Fook-Sin Wong

Enhanced degradation of 2,4-dichlorophenol by ultrasound in a new Fenton like system (Fe/EDTA) at ambient circumstance.

This study investigated the effect of ultrasound (US) enhancement on the degradation of 2,4-DCP in a new Fenton like system. An obviously synergistic effect was observed after introduction of US into the Fe/EDTA system. Good correspondences with pseudo-first-order kinetic were found in each reaction system. It was demonstrated that the degradation rate constant (kobs) of DCP in US/Fe/EDTA was 7 and 32 times higher than those in Fe/EDTA and US system alone. Simultaneously, lower first-order kobs was also obtained in the investigation of decomposition of EDTA. At 60 min reaction time, Removals of 81% TOC, complete DCP and 89% EDTA were achieved. Low molecular weight organic acids are identified as the main products, which contribute to the solution self-buffer at about pH 6.5 along with the reaction. In addition, the effect of initials condition, i.e., iron addition, EDTA dosage, DCP concentration and US input power as well as reaction temperature were studied and reaction activation energy (Ea) was also calculated.

Influence of organic and inorganic flocculants on physical-chemical properties of biomass and membrane-fouling rate.

The effects of addition of six types of flocculants (aluminium sulfate, ferric chloride, polyaluminium chloride, polymeric ferric sulfate, Chitosan, polyacrylamide) on mitigation of membrane fouling in membrane bioreactors (MBR) were investigated respectively. The biomasses in various MBRs were characterized by morphological properties (mean floc size (d(p)), fractal dimension (df)), physical parameters (surface charge, relative hydrophobicity (RH), dynamic viscosity) and the biochemical components of the mixed liquor (extracellular polymeric substances (EPS), soluble microbial products (SMP)). Statistical methods such as normalization, nondimensionalization and multiple linear regressions were used to identify the dominant membrane-fouling contributors and to simulate membrane-fouling rates. The results demonstrated that addition of flocculants had significant impact on sustainable filtration time and the key factors affecting membrane fouling varied in different flocculants added MBRs. For the organic flocculants added MBRs, membrane-fouling alleviation was mainly due to the decrease in SMP and df as well as the increase in d(p). For the inorganic flocculants added MBRs, the lower fouling rate could be mainly attributed to the decrease in SMP and surface charge as well as the increase in RH. For each type of flocculants, the empirical equations of sustainable filtration time (Gamma(45)) were simulated to predict membrane-fouling rates in different MBRs.

Rapid decolorization and mineralization of simulated textile wastewater in a heterogeneous Fenton like system with/without external energy.

A novel Fenton like system, employing Zero Valent Iron (ZVI) and air bubbling, was developed to treat a simulated textile wastewater containing azo dye Reactive Black 5 (RB5) and Ethylenediaminetetraacetic acid (EDTA). By dioxygen activation, H(2)O(2) was self-produced continuously in the system through a series of iron-EDTA ligands reactions. After 3h reaction, the removal rates of RB5, EDTA, Total Organic Carbon (TOC), and Chemical Oxygen Demand (COD) were 100%, 96.5%, 68.6% and 92.2%, respectively. The effects of pH, atmosphere as well as the initial concentration of RB5, EDTA and ZVI were also investigated. Two types of external energy-Ultrasound (US) and Ultraviolet (UV) were introduced into the Fenton like system, respectively. The effect of these external energies on the degradation of the wastewater was assessed. It was demonstrated that US presented significant synergistic effect on the degradation and mineralization of both RB5 and EDTA, while UV could not achieve any improvement.

