Nanotechnology, the broad discipline of the twenty-first century, has a remarkable influence on global economic success and the commercial sector. Utilization of nanotechnology is increasing day by day in the agriculture field, which involves cultivation, harvesting, processing, storage, packaging, and transportation of agricultural products. Nano-techniques have shown significant potential to improve food quality and agriculture products (Noman et al., 2020; Kaushik, 2021). A nanoparticle is a small particle that ranges from 1 to 100 nanometers in size with distinctive physical and chemical properties (Korbekandi et al., 2012). The nanoparticles, owing to the unique features, have gained the attention of scientists for use in different fields of life (Islam et al., 2018; Sharma et al., 2019), including medicine, wastewater treatment, agriculture, energy products, and the remediation of different environmental pollutants (Duhan et al., 2017; Singh et al., 2018; Noman et al., 2020; Zhang et al., 2020). For the treatment of wastewater, a range of techniques have been employed, including nanotechnology. Nano-photocatalytic technology has received a lot of attention in the field of water pollution prevention.

Various techniques, including physical, chemical, and biological, are considered for the synthesis of nanoparticles. Physical and chemical methods demand difficult conditions like high temperature and pressure, very costly equipment, large space to set up large machinery, and the use of toxic chemicals (Hoseinpour and Ghaemi, 2018). Numerous chemical and physical techniques use toxic substances that can have adverse effects on the environment. Consequently, there is a dire need to explore environmentally friendly and sustainable approaches. Researchers are investigating the potential of various biological entities, such as bacteria, fungi, higher plants, actinomycetes, and viruses, for the synthesis of nanoparticles (Agrawal et al., 2022). However, biological methods to synthesize nanoparticles are getting popularity as they are cost-effective and environmentally friendly (Castro et al., 2014). Numerous bacterial and fungal strains are recognized for their ability to synthesize nanoparticles. Bacteria, with their distinctive quality of metal reduction, play a vital role in the synthesis of nanoparticles. Their resistance to acute environmental conditions, including high temperature and pressure, makes them well-suited for the synthesis of nanoparticles (Das et al., 2014). Different microbial strains, such as Pseudomonas stutzeri, Morganella sp, Plectonema boryanum, Thermomonospora sp, Rhodococcus sp, and Pseudomonas aeruginosa, have been effectively employed in the biosynthesis of nanoparticles (Thakkar et al., 2010; Idris and Yuliar, 2022).

Micronutrients are required in very small quantities by the plant and can affect indirectly or directly photosynthesis and play a vital role in plant protein synthesis, respiration, and the reproductive system. Manganese (Mn) is a micronutrient that plays a crucial role in various plant functions, including respiration and photosynthesis. Nanoscale Mn is reported to be less effective in inhibiting plant growth physiological processes and more efficient at reducing abiotic stressors in plants than traditional bulk or ionic Mn molecules (Ye et al., 2019). Manganese nanoparticles are widely used in industry for a variety of purposes, including supercapacitors, catalysis, biosensors, ion sieves, molecular adsorption, high-density magnetic storage media, batteries, drug delivery systems, and magnetic resonance imaging (Aronson et al., 2000; Ammundsen and Paulsen, 2001). In recent studies, manganese oxide nanomaterials even outperformed MCM-22 and red mud in terms of their ability to adsorb a methylene blue dye (Chen and He, 2008). Furthermore, it was further shown that a hierarchical MnO₂-coated magnetic nanostructure displayed a significantly greater capacity for adsorption than pure magnetic nanoparticles (Kim et al., 2013).

Due to the limited availability of water sources in developing countries, wastewater is being used for agriculture near fields around industrial premises for growing vegetable crops (Roy and Edwards, 2019). Emerging pollutants like pesticides, chemical fertilizers, and other chemical substances such as dyes (Benkhaya et al., 2020; Slama et al., 2021), heavy metals (Engwa et al., 2019; Shrestha et al., 2021), hormones, beauty products, detergents, and drugs enter water supply systems and can either directly or indirectly damage human health. However, the presence of potentially hazardous substances (PTEs) is the primary issue with wastewater used for the irrigation of crops. The accumulation of PTEs in the soil and crops caused by wastewater irrigation had negative impacts not only on soil fertility but also on human beings (Qadir et al., 2010; Azimi et al., 2017). When plants are irrigated with wastewater, the elevated concentrations of sulfate and phosphate lead to accumulation within the plants. Plants require an optimal balance of nutrients, including nitrate, sulfate, and phosphate. The heightened levels cause a nutritional imbalance and disrupt the plant metabolism (Banon et al., 2011; Wardah et al., 2022). Agriculture serves as the foundation of the economy and is widely recognized as the primary source of income for rural people. According to Agricultural Organizations and Food organizations, the overall population of the world would increase by 9 to 10 billion by the year 2050 (Jaramillo and Restrepo, 2017). There is a need to increase food productivity by 25% to 70% to feed the growing population. Wheat (Triticum aestivum L.) is a staple food in many countries including, Pakistan, and an important part of the diet. One-third of the world’s population gets their nutritional needs met through wheat, which also has more nutritional value than other cereals.

