The complexation of protons, aluminium and calcium by aquatic humic substances: A model incorporating binding-site heterogeneity and macroionic effects

A model is presented that describes the competitive binding of protons and metal ions (Al³⁺, AlOH²⁺, Ca²⁺) by humic substances (HS) in the pH range 3–6 and at different ionic strengths, and allows the net humic charge to be calculated. The HS are treated in terms of two types of carboxyl group, together with other more weakly-acidic groups, and the influence of humic (macroionic) charge is taken into account. Eight parameters are involved: total humic acidity, which can be measured directly, content of COOH groups, 4 intrinsic equilibrium constants (2 for H⁺ binding, 2 for metal binding), and 2 parameters accounting for charge effects at different ionic strengths. The model was applied to 4 aquatic humic samples, parameters being estimated from acid-base titration data. The equilibrium contents did not vary greatly among the humic samples, which is consistent with the idea that the functional groups in each sample are chemically the same. The effect of humic charge on complexation varies considerably among the samples. The model was reasonably successful at predicting humic-bound Al in laboratory-prepared solutions and field samples. Calculations based on the model suggest that, (1) Ca²⁺ does not compete significantly with Al for binding to HS under natural acid conditions, and (2) that there is a direct relationship between humic solubility and net humic charge.     

混凝和活性炭联用对有机物质的去除效果

研究了混凝和粉末活性炭对水中腐殖酸和苯酚的去除效果,选用聚合氯化铝作为混凝剂和粉末活性炭分别和联合使用时对水中腐殖酸和苯酚的去除效果进行了考察,结果表明：单独使用聚合氯化铝对苯酚的去除效果不佳,先投加活性炭后投加聚合氯化铝比两种同时投加时效果更好。     

Testing and validation of a multiple nonlinear regression model for predicting trihalomethane formation potential

This paper summarizes a testing and validation analysis of a previously developed model for predicting trihalomethane formation potential (THMFP) in chlorinated waters containing THM precursors. The original model, in the form of a nonlinear multiple regression equation, tended to overpredict THM formation potential at lower chlorine concentrations and underpredict at higher chlorine concentrations. The model proved to be more accurate in simulating THM formation potential in waters with moderate levels of organic carbon/THM precursors. While the model did not provide a high degree of predictive accuracy, the general format of the nonlinear model represents a rational framework for developing source specific models applicable to a given water source.     

Isolation of dissolved organic matter from the suwannee river using reverse osmosis

A portable reverse osmosis (RO) system was constructed and used to concentrate dissolved organic matter (DOM) from the Suwannee River in southeastern Georgia. Using this RO system, 150–180 1/h of river water could be processed with 90% recovery of DOM. After further cation exchange and lyophilization of the concentrated river water samples, large quantities of low-ash freeze-dried products were isolated. We highly recommend this RO method for concentration of DOM in fresh waters because (1) a very high percentage of DOM is recovered, which indicates minimal fractionation of the original sample; and (2) the process is quite rapid, which permits large quantities of DOM to be concentrated in a reasonable length of time.     

腐殖酸特性及其对三卤甲烷形成的影响

以提取腐殖酸和商品腐殖酸为对象,研究了不同腐殖酸对加氯消毒后三卤甲烷生成量的影响,并对腐殖酸特性进行了分析。结果表明,伊春腐殖酸比松花江腐殖酸和商品腐殖酸具有更高的三卤甲烷生成量、生成速度和更高的卤代活性。松花江腐殖酸和商品腐殖酸中的芳香结构、不饱和双键的分子较少,分子质量较大,而伊春腐殖酸中芳香结构和不饱和双键的分子较多,分子质量较低。小分子质量和含不饱和双键的有机物通常是消毒副产物的主要前体物,因而伊春腐殖酸加氯消毒后的三卤甲烷生成量比松花江腐殖酸和商品腐殖酸高。     

Chemical aspects of coagulation using aluminum salts—II. coagulation of fulvic acid using alum and polyaluminum chloride

This is the second of a two-part series investigating chemical aspects of coagulation using AI salts. Part I of the series examined the hydrolytic reactions of AI. In this paper, the coagulation of fulvic acid (FA) by alum and polyaluminum chloride (PACI) is examined. An Al speciation methodology was used to examine complexation reactions between Al and FA for water treatment conditions. From pH 5 to 7 and at typical coagulant doses, hydrolysis and complexation of Al is described by a simple model based on the reaction stoichiometry between AI, FA and OH⁻. Model results show that when alum is used as a coagulant, Al complexed with FA is hydrolyzed to a ligand number, This is similar to the ligand number for the prehydrolyzed PACI and explains similarities in dose requirements for these coagulants. Effects of temperature on coagulation performance are shown to be largely chemical in nature. Chemical aspects of coagulation are discussed and the importance of complex formation in coagulation is examined.     

