Biotransformation of acyclovir by an enriched nitrifying culture

Abstract

This work evaluates the biodegradation of the antiviral drug acyclovir by an enriched nitrifying culture during ammonia oxidation and without the addition of ammonium. The study on kinetics was accompanied with the structural elucidation of biotransformation products through batch biodegradation experiments at two different initial levels of acyclovir (15 mg L and 15 μg L). The pseudo first order kinetic studies of acyclovir in the presence of ammonium indicated the higher degradation rates under higher ammonia oxidation rates than those constant degradation rates in the absence of ammonium. The positive correlation was found between acyclovir degradation rate and ammonia oxidation rate, confirming the cometabolism of acyclovir by the enriched nitrifying culture in the presence of ammonium. Formation of the product carboxy-acyclovir (P239) indicated the main biotransformation pathway was aerobic oxidation of the terminal hydroxyl group, which was independent on the metabolic type (i.e. cometabolism or metabolism). This enzyme-linked reaction might be catalyzed by monooxygenase from ammonia oxidizing bacteria or heterotrophs. The formation of carboxy-acyclovir was demonstrated to be irrelevant to the acyclovir concentrations applied, indicating the revealed biotransformation pathway might be the dominant removal pathway of acyclovir in wastewater treatment.

Understanding the biodegradation products and pathways of selected pharmaceuticals atenolol and acyclovir by an enriched nitrifying sludge through experiments and modeling

“…EXP4 was exclusively designed for atenolol biotransformation, where constant ammonium concentrations of 25 mg-N L -1 were provided using the dosing method in EXP3 during the experimental period. The contribution of sorption to removal of atenolol and acyclovir was insignificant based on our previous studies (Xu et al, 2017a;Xu et al, 2017b). This is in consistency with low sorption coefficient K D (0.04) and low octanol-water partition coefficient Log K OW (0.16) of atenolol and Log K OW (-1.59) of acyclovir .…”

“…The contribution of sorption to removal of atenolol and acyclovir was insignificant based on our previous studies (Xu et al, 2017a;Xu et al, 2017c). This is in consistency with low sorption coefficient K D (0.04) and low octanol-water partition coefficient Log K OW (0.16) of atenolol and Log K OW (-1.59) of acyclovir .…”

“…Experimental data from our previous biodegradation experiments of atenolol (Case I) and acyclovir (Case II) under different conditions by an enriched nitrifying sludge were used for model evaluation in this work (Xu et al, 2017a;Xu et al, 2017b). The chemicals used in the batch experiments and the enrichment of nitrifying culture in the sequencing batch reactor (SBR) are described in Text S1 and S2 in SI.…”

“…In Experiment 1, 30 mg L -1 allylthiourea (ATU) was added to inhibit nitrifying activities , leading to the dominant contribution from HET to pharmaceutical biotransformation (Xu et al, 2017a;Xu et al, 2017b;Xu et al, 2017c).…”

“…The contribution of sorption to removal of atenolol and acyclovir was insignificant based on our previous studies (Xu et al, 2017a;Xu et al, 2017b Photodegradation was also insignificant considering the turbidity of the sludge and the aluminium foil covering the reactor. Therefore, microbially induced biodegradation should be the main mechanism for pharmaceutical removal.…”