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This study investigated the removal of arsenite (As(III)) and arsenate (As(V)) in aqueous solution using iron-coated pomelo peel (ICPP). Batch adsorption experiments were performed to evaluate the effects of initial pH values (2.0–10), contact time (1–1440 minutes), initial concentration (0.05–5 mg/L) on the As(III) and As(V) removal capacity by ICPP. The Langmuir maximum adsorption capacities of ICPP of As(III) and As(V) at pH 7.0, and 25 °C were 1.51 mg/g and 1.64 mg/g, respectively. The capacities were significantly higher than that of raw pomelo peel (PP) material at the same condition (qmax As(III) = 0.032 mg/g and qmax As(V) = 0.036 mg/g). Adsorption kinetics data fitted well with the Elovich model and the adsorption process quickly reached an equilibrium at around 120 min. The results shows that the As(III) and As(V) adsorption performance of ICPP were much better than that of PP, granular activated carbon (GAC) and many iron-based adsorbents. Thus, ICPP has potential as a filter media for efficiently removing toxic arsenic ions from water.

Ammonium removal from drinking water to protect human and environmental health is one of the major global concerns. This study evaluates the performance of Purolite C100E, a commercial cation exchange resin, in eliminating ammonium in synthetic and real contaminated groundwater. The results demonstrate that the pH operation range of the resin for better ammonium removal is 3 to 8. Lower ammonium removal at low and high pH occurred due to competition from H+ and loss of ammonium as ammonia gas, respectively. Equilibrium data of ammonium removal fitted both the Langmuir and Freundlich isotherm models with the maximum Langmuir ion exchange capacities for initial ammonium concentrations of 10–200 mg/L and 50–2000 mg/L, reaching 18.37 mg/g and 40.16 mg/g, respectively. The presence of co-ions in the water reduced the ammonium removal efficiencies slightly ( Ca2+ > K+. The higher affinity of ammonium to adsorbent is due to its lower hydrated ionic radius and H-bonding. The maximum exchange capacity in the fluidized bed studies of the original Purolite C100E (bed height 27 cm, resin weight 75 g, initial ammonium concentration 17.4 mg/L, filtration velocity 0.5 m/h) was 10.48 mg/g. It progressively reduced slightly after three regeneration cycles to 8.79 mg/g. The column breakthrough data satisfactorily fitted the Thomas model. A household filter cartridge packed with 4 kg Purolite C100E (80 cm height) and operated at a filtration velocity of 1.9 m/h in Vietnam successfully reduced the initial 6 mg NH4+/L in groundwater (after sand filter pre-treatment) to well below the Vietnam drinking water standard (3 mg/L-QCVN 01:2009/BYT) continuously for 1 week, suggesting that such a filter can be adopted in rural areas to successfully remove ammonium from groundwater.

This study evaluated the performance of a low-cost natural laterite from Thach That (NLTT), Vietnam, for its capacity to remove arsenic (As) in a household filter with contaminated groundwater. The NLTT was initially tested in a laboratory column trial lasting 800 h. The breakthrough curves were found to fit the Thomas model very satisfactorily with adsorption capacities of 0.06 and 0.20 mg/g at a flow velocity of 0.85 m/h for the influent As(V) concentrations of 0.1 and 0.5 mg/L, respectively. In household filters at four sites, the median As concentration in groundwaters (0.04–0.19 mg/L) dropped to 0.026–0.054 mg/L after traditional sand filtration. However, following subsequent NLTT filtration through columns (14 cm inner diameter, 65 cm height) at 0.65 m/h flow velocity, it fell to below the Vietnam and WHO drinking water standard (0.01 mg/L) during seven months of continuous operation. Portland cement and lime were tested as binding agents for the exhausted NLTT waste in a solidification/stabilization process at different ratios. The best ratio of exhausted NLTT: Portland cement: lime for restraining mobility of As from this waste was 3:1:0.5. The concrete brick products exhibited a suitable compressive strength for using it as building materials in construction work.

Arsenic (As) contamination of drinking water supplies is a major concern in many countries due to its large concentration in groundwater and high toxicity. In this study, batch adsorption experiments on a natural laterite adsorbent from Vietnam (NLTT) were firstly conducted, followed by four column adsorption experiments using NLTT working with synthetic water under different experimental conditions (initial arsenate As(V) concentration: 0.1 and 0.5 mg/L; bed height: 0.15 and 0.41 m). Results from the batch equilibrium adsorption study show that all three models - Sips, Langmuir, and Freundlich - fitted the experimental data very well. The Sips and Langmuir maximum adsorption capacities were 0.76 mg/g and 0.58 mg/g, respectively. At an As(V) concentration of 0.5 mg/L, adsorption breakthrough occurred at 28 h and 122 h for column heights of 0.15 m and 0.41 m, respectively. When As(V) concentration fell to 0.1 mg/L, the breakthrough times rose to 144 h and 240 h, respectively. A linear driving force approximation (LDFA) model incorporating the Sips equation was calibrated with data from the equilibrium and kinetic adsorption experiments and one column adsorption experiment (initial concentration: 0.1 mg/L; bed height: 0.15 m). The LDFA model with the calibrated model coefficients could predict the breakthrough curves and adsorption time in the three other column experiments and four household column filters used to treat As contaminated groundwater in Vietnam. The study revealed that application potential for NLTT in column adsorption studies and field trials to remove As(V) is significant despite this study having limited data. Subsequently, refining the model based on simulation of results is cost-effective, saves time and effort, and negates the need for multiple experiments to optimize filter conditions.

Ammonium removal from drinking water to protect human and environmental health is one of the major global concerns. This study evaluates the performance of Purolite C100E, a commercial cation exchange resin, on eliminating ammonium in synthetic and real contaminated groundwater. The results demonstrate that the pH operation range of the resin for better ammonium removal is 3 to 8, while the optimum contact time was about 30 min. The kinetics of the ammonium removal process followed both the Pseudo-first order and Pseudo-second order models. Equilibrium data of ammonium removal fitted both the Langmuir and Freundlich isotherm models with the maximum Langmuir ion exchange capacities for initial ammonium concentrations of 10-200 mg/L and 50-2000 mg/L reaching 18.37 mg/g and 40.16 mg/g, respectively. The presence of co-ions in the water reduced the ammonium removal efficiencies in the order Mg2+> Ca2+> K+. The maximum exchange capacity in the fluidised bed studies of the original Purolite C100E (bed height 27 cm, resin weight 75 g, initial ammonium concentration 17.4 mg/L, filtration velocity 0.5 m/h) was 10.48 mg/g. It progressively reduced slightly after three regeneration cycles to 8.79 mg/g. The column breakthrough data satisfactorily fitted the Thomas model. A household filter cartridge packed with 4 kg Purolite C100E (80 cm height) and operated at a filtration velocity of 1.9 m/h in Vietnam successfully reduced the initial 6 mg NH4+/L in groundwater (after sand filter pre-treatment) to well below the Vietnam drinking water standard (3 mg/L) continuously for one week.

