# Enhanced Methyl _Tert_-Butyl Ether Removal by Mixed Consortium: Performance and Adaptability
## 3 Result and Discussion
### The Mixture of Three Pure Cultures Enhanced the Removal of MTBE
One of the characteristics of MTBE removal at 5-10 mg/L by mixed consortium was the lack of lag phase; that is, there was no delay in MTBE degradation at the beginning of the run. It is speculated that a synergism was developed between the mixture, resulting in a faster adaption to MTBE. As the MTBE concentration increased from 5 to 30 mg/L, the rate constant (k) of the mixed consortium increased firstly from 0.05 to 0.06 mg/(L-h) and then reduced to 0.03 mg/(L-h) (Table 1). It implies that the supplement of a carbon source could promote MTBE degradation at 5 mg/L. However, the stimulation was reversed into suppression at higher MTBE concentrations (30 mg/L). Compared with three pure strains, summarized in Table 2, the degradation rate of the mixed consortium was significantly raised by 0.04 mg/(L-h) at 10 mg/L. It indicates  
Figure 2: **The** comparison of the degrading capacity of pure strains and their mixture under different concentrations. **(a)** The efficiency of MTBE degradation by pure strains and their mixture. **(b)** Time course for MTBE degradation by mixed consortium and simulation results for three models. Symbols present the experimental data and curves show their statistic tendencies. ** represents \(p<0.01\). that although the efficiency of MTBE biodegradation by mixed consortium did not increase, the rate increased (at 10 mg/L). Traditionally, the time (x\({}_{0}\)) required to reach half the degraded concentration is also applied as an indicator to estimate the degradation rate, and Equations (4) and (5) were utilized to determine x\({}_{0}\). Notably, the x\({}_{0}\) varied dramatically with MTBE concentrations, and the x\({}_{0}\) was less than 20 h at all conditions, indicating that mixed consortium exhibited a strong degrading ability of MTBE. Furthermore, compared with three pure strains, the x\({}_{0}\) of mixed consortium was shortened by about 20 h at 10 mg/L. Some bacteria in consortium can degrade metabolites formed by another to reduce the accumulation and toxicity of metabolites, thus increasing the degradation rate [32]. This is consistent with the result characterized with rate constant. Additionally, the maximum growth rate of strains (\(\mu_{\text{max}}\)) was calculated by Equation (3), and the \(\mu_{\text{max}}\) of three pure strains and mixed consortium was 0.04, 0.06, 0.04, and 0.13 h\({}^{-1}\), respectively (at 10 mg/L). This corroborates the conclusion mentioned above that low concentrations (5-10 mg/L) were more suitable for the growth of the M3 strain. Although mixing three pure cultures did not increase the biomass, it accelerated the growth of bacteria. The results can be supported by the view that more enzymes are induced to catalyse the biodegradation through the synergism between organisms in mixed consortium [33]. As a result, the mixture of three pure cultures enhanced MTBE biodegradation, not only promoting the growth of bacteria, but also improving the degradation rate of MTBE, especially at low concentration (10 mg/L). \begin{table}
\begin{tabular}{c c c c} \hline
**Concentrations** & **5 mg/L** & **10 mg/L** & **30 mg/L** \\ \hline First-order model & & & \\ S\({}_{0}\) (mg/L) & 5.00 \(\pm\) 0.05 & 9.39 \(\pm\) 0.92 & 30.37 \(\pm\) 1.60 \\ k (mg/L-h) & 0.050 \(\pm\) 0.001 & 0.059 \(\pm\) 0.013 & 0.028 \(\pm\) 0.003 \\ R\({}^{2}\) & 0.9992 & 0.9391 & 0.9675 \\ Quiroga-Sales-Romero model & & & \\ S\({}_{0}\) (mg/L) & 4.99 \(\pm\) 0.10 & 9.98 \(\pm\) 0.21 & 29.94 \(\pm\) 0.40 \\ q (mg/L) & \(-\)0.06 \(\pm\) 0.22 & 1.72 \(\pm\) 0.56 & 8.20 \(\pm\) 0.32 \\ \(\mu_{\text{max}}\) (h\({}^{-1}\)) & 0.05 \(\pm\) 0.01 & 0.13 \(\pm\) 0.07 & 0.14 \(\pm\) 0.01 \\ R\({}^{2}\) & 0.9993 & 0.9991 & 0.9993 \\ Logistic model & & & \\ A\({}_{1}\) (mg/L) & 5.00 \(\pm\) 0.12 & 10.00 \(\pm\) 0.13 & 29.93 \(\pm\) 0.77 \\ x\({}_{0}\) (h) & 19.08 \(\pm\) 5.92 & 5.92 \(\pm\) 0.34 & 16.22 \(\pm\) 1.53 \\ R\({}^{2}\) & 0.9991 & 0.9997 & 0.9973 \\ \hline \end{tabular}
\end{table}