Analysis of the Partial Nitrification Process Affected by Polyvinylchloride Microplastics in Treating High-Ammonia Anaerobic Digestates

Large amounts of microplastics entering into wastewater treatment plants are retained as wasted sludges, which are usually transferred to the anaerobic digestion process afterward. The partial nitrification (PN) process is known for treating the high ammonia anaerobic digestate; its treatment performance that is affected by the existence of microplastics is rarely reported. This study investigated the effect of microplastics on the PN process with polyvinylchloride (PVC) abundances at 0, 1000, 5000, and 10,000 particles/L. Results indicated that the corresponding nitrite transfer rates with the existence of PVC were 90.97, 64.24, 52.88, and 46.66%. The ammonia oxidation rate was reduced to 0.69, 0.55, and 0.49 times as compared with control. The average dissolved nitrous oxide (N2O) emission was also mitigated to 0.58, 0.49, and 0.64 times with added microplastics as compared with control. The average gaseous form of N2O emitted was mitigated to 0.54, 0.45, and 0.37 times as compared with control. The first-order kinetic model fitted well with all tests. The highest NO2-N generation potential was found in the blank reactor at a coefficient of 1430.1 (R-2 = 0.9776), which was 1.9-2.3 times higher than the other reactors with added microplastics. This study indicated that PVC inhibited the PN process and mitigated N2O emission during such a process. The microplastic contamination effects on high-ammonia wastewater treatment during the PN process must be considered for investigation.