Po Lock Yue

Separation of pollutants from restaurant wastewater by electrocoagulation

The characteristics of restaurant wastewater were investigated. High oil and grease contents were detected. Electrocoagulation was used to treat this type of wastewater. Different electrode materials and operational conditions were examined. Aluminum was preferred to iron. Charge loading was found to be the only variable that affected the treatment efficiency significantly. The optimum charge loading and current density were 1.67–9.95 F/m3 wastewater and 30–80 A/m2 depending on the wastewater tested. The removal efficiency of oil and grease exceeded 94% for all wastewaters tested. The experimental results also show that the electrocoagulation can neutralize wastewater pH. Several mechanisms associated with pH variation are proposed.

SLUDGE DEWATERING AND DRYING

ABSTRACT The production of wastewater treatment sludge, the basic characteristics of the sludge and the state of the water in the sludge are described in this paper. The methods for the determination of bound water content are discussed. The literature (including patents) on sludge dewatering and drying is reviewed, including vacuum filters, belt presses, centrifuges, direct dryers, indirect dryers and combined mode drying systems. The issues related to drying are briefly discussed. Photographs or schematics of typical dewatering and drying systems are also included.

Improved photocatalytic activity of Sn4+ doped TiO2 nanoparticulate films prepared by plasma-enhanced chemical vapor deposition

Sn4+ ion doped TiO2 (TiO2–Sn4+) nanoparticulate films with a doping ratio of about 7∶100 [(Sn)∶(Ti)] were prepared by the plasma-enhanced chemical vapor deposition (PCVD) method. The doping mode (lattice Ti substituted by Sn4+ ions) and the doping energy level of Sn4+ were determined by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), surface photovoltage spectroscopy (SPS) and electric field induced surface photovoltage spectroscopy (EFISPS). It is found that the introduction of a doping energy level of Sn4+ ions is profitable to the separation of photogenerated carriers under both UV and visible light excitation. Characterization of the films with XRD and SPS indicates that after doping by Sn, more surface defects are present on the surface. Consequently, the photocatalytic activity for photodegradation of phenol in the presence of the TiO2–Sn4+ film is higher than that of the pure TiO2 film under both UV and visible light irradiation.

Investigation on the electrolysis voltage of electrocoagulation

Abstract The relation between electrolysis voltage and the other variables of an electrocoagulation process was analyzed. Theoretical models describing such a relation were established. Experiments were conducted to confirm the theoretical analysis and to determine the constants in the models. Both the theoretical analysis and experiments demonstrated that water pH and flow rate had little effects on the electrolysis voltage within a large range. The electrolysis voltage depends primarily on the inter-electrode distance, conductivity, current density and the electrode surface state. The models obtained can be used to calculate the total required electrolysis voltage for an electrocoagulation process.

Anodic oxidation of dyes at novel Ti/B-diamond electrodes

The physiochemical and electrochemical properties as well as the activity of novel Ti/B-diamond electrodes for anodic oxidation of various dyes were investigated. It was found that the Ti/B-diamond electrodes were much more active than Ti/Sb 2 O 5 -SnO 2 . All dyes tested, including orange II and 16 reactive dyes, could be mineralized effectively at Ti/B-diamond, with current efficiencies being 51.0-90.2%. The energy consumption ranges from 8.9 to 17.9 kW.h/m 3 . Operating variables could affect the process efficiency significantly. Low current density, high pH, and high temperature are beneficial for dye degradation.

Discoloration and mineralization of Reactive Red HE-3B by heterogeneous photo-Fenton reaction.

