MBR activated sludge filterability characterization in cross flow filtration

Dissertação apresentada na Faculdade de Ciências e Tecnologia da Universidade Nova de Lisboa para a obtenção do grau de Mestre em Engenharia do Ambiente, perfil Sanitária

The reliability of MBR operation and its capability to produce favorable results as regards water treatment, in comparison with conventional activated sludge systems, makes this technology so promising. Regarding the influence of different cross flow velocities on sludge filterability in cross flow filtration, velocities above 1m/s (considered as high velocity in this research), showed the strongest correlations between the filterability of activated sludge and its respective fractionation compounds (suspended solids, colloids and solutes). However as the MBR treatment process is a physical chemical process involving filtration and biological treatment, it leads to the phenomena of fouling – resulting in membranes becoming obstructed, requiring more energy and physical chemical cleaning, thus increasing the additional associated costs. In this thesis, a framework analysis of MBR technology uses is undertaken and the current state of the art regarding this technology. This research included an important experimental component, with the Delft Filtration Characterization method (DFCm) developed by TU Delft (Evenblij et al., 2005) for activated sludge filterability measurements, developed by Delft University of Technology in the Netherlands. Activated sludge filterability was compared with subsequent laboratory analyses: chemical oxygen demand, total organic carbon, total suspended solids, volatile suspended solids and particle counts in 0.4-5.0μm range. The aim of these analyses was a fractionation of sludge samples in suspended solids, colloids and solute. The sludge samples were collected on MBR full-scale in Heenvliet Wastewater treatment plant (WWTP), also in the Netherlands, where the treatment process also includes a conventional activated sludge system (oxidation ditch activated sludge). The influence of different cross flow velocities on sludge filterability in cross flow filtration was performed, using in-situ monitoring of Heenvliet WWTP. The results obtained in this study relating to monitoring of Heenvliet WWTP, showed a strong correlation between the activated sludge characteristics and the filterability.