[Adsorption of Methylene Blue and Cu(â ¡) by Activated Carbon/Macromolecule Composite Hydrogel].

Activated carbon/alginate/poly(vinyl alcohol) composite macromolecule hydrogels (CAP) were prepared as adsorbents to study their adsorption performance for methylene blue (MB) and Cu2+ in aqueous solution. The effect of dosage, pH, temperature, contact time, and initial concentrations of MB and Cu2+ on the adsorption process was investigated. SEM, FTIR, and BET analyses were conducted to identify the physicochemical properties of CAP. The results indicated that activated carbon was successfully loaded into the interconnected 3D porous network and CAP had rich -COOH and -OH groups. The surface area of the composite hydrogel was 112.7 m2·g-1. With the dosage and temperature increase, the adsorbed amount of MB and Cu2+ on CAP decreased, while with the increase in pH, the adsorbed amount increased. The adsorption isotherm was fitted to the Langmuir equation and the maximum monolayer adsorption capacities of MB and Cu2+ on CAP were 1940.75 and 190.48 mg·g-1, respectively. The adsorption was a fast process and 90% of the maximum adsorption capacity could be reached in 5 h. The kinetic data were fitted to the pseudo-second-order kinetic model reasonably well. CAP had excellent adsorption properties after five times of regeneration.

[Treating Simulated Dye Wastewater by an In Situ Copper Ferrite Process].

Four types of simulated dye wastewater containing methylene blue, tartrazine, Congo red, and crystal violet were treated by an in situ copper ferrite process, and the influencing factors of the operational parameters in this process were studied. The main mechanism of dye removal was suggested by reaction thermodynamics and solid products characterization for methylene blue removal. The results showed that an in situ copper ferrite process could effectively remove four kinds of simulated dyes by adjusting reaction conditions appropriately. The maximum capacities of the in situ copper ferrite process for methylene blue, crystal violet, tartrazine, and Congo red were 349.2, 382.2, 402.5 and 831.8 mg·g-1, respectively, under reaction condition of c(Cu2+) of 0.01 mol·L-1, c(Fe2+) of 0.025 mol·L-1, c(OH)/c(M)=1.7 (hydroxyl and metal molar ratio), reaction temperature of 40℃, and reaction time of 60 min. Comprehensive physical interactions, including a sweeping effect, encapsulation, and high active surface adsorption of the in situ Fe-Cu precipitates were the dominant mechanisms in dye removal by the process. Copper ferrite, as an effective magnetic adsorbent and a highly efficient environmental catalyst, was regenerated by magnetic separation, catalytic oxidation, and high temperature calcination.

[Relative Importance of Factors Influencing Iron Release in Drinking Water Distribution Systems].

Iron release in drinking water distribution systems (DWDSs) has attracted significant attention in recent years. There are many factors influencing iron release in DWDSs. In this study, we select pH, dissolved oxygen (DO), alkalinity (Alk), hardness, chloride (Cl-), sulfate (SO42-), temperature (T), and hydraulic retention time (HRT) as factors to investigate. Stepwise regression and partial correlation analysis are used as methods for establishing nonlinear power exponent iron release models and determining the relative importance of these factors by comparing standardized regression coefficients and partial correlation coefficients. The results show that the iron release models fit well. The important factors are SO42-, HRT, Cl-, and T, and the relative importance of the effect of the factors on iron release is SO42-≈HRT > Cl- > T, when measured by standardized regression coefficients; whereas, the important factors are HRT, SO42-, Alk, Cl-, and T, and the order of importance is HRT > SO42- > Alk > Cl- > T, when measured by partial correlation coefficients. Combining these two results, we conclude HRT, SO42-, and Cl- are the most important factors affecting iron release in pipes for the conditions in this study. The relative importance of T and Alk changes depending on the actual situation.

[Effect of Polysilicic Acid on the Deposition Behavior of Different Aluminum Species].

