Hydrogen peroxide as a passive oxygen source for plants in decoupled aquaponic systems

1 Introduction

The combination of different agricultural production techniques substantially saves valuable resources such as water, inorganic fertilizer, or energy, representing a sustainable way to address the pressing challenges of the 21st century with regard to water scarcity, resource depletion, and climate change. As such, aquaponics represents an integrated food production system that recycles nutrient-rich wastewater from recirculating aquaculture systems (RAS) to offer irrigation water and mineral nutrition to plants (Baganz et al., 2022; Kloas et al., 2015; Krastanova et al., 2022). Thereby, RAS offers a state-of-the-art production system, including biofilters and mechanical filters for continuous water treatment. In aquaponics, fish are mainly produced in these aquaculture systems, which are connected to hydroponic (soilless) plant production systems to transfer the nutrient-rich wastewater for recycling purposes (Martinez-Cordova et al., 2023; Rakocy, 2012; Yep and Zheng, 2019). The way of resource transfer and the extent of coupling and interconnection between the different production units might differ with regard to different system setups (Baganz et al., 2022; Monsees et al., 2017). In decoupled aquaponic systems (DAPS), the RAS and hydroponic units are partially connected with a unidirectional flow of water, often implemented with a special valve, ensuring the transfer of nutrients and water from RAS to hydroponic (HP), but not back (Baganz et al., 2022; Pinho et al., 2024). This enables a precise regulation of environmental parameters such as pH, nutrient profile, or oxygen concentration with each production unit, fostering increased yields, efficient resource utilization, and optimal management (Lastiri et al., 2018; Monsees et al., 2017; Pinho et al., 2021). While plant evaporation processes are the main drivers for water transfers in decoupled aquaponic systems (Monsees et al., 2017; Pinho et al., 2024), nutrient input is mainly derived via fish feed and RAS water source properties (Shaw et al., 2022, 2024).

Next to inorganic nutrients such as nitrate, phosphate, or potassium, mainly originating from the metabolic breakdown of fish feed, dissolved and particulate organic matter is also generated in RAS and consequently partly transferred to the hydroponic production system. These organic carbon sources, derived from feces and feed leftovers, largely removed by mechanical methods such as drum filters (Gupta et al., 2024), support heterotrophic bacteria growth, thus increasing the overall oxygen demand within the aquaponic system. Thus, not only the RAS design but also the choice of the hydroponic production systems has a major impact on plant performance. Eventually, the entire setup can have a distinct influence on plant growth. Generally, a sufficient and continuous supply of oxygen, especially in the root zone of plants, is beneficial for plant growth. In order to passively provide enough space for roots and oxygen, porous and inert media such as perlite, rockwool, or clay pebbles are commonly applied in hydroponic systems as submodules in aquaponics.

Next to the use of compressed air, hydrogen peroxide (H₂O₂) might be used as a supplemental oxygen source as well as to improve plant health and system hygiene. Thus, there is a potential that roots can be disinfected, pathogenic microbes can be suppressed, and oxygen availability can be increased through the oxidative properties of H₂O₂ (Duca and Travin, 2020), including potential beneficial effects on root respiration and nutrient uptake (Duca and Travin, 2020; Duca et al., 1995). This technology is especially interesting to mitigate production losses in remote low-tech systems with unstable power supply. However, overdoses of H₂O₂ can cause stress, irreversible crop damage, and production loss. As such, increased concentrations of H₂O₂ are likely to cause oxidative stress in plants (Watt et al., 2004), root cell damage, and impaired growth (Lau and Mattson, 2021). While some authors suggest applications of 1 mL L⁻¹ per week (H₂O₂ per water; 3% v/v) as an optimal level to prevent algae growth without root damage (Fernandez, 2009), the studies remain empirical, and a mechanistic applicable H₂O₂ safety corridor for hydroponic systems is still lacking. Thus, despite the potential benefits of H₂O₂ in HP, research on its use is limited. In fact, no scientific research document on the effects of passive H₂O₂ application on HP-produced lettuce and its advantages and/or risks in DAPS was found. This study aims to close this gap through creating a scientific frame for an H₂O₂ safety corridor by evaluating the effect of passive H₂O₂ application on the growth of lettuce in HP and DAPS.

