Reactions of chlorine and chlorine dioxide with resorcinol in aqueous solution and adsorbed on granular activated carbon

Resorcinol reacted with chlorine and chlorine dioxide at pH 7 in dilute aqueous solution and in the presence of granular activated carbon (GAC) to produce numerous chlorinated compounds. Major products included chlororesorcinols and various chlorinated cyclopentenediones. Few reaction products were found in common to both Cl₂ and ClO₂ when reacted with resorcinol in the absence of GAC. However, both oxidants produced the same major recoverable chlorinated product, a dichlorocyclopentenedione, when reacted with resorcinol preadsorbed on GAC columns. No products were found when aqueous resorcinol was applied to GAC columns following contact of the carbon with Cl₂ or ClO₂ solutions.     

Regeneration of granular activated carbon with adsorbed trichloroethylene using wet peroxide oxidation

The objective of this study is to clarify the regeneration of granular activated carbon (GAC) adsorbed trichloroethylene (TCE) using wet peroxide oxidation (WPO). TCE and TOC concentrations decreased during WPO, whereas Cl(-) accumulated in water indicating that TCE was not only decomposed but was also mineralized to Cl(-) and CO(2) using WPO. Regeneration efficiencies (q/q(0)) of GAC regenerated at 150, 165 and 180 degrees C (initial pH 4) were 0.36, 0.45, 0.48, respectively. In addition, regeneration efficiencies of GAC regenerated in the solution of various initial pH (2.5, 3.0, 4.0) at 180 degrees C were 0.71, 0.60, 0.48, respectively. These results suggest that regeneration of GAC is more effective at higher reaction temperature and lower initial pH of the solution. In the repeated regeneration of GAC, the adsorption capacity of GAC for TCE gradually decreased and regeneration efficiency of the regenerated GAC at sixth step was 0.40. The adsorption capacity loss of regenerated GAC is probably due to oxidation of GAC during WPO.     

Effects of chlorine on organophosphorus pesticides adsorbed on activated carbon: desorption and oxon formation

We investigated effects of chlorination on four organophosphorus pesticides (diazinon, isoxathion, malathion, and tolclofos-methyl) adsorbed on powdered activated carbon (PAC). Following adsorption of each pesticide on 10mg/L of PAC in water, chlorine was added. After 30min of chlorination, the corresponding oxons were detected in the water, but the parent compounds were not detected. Molar ratios of the oxon concentration in solution after 30min of chlorine addition to the initial pesticide concentration before the adsorption process were 4.1% and 7.9% for diazinon, 3.9% and 5.8% for isoxathion, 1.2% and 1.7% for malathion, and 1.4% and 1.4% for tolchlofos-methyl, in the case of 2 and 5mg/L of chlorine addition. The results suggested that the oxons were desorbed from the PAC by chlorination. The concentrations of the desorbed oxons gradually decreased with time, apparently owing to their readsorption by the PAC. Results from additional experiments suggest the following sequence of events: (i) adsorbed pesticides are oxidized by chlorine on the surface of the PAC and transformed into corresponding oxons; (ii) the oxons are released from the PAC; (iii) the released oxons are gradually readsorbed by the PAC, decreasing their concentrations in the water phase.     

Reactions of free chlorine with substituted anilines in aqueous solution and on granular activated carbon

Aqueous HOCl reacted with substituted anilines to form chlorinated derivatives. Some debromination and bromination products were also detected from two brominated anilines. When granular activated carbon was present, many additional products were formed. These compounds fall into several different groups: (1) N-acylation products, (2) N-carbomethoxylation products, (3) N=N dimerization products and (4) deamination and hydroxylation products.     

