Pentachlorophenol adsorption and desorption characteristics of granular activated carbon-II. Kinetics

The kinetics of pentachlorophenol (PCP) adsorption/desorption with Calgon F300 granular activated carbon (GAC) was studied. A previously-developed model of GAC adsorption/desorption kinetics was applied to the case of PCP for both batch and continuous plug-flow liquid conditions. The model predictions were found to be in good agreement with the experimental observations.     

Impact of pH on the adsorption and desorption kinetics of 2-nitrophenol on activated carbons

The adsorption and desorption kinetics of 2-nitrophenol (2NP) from aqueous solutions using F-400 and WV-B granular activated carbons (GAC) have been studied at pHs 1, 4.6 and 13, using batch tests. Adsorption and desorption kinetics of 2NP on to both carbons were adequately described by the homogeneous solid surface diffusion model (HSSD). The adsorption and desorption kinetics can be predicted at different pHs by using adsorption kinetics parameters of the pH 4.6 and the isotherm parameters for the corresponding pH. Thus, the differences in the rates of adsorption are primarily attributable to the differences in the equilibrium loadings at the various pHs.     

Single and competitive adsorption of Cd and Zn onto a granular activated carbon

Single and competitive adsorption of cadmium and zinc onto granular activated carbon DARCO 12–20 mesh has been investigated. This activated carbon has been shown as an effective adsorbent for both metals. Cadmium and zinc removals increased with pH and decreased with molar metal/carbon ratio. Surface precipitation phenomena have been detected for the higher pHs and molar ratios. The adsorption process has been modelled on the surface complexation Triple Layer Model (TLM). For this purpose, the amphoteric nature of the activated carbon has been studied. Single metal adsorption data have been used to calibrate TLM parameters. A dependence of the adsorption constants on pH and molar metal/carbon ratio has been observed, and a correlation for log K_ads has been determined. In the competitive system, the removal efficiency of the activated carbon decreased for both metals. The TLM model, using surface complexation constants determined from single adsorption experiments, successfully predicted cadmium and zinc removal from the two metal solutions.     

High loading denitrification by biological activated carbon process

High loading denitrification was studied using granular activated carbon (Calgon Filtrasorb 400, size: 0.8–1.4 mm) column with injecting carbon source (sucrose) only once a day. Under the condition of EBCT (empty bed contact time) = 80 min, C:N RATIO = 1.88, once per day injection mode of organic supply was able to sustain an average denitrification efficiency of 84 to 89% even with influent NO₃---N concentration of 80 mgl⁻¹. With an influent NO₃---N of 20 mgl⁻¹ and C:N ratio of 1.88, however, reduction of EBCT to 20 min resulted in very poor denitrification. In the latter case, 46% of the added carbon was lost in the effluent immediately after the injection. Short EBCT critically affected the process mainly due to insufficient adsorption rate. Microbial denitrification capability and fermentation might also limit the process. Extended organic injection is a possible option to improve the process efficiency. Occurrence of the sulfate reduction was limited in early phase of the cycle.     

The relation between activated carbon adsorption and water quality indexes

In order to estimate the adsorbability by activated carbon of organic compounds dissolved in aqueous solutions, the contribution of individual atoms to the adsorption process is calculated. The contribution of carbon, bromine and chlorine atoms is positive, that of oxygen atoms is negative, that of hydrogen atoms is very small and that of nitrogen atoms is influenced by the kind of functional group in which they are contained. The dominant factors governing adsorption are the numbers of carbon and oxygen atoms in a molecule. The activated carbon's effectiveness for adsorption of organic compounds dissolved in solutions can be predicted from such water quality indexes as total organic carbon, total organic nitrogen, total organic halogen an total oxygen demand.     

The repeated exhaustion and chemical regeneration of activated carbon

Following experimental research studies carried out at the University of Birmingham, U.K., this paper presents data on the repeated application of the cycle of exhaustion, chemical regeneration and re-exhaustion of activated carbon. The adsorbates studied were nitrobenzene (a small organic molecule of mol. wt approx. 123), Rhodamine B (a much larger adsorbate of mol. wt approx. 480) and humic acid (an ill-defined substance consisting of macromolecules of molecular weight predominantly in the range 20,000–50,000). The regenerants used were all organic with solubilising powers to encourage the physical displacement of the adsorbate molecule by the regenerant molecule. As a general conclusion, it may be stated that chemical regenerants could be used to regenerate granular activated carbon repeatedly with little loss of adsorption capacity. Earlier studies which considered the effect of water on the powers of the carboxylic acid regenerants were confirmed in the results reported here. Bonding between the acids and water hindered the regeneration process.     

