Chapter 7
Dye Removal
POLLUTION BY COLOR / DYE AND THEIR REMOVAL
Water pollution due to release of industrial waste water has already become a serious problem. Almost every industry uses dyes to color their products and the residual and unspent dyes are discharged into the environment, particularly aquatic environment. Color is the most obvious indicator of water pollution. The discharge of colored waste into streams not only affects their aesthetic nature but also interferes with the transmission of sunlight into streams and therefore reduces photosynthetic action. Effluents from the dye manufacturing industry, the textile industry and the pulp and paper industry are highly colored. The American dye-manufacturing institute showed that the basic dyes are generally more toxic than acid or direct dyes. Considerable research has been done on color removal from wastewater. The adsorption process provides an attractive treatment, especially if the adsorbent is inexpensive and readily available.
Parthenium Hysterophorus L. As An Adsorbent
In this case study Parthenium hysterophorus L. is used as an adsorbent for the removal of dye from waste water. Parthenium is an unwanted weed growing throughout the country without any input/effort.This is likely to serve basically two purposes, one it will help in protecting the environment from pollution and secondly, ever increasing unwanted weed, parthenium would be put to some use. Adsorbents prepared from Parthenium hysterophorus L. were successfully used to remove the methylene blue from an aqueous solution in a batch reactor. The adsorbents included sulphuric acid treated parthenium carbon (SWC) and phosphoric acid treated parthenium carbon (PWC). The effect of adsorbent surface change, initial pH, initial dye concentration, adsorbent dose and.contact time on dye removal have been studied. Similar experiments were carried out with commercially available activated carbon (AC) for comparison. The adsorption efficiency of different adsorbents were in the order AC>PWC>SWC. Initial pH had negligible effect on the adsorption capacity. Maximum dye was sequestered from the solution within 60-90 min. after the start of every experiment. After that, the concentration of methylene blue in liquid phase remained almost constant. The optimized dosage of biomass and initial dye concentration was found to be 0.4g/100 mL and 100ppm (mg/L) respectively for both the adsorbents under the optimized condition of pH and contact time. At equilibrium, the maximum total uptake by these adsorbents was 47.05 mg per g and 26.1 mg per g respectively. Kinetic of removal has been found to follow the first order rate equation and fit the Lagergren equation well. Langmuir and Freundlich isotherm models were applied to check the efficiency of these adsorbents. The study indicated that these adsorbents can be effectively and efficiently used for the removal of methylene blue from dilute synthetic solution.
A Beer-Waste Biosorbent
Textile industries consume large volumes of water and chemicals for the wet processing of textiles. The presence of very low concentrations of dyes in effluent discharged from these industries is highly visible and undesirable . Due to their chemical structure, dyes are resistant to fading when exposed to light, water and chemicals . Dyes usually have a synthetic origin and complex aromatic molecular structures, which make them more stable and difficult to biodegrade. Various physical, chemical and biological methods have been used for the treatment of dye-containing wastewater. Some chemical oxidations, such as Fenton reagent, ozone, UV plus H2O2 or NaOCl, result in aromaticring cleavage, which may generate chemical sludge or by-products that are likely to be even more toxic Physical adsorption technology, i.e. by activated carbons, has recently gained favor as its high efficiency in the removal of highly stable dyes, and is economically feasible compared to other methods . However, activated carbons are expensive and not easily regenerated Although ion exchange resins can be regenerated easily, the high cost hinders their wide application for the treatment of dye-bearing wastewater. Consequently, various types of (bio)sorbents, which are able to bind dye molecules and be easily regenerated, have been extensively searched and tested. The beer waste is generated in a great quantity from the beer plant in China. After an aerobic treatment at wastewater treatment process, this 1/6.waste is currently reclaimed. Thus, the main objective of this work is to utilize beer wastes as a low-cost sorbent for adsorption of a reactive dye, specifically Reactive Red 4 from aqueous solution, and to discuss the application of kinetic and isotherm models to the sorption.
The bio waste was collected from an aerobic waste water treatment in a China beer plant and treated with 1 M HNO3 solution for 24 h, replacing the natural mix of ionic species with protons. The acid-treated waste was washed several times with deionized distilled water to remove the excess of acid. It was then dried in an oven at 60 o C to yield protonated bio waste for 24 h. The resulting dried waste was stored in a desiccator and used as biosorbent in the sorption experiments. The protonated beer waste was used as a new type of adsorbent for the removal of Reactive Red 4.
Various experimental parameters were investigated. Adsorption reached equilibrium in 18 hours. Asthe solution pH decreased the dye uptake increased, and in alkaline conditions desorption was dominating. The pseudo-second-order model and Langmuir isotherm model provided a high degree of correlation with the experimental data for the biosorption processes. The rate constant, theequilibrium sorption capacity and the initial sorption rate were calculated. The maximum adsorptioncapacities of the beer waste were 82.23 ±8.67 and 72.50 ±6.45 mg/g at pH 1 and 2, respectively.Kinetic study showed a pseudo-second-order rate of adsorption with respect to the solution. These results of adsorption performance indicate the beer waste as a potentially economical adsorbent for dye removal.