不同催化剂对磷酸法制备颗粒活性炭的影响

以杉木屑为原料,在磷酸法颗粒活性炭捏合成型过程中,添加不同催化剂,选择不同的浸渍量,制备中微孔均较发达的木质颗粒活性炭。探讨工艺条件对颗粒活性炭碘吸附值、亚甲蓝吸附值及官能团的影响。结果表明:催化剂有助于提高活性炭的吸附性能,而且提高催化剂的量,有利于颗粒活性炭中孔和大孔的发展。因此选择不同的催化剂量,可以灵活调整活性炭微孔、中孔和大孔的比例,实现活性炭孔隙的调变;另一方面添加催化剂可以降低活化温度实现节能减排。     

氯苯和腐殖酸的活性炭竞争吸附模型曲面拟合

研究了氯苯和腐殖酸在活性炭上的竞争吸附。采用1stOpt和MATLAB数据拟合软件解决了氯苯和腐殖酸在活性炭上竞争吸附的多元非线性模型拟合问题,拟合得到的参数方程可以模拟氯苯和腐殖酸在活性炭上的竞争吸附行为。按照拟合方程绘制的三维图形表明,腐殖酸浓度越高,氯苯浓度越低,氯苯被活性炭吸附时受腐殖酸的影响越大,其影响程度可由方程计算得出,可为活性炭滤柱的设计提供基础参数。     

Volatile fatty acid impacts on nitrite oxidation and carbon dioxide fixation in activated sludge

Batch test were performed to assess nitrite removal, nitrate formation, CO2 fixation, gaseous nitrogen production and microbial density in activated sludge exposed to volatile fatty acid (VFA) mixtures. Nitrite removal and nitrate formation were both affected by the presence of VFAs, but to different degrees. Nitrate formation rates were reduced to a greater extent (79%) than nitrite removal rates (36%) resulting in an apparent unbalanced nitrite oxidation reaction. Since the total bacterial density and the nitrite oxidizing bacteria (NOB, Nitrospira) concentration remained essentially constant under all test conditions, the reduction in rates was not due to heterotrophic uptake of nitrogen or to a decrease in the NOB population. In contrast to the nitrogen results, VFAs were not found to impact CO2 fixation efficiency. It appeared that nitrite oxidation occurred when VFAs were present since the oxidation of nitrite provides energy for CO2 fixation. However, nitrate produced from the oxidation of nitrite was reduced to gaseous nitrogen products. N2O gas was detected in the presence of VFAs which was a clear indication that VFAs stimulated an alternative pathway, such as aerobic denitrification, during biotransformation of nitrogen in activated sludge.     

Determination of non-ionic surfactants and their biotransformation by-products adsorbed on alive activated sludge

A procedure has been developed for the determination of non-ionic surfactants (NS) adsorbed on particles of alive and dead activated sludge. The procedure also enables the determination of adsorption of major biodegradation by-products: short-chained ethoxylates, long- and short-chained PEG. The basis of measurement is the determination of NS concentration in a slurry of activated sludge and in a solution phase. The difference between these two concentrations represents the NS adsorbed on activated sludge. Separation of NS and their biotransformation by-products from samples and then on narrower fractions was performed by a sequential liquid-liquid extraction and precipitation with modified Dragendorff reagent. The indirect tensammetric technique (ITT) was applied for the final determination. The developed method was checked using the example of the treatment of the surfactant C12E10 (oxyethylated fatty alcohol) (C12E10) in the continuous flow activated sludge facility. No statistically significant accumulation of C12E10 on the alive activated sludge was detected, probably because of faster C12E10 fission than its adsorption. However, significant adsorption of the short-chained ethoxylates (including free alcohol) on the alive activated sludge was found, as well as statistically significant adsorption of long- and short-chained PEG. The adsorption of surfactant C12E10 and its biodegradation by-products on dead activated sludge was found to be higher than the species adsorption on alive activated sludge.     

