To assess the microalgae biomass production cost of any process, it is necessary to know the complete process flowchart in detail, including a list of equipment and equipment size in addition to raw material uptake and energy consumption (Kalk and Langlykke, 1986).

Figure 14.2 summarizes the steps necessary to define the major contributions to production cost: (1) depreciation, (2) raw materials and utilities, and (3) labor and supervision. The total production cost is calculated as the sum of depreciation plus direct production costs (raw ma­terials and utilities, along with labor and supervision). From the block diagram of the process (the conceptual approach), a detailed process flowchart can be defined based on production capacity and kinetic parameters of the different unit operations performed. The flowchart al­lows us to know the type and size of equipment necessary as well as the mass and energy

FIGURE 14.2

balances on the entire process. The cost of major equipment can be obtained from the sup­pliers or, alternatively, from bibliographic references or databases. From this information, the total fixed capital is calculated, multiplying by the corresponding Lang factors according to the nature of the item. The value of these factors is available for a wide variety of processes, values for microalgae-based processes being previously verified (Acien et al., 2012a). The de­preciation includes not only amortization of the fixed capital, which is a function of the esti­mated lifetime, but also the property tax, insurance, and purchase tax.

The direct production cost includes raw materials, utilities, labor, and others (supervision, maintenance, tax, contingencies, etc.). The amount of raw materials required is calculated from mass balances according to the specified flowchart, whereas the consumption of utilities is calculated from the power and water use of the process. The cost of raw materials has to include transport to the facility and the market values obtained from suppliers. With regard to power, the cost of electricity can vary according to consumption and energy required; there­fore, a detailed analysis of different suppliers is recommended.

Water is an important utility for microalgae production; thus its cost needs to be accurately determined. Water cost is a function of its quality (seawater, brackish water, freshwater, wastewater) and uptake volume. Moreover, in this section the cost of wastewater treatment of effluents from the facility has to be included. Whatever the quality of water used, the cost of pumping the water into and out of the facility has to be included in the power consumption item, separate from the power required to operate the facility, which is mainly related to wa­ter recirculation in the photobioreactors.

Labor consists of the workers necessary to correctly operate the process and the general costs of supervision and management, in addition to maintenance, taxes, and contingencies. To determine the direct production cost, it is necessary to know the cost of the raw materials, power, water, and labor, whereas the other costs are calculated by previously defined factors. The labor cost varies widely as a function of personnel qualification levels and facility location. Supervision and other costs are calculated based on the number of personnel directly involved in the operation of the facility and their salaries. Therefore, by reducing the number or salary levels of direct personnel, the labor and supervision cost greatly reduces.

Following this methodology, it is possible to ascertain the production cost of microalgae biomass for any facility. Moreover, the production cost at any other scale can also be approx­imated simply by modifying the cost of major equipment according to the scale chosen and
then multiplying the direct cost by the adequate factor in order to increase the production capacity. The process or equipment cost can be scaled up or down from a basic size using an exponential law for which a value of 0.85 is considered appropriate. This equation is not valid for large-scale changes because a certain technology can be feasible at one scale but might not be available on a larger scale. Thus, a maximum scale-up factor of 10 is consid­ered acceptable without revising the technology. Whenever larger requirements are needed, the scale-up has to be solved by multiplying the number of units.

SizeB 085

CostB = CostA S_l_ (14.1)

SizeA