Effects of pre-oxidation on residual dissolved aluminum in coagulated water: A pilot-scale study.

Residual dissolved aluminum (Al) in drinking water is becoming a serious concern due to its high potential risks to human health. However, the mechanism by which residual dissolved Al forms is yet to be elucidated in detail. In this study, the effects of pre-oxidation by ozonation and chlorination on the properties of dissolved organic matter (DOM) and residual Al concentrations remaining in solution after coagulation were explored in a pilot-scale test. Changes in the DOM properties caused by the water treatment process were characterized by ultraviolet-visible absorbance spectroscopy. Theprotonation-active sites, carboxylic- and phenolic-type groupsof DOM were quantified by spectral parameter DlnA400 (differential log-transformed spectra at wavelength 400 nm) in combination with the revised non-ideal competitive adsorption model. The results show that ozonation and chlorination significantly affect the properties of DOM and the amount of residual dissolved Al in coagulated drinking water. This effect was associated with the changes in the carboxylic- and phenolic-type groups in DOM. Results of the study show that residual dissolved Al in coagulated water can be controlled by affecting theAl binding sites in DOM by pre-oxidation before coagulation. The nature of pre-oxidation agent and its dosage should be selected depending on the quality of the raw water to be treated. Ozonation was concluded to be preferable pre-oxidation agent for the water in examined this study.

Competition between Al(III) and Fe(III) for binding onto natural organic matter: In situ monitoring by UV-Vis absorbance spectroscopy.

The ubiquitous presence of natural organic matter (NOM) in the aquatic and soil environment significantly affects the transport, fate and bioavailability of Al and Fe elements, NOM itself and other trace metals. In this study, the binding of Al(III) and Fe(III) and their competition for binding onto NOM at varying pH values were monitored in situ via UV-Vis absorbance spectroscopy. It demonstrated that the spectral parameter, e.g., the differential log-transformed absorbance at 400 nm (ΔLnA400), can quantify the amount of Al(III) and/or Fe(III) bound onto NOM in all examined cases and will show similar molar extinction coefficients that correspond to the amount of bound Al(III) and Fe(III). Therefore, this approach can not only demonstrate visibly the competition between Al(III) and Fe(III) based on their metal-specific features by evaluating differential absorbance spectra produced by metal binding but can also monitor the reaction kinetics of Al(III) and Fe(III) and their competition for binding onto NOM. To our knowledge, this study is the first to in situ monitor the competition between Al(III) and Fe(III) for binding with NOM quantitatively and at realistic environmental concentrations of both metal ions and NOM.

Influence of chlorination on metal binding by dissolved organic matter: a study using Log-transformed differential spectra.

This study employed the method of Log-transformed absorbance spectroscopy to probe interactions of Suwannee River fulvic acid (SRFA) and Aldrich humic acid (AHA) affected by chlorination with Fe(III), Al(III), and Cu(II) ions. Cl2/DOC ratios of 0.2 and 1.0 (mg/mg) were selected to represent chlorine doses that are commonly used in pre-chlorination and disinfection in water treatment processes. Spectroscopic data were interpreted based on non-ideal competitive adsorption coupled with a Donnan electrostatic sub-model (NICA-Donnan model) that was employed to quantify the constants describing relevant complexation equilibria. The data demonstrated that effects of chlorination on dissolved organic matter (DOM) and metal interactions depend on the metal, chlorine dose and intrinsic DOM properties. Fe(III) was observed to form strong complexes with DOM and relatively little change of Fe(III) binding were observed both SRFA and AHA affected by chlorine. The amount of bound Al(III) decreased significantly at high total Al(III) concentrations (>5µM) due to the reducing of phenolic groups after chlorination. The amount of bound Al(III) decreased only slightly for chlorinated SRFA but for AHA Al(III) binding increased at low total Al concentrations (<1µM) due to the generation of additional carboxylic groups after chlorination. It is different from Fe(III) and Al(III), the dominant involvement of Cu-DOM binding is carboxylic groups in both fulvic and humic acid, especially for humic acid, the increase of carboxylic group after chlorination for SRFA at low Cl2 dose and for AHA at both low and high dose lead to increase the total amount of bound Cu(II).

Investigation of the adsorption characteristics of natural organic matter from typical Chinese surface waters onto alumina using quartz crystal microbalance with dissipation.

The adsorption of natural organic matter (NOM) from eight typical Chinese surface waters onto alumina was investigated using quartz crystal microbalance with dissipation monitoring (QCM-D). The adsorbed masses of NOM varied between 25ngcm(-2) and 64ngcm(-2), and these showed significant correlation with geographical location, and NOM character and concentrations. Adsorbed mass correlated with DOC concentration (slope k=0.0676, R(2)=0.61) and hydrophobic acid (HoA) and weakly hydrophobic acid (WHoA) (k=0.0342 and 0.0183; R(2)=0.49 and 0.52 for HoA and WHoA, respectively) constituents present in the water samples. The process of adsorbed layer formation was investigated from changes in the ΔD/Δf ratio and viscosity of adsorbed layer with injected time. The adsorbed layer viscosity increased exponentially with injected time (R(2)>0.99) for most samples. Samples with low DOC concentration (k=-1091.8, R(2)=0.55) and low content of HoA and WHoA (k=-524.33 and -322.76; R(2)=0.41 and 0.64 for HoA and WHoA, respectively), the slope of logarithm viscosity value is steeper, the property of adsorbed layer and NOM is more inconsistent. The QCM-D technique provides a method to view the process of complexation between NOM and coagulant, and can provide useful information to establish a quantitative calculation model of the coagulation process.

Characterization of adsorption of humic acid onto alumina using quartz crystal microbalance with dissipation.

In this paper, a quartz crystal microbalance with dissipation monitoring (QCM-D) is used to investigate humic acid (HA) adsorption onto alumina (Al(2)O(3)). The amount of adsorption and layer structures of HA were determined by the real-time monitoring of resonance frequency and energy dissipation changes (Δf and ΔD). The effect of HA concentration, HA molecular characteristics (molecular weight and polarity), and pH on HA adsorption onto Al(2)O(3) were investigated. The mass of HA adsorption increases as the concentration of HA increases. The masses are about 24, 60, and 87 ng cm(-2) as the concentration of DOC is 1.0, 4.85, and 92.0 mg L(-1), respectively. The adsorbed layer of HA is more nonrigid, and the mass of HA adsorption is higher at weakly acidic pH values. It was 20, 80, 65, and 45 ng cm(-2) at pH values of 4.5, 5.5, 6.5, and 8.0, respectively. This reveals that efficient HA removal by coagulation at weakly acidic pH values is not just due to the hydrolysis of Al ions as previously presumed. The adsorbed layer of hydrophobic HA is more nonrigid than hydrophobic HA (fractionated by Amberlite XAD-8 resin), and the mass adsorption for the hydrophobic fraction is about four times higher than the hydrophilic fraction (120 ng cm(-2) and 30 ng cm(-2)). The method is of value in the research to establish a quantified calculation model for the coagulation process.