Lab Report 4

March 21, 2018 | Author: Carol Wei | Category: Adsorption, Chemistry, Physical Sciences, Science, Materials
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1.0 OBJECTIVES: 1.1 To immobilize fungal biomass on activated carbon for bioabsorbant. 1.2 To analyze the effect of cell immobilization for methylene blue dye removal by bioabsorbent. 2.0 THEORY: Various dyes have been used in textile, dyeing, paper pulp, plastic, leather, cosmetics and food industries. The effluents produced from these industries possess certain hazards and environmental problems. Most of these dyes are synthetic and exhibit complex aromatic structure. Thus, they are stable and difficult to be biodegraded. A common example of dyes is methylene blue. Methylene blue is a heterocyclic aromatic chemical compound that is very stable to light, oxidizing agents and resistance to aerobic digestion. So, these effluents have to be treated before discharge not only for their high chemical and biological oxygen demand but also for suspended solids of toxic properties to aquatic life. Several techniques have been developed to treat dye effluents such as microbial degradation, chemical oxidation, ion exchange, membrane separation, bioaccumulation, electrochemical treatment, adsorption and reverse osmosis. Adsorption is generally preferred among these techniques due to its high efficiency, easy handling, low energy input and availability of different adsorbents. The most commonly used adsorbent for dye removal was activated carbon. Activated carbon is carbon that has been treated with oxygen to open up millions of tiny pores between the carbon atoms. The highly porous charcoals have huge surface areas that give it countless bonding sites. As a result, activated carbons are widely used to adsorb odorous or coloured substances from gases or liquids. The adsorption process is one of the efficient methods to remove dyes from effluent and has an advantage over the other methods due to the excellent adsorption efficiency of activated carbon (powdered or granular) for organic compounds even from dilute solutions, but commercially available activated carbons are very expensive. The high adsorptive capacities of activated carbons are related to properties such as surface area, porosity, and surface functional groups. These unique characteristics are dependanton the type of raw material employed and method of activation. Basically, there are two different processes for the preparation of activated carbon: physical and chemical activation (Ahmadpour & Do, 1996).

Activated carbon has also some disadvantages. Both chemical and thermal regeneration of used carbon is expensive,impractical on a large scale and produces additional effluent and results in considerable loss of the adsorbent. It is also documented that adsorption with activated carbon and other technology like chemical precipitation was ineffective when the pollutant concentration range from 1 to 100 mg/L. On the other hand, ion exchange and membranes separation were effective at the range of 1–100 mg/L, but it was extremely expensive in treatment cost. Furthermore,some of these methods would produce huge quantity of toxic chemical sludge that required the secondary treatment (Li, Liu, Li, & Deng, 2008). Recently, several researchers have shown that biosorption can be regarded as a valid alternative to chemical-physical method and to microbial and/ or enzymatic biodegradation. Such researches have pointed out the capacity of various microbial biomass (bacteria, yeast, fungi, and algae) and waste materials from industry and agriculture to absorbor accumulate dyes (Crini, 2006; Ferrero, 2007). Among the various types of biomass, the fungal biomass has proved to be particularly suitable. Even if the mechanisms regulating biosorption have not yet been fully explained, it seems to take place at the cell wall level. The main attractions of biosorptions are its high selectivity and efficiency, good removal from large volumes and the potential cost effectiveness. Moreover, both living and dead biomass can be used to remove hazardous organics; dead cells are obviously preferable for wastewater treatment since they are not affected by toxic wastes and chemicals and do not pollute the environment by releasing toxins and/or propagules ( Aksu & Donmez 2005). However, dead and dried biomass can be stored for long periods at room temperature with little risk of putrefaction. This makes it easier to use and transport. Furthermore, these biosorbents are usually used in free forms, which would bring about the difficulty of separation between solid and liquid after adsorption. The traditional technologies of separation are adopted such as centrifugation and membranes separation. But it is generally difficult in continuous process for wastewater treatment. Even though separation would be successful, additional steps must result in the increase of cost. Recently, the immobilization of active compounds onto microbial biomass is an interesting technique to clear pollutants in wastewater. One of the advantages is that biomass can be retained on support under the working environment.

3.0 METHOD: 3.1 Preparation of fungal biomass 1. Phanerochaete chrysosporium was cultured at 32˚C for 7 days on potato dextrose agar plates. 2. Spores on agar plates were scraped by distilled water to form a spore suspension. 3. About 5ml of spore suspension per 100 ml of culture medium containing malt extract and activated carbon which is previously autoclaved at 121ºC for 15 minutes was added. The culture medium without activated carbon was set as a control. About 0.1g of activated carbon was used for preparation of fungal biomass. 4. The culture medium was incubated at 32˚C and 150 rpm for 2 days. 5. After 2 days, the mycelia balls were collected and were kept in oven at 80ºC for about 1 hour to prepare the fungal biomass. 6. The fungal biomass was ground into powder using a mortar and a pestle. 3.2 Preparation of dye solution 1. Stock solutions of methylene blue at different concentrations was prepared with distilled water. 3.3 Batch biosorption studies 1. About 0.1g of fungal biomass powder with 50ml of methylene blue solutions at 20mg/l and pH 10 were used. 2. The samples were shaken at 150rpm in incubator shaker at 30˚C for 60 minutes. 3. The samples were taken out from incubator shaker and were filtered to remove fungal biomass. 4. The supernatant was analyzed to determine the concentrations of remaining methylene blue in the solution using spectrophotometer set at a wavelength of 664 nm. 5. The concentrations of methylene blue in the supernatant were determined using a standard curve. 5.0 DISCUSSION: In this experiment, adsorption is used to remove the methylene blue dye in the aqueous solution. Phanerochaete chrysosporium is used to immobilize activated carbon for bioabsorbent. Both the fungal biomass and activated carbon are able to adsorb methylene blue from aqueous solution. In this experiment, the effects of cell immobilization for methylene blue dye removal by bioabsorbent are studied and are analyzed. Theoretically, there is a gradual increase in

