Observation of Spirulina platensis cultivation in a prototype household bubble column photobioreactor during 107 days

Figures & data

Figure 1. Schematic diagram of the prototype household bubble column PBR. 1: Observatory window and front door; 2: controlling panel; 3: PBR upper cover; 4: PBR column; 5: LED light source panel; 6: aeration pipe; 7: water tap.

Table 1. Concentration of nutrients in the cultivation medium used in this study.

Ingredients	Concentration (g·L^−1)
NaHCO3	10.00
K2HPO4	0.50
NaNO3	2.50
K2SO4	1.00
NaCl	0.50
MgSO4·7H2O	0.20
EDTA	0.04
CaCl2·2H2O	0.02
FeSO4·2H2O	0.02
H3BO3	2.80
MnCl2·4H2O	1.80
ZnSO4·7H2O	0.22
CuSO4·5H2O	0.05
Co(NO3)2·6H2O	4.4
(NH4)6Mo7O24·4H2O	0.01

Table 2. Harvesting events throughout the 107 cultivation days.

Day	AB560nm,1 ^a	AB560nm,2 ^a	Harvest (g)
15	0.580 ± 0.032	0.415 ± 0.029	46.213
27	1.747 ± 0.060	1.148 ± 0.039	155.334
28	1.221 ± 0.049	0.765 ± 0.030	132.196
31	1.38 ± 0.053	0.978 ± 0.035	123.652
34	1.092 ± 0.061	0.536 ± 0.024	157.525
41	1.261 ± 0.043	0.407 ± 0.028	209.245
45	0.91 ± 0.041	0.79 ± 0.022	36.458
48	1.3 ± 0.039	0.843 ± 0.032	149.134
49	0.853 ± 0.045	0.302 ± 0.020	146.283
56	0.853 ± 0.042	0.383 ± 0.026	140.137
61	1.38 ± 0.053	0.449 ± 0.027	303.497
64	0.982 ± 0.036	0.702 ± 0.038	80.843
69	1.240 ± 0.052	0.79 ± 0.028	117.755
77	1.112 ± 0.045	0.47 ± 0.021	211.235
92	0.879 ± 0.046	0.431 ± 0.021	106.736
107	1.306 ± 0.059	0.307 ± 0.026	290.874

^aThe subscripts 1 and 2 represent the AB_560nm before and after harvest, respectively.

Table 3. Nutrient replenishment and CO₂ aeration events throughout the 107 cultivation days.

Day	Nutrient replenishment (g)								CO2 aeration
	NaCl	NaHCO3	NaNO3	K2HPO4	K2SO4	MgSO4·7H2O	FeSO4·7H2O	EDTA	pH1 ^a	pH2 ^a
27	\	\	\	\	\	\	\	\	11.20 ± 0.03	9.47 ± 0.02
37	\	\	41.67	\	\	5.19	0.78	\	10.14 ± 0.02	9.68 ± 0.01
45	\	\	\	\	\	\	\	\	10.33 ± 0.01	9.27 ± 0.02
56	\	\	\	\	\	\	\	\	10.13 ± 0.02	8.00 ± 0.01
57	8.33	\	\	\	\	\	2	2	\	\
61	\	\	\	\	\	\	\	\	9.67 ± 0.03	7.71 ± 0.03
62	\	\	41.67	9.33	16.67	8	\	\	\	\
77	\	\	\	\	\	\	\	\	10.06 ± 0.02	9.2 ± 0.02
82	8.33	\	41.67	9.33	16.67	8	2	2	\	\
92	\	\	30	\	\	3	0.5	\	\	\

^aThe subscripts 1 and 2 represent the pH before and after CO₂ aeration, respectively.

Figure 2. Relationships between: (A) concentration change and AB_560nm; (B) real harvest and estimated harvest.

Table 4. Harvesting experiment conducted on Day 41.

Order	Harvest amount (g)	Cumulative amount (g)	Concentration change (g·L^−1)	AB560nm	Filtrated volume (L)
0	0.000	0.000	0.000	1.261 ± 0.049	0.000
1	39.038	39.038	−0.781	1.085 ± 0.041	7.800
2	35.918	74.956	−1.499	0.974 ± 0.059	8.500
3	39.968	114.924	−2.298	0.777 ± 0.051	10.920
4	32.058	146.982	−2.940	0.636 ± 0.034	10.920
5	33.728	180.710	−3.614	0.530 ± 0.047	15.600
6	28.538	209.248	−4.185	0.407 ± 0.037	18.720

Figure 3. Variations of C_biomass and N, P, Mg, K, Fe concentrations during cultivation. (A) Change of the C_biomass (left) and the five nutrient contents normalized to their values of Day 1 (right), with harvesting (yellow bars) and salt replenishing (purple bars) events marked in the picture; (B) Declining trends of the five nutrient contents. The data were taken from Figure 4(A) where the values decreased steadily and pieced together to show a continuous trend.

Figure 4. Variations of C_biomass and pH during cultivation. (A) Comparison between the C_biomass and pH variations during cultivation; (B) Change rate of C_biomass (g·L⁻¹·d⁻¹) vs. that of pH (d⁻¹).

Figure 5. Ozone sterilization effect to the Spirulina culture medium. (A) Variation of aerobic plate count (CFU/10⁴) with increasing sterilization time; (B) Variation of aerobic plate count in the days before and after sterilization. The symbols 0^1st and 0^2nd in the figure represent the time points before and after sterilization on Day 77, respectively.

Figure 6. Influence of (A) average C_biomass and (B) filtration sack mesh number on the harvest efficiency.

Data availability

The data that support the findings of this study are available from the corresponding author, Shudi Zhang, upon reasonable request.