Enhancement of filterability in MBR achieved by improvement of supernatant and floc characteristics via filter aids addition

Reduction of membrane fouling in membrane bioreactors (MBR) by addition of three typical filter aids (aluminum sulfate (Al(2)(SO(4))(3)), polymeric ferric sulfate (PFS) and Chitosan) was investigated. The effects of filter aids on membrane pore blocking, gel layer and cake layer resistance were analyzed respectively. Significant improvement of the sustainable filtration was demonstrated in the filter aids added MBRs. The membrane fouling rate of the MBRs operated under 20L/m(2)h flux was in the order of Control MBR (no filter aid added)>Al(2)(SO(4))(3) added MBR>Chitosan added MBR>PFS added MBR. Membrane inner fouling due to pore blocking was analyzed by means of Fourier-transform infrared microscope (FTIR). Compared to the control MBR, significantly low protein and carbohydrate concentrations were measured in the membranes of the filter aids added MBRs, indicating that filter aids could effectively alleviate membrane pore blocking. Gel Permeation Chromatography (GPC) analysis suggested that both the concentration and molecular weight distribution of the macromolecules in supernatant play an important role in gel layer formation and loss of membrane porosity. The reduction of fouling rate in the filter aids added MBRs could be attributed to lower concentration and reduction in molecular weight of macromolecules in supernatant. The specific cake resistance (alpha(c)), mean floc size (d(p)) and fractal dimension of the flocs (df) in the filter aids added MBRs were also investigated. It was demonstrated that alpha(c) decreased with the increase of d(p) and with the decrease of df, which is in consistent with the model prediction.

A dual membrane UF/RO process for reclamation of spent rinses from a nickel-plating operation—a case study

The objective of this work was to conduct treatability studies on rinse wastewater from process lines of a typical nickel-plating plant for reuse. The study comprised of three steps: (1) a plant process review and the treatability of different combinations of simulated spent rinses in the laboratory; (2) a variability monitoring of a combined rinse at the plant and a treatability study on a combined rinse in the laboratory; (3) a pilot study for reclamation of the combined rinse on site. The study established an optimum dual membrane ultrafiltration (UF)/reverse osmosis (RO) process for treating a combined liquor of spent alkaline, acidic and nickel-plating rinses which resulted in a treated water of a quality suitable for reuse as substitute for town water for the purpose of rinsing. The results of this study provided a good guide to the selection of a UF pretreatment combined with an RO membrane unit as the treatment system. The pilot plant had successfully operated for 6 months, consistently producing a high quality product water (< 95 microS cm-1) at an overall water recovery of 67.5%. The quality of reclaimed water was better than town water used at the factory. The product water from the pilot plant has been used as substitute of town water for in-process rinsing at the factory with no detrimental effects for 3 months.

Effect of feed pH on an integrated membrane process for the reclamation of a combined rinse water from electroless nickel plating

This study explored the effect of feed pH on an integrated membrane process of ultrafiltration/reverse osmosis (UF/RO) for the reclamation of spent rinse water from an electroless nickel-plating operation. Feed pH in the range of 2.54–6.64 was investigated. For UF pre-treatment, the experimental results showed that iron was not rejected by UF membrane when feed pH was below 3.68. However, when feed pH was raised to 3.68, iron rejection increased significantly and reached 98.7% at pH 6.64. For the RO process, it was found that for a particular wastewater containing weak acids and weak bases in this study, permeate pH was higher than the feed pH when the feed pH was low, but lower than the feed pH when the feed pH had reached 6.64. The critical point at which permeate pH would be equal to feed pH was about 6. This observation has not been reported previously. An attempt at explaining the observation was offered. The results showed that concentration of all measured contaminants in RO permeate decreased with an increase in feed pH. As a consequence, the permeate conductivity decreased with increasing feed pH. The membrane flux decreased with increasing feed pH. Total organic carbon (TOC) rejection increased with increasing feed pH due to the enhanced electrostatic repulsion between the negatively charged membrane surface and the negatively charged HOCH2CO2−. Moreover, the caustic soda consumption used for neutralization could be reduced by 39% in the integrated membrane process if the feed pH was set at 3.68 instead of 6.64. It was concluded that pH of the feed had a significant effect on the integrated membrane UF/RO process and the optimum pH of feed water for the treatment was in the range of 3.7–5.6.

