Biomass yield determination

We have seen that both the maintenance energy requirement and the P/O quotient of the process micro-organism influences the rate of product formation. In the following sections we will consider how these two factors can be determined, together with the maximum biomass yield. 

Aim3 aerobic bioprocess was operated in a continuous mode with nitrogen as the growth limiting nutrient. The steady state biomass concentration (x), the biomass yield coefficient (Yx/S) and the product yield coefficient (Yp/t) were determined at a low and at a high dilution rate (D). 

Determination of maintenance energy requirement and maximum biomass yield... 

In addition to the kinetics of the sewer processes described in Section 5.3, the stoichiometry of the transformations of the components is crucial for the mass balance. The stoichiometry of the biomass/substrate relationships is, according to the activated sludge model concept, determined by the heterotrophic biomass yield constant, YH, in units of gCOD gCOD-1. As depicted in Figure 5.5, the yield constant is an important factor related to the consumption of both Ss and S0 for the production of XBw. 

The addition of microsalts and EDTA resulted in a biomass yield on sucrose (Yx/S) of 0.24 g/g and CMC-1/dry cell weight of 54.5, quite different from that determined for the nonsupplemented medium, 0.08 g/g and 79.2, respectively. In a way, these results suggest that the presence of oligo-elements stimulates cell growth rather than bioproduct synthesis. 

Rubisco (EC 4.1.1.39) performs a pivotal role in determining biomass yield (for recent reviews, see refs. 1-3). The biosynthetic reaction catalyzed by this enzyme, the carboxylation of RuBP by CO2 to form two equivalents of 3-phospho-D-glycerate (PGA) (Fig. 1, upper pathway), is limited by both slow turnover (fecat = 2-5 s-i) and utilization of O2 in competition with CO2. The... 

Phytoextraction has the potential to remediate many metal and radionuclide contaminated sites using a less invasive form of treatment than traditional methods such as escavation and disposal. There are four factors that influence or determine the ability of phytoextraction to effectively remediate a metal contaminated site 1). Site arability and plant biomass yields 2) metal solubility and availability for uptake 3) the ability of the plant to accumulate metals in the harvestable plant tissues and 4) regulatory criteria. 

The redox and carbon balances were used to determine the amount of carbon in the form of ethanol loss by stripping off to the gas phase. Lactic acid production at steady state conditions was less than 0.03 g/g thus, it was excluded from carbon and redox balance calculations. For biomass production, biomass yield of 0.045 g/g was assumed [15, 16] with biomass composition CH155N0.23O0.45 [17]. When growing the strain in batch culture, the carbon balance was almost closed (SD 2%), indicating that no other end products are formed than that included in redox and carbon balances. 

In order to improve microbial production, serious attention was given to determine the effect of fermentation conditions on the production yield and on the polymers physicochemical properties. Generally, the yield and composition of the polysaccharide depend on the microbial species used, age of the producing microbial cells and growth, cultivation medium, and conditions. The chitinous compounds content also depends on the type of fermentation and extraction method. An increase in chitinous material can be obtained either by increased biomass yield or by an increase in the cell wall content of chitin/chitosan. A summary of the advantages and disadvantages of several biotechnological possibilities to produce chitin/chitosan can be found in Table 3.1. 

Another technique for organics measurement that overcomes the long period required for the BOD test is the use of continuous respirometry. Here the waste (full-strength rather than diluted as in the standard BOD test) is contacted with biomass in an apparatus that continuously measures the dissolved oxygen consumption. This test determines the ultimate BOD in a few hours if a high level of biomass is used. The test can also yield information on toxicity, the need to... 

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