Sustainable nutrient recovery through struvite precipitation from poultry and multi-substrate agricultural waste digestates

Abstract

This study addresses the multifaceted challenges stemming from the excessive application of manure or digestate, with the aim of mitigating problems of storage, emissions, contamination and transportation. It presents a unique-protocol for efficiently recovering nutrients in the form of struvite, a pure, easy-to-use magnesium ammonium phosphate compound. The objective is to explore struvite production via mono-digestion of poultry manure and co-digestion of various organic wastes, including poultry, dairy, pig manures, and wasted corn silage. Crystals are synthesized under optimized conditions: magnesium/phosphorus ratio of 1.5, pH 9, and mixing at 240 rpm. The process achieves ≥95 % TAN-recovery in moisture-free form for various digestates, with a significant 61.5 % reduction in volatile-fatty-acids. Approximately 0.33–1 g struvite is produced per 10 mL digestate. The study suggests using disodium or monopotassium phosphate for practical implementation, demonstrating the versatility of digestates. Integrating this method into anaerobic digestion promotes the circular-economy and sustainable management of waste nutrients.