This study reports landfill leachate treatment by the forward osmosis (FO) process using hydrogen peroxide (H2O2) for membrane cleaning. Although chemical cleaning is an effective method for fouling control, it could compromise membrane integrity. Thus, understanding the impact of chemical cleaning on the forward osmosis membrane is essential to improving the membrane performance and lifespan. Preliminary results revealed a flux recovery of 98% in the AL-FS mode (active layer facing feed solution) and 90% in the AL-DS (draw solution faces active layer) using 30% H2O2 solution diluted to 3% by pure water. The experimental work investigated the effects of chemical cleaning on the polyamide active and polysulfone support layers since the FO membrane could operate in both orientations. Results revealed that polysulfone support layer was more sensitive to H2O2 damage than the polyamide active at a neutral pH. The extended exposure of thin-film composite (TFC) FO membrane to H2O2 was investigated, and the active layer tolerated H2O2 for 72 h, and the support layer for only 40 h. Extended operation of the TFC FO membrane in the AL-FS based on a combination of physical (hydraulic flushing with DI water) and H2O2 was reported, and chemical cleaning with H2O2 could still recover 92% of the flux.

An attempt has been made in this review to provide some insights into the possible adsorption mechanisms of hexavalent chromium onto layered double hydroxides-based adsorbents by critically examining the past and present literature. Layered double hydroxides (LDH) nanomaterials are typical dual-electronic adsorbents because they exhibit positively charged external surfaces and abundant interlayer anions. A high positive zeta potential value indicates that LDH has a high affinity to Cr(VI) anions in solution through electrostatic attraction. The host interlayer anions (i.e., Cl−, NO3−, SO42−, and CO32−) provide a high anion exchange capacity (53–520 meq/100 g) which is expected to have an excellent exchangeable capacity to Cr(VI) oxyanions in water. Regarding the adsorption-coupled reduction mechanism, when Cr(VI) anions make contact with the electron-donor groups in the LDH, they are partly reduced to Cr(III) cations. The reduced Cr(III) cations are then adsorbed by LDH via numerous interactions, such as isomorphic substitution and complexation. Nonetheless, the adsorption-coupled reduction mechanism is greatly dependent on: (1) the nature of divalent and trivalent salts utilized in LDH preparation, and the types of interlayer anions (i.e., guest intercalated organic anions), and (3) the adsorption experiment conditions. The low Brunauer–Emmett–Teller specific surface area of LDH (1.80–179 m2/g) suggests that pore filling played an insignificant role in Cr(VI) adsorption. The Langmuir maximum adsorption capacity of LDH (Qomax) toward Cr(VI) was significantly affected by the natures of used inorganic salts and synthetic methods of LDH. The Qomax values range from 16.3 mg/g to 726 mg/g. Almost all adsorption processes of Cr(VI) by LDH-based adsorbent occur spontaneously (ΔG° 0) and increase the randomness (ΔS° >0) in the system. Thus, LDH has much potential as a promising material that can effectively remove anion pollutants, especially Cr(VI) anions in industrial wastewater.

Arsenic (As) contamination of drinking water is a major cause of As toxicity in many parts of the world. A study was conducted to evaluate As removal from water containing 100–700 μg/L of As and As to Fe concentration ratios of 1:5–1:1000 using the coprecipitation process with and without As/Fe adsorption onto granular activated carbon (GAC). Fe concentration required to reduce As concentrations in order to achieve the WHO standard level of 10 μg/L increased exponentially with the increase in initial As concentration. When small amounts of GAC were added to the As/Fe solutions the Fe required to remove these As concentrations reduced drastically. This decline was due to the GAC adsorption of Fe and As, enhancing the removal of these metals through coprecipitation. Predictive regression equations were developed relating the GAC dose requirement to the initial As and Fe concentrations. Zeta potential data revealed that As was adsorbed on the GAC by outer-sphere complexation whereas Fe was adsorbed by inner-sphere complexation reversing the negative charge on GAC to positive values. X-ray diffraction of the GAC samples in the presence of Fe had an additional peak characteristic of ferrihydrite (Fe oxide) compared to that of the GAC sample without Fe. The study showed that incorporating an adsorbent into the coprecipitation process has the advantage of removing As from waters at all concentrations of Fe and As compared to coprecipitation alone which does not remove As to the required levels if Fe concentration is low.

Calcium carbonate (CaCO3)-enriched biomaterial derived from freshwater mussel shells (FMS) was used as a non-porous biosorbent to explore the characteristics and mechanisms of cadmium adsorption in aqueous solution. The adsorption mechanism was proposed by comparing the FMS properties before and after adsorption alongside various adsorption studies. The FMS biosorbent was characterized using nitrogen adsorption/desorption isotherm, X-ray diffraction, scanning electron microscopy with energy dispersive spectroscopy, Fourier-transform infrared spectroscopy, and point of zero charge. The results of batch experiments indicated that FMS possessed an excellent affinity to Cd(II) ions within solutions pH higher than 4.0. An increase in ionic strength resulted in a significant decrease in the amount of Cd(II) adsorbed onto FMS. Kinetic study demonstrated that the adsorption process quickly reached equilibrium at approximately 60 min. The FMS biosorbent exhibited the Langmuir maximum adsorption capacity as follows: 18.2 mg/g at 10 °C Cd2+ > Cu2+ > Cr3+ > Zn2+. For column experiments, the highest Thomas adsorption capacity (7.86 mg/g) was achieved at a flow rate (9 mL/min), initial Cd(II) concentration (10 mg/L), and bed height (5 cm). The Cd(II) removal by FMS was regarded as non-activated chemisorption that occurred very rapidly (even at a low temperature) with a low magnitude of activation energy. Primary adsorption mechanism was surface precipitation. Cadmium precipitated in the primary (Cd,Ca)CO3 form with a calcite-type structure on the FMS surface. A crust of rhombohedral crystals on the substrate was observed by SEM. Freshwater mussel shells have the potential as a renewable adsorbent to remove cadmium from water.

