La oxygenation in aquatic environments It's one of those topics that cuts across disciplines: aquaculture, water treatment, agriculture, and even human consumption. When we talk about oxygenating water, we're referring to increasing the oxygen available for life and for the chemical and biological processes that maintain its balance. It sounds simple, but there's a lot of science behind it and, above all, practical consequences.
The heart of the matter is the dissolved oxygen (DO), that fraction of oxygen (O2) that remains in the water and can be used by fish, invertebrates, aquatic plants and microorganisms. It is expressed in milligrams per liter (mg/L) or parts per million (ppm), and also as saturation percentage, which compares the DO present with the maximum that water could contain at a specific temperature and pressure. A value around 5mg/L or higher It is usually considered healthy for most uses, although it all depends on the context.
What is water oxygenation and why does it matter?
Oxygenating water consists of increase DO concentration by natural means (turbulence, waterfalls, photosynthesis) or artificial means (aeration, oxygen injection, etc.). This oxygen is essential for the respiration of fish, invertebrates and aerobic microbes, which, among other things, degrade organic matter and close nutrient cycles. If the level drops too low, organisms suffer stress, unpleasant odors appear due to anaerobic activity, and the ecosystem suffers.
The OD is also a key quality indicator: High values are usually associated with clean, well-oxygenated water; low values indicate pollution, eutrophication or stagnation. Even aesthetic aspects such as the smell, clarity, and taste of water improve when oxygen is abundant and aerobic degradation works properly.
Dissolved oxygen sources and daily dynamics
Water obtains oxygen in several ways. The first is the exchange with the atmosphere, especially when there are waves, currents or turbulence that renew the surface film and facilitate the dissolution of O2The second major route is the photosynthesis of aquatic plants, like the ambulia, algae and phytoplankton, which release oxygen into the water during the day.
The overall reaction of photosynthesis can be simplified as follows: CO2 + H2O → O2 + C6H12O6 (in the presence of light and chlorophyll). During daylight hours the DO tends to increase, while at night, without photosynthesis, comes down Because all organisms continue to breathe. Therefore, in productive lagoons or ponds, oxygen minimums usually occur. at dawn.
In addition, a large proportion of global atmospheric oxygen comes from marine photosynthetic organisms, with phytoplankton playing a huge role. Although the figure varies depending on the source, it's clear that their contribution is essential for the planet and for the DO balance in natural waters.
Factors that determine OD levels
La temperature commands. Cold water dissolves more oxygen than warm water, so with heat the solubility falls and the available DO decreases. This is aggravated because fish and other organisms, being poikilotherms (cold-blooded), their metabolism increases with temperature and they consume more oxygen. A classic example: at 5°C a trout can use ~50-60 mg O2/h, but at 25 ºC you will need five or six times more.
La salinity It also reduces the solubility of gases: the more dissolved salts, less OD can hold water. Likewise, the atmospheric pressure and altitude influence: the higher the altitude, the lower the pressure and the less oxygen available for dissolution; pressure at depth increases solubility, although isolation from deep water can still lead to low levels if there is no mixing.
El water movement It is key. Currents, waves, waterfalls, or aeration increase gas exchange; on the contrary, stagnant or low-turbulence waters tend to present Lower ODs. In addition, the abundance of organic material (leaves, feces, food scraps) triggers bacterial respiration and oxygen demand, lowering DO. This is at the core of the eutrophication, which fertilizes the waters, triggers algal blooms and, when degraded, depletes oxygen.
It is important to avoid gas supersaturationAs a general rule, the sum of dissolved gases should not exceed 110%. Above this threshold there may be cases of “gas bubble disease"In fish (embolism, emphysema in fins or skin), a rare but possible phenomenon; aquatic invertebrates can also be affected, although at higher levels.
Adequate levels and reference ranges
As a guide, 4–5 mg/L OD is often considered the minimum to sustain diverse communities de pecesWhereas in good fishing waters It is not unusual to see stockings close to 9 mg / L. Below 3 mg / L serious problems begin and if the OD falls to 1–2 mg/L for a few hours may occur mass deaths.
