Table 6 Effect of important water cations and anions on the formaldehyde removal efficiency.
From: Evaluating the efficiency of formaldehyde degradation from aqueous environment by sonozone technique
Variables | Units | Value in reactor | Problem |
|---|---|---|---|
Calcium | mg/L as CaCO3 | 120 | Calcium ions cannot also act as radical scavengers, consuming ⋅OH radicals that are crucial for breaking down formaldehyde |
Dissolved oxygen | mg/L | 8.08 | Maintaining moderate DO levels (6–10 mg/L) ensures optimal performance. Higher DO generally improves removal efficiency, but extremely high levels can reduce cavitation intensity |
Nitrate | mg/L | 9.2 | At moderate levels, nitrates can enhance oxidation by forming reactive nitrogen species under ozonation and sonication. However, at high concentrations (> tens to hundreds of mg/L), nitrates act as radical scavengers, competing with formaldehyde for ⋅OH radicals and thereby reducing removal efficiency |
ORP | mV | 275 | Higher ORP values generally correspond to stronger oxidizing conditions, which enhance the breakdown of formaldehyde. However, extremely high ORP (> + 700–800 V) can also indicate excessive radical scavenging or instability of ozone, reducing efficiency. Ozone may decompose too quickly, and radicals may be consumed by competing ions (e.g., carbonate, nitrate, sulfate) |
pH | - | 7.14 | At higher pH, ozone decomposes faster into radicals, but excessive carbonate species (from calcium hardness) compete with formaldehyde for those radicals, reducing net removal efficiency |
Sulfate | mg/L | 94.3 | Sulfate ions in water can influence formaldehyde removal efficiency with Sonozone. At moderate concentrations, sulfates can enhance radical generation (via sulfate radicals, SO₄•⁻), improving oxidation. However, at high concentrations (> several hundred mg/L), sulfates act as scavengers, consuming ⋅OH radicals and reducing efficiency |
Temperature | °C | 20 | Water temperature strongly influences formaldehyde removal efficiency with Sonozone. Moderate heating (from ~ 25 °C to ~ 50 °C) enhances removal efficiency, but excessively high temperatures reduce performance due to ozone instability and radical scavenging |
Total Alkalinity | mg/L as CaCO3 | 120 | High alkalinity buffers the solution, stabilizing pH but also consuming radicals |
Ferrous ions | Mg/L | > 1–3 | Excessive iron can hinder performance due to radical scavenging and sludge formation |
