Research Journal of Environmental Sciences

Year: 2010 | Volume: 4 | Issue: 6 | Page No.: 566-572
DOI: 10.3923/rjes.2010.566.572

The Use of Some Food Industrial by Products for Waste Water Purification

A.B.S. Al-Barak and S.M. El-Said

Abstract: Most available technologies applied in the removal of metal contaminants in aqueous systems use the well established processes of adsorption. Adsorbents currently in use are either too expensive or not readily available for waste water treatment. There is a need to develop new adsorbents which are readily available at low cost to remove metal contaminants in aqueous system. In this work, okra wastes as a food canning processes by products were used as a potential adsorption of cadmium (II), iron (II) and zinc (II) removal from various aqueous solutions. Qualitative and quantitative analysis of okra wastes were investigated. Infrared spectra of the okra wastes were recorded to detect the function group that gained the capabilities of okra wastes for metal ion adsorption. Batch studies were performed to evaluate the adsorption process and it was found that the okra wastes were found to adsorb 96.4% of cadmium (II), 93.8% of iron (II) and 79.8% zinc (II). The rate of adsorption follows pseudo-second order kinetics before attaining equilibrium. This work proved that okra wastes can be used as an efficient adsorbent material for removal of heavy metals from water and waste water.

Keywords: okra waste, heavy metals, batch technique, Adsorption and kinetic studies

INTRODUCTION

The pollution of water resources due to the disposal of heavy metals has concern for the last few decades. It is well known that some metals have been responsible for several health problems with animals, plants and human beings. Cadmium (II), iron (II) and zinc (II) are introduced in to bodies of water from smelting, phosphate fertilizer, mining, pigments, stabilizers, alloy industries and sewage sludge. Toxicological studies have shown poisoning effects that in long term from cadmium, iron and zinc includes kidney damage and changes to the constitution of the bone, liver and blood. Short term effects include a number of acute and chronic disorders, such as renal damage, emphysema, hypertension and testicular atrophy (Leyva, 1997). Chemical precipitation, reverse osmosis, electrodialysis, ion exchange, adsorption and biosorption have been developed over the years to remove these heavy metals from waste water (Leyva et al., 2002; Pavasant et al., 2006; Ahluwalia and Goyal, 2007; Naddafi et al., 2007; Dahiya et al., 2008). However, the high price of the adsorbents is the disadvantage for adsorption treatment method. So, it is necessary to find some adsorbents with low cost and high efficiency for the removal of hazardous metals from waste water. In recent years, agricultural by products have been used as adsorbents for the adsorption of hazardous substances from waste water. Much work on the adsorption capacitance of some agricultural by products such as, maize cob, apricot stones and date stone have been carried out by El-Sayed (2004) and Al-Barrak and Elsaid (2005). This study may generate useful information for the utilization of native agricultural by products for the removal of cadmium (II), iron (II) and zinc (II) from waste water. Okra wastes, as agricultural by products from food canning industries, could be heavy metal adsorbents which could be selective for some metal ions. The capabilities of okra wastes for metal ion adsorption were tested at several experimental conditions. The effect of pH, metal concentration, adsorbent dose, particle size and temperature on the rate of removal of cadmium (II), iron (II) and zinc (II) were investigated.

MATERIALS AND METHODS

Adsorbent
The raw material used in this work as an adsorbent was the food industrial wastes (okra wastes). This waste is obtained from food canning processes. Okra wastes put in an electrical oven to a temperature of 60°C for 24 h. Dried okra wastes were broken to powder form in an electrical mixer. It was then sieved into particle sizes 0.5-4 mm. The infrared (IR) absorption spectrum apparatus was used to investigate the chemical structure of okra wastes.

Infrared Spectra of the Okra Waste
An infrared spectrum (IR) of okra wastes was obtained using a Perkin-Elmer 621 spectrophotometer. The infrared spectrum of the solid substance has been recorded on in the region 0.000-4000 cm^-1 using KBr technique. The observed frequencies have been assigned in terms of the fundamentals, overtones and combinations assuming D 2 h point-group symmetry (Bergland et al., 1993).

Chemical Analysis
The chemical analysis of okra wastes was measured to detect its main contents using High-Performance Liquid Chromatography (HPLC). A Shimadzu LC-6A high-performance liquid chromatography equipped with a Rheodyne model 7125 injector and a Hitachi model F-1050 fluorescence spectrophotometer was used. Also, qualitative and quantitative carbohydrate analysis of okra wastes were measured using (HPLC).

Adsorption Process
The sorption of cadmium (II), iron (II) and zinc (II) ions have been studied by batch experiments. Solutions of Cd²⁺ ions (20 mg L^-1), Fe²⁺ ions (20 mg L^-1) and Zn²⁺ (20 mg L^-1) were prepared from 1 g L^-1 stock solution of each salt using distilled water, respectively. When the solution volume for both cations was fixed at 100 mL, the adsorption percentage of Cd (II), Fe (II) and Zn (II) ions as a function of shaking time was investigated at a shaking speed of (220±5) min^-1. After the filtration, the concentrations of Cd²⁺, Fe²⁺ and Zn²⁺ ions in filtrate water were determined by High-Performance Liquid Chromatography-Hydride Generation Atomic Absorption Spectrophotometry (HPLC-HGAAS). The adsorption percentage is determined as:

where, η is the adsorption percentage of cations. C_o and C_e are the initial and the equilibrium concentrations of cations respectively, (mg L^-1). The average of adsorption percentage is adopted everywhere in this study after three measurements.