2 Materials and methods

2.1 Ethical statement

This study did not require an application for approval according to the communication with the Ethics Committee of the Landesamt für Gesundheit und Soziales (LAGeSo, Berlin). The study was carried out in compliance with the German legislation as authorized by the Regional Office for Health and Social Affairs Berlin (permit #: ZH 114).

2.2 Experiment and facilities

The experiment was conducted in one large climate-controlled growth room (8.2 m * 3.8 m * 2.5 m; L * W * H) including nine experimental growth tents (Royal Room C120S, 120 cm × 60 cm × 180 cm), each equipped with a hydroponics AeroFlo10 unit (Growstream1, GHE) and a two-rack light-emitting diode (LED) lighting system. The room was located at the Leibniz Institute of Freshwater Ecology and Inland Fisheries (IGB, Berlin, Germany). The overall room temperature and relative humidity set points were 17°C and 60%, respectively (controlled by an integrated cooling and dehumidification system). Each growth tent was equipped with two hydroponic gutters (110 cm × 50 cm × 50 cm) with five plant sites each, connected to a 45-L nutrient solution reservoir with a common pump (compactON 1000, Eheim GmbH, Germany). The nutrient solution was constantly oxygenated using compressed air and air stone diffusers (control: HP_air) or with a passive H₂O₂ supply via an Oxydator D (Dr. rer. nat. K. Söchting Biotechnik GmbH, Germany) instead of compressed air (HP_H2O2 and RAS_H2O2). In brief, a catalyst inside the container of the Oxydator is responsible for the decomposition of the H₂O₂ solution (here 6% H₂O₂) into oxygen and water. The oxygen produced in this process creates pressure in the container and allows H₂O₂ to seep through the open tip of the inverted container into the nutrient solution (Cohen, 1988; Söchting, 1984). The amount of hydrogen peroxide released into the nutrient solution is directly correlated to the ambient temperature, the concentration of the H₂O₂ solution, and the catalyst used. The lighting system consisted of one LED lamp (SANlight Q4WL S2.1 Gen2, 165 W), which had a distance of 60 cm to the top of the hydroponic unit and was adjusted to supply between 120 and 130 μmol m⁻² s⁻¹ photosynthetic photon flux density (PPFD) at the plant level for 12 h each day. The lights automatically switched on in every tent at 6 a.m. and off at 6 p.m., controlled by digital timers (LOGILINK ET0007 timer). Additionally, an automated fan (PK125 EC-TC Prima Klima) was installed in every tent to mitigate possible overheating, with a target air temperature of 22°C and humidity of 60%, using a minimum speed of 10% and a maximum speed of 20%. Air temperature and relative humidity in the tents were monitored by data loggers (HOBO UX100-011).

The aquaculture wastewater was taken from a RAS located at the IGB with a total volume of 20 m³. The RAS was stocked with adult Arapaima (Arapaima gigas) that were fed three times per week with Aller Primo, 8 mm (Aller Aqua, Germany) at 1% bdw day⁻1. The water treatment units consisted of a drum filter with a mesh size of 100 µm for solid removal, a moving bed filter with a total volume of 2 m³ with a biocarrier filling of 0.75 m³ (Hell-X, Christian Stöhr GmbH & Co.Elektro- und Kunststoffwaren KG), and an additional small trickling filter for CO₂ removal.

2.3 Treatment and experimental design

The experiment was conducted as a completely randomized design comprising three oxygenation treatments to evaluate lettuce growth responses in HP and DAPS. The treatments included i) conventional hydroponics with compressed air supply (H_air, control), ii) conventional hydroponics with passive hydrogen peroxide supply (HP_H2O2), and iii) aquaponic nutrient solution derived from a RAS combined with passive hydrogen peroxide supply (RAS_H2O2) (Figure 1). Each treatment was replicated three times, resulting in nine independent experimental units corresponding to the nine growth tents. Treatments were randomly assigned to the tents to avoid positional effects. This design allowed for direct comparison of oxygenation strategies and nutrient solution origins under controlled environmental conditions over the 34-day cultivation period.

