Dye adsorption by sewage sludge-based activated carbons in batch and fixed-bed systems

The present research work deals with the production of activated carbons by chemical activation and pyrolysis of sewage sludges. The adsorbent properties of these sewage sludges based activated carbons were studied by liquid-phase adsorption tests. Dyes removal from colored wastewater being a possible application for sludge based adsorbents, methylene blue and saphranine removing from solution was studied. Pure and binary adsorption assays were performed in batch and fixed bed systems. In all cases studied, the adsorbents produced from sewage sludges were able to adsorb both the compounds considered here. Nevertheless, time required for reaching equilibrium, adsorptive capacity and fixed bed characteristic parameters were different for these two compounds. Methylene blue adsorption occurred faster than that of saphranine, and it was preferably adsorbed when treating binary solutions. It could be concluded that the sewage sludge-based activated carbons may be promising for dyes removal from aqueous streams.     

Production and comparison of high surface area bamboo derived active carbons

High surface area activated carbons have been produced from the natural biomaterial bamboo, using phosphoric acid as the activating agent. The effects of phosphoric acid impregnation ratio, activation temperature, heating rate on the carbon surface area, porosity and mass yield are presented. Three of these bamboo derived active carbons, surface areas 1337, 1628 and 2123m(2)/g were assessed for their ability to adsorb Acid Red 18 dye from aqueous solution; these results were compared with three conventional adsorbents: activated carbon F400, bone char and peat. Isotherm data were analysed using Langmuir, Freundlich, Redlich-Peterson and Langmuir-Freundlich isotherms. Different isotherms provided the best fit correlations to the adsorption experimental data but the Langmuir-Freundlich equation provided the best overall correlation of data. The adsorption capacities of two of the selected bamboo derived carbons were much greater than the capacities of the other three adsorbents.     

Activated carbons from waste biomass by sulfuric acid activation and their use on methylene blue adsorption

Preparation of the activated carbons from sunflower oil cake by sulphuric acid activation with different impregnation ratios was carried out. Laboratory prepared activated carbons were used as adsorbents for the removal of methylene blue (MB) from aqueous solutions. Liquid-phase adsorption experiments were conducted and the maximum adsorption capacity of each activated carbon was determined. The effects of various process parameters i.e., temperature, pH, initial methylene blue concentration, contact time on the adsorption capacity of each activated carbon were investigated. The kinetic models for MB adsorption onto the activated carbons were studied. Langmuir isotherm showed better fit than Freundlich isotherm for all activated carbon samples. The rates of adsorption were found to conform to the pseudo-second-order kinetics with good correlation. The separation factor (R(L)) revealed the favorable nature of the isotherm of the MB activated carbon system.     

Lignin--from natural adsorbent to activated carbon: a review

The present review compiles the work done over the last few decades on the use of lignin and lignin-based chars and activated carbons as adsorbents for the removal of substances from water and focuses on the utilisation of lignin as adsorbent, its conversion to chars and activated carbons and the use of these materials as adsorbents. Moreover, the review also examines the textural and surface chemical properties of lignin-based activated carbons. The work so far carried out indicates that lignin is relatively non-reactive and probably the component of lignocellulosic precursors primarily responsible for the microporosity of activated carbons. Under appropriate conditions of activation it is possible to obtain materials with surface areas and pore volumes approaching 2000 m(2)g(-1) and 1cm(3)g(-1), respectively, and these materials have capacities for the aqueous phase adsorption of metallic pollutants that are comparable to those of commercial activated carbons. Relatively little work has so far been published and there is considerable scope for more detailed studies on the preparation, characterisation and adsorption applications of lignin-based activated carbons.     

