Enhanced phosphorus recovery from digestate via solid-liquid separation using Mg²⁺ and Ca²⁺ modified biochar

Area of Science:

• Environmental Science
• Agricultural Chemistry
• Waste Management

Background:

• Global phosphorus (P) reserves are diminishing, necessitating the recovery of P from alternative sources.
• Biogas digestate is a significant source of P, but its direct application can lead to nutrient runoff.
• Sustainable P recovery is essential for agricultural sustainability and circular economy principles.

Purpose of the Study:

• To investigate the efficacy of magnesium (Mg²⁺) and calcium (Ca²⁺) modified biochar for phosphorus recovery.
• To evaluate the use of metal salts, specifically kieserite (MgSO₄·H₂O) and calcium chloride (CaCl₂), for enhanced P recovery.
• To assess the impact of these treatments on P fractionation and nutrient availability in biogas digestate.

Main Methods:

• Laboratory-scale separation trials were conducted using Mg²⁺ and Ca²⁺ modified biochar.
• Metal salt treatments with kieserite and CaCl₂ were applied at varying concentrations and treatment times.
• Phosphorus fractionation analysis was performed to determine the forms of recovered P.

Main Results:

• Modified biochar increased phosphorus recovery to 52%, significantly higher than the control (35%).
• Metal salt treatments achieved even higher P recovery rates, reaching up to 65%.
• Metal ions promoted the formation of non-labile P, reducing potential nutrient runoff and enhancing long-term availability.

Conclusions:

• Modified biochar and metal salts are effective agents for sustainable phosphorus recovery from biogas digestate.
• These methods offer a viable solution for improving nutrient management in existing biogas plants.
• The study supports the integration of P recovery into circular economy practices within the agricultural sector, reducing environmental impact.