Chi-Wang Li

Tamkang University · Department of Water Resources and Environmental Engineering

Membrane filtration processes have demonstrated remarkable effectiveness in wastewater treatment, achieving high contaminant removal and producing high-quality effluent suitable for safe reuse. Membrane technologies play a primary role in combating water scarcity and pollution challenges. However, the need for more effective strategies to mitigate...

Per- and polyfluoroalkyl substances (PFAS) have been detected in soils worldwide, suggesting that soil serves as a substantial reservoir for these compounds. This paper provides a comprehensive overview of the origin of PFAS contamination in soil and sediment, as well as the environmental impacts associated with the distribution of PFAS in these me...

This study aims to present an overview of incorporating the Water Framework Directive into Italian law through Law 152/06. Subsequently, it will focus on a case study involving 34 rivers in the Salerno Province, utilizing data obtained from ARPA Campania. This work analyses the macro pollution indicators of the observed rivers using two aggregated...

The adverse effects of the accumulation of plastic on our planet are no longer sustainable; plastic is a major threat to all forms of life in all environments in addition to contributing to global warming. The academic world has been focusing on registering the damages caused by plastic pollution and finding solutions to refrain from and substitute...

An anaerobic ammonium oxidation (anammox) process was employed to remove nitrogen from wastewater generated from a coffee brewing facility. The effects of caffeine and chemical oxygen demand (COD) in coffee wastewater on anammox activity were investigated. The anammox activity was inhibited in synthetic wastewater with a caffeine concentration grea...

At a low COD:TN ratio (≤5) in influent, maintaining a longer HRT (≥9 h) and longer SRT (≥30 d) are suggested to improve higher N removal efficiency in case of operation at low DO (Dis-solved oxygen) level (0.9 ± 0.2 mg-O2/L). However, in case of operation at high DO level (4.0 ± 0.5 mg-O2/L), short HRT (1 h) and typical SRT (17 d) make it possible...

The release of air pollutants from the operation of wastewater treatment plants (WWTPs) is often a cause of odor annoyance for the people living in the surrounding area. Odors have been indeed recently classified as atmospheric pollutants and are the main cause of complaints to local authorities. In this context, the implementation of effective tre...

Alkaline chlorination, an efficient but high chemical cost process, is commonly employed for cyanide (CN−) removal from CN-rich wastewater streams. CN− removal and recovery through the precipitation of Prussian Blue (Fe4III[FeII(CN)6]3, PB) or Turnbull’s Blue (Fe3II[FeIII(CN)6]2, TB) were realized using iron salts, leading to a cost-effective and s...

Full-scale anaerobic, anoxic and aerobic (A²O) process is used worldwide for biological nutrient removal (BNR). However, operation parameters for nitrogen removals and information of microbial communities related to nitrogen removal in full-scale A²O wastewater treatment plants (WWTPs) having low and high COD/TN ratios are not available. Based on t...

The performance of an electrochemical reduction process was investigated for the treatment Cr(VI)-containing electroplating wastewater using a continuous-flow scrap iron packed column as an sacrificial anode. The effects of the key operating parameters including hydraulic retention time (HRT), current supply ratio (CSR), and inlet Cr(VI) concentrat...

This review paper aims to identify the main sources of carbon dioxide (CO2) emissions from wastewater treatment plants (WWTPs) and highlights several technologies developed to capture CO2 in this milieu. CO2 is emitted in all the operational units of conventional WWTPs, and even after the disposal of treated effluents and sludges. CO2 emissions fro...

A complete removal of Cu from CuEDTA complexes by replacement/precipitation reactions using ferrous ions was realized. The effects of pH, iron dosage and reactions time on Cu removal were evaluated. The results were explained with the aid of chemical equilibrium modeling. Fe(III) ions effectively liberate Cu(II) ions from CuEDTA complexes by the re...

The first case of Coronavirus Disease 2019 (COVID-19), which is caused by Severe Acute Respiratory Syndrome Coronavirus 2 (SARS-CoV-2), in Europe was officially confirmed in February 2020. On 11 March 2020, after thousands of deaths from this disease had been reported worldwide, the WHO changed their classification of COVID-19 from a public health...