Adsorption of Neutral Red onto Mn-impregnated activated carbons prepared from Typha orientalis

Activated carbon was prepared from an inexpensive and renewable carbon source, Typha orientalis, by H(3)PO(4) activation and then impregnated with different Mn salts and tested for its Neutral Red (NR) adsorption capacities. The amount of Mn impregnated in the activated carbon was influenced by the anion species. Impregnation with Mn decreased the surface area, changed the pore size and crystal structure, and introduced more acidic functional groups such as carboxyl, lactone and phenol groups. The optimum adsorption performance for all the activated carbons was obtained at pH 3.7, Mn-Carbon dose of 0.100g/100ml solution and contact time 4.5h. The adsorption isotherms fit the Langmuir isotherm equation. The kinetic data followed the pseudo-second-order model. The thermodynamic parameters indicated that the processes were spontaneous and endothermic. According to these results, the prepared Mn modified activated carbons are promising adsorbents for the removal of Neutral Red from wastewater.     

Preparation and characterization of activated carbon produced from rice straw by (NH4)2HPO4 activation

Effects of different pretreatment protocols in (NH(4))(2)HPO(4) activation of rice straw on porous activated carbon evolution were evaluated. The pore structure, morphology and surface chemistry of obtained activated carbons were investigated by nitrogen adsorption, scanning electron microscopy and Fourier transform infrared spectroscopy. It was found that pretreatment combining impregnation with (NH(4))(2)HPO(4) and preoxidation could significantly affect the physicochemical properties of prepared activated carbons. The apparent surface area and total pore volume as high as 1154 m(2)/g and 0.670 cm(3)/g were obtained respectively, when combined process of impregnation followed by preoxidation at 200°C and activation at 700°C was carried out. Meanwhile, the activated carbon yield and maximum methylene blue adsorption capacity up to 41.14% and 129.5 mg/g were achieved, respectively. The results exhibited that (NH(4))(2)HPO(4) could be an effective activating agent for producing activated carbons from rice straw.     

Study on activated carbon derived from sewage sludge for adsorption of gaseous formaldehyde

The aim of this work is to evaluate the adsorption performances of activated carbon derived from sewage sludge (ACSS) for gaseous formaldehyde removal compared with three commercial activated carbons (CACs) using self-designing adsorption and distillation system. Formaldehyde desorption of the activated carbons for regeneration was also studied using thermogravimetric (TG) analysis. The porous structure and surface characteristics were studied using N₂ adsorption and desorption isotherms, scanning electron microscopy (SEM) and Fourier transform infrared spectroscopy (FTIR). The results show that ACSS has excellent adsorption performance, which is overall superior to the CACs. Adsorption theory indicates that the ACSS outperforms the CACs due to its appropriate porous structure and surface chemistry characteristics for formaldehyde adsorption. The TG analysis of desorption shows that the optimum temperature to regenerate ACSS is 75 °C, which is affordable and economical for recycling.     

Development of quantitative methods for the detection of enteroviruses in sewage sludges during activation and following land disposal.

The development and evaluation of methods for the quantitative recovery of enteroviruses from sewage sludge are reported. Activated sewage sludge solids were collected by centrifugation, and elution of the solid-associated virus was accomplished by mechanical agitation in glycine buffer at pH 11.0. Eluted viruses were concentrated either onto an aluminum hydroxide floc or by association with a floc which formed de novo upon adjustment of the glycine eluate to pH 3.5. Viruses which remained in the liquid phase after lowering the pH of glycine eluate were concentrated by adsorption to and elution from membrane filters. The method of choice included high pH glycine elution and subsequent low pH concentration; it yielded an efficiency of recovery from activated sludge of 80% for poliovirus type 1, 68% for echovirus type 7, and 75% for coxsackievirus B3. This method was used to study the survival of naturally occurring virus in sludge at a sewage treatment plant and after subsequent land disposal of the solids after aerobic digestion. Reduction of enterovirus titers per gram (dry weight) of solids were modest during sludge activation but increased to a rate of 2 log 10/week after land disposal.     

Development of quantitative methods for the detection of enteroviruses in sewage sludges during activation and following land disposal.

