Effect of biomass concentration in membrane bioreactor design on alpha factor for two large pilot systems: Case study of mechanical surface aeration and air insufflation system

In the literature, the studies on wastewater treatment process have shown a great interest in aeration system, most of them were performed on small pilot lab-scale. However, it still an important need to provide useful information aiming at reducing the operating costs and providing decision support to choose aeration devices. Considering that membrane bioreactors operating with high biomass concentrations up to 20–30 g of suspended solids (SS) per liter, the present study was carried out on a larger pilot lab-scale ( ± 500 l) of insufflation system and mechanical surface aeration on the same fresh sludge with concentration varying between 4.6 and 19.8 g/l. The comparison with literature data shows good correspondence with values obtained with our insufflation system but a great difference from values obtained in a mechanical system. In addition, this research provides a better insight on the calculation method that can be used to estimate the critical parameters of the oxygen transfer, and analyses the feasibility of air diffusion substitution by surface aeration system of Louvain La Neuve wastewater treatment plant of 13000 population equivalent. This extrapolation proved that a saving of ± 50,000 € per year can be achieved by choosing surface aeration rather than aeration by air insufflation.