With the circular economy in mind, recovery of iron phosphate, i.e., ferric phosphate or ferrous phosphate, from industrial wastewater is realized and the products recovered could be used in the synthesis of lithium iron phosphate for Li-ion secondary batteries. The formation of iron phosphate highly depends on pH and dissolved oxygen (DO) level. T...

This study investigated the effect of low and high chemical oxygen demand (COD):N ratios on biological nitrogen removal and microbial distributions in full-scale step-feed (SF) municipal wastewater treatment plants (WWTPs) in Thailand (SF 1) and Taiwan (SF 2). The SF 1 WWTP had a low COD:N (4:1) ratio, a long solids retention time (SRT) (> 60 d), a...

In this study, an electro-replacement/precipitation/deposition/direct reduction (ERPDD) process with scrap iron packed in a Ti mesh cage as a sacrificial anode was investigated for the treatment of wastewater containing CuEDTA complexes. The ERPDD mechanisms were responsible for the removal of Cu from CuEDTA complexes and were verified by a series...

Triiodide, a larger charged molecule compared to iodide, is thermodynamically favored with the presence of both iodide and iodine, and is easier to be retained by membrane processes. For the first time, iodide was recovered in the form of triiodide by forward osmosis (FO) for thin-film transistor liquid crystal display industries by preoxidation of...

Ti-based Sb-SnO2 electrodes are attractive due to their excellent catalytic activity but have a short service life. Here, we report a highly stable and efficient Ti/TiONC/Sb-SnO2 electrode, which was fabricated through hydrothermal reactions using urea to form TiONC interlayers and electrodeposition-annealing to coat the active Sb-SnO2 catalysts. T...

For the first time, simultaneous iodide recovery and boron removal from thin-film transistor liquid crystal display wastewater were achieved using forward osmosis because iodide is a precious material and boron is toxic with 1 mg/L discharge standard in Taiwan. Cellulose triacetate and thin-film composite with aquaporin flat sheet membranes were te...

An electro-crystallization process equipped with a sacrificial aluminum anode was operated under an optimum condition to promote the formation of crystalline cryolite for the recovery of fluoride from synthetic F-containing wastewater. The effects of pH, Al/F molar ratio, initial F concentration, and electrolytes were investigated experimentally, a...

Ferrous ions are the major Fe species generated from sacrificial iron anodes, but ferric ions are the more active ingredients for the removal of organic matters in the acidic pH region. Therefore, a novel high-pressure electrocoagulation (HPEC) system was devised to facilitate the Fe(II)-to-Fe(III) conversion under acidic pH conditions. The effects...

Fluorescence of the hydrophobic acid fraction (HPOA) of Suwannee River natural organic matter and Tb³⁺ excitation spectra were measured in tandem using the instantaneous and time-resolved emission modes. The intensity of HPOA fluorescence decreased in the presence of Tb³⁺, while the intensity of the emission from Tb³⁺ cations bound by HPOA increase...

A novel sacrificial anode comprised of scrap iron packed inside a cage made of titanium mesh was developed for Cr(VI) reduction. With electric currents applied, the surface passivation of scrap iron electrode could be avoided. Due to the large surface area with open structures provided, the applied current densities (1.18–3.54 mA/cm²) were low, res...

Surface finishing wastewater having low pH ( 2) and high conductivity (>11 mS/cm) was treated by electrocoagulation (EC) or electrochemical Fenton (ECF) processes using sacrificial iron anodes. Under the same theoretical Fe dosage, the effects of electrolytic time, initial pH, and current density on the simultaneous removal of organic and heavy met...

A systematic investigation of Cr(VI) reduction using electrochemical reduction revealed that the Cr(VI) reduction was extremely fast with reaction kinetics limited by the anodic generation of Fe(II). The Cr(VI) reduction rate increased with decreasing pH at the initial stage of reaction but the time to reach complete Cr(VI) reduction is pH independ...

A chemical reduction process was proposed to recover copper from the retentate of polyelectrolyte enhanced ultrafiltration (PEUF). Three polyelectrolytes (PSS, PAA, and PEI) containing various functional groups and molecular weights were studied to explore their effects on the copper removal in PEUF and on the copper recovery by chemical reduction...

