Nanobubbles for Environmental Remediation

Degraded lakes, rivers, and groundwater aquifers share a common thread: the geochemical and microbial processes that would naturally maintain water quality have stalled, usually because a key input — oxygen, or in some cases an electron donor for bacteria that can only work anaerobically — is missing where it's needed. Conventional remediation often treats the symptom (chemical dosing, dredging, pump-and-treat extraction) rather than restoring the process itself.

Nanobubble delivery of three gases — oxygen, molecular hydrogen, and ozone — offers a way to restore these natural processes directly, without ongoing chemical addition. Each gas addresses a genuinely different class of problem. This guide covers the science behind each, what's well-established versus what's still an open question, and where the evidence actually stands.

The relationship between sediment oxygen status and phosphorus release is one of the most thoroughly documented mechanisms in limnology, first described by Mortimer in the 1940s and confirmed repeatedly since. Under aerobic conditions at the sediment-water interface, phosphate binds strongly to ferric iron (Fe³⁺) in insoluble complexes that seal phosphorus in the sediment. When the bottom water becomes anoxic — as happens in stratified eutrophic lakes during summer, once decomposing algal biomass consumes oxygen faster than it can be replenished — iron-reducing bacteria convert that iron to its soluble ferrous form (Fe²⁺). The phosphate bound to it is released directly into the water column, often in quantities that dwarf the external nutrient load.

Restoring dissolved oxygen at the sediment-water interface keeps iron in its ferric, phosphate-binding state. Because nanobubble dissolution is driven by interfacial surface area rather than diffusion from a surface source (see our technology page), oxygen can be delivered directly at depth, where it's needed, without requiring the destratification that conventional mixing approaches rely on — which itself risks bringing nutrient-rich bottom water to the surface and triggering the exact bloom event the treatment is meant to prevent.

In a healthy, oxygenated water body, ammonium (NH₄⁺) is converted to nitrate by nitrifying bacteria — a strictly aerobic process — and that nitrate is then converted to inert nitrogen gas by denitrifying bacteria at the anoxic sediment interface, permanently removing nitrogen from the system. In a hypoxic water body, nitrification stalls at the first step because there's no oxygen for it. Ammonium accumulates, acting as a direct algal nutrient and, at high concentrations, a toxin to fish and invertebrates.

Restoring dissolved oxygen at depth resumes nitrification, and the nitrate produced then undergoes denitrification at the anoxic sediment interface just below, driven by sediment organic carbon — restoring the complete nitrogen removal pathway from a single oxygen intervention. Multiple field programs using hypolimnetic oxygenation (delivering oxygen to the bottom layer of a stratified lake without disrupting the thermal structure above) have documented exactly this effect, alongside reductions in accumulated phosphorus and ammonia of 40–88% over sustained operation.

Anoxic bottom waters in eutrophic systems also accumulate hydrogen sulphide (H₂S), produced by sulphate-reducing bacteria in the absence of oxygen. H₂S is acutely toxic to fish and invertebrates at just a few micrograms per litre, produces the characteristic rotten-egg odour of degraded water bodies, and further poisons the nitrifying bacteria the nitrogen cycle depends on. Oxygen reacts rapidly with H₂S, oxidising it to sulphate — so the same oxygen delivery that addresses phosphate and nitrogen also eliminates this toxicant in the same treatment event, with odour reduction typically providing a fast, easily observable indicator that treatment is working.

Nitrate contamination of groundwater is one of the most widespread agricultural water quality problems globally — it leaches readily from fertilised soils and accumulates in aquifers over years to decades, routinely exceeding drinking water guidelines in agricultural regions across Australia, the US, Europe, and China. The carbon caveat flagged in Section 2 stops being a caveat here and becomes the central problem: groundwater aquifers, particularly confined systems geochemically isolated for long periods, typically have little to no organic carbon left at all.

Biological denitrification is the only process that permanently removes nitrate from water, but the conventional version — heterotrophic denitrification, driven by organic carbon as the electron donor — stalls in groundwater aquifers, particularly confined systems that have been geochemically isolated for long periods and have little to no organic carbon left. Conventional responses (pump-and-treat: extract, treat at surface, reinject) are energy-intensive and only address the extracted fraction while the aquifer keeps receiving recharge.

Denitrifying bacteria are facultative anaerobes — they can use either oxygen or nitrate as their terminal electron acceptor, and they strongly prefer oxygen because aerobic respiration yields more energy per mole of substrate. When dissolved oxygen is present, the genes encoding nitrate reductase and the downstream denitrification enzymes are transcriptionally repressed. Denitrification stops. This is well-established, foundational microbiology, not a nanobubble-specific finding — and it means any hydrogen delivery system for denitrification has to keep the treatment zone genuinely oxygen-free to work, or risk aerobic hydrogen-oxidising bacteria consuming the hydrogen before the denitrifying community can use it.

This constraint is also, in a specific sense, an opportunity. On-site hydrogen production via electrolysis (splitting water into H₂ and O₂) produces an oxygen co-product that has to go somewhere — and in most sites needing denitrification, there's a parallel, spatially separate need for oxygenation somewhere else in the same system (a stratified lake's aerobic zone, a nearby petroleum plume needing aerobic biodegradation, a receiving wetland). Treated as two separate delivery points rather than one mixed stream, the co-product becomes a second useful input rather than a waste stream to vent.

Petroleum hydrocarbon contamination of groundwater — from leaking underground storage tanks, pipeline spills, and industrial site runoff — is one of the most common groundwater quality problems in developed countries. The primary natural attenuation mechanism is aerobic biodegradation by hydrocarbon-oxidising bacteria, and it's limited by dissolved oxygen supply, which is rapidly depleted near a hydrocarbon plume. In-situ oxygen injection — biosparging — is a well-established response that delivers oxygen to depleted zones to stimulate that biodegradation.

The delivery-radius problem is the same one that applies to hydrogen in groundwater: conventional gas bubbles rise under buoyancy, follow preferential flow pathways, and bypass the lower-permeability zones where contamination often concentrates. A column study using micro-nano bubbles found oxygen mass transfer nearly 125 times faster than conventional air macro-bubbles, with no measurable impact on the sand's hydraulic conductivity — meaning the bubbles moved through the pore structure without clogging it. Separately, field-scale trials of ozone micro-nano-bubbles at a real trichloroethylene-contaminated site demonstrated measurable in-situ remediation efficiency using this same delivery approach, with a more recent field demonstration reporting comparable results at a different contaminated groundwater site. That's a genuinely useful data point: this delivery approach has moved beyond column studies into actual contaminated-site trials, for a chemically related (if not identical) treatment objective.