Water quality modeling in a river basin often faces the problem of having a large number of parameters yet limited available data. The important inputs to the water quality model are pollution concentrations and discharge from river tributaries, lateral inflows and related pollution load from different sources along the river. In general, such an extensive data set is rarely available, especially for data scarce basins. This makes water quality modeling more challenging. However, integration of models may be able to fill this data gap. Selection of models should be made based on the data that is available for the river basin. For the case of Cau River basin, the SWAT and QUAL2K models were selected. The outputs of SWAT model for lateral inflows and discharges of ungauged tributaries, and the observed pollutant concentrations data and estimated pollution loads of sub-watersheds were used as inputs to the water quality model QUAL2K. The resulting QUAL2K model was calibrated and validated using recent water quality data for two periods in 2014. Four model performance ratings PBIAS, NSE, RSR and R2 were used to evaluate the model results. PBIAS index was chosen for water quality model evaluation because it more adequately accounted for the large uncertainty inherent in water quality data. In term of PBIAS, the calibration and validation results for Cau River water quality model were in the “very good” performance range with ǀPBIASǀ

This study developed a layered double hydroxides (Mn/Mg/Fe-LDH) material through a simple co-precipitation method. The Mn/Mg/Fe-LDH oxidized arsenite [As(III)] ions into arsenate [As(V)] anions. The As(III) and oxidized As(V) were then adsorbed onto Mn/Mg/Fe-LDH. The adsorption process of arseniate [As(V)] oxyanions by Mn/Mg/Fe-LDH was simultaneously conducted for comparison. Characterization results indicated that (i) the best Mg/Mn/Fe molar ratio was 1/1/1, (ii) Mn/Mg/Fe-LDH structure was similar to that of hydrotalcite, (iii) Mn/Mg/Fe-LDH possessed a positively charged surface (pH

Although Vietnam has promoted the utilisation of highly active antiretroviral therapy (HAART) towards HIV elimination targets, adherence to treatment has remained under-investigated. We aimed to describe high-risk behaviours and clinical characteristics by adherence status and to identify the factors associated with non-adherence. We included 426 people living with HIV (PLWH) currently or previously involved in HAART. Most participants were men (75.4%), young (33.6 years), with low income and low education levels. Non-adherent PLWH (11.5%) were more likely to have a larger number of sex partners ( p-value = 0.053), sex without condom use ( p-value = 0.007) and not receive result at hospital or voluntary test centre ( p-value = 0.001). Multiple logistic regression analysis showed that demographic (education levels), sexual risk behaviours (multiple sex partners and sex without using condom) and clinical characteristics (time and facility at first time received HIV-positive result) were associated with HAART non-adherence. There are differences in associated factors between women (education levels and place of HIV testing) and men (multiple sex partners). Gender-specific programs, changing risky behaviours and reducing harms among PLWH may benefit adherence. We highlight the need to improve the quantity and quality of HIV/AIDS services in Vietnam, especially in pre- and post-test counselling, to achieve better HAART adherence, working towards ending AIDS in 2030.

This study reports landfill leachate treatment by the forward osmosis (FO) process using hydrogen peroxide (H

This study presents systematic investigations to evaluate the performance, rejection rate, fouling, cleaning protocols and impact of physical and chemical cleaning strategies on the performance of commercial cellulose triacetate (CTA) membrane. The treatment of landfill leachate (LFL) solution was performed in the active layer facing feed solution and support layer facing the draw solution (AL-FS mode), and active layer facing the draw solution and support layer facing the feed solution (AL-DS mode). Compared to the AL-FS mode, a higher flux for AL-DS mode was achieved, but membrane fouling was more severe in the latter. In both membrane orientations, the rejection rate of the FO membrane to heavy ions and contaminants in the wastewater was between 93 and 99%. Physical and chemical cleaning strategies were investigated to recover the performance of the FO membrane and to study the impact of cleaning methods on the membrane rejection rate. Physical cleaning with hot water at 35 °C and osmotic backwashing with 1.5 M NaCl demonstrated excellent water flux recovery compared to chemical cleaning. In the chemical cleaning, an optimal concentration of 3% hydrogen peroxide was determined for 100% flux recovery of the fouled membrane. However, slight membrane damage was achieved at this concentration on the active layer side. Alkaline cleaning at pH 11 was more effective than acid cleaning at pH 4, although both protocols compromised the membrane rejection rate for some toxic ions. A comparison of the membrane long-term performance found that cleaning with osmotic backwashing and hot water were effective methods to restore water flux without comprising the membrane rejection rate. Overall, it was found that physical cleaning protocols are superior to chemical cleaning protocols for forward osmosis membrane fouled by landfill leachate wastewater.

This study presents the removal of phosphate from aqueous solution using a new silver nanoparticles-loaded tea activated carbon (AgNPs-TAC) material. In order to reduce costs, the tea activated carbon was produced from tea residue. Batch adsorption experiments were conducted to evaluate the effects of impregnation ratio of AgNPs and TAC, pH solution, contact time, initial phosphate concentration and dose of AgNPs-AC on removing phosphate from aqueous solution. Results show that the best conditions for phosphate adsorption occurred at the impregnation ratio AgNPs/TAC of 3% w/w, pH 3, and contact time lasting 150 min. The maximum adsorption capacity of phosphate on AgNPs-TAC determined by the Langmuir model was 13.62 mg/g at an initial phosphate concentration of 30 mg/L. The adsorption isotherm of phosphate on AgNPs-TAC fits well with both the Langmuir and Sips models. The adsorption kinetics data were also described well by the pseudo-first-order and pseudo-second-order models with high correlation coefficients of 0.978 and 0.966, respectively. The adsorption process was controlled by chemisorption through complexes and ligand exchange mechanisms. This study suggests that AgNPs-TAC is a promising, low cost adsorbent for phosphate removal from aqueous solution.

