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This work demonstrates a novel chloride photo-electrochemical method for mineralizing citric acid. The electrolytic reactor with a length of 12 cm, a width of 12 cm and a height of 30 cm held 2.5 L of solution, which was involved in the batch reaction. Both anode and cathode were made of titanium coated with RuO2/IrO2. The results revealed that the solution pH dominated the production of hypochlorous acid (HOCl) oxidant in the presence of NaCl as direct current electricity was used. The chloride electrochemical process at pH 5.5 removed 59% of total organic carbon (TOC) in 4 h (NaCl = 200 mM, current = 5 A). UV irradiation (254 nm) in the reactor induced the photo-electrochemical reaction, increasing the TOC removal from 59% to 99.4%. Finally, the reaction pathway for citric acid mineralization was discussed with reference to the detection of intermediates using a liquid chromatography–mass spectrometry (LC–MS). [Copyright &y& Elsevier]

Abstract: Electroless nickel plating wastewaters commonly contain the citrate chelating complex and the coexisting hypophosphite, which is a scavenger of hydroxyl radicals, typically lowers the catalytic efficiency of H2O2 by Fe2+ in Fenton reaction. Hence, in this work, the Fered-Fenton method was adopted to remediate the citrate, and then alkaline precipitation was utilized to remove the freed nickel ions. The chemical oxidation demand (COD) of citric acid could be efficiently reduced by approximately 95% using 1080mM H2O2 (dosed in continual mode) and 20mM ferrous ions at a current density of 190Am−2 ([citric acid]=100mM and [Ni]=100mM). Meanwhile, 99.9% of the nickel that was liberated from the chelation of citric acid was removed by the cathodic deposition and the sequential precipitation. The hypophosphite did not significantly influence the COD or nickel removal efficiency. Finally, those optimal conditions for the successful management of simulated electroless plating wastewater consisted of citric acid and nickel ions coexisting with hypophosphite were then used to demonstrate the treatment of real wastewater (45,000ppm COD and 8000ppm nickel ions). The high COD removal, 93%, from the effluents of the electroless nickel plating process verified that the Fered-Fenton process can be practically applied. [Copyright &y& Elsevier]

Dyes are hazardous compounds commonly found in industrial wastewaters. Efficient and inexpensive removal of dye molecules from the water matrix has been demonstrated by adsorption processes. Magnetic nano-adsorbents, such as metal ferrites, can be efficiently recovered from the reaction mixture after treating the pollutant. Herein, MFe 2 O 4 @GO (M = Cu, Co or Ni) was synthesized via solution combustion method for the removal of dye molecules from aqueous solutions. The characteristics of the MFe 2 O 4 @GO, including surface area and pore diameter, surface functional groups, and elemental composition, were examined. Methylene blue was used as representative dye pollutant. Batch adsorption results conformed to the Langmuir isotherm. Maximum adsorption capacities of the MFe 2 O 4 @GO (M = Cu, Co or Ni) were 25.81, 50.15 and 76.34 mg g−1, respectively. Kinetics of methylene blue adsorption fitted the pseudo-second-order model. Overall, NiFe 2 O 4 @GO exhibited the highest adsorbent performance among the graphene-metal ferrites investigated, primarily because of its high specific surface area and presence of mesopores. [Display omitted] • MFe 2 O 4 @GO (M = Cu, Co or Ni) composites were prepared by solution combustion. • MFe 2 O 4 @GO composites were found to be effective adsorbents for methylene blue. • Chemical adsorption was the rate-controlling mechanism for methylene blue removal. • Highest dye removal for NiFe 2 O 4 @GO due to high surface area and mesoporosity. [ABSTRACT FROM AUTHOR]

Resource recovery in wastewater treatment is the major challenge for achieving sustainable development. Further than only treatment, the recovery and reuse of nitrogen (N) and phosphorus (P) as a slow release fertilizer from actual swine wastewater (SW) was performed in this study. The development of a novel technique of converting soft sludge into hard particles using homogeneous granulation process in a fluidized bed reactor helps address the recovery. Under conditions of pH 8.5 ± 0.2, an Mg:P ratio of 1.2, total suspended solids (TSS) < 100 mg/L, and a 25 m/h up-flow velocity, the removal of N and P reached 69.8% and 96.8%, respectively. XRD and SEM-EDS analysis confirmed that N and P were crystallized as magnesium ammonium phosphate hexahydrate (struvite, NH 4 MgPO 4 ·6H 2 O) phase with a purity greater than 68.3% and an average particle size of 0.88 mm. The increase in total suspended solids resulted in not only decreases in the removal efficiency and struvite purity but also an irregular morphology in the struvite crystals. Furthermore, increasing the magnesium concentration significantly reduced the crystal size of the pellets. The optimal up-flow velocity should be 1.5–2.4 times the minimum fluidization velocity (12.75 m/h). A cost-benefit estimation of actual swine wastewater treatment indicated a profit of approximately 0.345 USD per m3-actual swine wastewater. Fluidized-bed homogeneous granulation was proven to be a promising technology for recovering N and P from swine wastewater. [Display omitted] • Struvite (diameter = 0.88 mm) was recovered from actual swine and Mg-rich wastewater. • The maximum recoveries were 69.8% and 96.8% for N and P, respectively. • Total suspended solids greatly influenced N and P removal as well as struvite size and purity. • The purity of the struvite pellets was affected by solution pH, total suspended solids and Mg concentration. • Homogeneous granulation was the main mechanism for N and P removal. [ABSTRACT FROM AUTHOR]

Chemical oxo-precipitation (COP) has become a promising method for treating boron wastewater at room temperature; it uses hydrogen peroxide to convert boric acid to perborate species, which are precipitated using alkaline earth metals. In this work, solubility models of barium perborates were established to predict residual boron levels from COP. The solubility product constants (pK sp ) of two major barium perborates – amorphous Ba(B(OH) 3 OOH) 2 (A-BaPB) and crystalline BaB(OH) 2 (OO) 2 B(OH) 2 (C-BaPB) – were experimentally estimated (8.335 ± 0.109 and 9.190 ± 0.057, respectively) to define the solubility curves of BaPBs at given pH, ionic strength and concentrations of barium and peroxide species. The characterization of precipitates that were formed by COP confirmed that the boron levels in aqueous solution were governed by the phase transformation of A-BaPB to C-BaPB. The predictive solubility models of barium perborates can perfectly predict the residual concentration of boron after COP treatment and can be used to optimize the process for reducing boron concentrations in wastewater. [ABSTRACT FROM AUTHOR]