ADSORPTION OF DYES AND PHENOLS ONTO CARBONS PREPARED FROM BAMBOO
Most bamboos contain large amounts of ligneous fiber and can therefore be carbonized into chars, which can be used in decoration, in purifying drinking water, for indoor air filtering, dehumidifying, thermal insulation, electromagnetic wave shielding, etc. However, bamboo is rarely used as the raw material for activated carbon. Meso bamboo is grown profusely in Taiwan. Its stem diameter can reach up to 15 cm. In earlier days, itwas commonly used for building, furniture, eating and cooking utensils, foods, and food processes. Lately, there only use that seems to have remained, is that of using bamboo shoots for food. It is regrettable that the mature bamboo does not seem to have many uses any more. Since the utility value of bamboo has greatly dropped, bamboo-growing has mostly been abandoned reducing the number of plants. The reduction in the number of bamboos grown has caused severe ecological damage to the environment and to water-soil conservation. Bamboo grows fast, absorbing, CO2 from the atmosphere at great speed,so it effectively helps to slow down global greenhouse effect. In previous studies, oak, bamboo, coconut shell, and cedar were activated with steam to obtain activated carbons. The results showed that physical properties (BET surface area and pore volume) and adsorption capacities (chloroform adsorption) of the activated carbons derived from bamboo were lower than those from the other three raw materials Furthermore, studies have shown that of the carbons derived from bamboodust, coconut shells, groundnut shells, rice husks, and straw, straw carbon has the highest adsorption capacity being 5.9 times that of bamboo dust carbon, which is the lowest . From this evidence it is clear that it is not easy to make good activated carbon from bamboo.The aim of this work was to prepare porous carbons from Meso bamboo using KOH etchingand CO2 gasification processes. The physical properties of the carbons, namely the BETsurface area, pore size distribution, and the total pore volume were compared. Theircapacities for the adsorption of basic blue 1, methylene blue, p-cresol, p-chlorophenol, p-nitrophenol, and phenol from water were systematically investigated.
ADSORPTION OF DYES ONTO LDH-MODIFIED BENTONITE
Large amounts of aqueous waste generated by textile, paper, carpet and printing industries contain high concentration of coloured organic, often toxic compounds which has posed severe damage on the environment. It has been reported that there is a large amount of unused dyes existing in wastewaters discharged from dyeing process,especially for reactive dyes,because their hydrolysed form has no affinity for textile fabrics . Due to the toxic nature of most dyes to plants and micro-organisms, coloured wastewater can not be discharged directly without adequate treatment. Toremove dyes from wastewater, a number of physical, chemical and biological wastewater treatment techniques have been developed, such as membrane separation, flocculation-coagulation, adsorption, ozonatioin and aerobic or anaerobic treatment . Among these processes, adsorption has been found to be an effective and cheap process for removing dyes and having wide potential applicationsIt has been reported that many different types of adsorbents are effective to remove dyes from aqueous effluents Clay minerals, such as bentonite, have the potential as alternative low-cost adsorbents becausethey possess unique physiochemical properties. Bentonite is a clay with net negative charges in its lattice structure due to the isomorphous substitution. In order to maintain the electrical neutrality, some cations external to the lattice, like sodium or calcium ions, are commonly present in the interlayer region acting as offset cations. In general, these charge-compensating cations can be exchanged and replaced by others .present in the bulk of the suspension. The application of bentonite as an adsorbent is largely based on its cation exchange ability. It is this property that makes bentonite unable to adsorb anionic species. In order to remove the contaminants in effluent that normally contain both cationic and anionic materials,modification of bentonite is needed. We chose layered double hydroxides (LDHs), the anionic clay materials as the modifier.LDHs consist of positively charged metal hydroxide layers and interlayer anions. These anions together with water presented on the surface or the interlayer space can be exchanged with other anionic species . More particularly, the derived mixed oxides can be transferred back to the LDH structure by adsorbing anions present in water. In this work, bentonite was modified with Mg2Al-Cl-LDH and then calcined so that the composite is able to adsorb anionic species. The work aims to determine whether the LDH modified bentonite composite adsorbent hold the promise for the removal of two anionic dyes, acid red 18(AR18) and direct blue 1(DB1).
Materials and methods
Materials.s supplied by the IntegratedMineral Technology
Holdings Ltd, Australia. It was used without any further purification. Its cation exchange capacity (CEC) is 75 meq/100g. LDH, the modifying clay, with a designed formula of Mg2Al(OH)6Cl ·2H2O was synthesised in laboratory by coprecipitation of AlCl3 ·6H2O and MgCl2 ·6H2O in NaOH solution under vigorous stirring.The solid material was then collected via centrifugation and washed before being dispersed into a Teflon-lined action.Adsorbent.
LDH-modified bentonite was obtained by mixing the delaminated bentonite