In this study, magnetic snail shell (MSS) prepared by impregnating of iron oxide onto snail shell (SS) powder was used for removing Cr(VI) from aqueous solution. Among six different mass ratios of Fe/SS powder studied, the MSS25 produced at a ratio of 25% achieved the highest Cr(VI) adsorption capacity. Batch adsorption experiments were conducted to investigate the adsorption isotherm, kinetics, and mechanism of Cr(VI) onto MSS25. The results illustrated that adsorption of Cr(VI) onto MSS25 reached equilibrium after 150 min at pH 3. The adsorption kinetics could be well described by the pseudo-second order model (R2 = 0.986). The Langmuir model (R2 = 0.971) was the best-fitting model that described the adsorption isotherm of Cr(VI) onto MSS25. The maximum adsorption capacity was 46.08 mg Cr(VI) per gram of MSS25. Ion exchange, electrostatic attraction, and adsorption-coupled reduction were determined as the main adsorption mechanisms of Cr(VI) onto MSS25. The high percentages of CaCO3 and Fe3O4 found in the MSS25 structure made a significant contribution to the Cr(VI) adsorption process.

© 2018 Elsevier Ltd. All rights reserved. Understanding the interactions between sludge particles and polymers during sludge dewatering is necessary to: firstly, maximize dewatered cake solids content; and secondly, minimize polymer demand. In this study, two scientific methodologies, namely the 'y-intercept' concept and Higgins modified centrifugal technique (Higgins MCT) were used to identify the optimum polymer demand and type for effective conditioning and dewatering. Results from the 'y-intercept' concept show that a large amount of polymer required during conditioning of anaerobically digested sludge (ADS) is mainly due to neutralization of soluble biopolymers. In contrast, conditioning of aerobically digested sludge (AEDS) and waste activated sludge (WAS) is mostly controlled by a polymer bridging mechanism. The results indicated that, in order to achieve maximum dewatering performance with minimum conditioning polymer requirement, high charge density polymers are suitable for ADS while branched (or cross-linked) polymers can be used for AEDS and WAS. The new lab-scale technique, Higgins MCT, was successfully implemented for measuring cake solids content achievable by centrifuge and determining the optimum polymer demand (OPD). The Higgins MCT also helped to understand the relationship between digestion, conditioning and dewatering.

Recently, electrocoagulation (EC) has emerged as a promising method to treat contaminated water. In this study, a novel EC system using stainless steel electrodes was applied to remove arsenate (As(V)) in water. An operation time of 5 min, electrical potential difference of 7.5 V, and inter electrode distance of 1 cm were identified as optimal condition for removing As(V) (eliminated 92 % of As(V) from 0.1 mg As(V)/L solution). In the batch study using a 9 V rechargeable battery and a small 12 V solar panel, the EC reactor removed 93 % and 98 % of As(V) from 0.1 mg As(V)/L solution, respectively, and As(V) concentration in treated water was lower than that of the drinking water guideline of World Health Organisation (WHO) (0.01 mg/L). In the continuous water flow study, a small cost-effective system (reactor volume of 1 L, cost $15 AUD) using a small 12 V solar panel could successfully treat 12 L contaminated water per hour. During 4 h of continuous testing, the system’s efficiency in removing As(V) remained constant at >91 %. The operation cost for the treatment of As(V) – contaminated water in continuous operation mode is $0.240 AUD/m3 water for the direct current (DC) electrical system and $0.262 AUD/m3 for the solar system. In a pilot field study with contaminated groundwater (0.03 mg total As/L) in Hanam province, Vietnam, the EC system using solar energy (12 V) was able to reduce As concentration to below the Vietnamese and WHO permissible drinking water limit in 1 min.

This study investigated the phenomenon and mechanism of adsorption of methylene green 5 (MG5) on three pristine biosorbents: golden shower pod (GS), coconut shell (CC), and orange peel (OP). The results showed that the biosorbents possessed low specific surface areas, but abundant functional groups. Adsorption was strongly affected by the solution’s pH and ionic strength. As revealed in the kinetic study, equilibrium was rapidly established, requiring low activation energies; a removal rate of 30%–87% was achieved within 1 min. The maximum Langmuir adsorption capacities at 30°C exhibited the following order: GS (106 mg/g) > OP (92 mg/g) > CC (59 mg/g). Thermodynamic experiments suggested that the adsorption occurred spontaneously (−ΔG°) and exothermically (−ΔH°). The primary adsorption mechanisms involved electrostatic attraction, hydrogen bonding formations, and n-π interaction. Thermogravimetric analysis (TGA) revealed that three biopolymer components (i.e., hemicellulose, cellulose, and lignin)...

Arsenic contamination of drinking water is a serious water quality problem in many parts of the world. In this study, a low-cost manganese oxide ore from Vietnam (Vietnamese manganese oxide (VMO)) was firstly evaluated for its performance in arsenate (As(V)) removal from water. This material contains both Mn (25.6%) and Fe (16.1%) mainly in the form of cryptomelane and goethite minerals. At the initial As(V) concentration of 0.5 mg/L, the adsorption capacity of original VMO determined using the Langmuir model was 0.11 mg/g. The modified VMOs produced by coating VMO with iron oxide (Fea-VMO) and zirconium oxide (Zra-VMO) at 110 °C and 550 °C achieved the highest As(V) adsorption capacity when compared to three other methods of VMO modifications. Langmuir maximum adsorption capacities of Fea-VMO and Zra-VMO at pH 7.0 were 2.19 mg/g and 1.94 mg/g, respectively, nearly twenty times higher than that of the original VMO. Batch equilibrium adsorption data fitted well to the Langmuir, Freundlich, and Temkin models and batch kinetics adsorption data to pseudo-first order, pseudo-second order, and Elovich models. The increase of pH progressively from 3 to 10 reduced As(V) adsorption with a maximum reduction of 50–60% at pH 10 for both original and modified VMOs. The co-existing oxyanions considerably weakened the As(V) removal efficiency because they competed with As(V) anions. The competition order was PO43− > SiO32− > CO32− > SO42−. The characteristics of the original and modified VMOs evaluated using SEM, FTIR, XRD, XRF, surface area, and zeta potential explained the As(V) adsorption behaviour.

