Enhancement in adsorption potential of microplastics in sewage sludge for metal pollutants after the wastewater treatment process

Abstract

Microplastics (MPs) as new pollutants of environmental concern have been widely detected in sewage sludge, and may act as significant vectors for metal pollutants due to their adsorption property. Our findings show that Cd, Pb, and Co, but not Ni, contents in sewage sludge are lower than that of corresponding metal irons adsorbed on sludge-based MPs, indicating that the MPs accumulate such metal pollutants as Cd in the sludge samples. In contrast to virgin MPs, sludge-based MPs are one order of magnitude higher adsorption capacity for Cd, which reaches up to 2.523 mg g -1 , implying that there is a considerable enhancement in adsorption potential of the MPs for metals after the wastewater treatment process. SEM analysis shows that sludge-based MPs have rougher and more porous surface than virgin MPs, and FTIR spectra reveal that functional groups such as C-O and O-H are found on sludge-based MPs. Further, two-dimensional FTIR correlation spectroscopy indicates that C-O and N-H functional groups play a vital role in the process that sludge-based MPs adsorb Cd, which are not found in virgin MPs. The results imply that increased adsorption potentials of the sludge-based MPs to Cd are attributed to changes in the MP physicochemical properties during wastewater treatment process. In addition, such factors as pH value, and sludge inorganic and organic components also have an effect on the MP adsorption to Cd. Principal component analysis shows that the MPs could be divided into three categories, i.e. polyamide, rubbery MPs (polyethylene and polypropylene) and glassy MPs (polyvinyl chloride and polystyrene). Their adsorption potentials to Cd follow the decreasing order: polyamide > rubbery MPs > glassy MPs.

An evaluation of microplastics fate in the wastewater treatment plants: frequency and removal of microplastics by microfiltration membrane

“…The results of analyses showed that MPs were accumulated in the sludge at 183 MP/L. As previously reported, the accumulation of MPs in the sludge could have been due to the adsorption of these materials by the sludge matrix (Li et al 2019). Furthermore, from Table 3, it can be found that the quantity of MPs in the influent and effluent of the WWTP varied corresponding to the season.…”

Microplastics in freshwater fishes: Occurrence, impacts and future perspectives

“…This wastewater eventually passes through the sewage system to wastewater treatment plants (WWTPs), which treat domestic and industrial waste before release into the natural environment (often rivers and estuaries) (Ngo et al, 2019). Waste may undergo biological, chemical and physical processing to remove large debris, neutralize harmful chemicals and degrade biological materials, with these processes simultaneously degrading and modifying MPs throughout treatment (Enfrin et al, 2019; Li, Mei, et al, 2019). Furthermore, there is evidence that MPs may reduce the efficiency of the treatment processes if they contain harmful internal or bound chemicals that can inhibit biological processing stages (Zhang & Chen, 2019).…”

Microplastics in real wastewater treatment schemes: Comparative assessment and relevant inhibition effects on anaerobic processes

“…In the study of Suhrhoff and colleagues (Suhrhoff and Scholz-Böttcher, 2016), acetyl tri-n-butyl citrate (ATBC) was reported as the most dominant additive leaching from PE-MPs. Another possible reason for the methanogenesis inhibition due to MPs was proposed by demonstrating that MPs may act as significant vectors for metal pollutants in sewage sludge due to their adsorption property (Li et al, 2019).…”