bioadsorption with increasing contact time up to a certain length of time, the amount of dye being adsorbed by activated carbon is not significant. A standard curve for the methylene blue dye from the stock solutions was plotted by using the axis of absorbance read at 664 nm versus dye concentration in mg/l. From the curve plotted, it can be concluded that the higher the absorbance value, the higher the dye concentration is. This is due to the higher the concentration of methylene blue, the higher the intensity of the colour and hence the higher the absorbance value. From the standard curve, a linear equation of y = 0.123 x + 0.345 was obtained. By using this equation, the concentration of methylene blue in the solutions at any contact time (Ce) in mg/l can be calculated as listed in Table 2 for both control and activated carbon. As the contact time increases, the absorbance value as well as the concentration of dye in solution is decreasing. This is due to bioadsorption. Bioadsorption is a process where bioabsorbents like activated carbon and the fungal biomass adsorbs coloured substances (methylene blue) from the aqueous solution. Since bioadsorption was taking place, the colour intensity of the solutions will decrease as the time proceeds and hence there are decreases in absorbance value of the solutions as time proceeds. By comparing the concentration of methylene blue in the solutions at any contact time (Ce) in mg/l of control and PC activated with carbon, it can be noticed that the Ce for PC activated with carbon is lower than that of control at the same contact time. This can be concluded that the dye removal is done better and faster by the PC activated with carbon than the control. In addition, the removal efficiency, % of methylene blue dye by activated carbon immobilized with fungal biomass increases as the contact time increased as shown in Table 3. This means that the longer the contact time, the higher the removal efficiency. The results indicate that the removal is higher at the beginning and this is probably due to the larger surface area of the immobilized activated carbon being available at the beginning for the adsorption of methylene blue. The amount of adsorption at equilibrium (qe) can be calculated by using the equation below: qe = (Co- Ce)V/W From Table 4 and 5 which shows the amount of adsorption at equilibrium for PC activated with carbon and control respectively, it can be concluded that the amount of adsorption at equilibrium is increasing as the dye concentration in solution is decreasing.

Adsorption isotherms are mathematical models that describe the distribution of the adsorbate species among liquid and adsorbent, based on a set of assumptions that are mainly related to the heterogeneity/homogeneity of adsorbents, the type of coverage and possibility of interaction between the adsorbate species. The equilibrium adsorption data are usually analyzed by adsorption isotherms such as Langmuir and Freundlich isotherms. These isotherms relate the amount of adsorption at equilibrium, qe with the concentration of methylene blue in solution, Ce. The Freundlich isotherm is an empirical equation employed to describe the adsorption processes on surface sites that are energetically heterogeneous while the Langmuir isotherm takes an assumption that the adsorption occurs at specific homogeneous sites within the adsorbent. Graph of ln qs vs Cs (Freundlich) and graph of Ce/qe vs Ce (Langmuir) for both PC activated with carbon and control are plotted which are Figure 2, Figure 3, Figure 4 and Figure 5. From the graphs, it can be concluded that in this experiment, Freundlich isotherm fitted well than the Langmuir isotherm with a correlation coefficient of 0.664 for PC activated with carbon and 0.772 for control.

6.0 CONCLUSION: In conclusion, the higher the concentration of methylene blue, the higher the intensity of the color and hence the higher the absorbance value. As the contact time increased, the absorbance value as well as the concentration of dye in solution is decreasing due to bioadsorption. The removal is higher at the beginning because there is a larger surface area of the immobilized activated carbon being available at the beginning for the adsorption of methylene blue. The PC activated with carbon have performed better dye removal task than the control which do not have activated carbon since the dye concentration in PC activated with carbon is lower than that of control at the same contact time. This means that PC activated with carbon have removed higher concentration of methylene blue dye than that of the control.

7.0 REFERENCE: Ahmadpour, A., & Do, D. D. (1996). The preparation of active carbons from coal by chemical and physical activation. Carbon, 34(4), 471-479. Aksu, Z. (2005). Application of biosorption for the removal of organic pollutants: a review. Process Biochemistry, 40(3), 997-1026. Ferrero, F. (2010). Adsorption of Methylene Blue on magnesium silicate: Kinetics, equilibria and comparison with other adsorbents. Journal of Environmental Sciences, 22(3), 467-473. Gupta, V. K. (2009). Application of low-cost adsorbents for dye removal–A review. Journal of environmental management, 90(8), 2313-2342. Hameed, B. H., Ahmad, A. L., & Latiff, K. N. A. (2007). Adsorption of basic dye (methylene blue) onto activated carbon prepared from rattan sawdust. Dyes and Pigments, 75(1), 143-149. Li, H., Li, Z., Liu, T., Xiao, X., Peng, Z., & Deng, L. (2008). A novel technology for biosorption and recovery hexavalent chromium in wastewater by bio-functional magnetic beads. Bioresource technology, 99(14), 6271-6279.

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