Copper belongs to a category of elements called heavy metals, these are elements having high atomic density and a weight over five times greater than the weight of water. They include: mercury, lead, copper cadmium among many others. These elements have several uses ranging from domestic, industrial, agricultural, medical as well as technological leading to their widespread presence in the surrounding (Castro et al., 2011). This is a potential health and environmental hazards that is increasingly becoming a global health concern since these elements are non-biodegradable thus can stay indefinitely in the environment (Tchounwou et al., 2014). Some of the toxic effects of copper contamination includes, decreased plant food sources that lead to reduction in wildlife, interference with cell functions and reproduction in fish. In humans we can have chronic damage to circulatory system, nephrotoxicity and high risk of malignancies. Other symptoms of copper poisoning range from hematemesis, liver dysfunction, hypotension, jaundice, coma to malena.
Their removal from the surroundings like contaminated waters has attracted many studies in the recent years as a result of the toxic effects of the metal ions on the aquatic life. Different methods ranging from precipitation, electro coagulation, electro precipitation and ion exchange on resins have been utilized to eliminate these heavy metals. It’s their expensive cost and the strict environmental regulations rising from public health concerns that has led to heightened search for cheaper options to remove heavy metals from industrial wastewaters (Aslan, 2016).
Adsorption has shown great efficiency when activated charcoal, zeolite or clay are used though still too expensive hence the increasing need for a relatively low cost, efficient and readily available adsorbent materials. With the growth currently seen in the coffee industry, more coffee wastes such as husk which can be used as adsorbent are on the rise. the availability and lower costs involved has attracted researchers to explore this alternative (George, 2012). In this experiment we investigate the effectiveness of varying concentrations of coffee grounds in removing copper from wastewaters. It was hypothesized that ground coffee adsorbent is effective in removing heavy metals from waste water and the effect increases with increase in concentration of coffee. A spectrophotometer was to be used to determine the concentration of copper ions upon adding a dye that formed a complex with Cu2+ ions, the more the copper the darker the color of the solution. It followed the Beer Lambert’s law which stated that, absorbance has a direct proportionality relation to the concentration on the material sample. Spectrophotometry follow the principle in measuring the amount of light passing through the sample solution. Each compound in this case transmits light over a given range of wavelength to give the absorbance. The result will be compared with the calibration curve data which is the control.
Materials and Methods
Materials: spectrophotometer, weighing balance, copper (II) solution of concentration (0.1 – 10ppm), 15mL centrifuge tubes, safety glasses, labcoat, ethanoate buffer (pH 5), Alizarin Red solution, pipette, centrifuge, measuring cylinder, timers and specimen vials.
The important safety concerns: Safety glasses and lab coats must be put on throughout the practical session and heavy metal wastes were to be discarded in the using the containers given.
Part A: for calibration data, varying concentrations of copper ions ranging from 0 to 10ppm were put in six different jars and their absorbance tested using a spectrophotometer at 520nm wavelength. These measurements were taken before each set of tests.
Part B: 10mL of 10ppm copper (II) was put in four different centrifuge tubes containing coffee ground of different weights but not more than one gram added. The tubes were gently agitated using a vortex mixer and solutions allowed to rest for 10 minutes before being transferred to a centrifuge at 2000 rpm for five minutes. Tubes were removed from the centrifuge and the resulting solution pipetted into specimen vials. Five millilitres of ethanoate buffer and five millilitres of Alizarin Red solution were added to the specimen vials, a lid put followed by gentle shaking. The sample was transferred to a cuvette and absorbance from a spectrophotometer set at 520nm wavelength recorded in a spreadsheet. This procedure was repeated three time and average masses of coffee, final copper concentration, percentage of copper removed and standard deviation calculated.
Results
Figure 1: Calibration curve showing the relationship between absorbance and the concentration of copper (ppm).
Table 1: The removal of copper from wastewater using coffee grounds of different masses.
Average Mass of Coffee(g) ±0.00005 n=3
Original Copper Concentration (ppm)
Final Copper Concentration (ppm)
% Copper Removed
Std Dev
%RSD
0.2528
10
3.409
65.91
0.578530401
16.9715584
0.5019
10
3.219
67.81
0.624260687
19.39169085
0.7504
10
2.549
74.51
0.645866455
25.33527628
1.0002
10
2.271
77.29
0.547344454
24.09946743
Figure 2: The percentages of copper ions removed versus the mass ground coffee used.