Experimental study on adsorption capacity of an activated carbon-based adsorption water chiller

The objective of this study was to evaluate the adsorption capacity of a working pair for an adsorption water chiller. Activated carbon fibre–methanol, activated carbon fibre–ethanol and activated carbon pallet–ethanol were used as an adsorbent–adsorbate pair in this study. The experiment was conducted using a stainless steel adsorber, 110?mm diameter by 150?mm height, filled with adsorbent and transparent plastic evaporator, 100?ml capacity, filled with adsorbate. The experiment was performed by isobaric adsorption in the temperature range of 10–100°C at the evaporator temperature of 20°C (water chiller). An experimental investigation showed that the activated carbon fibre–methanol pair has the highest adsorption capacity (0.44?kg/kg) compared to the activated carbon fibre–ethanol and activated carbon pallet–ethanol pairs. The finding revealed that uniform structure and large surface area of adsorbent as well as low boiling point and large latent heat of adsorbate had highly significant effects on adsorption capacity. The effect of time and adsorber temperature on adsorption capacity is also discussed in this study.     

活性炭改性及其吸附甲苯和丁酮的初步研究

通过微波改性,电炉直接加热改性,氢氧化钠改性,硝酸改性等几种方法对活性炭进行改性,并对改性后活性炭的吸附能力进行研究,得出微波改性和电炉直接加热改性增强了活性炭吸附能力,氢氧化钠改性和硝酸改性则明显削弱其吸附能力。     

活性炭吸附去除重金属研究进展

介绍了国内外学者应用活性炭吸附去除包括:Cr(Ⅵ),Cu2 ,Zn2 ,Cd2 ,Pb2 ,Mn2 ,Hg2 以及混合重金属离子在内的各种废水的处理效果与影响因素,并对相应的吸附机理进行了讨论,以促进活性炭吸附去除重金属离子的进展。     

改性炭对磺胺甲噁唑的吸附及解吸特性

采用商品活性炭和金属氧化物改性炭作为吸附剂,研究了几种活性炭对磺胺甲噁唑(SMZ)的吸附及解吸特性。结果表明:SMZ在几种活性炭上的吸附动力学符合拟二级动力学方程;SMZ的吸附均可采用Freundlich、Langmuir和Langmuir-Freundlich模型进行拟合,Langmuir-Freundlich吸附模型能更好地描述活性炭和改性炭对SMZ的吸附行为;铁、锰氧化物的存在对活性炭的比表面或者孔结构影响不大,并且其对活性炭吸附水中SMZ的性能影响甚微;与AC-Fe和AC-Mn相比,AC-0上吸附的SMZ更易解吸,改性炭负载的金属氧化物与SMZ的表面络合作用增强了AC-Fe和AC-Mn对SMZ的化学吸附,并且改性炭的MnOx和FeOx能氧化降解部分SMZ。     

活性炭纤维吸附饮用水中硼的试验研究

通过静态试验,对经过简单预处理的活性炭纤维的除硼效果以及吸附时间、pH、温度和搅拌机转速等因素对吸附效果的影响进行了考察.结果表明.该吸附过程符合Freundlich吸附等温线模式,以物理吸附为主;最佳吸附时间为1 h;pH和温度对吸附效果影响均较大,pH值最佳范围为5～6.5,温度为15℃;搅拌机高速转动更利于吸附进行;采用了不同再生剂对吸附饱和的活性炭纤维进行再生试验,3%NaOH溶液再生效果最好,再生后吸附效率可达90.1%.     

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。     

Characterization of natural organic matter adsorption in granular activated carbon adsorbers

The removal of natural organic matter (NOM) from lake water was studied in two pilot-scale adsorbers containing granular activated carbon (GAC) with different physical properties. To study the adsorption behavior of individual NOM fractions as a function of time and adsorber depth, NOM was fractionated by size exclusion chromatography (SEC) into biopolymers, humics, building blocks, and low molecular weight (LMW) organics, and NOM fractions were quantified by both ultraviolet and organic carbon detectors. High molecular weight biopolymers were not retained in the two adsorbers. In contrast, humic substances, building blocks and LMW organics were initially well and irreversibly removed, and their effluent concentrations increased gradually in the outlet of the adsorbers until a pseudo-steady state concentration was reached. Poor removal of biopolymers was likely a result of their comparatively large size that prevented access to the internal pore structure of the GACs. In both GAC adsorbers, adsorbability of the remaining NOM fractions, compared on the basis of partition coefficients, increased with decreasing molecular size, suggesting that increasingly larger portions of the internal GAC surface area could be accessed as the size of NOM decreased. Overall DOC uptake at pseudo-steady state differed between the two tested GACs (18.9 and 28.6 g-C/kg GAC), and the percent difference in DOC uptake closely matched the percent difference in the volume of pores with widths in the 1-50 nm range that was measured for the two fresh GACs. Despite the differences in NOM uptake capacity, individual NOM fractions were removed in similar proportions by the two GACs.     

