Biomass growth

Human activity, particularly in the developing world, continues to make it more difficult to sustain the world s biomass growth areas. It has been estimated that tropical forests are disappearing at a rate of tens of thousands of hm per year. Satellite imaging and field surveys show that Brazil alone has a deforestation rate of approximately 8 x 10 hm /yr (5). At a mean net carbon yield for tropical rain forests of 9.90 t/hm yr (4) (4.42 short ton /acreyr), this rate of deforestation corresponds to a loss of 79.2 x 10 t/yr of net biomass carbon productivity. 

In cases of still higher levels of BOD an additional supply of biomass may become essential, and this can be easily obtained from cowdung or municipal waste. To supplement biomass growth, nutrients such as urea and di-ammonium phosphate may be added. 

The role of water in the life of plants is well known. In terms of its major effects this role consists in transporting the mineral nutrition, maintenance of intracellular pressure responsible for the vertical growth of plants and, finally, participation in photosynthesis which provide the biomass growth, or plainly speaking, the crop production. 

J. Wu, S. Gui, P. Stahl, R. Zhang, Experimental study on the reduction of soil hydraulic conductivity by enhanced biomass growth. Soil Sci. 762 741 (1997). 

As a third example let us consider the growth kinetics in a chemostat used by Kalogerakis (1984) to evaluate sequential design procedures for model discrimination in dynamic systems. We consider the following four kinetic models for biomass growth and substrate utilization in the continuous baker s yeast fermentation. 

Biofilm Effects. Particle size and density are especially important in determining the success of biofluidization. Bioparticle size and density are determined by the initial particle properties, the extent of biomass growth, and biofilm density. For a biofilm covered support, the apparent particle density is determined by Eq. (7) (Fan, 1989). 

Improvement of intraparticle mass transfer is the goal of some particle research efforts. One novel approach that has been recently tested is the co-immobilization of algae with bacteria the algae produced oxygen and the bacteria produced the desired product (Chevalier and de la Noue, 1988). Another method used microporous particles entrapped within alginate bead bioparticles to prevent excess biomass growth that could hinder intraparticle mass transfer (Seki et al., 1993). 

This is the major factor contributing to the accumulation of a high number of attached cells. After biofilm formation the biomass growth depends mostly on the medium content and might be as quick as the growth rate of microorganisms. 

FIGURE 5.4. The flow of substrate and biomass according to the activated sludge concept for aerobic, heterotrophic transformations. The three major pathways of the flow, biomass growth, hydrolysis and biomass decay, were included in the first attempt to describe the corresponding processes in the sewer. The components are defined in Section 3.2.6. 

Suspended biomass growth results in the removal of readily biodegradable substrate. A yield constant, YHw, typically about 0.55 g COD biomass produced... 

This growth expression requires a minimum of kinetics and stoichiometric coefficients to be determined, and no hydraulic details are included. The dynamics of sewer biofilm detachment are not quantitatively known, and a steady state biofilm with a biomass release to the bulk water phase, equal to the biomass growth within the biofilm, is therefore an estimate. 

It should be noticed that biomass growth and respiration for bulk water phase include details that are not taken into account in the simple half-order biofilm description. As an example and a consequence, the two yield constants, YHw and Yup are differently interpreted in terms of the substrate requirement of the biomass (Figure 5.5). 

Wastewater in sewers includes different and varying species of heterotrophic microorganisms. A simple relationship between biomass growth and substrate utilization is needed. Several studies performed with different types of wastewater and sewer solids have shown that a simple description is possible and acceptable (Bjerre et al., 1995 Vollertsen and Hvitved-Jacobsen, 1999). 

Biomass growth in bulk water -1/Tffw 1 (1 -YHw)/YHw Equation a... 

The idea behind the experiment is to let the biomass growth rate change from zero to its maximum value. By adding a known amount of substrate under controlled conditions, the interpretation of the OUR response can be described by the model concept (cf. Table 7.1) and the four central process parameters can be determined. The following two conditions are important for a successful outcome of the experiment ... 

Soil-related data (HM and BC content in soil parent materials) were included in calculations to account the values of HM weathering. Also we considered the influence of soil types on forest biomass productivity. Runoff data (at scale 0.5 x 0.50 were directly used to get input data on drainage water fluxes, Qie. Forest-type-related data (wood biomass growth and HM content in wood biomass) inserted into our database were subdivided depending on either coniferous, deciduous or mixed forests. 

Table 2. Parameters of wood biomass growth for main tree types in the forests of European Russia results of simulating based on EFIMOD (Chertov, Komarov, 1997).

The rates of uptake of substrate and oxygen are related to the biomass growth rate by appropriate yield constants ... 

It is interesting to discuss in slightly more detail the case of solar versus biomass. The issue here is the amount of energy to be produced per unit time and unit surface area for the two cases. The important conclusion is drawn when one considers the efficiency of surface area use photovoltaics. The rate of biomass growth is too slow. Figure 1.8 illustrates these differences. 

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