**6.2 Microbial growth and development of biofilm in sugars-broth**

Development of the biofilm is promoted by organic molecules through the formation of a conditioning layer on solid surfaces. M9 has been selected with the aim to prevent false results. Carbon source for this inoculum is glucose only, so that observed attachment could be put in relationship with bacteria capabilities only.

## *6.2.1 Influence of sugars*

Bacteria growth with sugar type and concentration has been obtained through spectrophotometric controls shifted by 1 hour. The findings have been depicted in **Figure 1** [38]. The curves have been obtained by data reparameterization according to Gompertz equation as modified by Zwietering et al. [39]. As expected, growth of microorganisms is characterized by a latency phase, an exponential growth, a steady-state growth and death. Resulting growth with time can be described by the following parameters:


$$y = A \cdot \exp\left\{-\exp\left[\frac{(\mu\_m \cdot e)}{A} \cdot (\lambda - t) + \mathbf{1}\right]\right\} \tag{2}$$

After 24 hours substrate clarification, foam formation and presence of filamentous forms caused by bacteria growth have been evaluated as shown in **Figure 2**. It

**Figure 1.** *Microbial growth in sugar-broth.*

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

**Figure 2.**

*Effects of substrate of microbial growth in sugar-broth.*

can be noted that glucose provides better results than saccharose, which produces both at high and low concentrations, a significant foam formation along with an intense turbidity. Glucose 1% promotes a faster colonies growth than glucose 0.05%: the former can be adopted during the start-up, the latter at the steady-state, where effluent quality matters. The microscopic observation of the attached mass, accomplished on 4 fragments for each test, has revealed the presence of filamentous forms in glucose test, as shown in **Figure 2**, where arbitrary unitless relative values have been assigned. However, this does not affect the quality of the effluent as stated before, as to ideal sugars. The microscopic observation has revealed that the fours tests have shown the same results in terms of biofilm formation, as illustrated in **Figure 3**, based again on relative unitless values. The biofilm was well developed and appeared as a dense, uniform and well-structured cells mass. In some instances, the subsequent cellular layers have been observed.
