Table 2.

Impacts of different sludge treatment processes on microplastics

Process	Impact on MPs	References
Lime stabilization	• Smaller size MPs due to elevated temperature, mechanical mixing, and pH • Shredded and flaked appearance	[90••]
AD	• Less MPs abundance in AD sludge when compared with lime stabilized sludge • Presence of deep cleavage in MPs • Alteration in micro-morphology of MPs	[27, 28, 90••]
Dewatering	• More than 50% reduction in MPs numbers after dewatering might be due to probable destruction of flocs in the digestive process that returned to WWTP with rejected water • Different average MPs concentrations (belt-type group > filter pressure > centrifuged group > plate-frame group)	[62, 73]
Pretreatment	• Pretreatment can influence the size, surface morphology, and adsorption potential • NaOH > high concentration of acids > low concentration of acids > H2O2 and Fenton	[91]
Thermal drying	• More melding, wrinkling, and fracturing in MPs in thermal dried sludge • Cracking in MPs after thermal heating and drying	[28, 90••]
Thermal hydrolysis	• An increase in MPs number	[28]