En aquacultureMany tropical species work well around 5–6ppm, but the management objective is usually a higher optimum, around 7 ppm or more, to provide a safety margin. It is also important to monitor the saturation percentage: values between 80-120% are considered excellent, and below 60% or above 125% you enter the risk zone.
Sensitivity depends on the species, size, physiological state, temperature and contaminants. The greater the activity (swimming, stress in fish, treatments), increased oxygen consumption; feeding raises metabolism and if DO is low, fish may stop eating (damaging the feed conversion and profitability). Therefore, fine control of DO is an economic as well as an environmental tool.
An important nuance: two waters with 5 mg / L OD's do not necessarily provide the same comfort for a fish if one is at a distance 10 ° C and the other to 30 ° CRelative saturation and metabolic demand change, so it's important to interpret mg/L in light of temperature and context.
Practical methods for oxygenating water
There are solutions for almost every scenario. aerators and diffusers They inject fine bubbles that improve oxygen transfer across the surface; they are common in water treatment plants and ponds. de peces. The waterfalls and fountains They take advantage of the turbulence of falling water, a natural and, incidentally, aesthetic way.
For high demands, the pure oxygen injection It is more efficient than atmospheric air: it allows high DO levels to be reached and sustained quickly, something highly valued in fish farms or recirculation systems. The mechanical agitators (paddle wheels, impellers) increase air-water contact and promote mixing in the column.
There are alternatives like electrolysis (separation of H2 me2 applying current) or the ozone systemsOzone is not pure oxygen, but when it decomposes in water it releases O2, while acting as oxidant and disinfectantHowever, it requires careful design and control to avoid byproducts or overdoses.
In the domestic sphere there are oxygenating equipment tap water through microdiffusion or venturi, providing water perceived as fresher. Although the direct physiological benefits of drinking “hydrogen peroxide” are a matter of debate, at the level of taste and smell Improvement is seen when anaerobic activity and certain organoleptic compounds are limited.
How dissolved oxygen is measured
Measuring well is half the solution. The classic method is the Winkler titration, which binds oxygen to the sample through a chain of reactions and allows its quantification with considerable precision. It is the laboratory standard for calibration and quality control.
For continuous operation, they are used electrochemical sensors (galvanic or polarographic) that measure the current generated by the reduction of O2 on a cathode. They require membrane and electrolyte maintenance, but provide real-time data.
The modern alternative is the optical luminescence sensors, which detect how oxygen “quenches” the fluorescence of a dye. They are stable, precise, and have less interference, ideal for continuous monitoring under demanding conditions.
Choosing the method depends on the budget, precision required and the environment (field, laboratory, process line). In any case, periodic calibration and good sampling practices make the difference.
Applications and benefits in different sectors
En aquaculture, a stable and elevated DO reduces stress, improves growth and lowers incidence of diseases. Proper management allows for increased crop densities without compromising welfare, optimizing the productivity.
En farming, watering with well-oxygenated water promotes healthy roots, absorption of nutrients and avoids reducing environments in compacted or saturated soils, minimizing toxic compounds for the crop.
En sewage treatmentOxygen is the fuel for aerobic microorganisms that degrade organic matter and nitrify ammonium into nitrites and nitrates. Maintaining DO in the correct range ensures efficient processes. efficient and stable.
En natural ecosystems, oxygenation helps reverse episodes of hypoxia, to combat eutrophication and restore aquatic life. There are documented cases in large rivers where, after decades of low levels, the recovery of DO increased biodiversity and recreational opportunities.
To human consumption, adequate levels of DO improve the flavor and the perception of freshness. Beware of the industrial counterpart: the more oxygen the process water has, the faster the corrosion in pipes and equipment, with the costs that this entails.
Oxygen in aquaculture: fine management and technologies
Cultivation systems present different realities. In ponds, daytime photosynthesis and nighttime respiration cause large oscillations; in sea cages, currents and thermal changes modulate the oxygen supply; in recirculation (RAS), the organic load and the efficiency of biological filters dictate the demand for O2Understanding the specific dynamics of the system is essential for effective control.
