ROORKEE: Hydrologists at IIT Roorkee have developed an “indigenous, low-cost technology” to address wastewater challenges linked to hydroponic farming. Hydroponics involves growing plants without soil using nutrient-rich water, but the wastewater generated often contains high concentrations of nitrate, phosphate and ammonia.
If released untreated, it can cause eutrophication in natural water bodies, leading to algal blooms and oxygen depletion that threaten aquatic life.To address this, researchers from the departments of hydrology and renewable energy at IIT Roorkee developed a cost-effective treatment technology based on microalgal photogranules. The study has been published in the international journal ACS ES&T Water.Conventional microalgae-based wastewater treatment systems face a major limitation: harvesting microscopic algae from water is energy-intensive and typically requires expensive centrifuges or chemical additives.
The IIT Roorkee team addressed this challenge by inducing microalgae to self-aggregate into dense, spherical granules. These photogranules contain microalgae, bacteria and cyanobacteria working together in symbiosis.The technology uses a light-driven photogranule reactor, where microorganisms self-aggregate into dense spherical granules under controlled mixing and illumination. These granules simultaneously remove nitrogen, phosphorus and organic pollutants from hydroponic wastewater through photosynthesis and microbial metabolism.
“A key advantage of this system is that once mixing stops, the granules naturally settle at the bottom due to their density. This allows clear treated water to be easily separated without expensive mechanical or chemical processes, significantly lowering operational costs,” said prof Sanjeev Kumar Prajapati, principal investigator of the project.In the reactor system, hydroponic wastewater is introduced into a controlled environment with light and mild mixing.
Under illumination, microalgae perform photosynthesis, absorbing carbon dioxide and assimilating nitrate and phosphate as nutrients for growth. At the same time, associated bacteria degrade organic pollutants, reducing biological and chemical oxygen demand. Over time, the microbial community produces extracellular polymeric substances that bind cells together, forming compact green granules measuring about 4–6 mm in diameter.According to Prajapati, experimental results showed nearly complete removal of biological and chemical oxygen demand, about 99% reduction in phosphate and ammonia, and nearly 90% removal of nitrate within a few days of treatment.“The system also showed substantial carbon dioxide fixation potential, adding a climate mitigation benefit. With low energy requirements, chemical-free operation and simplified biomass recovery, the microalgal photogranule-based technology offers a sustainable and scalable solution for managing wastewater from the rapidly expanding hydroponics sector,” he said.