2.4 Lettuce seedlings and growth conditions

A total of 250 lettuce seeds (Lactuca sativa L., Aquino RZ cv., Rijk Zwaan; De Lier, The Netherlands) were sown in rockwool cubes (Rockwool, Grodan, The Netherlands, 4 cm × 4 cm) and germinated during 14 days under controlled environmental conditions in a climate chamber (temperature: 18°C, PPFD: 250 μmol m⁻² s⁻¹, and humidity: 90% for 2 days and 60% for the remaining 12 days). There were 190 homogeneous plants that were selected and randomly placed in the nine growth tents: In every hydroponic unit, 10 plants (5 plants in each gutter: cf. Figure 1) were allocated at a plant density of 18 plants m⁻² and grown for 34 days until harvest. A 12-h day length was applied. The plants were irrigated with a continuous nutrient solution flow (1.5 L min⁻¹, constantly over 24 h), the roots fully immersed in the nutrient solution within the gutters. The reservoir of each hydroponics unit was filled with the respective nutrient solution (cf. Figure 1) before the allocation of the plants. The solutions were changed twice during the experiment [days after transplanting (DaT) 14 and 28]. On both occasions, the “old” nutrient solution was discharged and replaced with a fresh solution. A standardized formulation and preparation protocol was used in all three occasions (DaT 0, 14, and 28).

2.5 Preparation of nutrient solutions

Samples of tap water and aquaculture wastewater from the aquaponic treatment (RAS_H2O2) were analyzed 2 days prior to each reservoir filling procedure. Analysis of the respective nutrient concentrations was done using inductively coupled plasma-optical emission spectrometry (ICP-OES) and continuous flow analysis (CFA) (Table 1). The results of these analyses were used to calculate the amount of inorganic fertilizer to be added in the form of stock solutions. All nutrient solutions had a similar nutrient profile, targeting the Howard-Resh recipe for hydroponics lettuce nutrient solution (Table 1).

Table 1. Nutrient concentrations [mg L⁻¹] determined in samples of tap water and wastewater derived from a recirculating aquaculture system (RAS) as the basis for the preparation of hydroponic stock solutions.

RAS samples were collected over three sampling periods [days after transplanting (DaT) 0, 14, and 28] during the experiment. For the nutrient concentrations of local tap water, a median of three independent measurements from different experimental weeks is presented. The target nutrient profile for the stock solutions was according to the Howard–Resh recipe for hydroponics lettuce nutrient solutions.

For the control treatment (HP_air), the nutrient solution was prepared with 50% tap water and 50% distilled water, with nutrients added. The RAS_H2O2 treatment nutrient solution was prepared with wastewater from the RAS rearing Arapaima. For the aquaponics treatment, 135 L of aquaculture wastewater was used in the hydroponics units (45 L per RAS_H2O2 replicate) three times during the experiment: prior to day 0, day 14, and finally, day 28.

The calculation of the amount of mineral nutrients added to the water sources as a fertilizer mix was calculated using the HydroBuddy v1.91 program (Fernandez Pinto, 2022), formulating A+B concentrated stock solutions composed of multiple nutrients. Here, the HydroBuddy program provided information on the target nutrient profile in the final solution, the nutrient profile of the water sources (Table 1), and the composition of the applied fertilizers (Table 2). A total of 135 L of solution per treatment was considered in every reservoir filling procedure, and the concentration factor and volume of each A or B stock solution were set to 100 and 1.35 L, respectively. The water parameters for the final nutrient solution were set at EC 1.6 mS cm⁻¹ and pH 6.0.

Table 2. Distribution and composition of the applied fertilizers for experimental stock solutions A and B.

The individual fertilizers were weighed and allocated to six separate beakers (stock solutions A and B for each of the three treatments) according to the calculated outputs from HydroBuddy. Each beaker was initially filled with 1 L of distilled water and stirred until complete dissolution of all salts. The solutions were then topped up with distilled water to a final volume of 1.35 L, resulting in a 100-fold concentrated stock solution (corresponding to 1% of the final nutrient solution volume). Subsequently, stock solutions A and B were added to the respective 135 L tanks of the HP_air, HP_H₂O₂, and RAS_H₂O₂ treatments. The pH was adjusted to a target range of 6.1–6.3 using nitric acid to decrease it or sodium hydroxide to increase it. Once prepared, nutrient solution samples were collected in duplicate for nutrient analysis by ICP-OES and CFA. Finally, the prepared nutrient solutions were distributed from the 135-L tanks into the corresponding 45-L replicate reservoirs.