To understand the water quality problems caused by deposition and re-dissolution behaviors of residual aluminum in drinking water distribution system (DWDS), the effect of polysilicic acid on the deposition and re-dissolution behaviors of different aluminum species was investigated by using jar tests and quartz crystal microbalance, which could demonstrate the deposition behavior of different aluminum species and the physic-chemical properties of deposited layers. The results showed that the effect of polysilicic acid on the deposition behavior of different aluminum species was significant. Al0 (mainly monomeric species), Al13 and Al30 (polymeric species) could react rapidly with polysilicic acid, and some insoluble products formed. However, the stability of insoluble products from different aluminum species was distinct. The insoluble product formed by reaction of Al0 with polysilicic was relatively stable. With regard to the systems of polysilicic acid with Al13 and Al30, the dissolved aluminum concentration increased with reaction time, which indicated that the deposited product could be gradually transformed to soluble monomeric or oligomeric aluminum species. Compared with the influence of Al/Si ratio on Al0, the ratio of aluminum to silicon significantly affected the deposition and re-dissolution behavior of Al13 and Al30, and the re-dissolution rate of insoluble aluminum was the most rapid when the ratio of aluminum with silica was 0.2:20 (as mass ratio of Al to SiO2).

[Effect of the change in sulphate and dissolved oxygen mass concentration on metal release in old cast iron distribution pipes].

To understand the processes of corrosion by-product release and the consequent "red water" problems caused by the variation of water chemical composition in drinking water distribution system, the effect of sulphate and dissolved oxygen (DO) concentration on total iron release in corroded old iron pipe sections historically transporting groundwater was investigated in laboratory using small-scale pipe section reactors. The release behaviors of some low-level metals, such as Mn, As, Cr, Cu, Zn and Ni, in the process of iron release were also monitored. The results showed that the total iron and Mn release increased significantly with the increase of sulphate concentration, and apparent red water occurred when sulphate concentration was above 400 mg x L(-1). With the increase of sulfate concentration, the effluent concentrations of As, Cr, Cu, Zn and Ni also increased obviously, however, the effluent concentrations of these metals were lower than the influent concentrations under most circumstances, which indicated that adsorption of these metals by pipe corrosion scales occurred. Increasing DO within a certain range could significantly inhibit the iron release.

[Comparative study on adsorption behaviors of natural organic matter by powered activated carbons with different particle sizes].

The effect of powered activated carbon (PAC) particle size in the range of 10-100 microm on the adsorption of natural organic matter (NOM) in micro-polluted water was investigated, and the adsorption fractionation characteristics in terms of relative molecular mass distribution changes were evaluated. Three PACs with different median particle diameters were obtained through grinding and sieving of a commercial PAC product: PAC-1 (19 microm), PAC-2 (46 microm), and PAC-3 (76 microm). The adsorption results showed that with the decrease of particle size, the adsorption properties (both adsorption capacity and adsorption rate) of PAC for NOM in both simulated and real micro-polluted water were significantly enhanced. The faster adsorption rate of PAC with smaller particles was attributed to its more available adsorption sites and shorter diffusion distance for adsorbate molecules. The larger adsorption capacity of smaller particle PACs was mainly due to their greater specific external surface area per unit mass and higher mesopore volume, as the pore blockage effect from large relative molecular mass NOM was alleviated. For micro-polluted water sample, the decrease of PAC particle size significantly enhanced the adsorption of organic matter fractions with relative molecular mass > 2 000, but had no notable improvement for that with relative molecular mass < 800.

[Adsorption of perfluorooctanesulfonate (PFOS) onto modified activated carbons].

Modified coal and coconut shell based powdered activated carbons (PACs) were prepared by FeCl3 and medium power microwave treatment, respectively. Batch experiments were carried out to evaluate the characteristics of adsorption equilibrium and kinetics of perfluorooctanesulfonate (PFOS) onto original and modified PACs. Based on pore structure and surface functional groups characterization, the adsorption behaviors of modified and original PACs were compared. The competitive adsorption of humic acid (HA) and PFOS on original and modified coconut shell PACs were also investigated. Results showed that both Fe3+ and medium power microwave treatments changed the pore structure and surface functional groups of coal and coconut shell PACs, but the changing effects were different. The adsorption of PFOS on two modified coconut shell-based PACs was significantly improved. While the adsorption of modified coal-based activated carbons declined. The adsorption kinetics of PFOS onto original and modified coconut shell-based activated carbons were the same, and the time of reaching adsorption equilibrium was about 6 hours. In the presence of HA, the adsorption of PFOS by modified PAC was reduced but still higher than that of the original.

