Biochar enhance functional stability of ammonia-oxidizing bioprocess against toxic chemical loading

This study investigated the inhibitory consequences of cetylpyridinium chloride (CPC) on nitrification and the role of the addition of biochar (BC) in enhancing nitrification functional stability. A concentration of 10–40 mg/L CPC led to the pulsed disturbance of ammonium oxidation (AO) (an immediate disruption of 11–41%, followed by recovery) and the press disturbance of nitrite oxidation (NO) (a prolonged disruption of 14–39%). A BC-dosed bioreactor demonstrated significantly higher AO stability against CPC in terms of buffering and resilience to chemical disruption. The addition of BC limited the fraction of freely dissolved CPC in an aqueous (i.e., decreasing the bioavailable CPC) via preferential adsorption, thus mitigating CPC toxicity. While CPC reduced 90% of Nitrosomonas (particularly N. oligotropha) and 93% of Nitrospira (particularly Candidatus Nitrospira defluvii) in the suspended microbiome, which are responsible for AO and NO, respectively, the Nitrosomonas inhibited by CPC was largely recovered in the biofilm microbiome formed on the surface of the BC, enhancing the stability of AO in the presence of CPC. Our study provides a mechanistic explanation for nitrification disruption by toxic chemicals and suggests BC as an effective biowaste-derived additive for the mitigation of the chemical disruption.