Coadsorption of tetracycline and copper(II) onto struvite loaded zeolite – An environmentally friendly product recovered from swine biogas slurry

Abstract

In this study, an environmentally friendly struvite-loaded zeolite (S-NZ), prepared by nutrient recovery from swine biogas slurry, was used in the simultaneous removal of Cu (II) and tetracycline (TC) in solution for the first time. The adsorption behavior was systematically studied by accessing solution pH, kinetics, equilibriums in sole and binary systems. The results showed that the adsorption of Cu(II) and TC was fast and remarkably affected by solution pH due to pH-dependent speciation of adsorbates and the zeta potential of the S-NZ. Adsorption isotherms of TC and Cu(II) in binary system were well fitted by the Langmuir model and competitive Langmuir model, with the maximum adsorption capacities of 197.53 mmol TC/kg and 379.42 mmol Cu(II)/kg, respectively. The removal of TC could be significantly enhanced when Cu(II) coexisted, but not vice versa. Besides, the Coulombic interaction in the binary system at different pH was further supported by calculating relative charge distribution over the entire Cu(II)-TC complex and postulating the orientation of Cu-TC complex on the surface of S-NZ. Moreover, dissolved organic matter (DOM) impeded the adsorption of TC and Cu (II) onto S-NZ because of its formation of complex with Cu(II) and TC. This study shows new guidelines and useful methods for nitrogen and phosphorus recovery from livestock and poultry biogas slurry as well as its application in heavy metals and antibiotic pollution control.