Removing of fulvic acids by ozonation and biological active carbon filtration

It was studied the effect of the content of biodegradable organic carbon (BDOC) after the processes of aeration and ozonation of the fulvic acid (FA) solutions on the efficiency of its adsorption and biofiltration. It was found that the change of free energy of adsorption of the FA oxidation products correlated with the part of biodegradable organic carbon in total organic carbon content. Predicting the effectiveness of NOM solutions ozonation before filtration through BAC is more appropriate by determining the value of the free adsorption energy. It was established that ozonation of FA solutions with high initial BDOC content by ozone doses that are economically and technologically acceptable, leads to a decrease in the BDOC value. Ozonation of FA solutions leads to equalization of the adsorption ability of FA fractions and increases the adsorption energy of FA in most investigated systems with a high initial BDOC content.     

The impact of aromatic compounds on the efficiency of biofiltration through activated carbon

The article has investigated the sorption process on activated carbon of aromatic compounds with different functional groups (o- nitrophenol, o-aminophenol, aniline). We have showed the possibility of assessing the efficiency of biofiltration depending on such factors as the variation of the Gibbs free energy of adsorption of sorbates and the value of the specific load of an organic substance on activated carbon. For determining a contribution of the biological component to the total efficiency of the process we used the value of the ratio between the specific dynamic adsorption to the specific equilibrium adsorption at uniform loads in terms of the organic matter on biologically activated carbon.     

The effect of ozonation on natural organic matter removal by alum coagulation

Natural organic matter (NOM) was extracted from a moderately colored, eutrophic surface water source (Forge Pond, Granby, MA), and fractionated into quasi-homogeneous fractions. Fulvic acid (FA) and hydrophilic neutrals (HN) were the two most abundant NOM fractions that were isolated. Adsorption affinity of the isolated NOM fractions on preformed aluminum hydroxide flocs increased with increase in specific organic charge of the fractions, except for the two most highly charged fractions, FA and hydrophilic acids (HAA), which showed less adsorption affinity than expected based on their specific organic charge. Prior ozonation of FA and HN fractions resulted in a decline and an increase, respectively, in their adsorption affinity on aluminum hydroxide surface. Prior ozonation of Forge Pond raw water resulted in a progressive decline in dissolved organic carbon (DOC) removal by alum coagulation with increase in ozone dose. It appeared that ozone applied to raw water reacted preferentially with the humic fraction of NOM, resulting in the detrimental effects of ozonation on subsequent NOM removal by alum coagulation being magnified. Forge Pond raw water was pre-coagulated to remove humic substances. Ozonation of the pre-coagulated water demonstrated the beneficial effects of ozonation on the removal of non-humic NOM through alum coagulation. A strategy for staged coagulation with intermediate ozonation was proposed for waters containing both humic and non-humic NOM for maximum DOC and specific UV absorbance at 254nm (SUVA) removal.     

Influence of sodium azide on the removal of fulvic acids by activated carbon

The impact of sodium azide, as an inhibitor of biochemical reactions in aqueous solutions, on its interaction with activated carbon (AC) and on the characteristics of equilibrium adsorption of fulvic acids (FA) on AC has been studied. It was shown that additions of sodium azide during FA adsorption on AC under equilibrium conditions do not completely inhibit the biological activity in the system solution FA-AC. Sodium azide interacts with the AC surface changing the equilibrium adsorption characteristics of the system.     

Efficiency of activated carbon to transform ozone into *OH radicals: influence of operational parameters

Based on previous findings (Jans, U., Hoigné, J., 1998. Ozone Sci. Eng. 20, 67-87), the activity of activated carbon for the transformation of ozone into *OH radicals including the influence of operational parameters (carbon dose, ozone dose, carbon-type and carbon treatment time) was quantified. The ozone decomposition constant (k(D)) was increased by the presence of activated carbon in the system and depending on the type of activated carbon added, the ratio of the concentrations of *OH radicals and ozone, the R(ct) value ([*OH]/[O3]), was increased by a factor 3-5. The results obtained show that the surface chemical and textural characteristics of the activated carbon determines its activity for the transformation of ozone into *OH radicals. The most efficient carbons in this process are those with high basicity and large surface area. The obtained results show that the interaction between ozone and pyrrol groups present on the surface of activated carbon increase the concentration of O2*- radicals in the system, enhancing ozone transformation into *OH radicals. The activity of activated carbon decreases for extended ozone exposures. This may indicate that activated carbon does not really act as a catalyst but rather as a conventional initiator or promoter for the ozone transformation into *OH radicals. Ozonation of Lake Zurich water ([O3] = 1 mg/L) in presence of activated carbon (0.5 g/L) lead to an increase in the k(D) and R(ct) value by a factor of 10 and 39, respectively, thereby favouring the removal of ozone-resistant contaminants. Moreover, the presence of activated carbon during ozonation of Lake Zurich water led to a 40% reduction in the content of dissolved organic carbon during the first 60 min of treatment. The adsorption of low concentrations of dissolved organic matter (DOM) on activated carbon surfaces did not modify its capacity to initiate/promote ozone transformation into *OH radicals.     

