**6.6 Statistical analysis**

Experimental results have undergone statistical analysis, with the aim to assess the significance of the differences observed between the analyzed samples, notably,


*Experimental Investigation of Biomass Attachment to Wastewater Reactors DOI: http://dx.doi.org/10.5772/intechopen.94426*

**Table 11.** *Differential characteristics of isolated strains.*

**Figure 8.** *OD600 vs. CFU/ml at different dilution ratios.*

through Fischer and Yates variance ratio (F). Based on this ratio, significance of variability due to identified variation sources has been assessed, in relationship with the variability due to error. Here a F has been found to be equal to 380.764, so much greater than the tabulated value (3.14). The analysis has been refined further through Duncan's multiple range test [42]. This was necessary as the means were



*A = 6.5<sup>10</sup><sup>7</sup> CFU/ml; B = 1.6<sup>10</sup><sup>8</sup> CFU/ml; C = 3.1108 CFU/ml; D = 6.5108 CFU/ml; E = 1.3<sup>10</sup><sup>9</sup> CFU/ml; F = 1.6109 CFU/ml.*

#### **Table 12.**

*Spectrophotometric check (OD550) on 10-times repeated test – Elisa plate.*

different and, in fact, significant differences between the means of the readings of the various cells populations have been found. Specifically, internal variability of the series related to the blank and to the cell concentration of order of magnitude of 107 CFU/ml have resulted to be too high to conclude that means are different. This allows one to state that attachment phenomenon is a direct function of CFU/ml only, within a certain range of cell concentrations: in fact, the growth is weak and independent of the microbial population until around 10<sup>7</sup> CFU/ml, whereas within 10<sup>8</sup> e 10<sup>9</sup> CFU/ml it becomes exponential, after which becomes stable. The results of the statistical analysis have been reported in **Tables 13** and **14**.

*Experimental Investigation of Biomass Attachment to Wastewater Reactors DOI: http://dx.doi.org/10.5772/intechopen.94426*


#### **Table 13.**

*Results of ANOVA univariate.*


**Table 14.**

*Comparison between means based on variance (Duncan test).*

### **6.7 Growth-curve of a pure culture in presence of a complex substrate**

Strain B1 has been investigated as to its capacity to grow in presence of carbonaceous rich substrate such as ATP and of 1000 ppm of pure butanol in deionized water. For the purpose of the research, complex substrate is meant any substances whose degradation time is longer than those corresponding to municipal wastewater. B1 shows a rapid growth with ATP reaching the steady state in less than 8 hours, whereas with butanol it is reached in about 3 hours (**Figure 10**). Lack of nutrients

**Figure 10.** *Spectrophotometric checks for B1 growth (readings at 600 nm).*

plays a specific role in the observed behavior. On the other hand, the exponential growth shows that B1 tolerates butanol quite well and uses ii for its own development. This confirms Eckenfelder [43] and Benintendi [37] as to the time taken to completely assimilate the organic matter. It can be concluded that the biofilm can be effective in removing COD even in presence of xenobiotic substances.
