Suspended growth

In aerobic processes, the mean sludge residence time is typically 5 to 10 days. The hydraulic residence time is typically 0.2 to 0.3 days. Suspended growth aerobic processes are capable of removing up to 95 percent of BOD. 

Attached growth processes are capable of removing up to 90 percent of BOD and are thus less effective than suspended growth methods. 

Another suspended growth method is the upward-flow anaerobic sludge blanket illustrated in Fig. 11.6a. Here the sludge is contacted by upward flow of the feed at a velocity such that the sludge is not carried out of the top of the digester. 

The reac tor concepts described above can be utilized with any of the electron acceptor systems previously discussed, although some reactor types perform better with specific electron acceptors. For example, suspended growth systems are generally superior to fixed film systems when molecular oxygen is the electron acceptor because it is easier to supply oxygen to suspended growth systems. 

Residuals Produced. The residuals produced from suspended growth systems are the excess biomass produced as the result of biodegradation. In general, this biomass can be disposed without further treatment. However, site-specific conditions may require stabilization prior to disposal. 

Residuals Produced The residuals produced in a fixed-film reactor are normally small when compared to the residuals produced in a suspended growth system. There can be some sloughing of biomass during system ojjerations, and this may need to be separated from the effluent. The residuals, depending on site-specific requirements, may require additional treatment prior to ultimate disposal. 

Technology Description Hybrid reactors, as the name implies, are a combination of suspended growth and fixed-film reactor principles. In these systems, the fixed film is submerged and the reactor contents are continuously stirred. A large amount of biomass is maintained in the system. 

Residuals Produced As with the suspended growth and fixed-film systems, some biomass is produced which will require disposal. The pretreatment and disposal practices required will depend on site-specific requirements. 

There are two major types of biological treatment processes attached growth and suspended growth. 

Organisms such as actinomycetes may not produce well-suspended growth and shaking, for example, in baffled flasks or in flasks with coiled-wire inserts may be advantageous in partially overcoming this problem. 

The size of most biological reactors is determined by pollution load, for example, kg BOD (biochemical oxygen demand) or COD (chemical oxygen demand) per kg MLVSS (mixed liquor volatile suspended solids) per day in the case of suspended growth type systems, and kg BOD or COD per m3 of media or reactor volume in the case of fixed-film type systems. 

Nitrification-denitrification reactions can be carried out in suspended growth by separating the reactor into different cells. A typical arrangement would control the first cell under anoxic conditions to carry out the denitrification reactions. These reactions require organic carbon and this... 

Figure 26.8 Suspended growth anaerobic digestion using an upward flow anaerobic sludge blanket.

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