Abstract:
This study focused on quantifying and characterising microbeads in biosolids (i.e., treated sewage
sludge), and in examining interactions of microbeads with trace elements when biosolids are added to
soil. Under laboratory conditions, batch experiments were conducted to investigate the adsorption of Cu
onto pure and surface modified microbeads suspended in soil. The ecotoxicity of microbead-metal
complexes to soil microbial activities was also investigated by monitoring basal respiration and dehydrogenase
activity. Concentrations of the microbeads were 352, 146, 324, and 174 particles kg 1 biosolids
for 50, 50e100, 100e250, 250e1000 mm size fractions, respectively. The Scanning Electron Microscope
(SEM) images illustrated wrinkled and fractured surfaces due to degradation. The adsorption of dissolved
organic matter onto microbeads was confirmed through FT-IR microscopy, while using Inductively
Coupled Plasma Mass Spectrometer (ICP-MS) the presence of trace metals including Cd (2.34 ng g 1), Cu
(180.64 ng g 1), Ni (12.69 ng g 1), Pb (1.17 ng g 1), Sb (14.43 ng g 1), and Zn (178.03 ng g 1) was revealed.
Surface modified microbeads were capable of adsorbing Cu compared to the pure microbeads, which
may be attributed to the complexation of Cu with dissolved organic matter associated with the
microbeads in the matrix. It was further revealed that the biosolids derived microbead-metal complexes decreased soil respiration (up to ~ 26%) and dehydrogenase activity (up to ~ 39%). Hence, microbeads
reaching biosolids during wastewater treatment are likely to serve as a vector for trace element
contamination, transportation, and toxicity when biosolids are applied to soil.