2.6 Relative chlorophyll concentration and plant measurements

The relative leaf chlorophyll concentration [soil plant analysis development (SPAD) value] was measured in every lettuce plant 1 week before harvesting (DaT 28) using a Chlorophyll Meter SPAD-502Plus device (Konica Minolta, Japan). The SPAD value was determined for five leaves per plant. The device calculated the mean SPAD value of the five leaves automatically, resulting in the mean SPAD value of the lettuce plant. At the end of the experiment, all lettuce heads were harvested by cutting the organ directly above the rockwool cube. Immediately after harvesting, lettuce heads were weighed individually using a precision balance (Kern EWJ, Reichelt elektronik GmbH, Sande, Germany) to determine the fresh weight. Then, four lettuce heads per replicate were randomly selected to count the number of leaves as well as for the preparation of subsamples for further analyses. The subsamples were prepared by sampling one-quarter of each selected plant, weighed, placed into plastic bags, and stored at −80°C. Afterward, the subsamples were freeze-dried for at least 72 h (Christ Alpha 1–4, Christ; Osterode, Germany). Every subsample was weighted again using an analytical balance (Sartorius CP225D, Sartorius AG, Goettingen, Germany) to determine the dry weight as well as the fresh weight/dry weight ratio as well as for the estimation of the dry weight of the whole lettuce head.

2.7 Abiotic parameters, water analysis, and resource use

During the experimental period, abiotic parameters of the nutrient solutions—pH, temperature, electrical conductivity (EC; mS cm⁻¹), and dissolved oxygen (DO, mg L⁻¹) concentration—were measured across all replicates on every weekday. The DO concentration was measured using a dissolved oxygen meter, OxyGuard Handy Polaris. The pH, EC, and temperature of the nutrient solutions were measured with the Hach Lange HQ40d probe. Water consumption was measured three times at every water exchange event and at the end of the experiment. These data were used to estimate the volume of water needed per plant per day (Vw) by summing the differences of the initial (V0) and final (Vf) volume of the nutrient solution reservoirs of every replicate in the three measuring points (i = on days 14, 28, and 34): Vw = Σ(V0,i−Vf,i).

For nutrient analysis, all water samples were collected in duplicate, filtered with a 0.2-μm cellulose acetate membrane filter (GE Healthcare, United Kingdom), preserved by adding 150 μL of 2 M of hydrochloric acid (HCl) to 12 mL of the filtered sample, and stored at 4°C for subsequent analysis. The samples were analyzed right after the experiment ended. The concentrations of phosphorus (P), potassium (K), calcium (Ca), magnesium (Mg), sulfur (S), iron (Fe), boron (B), manganese (Mn), copper (Cu), zinc (Zn), sodium (Na), silicon (Si), and aluminum (Al) were determined by inductively coupled plasma-optical emission spectroscopy (ICP-OES) using the Thermo Scientific iCAP 7400 ICP-OES (Thermo Fisher Scientific Inc., USA). Continuous flow analysis (CFA) was performed using the FSR Seal High Resolution AA3 chemical analyzer (Seal Analytical, Germany) to determine nitrate (NO₃-N) and ammonium (NH₄- N) concentrations. In addition to the samples of tap water and fish wastewater (Table 1), water samples were collected for characterizing the nutrient solutions on days in all replicates on days 0, 8, 14, 21, 28, and 34 (Supplementary Table 1).

The cost analysis (Table 3) was done based on prices for stabilized H₂O₂ solution (Söchting Oxydator solution, 12%, 5 L) and distilled water from retailers in Germany, without special discounts for commercial applications. Additionally, average electricity prices for residential customers in Germany were used for the analysis (Destatis, 2026).

Table 3. Cost analysis with regard to the needs of electrical power (kWh) for the operation of an air pump for mechanical aeration or the consumption of hydrogen peroxide (L) for passive oxygen supply during an experimental period of 36 days.