According to our observation and knowledge, many studies were mentioned before synthesizing MnO-NPs from plants and chemically checking their potential for wastewater treatment, but not a single study on the production of manganese nanoparticles from Bacillus flexus and then application to wastewater treatment. Similarly, using B. flexus to produce MnO-NPs and then applying them to wastewater might be a new biosource. Based on the above-mentioned findings, we hypothesized that biosynthesized MnO-NPs may have a beneficial potential to remove contaminants from wastewater. In the current study, the synthesis of MnO-NPs was accomplished using pre-isolated B. flexus to treat the wastewater. Furthermore, the treated wastewater was applied to wheat seedlings to explore the potential of treated wastewater for agricultural purposes. In addition, the performance of wheat seedlings regarding physical growth, and physiochemical parameters were also studied under the impact of untreated and treated wastewater, and distilled water as irrigational water.

The present study reported microbial synthesis, characterization, and application of manganese nanoparticles (Mn-NPs) prepared by using a bacterial strain, namely B. flexus. The brown color of the synthesized nanoparticles was caused by surface plasmon resonance, which was induced by the oscillation of electrons on the nanocomposite’s surface (Wadhawan et al., 2020). The absorption spectra of MnO-NPs illustrate a sharp peak at 325.23nm due to the transmission of electrons from the valance band to the conduction band ( Figure 2 ). The absorption spectral test was performed, and it complied with the result performed by Jayandran et al. (2015), whose absorption peak was in the range of 350-410 nm. The findings from the XRD analysis exhibited diffraction peaks at 101, 201, and 210, indicating the crystalline structure of MnO-NPs ( Figure 3 ). Similar results for the MnO-NPs were reported by Moon et al. (2015). Figure 5 illustrates the FTIR spectrum of MnO-NPs at a broad peak of 3397.55 cm^-1, 2958.31 cm^-1, 2925.46 cm^-1, and 1725.41 cm^-1. The peak at 3394 cm^-1 was confirmed by the OH group, which is parallel to Saod et al. (2022), in which the OH and CH groups were confirmed at peaks of 3360 cm^-1 and 2800 cm^-1.

Biosynthesized manganese nanoparticles were found to be efficient in wastewater treatment. In the present study, MnO-NPs showed great potential for the treatment of wastewater. The biosynthesized MnO-NPs at the concentration of 1g L^-1 were used for the photocatalytic degradation and adsorption of phosphates, sulphates, COD, TDS, and color intensity of wastewater. Maximum results were gained at the concentration of 1g L^-1 for the treatment of wastewater under sunlight for seven hours which was also previously reported by (Islam et al., 2018). The result was also positively correlated with Jain et al. (2022) in which they used MnO-NPs at 1mg L^-1 for the treatment of wastewater. MnO-NPs play a crucial role in the decolorization and degradation of pollutants in wastewater (Cui et al., 2015; Shoiful et al., 2020). When exposed to light, they generate electron-hole pairs, which subsequently interact with oxygen and water (Fouda et al., 2021). This interaction leads to the formation of highly reactive species, such as hydroxyl radicals (Wang et al., 2020). These radicals are responsible for the effective decolorization and degradation of pollutants in the wastewater. These free radicals interact with the contaminants and transform them into less toxic and simpler molecules (Zhao et al., 2015; Yamaguchi et al., 2018). Gupta et al. (2015) reported that use of nano particles is a useful approach to remove the noxious metal ions from the wastewater as they have specific surface characteristics and unique structure. Nanosized metal oxides, including manganese oxides, possess high surface area and specific affinity along with other mechanisms like electrostatic interaction, ion exchange, surface complexion and hard/soft acid-base interaction to absorb impurities from wastewater.