RESULTS

Infrared Analysis

The amount of information that can be obtained from the IR spectrum of okra wastes is rather limited. The spectra are reported principally for any future identification (Fig. 1), since the absorption bands for such complex compounds are usually broad and diffuse (Glicksman, 1969). Table 1 was showed the chemical groups corresponding the wave number of bonds cm^-1. A part from the usual bands for hydroxyl (3500 cm^-1) and ester carbonyl (l730 cm^-1) groups, nitrogen of protein (1430 cm^-1), amide deformation (1200 cm^-1) and ether group (950 cm^-I) can be distinguished.

Chemical Analysis

The results of the chemical analysis of okra wastes are useful in giving a hint of relative proportions of the different components. The contents of cellulose, protein and minerals are shown in Table 1 for the okra wastes. So, the main constituent of okra wastes are α-cellulose and protein. This could indicate a high adsorption capacity of okra wastes which referred to the negative charge of both N and O of α-cellulose and protein that absorb positive charged metals. Qualitative and quantitative carbohydrate analysis of okra wastes solutions were also analyzed. The carbohydrate analysis were recorded 74.13, 52.01, 43.65 and 37.73 (mg sugar g^-1 okra waste) for rhamnose, galactose, glucose and rabinose, respectively.

Adsorption Process
The effects of shaking time on the adsorption of Cd²⁺, Fe²⁺ and Zn²⁺ ions on okra waste are shown in Fig. 2, which indicates that the removal of cations by okra wastes are improved with increasing shaking time. The adsorption reaches equilibrium at about 90 min on okra wastes and the maximum adsorption percentages are 96.4, 93.8 and 79.8% for Cd (II), Fe (II) and Zn (II), respectively.

Adsorption Kinetics
According to Fig. 2, the adsorption rate of Cd²⁺, Fe²⁺ and Zn²⁺ ions increase sharply in 60 min and then reaches equilibrium gradually at about 90 min. Quantifying the changes in sorption with time requires that an appropriate kinetic model is used and traditionally. The pseudo-first order equation (Huang et al., 2007), is generally expressed as Eq. 3 and 4:

where, q_e and q_t (mg g^-1) are the sorption capacities at equilibrium and at time t, respectively. K_ad is the rate constant of pseudo-first order adsorption (min^-1).

After integration and applying boundary conditions t = 0 to t = t and q_t = 0 to q_t = q_t, the integrated form of Eq. 2 becomes:

A plot of log (q_e–q_t) vs. time should give a straight line to confirm the applicability of the kinetic model and a derivation of the constant. Figure 3 shows a plot of log (q_e–q_t) vs. t for the 5 mg L^-1 metal adsorption on okra wastes. Recently, a pseudo-second order equation has been suggested as being more appropriate for describing this type of adsorption (Wasedaj and Forester, 1996):

Plots of t vs. t/q are shown in Fig. 4. It can be seen from Fig. 4 that the pseudo-second order kinetic model provides a good correlation for the adsorption of Cd²⁺, Fe²⁺ and Zn²⁺ ions by okra wastes in contrast to the pseudo-first order model.

The correlation coefficients of the pseudo-second order kinetic model are very high and the q_e values are close to the calculated q_e values (Table 2).

DISCUSSION

The chemical analysis of okra wastes show that they have a high sugar, cellulose, lignin and protein contents, (containing higher percentage of N, P and O). Also, infrared analysis show a high percentage of [OH], [C=O], [N], [C-O-C] and [C=C] in the okra wastes constituent. Lone pair of electrons that exist at oxygen and nitrogen atom represent a high negative charge. Hence, okra wastes become highly negatively charged and capable to absorb the positively charged metals of Cd²⁺, Fe²⁺ and Zn²⁺. The adsorption experiments of metal ions on the okra wastes showed a high relatively ion exchange capacity. Also, the adsorption of investigated metals by okra waste could be attributed to the cellulose, protein, lignin and sugars component of the okra waste where site-binding adsorption might be occurring. This could be due to the surface complexation phenomenon of functional groups present in the okra wastes. The removal of Cd (II), Fe (II) and Zn (II) ions, is probably due to the mixed effect of ion exchange and surface complexation on the surface of okra wastes, these results were supported by Hashem (2007). The adsorption kinetics results showed that the second-order equation was the more appropriate and it was, therefore, used to analyze the data for all the sorption/time trials. These results were contradicted with Prasad and Sund (1995), they suggested that the optimum sorption conditions for Cu²⁺, Cd²⁺, Zn²⁺, Pb²⁺, Co²⁺, Ni²⁺ and Fe³⁺ under static and dynamic (column) methods were ascertained. Also, the relatively fast kinetics of the sorbent with the time required to reach half of the maximum sorption (t_1/2 value 2 min).

CONCLUSION

The results clearly show that the low cost adsorbent (okra wastes) is a better adsorbent for Cd²⁺, Fe²⁺ and Zn²⁺. The most explanation of the highly sorption capacity of okra waste is that the negative charge of okra waste that make it capable to absorb the positively charged metals of for Cd²⁺, Fe²⁺ and Zn²⁺. From the kinetic model analysis using coefficient of determination, the pseudo-second order model was the most fitting for the description of Cd²⁺, Fe²⁺ and Zn²⁺ transport from the bulk solution onto the surface of okra wastes adsorbents.

REFERENCES