| Black carbon (BC), a ubiquitous subdomain of organic carbon matter in sediments, is considered a promising novel material of controlling hydrophobic organic contaminants (HOCs) due to its strong adsorption property, low production cost and less secondary pollution. But seldom systemic research was conducted to investigate effect of BC on NP migration and fate, especially on biodegradation rate, in long term. On the one hand, super adsorptivity of BC could reduce the desorption and access of HOCs, which extended the biodegradation and kept more residual HOCs in the sediment. On the other hand, BC could also enhance the microbial degradation of HOCs by lowering the acute toxicity of HOCs as well as promoting the growth of microbe and forming biological membrane. Therefore, we carried out the reasearch which aims nonylphenol (NP), a kind of endocrine-disrupting contaminants (EDCs) and persistent organic pollutants (POPs), as the research object to study the influence of BC on sorption/desorption and biodegradation of NP in sediment and provide theoretical foundation for remediation of HOCs pollution in water environment. First, sorption and deorprion of NP on fresh and aged two BC-sediment system (rice straw black carbon, RC and flyash carbon, FC) was studied, and RC with higher sorptity to NP was chosen to carry out the followed research. Three conditions were simulated by different spiking order to assess the feasibility of RC fixing NP in the aquatic environment. Based on the sorption and desorption experiment, the influence of RC on the degradation of NP in natural sediment were also studied. And the main results were as follows:(1) RC and fly ash carbon were produced and characterized, respectively. The structure and property of the two BC vary significantly, and RC posed lager BET (72.10 m2/g), pore volume (0.13 mL/g) and more surface functional groups than FC. Sorption data showed that Kf was 43507.13±1157.22 and 3423.65±81.89 (mg/Kg)/(mg/L)n, n was 0.39±0.037 and 0.55±0.043, for RC and FC respectively, suggesting the sorption capacity and nonlinearity of RC to NP is far higher than FC.(2) The sorption and desorption mechanismof freshly BC-sediment system onNP was studied. Both BC amendments increased the sorption capacity and nonlinearity (For example, Kf increased from 110.63 ±1.77 to 1055.43 ± 34.29 (mg/Kg)/(mg/L)n when 5.0% RC was added into sediment), decreased desorptionof NP to sediment, but influence of RC is stronger than FC due to the larger surface area, porosity and amounts of functional group of RC. The modified two domain model (MM) fitted desorption data of NP better after BC amended (R2=0.986-0.995). And sorption-desorption coupled model was built, from which NP releasing risk can be predicted by sorption data. Furthermore, NP in partition fraction, can desorb completely and NP in adsorption fraction, resist to desorb, which supplement the theory about relationship between sorption domains and desorption sites suitable for natural sediment dominated by rubbery phase. Pore of BC is responsible for the nonlinear adsorption and sequestration of NP in sediment.(3) The effect of aging time on the adsorption property of cabon-sediment was studied and the prediction model was also established. Sorption capacity of NP decreased (For example, Kf of 5.0% RC-sediment system was also up to 853.28 ± 8.76 (mg/Kg)/(mg/L)n, even after aged for 120 d), and rapid desorption amounts of NP increased with contact time in two aged BC-sediment system But RC also posed high affinity to NP and inhibited the release of NP in sediment, even after aged. Models were built for Kf, n and Qmax with BC contents and contact time, Kom with BC contents, respectively, from which sorption of NP can be predicted if the BC contents and contact time was known.(4) Three practical conditions were simulated via different mixing spiking orders to assess the practicability of RC on NP control. In this study, desorption in three practical conditions were simulated, by three mixing spiking orders among NP, RC and sediment (The order of mixing spiking is (RC+sediment)+NP, (sediment+NP)+ RC and (RC+NP)+ sediment, for situation 1,2 and 3, respectively), to discuss the feasibility of using RC to remedy NP pollution. Results demonstrated that no significant differences were observed for desorption among the three fresh situations. However, after aged for 40 d, Fr for situation 3 was higher than the other two situations, due to NP diffusion into the irreversible sorption sites of RC, reducing the releasing risk of NP. Regardless of time, Fr of three situations was all>0.5, suggesting RC is an effective sorbent for remedying NP pollution in the aquatic environment.(5) The effect of RC on NP biodegradation in sediment was also studied. Influence of BC on NP biodegradation varied at different NP concentrations. And biodegradation data demonstrated that at low NP concentration, RC suppressed the degradation of NP by reducing NP bioavailability. While at high NP concentration, moderate RC addation (0.1% and 0.2%) enhanced biodegradation and improved the biodegradation rate in short term by reducing toxicity of NP to microbe. But moderate RC finally inhibited NP biodegradation by reducing NP bioavailability in long term. NP biodegradation was inhibited by reducing NP bioavailability during the whole biodegradation process at higher RC content (≥ 0.5%). Hence, there is an optimal BC content in RC-sediment biodegradation system at different NP concentrations, which strengthened HOCs biodegradation process and accelerated biodegradation rate, forming RC-biodegradation coupled bioremediation. There was postive correlation between NP residue and RC content per surface area and pore volume, suggesting the effect of RC on NP bioavailability was likely due to the chemical composition and physical structure of RC.(6) The mechanism of NP biodegradation by RC was analyzed. Single point Tenax desorption was applied to measure species change of NP during biodegradation. And results showed that ratio of desorbable NP to residual NP decreased fistly, then increased, and decreased again at last. Comparison between desorption and biodegradation amounts indicated that sorbed NP can be utilized directly by forming biofilm and overcoming NP mass diffusing barrier. Microbial data showed that NP affected the microbial community structure significantly (P<0.01), while influence of RC wasn’t apparent (P>0.05). Furthermore, Pseudomonas, Sphingomonas, Lysobacter, Flavobacterium and Tolumonas genus played a crucial role in biodegradation of NP. And Pseudomonas and Sphingomonas genus was identified as the dominated degrading bacteria at high and low NP concentration, respectively. Dechloromonas and Zoogloea genus were considered involving in the biofilm formation,... |
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