bisulfate monohydrate (NaHSO(4).H(2)O) as a catalyst, followed by treatment with sodium sulfide nonahydrate (Na(2)S.9H(2)O). Characterization of thiol-functionalized spent grain (TFSG) was performed using X-ray photoelectron spectroscopy (XPS) and Fourier transform infrared (FTIR) spectroscopy. These analytical results revealed the emergence of S-H and C=O groups after the chemical modification, indicating that thiol groups were successfully grafted onto TFSG. As compared with SG, TFSG showed significant improvement in terms of metal loading capacity. Typically, adsorption capacity for Zn(2+) was increased from 125.76 mg g(-1) of SG to 227.37 mg g(-1) of TFSG, which was confirmed by X-ray fluorescence (XRF) analysis. This increase may be attributed to both the formation of ester linkage and the grafting of thiol groups onto TFSG. The experimental results indicate that TFSG is a promising adsorbent for removal heavy metals from contaminated water.

Understanding the formation of colloidal mercury in acidic wastewater with high concentration of chloride ions by electrocapillary curves

Acidic wastewater with high concentration of chloride ions was generated from washing elemental mercury (Hg0) existed in the roast flue gas by water. This process was simulated by mercury drops entering the electrolytes with its composition changed according to the characteristics of acidic wastewater. Electrocapillary curves of different electrolytes were determined by dropping mercury electrode to explore the formation mechanism of colloidal mercury in acidic wastewater. The changes of zeta (ζ) potentials were also obtained. The results indicate that chloride ions have a great impact on the formation of colloidal mercury. Thermodynamic calculation demonstrated that the main mercury species in acidic wastewater were HgCl2 (aq), HgCl3−, and HgCl42−. Moreover, the model of colloidal mercury structure in acidic wastewater was established. Based on the changes of Gibbs free energy for ions passing through stern layer and metallic bond theory, it can be inferred that HgCl42− was preferentially over-adsorbed on the mercury interface by the weak π chemical bond, and then positive charge ions such as heavy metal ions and H+ were adsorbed due to the electrostatic force; thus, the colloidal mercury was formed.

Formation of tooeleite and the role of direct removal of As(III) from high-arsenic acid wastewater

In this study, an earth-mimetic method was proposed for the direct removal of As(III) by the formation of tooeleite, a ferric arsenite sulfate mineral. A series of batch experiments was used to study the relationship between the formation of tooeleite and the removal of As(III). The results indicate that As(III) removal efficiency reached up to 99% under the treatment condition of pH 1.8-4.5, initial As(III) concentration higher than 0.75g/L, and Fe/As ranged from 0.8 to 2 at room temperature. Various characterizations confirm that the precipitate obtained by this treatment was tooeleite with relatively high stability. In addition, it is assumed that ferrihydrite exists as a precursor, which is vital to the formation of tooeleite and the removal of As(III). This study suggests that tooeleite formation may be an alternative method in the direct removal of As(III) from high-arsenic acid wastewater.

Enhanced removal of Hg(II) from acidic aqueous solution using thiol-functionalized biomass

Spent grain, the low-cost and abundant biomass produced in the brewing industry, was functionalized with thiol groups to be used as an adsorbent for Hg(II) removal from acidic aqueous solution. The adsorbents were characterized by the energy-dispersive X-ray analysis (EDAX) and Fourier transform infrared (FTIR) spectroscopy. Optimum pH for Hg(II) adsorption onto the thiol-functionalized spent grain (TFSG) was 2.0. The equilibrium and kinetics of the adsorption of Hg(II) onto TFSG from acidic aqueous solution were investigated. From the Langmuir isotherm model the maximum adsorption capacity of TFSG for Hg(II) was found to be 221.73 mg g(-1), which was higher than that of most various adsorbents reported in literature. Moreover, the adsorption of Hg(II) onto TFSG followed pseudo-second-order kinetic model.

Complexation of arsenate with ferric ion in aqueous solutions

Interactions between arsenic and iron play an important role in arsenic removal from water. For the purpose of understanding the complexation of arsenate with ferric ion, arsenate solutions were prepared to react with ferric ion under various pH and temperature conditions. The formation of ferric–arsenate complex was examined using UV-Vis spectroscopy. The complex substance was proposed to exist as FeH2AsO42+ and FeHAsO4+, which transformed into gel-like material under higher pH (pH ≥ 2.38) or higher temperature (T ≥ 90 °C). The solid phase of gel-like material was verified as poorly crystallized ferric arsenate by XRF, XRD and FTIR. Moreover, the competitive complexation of ferric between sulfate and arsenate was also concerned. This study is beneficial for the better understanding of the fate and solubility of arsenic and ferric in water.

Pathway of zinc oxide formation by seed-assisted and controlled double-jet precipitation

Zinc oxide formation in seed-assisted and controlled double-jet precipitation (CDJP) was explored. Results show that the formation of ZnO involves the initial surface precipitation of β-Zn(OH)2 intermediates on seed surfaces, followed by fast surface phase transformation to ZnO. During this process, the seeds play the role of crystallization catalysts to promote ZnO formation in a short time at room temperature via changing the precipitation pathway. Meanwhile, CDJP ensures the effects of the seeds by controlling the solution supersaturation.

A comparative study of Ag(I) adsorption on raw and modified spent grain: kinetic and thermodynamic aspects.

The capability of modified spent grain (MSG) to adsorb silver (I) [Ag(I)] from aqueous solution was investigated and compared with raw spent grain (RSG) regarding their adsorption isotherms, kinetics, and thermodynamics. The monolayer adsorption capacity was 30.28 mg/g for RSG and 158.23 mg/g for MSG according to the Langmuir isotherm. The Ag(I) adsorption on MSG was approximately 4 times higher than that on RSG. The pseudo-second-order kinetic model provided the best description of Ag(I) adsorption on the two adsorbents. The calculated activation energy (Ea) implies that the adsorption of Ag(I) on RSG is a physical adsorption and on MSG is of a chemical nature. Thermodynamic results suggest that the adsorption of Ag(I) is an exothermic process for RSG and an endothermic process for MSG, whereas both adsorption processes are spontaneous in nature.

Droplet migration on hydrophobic–hydrophilic hybrid surfaces: a lattice Boltzmann study

In this paper, the fundamental features and mechanism of droplet migration on hydrophobic–hydrophilic hybrid surfaces are investigated using the lattice Boltzmann method. The hybrid surfaces are textured with pillars, which consist of hydrophobic side walls and hydrophilic tops. First, we study the cases with wettability differences between the sides and the tops of the pillars. It is found that, with an insufficient wetting contrast, the upper contact lines are pinned at the edges of the top surface. With an increase of the contact length between the droplet and the side wall of the pillar, a larger wettability difference is required to induce droplet migration. Meanwhile, it is observed that the migration process is gradually speeded up when the droplet covers more hydrophilic regions of the pillar. Moreover, the influence of the bottom substrates wettability is investigated. Two types of hybrid surfaces are considered, one of which adopts a wettability difference between the bottom substrate and the sides of pillars. The results show that the droplet migration can be promoted by applying a wetting contrast between the bottom substrate and the sides of the pillars, because the contact length between the droplet and the surface can be reduced with an increase in the hydrophobicity of the bottom substrate.