[Effect of physico-chemical characteristics of activated carbon on the adsorption of organic pollutants in natural water].

In this paper, the adsorption characteristics of two synthetic organic compounds (SOCs), i. e., methyl parathion(MP) and trichloroethylene (TCE), and natural organic matter (NOM) on powdered activated carbons (PAC) in natural water were studied. On the basis of fully characterizing the physical and chemical characteristics of PAC, the effect of physical and chemical properties of PAC on the adsorption of low molecular weight SOCs in natural water was studied by correlation analysis. The effect of molecular weight fractionation on the adsorption of NOM on PAC was investigated using high performance size exclusion chromatography (HPSEC). It was found that, compared to the surface chemistry, the physical property (pore properties) of PAC was the critical factor to determine its adsorption capacity of MP and TCE in natural water. The adsorption of the low molecular weight SOC and NOM with apparent molecular weight (AMW) < 500 on PAC was primarily impacted by the micropore surface area, and that of NOM with 500 < AMW < 3 000 was affected by the mesopore surface area combined with the mesopore size distribution.

[Sorption of atrazine onto nano-SiO2 and nano-kaolin particles].

With the widespread application of nano-materials, more and more attentions are paid to the potential environmental effects of the nano-materials and their roles in the transport and transformation processes of organic pollutants. The sorption behaviors of atrazine onto nano-SiO2 and nano-kaolin were studied using a batch equilibration method, and the influences of ionic strength, sorbents concentration and pH were also investigated. The results showed that the sorption of atrazine onto nano-SiO2 and nano-kaolin decreased with the increase of ionic strength. Freundlich coefficient (Kf) of nano-SiO2 and nano-kaolin decreased from 25.55 to 18.35 and from 85.85 to 20.57 respectively when ionic strength increased from 0.001 mol x L(-1) to 0.1 mol x L(-1). The variation in concentration of nano-SiO2 had no significant influence on the sorption of atrazine. However, Kf decreased from 71.55 to 37.22 when the concentration of nano-kaolin increased from 5 g x L(-1) to 20 g x L(-1). With the increase of pH, the sorption of atrazine onto the two nano-particles decreased obviously, which indicated the speciation change of atrazine was the dominant factor controlling its sorption processes on two nanoparticles.

Seasonal variations of chemical and physical characteristics of dissolved organic matter and trihalomethane precursors in a reservoir: a case study.

Dissolved organic matter (DOM) and its potential to form disinfection by-products (DBPs) during water treatment are of great public health concern. Understanding the seasonal changes in DOM composition and their reactivity in DBP formation could lead to a better treatment of drinking water and a more consistent water quality. DOM from the East-Lake, a reservoir in the south-China, was fractionated and characterized by XAD resin adsorption (RA) and ultrafiltration (UF) techniques during different seasons within a year. The properties of chemical fractions (isolated by RA) appeared more stable than those of physical fractions (separated by UF) throughout the sampling period. The relative contribution of each chemical fraction to the total dissolved organic carbon (DOC), UV(254) absorbance and trihalomethane formation potential (THMFP) remained relatively constant across the sampling period. However, the physical (molecular weight) fractions of the DOM exhibited large seasonal changes in UV(254) and THMFP. Compared to the parameter of DOC, the THMFP and specific THMFP (STHMFP) of either chemical or physical fractions were more variable. In terms of DOC concentration, the hydrophobic acids (HoA) and hydrophilic matter (HiM) dominated in the DOM in most of the seasons; while the components with molecular weight of 10-30 kDa and less than 1 kDa were the predominant physical fractions.

Transformations of particles, metal elements and natural organic matter in different water treatment processes.

