Biomass retention

Biodegradation of MTBE in a High Biomass Retention Reactor... 

Both steps are influenced by dissolved oxygen and the corresponding substrate concentration. The nitrification as a wastewater treatment process benefits greatly from biomass retention, owing to the relatively slow growth rates of the nitrifiers. 

Zart, D., and Bock, E. (1998). High rate of aerobic nitrification and denitrification by Nitrosomonas eutropha grown in a fermentor with complete biomass retention in the presence of gaseous NO2 or NO. Archives of Microbiology 169, 282—286. 

The chapter focuses on membrane bioreactors where a UF or MF membrane is employed for biomass retention and filtration. However, membrane bioreactors where the membrane provides a support for biofilms are an alternative form of membrane bioreactor for wastewater treatment application. Two processes, in particular, the membrane-aerated biofilm reactor (MABR) and the extractive membrane bioreactor (EMB), have seen significant interest in recent years. Figure 36.4 shows these two technologies schematically. The application of biofilms reactors for wastewater treatment systems is advantageous in view of... 

Ex situ bioremediation relies on management of groundwater flow, with optimization of retention times in the bioreactor, biomass retention in bioreactors, temperature and pH control and most importantly, maintaining aerobic conditions. In addition, co-contaminants as BTEX compoimds or iron, Fe(lll), can jeopardize aerobic degradation of MTBE, both in and ex situ. 

A second example of suspension reactors is a sequencing batch reactor (SBR). This reactor is operated in different sequential stages to optimize MTBE-removal and biomass retention [92]. The same setup was used to enrich TBA-degrading bacterial consortia [20,93]. 

The second reactor setup type is commonly referred to as a biofilm bioreactor. This reactor is filled with packing material onto which a microbial biofilm is allowed to develop and biomass retention is achieved without the need for special membranes. Selected examples of this second type of reactor are provided in Table 7. 

Biomass retention in immobilized systems relies on a balance between attrition of bacteria because of high shear forces due to influent flow and the growth of new biomass. Therefore, the main difficulty in treating MTBE-contaminated groundwater with fixed film bioreacfors is fhe low reported biomass yield with growth on MTBE in continuous systems, typically... 

Only articles that raise the productivity of a bioprocess by removing the product selectively are included. Therefore, processes that improve their productivity by the implementation of a simple cell recycle or another immobilization system are not taken into account. Nor is dialysis, which is mainly used as a biomass retention system or sometimes as a means of removing unwanted by-products. Information about dialysis cultures is available in the review by Portner and MSrkl [32]. 

FIL filtration, e.g., sand filtration BIO biological treatment and nitrification/denitrification UF ultrafiltration for biomass retention ADS adsorption, e.g., activated carbon adsorption OX oxidation, e.g., ozonation RO reverse osmosis NF nanofiltration DC ion exchange EVA evaporation DRY dryings EXT external concentrate removal N2 nitrogen recovery, e.g., ammonia stripping. Source [17],... 

The hydraulic retention time (HRT) is defined as the theoretical amount of time that the liquid is resident within the reactor. For completely mixed systems without biomass recycling, the HRT is the same as the SRT. For systems designed to encourage greater biomass retention, the SRT is generally longer that the HRT. Separating both parameters in this manner improves process stability and efficiency. 

Stimulate formation of small spherical cell pellets (Zhou 1999). Roa Engel et al. (2011) showed from measurements with a microsensor that 0.25 mm inside a pellet the level was less than 5% of the concentration outside the pellet. Zhou et al. (2011) demonstrated that smaller pellets produce more fumaric acid, which could have been caused by the absence of oxygen limitation inside the pellets. By reducing clumps formation the viscosity of the broth is also reduced, even if CaCOj is present. Moreover, pellets can facilitate biomass retention. For R. oryzae a large number of factors have been optimized to favor pellet formation during cell cultivation (Zhou et al. 2000, 2011 Liu et al. 2008 Roa Engel et al. 2011). These include pH, temperature, nutrients, spore concentration and age, stirring frequency, and culture volume. 

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