Results showed the removal of 79% COD, 37% TDS, 64% sulfates, 64.5% phosphate, 77.05% color intensity, pH reduction from 8.7 to 7.3, and EC reduction from 5.33 to 3 ( Table 1 ). COD is the parameter against which MnO-NPs show the highest efficiency. MnO-NPs are effective adsorbents for removing pollutants from wastewater due to their higher surface area and higher reactivity, which are caused by their absorption properties (Islam et al., 2018). Various contaminants, such as heavy metals, organic compounds, and dyes, can be adsorbed by MnO-NPs (Martinez-Vargas et al., 2018). Such results have also been reported in previous studies (Shabanloo et al., 2020; Jothinathan et al., 2022; Munir et al., 2023). Results of the experimentare supported by the findings of Yaashikaa et al. (2022), who stated that MnO-NPs can efficiently adsorb heavy metals and other contaminants and ultimately degrading COD TDS, phosphates, sulfates, pH, and EC. The findings of the present studies, like removal of 37% TDS, are in line with the outcomes of Kumar and Chopra (2018), who stated that a reduction in TDS was observed by using phytoremediation for wastewater treatment. The TDS might be removed from wastewater by the process of adsorption due to unique properties NPs, like the high surface area to volume ratio and the large number of active sites that interact with TDS (Hendren et al., 2013).

The results revealed that the growth parameters of wheat were significantly increased in treated wastewater as compared to untreated wastewater. The germination rates observed in treated wastewater were as follows: 87% on day nine, 75% on day six, and 62% on day three ( Figure 6 ). The germination rate in treated wastewater jumped due to a variety of factors that affected the sustainability of seeds and growth (Dimkpa et al., 2018). The absence of pollutants or hazardous compounds in treated wastewater can generate a more favorable environment for germination as compared to untreated wastewater (Kannan and Upreti, 2008; Huma et al., 2012). The greater germination rates may be due to improved quality of water and nutrient availability in treated wastewater (Nsiah-Gyambibi et al., 2022). Results obtained through the current experiment are supported by Helaly et al. (2018), who concluded that an increase was found in shoot and root lengths of mango plants by the application of treated wastewater. The application of wastewater adversely affected the plant’s primary root elongation, lateral root formation, and growth of aerial parts. Biochemical compounds, like chlorophyll pigments, were decreased in the mesophyll cells by the application of wastewater (Hong et al., 2019).

Wastewater disturbs the physical and physicochemical system of wheat due to the high concentration of COD, TDS, and nutrients (Zhang et al., 2021). The high amounts of phosphate and nitrate disturb metabolism by unbalancing the nutritional system of plants and accumulating in cells and tissues (Ahmad et al., 2020). The chlorophyll parameters of wheat decreased considerably under wastewater treatment as compared to treated wastewater ( Figure 8 ). The pollutants present in wastewater reduced oxygen availability by contaminating the soil around wheat, thus reducing physical growth (Khan et al., 2009). The result revealed that the chlorophyll content of wheat increased with the application of treated wastewater, and the health of any plant is depicted by its chlorophyll content (Kamble et al., 2015). Prior research found that treating wheat plants with Mn salt, increased the formation of chlorophyll (Sheng et al., 2016), however, excessive Mn exposure (378 mg/L) decreased chlorophyll concentration (Jhanji et al., 2014). It is well known that Mn is needed in the shoots (leaves) for the functions of chlorophyll and photosynthesis, depending on the effects of soil versus foliar exposure (Narwal et al., 2012). By adding nanoparticles to treat the wastewater, which contains vital nutrients like nitrogen and phosphorus needed for the synthesis of chlorophyll (Khan et al., 2009). The outcomes of the current study are in line with the findings of Jhanji et al. (2014), they reported a consistent outcome, whereby the application of treated wastewater resulted in a significant increase in chlorophyll content in wheat plants.

The results showed that wheat seedlings irrigated with wastewater have higher concentrations of zinc and copper in their roots and shoots than wheat seedlings irrigated with treated wastewater. In industrial discharges, wastewater may include higher quantities of Zn and Cu (Tariq et al., 2020). When such wastewater was used for irrigation, these pollutants may accumulate in the soil and, as a result, in the plant parts. Manganese oxide nanoparticles in treated wastewater may have absorbed or immobilized some of Zn and Cu ions present in the wastewater (Islam et al., 2018). This can make these elements less available for plant absorption, resulting in lower concentration of these elements in plant parts (Zwolak et al., 2019). Wheat seedlings irrigated with treated wastewater have higher levels of manganese and iron than irrigation with distilled water. Manganese oxide nanoparticles have the potential to boost manganese solubility and bioavailability in water, making them more available for plant absorption (Gillispie et al., 2019).