Characterizing natural organic matter (NOM), particles and elements in different water treatment processes can give a useful information to optimize water treatment operations. In this article, transformations of particles, metal elements and NOM in a pilot-scale water treatment plant were investigated by laser light granularity system, particle counter, glass-fiber membrane filtration, inductively coupled plasma-optical emission spectroscopy, ultra filtration and resin absorbents fractionation. The results showed that particles, NOM and trihalomethane formation precursors were removed synergistically by sequential treatment of different processes. Pre-ozonation markedly changed the polarity and molecular weight of NOM, and it could be conducive to the following coagulation process through destabilizing particles and colloids; mid-ozonation enhanced the subsequent granular activated carbon (GAC) filtration process by decreasing molecular weight of organic matters. Coagulation-flotation and GAC were more efficient in removing fixed suspended solids and larger particles; while sand-filtration was more efficient in removing volatile suspended solids and smaller particles. Flotation performed better than sedimentation in terms of particle and NOM removal. The type of coagulant could greatly affect the performance of coagulation-flotation. Pre-hydrolyzed composite coagulant (HPAC) was superior to FeCl3 concerning the removals of hydrophobic dissolved organic carbon and volatile suspended solids. The leakages of flocs from sand-filtration and microorganisms from GAC should be mitigated to ensure the reliability of the whole treatment system.

[Separation and purification of Al13 by chemical precipitation and metathesis].

PACls with different concentrations were prepared by adding sodium carbonate powder into AlCl13 solution. Medium concentration and high Al13 content of PACl was chosen to carry out Al13 separation processes. The influences of SO4/Al molar ratio and the initial total Al concentration on the precipitation reactions of sulfate with different Al species were investigated. The factors influencing the metathesis reaction between solid Al13-SO4 and Ba(NO3)2 were evaluated. Results showed that high Al13 PACl could be obtained at the medium high concentration range of 0.4 - 0.6 mol/L, the optimum SO4/Al ratio was 0.6:1 for precipitation- separation of Al13, Al13 -SO4 precipitates were mostly consisted of tetrahedral crystals. During the metathesis reaction, Ba/SO4 molar ratio of 1:1 is the optimal value. Small range temperature variation and ultrasonic action had no marked influence on metathesis reaction rate and final Al13 concentration. Higher initial Ba(NO3)2 concentration could produce higher concentration Al13 accordingly. The purity of Al13 solution could be reached to 92.1% statistically.

Effects of pre-ozonation on organic matter removal by coagulation with IPF-PACl.

Ozone plays an important role as a disinfectant and oxidant in potable water treatment practice and is increasingly being used as a pre-oxidant before coagulation. The purpose of this study is to obtain insight into the mechanisms that are operative in pre-ozonized coagulation. Effects ofpre-ozonation on organic matter removal during coagulation with IPF-PACl were investigated by using PDA (photometric disperse analysis), apparent molecular weight distribution and chemical fractionation. The dynamic formation of flocs during coagulation process was detected. Changes of aquatic organic matter (AOM) structure resulted from the influence of pre-ozonation were evaluated. Results show that dosage of O3 and characteristics of AOM are two of the major factors influencing the performance of O3 on coagulation. No significant coagulation-aid effect of O3 was observed for all experiments using either AlCl3 or PACl. On the contrary, with the application of pre-ozonation, the coagulation efficiency of AlCl3 was significantly deteriorated, reflected by the retardation of floc formation, and the removal decreases of turbidity, DOC, and UV254. However, if PACl was used instead of AlCl3, the adverse effects of pre-ozonation were mitigated obviously, particularly when the O3 dosage was less than 0.69 (mg O3/mg TOC). The difference between removals of UV254 and DOC indicated that pre-ozonation greatly changed the molecular structure of AOM, but its capability of mineralization was not remarkable. Only 5% or so DOC was removed by pre-ozonation at 0.6-0.8 mg/L alone. Fractionation results showed that the organic products of pre-ozonation exhibited lower molecular weight and more hydrophilicity, which impaired the removal of DOC in the following coagulation process.