Jiangya Ma

Matrix-Assisted Photochemical Vapor Generation for the Direct Determination of Mercury in Domestic Wastewater by Atomic Fluorescence Spectrometry

ABSTRACT In this article, matrix-assisted photochemical vapor generation is proposed for the direct determination of mercury in domestic wastewater by atomic fluorescence spectrometry. With the ultraviolet light irradiation, the matrix (low-molecular-weight organic compounds) in domestic wastewater samples can produce reducing species. These reducing species could reduce mercury from mercury (II) to elemental mercury, subsequently swept by argon to atomic fluorescence spectrometry for detection. The effects of several factors, such as material of the photoreaction coil, ultraviolet light wavelength, ultraviolet light irradiation time, and flow rate of carrier gas, were investigated. Under the optimized condition, a limit of detection of 0.1 µg L−1 was obtained. The standard addition method was used for the spiked mercury domestic wastewater sample analysis, with a relative standard deviation (n = 11, at 20 µg L−1) of 4.8%, and recovery test results ranged from 81% to 110%. The proposed method was applied to analyze two certified reference materials and four domestic wastewater samples, with analytical results in good agreement with certified values or those obtained by ICP-MS. Interferences from common transition metals and alkaline metals as well as alkaline earth metals were also investigated. This is a simple, reagent-free, cost-effective, green method for mercury determination in domestic wastewater.

Response surface methodology approach to optimize coagulation-flocculation process using composite coagulants

Response surface method and experimental design were applied as alternatives to the conventional methods for optimization of the coagulation test. A central composite design was used to build models for predicting and optimizing the coagulation process. The model equations were derived using the least square method of the Minitab 16 software. In these equations, the removal efficiency of turbidity and COD were expressed as second-order functions of the coagulant dosage and coagulation pH. By applying RSM, the optimum condition using PFPD1 was coagulant dosage of 384 mg/L and coagulation pH of 7.75. The optimum condition using PFPD2 was coagulant dosage of 390 mg/L and coagulation pH of 7.48. Confirmation experiment demonstrated a good agreement between experimental values and model predicted. This demonstrates that RSM and CCD can be successfully applied for modeling and optimizing the coagulation process using PFPD1 and PFPD2.

Photoinitiated polymerization of cationic acrylamide in aqueous solution: synthesis, characterization, and sludge dewatering performance.

A copolymer of acrylamide (AM) with acryloyloxyethyl trimethyl ammonium chloride (DAC) as the cationic monomer was synthesized under the irradiation of high-pressure mercury lamp with 2,2-azobis(2-amidinopropane) dihydrochloride (V-50) as the photoinitiator. The compositions of the photoinduced copolymer were characterized by Fourier transform infrared spectra (FTIR), ultraviolet spectra (UV), and scanning electron microscope (SEM). The effects of 6 important factors, that is, photo-initiators concentration, monomers concentration, CO(NH2)2 (urea) concentrations, pH value, mass ratio of AM to DAC, and irradiation time on the molecular weight and dissolving time, were investigated. The optimal reaction conditions were that the photo-initiators concentration was 0.3%, monomers concentration was 30 wt.%, irradiation time was 60 min, urea concentration was 0.4%, pH value was 5.0, and mass ratio of AM to DAC was 6 : 4. Its flocculation properties were evaluated with activated sludge using jar test. The zeta potential of supernatant at different cationic monomer contents was simultaneously measured. The results demonstrated the superiority of the copolymer over the commercial polyacrylamide as a flocculant.

Optimization of flocculation process by response surface methodology for diethyl phthalate removal using anionic polyacrylamide

AbstractDiethyl phthalate (DEP) are classified as endocrine disruptors in water. In the present study, response surface methodology (RSM) was employed for flocculation process optimization in DEP removal from water. Two different copolymers, anionic polyacrylamide (APAM), were used as flocculants in this flocculation process including APAM1 and APAM2. APAM1 was polymerized by ultraviolet (UV) initiation, and APAM2 was polymerized without UV-initiation. The analysis result of variance demonstrated that the model was highly significant and reliable. Optimization by RSM with APAM1, the optimum conditions were dosage of 11.01 mg L−1, pH of 8.93, and stirring time of 6.29 min. And the optimum conditions with APAM2 were dosage of 13.68 mg L−1, initial pH of 8.73, and stirring time of 6.80 min. DEP removal efficiency of 83.97% was achieved by using flocculants APAM1 and 72.47% for APAM2. Scanning electron microscopy images and spectrum from nuclear magnetic resonance spectrometer (1H NMR) suggested that UV-initi...

UV-Initiated Polymerization of Cationic Polyacrylamide: Synthesis, Characterization, and Sludge Dewatering Performance

P(AM-DAC-BA) was synthesized through copolymerization of acrylamide (AM), acryloyloxyethyl trimethyl ammonium chloride (DAC), and butylacrylate (BA) under ultraviolet (UV) initiation using response surface methodology (RSM). The influences of light intensity, illumination time, and photoinitiator concentration on the intrinsic viscosity [η] of P(AM-DAC-BA) were investigated. RSM model based on the influencing data was established for optimizing synthetic conditions. It was found that, at light intensity 1491.67 μw·cm−2, illumination time 117.89 min, and photoinitiator concentration 0.60‰, there was a better material performance achieved. Thus P(AM-DAC-BA) prepared under the above conditions showed excellent dewatering performance that, with 40 mg·L−1 P(AM-DAC-BA) at pH 7, the residual turbidity of supernatant and the dry solid content were up to 38 NTU, 28.5%, respectively.