Thermal Hydrolysis of Sludge Counteracts Polystyrene Nanoplastics-Induced Stress during Anaerobic Digestion

Abstract

Microplastics (MPs)/nanoplastics (NPs) have been widely detected in wastewater treatment plants (WWTPs). They are captured mainly by sludge and unavoidably move into the anaerobic digestion (AD) process. Recent studies suggested that MPs/NPs could induce oxidative stress to the microbiome in digesters. The thermal hydrolysis process (THP) has been implemented for sludge pretreatment in many full-scale WWTPs. To date, there is limited knowledge about how THP can influence MPs/NPs-induced stress during AD. This study systematically investigated the impact of THP (80 and 160 °C) on AD of sewage sludge exposed to different levels (50–150 μg/L) of polystyrene nanoplastics (PsNPs), one of the most found MPs/NPs in WWTPs. Compared to the control, higher PsNPs levels of 100 and 150 μg/L decreased methane yields by 17.98 and 29.34%, respectively. Moreover, reactive oxygen species (ROS) levels increased by 17.18 and 34.84%. Our results demonstrated that THP counteracted the suppression of methane production imposed by such PsNPs concentrations, with decreased ROS levels. Also, THP reduced antibiotic resistance gene (ARG) propagation that can be encouraged by PsNPs, thus minimizing the ARG transmission risks of digestate biosolids. These findings suggest that THP holds a high promise to further develop as a remediation method for MPs/NPs in WWTPs.

Propagation of antibiotic resistance genes during anaerobic digestion of thermally hydrolyzed sludge and their correlation with extracellular polymeric substances

“…THP is often considered more economically attractive than other pretreatment methods (e.g., mechanical, chemical methods) due to energy recovery as heat from pretreated sludge 8 . To date, a few studies demonstrated that THP could provide removal of ARGs before AD 2 , 12 , 14 , 17 . It has been suggested that applying high temperature and pressure during THP can result in disintegration of cell walls and hydrolytic destruction of ARGs 2 , 18 .…”

Sludge Thermal Hydrolysis for Mitigating Oxidative Stress of Polystyrene Nanoplastics in Anaerobic Digestion: Significance of the Solids Content

“…32 Moreover, some previous studies also reported that exposure to MPs/NPs can induce ROS generation in AD. 1,33 This ROS level increment may lead to cell peroxidation and redox imbalance, causing inhibition and metabolic disturbance. 27 Most of the cells can mediate oxidative stress via antioxidant enzymes such as catalase and superoxide dismutase, 27 which can act as the ROS scavengers and defense line against ROSinduced damage.…”

“…Due to the extensive production, use, and uncontrolled disposal of plastics to the environment, microplastics (MPs, a particle size of <5 mm) and nanoplastics (NPs, 1 to 1000 nm) are released into the environment. 1 Considering their ubiquitous detection in oceans, freshwater, air, soils, and polar regions, they are a potential menace to the environment. 2 Also, recent studies indicated the existence of MPs/NPs in human placentas, lung tissues, and blood, 3 which can cause detrimental and severe health issues.…”

“…12 For instance, polystyrene nanoplastics (PsNPs) can interfere with digester operation by inducing reactive oxygen species (ROS), leaching of toxic chemicals/additives, inhibiting activities of critical enzymes, and cell apoptosis via penetration. 1,5 Also, MPs/NPs in sewage sludge can promote ARGs proliferation and inevitably increase the chance of spreading ARGs through land application of digestate. The thermal hydrolysis process (THP) is a commonly used pretreatment approach for enhancing sludge solubilization, hydrolysis rate, methane recovery, and solids removal in AD.…”

Microplastics and Their Role in the Maintenance and Spread of Antibiotic Resistance Genes in Marine Ecosystems

“…Токсическое воздействие микропластика на представителей морской биоты наблюдалось на поведенческом, репродуктивном, метаболическом уровнях и в появлении физических аномалий развития. Кроме того, были выявлены клеточные реакции, включая изменения в экспрессии генов, продукции активных форм кислорода и активности ферментов [11,38,48,49].…”