Optimising natural organic matter removal from low turbidity waters by controlled pH adjustment of aluminium coagulation

Effective removal of soluble natural organic matter (NOM) from low-turbidity waters can be achieved by aluminium coagulation provided due attention is paid to micro-floc formation (coagulation) and macro-floc development (flocculation). This work provides guidelines and an explanation of how pH should be controlled to maximise soluble NOM removal while at the same time making full use of pH-influencing chemicals (acid, alum, and lime). For low-turbidity waters, essential floc nucleating sites can be provided by the lime that is used for pH and alkalinity adjustment, provided that the lime is added in sufficient quantity and at a point where it retains some of its particulate nature, i.e. immediately after coagulant addition. Adjusting the pH downwards to between 4 and 5 prior to coagulant addition allows the formation of soluble NOM-aluminium complexes that link to each other, thereby forming large insoluble bridged complexes (micro-flocs), that also act as nuclei for macro-floc development (flocculation).     

Fractionation of dissolved organic matter from surface waters using macroporous resins

To obtain fractions enriched with biodegradable dissolved organic carbon (BDOC) or with organic compounds responsible for the chlorine demand (CID) and for trihalomethane formation potential (THMFP), Seine river water samples were percolated on various macroporous resins (anionic, cationic and non-ionic) and compared with granulated activated carbon (GAC). In addition, measurement of UV absorbance at 254 nm and the fluorescence index (λ_excitation 320 nm) had allowed to follow up the retention of dissolved organic matter by the different adsorbants. In contrast to cationic and non-ionic resins, anionic resins confirm their excellent retention capacity of organic compounds responsible for UV 254 absorbance and fluorescence index. The relative values of BDOC/DOC ratio (mg-C/mg-C) are slightly increased in the effluents of anionic resins, indicating that they retain a little preferentially the refractory fraction instead of the biodegradable fraction. There is no significant difference between the ratio of CID/DOC (mg-Cl₂/mg-C) in influent and effluent of anionic resins. Cationic resin has a low capacity for retention of DOC, but they seem to retain significantly the organic compounds responsible for CID. The capability of anionic resins to retain THMFP is similar to that of GAC.     

Empirical rate equation for trihalomethane formation with chlorination of humic substances in water

Trihalomethane (THM) in drinking water is formed by chlorination of humic substances. In this study, the rates of THM formation in aqueous solution of humic acid were examined under various conditions. The following rate equation was obtained empirically. [THM] = k (pH − a)[TOC][Cl₂]₀^mtⁿ.

Here, [THM] is the concentration of total THM after t h, [TOC] and [Cl₂]₀ are the concentrations of total organic carbon and chlorine dose, k is the rate constant and a, m and n are parameters. The values of k, a, m and n for humic acid as reagent were obtained as 8.2 × 10⁻⁴ (l^mmg^−mh⁻ⁿ), 2.8, 0.25 and 0.36, respectively. The activation energy was obtained as 37 kJ mol⁻¹. Further, it was proved that the above equation could be applied to the rates of THM formation from precursors in actual river and lake waters.     

The effect of humic acids on the cytotoxicity of silver nanoparticles to a natural aquatic bacterial assemblage

The effect of a terrestrial humic acid (HA) and a river HA on the cytotoxicity of silver nanoparticles (AgNPs) to natural aquatic bacterial assemblages (0 μM, 2.5 μM and 5 μM) was measured with spread plate counting. The effect of HA (20 and 40 ppm) on the cytotoxicity of AgNPs ranging in size between 15 and 25 nm was tested in the presence and in the absence of natural sunlight. The experiment was a full factorial, completely randomized design and the results were analyzed using the General Linear Model in SAS. LSMEANS was used to separate the means or combinations of means. Significant main effects of all independent variables, plus interaction effects in all cases except HA/LI and HA/AgNPs/LI were observed. The toxicity of AgNPs to natural aquatic bacterial assemblages appears to be concentration dependent for concentrations between 0 μM and 5 μM. The data indicate that the light exposure inhibited viability more than the darkness exposure. The HA treatment groups in the presence of light showed greater reduced viability count compared to darkness exposure groups. The inhibition of bacterial viability counts by AgNPs exposure was less in the light treatment groups containing a terrestrial HA compared to that with a river HA. Difference in the extent of reactive oxygen species formation and adsorption/binding of AgNPs was speculated to account for the observed phenomenon.     

