Recovery of the nitrifying ability of acclimated biomass exposed to para-nitrophenol.

Para-nitrophenol (PNP) is often detected in industrial wastewater that is discharged into municipal wastewater treatment plants. Intermittent discharge of PNP into municipal treatment facilities puts their biological process at risk of inhibition, and the risk is especially great for nitrification. In this work, nitrifying biomass was acclimated to PNP. The acclimated biomass retained most of its ammonium-removal activity when it was exposed to PNP at up to 100 mg/L, while the normal (unacclimated) biomass had nearly complete inhibition. PNP was effectively biodegraded by the acclimated biomass, but the normal biomass had minimal PNP biodegradation. After PNP disappeared, the acclimated biomass recovered its ability for NH4+-N removals within one to two days, but the normal biomass did not fully recovery even after seven days. The acclimated biomass had superior ability to sustain nitrification due to its ability to biodegrade PNP and its selection of nitrifying bacteria more resistant to PNP. The PNP-acclimated community was enriched in genera that could have been active in the biodegradation of PNP, such as Chloroflexi. Although the abundance of well-known nitrifiers, Nitrosomonas and Nitrospira, decreased, Nitrosospira and other genera within the Proetobacteria phylum increased, presumably because they were more resistant to PNP.

Nitrifying biomass can retain its acclimation to 2,4,6-trichlorophenol.

Many municipal wastewater treatment plants in China receive industrial wastewater that contains inhibitory organic chemicals, such as chlorinated phenols. For the common aerobic biological treatment, nitrification is a key step, but nitrifying bacteria are notably sensitive to inhibition by chlorinated phenols. In this work, normal activated sludge (containing nitrifying biomass) was acclimated to 2,4,6-trichlorophenol (TCP). The acclimated biomass had more than 2-fold faster nitrification kinetics than normal biomass when exposed to TCP, and it also achieved effective TCP removal in parallel. When suddenly exposed to TCP after as much as two months without TCP input, the acclimated nitrifying biomass retained effective nitrification and TCP biodegradation: The nitrification rate and TCP removal rate were 0.325 mM/h and 0.049 mM/h for the acclimated biomass, compared to only 0.165 mM/h and 0.001 mM/h for normal biomass. Resistance to TCP inhibition also was retained for 5 generations of sub-culturing without TCP exposure. High-throughput sequencing confirmed that the acclimated biomass contained nitrifying bacteria and heterotrophic bacteria capable of degrading TCP, although the key genera changed during sub-culturing.