Energy maintenance

Capital investment decisions are best made within the context of a life-cycle cost analysis. Life-cycle cost analysis focuses on the costs incurred over the life of the investment, assuming only candidate investments are considered that meet minimally acceptable performance standards in terms of the non-inonetary impacts of the investment. Using life-cycle analysis, the capital investment decision takes into account not just the initial acquisition or purchase cost, but maintenance, energy use, the expected life of the investment, and the opportunity cost of capital. When revenue considerations are prominent, an alternative method of analysis such as net benefit or net present value may be preferred. 

Ideally, we would wish for high substrate uptake in the absence of growth and in the absence of maintenance energy requirements. Since aerobic micro-organisms control their rates of substrate uptake when growth is slow or absent, manipulation of substrate uptake may be necessary. 

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. 

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

Cells need a certain amount of energy for maintenance. The maintenance energy is, for instance, needed for maintaining the proton motive force which is, among other purposes, used for maintaining the ion gradients across the cell membrane. Furthermore, energy is needed for the turnover of proteins and mRNA, for repair and for movement (if mobile). 

Maintenance energy requirements can be defined in terms of rate of substrate consumption per unit of biomass for maintenance this is known as the maintenance coefficient (m). 

Carbon from the substrate glucose is converted into the carbon of the cells, phenylalanine, carbon dioxide and byproducts. Carbon balance calculations thus give us more understanding of the amount of carbon in glucose used for cell mass production, for synthesis of the wanted produd, maintenance energy and byproduct formation. 

This discrepancy is due to die fact that other products such as formate, are formed in very small amounts as byproducts of the metabolic routes leading to L-phenylalanine and polymer synthesis. Of course, part of die glucose is also used for die metabolic activities in the micro-organism necessary to maintain the cells in a viable state, this is termed the maintenance energy requirement... 

Model 4 (Monod kinetics with constant maintenance energy)... 

Outdoor sows can be as productive as those kept indoors, but their nutritional requirements are different. The higher feed requirements of outdoor sows result from their higher maintenance energy... 

Many are the advantages of CWs for treating wastewater and runoff. They are a cost-effective and technically feasible technology. The expenses of operation and maintenance (energy and supplies) are low, requiring only a periodic, rather than continuous, on-site labor. CWs are tolerant to fluctuations in flow and facilitate water reuse and recycling. Additionally, they provide habitat for many wetland organisms and benefits to wildlife habitat.37... 

At this level, research focuses on planning, production engineering and management, supply of material resources, transport waste material processing and maintenance. Energy flows are closely related to the running of these activities that may be affected by production plans, scheduling times and parameters. 

The three major cost elements for pipelines are (1) construction costs (e.g., materials, labour, booster station, if needed, and others), (2) operation and maintenance costs (e.g., monitorisa-tion, maintenance, energy costs) and (3) other costs (design, insurance, fees, and right-of-way). 

Few models include the effects of in situ gas formation on the fluidization properties of the reactors this improvement, along with improvements in other areas, such as inclusion of improved structured models of microbial kinetics or inclusion of maintenance energy requirements or the effects of suspended cells on the reaction rate, might produce more accurate models, though it is unclear at this point whether the increased complexity would be justified. 

The maintenance energy requirement rate, /mam[, of the suspended biomass is as follows ... 

If Ss is not sufficiently available to support the biomass maintenance energy requirement. 

Tempest, D.W. andO.M. Neijssel (1984), The status of YATP and maintenance energy as biological interpretable phenomena, Ann. Rev. Microbiol., 38, 459-486. 

Maintenance energy requirement Hydrolysis, fraction 1 (fast) -1 1 -1 -1 1 Equation b Equation c,n= 1... 

Before adding the readily biodegradable substrate, the maintenance energy requirement of the active biomass should ideally correspond to the amount of readily biodegradable substrate produced by hydrolysis of the slowly biodegradable COD fraction, i.e., an equilibrium corresponding to an almost constant OUR must be seen. 

Only 1.2% of the carbon of 2,4-D added to stream water was converted to organic particulate matter, the solids fraction in water containing the microbial cells. This lack of significant carbon assimilation may be a result of the inability of the microorganisms to obtain carbon and energy for biosynthetic purposes at these low concentrations, the immediate use of the carbon for respiration in order for the cells to maintain their viability (i. e., for maintenance energy), or the rapid decomposition and mineralization of the cells and their constituents. 

The most successful and widely used of the equations in Table 5.17 is that due to Monod and, although it may not be universally applicable, it gives a reasonable description of the variation of growth rate with substrate concentration in a surprisingly large number of cases. Whilst it does not allow for the lag phase at the beginning of a batch process, it may be modified by the addition of one extra term to allow for the consumption of cellular material to produce maintenance energy. 

Pirt, S. J. Proc. R. Soc. B163 (1965) 224. The maintenance energy of bacteria in growing cultures. 

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