The impact of preoxidation of SAS on biosorption efficiency on activated carbon

We have studied the process of a prolonged dynamic filtration on activated carbon in two biosorption systems — without preoxidation treatment of the initial matter and after ozonization. It has been shown that given the uniform load on activated carbon terms of the organic matter the efficiency of the biosorption process after preozonization is 2.3 times as small compared with that that without pretreatment, which correlates with the change of adsorption free energy.     

Investigation of microbially available phosphorus (MAP) in flemish drinking water

Several researchers have reported phosphorus growth limitations of heterotrophic bacteria instead of main energy source--organic carbon. Usually this phenomenon was noticed in waters with high organic carbon content, where phosphorus concentration was deficient to maintain the growth on level suggested by high organic carbon amount. We analysed the microbially available phosphorus (MAP) and assimilable organic carbon (AOC) in several drinking waters in Flanders, Belgium. Our aim was the investigation whether organic carbon or phosphorus is the restricting nutrient in specific water and determination of the impact of some treatment processes on MAP content. We obtained a wide range of MAP concentrations being from 0.3 to 15.2 microg P-PO(4)/l in finished drinking water. In a treatment unit applying ozone, MAP was found to be the nutrient that limits bacterial growth instead of organic carbon. Moreover, ozone caused slight MAP decrease. Granular activated carbon (GAC) filtration was able to diminish further the MAP content significantly but not below a certain level. The biofilm monitor supplied with the MAP-limited water resulted in significantly lower biofilm formation rate (BFR) value than the same installation fed with AOC-limited water.     

Mineralisation of coloured aqueous solutions by ozonation in the presence of activated carbon

The degradation of organic matter in coloured solutions of different classes of dyes by ozonation in the presence of activated carbon is investigated. The kinetics of the decolourisation and mineralisation of three different dyes solutions (CI Acid Blue 113, CI Reactive Red 241 and CI Basic Red 14) were studied in a laboratory scale reactor by three different processes: adsorption on activated carbon, oxidation with ozone and ozonation in the presence of activated carbon. The mineralisation of the solutions was followed by measuring the total organic carbon (TOC). Under the experimental conditions used in this work, activated carbon was not capable of completely removing the colour of the solutions in reasonable time. On the other hand, ozonation quickly decolourised all the solutions, but satisfactory removal of TOC was never achieved by this process. The combination of activated carbon with ozone enhanced the decolourisation of the solutions and especially the mineralisation of the organic matter. Activated carbon acts both as an adsorbent and as a catalyst in the reaction of ozonation. The surface chemistry of the activated carbon is an important parameter; it was observed that basic samples improve TOC removal. The main conclusions of this work were validated by treating a real textile effluent collected after the conventional biological treatment.     

The impact of surface chemistry of activated carbon and its structure on adsorption of fulvic acids from aqueous solutions

We have quantitatively assessed the impact of surface chemistry and the structure of activated carbon on adsorbability of fulvic acids from aqueous solutions. For assessing adsorption energy of different fractions of fulvic acids the method of “conditional component” was used. It has been shown that in the first approximation in the solution of fulvic acids one can separate weakly- and strongly adsorbing fractions. It has been found that the change of energy heterogeneity of the surface of activated carbon as a result of oxidation leads to the reduction of adsorption energy of fulvic acids and an increase of the concentration range of the conditional share of the weakly adsorbing fraction.     

The effect of water ozonation on the efficiency of extracting natural organic matter during filtration through biologically activated carbon

The effect of the varied content of biodegradable organic carbon (BDOC) in solutions of fulvic acids (FA) after the aeration and ozonation processes on the efficiency of adsorption and biofiltration of FA solutions through the activated carbon has been investigated. It has been found that the reduction of the BDOC fraction in FA solutions enhances the efficiency of their adsorption, but decreases the efficiency of biofiltration. It has been shown that the performance period of adsorption filter can be significantly extended for obtaining biologically stable drinking water by increasing the BDOC content in FA solutions at the expense of the intermediate ozonation after adsorption.     

