Generally, it has been reported that some of the adsorption phenomena are of pH dependent. Some studies have shown that the effective removal of contaminants from wastewaters/aqueous media can be either done at lower, neutral or higher pH value due to the surface chemistry of adsorbents and nature of adsorbate (contaminant). As we know that the normal range for pH in surface water systems is 6.5 to 8.5.
(a) So, is there any advantage on adsorption process to be conducted at solution pH near to 7, so that before the treated wastewater (effluent) released to aquatic environment, it should have a pH corresponding to the surrounding water.
(b) What's the effect behind if the effluent which is released into aquatic environment has pH that does not match the surrounding?
I would say, No. Aquatic environment and effluents have different pHs depending on the location, ..... So, it is better to have a pH independent adsorbent or an adsorbent with maximum adsorption capacity at pH close to a given water.
If an effluent with a different pH than the released to an aquatic environment, depending on the effluent volume, the pH of the aquatic environment may change or not. Any how, an efficient adsorbent should be able to treat the targeted solution. So, the targeted solution (effluent or aquatic environment) should be chosen and an efficient adsorbent corresponding to the adsorption medium (in terms of pH, chemical stability, etc.) should be used.
@Ali Nematollahzadeh thank you for good explanation. I'm grateful
@Augustine Ifelebuegu Thank you very much. This is a very useful information to me.
From laboratory experiments perspective, this depends mostly on the properties of pollutants/organics compounds being adsorbed as well as the zeta potential of adsorbent being use. Pharmacutical and pesticide exist in different form at different pH (i.e. protonated, netural and deprotonated form). Each of this form has distinct properties which affect their removal by adsorption. If the adsorbent is negatively charged like clay materials, it will have high affinity for deprotonated form of the organic and vise versa.
In addition to Soliu comment, I would like to add a minor comment on pharmaceuticals:
Some pharmaceuticals (being ionic at neutral pH) possess little adsorption potential to adsorbent (typically wastewater sludge) compared to the basic pharmaceuticals. This means that acidic pollutants are more likely to remain in the water whereas, basic pharmaceuticals can easily adsorb on adsorbent.
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