Biosorption of Congo Red from aqueous solution by crab shell residue: a comprehensive study
© Mohan Rao and Venkata Basava Rao. 2016
Received: 18 August 2015
Accepted: 6 April 2016
Published: 27 April 2016
The abundantly available bio waste, crab shell powder was used as an adsorbent for the removal of pollutants like Congo Red. The morphological, textural and chemical characterization of the biomass was done with SEM, XRD, EDS and FT-IR studies. The nature and mechanism of the process were determined from equilibrium, kinetic and thermodynamic studies. The results exhibited that the bio waste surface is fractured, rough and porous. It is composed of various surface functional groups which attracts organic pollutants. Equilibrium studies conclude Adsorption is a favorable process and it is a monolayer covering the surface. The maximum adsorption capacity, given by non-linear Langmuir isotherm was 124.9 mg/g. In kinetic studies pseudo-second order model best described the sorption kinetics compared to other models. Thermodynamic studies conclude that the process is spontaneous, endothermic and a physical adsorption.
By 2030, the world’s population is expected to increase to 8.3 billion and total seafood demand is estimated to be 183 million tons, while the estimated global seafood market is predicted to reach US$ 100 billion per annum. In addition, the world demand for seafood is currently increasing by 3 % every year. High-end sea food products, such as lobster and crab, are consumed more often at restaurants than at home. Crab continues to compete well against other seafood proteins, ranking in the top 10 highest consumed sea food products, while being the most expensive species on the list. American per capita crab consumption amounts to 0.7 pounds per year. In 2012, US alone imported 5.4 million pounds in a month. Only 20–30 % of the weight of the crab is processed for human food consumption. The remaining 70–80 % is generally discarded, causing surface and ground water pollution and increase of BOD and COD (Gupta and Suhas 2009).
At present, total dye production is estimated as 7 × 105–1 × 106 tons per year. More than 1 × 105 commercial dyes are produced, of which nearly 70 % are azo dyes. About 66 % of the total dye stuff produced is used in the textile industry, where nearly 100 L of water is required to process every kilogram of dye, and 10–15 % of the used dyes enter the environment through effluents. Most dyes are carcinogenic and cause skin and eye irritation. Presence of dyes in water bodies is highly objectionable on aesthetic grounds, and it disturbs the aquatic ecosystem by interfering with light transmission (Grag et al. 2003; Sirianuntapiboon and Srisornak 2007; Rangabhashiyam et al. 2014).
Congo Red (CR) is the first synthetic azo dye produced for dying cotton directly. It is used in a number of industrial activities, and consequently, found commonly in effluents (Vimonses et al. 2009; Purkait et al. 2007). Treatment of such effluents is difficult because CR is resistant to bio and photo-degradation due to its complex aromatic structure, physicochemical, thermal, and optical stability properties (Pielesz 1999; Smaranda et al. 2011).
Various physical, chemical, biological, acoustic, radiation, and electrical methods are adopted for dye removal. Of these, the biological method is commonly used because it is cost-competitive and suitable for a variety of dyes. However, it has the disadvantages of large space and longer process times requirements and less flexibility in design and operation (Zvezdelina and Nedyalka 2012; Robinson et al. 2011). Adsorption, generally using activated carbon, is considered the best alternative. However, because activated carbon is expensive and difficult to regenerate, it is important to find cheaper and environmentally friendly alternatives (Bhattacharyya and Sarma 2003). The concept of industrial ecology encourages the use of waste from one industry in the processes of another. In recent years, usage of biomass and solid waste as low-cost adsorbents has gained much attention (Ali and Gupta 2007).
In this study, we discuss the use of solid waste from the sea food industry for the treatment and elimination of toxics from waste water. Crab shell powder (CSP) has several advantages for use as an adsorbent, including ease of availability, low cost, and high biocompatibility. We extend our investigation to estimate the limitations and binding mechanism through kinetic, isothermal, and thermodynamic studies.
Congo Red, NaOH, and HCl supplied by Merck (Mumbai, India).
Preparation of CSP
Crab shells were collected directly from a local market (Bapatla, Andhra Pradesh, India), washed with tap water to remove slime and other debris, rinsed with distilled water, and then dried in an oven at 60 °C to a constant weight. The dried shells were crushed to a particle size of 40–120 µm. Acid-base treatments were given using 1N HCl and 1N NaOH, followed by repeated washing with deionized water, and drying in an oven at 60 °C over night. The treated particles were crushed again, separated using British Standard Sieves (BSS), and stored in dry vacuum packs to prevent moisture penetration for ready use as an adsorbent.