活性炭在微污染水源水处理中的应用综述

介绍了活性炭在微污染水源水处理中的应用情况,包括活性炭吸附、生物活性炭、臭氧活性炭技术等的对水源中有机物的去除效果和工艺特点,指出活性炭对去除水中微量有机物污染方面是其他水处理单元难以取代的,在微污染水源水处理中有较广泛的应用.     

Identification and treatability of organics in oil shale retort water

Analysis by GC-MS of the process water derived from Fischer Assay retoring of oil shale from Rundle, Australia has provided positive identification of the major organic constituents present. This is the first detailed analysis of retort water from Australian oil shales and showed that the compounds ranged from being highly biodegradable to highly inhibitory and resistant to biological oxidation. The major classes of compounds found in a composited sample included normal carboxylic acids, alkyl pyridines, quinolines and cyclic saturated and unsaturated ketones. Separation of the retort water into its acid, base and neutral fractions was brought about by solvent extraction using methylene chloride. A series of treatability studies on the retort water confirmed the hypothesis that only a portion of the organic carbon was amenable to biological treatment. In addition, high ammonia levels further inhibited biological action. Adsorption of the retort water with activated carbon proved most successful in removing the non-biodegradable fraction of the organic species. Chemical oxidation by ozone does not appear attractive because it lacks the specificity of adsorption.     

Removal of aromatic compounds from water on biologically activated carbon

We have carried out an assessment of the content of aromatic compounds (o-nitrophenol, o-aminobenzoic acid) in grains of activated carbon of a biofilter at the stage of stationary water treatment. It was found that the removal degree of aromatic compounds by the biofilm of biologically activated carbon in great measure is determined by the value of the decreasing of Gibbs free energy of adsorption (−ΔG _a ). It is shown that due to the competing action of the biofilm part of the accessible surface of activated carbon is not used for adsorption of organic matter.     

臭氧多相催化氧化技术在水厂深度处理中的应用

通过生产性对比试验考察了臭氧催化氧化技术用于给水深度处理时对有机物的去除效能.结果表明,相对于单纯的臭氧氧化,臭氧催化氧化明显地提高了对TOC及微量有机物的去除率,并使水中的剩余臭氧浓度降低了0.2 mg/L,有效地抑制了溴酸盐的生成.该技术可明显降低后续处理工艺的污染物负荷,并使有机物在活性炭上的吸附性能提高了近一倍,与生物活性炭联用后,对有机物的综合去除能力提高了14%～24%.臭氧催化氧化及其联用技术在兼顾有机物去除与臭氧化副产物控制方面具有明显的优势.     

两种碳基材料对二级出水中有机物的去除特性

针对活性炭与活性焦两种碳基吸附材料,分别开展静态吸附与动态过滤实验,考察了两者对城镇再生水厂二级出水中有机物的去除效果。结果表明:活性焦介孔及大孔丰富,对应孔体积为0.436 cm³/g,为活性炭的1.6倍;准二级动力学模型更适用于两种材料对COD的吸附动力学拟合,活性焦动力学吸附速率常数k₂为活性炭的2倍;水温为22℃时,活性焦与活性炭对COD的Langmuir饱和吸附量分别为230.38、94.14 mg/g。在近4个月的连续运行中,活性焦滤柱对有机物的去除效果全程优于活性炭滤柱,尽管两滤柱在由单纯吸附向生物吸附降解转化的过程中对有机物的去除率有所降低,但对COD的去除率仍可分别稳定在28.43%和22.26%。活性焦颗粒与活性炭颗粒表面ATP含量最高分别为7032.94、5753.52 ng/g。此外,活性焦滤柱对1~10 ku有机物组分,以及腐殖酸类物质、溶解性微生物代谢产物等不同荧光特性有机物均有较好的去除效果。与活性炭相比,活性焦对再生水厂二级出水中有机物的去除效果更优。     

