Biodegradation of low, medium and high molecular weight phthalate by Gordonia sp. in a batch system: Kinetics and phytotoxicity analyses

Abstract

Phthalic acid esters (PAEs) are highly toxic compounds and can disrupt the hormonal balance of human, animal, and aquatic organisms. Due to the hazardous nature of such compounds, their removal from constituent wastewater before discharging into the environment is mandatory. This study focused on the biodegradation of dimethyl phthalates (DMP), di-n-butyl phthalates (DBP), and di-n-octyl phthalates (DnOP) by Gordonia sp. in a batch system. Initially, five different concentrations of DBP, DMP, and DnOP (200-1000 mg/L) were chosen individually as the sole carbon source to examine their effect on the biodegradation and biomass growth of Gordonia sp. Complete degradation of DBP and DMP was achieved up to 1000 mg/L initial concentration within 96 h, whereas in case of DnOP, the degradation value was only 83.5% at 120 h for the same initial concentration. The experimental data were fitted into various substrate inhibition kinetic models, and accurate predicted values of degradation of all the three PAEs were obtained using the Tiesser model in comparison with other models, which yielded the highest and lowest R² and SSE values of 0.99 and 0.02 × 10^-4, respectively. In addition, the phytotoxicity of PAEs degraded samples was assessed and more than 50% germination index value was observed for DMP and DBP degraded sample which established the treatment efficiency of Gordonia sp. in degrading DMP and DBP. Hence, high DMP and DEP degradation and phytotoxicity removal efficiency of Gordonia sp. demonstrate its potential for the treatment of PAEs contaminated wastewater.

Keywords: Chickpea; Di-n-butyl phthalates; Di-n-octyl phthalates; Dimethyl phthalates; Substrate inhibition.

Figure 1.

Chemical structure of DMP, DBP and DnOP.

Figure 2.

Effect of different parameters on phthalate degradation by Gordonia sp.: (a) MSM, (b) temperature and (c) pH.

Figure 3.

Time profile of experimental and model predicted values of biomass growth of Gordonia sp. on (a) DMP, (b) DBP and (c) DnOP.

Figure 4.

Time profile of percentage biodegradation of (a) DMP, (b) DBP and (c) DnOP at different initial concentration by Gordonia sp.

Figure 5.

Experimental v/s model predicted results of biodegradation of (a) DMP, (b) DBP, and (c) DnOP at different initial concentration ranging from 200 to 1000 mg/L.

Figure 6.

Experimental specific substrate degradation rate values v/s model predicted data for various initial concentration of (a) DMP, (b) DBP, and (C) DnOP.

Figure 7.

Experimental specific biomass growth rate values v/s model predicted data for various initial concentration of (a) DMP, (b) DBP, and (c) DnOP.

Figure 8.

Image of chickpea seeds soaked in (a) distilled water (b) tap water, (c - e) degraded and (f - h) raw/untreated DMP, DBP, and DnOP, respectively, after 48 h.