Housefly larva bioconversion enhances heavy metal stabilization and antibiotic degradation during chicken manure composting

Abstract

This study assessed the integration of housefly larva bioconversion with aerobic composting for chicken manure (MC) over a 45-day period (4 days of larval bioconversion + 41 days of aerobic composting) and compared it with direct composting (CK1) and sawdust-amended composting (CK2). Larval activity enhanced moisture reduction and substrate porosity, yielding 6.08% (w/w) maggot protein and reducing nutrient losses of C, N, P, and K by 13.45%, 35.08%, 62.15%, and 70.89%, respectively, relative to CK2. MC treatment accelerated humification, as evidenced by increased aromatic and humic acid content, which immobilized heavy metals, Particularly Zn and Cd via HA-metal complexation. Multivariate analyses (redundancy and CART) identified moisture (< 63 - 74%), composting duration, organic matter, and K⁺ release as principal drivers for heavy metal passivation. In the three treatmengt, degradation of tetracycline antibiotics followed the sequence OTC > CTC > DOX with MC reducing the half-life of CTC to 2.57 days through thermophilic degradation coupled with HA- and K⁺-mediated adsorption and chelation; quinolone antibiotics remained largely recalcitrant. These results demonstrate that MC composting enhances nutrient retention, heavy metal stabilization, and tetracycline removal, thereby improving the agronomic value and environmental safety of chicken manure-derived biofertilizer.

Keywords: Aromatic structures; Humic substances; Maggot protein; Nutrient retention; Tetracyclines.

Fig. 1

Changes in major physicochemical properties during the three composting processes: (a) temperature; (b) moisture content; (c) pH value; (d) organic matter content; (e) total nitrogen content; (f) seed germination index.

Fig. 2

Changes in humic substances and the FT-IR spectra during the three composting processes: (a) Total humic substance (HS) content (g·kg⁻¹); (b) Fulvic acid (FA) content (g·kg⁻¹); (c) Humic acid (HA) content (g·kg⁻¹); (d) FT‑IR spectra of MC at key composting stages; (e) FT‑IR spectra of CK1 at key composting stages; (f) FT‑IR spectra of CK2 at key composting stages.

Fig. 3

Effects of three composting treatments on the immobilization of heavy metals over time: (a) Cu, (b) Zn, (c) Cd, (d) Cr, (e) As, and (f) Pb.

Fig. 4

Effects of three different composting methods on the changes in the antibiotic content of tetracycline during composting: (a) oxytetracycline (OTC), (b) chlortetracycline (CTC), and (c) doxycycline (DOX).

Fig. 5

Effects of three different composting methods on the changes in the quinolone antibiotic content during composting: (a) ciprofloxacin (CIP), (b) enrofloxacin (ENR), and (c) norfloxacin (NOR).

Fig. 6

Correlation analysis of environmental factors with heavy metal bioavailability and changes in the antibiotic content of tetracycline in three composting processes: (a) RDA biplot for the MC treatment showing heavy-metal bioavailability factors (red arrows) and environmental variables (blue arrows). Axes labels give the percentage of explained constrained variance (RDA1 82.07%, RDA2 7.29%); (b) RDA biplot for the CK1 treatment (RDA1 77.09%, RDA2 8.24%); (c) RDA biplot for the CK2 treatment (RDA1 82.57%, RDA2 6.38%).