Dynamic pesticide removal with activated carbon fibers

Rapid small-scale minicolumn tests were carried out to simulate the atrazine adsorption in water phase with three pelletized pitch-based activated carbon fibers (ACF) and one commercial granular activated carbon (GAC). Initial atrazine solutions were prepared with pretreated ground water. Minicolumn tests showed that the performance of highly activated carbon fibers (surface area of 1700 m2/g) is around 7 times better than the commercial GAC (with surface area at around 1100 m2/g), whereas carbon fibers with medium activation degree (surface area of 1500 m2/g) had a removal efficiency worse than the commercial carbon. The high removal efficiency of the highly activated ACF is due to the wide-opened microstructure of the material, with an appreciable contribution of the low size mesopores, maintaining at these conditions a fast kinetic adsorption rate rather than a selective adsorbent for micropollutants vs. natural organic matter.     

预处理强化生物活性炭工艺研究

研究了不同水处理组合工艺的除污染效能,包括化学预处理、常规处理、生物活性炭或臭氧生物活性炭技术的联用。试验结果表明,臭氧预氧化、高锰酸盐复合药剂（PPC）预氧化均能强化生物活性炭或臭氧生物活性炭工艺对各项指标的去除,可提高对浊度、UV254、CODMn的去除率;PPC预氧化与生物活性炭联用技术可强化AOC、BDOC的去除效果,达到生物稳定性的控制要求,是适合我国水厂改造的水处理技术。     

Anaerobic microbial mobilization and biotransformation of arsenate adsorbed onto activated alumina

Due to the enactment of a stricter drinking water standard for arsenic in the United States, larger quantities of arsenic will be treated resulting in larger volumes of treatment residuals. The current United States Environmental Protection Agency recommendation is to dispose spent adsorbent residuals from arsenic treatment into non-hazardous municipal solid waste (MSW) landfills. The potential of microorganisms to alter the speciation affecting the mobility of arsenic in the disposal environment is therefore a concern. The purpose of this paper was to evaluate the potential of an anaerobic microbial consortium to biologically mobilize arsenate (As(V)) adsorbed onto activated alumina (AA), a common adsorbent used for treating arsenic in drinking water. Three anaerobic columns (0.27 l) packed with 100 g dry weight of AA containing 0.657 mg adsorbed As(V) (expressed as arsenic) per gram dry weight were continuously flushed with synthetic landfill leachate for 257 days. The fully biologically active column was inoculated with methanogenic anaerobic sludge (10 g volatile suspended solids l(-1) column) and was operated with a mixture of volatile fatty acids (VFA) in the feed (2.5 g chemical oxygen demand l(-1) feed). At the end of the experiment, 37% of the arsenic was removed from the column, of which 48% was accounted for by arsenical species identified in the column effluent. The most important form of arsenic eluted was arsenite (As(III)), accounting for nearly all of the identified arsenic in periods of high mobilization. Additionally, two methylated metabolites, methylarsonic acid and dimethylarsinic acid were observed. Mobilization of arsenic is attributed to the biological reduction of As(V) to As(III) since literature data indicates that As(III) is more weakly adsorbed to AA compared to As(V). Batch and continuous assays confirmed that VFA, present in landfill leachates, served as an electron donating substrate supporting enhanced rates of As(V) reduction to As(III). Two control columns, lacking inoculum and/or VFA in the feed displayed low mobilization of arsenic compared to the fully biologically active column. Therefore, leachates generated in MSW landfills could potentially result in the biologically catalyzed mobilization of arsenic from As(V)-laden drinking water residuals.     