2.8 Statistical analysis and data evaluation

Data were pre-processed using Microsoft Excel and analyzed in MATLAB (ver. 2020b, “Statistics and Machine Learning” toolbox, The MathWorks Inc., Portola, CA, USA). Shapiro–Wilk’s and Levene’s tests were applied to all data to check normality and homogeneity of variances, respectively. When assumptions were met, one-way ANOVA was performed to evaluate treatment effects on fresh weight and SPAD values. Dry weight, number of leaves, and water consumption did not meet parametric assumptions and were therefore analyzed using the non-parametric Kruskal–Wallis test. Environmental variables, including dissolved oxygen, nutrient solution temperature, pH, EC, air temperature, and relative humidity, were averaged by experimental week prior to statistical analysis. For each environmental variable and each week, normality and homogeneity of variances were assessed independently, and either one-way ANOVA or the Kruskal–Wallis test was applied depending on the fulfilment of these assumptions. The week-specific selection of statistical tests for each environmental variable is provided in the Supplementary Material (Supplemetary Table 2). In cases where significant treatment effects were detected (p < 0.05), Tukey’s honestly significant difference (HSD) test (following ANOVA) or Dunn’s test (following Kruskal–Wallis) was conducted for pairwise multiple comparisons. All statistical tests were conducted at a significance level of α = 0.05. Although the primary interest was whether the alternative oxygenation strategies produced comparable plant responses, the study was analyzed to test for detectable treatment effects at α = 0.05. Non-significant results were interpreted as no evidence of differences under the present experimental conditions and replication level, rather than proof of equality. To aid interpretation, treatment means are reported together with standard deviations. Descriptive statistics were used to present the results for abiotic conditions and nutrient concentrations in nutrient solutions. In the tables, values represent means ± standard deviations.

3 Results

3.1 Growth parameters, water use and cost comparison

The application of H₂O₂ (using a safe, passive application method) to a hydroponic and an aquaponic treatment group resulted in similar lettuce yields compared to the hydroponic control group, using compressed air instead of H₂O₂ for oxygen supply. As presented in Table 4, the lettuce fresh and dry weight, the number of leaves, and SPAD values showed no evidence for differences among all treatments (p > 0.05). Additionally, no evidence for differences was found for the daily water use per plant (p > 0.05).

Table 4. Growth parameters, SPAD values, water use, and *p-values for the three treatments: compressed air (HP_air, control), conventional hydroponic nutrient solution supplied with a passive H₂O₂ dispenser (HP_H2O2), and aquaponic nutrient solution from a recirculating aquaculture system (RAS) supplied with a passive H₂O₂* dispenser (RAS_H2O2).

Values are presented as means ± standard deviation. One-way ANOVA () or Kruskal–Wallis test (*) was used to assess statistical differences among treatments.

The abiotic growth conditions in the experimental units were maintained within the desired range in all groups, with the mean air temperature and relative humidity of 21.3°C ± 0.7°C and 65.1% ± 5.5%, respectively (Figure 2). Similarly, the abiotic parameters dissolved oxygen, temperature, and pH in the nutrient solution were comparable between the groups and were within the desired range of 7.8 ± 0.1 mg L⁻¹, 21.0°C ± 0.4°C, and 6.3 ± 0.1. Only in the last experimental week, dissolved oxygen differed significantly among the treatments (Kruskal–Wallis, p = 0.0116), with HP_air showing slightly higher O₂ (7.91 ± 0.12 mg L⁻¹) than HP_H2O2 (7.83 ± 0.06 mg L⁻¹) and RAS_H2O2 (7.80 ± 0.07 mg L⁻¹). Additionally, significant differences were observed with respect to EC: throughout the experiment, EC was significantly higher in RAS_H2O2 compared to both HP treatments [1.7 ± 0.1 or 1.5 ± 0.1 mS cm⁻¹ (both HP), respectively] (Figure 2).

Nutrient concentrations within each treatment could be regarded as constant, i.e., no differences were observed within the three replications of each treatment (Supplementary Table 1). Between treatments, differences in the nutrient solutions were generally small, while only Si and Na were significantly elevated in RAS_H2O2; i.e., compared to HP, RAS_H2O2 consistently resulted in approximately two-fold elevated concentrations. This supports the successful realization of the treatments, while elevated Na and Si in DAPS are a typical consequence in fish-based wastewater use for hydroponics.

H₂O₂ consumption was in a comparable range for the two respective treatments—RAS_H2O2 and HP_H2O2—supporting the validity of the results when directly comparing plant variables of RAS and HP (Table 5).

Table 5. H₂O₂ consumption in mL during the experimental period within the two different treatment groups.

Cost comparison for either the supply of electrical energy for active aeration or the consumption of H₂O₂ for passive oxygen supply revealed a comparable price range within the experimental period (Table 3).

4 Discussion

4.1 Principal findings and plant growth response

In order to provide new insights into alternative opportunities for passive oxygen supply for hydroponics and aquaponics by avoiding power use and thus the necessary supply, the use of hydrogen peroxide was tested in an experimental approach. Moreover, in this study, a passive application method for hydrogen peroxide was used to examine the potential effects on the lettuce growth produced under hydroponic and aquaponic conditions.

