Domestic wastewater reuse in hydroponic systems: A systematic review of adoption, nutrient variability, challenges, and future directions

Reusing treated domestic wastewater in agriculture is gaining attention in Africa with the potential to provide both irrigation water and crop nutrients, especially as climate change accelerates the depletion of freshwater sources. This intervention offers a sustainable alternative to reduce the competition for freshwater in domestic, industrial, and agricultural use. Also, the combined impact of climate change, population growth, and the need to achieve food security makes this a worthy cause. This systematic review evaluated the integration of domestic wastewater for hydroponic crop production focusing on nutrient variability and effects on crop performance. Using the "Preferred Reporting Items for Systematic Reviews and Meta-analyses" (PRISMA) framework, a systematic search was conducted to identify papers published over the last 10 years. Following the PRISMA guidelines, studies were selected based on their relevance to wastewater reuse in hydroponics. A total of 22 studies were included in the final synthesis. The review found that wastewater reuse in hydroponics is relatively an emerging practice globally. In Africa, 3 of the 54 countries have made research contributions to domestic wastewater reuse in hydroponic systems. The review also reports on the successful cultivation of various crops using treated domestic wastewater. However, the review found that the nutrient variability of wastewater and its reuse in passive and non-circulating hydroponic systems present significant issues that require research attention. This review concludes that efficient management and reuse of wastewater in hydroponic crop production presents an innovative strategy that holds promise in fostering sustainable urban agriculture and ensuring food security.