Hybrid bioreactors biomass characteristic

In this research relatively wide (but typical for activated sludge reactors) range of activated sludge flocs size was observed: 150-500 pm in all reactors.

The biomass attached to the moving bed carriers surfaces was poorly developed. Attached biomass did not cover the outside carriers surface and existed only on the inert surface not as continuous film but as separate small mushroom shape colonies. Small colonies of stalked ciliates (figure 11) were observed on the inner surface of carriers. There were observed some differences between biofilm and activated sludge flocks groups of organisms, in both biomass forms. Stalked, creeping and free-swimming ciliates, filamentous microorganisms, rotifers and nematodes were observed.

Epistylis and Vorticella were dominating genera of ciliates in both suspended and attached biomass. Stalked ciliates were observed in relatively high number both in attached and suspended biomass. The domination of this form of Ciliata was probably related to good pollutant removal efficiency, what was reported by other authors [1, 54].

The observed number of rotifers in the attached biomass was much higher than in suspended biomass (t-Student statistics; t calculated: 2.83, critical value: 2.78, a: 0.05, replications no.: 5, df: 4), what was the most evident in period 3 in SBRs, and was probably related to the long time of growth of rotifers. Also the differences in concentrations of filamentous microorganisms were observed — in continuous flow reactors the number of filamentous microorganisms was often lower in attached biomass than in suspended biomass (figure 12). Filamentous microorganisms concentration was the highest in the


highest COD loaded reactor: R3 (t-Student statistics; t calculated: 8.98, critical value: 2.2, a: 0.05, replications no.: 13, df: 11).



Figure 11. The inner surface of a carrier covered by a small stalked ciliates colony [16]



Figure 12. Filamentous organisms in reactor R2 during stage II [16]



Figure 13. Biofilm on the MBBR carrier