Photocatalytic Degradation of Domestic Wastewater Using ZnO: A Pathway to Sustainable Irrigation

Abstract

The increasing challenges of water shortages and wastewater management in urban areas have prompted the exploration of sustainable, cost-efficient treatment systems. This work investigates the viability of utilizing zinc oxide (ZnO) as a photocatalyst for the degradation of organic pollutants in hostel wastewater, with the objective of rendering the treated water appropriate for reuse in irrigation. ZnOwas synthesized using the sol-gel process and utilized in photocatalytic wastewater treatment under ultraviolet (UV) light irradiation. The photoactivity of ZnO was assessed by quantifying the reduction in COD, BOD, TDS, turbidity, and surfactants. Additionally, pot experiments with Spinaciaoleracea (Spinach Plant) were conducted to evaluate the viability of treated wastewater for agricultural irrigation. Spinaciaoleracea cultivated in treated water exhibited comparable development to those grown in potable water; however, plants grown in untreated wastewater showed stunted growth and phytotoxicity. ZnO-based photocatalysis has been identified as an effective, cost-efficient, and environmentally sustainable method for wastewater treatment, offering significant potential for water reuse in agriculture. This study contributes to the advancement of wastewater management methodologies by promoting the implementation of nanotechnology-based resource recovery systems and circular water management systems.

Introduction

1. Background and Motivation

• Water scarcity and the need for clean water are pressing global issues exacerbated by urbanization, population growth, and climate change.

• According to WHO (2019), 2.2 billion people lack access to safe drinking water.

• Greywater (wastewater from bathing, washing, etc.) is a significant but underutilized resource on academic and institutional campuses.

• Greywater is less contaminated than blackwater but contains various organic and inorganic pollutants, including trace heavy metals and surfactants.

• Conventional treatment methods are often insufficient, prompting the need for advanced oxidation processes (AOPs) like photocatalysis.

2. Photocatalysis and ZnO

• Photocatalysis is a sustainable, low-energy process where light-activated semiconductors degrade organic pollutants into harmless products.

• Zinc Oxide (ZnO) is a preferred photocatalyst due to:

  • Wide band gap (~3.37 eV)

  • High oxidative power

  • Low toxicity

  • Stability and cost-effectiveness

• ZnO can be synthesized through various methods (e.g., sol-gel, hydrothermal) and its activity depends on particle size, morphology, and crystallinity.

3. Objectives of the Study

• RO1: Investigate the impact of pH, catalyst dosage, and exposure time on degradation efficiency.

• RO2: Evaluate the suitability of treated wastewater for reuse in irrigation based on physicochemical parameters.

4. Literature Insights

• ZnO is widely researched for dye and pollutant degradation, but limited studies focus on real-world wastewater like hostel greywater.

• Reusing treated wastewater for non-potable uses (e.g., irrigation) is crucial in mitigating water stress.

5. Methodology

A. ZnO Synthesis:

• ZnO nanoparticles were synthesized using the sol-gel method (zinc acetate + NaOH in ethanol), followed by drying and purification.

B. Characterization:

• Techniques used: XRD, SEM, UV–Vis spectroscopy, FTIR

• Assessed crystallinity, particle size, morphology, surface functional groups, and band gap.

C. Wastewater Sampling & Analysis:

• Samples collected from hostel bathrooms and laundries during peak hours.

• Key parameters measured: pH, BOD, COD, TDS, turbidity, surfactant concentration.

D. Photocatalytic Treatment:

• Conducted in a batch reactor with ZnO (0.5 g/L) under UV light (254 nm).

• Experiments run for 30 to 180 minutes.

• Control tests confirmed that both ZnO and UV light were essential for degradation.

6. Key Findings

• ZnO effectively degraded organic pollutants in hostel wastewater under UV light.

• The process significantly reduced COD, BOD, surfactants, making the water potentially reusable for irrigation.

• This method offers a low-cost, eco-friendly alternative to conventional wastewater treatment.

Conclusion

This study successfully demonstrated the potential of zinc oxide (ZnO) as an effective and sustainable photocatalyst for the degradation of organic pollutants in hostel wastewater. The synthesized ZnO, characterized by favourable physicochemical properties, exhibited high photocatalytic activity under UV irradiation, leading to substantial reductions in chemical oxygen demand (COD), biological oxygen demand (BOD), turbidity, total dissolved solids (TDS), and surfactant concentrations. These improvements in water quality were achieved within a relatively short irradiation period, emphasizing the efficiency of the process. Importantly, the treated water was evaluated for reuse in irrigation through controlled plant growth experiments. Spinach plants irrigated with photocatalytically treated wastewater exhibited comparable growth performance to those irrigated with clean tap water, while those exposed to untreated wastewater showed significant phytotoxic effects. This confirms the feasibility of reusing treated hostel wastewater for agricultural purposes, thereby supporting a circular and resource-efficient approach to campus water management. Overall, this research highlights the applicability of ZnO-based photocatalysis as a low-cost, low-energy, and environmentally friendly method for decentralized wastewater treatment. The approach aligns with sustainable development goals related to clean water, sanitation, and responsible consumption. Future work may explore the use of solar-driven photocatalysis and the integration of this system into pilot-scale treatment units to further enhance practicality and scalability.

References

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Copyright

Copyright © 2025 Hitendra Singh Tomar, Megha Jaiswal , Ravindr Soni, Kalpana Gawali. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.