No abstract

Microplastics are regarded as vectors of hazardous contaminants due to their ability to adsorb xenobiotic chemicals. This has led to increased interest in the risk of previously neglected microplastic contaminants in the aquatic environment. Here, we assessed the possibility of transferring chemical contaminants to microplastics by evaluating the adsorption performance of (in)organic pollutants on various types of microplastics (polystyrene, PS; polyethylene terephthalate, PET; high-density polyethylene, HDPE; and low-density polyethylene, LDPE;). Considering the toxicity and polarity of each pollutant, dyes (BB9 and RR120) and heavy metals (Cd(II), Pb(II), As(III), and As(V)) were selected for the adsorption experiments. Dye was found to be adsorbed through physical adsorption. The adsorption capacity of microplastics for RR120 and BB9 was the highest for HDPE-1 and LDPE-1, respectively. Additionally, the smaller the size of the microplastics, the higher the adsorbed amounts. The main adsorption mechanism of heavy metals was found to be through physical and chemical adsorption. And adsorption mechanism of dye depends on physical adsorption. Thus, the adsorption of microplastic contaminants was affected more by the condition than by the type of microplastics.

The potential use of wastewater sludge as a biosorbent for the removal of various metals and metalloids from aqueous solutions was investigated. The sludge was immobilized in a rod shape with chitosan to improve sorption capacity and solid–liquid separation ability. An optimal condition for the production of rod-shaped chitosan-immobilized sludge (RCS) was determined by considering the biosorbent production potential and As(V) removal efficiency. The optimal sludge and chitosan contents and RCS thickness were 6.0%, 4.0%, and 0.2-0.3 mm, respectively. The anion removal performance of RCS was investigated for As(V), Cr(VI), and Mn(VII), and the cation removal performance was investigated for Cd(II). Pseudo-first-order and pseudo-second-order models adequately explained the kinetic data for the RCS, while the Langmuir and Freundlich models explained the equilibrium data for the RCS. These results showed that RCS has a higher adsorption capacity for anions than for cations. The results also indicated that electrostatic attraction or ion exchange is the main mechanism for metal/metalloid removal by RCS, except for the case of Mn(VII) where an adsorption-coupled reduction mechanism may be suggested.