This study systematically investigated the performance and microbial response of a two-stage partial denitrification/anammox (PD/A) system treating printed circuit board (PCB) wastewater. The front-end partial denitrification reactor was intended to function as a biobarrier to mitigate toxicity and protect downstream anammox activity. However, sustained exposure to PCB wastewater severely inhibited its performance, reducing the NO2--N accumulation rate (SNO2’) by 67% and shifted metabolic pathways toward complete denitrification. As a result, severe NO2--N deficiency impaired anammox bacteria (AnAOB), decreasing their nitrogen removal contribution from 57.60% to negligible levels. High-throughput sequencing analysis revealed significant microbial community restructuring, marked by the enrichment of the sulfide-oxidizing genus Thiobacillus from 0.10% to 15.57%, confirming S2- as a critical toxic agent. Further microbial profiling demonstrated functional divergence between nirS-and nirK-type denitrifiers under stress. Although partial denitrification activity recovered after PCB withdrawal, the system did not essentially restore its PD/A synergistic function as Phase I due to AnAOB exhibited persistent suppression of key functional genes and compromised metabolic connectivity. These findings underscore that the dual inhibition from toxic wastewater constituents and NO2--N scarcity constitutes the major bottleneck for implementing the PD/A process in treating such industrial effluents.
Ouyang et al. (Sat,) studied this question.