Coupling Effect And Mechanism Of Biochar On Sorption-biodegradation Of Nonylphenol And Its Isomers

As the super adsorbent for hydrophobic organic contaminants (HOCs), biochar (BC) is considered to be a promising novel material for HOCs remediation. Many recent researchers have studied the effect of BC on the fate of HOCs and different results have been reported. On one side, BC application could significantly inhibit HOCs degradation due to bioavailability reduction caused by strong sorption, resulting in the extension of half-lives of HOCs; on the other side, BC application may promote microial growth, facilitate the formation of biofilms, and finally accelerate HOCs mineralization. Which aspect is more important and wether BC addition promoted HOCs biodegradation or not, remained poorly understood. Therefore, to figure out the comprehensive function of BC in HOCs fate, nonylphenol (NP), the typical HOCs and exogenous estrogen, was selected as the target contaminant, and the rice straw BC was chosen as the adsorbent. The application and mechanism of BC-microorganisms coupled remediation in NP contamination were investigated in this study. On one side, impact of different BC dosages on NP biodegradation was studied, and three forms of NP during biodegradation were quantified by Tenax desorption model. On the other side, the effect of BC on NP isomers biodegradation was also investigated, and the profile of NP isomers during NP attenuation was evaluated to figure out the influence of BC on the fate of different NP isomers. The main results were as follows:(1) A mixed cultivation inoculum, able to utilize NP as a sole carbon source for growth, was isolated from sediment sampled in the Qiantang River. Based on the mixed culture, a NP-degrading strain, N-1, was obtained by separation and purification continuously. N-1 was identified as Pseudoxanthomonas sp., and named after Pseudoxanthomonas sp. N-1. The optimal degradation conditions for the mixed culture and Pseudoxanthomonas sp. N-1 were both 30℃, and pH of 7.0. In this optimal condition, the biodegradation rates of 10 mg/L NP by the mixed culture and Pseudoxanthomonas sp. N-1 were 85.6 and 80.6% during 7 d incubation, respectively.(2) At the low NP concentration (C0= 6 and 30 mg/L), NP biodegradation was significantly decreased due to the strong sorption of BC, while at the high NP concentration (C0= 50 and 100 mg/L), appropriate BC addition could decrease the NP aqueous concentration, alleviate the acute toxicity of NP to microorganisms, and promote NP biodegradation. In the long term, NP could overcome the flow resistance between aqueous and solid phases by forming biofilms on BC, allowing efficient in-situ treatment of NP contamination. Therefore, there was an appropriate biochar dosage range for sorption-biodegradation coupling remediation at each given concentration of NP, namely, the positive effect of BC on abundance of microorganisms could exceed the negative effect of BC on bioavailability reduction, resulting in BC promoting NP biodegradation.(3) Three NP forms, rapidly desorption fraction (frap), slowly desorption fraction (fslow), and resistant desorption fraction (fr) underwent a gradual reduction during incubation, including the most reduction of fr(P< 0.01). The results from quantitative model of frap, fslow and fr, as well as linear relationship between the biodegradation fraction (fbio) and frap,frap+ fslow, showed that the biodegradability of frap and fslow was considerable, and fr could be partly degraded as well, which was dually influenced by NP concentration and BC dosages.(4) The biodegradation of NP isomers was isomer-specific, namely the biodegradability of NP isomers was diverse due to their molecular structures. Generally, the biodegradability of NP isomers was positively correlated with side chain length, while negatively correlated with the complexity of a and β-substituent. The transformation of NP isomers was significantly inhibited by overdose BC, while appropriate dosage of BC accelerated the degradation of the majority of NP isomers, but NP194 and NP193a+b degradation showed no difference because of their bulky substituents and short side chain. Therefore, it was reasonable to speculate that NP194 and NP193a+b may be the major components of residual NP isomers caused by their limited biodegradability.Above all, BC-microorganisms played a very prominent role in NP contamination remediation, and showed sorption-biodegradation coupling remediation in NP contaminated sites at appropriate BC dosage. Besides, the influence of BC on the biodegradation of NP isomers was similar to that on the matrix NP, but NP194 and NP193a+b were poorly degraded because of the bulky structure, resulting in NP194 and NP193a+b to become the main residue, which should be taken into consideration when BC-microorganisms is applicated in remediation of isomer contaminants like NP. The paper may help providing theoretical foundation and technical support for BC-Microorganisms application in remediation engineering of HOCs contamination.