Hydrodynamic cavitation in agriculture and food

Where cavitation fits in agriculture

Hydrodynamic cavitation has been tested at four points between field and food: gas in irrigation water, crop residues, liquid foods and extracts, and feedstocks for farm biogas.

The device works the same way in each. Liquid speeds up through a constriction such as a Venturi or an orifice plate, its pressure falls below the vapor pressure, and vapor cavities form and collapse as the pressure recovers. A review describes the collapse as producing very high local pressures and temperatures for a fraction of a second Arya et al., 2023. The physics is in What hydrodynamic cavitation is and What cavitation does to water.

Gas in irrigation water

The field evidence for adding gas to irrigation water with a Venturi comes from oxygation: air drawn into subsurface drip water by a Venturi injector. These trials measured aeration; they did not report whether the injector cavitated.

In tub trials and in field trials in central Queensland, Australia, oxygation raised root-zone oxygen by 2.4–32.6% over the control at the same depth, and soil respiration by 42–100% Chen et al., 2010. Pineapple fruit yield rose by 17% in a field trial.

The longest record is for cotton on a heavy clay Vertosol, where frequent drip irrigation leaves roots short of oxygen. Over seven seasons, cotton irrigated with Venturi-aerated water yielded 200.3 g m⁻² against 182.7 g m⁻² for the control, 10% more on average Pendergast et al., 2013. The authors credited more root growth and light capture as root-zone hypoxia was relieved.

Venturi geometry can also make fine bubbles. A laboratory Venturi-type cavitation device produced bulk nanobubbles with a mean diameter of 180–210 nm, and those made at 3 bar stayed in suspension for 72 hours Li et al., 2021. Nanobubble irrigation results are in Root zone mechanisms, Nutrient use efficiency and yield and Hydroponics and soilless culture. No cited study irrigated a crop with cavitation-treated water and measured the plants.

Crop residues and lignocellulosic biomass

In residue pretreatment, cavitation has intensified chemistry rather than replaced it. Residues such as bagasse and straw lock cellulose and hemicellulose inside lignin, which slows the enzymes and microbes that digest them. A review describes cavitation as favoring disruption of this lignin–carbohydrate matrix, and reports it combined with other pretreatments Bimestre et al., 2022.

With sodium hydroxide (NaOH) flowing through orifice plates, the best laboratory condition, 3 bar, 70 °C and 0.3 M NaOH, gave enzymatic hydrolysis yields of 93.05% for cellulose and 94.45% for hemicellulose within 30 minutes Terán Hilares et al., 2017. The plates had cavitation numbers of 0.017 and 0.048.

A follow-up ran cavitation with alkaline hydrogen peroxide in continuous mode. With an average residence time of 7.5 minutes, enzymatic hydrolysis released 38–46 g of glucose per 100 g of bagasse Terán Hilares et al., 2019.

The alkali or peroxide stayed in every process; cavitation let it work at mild conditions and short times. Digestion to biogas is covered in Biogas and sludge hydrolysis.

Extraction and liquid-food processing

Cavitation suits liquid foods because the pressure drop and recovery happen in a flowing liquid. A review lists emulsification, extraction of polyphenols, essential oils and pigments, waste valorization and beer brewing among its uses Arya et al., 2023.

Two studies worked at real scale. In a 230 L microbrewery, cavitation made dry milling of the malt and boiling of the wort unnecessary, lowered the saccharification temperature and saved energy Albanese et al., 2017. Waste orange peel, processed in more than 100 L of water with no other raw materials in a Venturi-shaped reactor, yielded pectin, polyphenols and terpenes within a few minutes Meneguzzo et al., 2019.

The comparison with heat matters for food safety. Tomato juice in 1 L batches passed through a Venturi at 5–15 psi for 5–30 minutes Vigneshwaran et al., 2022. At 10 psi for 10 minutes it kept 93% of its ascorbic acid and 96.6% of its phenolics. Heating at 90 °C for 90 seconds reduced pectin methylesterase activity by 92.2% and the total plate count by 5 log; cavitation reached at most 4.9% and 1 log. It kept more nutrients, but did not match heat on enzyme and microbial measures.

Manure, digestate and farm biogas

At farm biogas plants, cavitation pretreatment has raised methane output modestly, and its energy use decides whether it pays.

A full-scale agricultural biogas plant, which also used molasses and corn meal as supplementary energy sources, ran cavitation at 470 kJ/kg of total solids. Nearly six months of data showed about 10% higher specific methane production. Changes in digestate viscosity and particle size also reduced the energy needed for mixing, heating and pumping Garuti et al., 2018.

On cattle manure treated by swirling-jet cavitation at 6–8 bar, 7 bar gave the best methane production; the authors suggested that higher pressures may form compounds that inhibit digestion Langone et al., 2017. For dairy-farm waste in large-scale trials, 8 minutes of cavitation gave 327 L of biogas per kg of chemical oxygen demand, at 62.9% methane, but the net energy yield was only 3.1% above no pretreatment Dębowski et al., 2024.

How cavitation breaks up sludge and manure solids is covered in Manure management and cavitation.