Ecological equilibrium on biological activated carbon

This paper examines the potential of a biological activity control system (BACS) for biological activated carbon (BAC) in comparison to granular activated carbon (GAC) for the treatment of potable water. The overall objective of the project is to produce drinking water of a higher quality more economically by developing a BACS for exhausted GAC that can be transformed to BAC by the development of a natural biofilm during the bio-regeneration mode. The research therefore may be interesting for water companies and the activated carbon industry. Findings show that the lifetime of a GAC filter can be significantly extended by maintaining an active biofilm that has to be controlled in order to avoid filter clogging. The most important parameters are dissolved oxygen (DO), pH and a correct balance of nutrients, which enables a natural control of the biomass. pH control was required to maintain an optimal bacteria-protozoa level. Excessive growth of filamentous bacteria can be prevented by a decrease in DO, increase in pH and the reduction of one essential nutrient, e.g. total phosphorus (P). Total organic carbon (TOC) and chemical oxygen demand (COD) values were reduced by bioactivity. DO, turbidity and suspended solids (SS) values were kept in acceptable ranges with respect to drinking water objectives. Plants without a significant population of protozoa deliver turbid low quality effluent high on SS and biochemical oxygen demand (BOD). It was possible to control the biofilm on GAC containing a natural biofilm and BAC during the bio-regeneration mode. Natural and artificial bio-regeneration lead to similar performance characteristics.     

Adsorption of p-nitrophenol on activated carbon fixed-bed

Carbon fixed-beds are usually used to remove organic contaminants. Adsorption in a carbon filter is a dynamic, non-steady process which is not yet completely understood. The objective of this paper is to establish a methodology to simplify the study of this process based on the wave theory, rapid small-scale column test and experimental design/surface response analysis. The constant pattern wave hypothesis was confirmed by the experimental data. The influence of the inlet concentration of p-nitrophenol and the flow rate on dynamic adsorption was studied at 20 degrees C following a central composite design using a second-order model. Both parameters have an important influence on the response variables studied. The methodology used is a useful tool for studying the dynamic process and shows interactions that are difficult to verify by the classical step-by-step method.     

用活性炭盒法测量室内空气中氡的探讨

研究表明有10%的肺癌归因于室内氡,并且氡是人类受到天然辐射剂量的最主要来源,已经越来越受到公众及相关部门的重视.因此探测下限低,操作方便,成本低的活性炭盒法测氡得到了广泛的应用,但是由于此种方法在标准中描述的不够具体,不便于操作,影响了检测机构对其的掌握与运用,本文就标准中的方法进行了一些探讨,并且提出了一些相关建议.     

Competitive adsorption of benzoic acid and p-nitrophenol onto activated carbon: isotherm and breakthrough curves

Three series of batch tests at 25 degrees C were performed to determine the benzoic acid and p-nitrophenol (PNP) binary adsorption isotherms onto GAC in the aqueous solutions and the experimental data were fitted to the extended Langmuir isotherm model successfully. The experimental data and the isotherm model parameters showed that the GAC used in this study had a higher affinity to PNP than benzoic acid. Three column tests were performed to determine the breakthrough curves and effluent solution pH with varying feed compositions. According to the experimental results, the weakly adsorbed BA exhibited an intermediate zone of effluent concentration higher than its feed one; the effluent solution pH could serve as a good indicator for breakthrough. The breakthrough curves with varying feed compositions could be predicted by the non-linear wave propagation theory satisfactorily. Only the adsorption isotherm models were required to construct the composition path diagram with which the breakthrough curves could be predicted.     

Adsorption of Sevin and Baygon on granular activated carbon

Adsorption of Sevin and Baygon on granular activated carbon was investigated. Adsorption parameters of Freundlich and Langmuir isotherms are useful indications of the adsorption capacity of carbon and the anticipated sharpness of breakthrough front. Adsorption of tested carbamates depends on their chemical structure and branching of the side chains. Contact time tends to be the most important factor controlling the efficiency of the adsorption process and a linear relationship was obtained between the logarithm of contact time and volume of effluent passing the column before breakthrough of Sevin.     

