The role of biochar and zeolite in enhancing nitrogen and phosphorus recovery: A sustainable manure management technology

Abstract

Swine manure is a potential source of plant-available ortho-phosphate (ortho-P) and ammonium (NH4+). However, transport and application issues restrict its widespread use in agriculture and cause water quality degradation. This study investigates the potential of biochar (BC) produced from corn stover (control-BC) and FeSO4 pretreated corn stover (Fe-BC) and zeolite to recover ortho-P and NH4+ from liquid swine manure. Chemisorption increased ortho-P sorption from manure onto Fe-BC (29,831 mg kg−1) relative to control-BC (19,000 mg kg−1). During Mehlich III (M−III) desorption study, manure-treated Fe-BC and control-BC released 34% and 80% of adsorbed ortho-P, respectively. Increasing the BC loading rate from 5 g/L to 25 g/L in manure significantly dropped the M−III P desorption (<10%) for the Fe-BC but not for the control-BC. Sorption of manure NH4+ on Fe-BC, control-BC, and zeolite occurred by I) specific adsorption on surfaces and within pores, II) co-adsorption of NH4+ with manure colloids, and III) precipitation as N-mineral (struvite). The NH3 volatilization and KCl desorption studies revealed that NH4+ sorption/desorption from manure to BC cannot be explained by simple ion exchange or volatilization loss. The BC-zeolite combination increased the NH4+ recovery from manure (28–38%) relative to BC’s without zeolite addition. SEM-EDS and XRD analyses revealed the association of P with both Mg and Fe and the presence of struvite (NH4MgPO4·6H2O) in batch and centrifuge studies. Our results suggest that low-cost BC and zeolite can recover ortho-P and NH4+ from liquid swine manure, which may facilitate its easy transport and widespread application in agriculture.