The findings of the study indicated that the application of treated wastewater resulted in an augmentation of antioxidants activities in wheat ( Figure 9 ). The previous observation of Hashmat et al. (2021) that higher levels of antioxidant activities predominated in plants kept in under-treated wastewater applications was confirmed by a considerable rise in SOD and POD activities in treated plants. The antioxidants operate effectively as a cooperative network because of a series of redox reactions (Ali and Alqurainy, 2006). It is plausible to assume that enhanced enzymatic activities were caused by higher production of H₂O₂ in a water-scarce environment (Ahmad et al., 2019; Faria et al., 2020). An ecological response for plants in stressful settings may be provided by the increase in CAT and POD activities in water-stressed plants (Panyuta et al., 2016). Plant species with poor POD activity may find it difficult to cope with stress because lipid peroxidation reduces the permeability of their membranes (Zarinkoob et al., 2021). During stress, reactive oxygen species (ROS) like H₂O_2, and MDA are produced (Das and Roychoudhury, 2014). Results revealed that ROS decreased in treated wastewater as compared to untreated wastewater. H₂O₂ reacts with lipid membranes and damages the permeability of the cell (Javed et al., 2017).

The higher MDA and H₂O₂ concentrations were probably caused by oxidative stress induced by the higher absorption of hazardous wastewater components, affecting plant development and yield (Dudziak et al., 2019). It was hypothesized that elevated levels of lipid peroxidation and H₂O₂ would result in reduced cellular membrane functions due to heavy metal interference and absorption with mineral nutrients in fertigated soil wastewater (Hashmat et al., 2021).

Furthermore, treated wastewater has beneficial potential for the reduction of various plant parameters, such as MDA and H₂O₂. Moreover, it significantly (p ≤ 0.05) enhanced the growth and antioxidant parameters. According to the findings of Kanwal et al. (2020), physiological and biochemical attributes, including photosynthetic rate, respiration rate, stomatal conductance, chlorophyll, and carotenoids were significantly reduced by the application of wastewater. Application of wastewater as irrigational water resulted in a significant reduction in the morphological, physiological, anatomy, and yield parameters of wheat cultivars (Hajihashemi et al., 2020).

Based on the finding of the study, it is suggested that treatment of wastewater through manganese oxide nanoparticles hold significant implications for agricultural practices, particularly in regions grappling with water scarcity and wastewater management challenges. By demonstrating the effectiveness of MnO-NPs in enhancing both wastewater treatment and wheat seedling growth, the research suggests a potential solution for sustainable agriculture in water-stressed areas. Implementing this technology could lead to more efficient utilization of limited water resources, as treated wastewater could be safely reused for irrigation. Additionally, the antioxidant properties of MnO-NPs could bolster plant resilience to environmental stressors, potentially leading to higher crop yields. Based on the utilization of MnO-NPs in treating wastewater for agricultural purposes, several practical recommendations can be offered for farmers and policymakers. It is advisable to explore their incorporation into wastewater treatment strategies for agricultural irrigation by considering the effectiveness of MnO-NPs in enhancing wastewater quality and promoting plant growth. It can lead to more sustainable water use practices, particularly in regions facing water scarcity. Additionally, the study underscores the importance of carefully monitoring the concentrations and application methods of MnO-NPs to ensure their optimal and safe utilization in agricultural settings. However, it is crucial to acknowledge potential limitations and risks, such as the need for thorough assessments of long-term environmental impacts, including effects on soil health and microbial communities.

It can be concluded that the utilization of manganese nanoparticles (MnO-NPs) has a potential to treat wastewater by lowering sulfates, phosphates, color intensity, pH, electrical conductivity, total dissolved solids, and chemical oxygen demand. Furthermore, treated wastewater positively influenced the growth parameters, physiological parameters, and antioxidant defense systems of wheat, except malondialdehyde, and H₂O₂. Based on the findings, it is concluded that treated wastewater can be effectively utilized to cultivate wheat crop under limited availability of good quality water.

The raw data supporting the conclusions of this article will be made available by the authors, without undue reservation.

AI: Conceptualization, Data curation, Methodology, Writing – original draft. MS: Conceptualization, Data curation, Project administration, Supervision, Writing – original draft. MN: Methodology, Resources, Writing – review & editing, Investigation, Project administration. DI: Methodology, Writing – original draft, Data curation, Formal analysis, Resources, Writing – review & editing. SH: Conceptualization, Data curation, Formal analysis, Writing – original draft. TS: Formal analysis, Writing – original draft, Investigation, Methodology. FM: Investigation, Conceptualization, Software, Writing – review & editing. AR: Conceptualization, Investigation, Formal analysis, Resources, Writing – original draft. SG: Conceptualization, Data curation, Methodology, Supervision, Writing – review & editing. A-RG: Conceptualization, Methodology, Writing – review & editing, Investigation, Project administration, Resources. MH: Formal analysis, Methodology, Resources, Writing – review & editing, Software. SK: Conceptualization, Methodology, Resources, Writing – review & editing, Validation, Writing – original draft.