In this world of nanotechnology, nanofibrous structures offer specialized features, such as mechanical strength and a large surface area, which makes them attractive for many applications. Their large surface area to volume ratio also makes them highly efficient. Among all the techniques for generating nanofibers, electrospinning is an emerging and...

The chemical precipitation of Ni ions from industrial wastewater at alkaline pH values creates waste chemical sludge (e.g., Ni(OH)2). We herein focused on Ni removal via chemical reduction using dithionite, by converting Ni(II) to its elemental or other valuable forms. Without the presence of a chelator (e.g., citrate), the nickel reduction efficie...

Forward osmosis is a membrane technology which is of high interest for water reclamation and desalination. To stabilize the forward osmosis (FO) process practical and cost-effective, selection of an appropriate draw solute is essential. Chlorhexidine gluconate based mouth-wash (CMW) has been determined to have high osmolality and low toxicity, rend...

For the first time, KOH in the waste stream of a thin film transistor liquid crystal displays (TFT-LCD) plant was utilized as a draw solution to recover iodide in the waste stream through forward osmosis (FO). In long-term operation, the pressure-retarded osmosis mode provided concentration efficiency greater than that of the FO mode. The maximum w...

A novel approach was designed to simultaneously enhance nutrient removal and reduce membrane fouling for wastewater treatment using an attached growth biofilm (AGB) integrated with an osmosis membrane bioreactor (OsMBR) system for the first time. In this study, a highly charged organic compound (HEDTA3−) was employed as a novel draw solution in the...

Wastewaters containing Cu(II) and ligands are ubiquitous in various industrial sectors, and efficacy of copper removal processes, especially precipitation, is greatly compromised by ligands. Chemical reduction, being commonly employed for production of metal nanoparticles, is also effective for metal removal. Adjustment of pH and addition of ligand...

Volume reduction and the concentration of long-lived radioactive species are critical issues for the management of liquid low-level radioactive waste. This study investigated and compared the performances of low-pressure reverse osmosis (LPRO) and polyelectrolyte-enhanced ultrafiltration (PEUF) for the removal of target metals (Co and Sr) from simu...

Forward osmosis (FO) is an emerging process for dewatering solid-liquid stream which has the potential to be innovative and sustainable. However, the applications have still been hindered by low water flux and membrane fouling when activated sludge is used as the feed solution due to bound water from microbial cells. Hence, a novel strategy was des...

Chemical reduction was firstly employed to treat synthetic wastewaters of various compositions prepared to simulate the retentate stream of polyelectrolyte enhanced ultrafiltration (PEUF). With fixed Cu:polyethylenimine (PEI) monomer:dithionite molar ratio, increasing copper concentration increases copper removal efficiency. Under fixed Cu:dithioni...

The reverse salt flux phenomenon of forward osmosis affects the quality of the feed water, reduces water flux, and increases the cost for replenishing lost draw solute. In this study, a novel draw solution comprising a mixture of Triton X100 and Na3PO4 for minimizing the reverse salt flux during forward osmosis (FO) was explored. The results indica...

This study investigated the recovery of fluoride (626.5mg/L) from an industrial wastewater as perovskite-like minerals. Effects of equilibrium pH (pHeq), molar ratio of Na to F (Na/F), and types of pH reagents were examined. Fluoride was recovered and confirmed by XRD as elpasolite (K2NaAlF6) when pH reagent was KOH. High fluoride removal efficienc...

The applications of forward osmosis (FO) have been hindered because of the lack of an optimal draw solution. The reverse salt flux from the draw solution not only reduces the water flux but also increases the cost of draw solute replenishment. Therefore, in this study, Tergitol NP7 and NP9 with a long straight carbon chain and low critical micelle...

Wastewaters containing Cu(II) along with ligands are ubiquitous in various industrial sectors. Efficacy of treatment processes for copper removal, especially precipitation, is greatly debilitated by ligands. Chemical reduction being commonly employed for production of metal nanoparticles has also been used for removing copper. Addition of ammonia w...

Dye manufacturing process wastewater (DMPW) generated from production of metal complex dyes might be mainly consisted of organic chelates. It is hypothesized that these organic chelates might form complex with metal ions. As the result, coagulation, frequently employed for dyeing wastewater treatment through sweep-floc mechanism, might not be an ef...

