Closed Loop Phosphorus Recovery and Recycling for Sustainable Hydroponic Farming

Abstract

This study explores the viability of in-situ recycling of hydroponic waste nutrient solutions using alkali treatment to produce micro-calcium phosphate. The recovered precipitate was converted into a usable liquid form (called Part C) and assessed for its effectiveness as a source of phosphorus, replacing 40% of the commercial Part B fertiliser in a hydroponic nutrient solution. The pilot study was conducted in a controlled greenhouse equipped with an automated fertigation system to ensure precise nutrient delivery and environmental control. Snow peas (Pisum sativum L.) were grown for 21 days using this nutrient solution, and its performance was compared with a control system employing commercial fertilisers. Results demonstrated that the test system, incorporating Part C, required 33% less commercial fertiliser while maintaining comparable plant growth, yield, and nutrient uptake. Except for a slightly lower chlorophyll content, plants in the test system exhibited no nutrient deficiencies; exhibited stable phosphorus, and enhanced calcium and magnesium uptake. Moreover, Part C contributed to improved pH and EC stability, reducing the need for frequent nutrient adjustments compared to the control. The economic analysis indicated a significant cost reduction without compromising plant health or productivity, highlighting the potential for broader application in sustainable hydroponic farming.