الفهرس 
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Abstract
especially when industrial effluents are present in water bodies. Tanneries effluents are one of the biggest sources of concern in wastewater management because they are loaden with heavy metals, especially chromium in the form of chromium (VI) and chromium (III). Many if not all, small-scale tanning industries cannot afford the expensive conventional methods of wastewater treatment such as adsorption, precipitation, and ion exchange. Those the application of such methods cannot completely remove the toxic metals from the effluent. The result is that industries channel untreated or partially treated effluents with chromium and others.
The aim of the present study:
The present study aims to investigate the effectiveness of low-cost and environmentally friendly materials such as agricultural waste (banana peels and watermelon peels) for removal hexavalent chromium from aqueous solutions or tanneries wastewater.
The study was focused in:
1. Evaluation the content of chromium in tannery wastewater.
2. Preparation of adsorption of natural materials i.e. banana peels and watermelon peels in different forms (raw materials, nano materials, acid treated materials, and alkaline-treated materials).
3. The adsorption experiment to remove chromium was done under different conditions i.e. contact time (30, 60, and 120 min), the dosage of adsorbents (2.0, 4.0, and 8.0 g), the concentration of chromium (400 and 600 ppm.) and pH (1.0, 2.0, 3.0 and 4.0).
4. Determination of the removal percentages of chromium by different form peels
The obtained results could be summarized in the following points.
Firstly, removal chromium from contaminated water by using different forms of banana peels.
1. The FT-IR spectra of normal and nano banana peel had similar spectra, indicating similar characteristic functional groups and similar structural chemistry across all samples.
2. The property of banana peel with a highly porous structure plays an important role in the adsorption process.
3. The adsorption capacity reached 10.02 mg/g using natural banana peels at a time of 120 minutes, while it reached higher amount (14.03 mg/g) at a time of 30 minutes using nano metric banana peels.
4. The efficiency of nanometric banana peels reached 1.7 times that of natural banana peels.
5. It has been observed from the data that the percentage of chromium removal from aqueous solutions was increased by increasing the weight of the adsorbent material.
6. The optimum pH for the maximum removal of Cr (VI) was found to be pH 4.
7. The adsorption data are in close agreement with the Langmuir isotherm model. The R2 values are less than one which illustrate that the adsorption data are fully fitted with the Langmuir isotherm model and the adsorption of Cr (VI) onto banana peel is favorable.
8. The obtained results showed that banana peels, whether of normal or nano size, had a superior ability to absorb chromium from tannery wastewater, so the adsorption efficiency reached 81.06 and 97.95 % for both normal and nanometric peels, respectively.
9. It has been noticed from the accomplished results that there were clear differences by using both hydrochloric acid and sodium hydroxide to prepare the adsorbent material from banana peel comparing with the raw material of the peels where the results showed that by hydrochloric acid had a superior effect in removal chromium from the aqueous solution.
10. The removal rate reached 99.54% using HCl treatment, while the maximum removal rate of chromium from the aqueous solution reached 74% by sodium hydroxide treatment on banana peels.
11. . It is worthy to note that the maximum removal of chromium from the aqueous solution by the application of sorbent material treated with acid and alkali compared to the raw material which was in the following order: HCl (99.5%) > NaOH (74.0%) > Raw material (72.45%)
Secondly, removal chromium from contaminated water using different forms of watermelon.
1. Normal and nano watermelon peel had similar spectra (FT-IR), indicating similar functional groups and hence similar structural chemistry across.
2. Irregular-shaped pores are present in TEM graphs for watermelon, however, seem to be uniformly distributed on the entire surface and smooth.
3. The efficiency of nanometric watermelon peels has reached 1.5 times that of natural watermelon peels.
4. The adsorption was increased with the increment of adsorbent dosage.
5. The maximum removal has been achieved with conventional peels which reached 77.61%, at 8.0 grams and 400 ppm Cr (VI).
6. The obtained results showed that by increasing the concentration of chromium in the solution, the percentage of its removal from the aqueous solutions of both normal and nanometer peels was decreased. The average removal percentage reached 77.61% and 100%, respectively for the concentration of 400 ppm while 62.31 and 74.45% respectively for the concentration of 600 ppm for both normal and nanometer peels, respectively.
7. The optimum pH for the maximum uptake of Cr (VI) was found to be pH 4
8. The adsorption results were in close agreement with the Langmuir isotherm model. The R2 values were less than one which shows that the adsorption data are fully fitted with the Langmuir isotherm model and the adsorption of Cr (VI) onto watermelon is favorable.
9. By the application of tannery wastewater, the outcomes demonstrated that watermelon peels of any size, whether regular or nano, had a greater capacity to removal chromium, as evidenced by the adsorption efficiency which reached 82.53 and 95.77% for normal and nanometric peels, respectively.
10. Maximum removal of Cr (VI) has been achieved by acid-treatment watermelon peel, removal percentage reached 84.75% to comparing with normal size peel which reached 77.61%
11. The outcomes demonstrated that watermelon peels of any size, whether regular or nano, had a greater capacity to removal chromium, as evidenced by the adsorption efficiency which reached 45.5 and 84.75% for samples treated with NaOH and HCl peels, respectively.
Finally, it has been concluded that, it could be utilized banana and watermelon peels, especially in the forms of nano particles and treated samples with HCl or NaOH for the removal of heavy metals i.e. chromium. But for the application of this study, it could be more of studies, specially from the economical point of view.