Influence of coagulant type on nutrient uptake of plants and the nutrient and micropollutants leaching from anaerobically digested sludge amended soils

Highlights • Coagulant type had a measurable effect on short-term/incidental nutrient leaching. • Organic coagulant-derived biosolids had higher nitrogen and phosphorus leaching. • Organic coagulant biosolid-fertilized microplots produced larger leaf areas. • Micropollutants from biosolids were absent in the drainage waters and soil mixtures. Abstract Coagulant-precipitated sewage sludge subjected to biological stabilization (i.e., anaerobic digestion (AD)) raises concerns pertaining to nutrient availability and risks of pollutant leaching and soil contamination when used as a biofertilizer. The study investigated the influence of different coagulant types on contaminant leaching and nutrient uptake in soils fertilized with anaerobically digested sludge (AD-biosolids). Microplots were fertilized using biologically stabilized solids produced from inorganic coagulant (IC)- polyaluminium chloride (PAC) and synthetic organic coagulant (OC)- epichlorohydrin-dimethylamine (pAmine) and semi-natural OC- Chitosan in Poa pratensis cultivation. Controlled conditions and artificial rain events were employed. Monitoring included nutrients (total nitrogen (tot-N) and total phosphorous (tot-P)), metals (e.g., aluminium and iron), micropollutants, grass growth, and chlorophyll(tot-chl) content. Results indicated that coagulant type influenced contaminant leaching and nutrient availability. pAmine treatment showed the highest tot-P discharge load and content in grass leaves, while Chitosan treatment showed the highest tot-N discharge load (>66 % compared to control) and content, with the highest N-recovery efficiency. IC-PAC-fertilized grass had lower chlorophyll and smaller leaf areas compared to OCs-fertilized grass. Micropollutants initially present in AD-biosolids were not detected in the drainage water nor in soil substrates. These findings highlight the importance of coagulant selection in AD-biosolids fertilization for minimizing environmental risks and maximizing nutrient uptake by plants.