Microplastics and nanoplastics (MPs/NPs) have been extensively
detected in sewage sludge. They inevitably transfer to anaerobic digestion
(AD) used for sludge processing and induce oxidative stress on the
anaerobic microbiome. The thermal hydrolysis process (THP) is a widely
implemented sludge pretreatment process to boost methane generation
and solids reduction in AD. Although few recent reports indicated
that the THP could alleviate oxidative stress of MPs/NPs in AD, little
is known about how different solids contents of sludge would influence
its effectiveness. This study scrutinized how the THP (160 °C,
60 min) affects AD of primary sludge with 4, 8, and 12% total solids
(TS) when exposed to polystyrene nanoplastics (PsNPs). The presence
of PsNPs (150 μg/L) substantially enhanced reactive oxygen species
(ROS) levels at lower TS (4 and 8%) compared to a higher TS of 12%
(16.20–16.71% vs 8.79%). Consequently, methane production decreased
by 7.25–15.07% for 4–8% TS. Nonetheless, applying the
THP could effectively mitigate ROS-induced stress and the propagation
of most antibiotic resistance genes (ARGs). Moreover, a positive correlation
was observed between the changes in extracellular polymeric substances
due to the THP and the impact of PsNPs. These results provide new
insights into understanding the significance of the sludge solids
content in the THP for coremediation of PsNPs-induced oxidative stress
and ARGs propagation in AD.