The development and evaluation of methods for the quantitative recovery of enteroviruses from sewage sludge are reported. Activated sewage sludge solids were collected by centrifugation, and elution of the solid-associated virus was accomplished by mechanical agitation in glycine buffer at pH 11.0. Eluted viruses were concentrated either onto an aluminum hydroxide floc or by association with a floc which formed de novo upon adjustment of the glycine eluate to pH 3.5. Viruses which remained in the liquid phase after lowering the pH of glycine eluate were concentrated by adsorption to and elution from membrane filters. The method of choice included high pH glycine elution and subsequent low pH concentration; it yielded an efficiency of recovery from activated sludge of 80% for poliovirus type 1, 68% for echovirus type 7, and 75% for coxsackievirus B3. This method was used to study the survival of naturally occurring virus in sludge at a sewage treatment plant and after subsequent land disposal of the solids after aerobic digestion. Reduction of enterovirus titers per gram (dry weight) of solids were modest during sludge activation but increased to a rate of 2 log 10/week after land disposal.     

Activated carbons from flax shive and cotton gin waste as environmental adsorbents for the chlorinated hydrocarbon trichloroethylene

Agricultural by-products represent a considerable quantity of harvested commodity crops. The use of by-products as precursors for the production of widely used adsorbents, such as activated carbons, may impart a value-added component of the overall biomass harvested. Our objective in this paper is to show that flax shive and cotton gin waste can serve as a precursor for activated carbon that can be used for adsorption of trichloroethylene (TCE) from both the liquid and gas phases. Testing was conducted on carbon activated with phosphoric acid or steam. The results show that activated carbon made from flax shive performed better than select commercial activated carbons, especially at higher TCE concentrations. The activation method employed had little effect on TCE adsorption in gas or vapor phase studies but liquid phase studies suggested that steam activation is slightly better than phosphoric acid activation. As expected, the capacity for the activated carbons depended on the fluid phase equilibrium concentration. At a fluid concentration of 2 mg of TCE/L of fluid, the capacity of the steam activated carbon made from flax shive was similar at 64 and 80 mg TCE/g of carbon for the vapor and liquid phases, respectively. Preliminary cost estimates suggest that the production costs of such carbons are $1.50 to $8.90 per kg, depending on activation method and precursor material; steam activation was significantly less expensive than phosphoric acid activation.     

Comparison on pore development of activated carbon produced from palm shell and coconut shell

A series of experiments were conducted to compare the pore development in palm-shell and coconut-shell-based activated carbons produced under identical experimental conditions. Carbonization and activation processes were carried out at 850 degrees C using a fluidized bed reactor. Within the range of burn-off studied, at any burn-off, the micropore and mesopore volumes created in palm-shell-based activated carbon were always higher than those of coconut-shell-based activated carbon. On macropore volume, for palm-shell-based activated carbon, the volume increased with increase in burn-off up to 30% and then decreased. However, for coconut-shell-based activated carbon, the change in macropore volume with burn-off was almost negligible but the absolute macropore volume decreased with burn-off.     

Adsorption of heavy metals onto sewage sludge-derived materials

Two materials were produced from sewage sludge by: (1) pyrolysis of dried sewage sludge (PS); (2) chemical activation of dried sewage sludge with ZnCl(2) followed by pyrolysis (AS). The aim was to study the application of these materials for metal purification from water and to determine the efficiency of each material. Although AS displayed higher capacity, both PS and AS were able to adsorb these metals and the preferential order was equal: Hg(II)>Pb(II)>Cu(II)>Cr(III). For each metal-adsorbent pair, metal adsorption was highly pH dependent. In all cases the equilibrium was well described both by the Langmuir and the Freundlich isotherms. At the corresponding optimum pH, AS showed the following adsorption capacities: 175.4, 64.1, 30.7 and 15.4 mg/g of Hg(II), Pb(II), Cu(II) and Cr(III), respectively. These results indicate the potential application of these sewage sludge based adsorbents for the treatment of metal polluted effluents.     

Magnetization of activated sludge by an external magnetic field

Magnetization of acclimated activated sludge with the application of an external magnetic field was observed using a magnetic force microscope and can be expressed as the visual magnetic flux density graph. FeCl₃ addition up to 0.1% (w/v) into the sludge, which was acclimated with synthetic sewage wastewater, enhanced the magnetization. Such magnetization was also observed in the activated sludge obtained from the practical wastewater treatment plants of a food processing plant and sewage wastewater. FeCl₃ addition also enhanced the sludge magnetization. The possibility is suggested that this magnetization causes the flock to enlarge and enhance sedimentation of the activated sludge on application of an external magnetic field.     

