Polyvinyl Chloride Microplastics Facilitate Nitrous Oxide Production in Partial Nitritation Systems

Abstract

Partial nitritation (PN) is an important partner with anammox in the sidestream line treating high-strength wastewater and primarily contributes to nitrous oxide (N 2 O) emissions in such a hybrid system, which also suffers from ubiquitous microplastics because of the growing usage and disposal levels of plastics. In this study, the influences of polyvinyl chloride microplastics (PVC-MPs) on N 2 O-contributing pathways were experimentally revealed to fill the knowledge gap on N 2 O emission from the PN system under microplastics stress. The long-term results showed that the overall PN performance was hardly affected by the low-dose PVC-MPs (0.5 mg/L) while obviously deteriorated by the high dose (5 mg/L). According to the batch tests, PVC-MPs reduced biomassspecific ammonia oxidation rates (AORs) by 5.78−21.94% and stimulated aerobic N 2 O production by 9.22−88.36%. Further, upon increasing dissolved oxygen concentrations from 0.3 to 0.9 mg O 2 /L, the degree of AOR inhibition increased but that of N 2 O stimulation was lightened. Site preference analysis in combination with metabolic inhibitors demonstrated that the contributions of hydroxylamine oxidation and heterotrophic denitrification to N 2 O production at 0.3 mg O 2 /L were enhanced by 18.84 and 10.34%, respectively, accompanied by a corresponding decreased contribution of nitrifier denitrification. Finally, the underlying mechanisms proposed for negative influences of PVC-MPs were bisphenol A leaching and reactive oxygen species production, which led to more cell death, altered sludge properties, and reshaped microbial communities, further resulting in enhanced N 2 O emission. Overall, this work implied that the ubiquitous microplastics are a hidden danger that cannot be ignored in the PN system.

Biodegradable Microplastics Increase N2O Emission from Denitrifying Sludge More Than Conventional Microplastics

“…The sequential reduction of nitrogen oxides (NO x ) is strongly dependent on the electron transport and consumption system (ETCS), and the electron distribution among different reductases directly influences the accumulation of intermediates such as nitrous oxide (N 2 O). − As the third most abundant greenhouse gas, N 2 O is approximately 300-fold more potent than CO 2 , enabling it to contribute 50–80% of the entire carbon footprint at wastewater treatment plants (WWTPs) . Meanwhile, denitrification is effectively considered as an important N 2 O sink, mitigating a fraction of N 2 O. , Previous research on microplastics affecting denitrification and associated N 2 O production mainly focused on natural ecosystems, which are fundamentally different from engineered wastewater treatment systems with respect to nutrient concentrations, substrate transfer, and interaction with microplastics. , Our recent studies have demonstrated that long-term exposure to polyethylene terephthalate (PET) and polyvinyl chloride (PVC) microplastics significantly altered N 2 O emissions in wastewater treatment. , However, the mechanisms of the effects of microplastics on N 2 O emission from denitrifying sludge are unknown, especially from the point of view of electron distribution. More importantly, little is known about the effects of BMPs, which are as prevalent in wastewater as conventional NBMPs but exhibit greatly different physicochemical properties and eco-impacts. , …”