The adoption of PSA oxygen generators (pressure swing adsorption) allows the production of O2 in situ from ambient air. This technology selectively separates nitrogen and delivers a stream of concentrated oxygen, reducing logistics costs compared to cylinders or liquids. It also provides stability and reduces the transportation footprint.
Maintain optimal and constant levels with O2 high purity improves the fish health, raises growth rates and reduces stress events. In terms of production, lower mortality and better feed conversion translate into higher profitabilityOf course, the system must be sized wisely and operated with continuous monitoring.
Key good practices: use blowers and diffusers of well-distributed fine bubbles, install monitoring systems of OD, temperature and flow rate, and ensure a regular maintenance (cleaning diffusers, checking pumps, power backup). This prevents unexpected drops in oxygen levels, which can be very costly.
Let's not forget the management of organic load: Food scraps and feces increase oxygen demand. Efficient filtration, siphoning, and partial water renewal help maintain DO. It should also be considered that larger animals, with increased activity or intensive eating, consume more oxygen; scheduling feedings and adjusting rations to the available DO is a very useful management tool.
Water chemistry: redox, nutrients and anoxia
Oxygen is the protagonist of numerous redox reactions that govern aquatic chemistry. In well-oxygenated environments, processes such as nitrification convert ammonium into nitrites and nitrates, forms that are more easily assimilated by plants. When oxygen is scarce, conditions arise hypoxic or anoxic and unwanted substances (e.g., hydrogen sulfide) from sediments, with impacts on odor and toxicity.
For all these reasons, the OD is not just a number: it is the thread they pull. water quality, ecological balance and process performance. Keeping it within optimal range prevents unpleasant surprises in physical, chemical, and biological indicators.
Drinking water and industry: taste, corrosion and boilers
In supply networks, a high OD is often associated with better taste. However, from an engineering point of view, a high concentration accelerates the corrosion of pipes and equipment. Therefore, many industries try to minimize oxygen in process water to protect assets and ensure product quality.
In boilers, the standard is extremely demanding: even in equipment of low pressure less is sought than 2 mg / L, and in many cases values close to 0,007 mg / L (7 µg/L). Deoxygenation by thermal deaerators and the use of oxygen scavengers is part of any plant's survival manual.
Strategies to improve and maintain OD
If the goal is to optimize and sustain dissolved oxygen, there are three fronts. First, aeration and mixing appropriate: size aerators, adjust their location, and take advantage of natural currents. Second, load control: reducing the input of fertilizers, runoff, and organic matter; in agriculture and urban environments, this implies good soil management practices. Third, monitoring: Without real-time data, the margin for reaction is reduced.
When levels are critical, the oxygen injection (PSA or O sources2) offers the most powerful response. In less pressing situations, improving the turbulenceInstalling waterfalls or redesigning recirculation may be enough. The trick is balancing cost, risk, and water quality objectives.
It is also worth remembering that the supersaturation It's not harmless. Designing systems that avoid significantly exceeding 100% total gas saturation will help avoid bubble pathology in aquatic fauna. Automated control with alarms for DO or total gas peaks is pure gold.
Reference values and intelligent data reading
Beyond general rules, every body of water has its own “personality.” Still, aiming for ≥5 mg/L as a base and work in the range of 80–120% saturation It is a useful guide in ecosystems, aquaculture, and processes. Recording the daily pattern (minimum at dawn, maximum in mid-afternoon) helps identify mismatches now act before the problem explodes.
The joint interpretation of DO, temperature, salinity and organic load This is what gives the complete picture. With this information, you can program aerators, adjust feed rations, plan water renewals, and decide whether it's worth investing in on-site oxygen generation.
Aquatic oxygenation, well designed and monitored, results in healthier ecosystems, more efficient processes, and more profitable operations. Controlling dissolved oxygen isn't a technical luxury: it's life insurance for the water we use and the life that depends on it.