生物活性炭在饮用水处理中的应用

介绍了活性炭的物理特性、使用寿命、在水处理中的作用以及生物活性炭工艺主要的影响因素.研究表明,压块破碎活性炭具有均匀、粗糙的表面,适合细菌的附着和生长,其丰富的孔结构能够保护细菌不受生物杀灭剂、杀虫剂和其他毒素的干扰.同时,与其他方法制得的活性炭相比,压块破碎活性炭具有更强的调节食物供给能力.     

First approach of desorption energies of water and organic molecules onto activated carbon by differential scanning calorimetry studies

The authors have determined the adsorption energies of water and organic materials on saturated and unsaturated activated carbons. The original technique used is the differential scanning calorimetry method (DSC). Water is always found to be present in the inner structure of the activated carbons. This water has a low energy of interaction. The desorption enthalpies have been determined for carbon loaded with organic compounds. An energy distribution is shown for some molecules and then approaches of the adsorption mechanisms are confirmed. The energy values are compared with the literature data determined by other analytical methods. The energies of solid solute interactions have been related to physical and chemical parameters of the solute. A good correlation is found for families of molecules.     

Phosphorus removal by granular activated alumina

Phosphorus removal from wastewater may be carried out by fixed-bed adsorption using activated alumina. In order to prevent unacceptable head-losses coarse-grained alumina must be used. Such systems have been referred to by several authors in literature. The mass transport characteristics of the system has so far, however, not been given a thorough investigation. This study uses the homogeneous surface diffusion model (HSDM) to describe the process as influenced by the system parameters.A sensitivity analysis is presented to optimize the process design for given conditions. The pH, the alumina particle size and the column length are found to be very important parameters determining the column performance. The process is very well suited for designing a beds-in-series system.     

Discriminating and assessing adsorption and biodegradation removal mechanisms during granular activated carbon filtration of microcystin toxins

Microcystins are cyanobacterial toxins that are problematic for water authorities due to their resistance to conventional water treatment. Granular activated carbon (GAC) filtration has been shown to be effective in removing microcystin from water using both adsorption and biodegradation removal mechanisms; however, little is known regarding which removal mechanism predominates and to what extent. In this study, microcystin removal due to adsorption and biodegradation in GAC filtration were discriminated and assessed by commissioning three parallel laboratory columns, including a sterile GAC column, a conventional GAC column and a sand column. The results demonstrate that biodegradation is an efficient removal mechanism once it commences and that the rate of biodegradation was dependent upon temperature and initial bacterial concentration. Adsorption of microcystins was prevalent during the initial stages of the GAC columns and was modelled using the homogeneous surface diffusion model (HSDM). The HSDM provided evidence that an active biofilm present on the surface of the conventional GAC hindered adsorption of microcystin compared with the sterile GAC with no active biofilm. Up to 70% removal of microcystin-LR was still observed after 6 months of operation of the sterile GAC column, indicating that adsorption still played a vital role in the removal of this toxin.     

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.     

The contribution of exopolysaccharides induced struvites accumulation to ammonium adsorption in aerobic granular sludge

Aerobic granular sludge from a lab-scale reactor with simultaneous nitrification/denitrification and enhanced biological phosphorus removal processes exhibited significant amount of ammonium adsorption (1.5 mg NH₄⁺-N/g TSS at an ammonium concentration of 30 mg N/L). Potassium release accompanied ammonium adsorption, indicating an ion exchange process. The existence of potassium magnesium phosphate (K-struvite) as one of potassium sources in the granular sludge was studied by X-ray diffraction analysis (XRD). Artificially prepared K-struvite was indeed shown to adsorb ammonium. Alginate-like exopolysaccharides were isolated and their inducement for struvite formation was investigated as well. Potassium magnesium phosphate proved to be a major factor for ammonium adsorption on the granular sludge. Struvites (potassium/ammonium magnesium phosphate) accumulate in aerobic granular sludge due to inducing of precipitation by alginate-like exopolysaccharides.