Aerobic biodegradation of polydiallyldimethylammonium chloride-acrylic-acrylamide-hydroxyethyl acrylate/ZnO nanocomposite in an activated sludge system

Abstract

Biodegradation studies of polydiallyldimethylammonium chloride-acrylic-acrylamide-hydroxyethyl acrylate/ZnO (P(DMDAAC-AA-AM-HEA)/ZnO) nanocomposite were performed in a simulated aerobic activated sludge system. Batch experiments were conducted with different initial substrate concentrations between 100 and 1000 mg L⁻¹ at pH 7 and 25 °C. The biodegradability tests of the samples by activated sludge exhibited significant degradation after 30 days of inoculation. The removal ratios were 71.8%, 67.1% and 63.6% at initial P(DMDAAC-AA-AM-HEA)/ZnO concentrations of 100, 500, and 1000 mg L⁻¹, respectively, indicating that the biodegradation efficiency decreased with increasing initial substrate concentration. Kinetic studies showed that the Monod model could accurately describe the biodegradation process. The estimated values of the maximum specific rate of substrate degradation (ν_max) and saturation rate constant (k_s) were 2.56 h⁻¹ and 336 mg L⁻¹, respectively. The biodegradability of the P(DMDAAC-AA-AM-HEA)/ZnO nanocomposite was further confirmed through dynamic light scattering (DLS), scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDS), Fourier transform infrared spectroscopy (FT-IR) and gel permeation chromatography (GPC) analysis. The action of microorganisms in the activated sludge caused the partial disruption of nano ZnO-matrix bonding, and was followed by random chain scission in the P(DMDAAC-AA-AM-HEA) polymer chains. These changes were accompanied by significant losses in the concentration and molecular weight of the samples.