Why and How Membrane Bioreactors with Unsteady Filtration Conditions Can Improve the Efficiency of Biological Processes

Abstract

A membrane bioreactor (MBR), an association of a bioreactor with a crossflow filtration unit, enables continuous processes with total cell retention within the reactor to be realized. Provided that high dilution rates can be applied and that inhibition processes are avoided, very high biomass concentrations can be reached, thereby improving the volumetric productivities. These membrane bioreactors have been successfully applied to various microbial bioconversion, such as alcoholic fermentation, solvents, organic acid production, starters, and wastewater treatment. On the basis of the biological reaction characteristics and bibliographic results, the potentialities and bottlenecks of this methodology are discussed. Depending on the application, it is shown how the performance of the membrane bioreactor can be enhanced by acting either on the biological reaction achievement, by controlling the balance between cell growth and death, or on the dilution rate, by increasing the permeate flux through the filtration unit. This discussion is based on results obtained in specific biological treatments applied to polluted liquid and gas.

Soil degradation as a reason for inadequate human nutrition

“…Assessing by remote sensing critical plant nutritional stresses for managing soil quality by using the Normalized Difference Vegetation Index or NDVI (Raun et al 2001) 2. Using zerolites and nanoenhanced materials to enhance use efficiency of fertilizers and improve plant-available water capacity of the soil (Kijne 2001(Kijne , 2004, increase the availability of micronutrients (e.g., Zn) (Oren and Kaya 2006), and improve the quality of irrigation water through wastewater treatment (Daubert et al 2003) 3. Inoculating soils with endophytic bacteria that can increase BNF capacity and improve soil fertility (Lodewykx et al 2002) 4.…”

Membrane Biological Reactors

“…Yang et al (2006) argued that extractive or aeration MBRs present a significant opportunity for researchers as niche areas of application as these novel processes remain unexplored. Hazardous waste treatment and toxic waste cleanup present two potential areas for the EMBR (Brookes and Livingston, 1994;Dossantos and Livingston, 1995;Livingston et al, 1998), whereas hydrogenotrophic denitrification of groundwater (Clapp et al, 1999;Mo et al, 2005;Modin et al, 2008;Nuhoglu et al, 2002;Rezania et al, 2005) and gas-extractionassisted fermentation (Daubert et al, 2003;Lu et al, 1999) are potential research areas for the AMBR. It is also important to recognize the fact that these three membrane processes are not mutually exclusive and, if necessary, could be coupled into one bioreactor (Brindle and Stephenson, 1996).…”