3.2. The effect of pH of the background solution on the respiratoryactivity of encapsulated cellsMethyl alcohol production wastewater are classified as veryacidic, so it is important to assess the ability of the silica shellsaround cells to demonstrate their protective qualities underextreme pH values. A phosphate-citrate buffer at pH values rangingfrom 2 to 12 was used to determine the effect of widely changing pHvalues without changing the buffer type. In the presence of methylalcohol the respiratory activity of the microorganisms increasesand this can be detected using an oxygen electrode. Encapsulatedyeast cells were placed on the surface of a Clark oxygen electrode,and a measuring cell was filled with a buffer solution of a specific pHvalue and methyl alcohol. For comparison, yeast cells unprotectedby silica shell were also placed on the surface of the oxygen elec-trode on the glass fiber filter. The results of the microbial respirationas a function of pH value are shown (Fig. 2).Most respiratory activity was observed in the pH range from 7to 9, which is in agreement with the optimum pH for the methy-lotrophic yeast [21]. At low and high pH values the respiratoryactivity of yeast cells without encapsulation was completely inhib-ited, whereas the encapsulated cells retained 25% of their activityeven in a strongly acidic (pH = 2) and strongly alkaline (pH = 12)environments. Filling in the measuring cell with a buffer with theoptimum pH value resulted in a complete restoration of the orig-inal level of the encapsulated cells’ respiration, while the activityof the cells which do not have the protective shell was inhibitedirreversibly