A pilot study on a membrane process for the treatment and recycling of spent final rinse water from electroless plating

A hybrid process that includes microfiltration, UV irradiation, carbon adsorption, nanofiltration and ion exchange for treating and recycling spent final rinse water from an electroless plating operation has been developed. The process comprises four steps: (1) wastewater stream segregation, in which spent final rinses are segregated from other more heavily contaminated rinses and are combined to form a raw feed water stream for treatment; (2) pretreatment, in which the raw feed water stream is treated to remove particulates, microorganisms and free chlorine, and to reduce TOC; (3) heavy metal removal, in which the pretreated water is separated into a concentrate stream (containing salts) and a permeate stream (clean water) using a nanofiltration membrane; (4) polishing step, in which the permeate is further deionised using a mixed bed. The polished permeate stream is then recycled back to the plating operation rinsing system. The results of a pilot study showed that high quality product water (heavy metals free and <5 μS/cm in conductivity) is being consistently produced using a NF membrane system with an overall water recovery of 90%. The product water treated using this hybrid process is being recycled for use in the plant operation with no detrimental effects. The design data for a full scale NF plant with a treatment capacity of 25 m3/h has been obtained and the estimated payback period is between 13 and 18 months. The process is more applicable for reclaiming wastewater containing mainly heavy metals but low in monovalent ions.

The role and fate of EDTA in ultrasound-enhanced zero-valent iron/air system.

In this study, factors such as ZVI loading, ultrasound (US) input power, reaction temperature and solution pH that could affect the EDTA degradation in the US-enhanced zero-valent iron/air (US/ZVI/air) system were investigated. In the system, EDTA also served as an agent for complexation with the dissolved Fe(2+) and producing H(2)O(2) that would trigger Fenton-like reaction and degrade the EDTA itself. US played a threefold role in enhancing the overall EDTA degradation rate through: (1) accelerating ZVI corrosion and production of Fe(2+); (2) enhancing H(2)O(2) production through overcoming the kinetic barrier of oxygen activation by iron-EDTA complex; (3) improving EDTA mineralization while reducing its harmful by-products. The EDTA degradation rate with the US/ZVI/air system was 7.8 times higher than the combined rates achieved with US/air and ZVI/air operated as individual systems, indicating a significant synergistic effect. A hypothetical scheme illustrating the role and fate of EDTA in the US/ZVI/air system is proposed, indicating a complex auto-oxidation process enhanced by the US. It is postulated that ferryl-EDTA complex ([Fe(IV)O]EDTA) rather than OH was the dominant oxidant generated in the US/ZVI/air system that oxidized the EDTA even under the circumneutral condition.

Hypochlorite treatment of hydrophilic hollow fiber ultrafiltration membranes for high fluxes

Hydrophilic hollow fiber ultrafiltration membranes produced from a blend of polysulfone/poly(vinyl pyrrolidone) (PVP, K90) were post-treated with a hypochlorite solution. The results showed that the fluxes of all membranes that were treated with hypochlorite were 4.7–5.3 times higher but the rejections of the treated membranes were much lower than that of an untreated membrane. This suggests that hypochlorite treatment can alter the pore size of treated membranes while eliminating swelling of PVP in the pores. The results also showed that there was an optimum treatment time with hypochlorite to achieve a hydrophilic membrane with a high flux.

Microbial population dynamics of granular aerobic sequencing batch reactors during start-up and steady state periods

This study investigates microbial population dynamics in granular sequencing batch reactors (GSBR). The experimental results of DGGE fingerprint of sludge demonstrated that the microbial community structure of sludge shifted significantly during granulation period and nutrient removal improvement period. After reactor performance and physical characteristics of sludge reached steady state, microbial population of sludge became relatively stable. The high similarity of microbial community structure between co-existed flocculated sludge and granular sludge in GSBR at different operation phases indicated that similar microbial consortium could exist in compact aggregated form or in amorphous flocculated form. Therefore, strong selection pressure was still required to wash out flocs to maintain the stability of reactor operation. In addition, it was found that substrate type had considerable impact on microbial species selection and enrichment in granular sludge. The clone library of granular sludge showed that microbial species in divisions of α-Proteobacteria, β-Proteobacteria, γ-Proteobacteria and Bacteroidetes existed within acetate-fed granule communities and Thauera spp. from β-Proteobacteria accounted for 49% of the total clones in the whole clone library. It is thus speculated that Thauera spp. are important for the formation of acetate-fed granules under the conditions used in this study, maintaining the integrity of granules or substrate degradation.