Biosorption of a reactive dye (Rhodamine-B) from an aqueous solution using dried biomass of activated sludge

Low cost, locally available biomaterial was tested for its ability to remove reactive dyes from aqueous solution. Granules prepared from dried activated sludge (DAS) were utilized as a sorbent for the uptake of Rhodamine-B (Rh-B) dye. The effects of various experimental parameters (dye concentration, sludge concentrations, swelling, pretreatment and other factors) were investigated and optimal experimental conditions were ascertained. Nearly 15min was required for the equilibrium adsorption, and Rh-B dyes could be removed effectively. Dye removal performance of Rh-B and DAS increased with increasing concentrations. The acid pretreated biomass exhibited a slightly better biosorption capacity than alkali pretreated or non-pretreated biomass. The optimum swelling time for dye adsorption of the DAS within the swelling time range studied was 12h. Both the Freundlich and Langmuir isotherm models could describe the adsorption equilibrium of the reactive dye onto the activated sludge with the Langmuir isotherm showing the better agreement of the two. Second-order kinetic models confirmed the agreement.     

Activated carbon from olive kernels in a two-stage process: industrial improvement

Activated carbons have been prepared from olive kernels and their adsorptive characteristics were investigated. A two stage process of pyrolysis-activation has been tested in two scales: (a) laboratory scale pyrolysis and chemical activation with KOH and (b) pilot/bench scale pyrolysis and physical activation with H(2)O-CO(2). In the second case, olive kernels were first pyrolysed at 800 degrees C, during 45 min under an inert atmosphere in an industrial pyrolyser with a throughput of 1t/h (Compact Power Ltd., Bristol, UK). The resulting chars were subsequently activated with steam and carbon dioxide mixtures at 970 degrees C in a batch pilot monohearth reactor at NESA facility (Louvain-la Neuve, Belgium). The active carbons obtained from both scales were characterized by N(2) adsorption at 77 K, methyl-blue adsorption (MB adsorption) at room temperature and SEM analysis. Surface area and MB adsorption were found to increase with the degree of burn-off. The maximum BET surface area was found to be around 1000-1200 m(2)/g for active carbons produced at industrial scale with physical activation, and 3049 m(2)/g for active carbons produced at laboratory with KOH activation. The pores of the produced carbons were composed of micropores at the early stages of activation and both micropores and mesopores at the late stages. Methylene blue removal capacity appeared to be comparable to that of commercial carbons and even higher at high degrees of activation.     

Bilirubin removal from human plasma by Cibacron Blue F3GA using immobilized microporous affinity membranous capillary method

A novel affinity sorbent system for direct bilirubin removal from human plasma was developed. These new adsorbents comprise Cibacron Blue F3GA as the specific ligand, and microporous membranous poly(tetrafluoroethylene) capillary (modified by coating with a hydrophilic layer of poly(vinyl alcohol) after activation) as the carrier matrix. The affinity adsorbents carrying 126.5 micromol Cibacron Blue F3GA/g polymer was then used to remove bilirubin in a flow-injection system. Non-specific adsorption on the poly(vinyl alcohol) coated capillary remains low, and higher affinity adsorption capacity, of up to 76.2 mg/g polymer was obtained after dye immobilization. The bilirubin adsorption capacity of the affinity capillary decreased with increase in the recirculation rate of plasma. The adsorption capacity increased with increase the temperature while decreased with increase the ionic strength. The maximum adsorption was only observed in neutral solution (pH 6-7). The adsorption isotherm fitted the Langmuir model well. These new adsorbents have higher velocity of mass transfer, better adsorption capacity, less fouling, longer service life and good reusability. The results of blood tests suggested the dye affinity capillary has good blood compatibility.     