Based on the results of the current study, it can be concluded that using oxygen supply by passive application of hydrogen peroxide in hydroponics/aquaponics nutrient solutions is a promising alternative. With that simple solution, the use of electrically driven compressors, diffusors, or aerators, commonly used in hydroponic and aquaponic plant production, might be supplemented or, in some cases, even avoided (Modarelli et al., 2023; Tůmová et al., 2025; Vanacore et al., 2024; Yang and Kim, 2019).

4.2 Root zone oxygenation and physiological context

Plants produced in DAPS grow as well as those produced in HP (Delaide et al., 2019; Monsees et al., 2019; Pinho et al., 2024; Suhl et al., 2016; Tůmová et al., 2025), and the main effect of DAPS is in saving resources, especially water and nutrients (Körner et al., 2026). As described in the present study, no evidence for differences in any plant physiological trait was detected, and it can be argued that the passive aeration procedure neither harmed the plants nor enabled the H₂O₂ supplement to function as a growth accelerator. Achieving similar yields in aquaponics, through the recycling of aquaculture-derived wastewater, compared to stand-alone hydroponic systems is a positive and desirable outcome, especially considering that the primary reason for establishing aquaponic systems is to optimize resource use (Ghamkhar et al., 2020; Pinho et al., 2024).

Besides the complexity of a range of interacting production factors in aquaponics/hydroponics, optimal oxygen levels are one key factor to achieve optimal crop yield (Nitu et al., 2024; Somerville et al., 2014). Moreover, it is known that a healthy root system is essential for the general maintenance of the plant, especially with regard to water and nutrient uptake, as well as a good foundation against root-borne diseases (Nitu et al., 2024; Somerville et al., 2014). A good way to support and maintain a healthy root system is by creating a sufficiently oxygenated root zone (Chérif et al., 1997; Roosta et al., 2016).

Still, H₂O₂ is a strong oxidant, and care should be taken with regard to the application method (passive or active, Oxydator, peristaltic pumps, spray, etc.), the concentration of the H₂O₂ solution, and the amount of H₂O₂ added over a specific period of time. Since reactive oxygen species (ROS), including H₂O₂, can damage DNA and other cellular components and act as important signaling molecules regulating normal plant growth as well as stress responses (Huang et al., 2019), plants are able to cope with these effects. Generally, plants have a multi-step antioxidant defense system to detoxify ROS, involving enzymatic components such as superoxide dismutase (SOD), catalase (CAT), and peroxidases such as ascorbate peroxidase (APX) and glutathione peroxidase (GPX) (Apel and Hirt, 2004; Huang et al., 2019) as well as non-enzymatic systems mainly mediated by low molecular mass antioxidants, such as glutathione, ascorbic acid, and flavonoids (Gechev et al., 2006). In the study of Wang et al. (2023), two lettuce varieties were daily treated (i.e., were sprayed) with five different concentrations of H₂O₂. The spraying with a 10 mmol L⁻¹ H₂O₂ solution showed maximum impacts in maintaining biomass production and improved enrichment of antioxidants, including phenolic compounds, mineral nutrients, and antioxidant capacity in lettuce. On the other hand, significantly reduced growth traits were reported at concentrations of 40 mmol L⁻¹ H₂O₂ (Wang et al., 2023), underscoring the importance of the careful application of H₂O₂ and the need for further research in order to establish safe levels for practical operations.

4.3 EC and nutrient solution differences

In line with earlier reported findings, compared to hydroponics, significantly higher EC was observed in DAPS (Delaide et al., 2016; Monsees et al., 2019; Pinho et al., 2024). Elevated EC in DAPS nutrient solution usually results from increased two sources: the mineral content in fish feed and the commonly applied base Ca(OH)₂) for pH stabilization (Lunda et al., 2019; Monsees et al., 2019; Tellbüscher et al., 2025, 2026), which introduces Na, Cl, K, P, and Ca and subsequently increases EC (Monsees et al., 2019; Tellbüscher et al., 2025).

4.4 Practical relevance

Beyond the general observation that the tested treatments did not negatively affect plant growth, it is important to highlight that a passive, non-power-consuming method for oxygen supply may offer additional advantages in certain production scenarios. This is particularly relevant for low-tech and/or small-scale systems located in remote locations. In those circumstances, power outages may occur regularly and compromise conventional aeration systems.

