Polycyclic aromatic hydrocarbons (PAHs) belong to the group of recalcitrants that on reaching wastewater can irreversibly inhibit some sensitive biological processes in activated sludge such as nitrification. This situation leads to wastewater treatment failure due to the influence of these substances on bacteria responsible for important biochemical processes. Observation of the changes in bacterial diversity using molecular tools, such as denaturing gradient gel electrophoresis (DGGE), could be the first step in finding a way of preventing wastewater treatment failure. The aim of this experiment was to monitor bacterial biodiversity in a membrane bioreactor (MBR) dealing with synthetic wastewater contaminated with high concentration of petroleum organic compounds (POCs) and to study the influence of POCs contamination on bacterial changeability in activated sludge. COD removal in investigated membrane bioreactors was at a level of 93%. The organics removal efficiency was not affected by the maximal tested dose of petroleum contamination ( l OOO μl POCs/l of wastewater) and the MBRs wastewater treatment performance was undisturbed. DGGE analysis revealed that the biodiversity fluctuated slightly in control MBR, while in experimental MBR the biodiversity index decreased drastically after adding the highest experimental concentration of POCs. These results suggest that concentrations of POCs at levels from 50 μl/l to 500 μl/l stimulate biodiversity growth, while the concentration I OOO μI POCs/1 of wastewater seems to inhibit the most sensitive processes in wastewater treatment by influencing the bacterial biocenosis.

Two types of submerged membrane bioreactors (MBR): hollow fiber (HF) and hollow sheet (HS), have been studied and compared in terms of energy consumption and average shear stress over the membrane wall. The analysis of energy consumption was made using the correlation to determine the blower power and the blower power demand per unit of permeate volume. Results showed that for the system geometries considered, in terms the of the blower power, the HF MBR requires less power compared to HS MBR. However, in terms of blower power per unit of permeate volume, the HS MBR requires less energy. The analysis of shear stress over the membrane surface was made using computational fluid dynamics (CFD) modelling. Experimental measurements for the HF MBR were compared with the CFD model and an error less that 8% was obtained. For the HS MBR, experimental measurements of velocity profiles were made and an error of 11% was found. This work uses an empirical relationship to determine the shear stress based on the ratio of aeration blower power to tank volume. This relationship is used in bubble column reactors and it is extrapolate to determine shear stress on MBR systems. This relationship proved to be overestimated by 28% compared to experimental measurements and CFD results. Therefore, a corrective factor is included in the relationship in order to account for the membrane placed inside the bioreactor.

The increasingly stringent requirements for wastewater treatment enforce the adoption of technologies that reduce pol-lution and minimize waste production. By combining the typical activated sludge process with membrane filtration, biolog-ical membrane reactors (MBR) offer great technological potential in this respect. The paper presents the principles and ef-fectiveness of using an MBR at the Głogów Małopolski operation.Physicochemical tests of raw and treated wastewater as well as microscopic analyses with the use of the FISH (fluorescence in situ hybridization) method were carried out. More-over, the level of electric energy consumption during the operation of the wastewater treatment plant and problems related to fouling were also discussed. A wastewater quality analysis confirmed the high efficiency of removing organic impurities (on average 96% in case of BOD5 and 94% in case of COD) and suspension (on average 93%).