Determination of soluble aluminium concentration in alkaline humic water using atomic absorption spectrophotometry

The steps of the standard method to determine soluble aluminium concentration are filtering, followed by acidifying, then analysing with the atomic absorption spectrophotometer (AAS). When applied to alkaline humic water, acidification gives rise to the formation of humic acid as a brown particulate matter. Of the total soluble aluminium in the original water, 49-61% forms complexes with the particulate humic acid upon acidification. Although the AAS is capable of detecting the binding aluminium, the particulate nature of humic acid easily induces inaccurate readings as a result of the non-uniform distribution of the particulate matter. A more precise analysis of soluble aluminium concentration of alkaline humic water is shown to be achievable in basicified solutions instead. Basicified solutions keep humic acid in the soluble form; hence maintain the homogeneity of the sample.     

Effect of inorganic salts and adsorption in sephadex-gel chromatography of aquatic organic substances

Effect of inorganic salts in Sephadex-gel chromatography of aquatic organic substances were studied using Sephadex G-15 and samples of peatbog water, river water, and a secondary effluent. A substantial proportion of organic substances from all the water types showed a pH-dependent reversible adsorption affinity to the gel matrix. The presence of inorganic salts in the samples before fractionation can manifest itself in entirely misleading results of the separation of organic substances according to their molecular weights, as it causes the formation of peaks of organic substances. These peaks appear due to the changes in pH within the gel column during elution of inorganic salts and contain molecules of similar adsorptive and dissociative properties rather than those of similar molecular weights. The use of Sephadex-gel chromatography for the correct determination of molecular weight distribution of aquatic organic substances is briefly discussed.     

Organics isolation from fresh and drinking waters by macroporous anion-exchange resins

A research on the isolation of organic pollutants from water is presented. Five macroporous anionic resins: Varion AT400, Asmit 229N, Zerolite 553N, Wofatite EA60 and Amberlite IR93 were used for humic substances and other anionic organics isolation. Varion AT400 resulted to be the best anionic resin (about 90% recovery of humic substances and a lower recovery for other anionic substances). Nearly complete desorption was achieved by NaCl/NaOH 10%/2% solution, at a volume of about 3.5 times the resin bed volume.     

Binding of organic solutes to dissolved humic substances and its effects on adsorption and transport in the aquatic environment

Humic substances constitute a major fraction of dissolved organic matter in natural water and effluents. Their effect on the adsorption of organic contaminants to aquifer material was elucidated, and a model was proposed for the adsorption of organic solutes to aquifer solids in the presence of dissolved humic substances. The model is based on the assumption that organic solute binds to dissolved humic substances in a reversible manner to form a solute-humate complex. Following binding, both free and bound fractions of the organic solute are independently adsorbed onto the solid phase. In order to evaluate the validity of the model, the following parameters were determined: (1) the adsorption coefficient of the organic solute to clay; (2) the binding constant of the solute-humate complex; and (3) the adsorption of humic acid (HA) to clay, assuming that the solute-humate complex is adsorbed similarly to humic acid itself. Using these parameters in the model enabled the effect of dissolved humic substances on adsorption to be evaluated. Experimental results obtained for the adsorption of fluoranthene (a model compound of the PAH group) to clay in the presence of dissolved HA were compared with calculated values derived from the model described above. The sensitivity of the model to various parameters was evaluated and a prediction was made with respect to the effect of dissolved humic substances on the adsorption of a variety of organic solutes. It appears that dissolved humic substances solubilize organic solutes which have higher adsorption coefficients to clay than humic substances, but increase the adsorption of solutes having lower adsorption coefficients relative to humic substances.     

聚硅酸铁混凝剂对腐殖酸的氧化性能研究

以水玻璃、硫酸亚铁及氯酸钠为原料，采用独特共聚工艺制备了聚硅酸铁（PSF）混凝剂，考察了PSF对腐殖酸（HA）的氧化性能及高岭土对被氧化HA的吸附效果，同时进行了复合铝铁（PFA）的对比试验。结果表明，PSF是一种具有氧化性能的混凝剂，因其改变了HA的分子结构，从而使HA的表面性质以及HA／水溶液的界面性质发生变化，使亲水性HA转化为憎水性HA,导致高岭土对其吸附性能增强；不同pH值下PSF均有良好的氧化性能，而PFA仅在酸性时具有氧化性；pH值对HA、PSF、高岭土之间的络合模式具有较大影响，中性下时DOMs的去除效果较好。