© 2019 Elsevier Ltd Arsenic is a major drinking water contaminant in many countries causing serious health hazards, and therefore, attempts are being made to remove it so that people have safe drinking water supplies. The effectiveness of arsenic removal from As(V) solutions using granular activated carbon (GAC) (zero point of charge (ZPC) pH 3.2) and iron incorporated GAC (GAC-Fe) (ZPC pH 8.0) was studied at 25 ± 1 °C. The batch study confirmed that GAC-Fe had higher Langmuir adsorption capacity at pH 6 (1.43 mg As/g) than GAC (1.01 mg As/g). Adsorption data of GAC-Fe fitted the Freundlich model better than the Langmuir model, thus indicating the presence of heterogeneous adsorption sites. Weber and Morris plots of the kinetic adsorption data suggested intra-particle diffusion into meso and micro pores in GAC. The column adsorption study revealed that 2–4 times larger water volumes can be treated by GAC-Fe than GAC, reducing the arsenic concentration from 100 μg/L to the WHO guideline of 10 μg/L. The volume of water treated increased with a decrease in flow velocity and influent arsenic concentration. The study indicates the high potential of GAC-Fe to remove arsenic from contaminated drinking waters in practical column filters.

In the Red River Delta, Vietnam, arsenic (As) contamination of groundwater is a serious problem where more than seventeen million people are affected. Millions of people in this area are unable to access clean water from the existing centralized water treatment systems. They also cannot afford to buy expensive household water filters. Similar dangerous situations exist in many other countries and for this reason there is an urgent need to develop a cost-effective decentralized filtration system using new low-cost adsorbents for removing arsenic. In this study, seven locally available low-cost materials were tested for arsenic removal by conducting batch adsorption experiments. Of these materials, a natural laterite (48.7% Fe2O3 and 18.2% Al2O3) from Thach That (NLTT) was deemed the most suitable adsorbent based on arsenic removal performance, local availability, stability/low risk and cost (US$ 0.10/kg). Results demonstrated that the adsorption process was less dependent on the solution pH from 2.0 to 10. The coexisting anions competed with As(III) and As(V) in the order, phosphate > silicate > bicarbonate > sulphate > chloride. The adsorption process reached a fast equilibrium at approximately 120–360 min, depending on the initial arsenic concentrations. The Langmuir maximum adsorption capacities of NLTT at 30 °C were 512 μg/g for As(III) and 580 μg/g for As(V), respectively. Thermodynamic study conducted at 10 °C, 30 °C, and 50 °C suggested that the adsorption process of As(III) and As(V) was spontaneous and endothermic in nature. A water filtration system packed with NLTT was tested in a childcare centre in the most disadvantaged community in Ha Nam province, Vietnam, to determine arsenic removal performance in an operation lasting six months. Findings showed that the system reduced total arsenic concentration in groundwater from 122 to 237 μg/L to below the Vietnam drinking water standard of 10 μg/L.

© 2019, © 2019 Taylor & Francis Group, LLC. Contaminants in water bodies cause potential health risks for humans and great environmental threats. Therefore, the development and exploration of low-cost, promising adsorbents to remove contaminants from water resources as a sustainable option is one focus of the scientific community. Here, we conducted a critical review regarding the application of pristine and modified/treated biosorbents derived from leaves for the removal of various contaminants. These include potentially toxic cationic and oxyanionic metal ions, radioactive metal ions, rare earth elements, organic cationic and anionic dyes, phosphate, ammonium, and fluoride from water media. Similar to lignocellulose-based biosorbents, leaf-based biosorbents exhibit a low specific surface area and total pore volume but have abundant surface functional groups, high concentrations of light metals, and a high net surface charge density. The maximum adsorption capacity of biosorbents strongly depends on the operation conditions, experiment types, and adsorbate nature. The absorption mechanism of contaminants onto biosorbents is complex; therefore, typical experiments used to identify the primary mechanism of the adsorption of contaminants onto biosorbents were thoroughly discussed. It was concluded that byproduct leaves are renewable, biodegradable, and promising biosorbents which have the potential to be used as a low-cost green alternative to commercial activated carbon for effective removal of various contaminants from the water environment in the real-scale plants.

This study developed a new adsorbent, specifically activated carbon-loaded silver nanoparticles (AgNPs-AC) by coating the silver nanoparticles (AgNPs) onto activated carbon (AC). The obtained AgNPs-AC were characterized by scanning electron microscopy (SEM), energy-dispersive spectrometry (EDS), Fourier transform infrared spectroscopy (FTIR), and Brunauer-Emmett-Teller (BET). The ability of AgNPs-AC to remove methylene blue (MB) was evaluated using different experimental factors, these being pH solution, contact time, adsorbent dose, and initial MB concentration. Results indicated that the highest adsorption capacity of MB onto AgNPs-AC was obtained when the AC was loaded onto AgNPs at the impregnation ratio of 0.5% w/w for AC and AgNPs. The best conditions in which AgNPs-AC could remove MB were as follows: pH 10, contact time lasting 120 min, and adsorbent dose being 250 mg/25 mL solution. In this scenario, the maximum adsorption capacity of MB onto AgNPs-AC was 172.22 mg/g. The adsorption isothermal equilibrium was well described by the Langmuir, Freundlich and Sips models. The Sips equations had the highest correlation coefficient value (R2 = 0.935). The pseudo-first-order and pseudo-second-order kinetic models agree well with the dynamic behavior of the adsorption of dye MB on AgNPs-AC.

Three saccharides (glucose, sucrose, and xylose) were used as pure precursors for synthesizing spherical biochars (GB, SB, and XB), respectively. The two-stage synthesis process comprised: (1) the hydrothermal carbonization of saccharides to produce spherical hydrochar’ and (2) pyrolysis of the hydrochar at different temperatures from 300°C to 1200°C. The results demonstrated that the pyrolysis temperatures insignificantly affected the spherical morphology and surface chemistry of biochar. The biochar’ isoelectric point ranged from 2.64 to 3.90 (abundant oxygen-containing functionalities). The Brunauer–Emmett–Teller (BET)-specific surface areas (SBET) and total pore volumes (Vtotal) of biochar increased with the increasing pyrolysis temperatures. The highest SBET and Vtotal were obtained at a pyrolysis temperature of 900°C for GB (775 m2/g and 0.392 cm3/g), 500°C for SB (410 m2/g and 0.212 cm3/g), and 600°C for XB (426 m2/g and 0.225 cm3/g), respectively. The spherical biochar was a microporous material with approximately 71–98% micropore volume. X-ray diffraction results indicated that the biochar’ structure was predominantly amorphous. The spherical biochar possessed the graphite structure when the pyrolysis temperature was higher than 600°C. The adsorption capacity of GB depended strongly on the pyrolysis temperature. The maximum Langmuir adsorption capacities () of 900GB exhibited the following selective order: phenol (2.332 mmol/g) > Pb2+ (1.052 mmol/g) > Cu2+ (0.825 mmol/g) > methylene green 5 (0.426 mmol/g) > acid red 1 (0.076 mmol/g). This study provides a simple method to prepare spherical biochar – a new and potential adsorbent for adsorbing heavy metals and aromatic contaminants.

