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The article discusses the resource utilization of Fe-rich sludges. Topics discussed include an explanation of Fe-rich sludges which a waste product of water treatment, hydrometallurgy, surface finishing, and dye chemical industries; discussed further purification of sludge for creating new commercial products including red and black dyes, an iron concentrate powder, etc. and mentions a table characterizing the types of Fe-rich sludges.

A liquid–gas two-phase computational fluid dynamics (CFD) model was developed to simulate flow field and gas hold-up in a pilot-scale oxidation ditch (OD). The volume of fluid (VOF) model and the mass flow inlet boundary condition for gas injection were introduced in this model. The simulated values of the flow velocities and the gas hold-up were verified by experimental measurements in the pilot-scale OD. The results showed that the gas hold-up at test-site 3, immediately downstream of the surface aerator, was the highest among all three test-sites. Most of the gas existed in the upper portion of the ditch and was close to the inner side of the channel. Based on the liquid–gas two-phase CFD model, three operating conditions with different setting height ratios of the submerged impellers were simulated. The simulated results suggested that the setting heights of the submerged impellers have significant impacts on the flow velocity distribution. Lowering the setting height could increase the flow velocity in the pilot-scale OD. An optimal setting height ratio of 0.273 was proposed, which would be beneficial for minimizing sludge sedimentation, especially near the inner side of the curve bend. [ABSTRACT FROM AUTHOR]

Lead-carbon batteries could provide better performance on high-rate partial-state-of-charge (HRPSoC) cycles than lead-acid batteries (LABs), making them promising for the new-generation of hybrid electric vehicles. The addition of carbon allotropes to the negative active material (NAM) could induce a significant improvement to the battery performance. Herein, an environmentally friendly strategy is demonstrated to prepare lead oxide and carbon (PbO@C) composite by pyrolyzing the lead citrate precursor derived from the spent lead paste of LABs. When the PbO@C composite is used as an additive to the NAM of lead-carbon batteries, the utilization efficiency of the NAM is improved from 56.9% to 72.5%, and the cycle life of the cell in HRPSoC is tremendously extended by four times compared with the control one. The enhancement in battery performance is attributed to the hydrophilic carbon in the composite, which acts as a 3D electroosmotic pump facilitating electrolyte diffusion, and hindering the tendency to excess sulfation during the HRPSoC operation. This proposed research provides a sustainable and scalable strategy to recycle the discarded/spent LABs into high-performance lead-carbon batteries. [ABSTRACT FROM AUTHOR]

In this study, anaerobic granular sludge (AGS) was used as a novel adsorbent for hexavalent chromium (Cr (VI)) removal from aqueous solutions. Factor experiments were conducted to find out the effects of different variables on the biosorption process. Among these terms, the impact of three main independent variables (contact time, initial pH and AGS dosage) on the removal efficiency of Cr (VI) was modeled using a well-fitting polynomial equation (R² = 0.9044), by conducting 20 batch experiments designed by a central composite. The experimental isotherm data were successfully described by the Freundlich isotherm and the pseudo-second-order kinetic model was more suitable for explaining the kinetics process of adsorption. The AGS can be disposed using 0.1 M NaOH with 96.4% desorption efficiency. The results of the analyses (X-ray photoelectron spectroscopy and Fourier transformed infrared spectroscopy) suggested that Cr (VI) adsorption most likely involved electrostatic adsorption, redox reaction and complexation. [ABSTRACT FROM AUTHOR]

Lead citrate is a key precursor for the green recycling of spent lead acid battery paste in a citric acid/sodium citrate (CA/SC) solution. In this study, the main paste component, PbSO4, was leached and crystallized to yield lead citrate. Results showed that the leaching of PbSO4 in citric acid/sodium citrate solution was remarkably enhanced by an increase in temperature from 35 °C to 95 °C and an increase in sodium citrate (SC) concentration from 50 to 650 g/L. In comparison, increasing the citric acid/sodium citrate molar ratio inhibited this leaching. Controlled crystallization through cooling the solution or adjusting the pH of the solution can effectively produce lead citrate crystals. The X-ray diffraction patterns of four products obtained in a comparison test were all consistent with Pb3(C6H5O7)2. However, the scanning electron microscopy analysis suggested that the morphology was distinct from rods to sheets, which were mainly affected by the temperature variation. [ABSTRACT FROM AUTHOR]

Activated persulfate generated from Fe2+-sodium persulfate (SPS) was used as a conditioner for dewatering of waste activated sludge. The effects of Fe2+-SPS on dewaterability were investigated by specific resistance to filtration (SRF) and capillary suction time (CST), as well as further confirmed the results with diaphragm filter press dewatering process in laboratory. The amount of extracellular polymeric substances (EPS) and zeta potentials were analyzed. With 30 mg Fe2+ per gram dry solid (DS) and 100 mg SPS per gram DS, 89.0% of SRF and 84.1% of CST reductions were achieved, respectively. Furthermore, the dewatered cake moisture content was as low as 52.6% in the diaphragm filter press dewatering. The EPS fractions and zeta potential of the sludge floc were found to have significantly changed during the Fe2+-SPS conditioning. Proteins and polysaccharides contents in filtrate all increased with increase in the amount of Fe2+-SPS, but decreased in tightly bound EPS (TB-EPS). The change of proteins content in loosely bound EPS (LB-EPS) was more significant than polysaccharides. Scanning electron microscope images further demonstrated that the Fe2+-SPS pre-treatment ruptured the sludge floc resulting in the formation of permeable and incompressibility structure in filtration process. [ABSTRACT FROM AUTHOR]

The influence of pretreated phosphogypsum on water resistance of composite binders containing phosphogypsum (CBPG) was investigated. Six pretreatment processes in total were conducted on phosphogypsum using autoclaving and calcination. Three parameters of the CBPG mortars were comparatively studied to evaluate their water resistance: the ratio of the compressive strength in the wet-saturated state to that in the dry state (W/D); weight loss after static water attack (WLSW); and weight loss after flowing water attack (WLFW). The crystalline phases could be transformed and the impurities could be effectively purified for original phosphogypsum by the pretreatment process. Therefore, water resistance of the CBPG mortars from pretreated phosphogypsum was improved significantly when compared to that of the mortars from original phosphogypsum. Regarding the weight loss and strength after static or flowing water attacks, WLSW and WLFW could effectively evaluate the water resistance of CBPG mortars, when compared with traditional evaluation by W/D. [ABSTRACT FROM AUTHOR]

In order to optimize the flow field in a full-scale Carrousel oxidation ditch with many sets of disc aerators operating simultaneously, an experimentally validated numerical tool, based on computational fluid dynamics (CFD), was proposed. A full-scale, closed-loop bioreactor (Carrousel oxidation ditch) in Ping Dingshan Sewage Treatment Plant in Ping Dingshan City, a medium-sized city in Henan Province of China, was evaluated using CFD. Moving wall model was created to simulate many sets of disc aerators which created fluid motion in the ditch. The simulated results were acceptable compared with the experimental data and the following results were obtained: (1) a new method called moving wall model could simulate the flow field in Carrousel oxidation ditch with many sets of disc aerators operating simultaneously. The whole number of cells of grids decreased significantly, thus the calculation amount decreased, and (2) CFD modeling generally characterized the flow pattern in the full-scale tank. 3D simulation could be a good supplement for improving the hydrodynamic performance in oxidation ditch designs. [ABSTRACT FROM AUTHOR]