Discussion
From table 1, the concentration of copper ions in solution decreased with increasing mass of ground coffee while the percentage of extracted copper increased. This is consistent with the calibration data in figure one showing a proportional relationship between the concentration of copper ions in the solution and absorbance. Calibration was done to act as a standard reference to determine how absorbance of copper varies at different concentrations, it acts as the standard. The graph in figure 2 further confirmed that observation, whereby percentage of copper removed increased with increasing mass of ground coffee. This showed that as the concentration of the adsorbent (coffee) increases more active sites are available to interact with the copper ions in the solution thus the trend (Sabela et al., 2016). This trend however applies as long as certain conditions are met, pH, agitation rates, saturation of active sites and temperature must be maintained. That is why sodium ethanolate buffer was used to provide an optimal environment for functioning of the adsorbent which is optimal in the pH of five and beyond which precipitation occurs.
Since coffee contains both weak acid and basic groups, it then follows the principle of acid-base equilibria existing in the pH range of between 2 to 7. The binding of copper here is mainly guided by the state of dissociation the weak acid. It’s the carboxy groups in the coffee responsible for the adsorptive property in these materials. Since the pH was kept constant by the buffer, the number of H+
ions did not change so it is only the number of negative ions of carboxyl groups that were at play. Increase in mass of coffee ground led to increase in negative ions that provided more surface for electrostatic attraction to positive copper (II) ions leading to the observed increase in amount of copper removed (George, 2012).
The procedure was repeated three times in order to build confidence in the data as far as accuracy, reliability and reproducibility of the method is concerned. In order to obtain a reliable data, the test results must be accurate; the right value must be obtained providing a consistent and unambiguous representation. For this reason, it is always advisable to run the same test at least three times and find the average values. The calculation gave a ±0.00005g difference on the average weight of the three runs. The small value of the standard deviation indicates that the data is tending towards mean an indication that the data is consistent. This also help with correcting the errors that may occur in the method applied or with faulty equipment thus making the results more reliable.
From the results it’s clear that the study objective was met however, these data offer limited information for making far reaching decisions. For instance, it did not adequately capture other factors such as temperature, time and pH that influence the efficiency of the adsorbent so this opens the field for more research.
Conclusion
This study has supported the earlier hypothesis that ground coffee adsorbent is effective in removing heavy metals from waste water and the effect increases with increase in concentration of coffee. It has been confirmed from the results from different weights of coffee that were used which showed results similar to those of other commonly used adsorbents like activated charcoal. In searching for cheaper and effective alternatives for removal of heavy metals from wastewaters for industrial application, coffee apart from being readily available, cheap they are also effective. This calls for more research to explore its potentiality as well as eventually availing it for commercial use.
References
Aslan, S., 2016. Adsorption Of Heavy Metals Onto Wastewater Treatment Plant Sludge. European Scientific Journal, ESJ, 12(10).
Castro, R.S., Caetano, L., Ferreira, G., Padilha, P.M., Saeki, M.J., Zara, L.F., Martines, M.A.U. and Castro, G.R., 2011. Banana peel applied to the solid phase extraction of copper and lead from river water: preconcentration of metal ions with a fruit waste. Industrial " Engineering Chemistry Research, 50(6), pp.3446-3451.
GEORGE Z. KYZAS. (2012). Commercial Coffee Wastes as Materials for Adsorption of Heavy Metals from Aqueous Solutions. Materials. 5, 1826-1840.
Sabela, M.I., Kunene, K., Kanchi, S., Xhakaza, N.M., Bathinapatla, A., Mdluli, P., Sharma, D. and Bisetty, K., 2016. Removal of copper (II) from wastewater using green vegetable waste derived activated carbon: An approach to equilibrium and kinetic study. Arabian Journal of Chemistry.
Tchounwou, P. B., Yedjou, C. G., Patlolla, A. K., " Sutton, D. J., 2012. Heavy metal toxicity and the environment. Experientia supplementum (2012), 101, 133-64.