Heterogeneous reactions of ozone and D-limonene on activated carbon

If released in significant amounts, products formed by reactions between ozone (O3) and volatile organic compounds (VOCs) sorbed on activated carbon (AC) filters could degrade indoor air quality (IAQ). Heterogeneous reactions were investigated in laboratory experiments aimed at characterizing reaction products. Effluent air of AC loaded with limonene and exposed to O3 (5.8 ppm) yielded unreacted limonene (501+/-197 microg/m3), low levels of 4-acetyl-1-methylcyclohexene (AMCH) (20+/-2 microg/m3), and limonene oxides (25+/-7 microg/m3). Most of the O3-limonene products remained on the AC, and most (58%) of the limonene remained unreacted on the AC after exposure to a stoichiometric excess of O3 for 48 h. Thus, in addition to known homogenous reactions, O3-limonene reactions occur heterogeneously on AC but to a much lesser extent. However, the fate of 95% of the depleted limonene was not determined; much of the missing portion was attributed to desorption from the AC, but the formation of other secondary indoor air pollutants is possible. VOC-loaded AC air filters exposed to O3 seem unlikely, however, to constitute a significant emission source of reaction products. More studies are necessary to investigate other pollutants, effects of environmental conditions, and VOC releases from AC that may be enhanced by O3 exposure. PRACTICAL IMPLICATIONS: Reactions between ozone and certain volatile organic compounds such as limonene (a common ingredient of many consumer products) occurring on the surface of ventilation filters could impact indoor air quality if products are released in significant amounts. This study suggests that although very small amounts of limonene adsorbed on a filter will react with O3, ventilation filters are not likely to be significant sources of ozone oxidation products. More studies are needed to investigate whether ozone exposure enhances desorption of pollutants from ventilation filters and to measure the formation of formaldehyde and other products that are not easily retained by charcoal filters.     

Effects of activated carbon on the reactions of combined chlorine with phenols

In the presence of ammonia, prechlorination in drinking water treatment results in contact of combined chlorine (monochloramine) with activated carbon, which is used to remove organic compounds from water. Monochloramine reacts very slowly with phenolic compounds in aqueous solution, giving low yields of chlorinated phenols. When monochloramine reacts with phenols adsorbed on granular activated carbon (GAC), however, several oxidized products, principally hydroxylated biphenyls, are formed. Some of the hydroxylated biphenyls are chlorinated (hydroxylated PCBs). Their formation is particularly important because of their potential toxicity. Such compounds are major reaction products from chlorophenol, but they are also formed in small amounts from nonchlorinated phenols. Most of the monochloramine-GAC-phenolic compound reaction products are also produced in similar reactions with free chlorine, indicating that similar reaction mechanisms (free radical mechanisms) take place on carbon's surface. No organic compounds are produced from the reaction of monochloramine with GAC alone.     

Solvent regeneration of activated carbon

Nineteen solvents were evaluated in batch tests involving the desorption of a representative organic adsorbate (phenol) from activated carbon. Three of the better solvents which also possess complete miscibility with water (acetone, dimethylformamide, methanol) were tested further in fixed-bed runs. The effects of solvent temperature and solvent flow rate on phenol desorption were evaluated. In addition, the recovery of phenol adsorption capacity by an activated carbon bed operated cyclically using a sequence of phenol adsorption, desorption with methanol, and rinsing with water was determined. It was found that solvent temperature and flow rate are not critical variables. Solvent volume and type were the most important factors in phenol desorption. A modest volume of methanol restored 88% of the fixed-bed adsorption capacity for phenol after 1 regeneration, and the capacity essentially leveled off after 5 regenerations at a value of 81% of the capacity of fresh carbon. Methanol regeneration is effective, easy to perform and offers convenient solvent recovery. Thus, it is an attractive alternative to thermal regeneration methods.     

Structural and sorption properties of activated carbon modified with iron oxides

The structural and sorption characteristics of activated carbon modified with iron oxides were investigated and static exchange capacity of its surface functional groups of basic and acidic nature was determined. The modification of carbon with iron oxides was found to result in insignificant (7–13%) reduction of micropore and mesopore volume and in basification increase of the sorbent surface. The modified activated carbon is highly efficient in removing phenolic compounds from water.