Discoloration and mineralization of Reactive Red HE-3B were studied by using a laponite clay-based Fe nanocomposite (Fe-Lap-RD) as a heterogeneous catalyst in the presence of H2O2 and UV light. Our experimental results clearly indicate that Fe-Lap-RD mainly consists of Fe2O3 (meghemite) and Fe2Si4O10(OH)2 (iron silicate hydroxide) which have tetragonal and monoclinic structures, respectively, and has a high specific surface area (472 m2/g) as well as a high total pore volume (0.547 cm3/g). It was observed that discoloration of HE-3B undergoes a much faster kinetics than mineralization of HE-3B. It was also found that initial HE-3B concentration, H2O2 concentration, UV light wavelength and power, and Fe-Lap-RD catalyst loading are the four main factors that can significantly influence the mineralization of HE-3B. At optimal conditions, complete discoloration of 100 mg/L HE-3B can be achieved in 30 min and the total organic carbon removal ratio can attain 76% in 120 min, illustrating that Fe-Lap-RD has a high photo-catalytic activity in the photo-assisted discoloration and mineralization of HE-3B in the presence of UV light (254 nm) and H2O2.

The influence of surface properties on the photocatalytic activity of nanostructured TiO2

Nanostructured TiO2 with 11- (P11) and 5-nm (P5) crystal sizes were prepared by a modified sol–gel method. Controlled crystallization and a pretreatment process were employed to obtain TiO2 with different surface roughness and degree of hydroxylation, while maintaining an identical crystal (i.e., 11 or 5 nm) and aggregate (i.e., 100 nm) sizes, phase structure (i.e., anatase), and crystallinity (i.e., X-ray diffraction peak intensity). Using the photooxidation of airborne trichloroethylene as a probe reaction, we were able to identify that the hydroxyl groups on low-coordinated titanium atoms are responsible for the generation of dichloroethylene and dichloroacetaldehyde by-products. Their presence usually means lower TCE conversion and in some cases leads to catalyst deactivation.

Synthesis and photocatalytic oxidation properties of iron doped titanium dioxide nanosemiconductor particles

The structure, physical characteristics and selective photocatalytic oxidation properties of quantum confined nanosize iron doped TiO2 (Q-TiO2/Fe3+) particles were studied by TG-DSC, XRD, DRS, EPR and Selective Oxidation Photocatalytic Measurements. It is shown that the solubility of iron in the obtained Q-TiO2/Fe3+ nanoparticles is 1.0 atom% and the iron doping level has a great influence on the transformation of anatase to rutile (A-R). The quantum confined effect was observed for Q-TiO2/Fe3+ nanoparticles. All of the samples have EPR Bulk-Fe3+ and Surf-Fe3+ signals, which are located in the bulk and surface of TiO2 nanoparticles respectively. Quantitative EPR results indicate that the relative EPR intensity of these paramagnetic centers shows regular change with varying corresponding iron modification level. In situ EPR indicates that the photo-generated charge carrier (h+, e−) could be trapped by different Fe3+ sites simultaneously, i.e., trapping of h+ is due to Surf-Fe3+ sites at g = 4.30, whereas that of e− is attributed to Bulk-Fe3+ sites at g = 1.99. Selective photocatalytic oxidation of cyclohexane into cyclohexanol with higher selectivity has been obtained by molecular oxygen activation over Q-TiO2/Fe3+ nanoparticles under mild conditions. It is thought that the optical surface state of Q-TiO2/Fe3+ nanoparticles play a key role in the selective photocatalytic oxidations.

Performance of a membrane-catalyst for photocatalytic oxidation of volatile organic compounds

The performance of a hybrid Sil-1/nanostructured anatase TiO2 membrane-catalyst and a catalytic titanium silicalite-1 (TS-1) membrane was evaluated for gas-phase photocatalytic oxidation (PCO) of trichloroethylene. The membrane-catalyst outperformed the catalytic plate coated with a similar amount of nanostructured TiO2 catalyst. However, the activity of the catalytic TS-membrane for PCO is low due to the insufficient number of active titanium sites in the TS-1 zeolite.

Copper/activated carbon as catalyst for organic wastewater treatment

Abstract A new heterogeneous copper catalyst was developed using highly porous activated carbon as the catalyst support. The catalyst was designed to promote the oxidation of organic pollutants in dyeing and printing wastewater from the textile industry, which was carried out in a 2 l high-pressure reactor. The new catalyst enhanced the conversion of organic compounds in dyeing and printing wastewater, shortened the reaction time, and lowered the reaction temperature and the system total pressure. The conditions for preparing the catalyst were experimentally optimized according to their catalytic oxidation efficiency in wastewater treatment.