Investigation of tetracyclines transport in the presence of dissolved organic matters during struvite recovery from swine wastewater

Abstract

Struvite (MgNH4PO4·6H2O) crystallization is preferable for phosphorus recovery from swine wastewater. However, the extensive existence of tetracyclines (TCs) in the wastewater will pose pharmacological threats of recovered products to the environment. In this study, the evolution effects of dissolved organic matters (DOM), as a common media, in the wastewater on TCs migration during struvite recovery from swine wastewater were investigated. Compared to 1.85–7.29 μg/g TCs adsorbed by pure struvite crystals, 148.3–303.9 μg/g TCs were detected in the struvite products recovered under real wastewater. Struvite crystals adsorbing DOM-TCs complex contributed 26.4–30.1% of total TCs migration in the recovery process. A tangential flow filtration system was employed to divide DOM into five fractional parts on the basis of molecular weight cut-offs, i.e. 100 kDa-0.45 μm (FDOM1), 30–100 kDa (FDOM2), 5–30 kDa (FDOM3), 1–5 kDa (FDOM4) and <1 kDa (FDOM5), respectively. Results revealed that struvite recovery under FDOM1, FDOM2 and FDOM3 with larger molecular weights underwent more organic loss in the aqueous phase due to aggregation and struvite adsorption, and thereafter possessed higher TCs residues in the recovered solids. Due to the electrostatic force, humic acid-like and soluble microbial by-product-like organics were prone to complex with TCs, which promoted TCs transport through the adsorption onto formed struvite crystals. The outcomes were helpful to understand the behaviors of antibiotic migration and develop abatement methods for phosphorus recovery.