There is a need to remove arsenic (As) in drinking water supplies by simple and cost-effective techniques. A column adsorption study was conducted to remove As(V) from water employing an iron (Fe) and zirconium (Zr) grafted Vietnamese manganese oxide ore (Fea-VMO and Zra-VMO). At a flow rate of 0.15 L/h, the bed volumes of water (As(V) concentration 0.1 mg/L) treated by Zra-VMO and Fea-VMO to produce water with As(V) concentration below the WHO guideline concentration (10 μg/L) were 6 and 8 times higher than for VMO, respectively. An increase in influent As concentration increased the adsorption capacity, but the increase of flow rate reduced the adsorption capacity. The maximum adsorption capacities derived from the Thomas model for VMO, Fea-VMO, and Zra-VMO at an influent concentration of 0.25 mg As(V)/L and flow rate of 0.15 L/h were 0.151, 1.145, and 0.925 mg/g, respectively. These values fell when influent As concentration decreased or the flow rate increased. Solidification/stabilisation method was applied to immobilise As(V) in the exhausted absorbent wastes by replacing 5, 10, 15, and 20 % of sand in a sand/cement concrete mixture by the adsorbent waste. This solidified material had satisfactory compressive strength, rapid chloride penetrability test, and volume of permeable voids, which indicated the material had good stability, making it suitable for use as a building material in construction work. The As(V) leaching from these materials, as measured by Method 1313 of the Leaching Environmental Assessment Framework of USEPA, proved to be very negligible.

This study aims to investigate the environmental issues regarding the construction phase of the wastewater treatment plant (WWTP) and explore the roles of different materials through their environmental impacts. Detailed inventories of the two WWTPs were conducted by involving materials and transportation for civil works undertaken. EPD 2018 and ReCiPe life cycle impact assessment methods were employed to measure all the impact categories. Five treatment processes - (1) pumping, (2) primary treatment, (3) secondary treatment, (4) sludge line, and (5) building landscape - were considered for the assessment. It was found that concrete and reinforcing steel played similarly vital roles in most of the EPD 2018 impacts. The significant score of reinforcing steel was found on human cancer toxicity, which contributed more than 90% of the impacts. The contribution of diesel on ozone formation was 5% higher than that of reinforcing steel. Glassfiber was responsible for 70% of the burdens on ozone depletion, showing much higher than the total share of concrete and reinforcing steel. Primary treatment units only contributed 9.5% of the construction impacts in the Girona WWTP but up to 43.8% in Mill Creek WWTP mainly because of the proportion of consumed materials. In short, the comprehensive data inventories were necessary when evaluating the total environmental impacts of the WWTP.

Porous luffa plant fibre (LF) was grafted with Fe and Zr, and the ability of the fabricated adsorbents to remove arsenate (As(V)) from water was investigated in batch and column adsorption experiments. The Langmuir adsorption capacity (mg g-1) at pH 7 of LF was found to be 0.035, which increased to 2.55 and 2.89 after being grafted with Fe (FLF-3) and Zr (ZLF-3), respectively. Grafting with Fe and Zr increased the zeta potential and zero point of charge (ZPC) of LF (from pH 3.9 to 7.4 for Fe grafting and to 7.6 for Zr grafting), due to chemical bonding of the metals, possibly with the hydroxyl and carboxylic groups in LF as indicated in FTIR peaks. Zeta potential and ZPC decreased after As adsorption owing to inner-sphere complexation mechanism of adsorption. The increase of pH from 3 to 10 progressively reduced the adsorbents' adsorption capacity. Co-existing anions weakened the As(V) removal efficiency in the order, PO43- > SiO32- > CO32- > SO42-. Adsorption kinetics data fitted well to the Weber and Morris model, which revealed initial fast and subsequent slow rates of intra-particle As diffusion into the bigger pores and smaller pores, respectively. Column adsorption data fitted well to the Thomas model with the predicted adsorption capacities in the same order as in the batch adsorption experiment (ZLF-3 > FLF-3 > LF).

This study aims to characterize anaerobically digested sludge (ADS) and correlate the sludge characteristics in terms of soluble organic compounds with polymer demand (PD) during sludge conditioning. The PD required to achieve maximum dewatering of the ADS studied is in the range of 8–10 kg polymer/dry ton. The commonly used capillary suction time parameter to evaluate the solid–liquid separation ability was not a reliable indicator for assessing dewatering. Instead, in this study, a modified centrifugal technique proposed by Higgins (Higgins MCT) was used to assess the maximum achievable dry solids content of the biosolids cake. The Higgins MCT is readily obtained using a bench-scale centrifuge equipped with a modified centrifuge bucket. Using the Higgins MCT, the maximum dry solids contents obtained from conditioned ADS was 30 wt%. These values were comparable to the dry solids content obtained from the same sludge at full-scale level. Our results suggest Higgins MCT is suitable for assessing th...

For decades, there has been a strong interest in mitigating greenhouse gas (GHG) emissions from wastewater treatment plants (WWTPs). Numerous models were developed to measure the emissions and propose the quantification. Existing studies looked at the relationship between GHG emissions and operational cost (OCI), which is one of the most important indicators for decision-makers. Other parameters that can influence the control strategies include the effluent quality (EQI) and total environmental impacts. Plant-wide models are reliable methods to examine the OCI, EQI and GHG emissions while Life cycle assessment (LCA) works to assess the potential environmental impacts. A combined LCA and plant-wide model proved to be a valuable tool evaluating and comparing strategies for the best performance of WWTPs. For this study involving a WWTP, the benchmark model is used while LCA is the decision tool to find the most suitable treatment strategy. LCA adds extra criteria that complement the existing criteria provided by such models. Complementing the cost/performance criteria is proposed for plant-wide models, including environmental evaluation, based on LCA, which provides an overall better assessment of WWTPs. It can capture both the dynamic effects and potential environmental impacts. This study provides an overview of the integration between plant-wide models and LCA.

