Discussion
Effect of initial concentration of humic materials in water on efficiency of XAD-8 resin
XAD absorbent resin may use large amounts of water (10-100 L) to separate humic materials
5. All XAD resins mostly absorb organic materials by hydrophobic link. The precise mechanism of absorbance is still unknown. XAD, XAD-2, and XAD-8 are mostly used to separate humic materials from aqueous environment
13.
The efficiency of XAD resins is influenced by the concentration of humic materials; as though, the higher concentration of these materials leads to the lower performance of the resin. The low extraction of humic materials from XAD resins justifies the interruption of some humic compounds and resin materials, implying that some humic materials have been trapped inside the resin pores. The efficiency of absorbance is actually influenced by the fact that there are some hydrophilic compounds in humic materials that are not adsorbed on resin surfaces
7. The effect of initial concentration of water on the efficiency of XAD-7HP resin is shown in Figure 2. As observed in this figure, an increase in initial concentration of humic materials reduces the efficiency of XAD-7HP resin, but the Pearson correlation statistical test doesn’t show the significant difference between humic materials and resin efficiency (p-value > 0.05).
Effect of water pH on the efficiency of XAD-7HP resin
As earlier mentioned, pH is one of the important parameters on adsorption and extraction of humic materials as it effectively influences the extraction processes. Figure 3 shows the results related to the effect of pH changes on the efficiency of XAD - 7HP resin. The obtained results show that XAD - 7HP anionic resin has the maximum absorption efficiency in the extraction of humic materials in acidic pH which is observable in all real and standard samples. Pearson correlation statistical test shows the effect of pH changes on the efficiency of XAD-7HP (p-value < 0.05).
Effect of electric conduction (EC) on the efficiency of XAD-7HP resin
EC is a physical property of water that shows the conductivity of electricity. There is a close relationship between EC and total soluble solids (TDS) in water, because anions are the main factor for electricity transfer in solutions and they indicate electrical conductivity. Changes in EC and the effect of this parameter on the efficiency of XAD-7HP anionic resin is shown in Figure 4. It is observed that increasing EC decreases the efficiency of resin due to increase in TDS probability and as a result, occupancy of resin adsorbent surface by these materials. Although the efficiency of XAD - 7HP resin decreases by increasing EC, Pearson correlation statistical test didn’t show any significant relationship between them (p-value > 0.05).
Effect of water sample turbidity on the efficiency of XAD-7HP resin
Turbidity is one of the most serious problems in extracting humic materials from water samples by resins. According to the turbidity of raw water samples, it seems that occupancy of adsorbent resin sites by turbidity agents can be a reason of turbidity effect on reduction of adsorption of the humic materials. In general, increasing turbidity reduces the efficiency of the mentioned anionic resin
14. As earlier mentioned, the reason for this is adsorbent sites limitation by resin and their occupancy by turbidity. The results related to the effect of turbidity on the efficiency of XAD-7HP anionic resin is shown in Figure 5. It can also be observed that the efficiency of resin is reduced with the increasing turbidity. Pearson correlation statistical test shows that the relationship between turbidity value and the efficiency of XAD - 7HP anionic resin is significant (p-value < 0.05).
The effect of sample temperature on the efficiency of XAD-7HP resin
The seasonal changes of raw water and biological activity influence the quality of input water and its treatment capacity
14. The NOM amounts might be high during the warmest months of the year which is coincident with the season water is needed at its peak. Therefore, extraction and measurement of humic materials is essential and important. The degradation of aqueous environment consequently results in an increase in organic materials. Also algae and bacterial population increase in high temperatures, resulting in a corresponding increase in biological activities. Thus, an increase in the temperature of water results in a corresponding increase in its humic materials which are compound of various organic materials
15. The related results to temperature on the efficiency of XAD - 7HP anionic resin is shown in Figure 6. As seen in this figure, resin efficiency decreased with an increase in the temperature of water. This reduction in efficiency can be attributed to the increase in organic load of aqueous environment and also in the biological activity of resin including the occupancy of absorbance sites by biological factors
12. Although resin efficiency decreases by increasing temperature, Pearson correlation statistical test doesn’t show any significant relationship between temperature and efficiency of XAD-7HP resin (p-value > 0.05).
Conclusion
It can be concluded that the use of anionic resins is a proper technique with high efficiency in the extraction of humic materials from aqueous environments. Anionic Amberlite XAD - 7HP resin is a proper resin to extract the humic materials from the raw surface water entrance to the water treatment plant whose efficiency was obtained as 77% in this research. In this study, pH was discovered to be an important and effective parameter in the efficiency of resin, such that the maximum efficiency of resin was obtained at a pH < 2.
Acknowledgements
The authors would like to gratefully acknowledge the Isfahan water treatment plant for their help in the collection of water samples.
Funding
The work was not funded.
Conflict of interest
We affirm that this article is the original work of the authors and have no conflict of interest to declare.
This is an Open Access article distributed in accordance with the terms of the Creative Commons Attribution (CC BY 4.0) license, which permits others to distribute, remix, adapt and build upon this work, for commercial use.
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