Polystyrene and low-density polyethylene pellets are less effective in arsenic adsorption than uncontaminated river sediment

Abstract

The adsorption process of inorganic arsenic (As) plays an important role in its mobility, bioavailability, and toxicity in the river environment. In this work, the adsorption of dissolved arsenite (As(III)) and arsenate (As(V)) by microplastics (MPs) pellets (polystyrene (PS) and low-density polyethylene (LDPE)), river sediment, and their mixture were investigated to assess the adsorption affinities and mechanism. The adsorption kinetics showed slow and mild rising zones from the natural behavior of the chemical adsorption. The results indicated that both MP characteristics and water properties played a significant role in the adsorption behavior of inorganic As species. The As adsorption equilibrium was modeled well by both Langmuir and Freundlich isotherms and partly fitted with the Sips model suggesting that both mono-layer and multi-layer adsorption occurred during adsorption The spontaneous adsorption process for both As(III) and As(V) was evidenced by the adsorption thermodynamics. The maximum adsorption capacities of As(III) and As(V) reached 143.3 mg/kg and 109.8 mg/kg on PS in deionized water, which were higher than those on sediment-PS mixture (119.3 mg/kg, 99.2 mg/kg), which were all lower than on sediment alone (263.3 mg/kg, 398.7 mg/kg). The Fourier transform infrared spectroscopy analysis identified that As(III) and As(V) interaction with sediment surface functional groups was the main adsorption mechanism from surface complexation and coordination. Two functional groups of polystyrene (-NH2, -OH) were mainly involved in the adsorption of inorganic As species on PS, while -COO- and -OH functional groups contributed to the adsorption mechanism of inorganic As species on LDPE. The findings provide valuable insight on the adsorption behavior and mechanisms of As(III) and As(V) in river systems in the presence of MPs particles. Both PS and LDPE were shown to be less effective than river sediment in the adsorption of As species from water, which provides a different perspective in understanding the scale of MPs impact in pollutant transport in the aquatic environment. Graphical Abstract

Removal of Contaminants in Water with Scallop Shell Waste

“…Table 6 shows a comparison between the removal percentages obtained in this work and those of materials commonly used in wastewater treatment for these specific contaminants. Results indicate that northern scallop shell waste has a high potential in water decontamination applications, as many of the adsorbents reported on Table 6 are either synthetized by using several chemical reactives [62][63][64][65][66], have a high energy consumption [67][68][69][70][71], or require large infrastructures [69][70][71][72] compared to scallop shell waste, which is processed at a low energy cost and does not require complex infrastructure nor any additional chemical reactive. Figure 12 shows the pore size distribution of the different particle size ranges of scallop shell waste (BS, MS, and SS) used in this study, which was determined by the Barret-Joyner-Halenda (BJH) method.…”