Particularly, in aquaponic plant production, systems are often small- to medium-sized and frequently operated by hobbyists or as secondary income activities (Love et al., 2015). In some cases, these systems are located in remote areas, where occasional power outages may occur, disrupting conventional aeration systems. While backyard aquaponic systems often only employ aeration in the fish tank and biofilter (Bodenmiller, 2017), additional aeration of the hydroponics compartment ensures optimal plant growth (Palm et al., 2019). Thus, a simple measure can lift plant production and quality and, thus, the economic feasibility of DAPS.

As passive hydrogen peroxide addition neither moves the water body nor causes any friction, heavy aeration is avoided. In fact, this reduces possible risks in hydroponics cultivation, where heavy aeration can lead to negative side effects, such as elevated pH due to constant CO₂ removal (Bodenmiller, 2017). Nevertheless, if professionally managed and adjusted, active aeration is beneficial for hydroponic plant production without negative side effects, as shown in the current study.

A simple cost comparison (Table 3) showed that using H₂O₂ might not incur higher costs, as the amount of H₂O₂ used in this study was, in this case, even slightly cheaper than the electrical power that was necessary to run a small air pump. Nevertheless, many factors are influencing this comparison, and a clear result or recommendation is difficult, since this was not the aim of the current study. Average electricity prices of 0.41 Euro/kWh in Germany are very high (Destatis, 2026), and the outcome in other countries with lower prices might be in favor of air pumps. Additionally, for commercial applications, lower prices would apply for both electricity and H₂O₂. Here, it might be a very individual, location- and situation-based decision to either use passive oxygenation or not.

4.5 Conceptual contribution to oxygen management in DAPS

Beyond the practical implications, the present study contributes to the conceptual understanding of oxygen management in decoupled aquaponic systems. By demonstrating that passive hydrogen peroxide application maintained dissolved oxygen concentrations within a biologically sufficient range without impairing plant performance, the study provides experimental evidence that controlled, low-dose H₂O₂ can function as a physiologically neutral oxygen source under stable environmental conditions. In this context, the results help to define a preliminary operational “safety corridor” for passive H₂O₂ use in hydroponic and decoupled aquaponic systems.

In the future, this method could also be extended to the fish production unit in aquaponic systems, as the passive application devices used were originally developed for fish-keeping purposes. Lettuce was chosen as the target crop since it is one of the main plants scientifically and commercially produced in aquaponics (Yep and Zheng, 2019).

4.6 Conclusion

The present research provides clear evidence that the passive (non-electric) application of hydrogen peroxide can serve as a safe and simple method to maintain sufficient oxygen concentrations in hydroponic and decoupled aquaponic production systems. This approach may be particularly valuable in remote areas or in systems where interruptions of the electrical supply occur regularly, since hydrogen peroxide can be stored safely, over long periods without the need for additional electricity.

In addition, hydrogen peroxide application may offer further potential benefits, such as increasing the redox potential of the nutrient solution, reducing algae formation in reservoirs, and possibly limiting waterborne pathogens. However, these aspects were not directly investigated in the current study and require further experimental validation.

Overall, the present study should be regarded as an initial step toward defining a practical safety corridor for passive H₂O₂ use in hydroponic and aquaponic systems such as DAPS. The results demonstrate that the applied passive method, using hydrogen peroxide as an oxygen source, represents a feasible option with low risk and without detectable negative effects on crop growth under the tested conditions—here validated by a common crop, lettuce. However, looking ahead, future research should investigate different H₂O₂ concentrations, also assessing the feasibility of passive oxygenation for the entire aquaponic systems including fish production, compare passive and active dosing strategies (e.g., peristaltic pump application), and evaluate potential effects on nutrient uptake, photosynthetic performance, stomatal behavior, algae development, and waterborne pathogens. Nevertheless, the current research creates a fundamental foundation for the application of passive oxygenation in hydroponic lettuce production and highlights a potential option for the electrical grid-independent oxygenation of DAPS.

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Supplementary material

The Supplementary Material for this article can be found online at: https://www.frontiersin.org/articles/10.3389/faquc.2026.1819403/full#supplementary-material

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Supplementary material Supplementary material at the source

Footnotes

Edited by: Isabela Pinheiro, Alfred Wegener Institute Helmholtz Centre for Polar and Marine Research (AWI), Germany

Reviewed by: Harshata Pal, Amity University Kolkata, India

Andréa Ferretto Da Rocha, Seapi, Brazil