Functioning and toxicity of artificial soil mixtures with metal-bearing sewage sludge

Various artificial soil mixtures were prepared by mixing two different toxic metals containing sewage sludge from Ljubljana and Maribor wastewater treatment plants with natural mineral soil. The plots with mixtures were exposed to field environmental conditions for a period of 1 year, after which we assessed soil toxicity (germination test with Lactuca sativa), potential metal phyto-accessibility (diethylenetriamine pentaacetic acid – DTPA extraction test), soil functioning (by soil enzymes activity) and conducted a field growth test with Lollium perenne L. as a metal bio-indicator plant. The metal phyto-accessibility extraction test (DTPA) showed lower values than the metal accumulation test with L. perenne L., which also showed higher metal concentrations in roots compared to leaves. With the exception of the mixture containing 30% (w/w) of sludge from the Ljubljana wastewater treatment plant, all mixtures containing more than 20% of sludge negatively affected root elongation of L. sativa seeds, indicating an increase in artificial soils toxicity. Increasing the ratio of sludge from the Ljubljana plant increased dehydrogenase and decreased phosphomonoesterase, while the addition of sludge from the Maribor plant increased phosphomonoesterase activity. Overall, the effect of sludge addition on artificial soil properties, toxicity and functioning not only depended on dosage but was also sensitive to the source and pre-treatment of the sewage sludge.     

Waste-derived activated carbons for removal of ibuprofen from solution: Role of surface chemistry and pore structure

The removal of a widespread used drug (i.e., ibuprofen) from water was investigated using high valuable carbon adsorbents obtained from chemical and physical activation of a bioresource (cork) and a municipal waste (plastic). The waste-derived carbons outperformed the adsorption capacity of commercial carbonaceous adsorbents due to their adequate features for the removal of the targeted compound. Regarding the adsorption mechanism, the results obtained point out that ibuprofen retention is favored in activated carbons with basic surface properties. On the other hand, the textural features also play an important role; the presence of a transport pores network (i.e., mesopores) is crucial to ensure the accessibility to the inner porosity, and the microporosity must be large enough to accommodate the ibuprofen molecule. Specifically, adsorbents with a large fraction of ultramicropores (pore widths <0.7 nm) are not adequate to effectively remove ibuprofen.     

Effectiveness and mechanisms of dye adsorption on a straw-based biochar

A biochar (BC) generated from straw as a cost-effective substitute for activated carbon (AC) was tested for its adsorptive ability toward reactive brilliant blue (KNR) and rhodamine B (RB). BC and AC had similar surface areas but differed in porosity, surface acidity and point of zero surface charge. The two carbons were highly effective adsorbents for both dyes at pH 3.0 and 6.5. BC was slightly more effective than AC to adsorb RB due to the RB–BC electrostatic interactions and RB protonation at low pH. The two carbons reversed in their effectiveness to adsorb KNR for similar reasons. The π–π interactions between dye molecules and graphene layers of BC, the direct dye-BC electrostatic attraction/repulsion and the intermolecular hydrogen bonding are proposed to be the combined mechanisms for dye adsorption. Rich phenolic hydroxyls on the surface of BC are expected to enhance the π–π interactions.     

Involvement of Acinetobacter sp. in the floc-formation in activated sludge process

The coaggregation behavior of Acinetobacter johnsonii S35 isolate with sewage bacteria was assessed by a spectrophotometric assay using different samples from a municipal wastewater treatment plant and a community plant. A. johnsonii S35 coaggregated well with other free bacteria and microflocs at the mixing ratios of 0.2:1-0.6:1 of A. johnsonii S35 and sewage samples. In addition, the size of coaggregates became larger (100 μm or more) under the same conditions. A. johnsonii S35 cells were highly adsorbed (adsorption=93-99%) onto sludge samples. Microbial adhesion to hydrocarbon (MATH) test and adsorption to octyl-Sepharose CL-4B showed that A. johnsonii S35 cells and sludge samples had a hydrophobic character. The population of Acinetobacter spp. in sewage treatment plants was 2-7% and its role in bioflocculation was discussed. The present study revealed that A. johnsonii S35 isolate can play as a bridging organism and contribute in floc-formation in activated sludge process.