Digital weighting balance—SHIMADZU–AX200
Digital pH meter–ELICO-L 1 612
Temperature controlled rotating orbital shaker— REMI CIS 24 BL
High speed centrifuge-REMI C 24
The surface morphology of CSP was examined by scanning electron microscopy (SEM, Carl Zeiss, EVO-18) equipped with EDS analyser. IR spectra of CSP obtained with a SHIMADZU, FTIR 8400SFourier transform infrared spectrometer FTIR.
Results and discussions
Effect of particle size
Effect of dosage
Effect of initial dye concentration
Effect of pH
Isothermal parameters from linear models
KF (mg/g) (L/mg)1/n
Isothermal parameters from non-linear models
KF (mg/g) (L/mg)1/n
Design of adsorption process depends on the rate which can be estimated from kinetic study. The kinetics plays a key role in choosing the best operating conditions for the full-scale batch process. It also gives an idea about mechanism of mass transfer and rate controlling steps.
Kinetic parameters from linear models
The qe values estimated from the pseudo first-order kinetic model significantly differed with that of experimental values. Where as they agreed well with the estimates of pseudo second-order kinetic model with high correlation coefficient (R2 ≥ 0.994). Hence, the kinetics for sorption of CR on to CSP is analogous to pseudo second-order type. Similar phenomena were also observed in the adsorption of Congo red on activated carbon, calcium-rich fly ash and CaCl2 modified bentonite (Purkait et al. 2007; Lian et al. 2009).
In general mass transport through solid/liquid interface takes place by three different mechanisms, film diffusion, intra particle diffusion, and mass action. Mass action is a very rapid process and can be negligible for physical adsorption. Thus, the kinetic process of adsorption is controlled by either liquid film diffusion or intra particle diffusion or both.
Weber Morris found that in many adsorption cases solute uptake varies almost proportionally with t1/2 rather than with the contact time t. Where qt, C, ki refers to the amount of dye adsorbed in mg/g at time t, parameter indicating the boundary layer effect and Intra-particle diffusion rate constant (mg/g. min1/2). A plot between the amount of dye adsorbed and square root of time gives the rate constant. The plot should be the straight line passing through the origin if the intra particle diffusion is the sole rate limiting step (Kumar et al. 2007).
A plot of −ln(1 − qt/qe) vs. t should be a straight line with a slope R′ if the liquid film diffusion is the rate limiting step. The liquid film mass transfer equation has been successfully applied to model several liquid adsorption systems.
The adsorption is endothermic since the values of ΔH0 are positive. The values of enthalpies at all concentrations are less than 25 kJ/mol indicates the interfacial interaction is by physical forces and hence, it is physical adsorption. Positive values of ΔS0 indicate increased randomness at solid liquid interface thereby increase in adsorbate concentration on solid phase during sorption process. All the values of ΔG0 are less than −27 kJ/mol. The negative values indicate feasibility and spontaneity of the process.
EDS for elemental analysis of CSP
Sea food industry is one of the major sources of solid waste posing disposal problems. It can be used to remove organic pollutants emanating from various industries. In the present study, Crab shells were powdered and used to remove Congo red dye from water effluent. CSP is a rough and porous material primarily composed of calcium sulfate, calcium carbonate and chitin. It has functional groups of amine, hydroxyl and acyl groups along with sulfates and carbonates. CR diffuses and binds to CSP in aqueous phase, favored by intermolecular forces. The maximum adsorption capacity given by non-linear Langmuir isotherm was 124.9 mg/g. Both intra particle and film diffusion limits the rate while pseudo second order is the kinetic model representing the process. Thermodynamic studies reveal the removal was spontaneous and endothermic in nature.
MRT involved in experimental studies and results analysis. VBRV participated in the sequence alignment and drafted the manuscript. All authors read and approved the final manuscript.
We thank Prof. J. S. Rao & Dr P. Jawahar Babu of Bapatla Engineering College, for providing necessary facilities for the experimental work.
The authors declare that they have no competing interests.
Open AccessThis article is distributed under the terms of the Creative Commons Attribution 4.0 International License (http://creativecommons.org/licenses/by/4.0/), which permits unrestricted use, distribution, and reproduction in any medium, provided you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons license, and indicate if changes were made.
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