Silver chloride thin film (SCTF) with high specific surface area was synthesized through precipitation reaction by adding sodium chloride solution on top of frozen silver nitrate solution. Effects of precipitation time and silver nitrate concentration on the morphology of SCTFs were investigated. SEM images show that small crystal AgCl grains formi...

Fluoride removal by precipitation of calcium fluoride is the most common practice in Taiwan to treat fluoride-containing wastewater in semiconductor or optoelectronic industries. Due to very fine CaF2 precipitates (∼0.1 μm), coagulants/flocculants are needed to facilitate sedimentation of CaF2. In turn, large amount of sludge is produced by CaF2 pr...

Separation mechanisms for the three model divalent cations with very similar atomic weights (Cu, 63.5 Da; Co, 58.9 Da and Ni, 58.7 Da) by two nanofiltration (NF) membranes (Nitto Denko ESNA and GE Osmonics DK) were studied in a cross flow module from pHs 3 to 5. The results show that the rejection order for the two selected membranes was Ni2 + > Cu...

Aerobic granules (AG) have good settling ability and are relatively insensitive to the variation of organic loading rate. When sizes of granules become bigger, substrate and oxygen become limited in the granule core, leading to cell lysis and disintegration of granules. The higher the dissolved oxygen, the deeper the oxygen penetration inside AG. A...

Due to granule size, substrate and oxygen become limited in the core of granules leading to cell lysis at the core. Loss of granule stability is still a major barrier for practical application of AG. Compared to ambient pressure condition (AP), operation of AG under high pressure (HP) is a favorable condition for formation and stability of granules...

A new technology using the TiO2 photocatalysis combining electrodialysis was proposed for the simultaneous oxidization of ethylenediaminetetraacetic acid (EDTA)/reduction of hexavalent chromium (Cr(VI)) by electron–hole (e–h) pairs. The application of a cationic exchange membrane in this system was used to enhance the efficiency for the prevention...

Coagulation enhancement of nonionic surfactant nonylphenol polyethoxylate with 9 mol of ethoxylate (NP9EO), was conducted by partial oxidation using zero-valent iron (ZVI)/hydrogen peroxide (H2O2) since coagulation is a typical process in many small-scale wastewater treatment plants but it is difficult to remove NP9EO due to micelle formation, and...

The aim of this study was to determine the synergistic effect of nisin and green onion extract (GOE) on the inhibition of Listeria monocytogenes cocktail found in full-fat milk (M1), fat-free milk (M2), nano-calcium milk (M3) and nano-iron milk (M4). GOE at concentrations of 2, 5 and 8% revealed significant antilisterial effect against L. monocytog...

Effects of pH, extractant/diluent ratios, and metal concentrations on the extent of extractant dissolution during liquid-liquid extraction were investigated. Experimental result shows that D(2)EHPA dissolution increases dramatically at pH above 4, leveling off at pH 6-7. The phenomenon is consistent with deprotonation of D(2)EHPA and the domination...

The removal of natural organic matter (NOM) by adsorption onto iron oxide coated sand (IOCS) can be interpreted based on analysis of the absorbance and fluorescence spectra of the water before and after treatment. The useful spectral parameters include SUVA254, the widths of the benzenoid and electron transfer absorbance bands (WBz, and WET, respec...

A pressurized activated sludge reactor with a sand layer installed at the bottom of the reactor for filtration purposes was employed for treating synthetic organic wastewater. The intermittent high-pressure sequential bioreactor (IHPSB) was pressurized to facilitate efficient oxygen transfer under elevated biomass conditions with pressure released...

In our previous publications, compressed air-assisted solvent extraction process (CASX) was developed and proved to be kinetically efficient process for metal removal. In the current study, CASX with a ceramic MF membrane integrated for separation of spent solvent was employed to remove and recover metal from wastewater. MF was operated either in c...

Compressed air-assisted solvent extraction (CASX), was employed to remove Cr(VI) from synthetic wastewater and electroplating wastewater with the effects of pH, extractant/diluent ratio, solvent dosage, and competing anion concentration on Cr(VI) removal efficiency explored. The dosages required for Cr(VI) removal are dependent upon the speciation...

