Combining gases and cavitation

What combining cavitation and gases does

Pairing HC (hydrodynamic cavitation) with a reactive gas such as ozone, or with a liquid oxidant such as hydrogen peroxide (H₂O₂), creates a hybrid AOP (advanced oxidation process). In the studies below, these hybrids degraded pollutants faster than either step on its own. The mechanism is that collapsing cavitation bubbles act as micro-reactors, breaking oxidants down into non-selective radicals.

Cavitation plus ozone

Cavitation improves ozonation in two ways Wang et al., 2022:

• Physical: intense turbulence and micro-circulation reduce mass transfer resistance and break ozone gas into micro-nanobubbles that dissolve rapidly.
• Chemical: the extreme conditions of cavity collapse (hot spots) thermally decompose ozone (O₃) into atomic oxygen (O) and oxygen molecules (O₂). The atomic oxygen reacts with water to form hydroxyl radicals (•OH), which are far more reactive than molecular ozone.

The benefit is expressed as a synergy index. In the degradation of the pesticide methomyl, the combined process reached a rate of 915.94 × 10⁻³ min⁻¹, against 2.1 × 10⁻³ min⁻¹ for ozonation and 17.1 × 10⁻³ min⁻¹ for cavitation alone, a synergy coefficient of up to 47.6 Mohod et al., 2023; Wang et al., 2022.

The same pattern appeared in dye wastewater. With Reactive Blue 13, the hybrid system decolorized the water within 15 minutes and reduced total organic carbon (TOC) by 72% in 120 minutes, faster than either process alone Wang et al., 2022.

Cavitation plus hydrogen peroxide

Cavitation splits H₂O₂ into two hydroxyl radicals more efficiently than heat or UV activation alone. The dose has an optimum: excess H₂O₂ scavenges the radicals it produces and forms weaker hydroperoxyl radicals (HO₂•), which lowers efficiency Mohod et al., 2023.

Side-by-side gas comparisons in oil recovery

Direct comparisons of nanobubble gases show that the choice of gas changes fluid behavior:

• CO₂ versus air: CO₂ nanobubbles reduced the surface tension of a surfactant-polymer solution by about 20.3%, to 31.7 mN/m, while air nanobubbles reduced it by about 7.1%, to 59.7 mN/m English, 2025.
• CO₂ in water flooding: in core-flood tests, water flooding enhanced with CO₂ nanobubbles reached an ultimate recovery of 71–72%, about 45% above the control, which the review attributed to oil swelling and viscosity reduction English, 2025.
• Nitrogen versus water: in spontaneous imbibition tests on oil-wet carbonate rock, nitrogen nanobubble solutions reached 32.6% ultimate recovery, against 21% for distilled water, pointing to wettability change or slippage Elnaggar et al., 2025.

Energy and cost: hydrodynamic versus acoustic cavitation

Energy cost is a main barrier to industrial use, and the reviews cited here favor HC over acoustic cavitation (AC) for bulk processing:

• Biodiesel: HC reactors with multi-hole orifice plates reached 99% biodiesel yield in 5 minutes; ultrasonic bath methods needed 90 minutes to reach 95%. Processing cost was estimated at 4.80 USD/m³ for HC, against 6.7–10.8 USD/m³ for acoustic methods Cako et al., 2022.
• Pollutant degradation: for methyl parathion, the cavitational yield of HC was 4.44 × 10⁻⁶ mg/J, against 2.098 × 10⁻⁷ mg/J for AC Mohod et al., 2023.
• Fuel desulfurization: vortex-diode HC systems reported costs as low as 36 USD/m³ at 100% reported efficiency. Comparable acoustic methods were estimated to cost more, because converting electrical energy into sound is inefficient Cako et al., 2022.

Aeration economics

A net present value (NPV) analysis compared conventional blowers with electric-field nanobubble generation for wastewater aeration. It suggested that nanobubble aeration costs scaled roughly linearly with treatment level, avoiding the exponential cost curve it attributed to conventional aeration at high cleanliness requirements English, 2022.