Our data sources are mainly two parts, one is the human practice group's interface with
China Fujian Shenliu company to obtain the cost data of the basic fixed assets depreciation,
labor cost and fuel consumption consumption of the microalgae plant; on the other hand, it is
obtained from the national public information, where the data of tax and insurance are obtained
from the National Tax Bureau and the data of land cost are obtained from the national land network
data.

By observing the growth curve of microalgae, we can find that the cultivation time required to
reach the maximum density of microalgae is not necessarily the time required to maximize the
benefits of the plant, because it often takes longer to cultivate the algae to reach the maximum
density, and there is a certain cost for the daily operation of the plant. Therefore, it is also
important to balance the relationship between microalgae density and time cost. In this paper, we
use a goal planning model to calculate the cultivation time required to maximize benefits as well
as to analyze the effect of various additives on microalgae production, which further affects the
profitability of the plant.

This model is used to calculate the cost and revenue of a culture tank, assuming that the
profit generated by 1g of microalgae is a, the daily labor cost of the plant's algae culture staff
is c, and the rest of the plant's daily operating costs are shown in the table above. Let the
production on day Xi be mi(g), then the following 0-1 planning model for calculating the profit
is obtained.

MATLAB was used to solve the solution and the results were analyzed as follows, where i
denotes the optimal number of days of cultivation and c denotes the daily labor cost.

（1）No additives added：

The results showed that the optimal incubation time should be day 7 when the labor cost ranged
from $20.22 to $33.91 and day 5 when the labor cost ranged from $33.92 to $40.44. The
expected variation in profit ranged from $132.03 to $59.39. The maximum average daily
profit available was $18.86.

（2）Add 80mg/L ascorbic acid：

The results showed that when labor costs ranged from $20.22 to $40.44, the best incubation
time was day 8, when time costs had less effect on profits and yield played a decisive role.
The expected variation in profit ranged from $130.09 to $28.98. The maximum average daily
profit available was $18.58.

（3）Add 200mg/L ascorbic acid：

The results showed that when labor costs ranged from $20.22 to $40.44, the optimal incubation
time was all on day 7, and the expected variation in profit ranged from $112.59 to $11.49.
The maximum average profit obtainable per day was $16.08.

（4）Add 250mg/L ascorbic acid：

The results showed that the optimal incubation time should be day 10 when the labor cost was
between $20.22 and $35.15, and day 4 when the labor cost was between $33.16 and $40.44,
with an expected profit variation range of $216.27 to $39.59. The maximum average daily
profit available was $21.63.

（5）Add 300mg/L ascorbic acid：

The results showed that when the labor cost was between $20.22 and $40.44, the optimal cultivation
time would be day 3 and the expected variation in profit would range from $-3.73 to $-23.95.
At this point, instead of increasing the density of algae growth, the addition greatly
reduces the amount of algae produced and may cause the plant to lose money.

In order to observe the variation of profit with cost more intuitively, the curves of cost and profit
of various additives were plotted in this paper, as shown in the following figure, it can be found that
a maximum point exists in the addition of 250 mg/L L-ascorbic acid, i.e. the maximum value
of profit can be reached in the addition of 250 mg/L L-ascorbic acid.