This study focused on the effects of pH and organic ligands, namely ethylenediaminetetraacetic acid (EDTA), nitrilotriacetic acid (NTA), and citric acids, on the removal and recovery of Cd(II) in polyelectrolyte enhanced ultrafiltration (PEUF). Polyethylenimine (PEI), which can bind with both positively charged metal ions by coordination bonding an...

A designed two-stage electrodialysis system is proposed to concentrate and purify chromate from a low pH electroplating wastewater using monovalent selective electrodialysis membranes. With low pH of the raw water (pH 2.2) in the first stage, chromate was presented as HCrO(4)(-) and monovalent ions (HCrO(4)(-), NH(2)SO(3)(-), Na(+) and Cl(-)) were...

A novel process, compressed air-assisted solvent extraction (CASX), was developed to generate micro-sized solvent-coated air bubbles (MSAB) for metal extraction. Through pressurization of solvent with compressed air followed by releasing air-oversaturated solvent into metal-containing wastewater, MSAB were generated instantaneously. The enormous su...

A fluidized zero valent iron (ZVI) reactor pressurized by CO(2) gas for controlling pH was employed for nitrate reduction. The proposed CO(2) pressurized system potentially has advantages of using less CO(2) gas and reaching equilibrium pH faster than CO(2)-bubbled system. However, due to weak acid nature of carbonic acid, system pH gradually incre...

Fenton process was employed to treat synthetic dye wastewater with supply of Fe(II) electrolytically generated from iron-containing sludge which was recycled and reused throughout the study. Treated water quality and properties of iron sludge after being repeatedly used were reported and discussed. Experimental results showed that COD was mainly re...

Fluidized zero valent iron (ZVI) process was conducted to reduce hexavalent chromium (chromate, CrO(4)(2-)) to trivalent chromium (Cr(3+)) from electroplating wastewater due to the following reasons: (1) Extremely low pH (1-2) for the electroplating wastewater favoring the ZVI reaction. (2) The ferric ion, produced from the reaction of Cr(VI) and Z...

A nonionic surfactant, polyoxyethylene Octyl phenyl ether (Triton-X), is added to a micellar-enhanced ultrafiltration process to lower the critical micellar concentration (CMC) of an anionic surfactant, sodium dodecyl sulfate (SDS). The effects of adding Triton-X on the copper removal efficiency, the permeate SDS concentration, the copper binding c...

A novel process combining an outside-in ultrafiltration membrane and suspended pellets in a stirred tank reactor for removing lead (Pb) from aqueous solutions was investigated. The incorporation of the membrane avoids breakthrough of fine particulate matter, which can plague conventional fluidized pellet reactors. The Pb removal efficiency increase...

The removal of color, dye and dissolved organic carbon by Fenton discoloration was investigated using the synthetic dye wastewaters containing various dyes (reactive blue 19, Eriochrome Black T or Fast Green FCF). The results indicated that discoloration of dyes was very rapid but mineralization of dyes was insignificant based on the removal of dis...

A fluidized zero valent iron (ZVI) reactor is examined for nitrate reduction. Using the system, the pH of solution can be maintained at optimal conditions for rapid nitrate reduction. For hydraulic retention times of 15 min, the nitrate reduction efficiency increases with increasing ZVI dosage. At ZVI loadings of 33 gl-1, results indicate that the...

A novel treatment process combining a membrane with outside-in flow configuration and a fluidized pellet rector for removing hardness was studied. The effects of influent water quality, e.g., concentrations of natural organic matter (NOM) and phosphate along with the hydrophobicity of NOM, on the hardness removal efficiency of the novel process wer...

A novel hybrid treatment process combining electrolysis process and micellar enhanced ultrafiltration process (MEUF) is proposed for removing metals. While MEUF is employed to retain metals inside the reactor, the electrolysis process liberates metal ions from the surfactant micelle–metal complexes and continuously removes these liberated ions by e...

The objectives of this study are to investigate the effects of acidification and alkalization on volume/solid reduction, dewaterability, and coagulant recovery from textile chemical sludge. The results indicate that solid reduction by acidification and alkalization was mainly due to the dissolution of Al. The best conditions for acidification and a...