High polymer demand in sludge conditioning is an intractable aspect of the water industry. This study investigated the effects of extracellular polymeric substances (EPS) fractions on polyacrylamide demand for conditioning and dewatering performance. Specifically, it examined aerobically and anaerobically digested sludges from seven full-scale wastewater treatment plants (WWTPs). Our study successfully quantified the contributions of soluble EPS to polyacrylamide demand during conditioning and explained the role of tightly bound EPS (TB-EPS) in determining the digested sludges’ dewatering performance. Results show that the concentrations of soluble EPS in the sludges varied between 92 and 1148 mg/L. Experimental results also demonstrated that between 25% and 80% of polyacrylamides used for conditioning were wasted in “parasitic” reactions with soluble EPS. The residual cationic polyacrylamide left in solution, after the parasitic reactions, was substantial and varied between 35 and 254 mg/L. Despite this outcome, the zeta potential values of dewatered sludge cakes remained negative, i.e. between −24 and −35 mV. These indicated that the residual soluble cationic polyacrylamides would not have been absorbed on the negatively charged sludge particles. This explained the relatively poor performance of the dewatering stage in the treatment plants studied. Furthermore the results suggested the TB-EPS attached to the sludge particles would be responsible for the poor dewatering. We postulated that the TB-EPS would gelify and immobilize the water surrounding the sludge particles. Our study suggested that new and more effective polymers for conditioning are needed to both: (i) reduce polymer demand; and (ii) improve the dewatering performance.

This study developed a low cost catalyst, namely, zinc slag (Zn-S) for the ozonation process of Direct Black 22 (DB22) from aqueous solutions. Among five different kind of low cost metal slags including Fe-S, Cu-S, Cd-S, Pb-S and Zn-S, the Zn-S slag was selected as an efficient catalyst in this study. Zn-S contained mainly zinc (Zn) and calcium (Ca) discharged from zinc slag waste in Vietnam. It was found that Zn-S could effectively decolonize and mineralize DB22 through heterogeneous catalytic ozonation. The degradation kinetic of DB22 followed the pseudo-first order model. The best removal efficiency of DB22 (Zn-S/O3/H2O2 (76%) > Zn-S/O3 (69%) > O3/H2O2 (66%) > O3 (55% for COD) occurred at pH 11 for heterogeneous catalytic ozonation processes with Zn-S as the catalyst as well as ozone alone and perozone processes due to fast decomposition of O3 in alkaline solution to generate powerful and non-selective OH radicals. An increase in decolonization and mineralization rate was observed when increasing the Zn-S dosage from 0.125 g/L to 0.75 g/L for Zn-S/O3 and 0.125 g/L to 1.0 g/L for Zn-S/O3/H2O2. The K values of the pseudo-first order model followed the same sequence as mineralization rates of DB22 in term of COD removal. Ca and Zn constituents in the Zn-S catalyst contributed to the increase in O3 decomposition and improvement of reaction rate with H2O2. Subsequently, the degradation of DB22 by the ozonation process with Zn-S catalyst was enhanced through the enrichment mechanism of hydroxyl radicals (*OH) and surface adsorption. The degradation mechanism of DB22 by hydroxyl radicals was surely affirmed by tests with the decrease in degradation percentage of DB22 in case of the presence t-butanol, Cl− and CO32−.

Excessive levels of heavy metals in water are an environmental hazard. An Australian zeolite with (ICZ) and without (Z) iron-coating, was used to remove five heavy metals from aqueous solutions using adsorption in batch and column experiments. The batch study showed that the Langmuir adsorption capacities of heavy metals on Z and ICZ at pH 6.5 and ionic strength 10 −3 M NaNO 3 were in the order Pb > Cu > Cd > Cr, Zn for single metal (5.0–11.2 mg/g) and for mixed metals solution (3.7–7.6 mg/g). The data for the kinetics of adsorption satisfactory fitted to both the pseudo-first and second order models with fits slightly better for the latter model. Data fitted to a diffusion model revealed that adsorption took place in two or more than two different stages: a fast external surface adsorption, and a gradual adsorption controlled by both film diffusion and intra-particle diffusion. The column adsorption data were fairly well described by Thomas model, with the order of Thomas adsorption capacity following a similar trend as in the batch study. In both batch and column experiments, the adsorption capacities were higher for ICZ than for Z and were generally lower in mixed metals system than in single metals system. Leaching of used ICZ columns with 0.1 M HCl, resulted in 64–93% of adsorbed metals being desorbed, and 10% of Fe being dissolved from the ICZ.

© 2015 Balaban Desalination Publications. All rights reserved. Advanced treatment processes are vital if organic matter is to be removed from water as efficiently as possible. To produce high quality water that has low concentrations of natural organic matter (NOM), the Gunbower water treatment plant (WTP) in northern Victoria, Australia has implemented a number of processes including magnetic ion exchange (MIEX), coagulation, clarifier, ultrafiltration (UF), and granular activated carbon (GAC) filtration. This research evaluated the efficiencies of these processes in removing NOM employing various analytical methods, namely liquid chromatography–organic carbon detector (LC–OCD) and three-dimensional fluorescence excitation emission matrix (3D-FEEM). In addition, the fouling potential of source water and treated water was assessed using a modified fouling index with ultrafiltration (MFI-UF). Biological stability was also tested using a modified assimilable organic carbon (AOC) detection method. The combination of MIEX, clarifier, coagulation, UF membrane, and GAC filtration resulted in dissolved organic carbon (DOC) being removed (from 6.01 to 0.47 mg/L). Furthermore 3D-FEEM analysis revealed that these treatment processes reduced humic and fulvic-like organics. AOC and MFI-UF decreased from 79.94 μg-C glucose equivalents/L and 46,350 s/L2 in the source water to 4.06 μg-C glucose equivalents/L and 2,057 s/L2 in the treated water, respectively.

