A Cyclic Graywater Treatment Model for Sustainable Wastewater Management Applied in a Small Scale

Water scarcity presents a critical challenge to global sustainability, exacerbated by population growth, climate change, and environmental pollution. In this context, graywater reuse has emerged as a promising solution, offering substantial water savings with significant potential for agricultural applications. However, efficient treatment methods are essential to ensure safe reuse, as contaminants vary depending on the source. This study introduces a cyclic graywater treatment system that integrates both mechanical and biological filtration processes. A key feature of this system is the inclusion of Chenopodium quinoa, a resilient plant known for its phytoremediation potential, which enhances filtration efficiency and facilitates contaminant removal. The study examines the impact of treated graywater on soil and quinoa properties, focusing on its suitability for irrigation. The results show that the cyclic treatment system significantly improves graywater quality, enhancing the removal of biological and microbiological contaminants, such as BOD, with a significant decrease ranging from 31.33 mg O2/L to 15.74 mg O2/L is observed after treatment. For COD, the average values decreased from 102.64 mg O2/L to 54.19 mg O2/L after treatment, making the treated graywater compliant with Tunisian regulation NT 106.03 and WHO guidelines. Cyclic treatment significantly reduced the microbial load of graywater. For example, for E. coli, the average decreased from 0.87 log 10/100 mL in RGW to 0.58 log 10/100 mL in GWT3. The results demonstrate that the cyclic treatment process can predict the graywater quality beyond the three tested stages. This study highlights the potential of plant-based cyclic graywater treatment systems as an eco-friendly and scalable approach for sustainable water management in agriculture.