A nonionic surfactant, polyoxyethylene Octyl phenyl ether (Triton-X), is mixed with an anionic surfactant, sodium dodecyl sulfate (SDS), to low the critical micellar concentration (CMC) of the anionic surfactant. Combination of the surfactant mixtures with ultrafilter, i.e., micellar-enhanced ultrafiltration process (MEUF), was employed for removin...

This article proposes a novel technology combining electrochemical and ultrasonic methods to produce nanoscale zero valent iron (NZVI). With platinum placed in the cathode and the presence of the dispersion agent, 0.2g/l cetylpyridinium chloride (CPC), a cation surfactant, in the solution, the nanoscale iron particle was successfully produced with...

The effects of the type and concentration of ligands on the removal of Cu by micellar-enhanced ultrafiltration (MEUF) with the help of either anionic or cationic surfactants were investigated. The removal efficiency of copper by anionic surfactant-(SDS-) MEUF depends on the ligand-to-Cu ratio and the ligand-to-Cu complexation constant. At fixed lig...

Electroplating method was employed to recover copper and surfactant simultaneously from synthetic solutions prepared to simulate concentrated waste stream generated from micellar-enhanced ultrafiltration. Effects of surfactant and copper (II) concentrations, surfactant to copper (II) molar ratio (S/M), electroplating voltage and time, solution pH,...

Fouling characteristics of membranes with various molecular weight cut-offs (MWCO) were investigated. The effects of the molecular weights (MW) of humic acids and pre-treatment with PAC on membrane fouling were studied. It was found that the hydraulic resistance caused by fouling materials calculated using cake resistance in series model is a bette...

Fluidized-bed pellet reactor technology was developed to remove water hardness with minimal sludge production. Operation procedures of this process include adding pellets into a column reactor and directing raw water and chemicals through the bottom of the column, keeping pellets fluidized to prevent them from being coagulated. In this study a proc...

In this study, the complexation of Tb3+ with natural organic matter (NOM) was studied by the method of time-resolved fluorescence spectroscopy. In the presence of NOM, the excitation of Tb3+ was observed in a wide range of wavelengths, for which virtually no excitation of free Tb3+ took place. The pseudo-quantum yield spectra (excitation intensity...

The change in the absorbance upon chlorination (the differential absorbance, AA) of natural organic matter (NOM) that has been concentrated, isolated, and/or fractionated from five sources was explored as a possible indicator of the formation of total organic halogen (TOX) in the samples. The results demonstrate that concentration and isolation of...

The ability of iron oxide-coated sand (IOCS) to adsorb strontium from synthetic wastes simulating the tank wastes at the Hanford Nuclear Reservation was examined in this study. These wastes have high pH and high ionic strength, containing up to 5.5 M Na+, 3.7 M NO3-, and 1.2 M OH-. The use of IOCS in such applications may be advantageous because it...

Simple and reliable relationships exist between the change in UV absorbance (ΔA) of NOM when it is chlorinated and the formation of chlorinated byproducts. These relationships provide an approach for obtaining large amounts of data that can be used to interpret the kinetics, stoichiometry, and mechanism of the reactions. Analysis of these relations...

Differential absorbance spectroscopy is a powerful tool for monitoring transformations in the chemical state of humic species (HS). Differential spectra for halogenation of HS are remarkably similar for a wide range of raw and treated waters but are dramatically different from those of model compounds such as resorcinol. These differences might be...

Differential absorbance spectroscopy is a powerful tool for monitoring transformations in the chemical state of humic species (HS). Differential spectra for halogenation of HS are remarkably similar for a wide range of raw and treated waters but are dramatically different from those of model compounds such as resorcinol. These differences might be...

Three types of fluorophores (decay times 1.2, 4.3, and 10.7 ns, respectively) participate in the fluorescence of Suwannee River hydrophobic acid (HPOA). The emission of the fast-decaying fluorophores (FDF) is red-shifted compared with that of longer-decaying groups. Upon chlorination, the FDF contribution (IFDF) to the emission declines, the specif...

A new application uses differential UV spectroscopy to monitor DBP formation easily, rapidly, and inexpensively. The decrease in the ultraviolet (UV) absorbance of natural organic matter (NOM) induced by chlorination can be characterized by the differential UV spectrum of the water. Differential UV spectra of chlorinated NOM are remarkably similar...