基于有机物分子质量分布的饮用水处理工艺选择

为应对市内运河排洪造成的出水有机物超标问题,建立了臭氧／活性炭中试装置,采用滤膜法测试了运河水、现有水厂各工艺段及臭氧／活性炭出水中有机物的分子质量分布,在此基础上对现有水处理工艺进行了评价。结果表明,由于原水受到工业污染,其大分子有机物含量较高,并且亲水性强而易被氧化,造成混凝沉淀的去除效果不好,而运河水中的溶解性小分子有机物含量较高,也不易被混凝沉淀去除,采用臭氧／活性炭深度处理工艺是一个很好的选择。臭氧和活性炭联用提高对有机物去除效果的原因在于,臭氧能有效地氧化大分子有机物为小分子有机物,有利于活性炭的吸附、降解去除。     

Analysis of selected trace organics in advanced wastewater treatment systems

Effluents through four different pilot tertiary wastewater treatment systems were monitored for selected trace organic compounds. The effects of using ozone, free and combined chlorine residuals in these systems were also studied. Advanced treatment of secondary effluent using various combinations of flocculation (alum and polymer), dual media filtration, and carbon adsorption were evaluated for production/removal of volatile halogenated organics, polynuclear aromatics, chlorinated pesticides, and polychlorinated biphenyls. Gas chromatographic methods were used for the analysis of these different classes of compounds: specific techniques and analytical parameters are described. Salient results included: drastic increases in trihalomethane production using free chlorine residuals: disinfection with combined chlorine species does not produce significant levels of trihalomethanes: approximately 90% reduction in trihalomethane levels by carbon adsorption: absence of detectable quantities of polynuclear aromatics: significant decreases in pesticide and PCB levels by carbon adsorption and chlorination. Statistical dependence of trihalomethane production on soluble COD, suspended solids and chloramine levels was evident from multiple linear regression calculations.     

Modeling high adsorption capacity and kinetics of organic macromolecules on super-powdered activated carbon

The capacity to adsorb natural organic matter (NOM) and polystyrene sulfonates (PSSs) on small particle-size activated carbon (super-powdered activated carbon, SPAC) is higher than that on larger particle-size activated carbon (powdered-activated carbon, PAC). Increased adsorption capacity is likely attributable to the larger external surface area because the NOM and PSS molecules do not completely penetrate the adsorbent particle; they preferentially adsorb near the outer surface of the particle. In this study, we propose a new isotherm equation, the Shell Adsorption Model (SAM), to explain the higher adsorption capacity on smaller adsorbent particles and to describe quantitatively adsorption isotherms of activated carbons of different particle sizes: PAC and SPAC. The SAM was verified with the experimental data of PSS adsorption kinetics as well as equilibrium. SAM successfully characterized PSS adsorption isotherm data for SPACs and PAC simultaneously with the same model parameters. When SAM was incorporated into an adsorption kinetic model, kinetic decay curves for PSSs adsorbing onto activated carbons of different particle sizes could be simultaneously described with a single kinetics parameter value. On the other hand, when SAM was not incorporated into such an adsorption kinetic model and instead isotherms were described by the Freundlich model, the kinetic decay curves were not well described. The success of the SAM further supports the adsorption mechanism of PSSs preferentially adsorbing near the outer surface of activated carbon particles.     

Ozonation effect on natural organic matter adsorption and biodegradation - Application to a membrane bioreactor containing activated carbon for drinking water production

More stringent legislation on dissolved organic matter (DOM) urges the drinking water industry to improve in DOM removal, especially when applied to water with high dissolved organic carbon (DOC) contents and low turbidity. To improve conventional processes currently used in drinking water treatment plants (DWTPs), the performances of a hybrid membrane bioreactor containing fluidised activated carbon were investigated at the DWTP of Rennes. Preliminary results showed that the residual DOC was the major part of the non-biodegradable fraction. In order to increase the global efficiency, an upstream oxidation step was added to the process. Ozone was chosen to break large molecules and increase their biodegradability. The first step consisted of carrying out lab-scale experiments in order to optimise the necessary ozone dose by measuring the process yield, in terms of biodegradable dissolved organic carbon (BDOC). Secondly, activated carbon adsorption of the DOC present in ozonated water was quantified. The whole process was tested in a pilot unit under field conditions at the DWTP of Rennes (France). Lab-scale experiments confirmed that ozonation increases the BDOC fraction, reduces the aromaticity of the DOC and produces small size organic compounds. Adsorption tests led to the conclusion that activated carbon unexpectedly removes BDOC first. Finally, the pilot unit results revealed an additional BDOC removal (from 0.10 to 0.15 mg L⁻¹) of dissolved organic carbon from the raw water considered.