In order to achieve high quality water reuse, a dual membrane hybrid system (combining microfiltration–granular activated carbon (MF–GAC)) adsorption hybrid system followed by nanofiltration (NF)) was used. This system׳s performance was evaluated in terms of organic matter, pharmaceuticals and personal care products (PPCPs), and removal of inorganic matter. Biologically treated sewage effluent (BTSE) collected from a water reclamation plant in Sydney, Australia was used as the water source. The removal efficiency of dissolved organic carbon (DOC) of MF–GAC strongly depends on the dose of GAC and filtration flux. MF–GAC system effectively removed hydrophobic organics (45–80%) as well as hydrophilic organics (50–80%). The removal of various PPCPs ranged from 33% to 92%, and as expected, the amount of inorganic matter removed by the MF–GAC system was very small. Hence, the NF system, as a second membrane system, was employed to polish the effluent from the MF–GAC hybrid system. The NF system rejected most of DOC (>95%), sulfates (99%) and a substantial amount of calcium (70%), and magnesium (60%) from MF–GAC effluent. Further, more than 90% of PPCPs were removed by the NF system. Overall the dual membrane hybrid system proved to be very effective in removing organics, PPCPs and inorganic matter. The MF–GAC followed by NF results in high quality water reuse and this system can serve as an effective treatment option for water reuse schemes.

The optimum conditions for the removal of leather tanning agent syntan from aqueous solution by Fenton oxidation at 22 °C for an initial syntan concentration of 500 mg/L were pH 3, and concentrations of H 2 O 2 and FeSO 4 of 300 mg/L and 500 mg/L, respectively. Fenton oxidation followed by granular activated carbon (GAC) adsorption in fixed-bed column resulted in more than 95% removal of dissolved organic carbon, compared to 55–70% removal by Fenton oxidation alone and GAC adsorption alone. The removal of individual organic fractions was also higher for the combined treatment compared to the Fenton oxidation alone.

© 2017, Springer-Verlag GmbH Germany. Heavy metals can be serious pollutants of natural water bodies causing health risks to humans and aquatic organisms. The purpose of this study was to investigate the removal of five heavy metals from water by adsorption onto an iron industry blast furnace slag waste (point of zero charge (PZC) pH 6.0; main constituents, Ca and Fe) and a coal industry fly ash waste (PZC 3.0; main constituents, Si and Al). Batch study revealed that rising pH increased the adsorption of all metals with an abrupt increase at pH 4.0–7.0. The Langmuir adsorption maximum for fly ash at pH 6.5 was 3.4–5.1 mg/g with the adsorption capacity for the metals being in the order Pb > Cu > Cd, Zn, Cr. The corresponding values for furnace slag were 4.3 to 5.2 mg/g, and the order of adsorption capacities was Pb, Cu, Cd > Cr > Zn. Fixed-bed column study on furnace slag/sand mixture (1:1 w/w) revealed that the adsorption capacities were generally less in the mixed metal system (1.1–2.1 mg/g) than in the single metal system (3.4–3.5 mg/g). The data for both systems fitted well to the Thomas model, with the adsorption capacity being the highest for Pb and Cu in the single metal system and Pb and Cd in the mixed metal system. Our study showed that fly ash and blast furnace slag are effective low-cost adsorbents for the simultaneous removal of Pb, Cu, Cd, Cr and Zn from water.

As with other water treatment systems, arsenic treatment creates not only quality water but arsenic waste as well. Management of arsenic waste is now becoming a major public concern due to its harmful effects on the surrounding environment, including serious health problems such as skin cancers and various internal carcinomas. The main aim of this paper is to review: (i) the characteristics of arsenic waste produced by arsenic treatment systems; and (ii) the treatment and disposal methods of this waste. Arsenic waste type or its characteristics play an important role in choosing the best method of treatment and disposal. Currently, encapsulation of arsenic waste through solidification/stabilization (S/S) techniques is considered to be the most attractive solution and this method is the focus of this review. A number of studies have used cement by itself and in combination with additives such as lime, iron, silicates, or fly ash in the S/S process. Although there is a lack of systematic investigations and differing procedures for testing the effectiveness of the treatment methods, it was agreed that incorporating additives could increase the effectiveness of the S/S process depending on the type and dose of additives.

The performance of ion exchanger Purolite A502PS in treating biologically treated sewage effluent (Reverse Osmosis feed) was evaluated in a submerged membrane ion exchange hybrid system (SMIHS). The experimental results showed that adding a small amount of Purolite A502PS of 0.5 g/L increased the organic removal of the submerged membrane reactor from less than 10% to above 40%. The homogeneous surface diffusion model (HSDM) could predict the adsorption kinetics of Purolite A502PS. A higher dose of Purolite A502PS in SMIHS led to better organic removal as well as reduced membrane resistance. After one hour of operation at a flux of 36 LMH, the amount of organic matter retained on the membrane surface decreased from 2.11E-9 kg/m2 s to 8.25E-10 kg/m 2 s when 1 g/L of Purolite A502PS was added into the submerged membrane reactor. Although the increase of membrane flux from 36 L/m2 h (LMH) to 60 LMH did not have much effect on organic removal, more organics were adsorbed onto the membrane surface. This led to a higher transmembrane pressure (TMP) of 12 kPa in the SMIHS after eight hours operation at a flux 60 LMH. The increase in TMP was approximately four times higher than that at a flux of 36 LMH.© 2013 Elsevier B.V. All rights reserved.

High polyacrylamide (polymer) demand for conditioning of sludge, especially anaerobically digested sludge (ADS), is a major issue for the water industry. Currently, this problem is being investigated and the reasons for doing so are varied. It has been demonstrated that excess amounts of soluble extracellular polymeric substances (EPS) can lead to high polymer demand for conditioning. This study developed a simple and unique yet effective method for quantifying the contribution of soluble EPS to conditioning polymer demand. It did this by measuring absorbance at 191.5 nm wavelength of the supernatant derived from conditioned ADS. Experimental results confirmed that approximately 87 wt% of soluble EPS interacted with polyacrylamides during the conditioning process. Furthermore, they revealed that a specified amount of soluble EPS could not be removed by polymer flocculation despite high polymer dosage. This study concluded that about 86 wt% of the polyacrylamide used for conditioning was consumed solely by soluble EPS. These results confirm the important role of reducing this EPS fraction in ADS in order to curtail significant chemical costs for sludge conditioning and dewatering.