Kinetic modeling to optimize synergistic dynamics of nitrogen and phosphorous affected lipid productivity in Chlorella minutissima for biodiesel production Neha Arora, Alok Patel, Parul A. Pruthi and Vikas Pruthi* Molecular Microbiology Laboratory, Biotechnology Department, Indian Institute of Technology Roorkee Roorkee, Uttarakhand 247667, India Email id:
[email protected]
Microalgae Biodiesel Microalgae Triacylglycerols (TAGs) are one of the most promising renewable substitutes to fossil fuels which can be transesterified to form biodiesel and simultaneously reduce the GHGs emissions.
TAG detection
Cellular response
Ludeking-Piret model for lipid production
Integrating the above equation: TAG C
Mass production of biodiesel derived from microalgae, the economic feasibility depends prominently on the lipid (TAG) productivity and optimizing scaling up which requires kinetic modeling. Growth physiology influences the quality and quantity of algal lipid produced. Environmental cues, both biotic and abiotic impact the rate of lipid synthesis.
where P(t) = Lipid production at time t (mg/L) α= lipid formation coefficient (mg/mg) β= non growth associated correlation coefficient (mg/mg/d) Origin Pro 2015 was used to fit the data, calculate various parameters with standard error and perform sensitivity analysis.
Results Growth and lipid kinetic modeling
Nitrogen (N) and phosphorous (P) are the two important macronutrients required for growth and metabolism of algal cells. N and P starvation/limitation shifts the lipid metabolism from membrane lipid synthesis to neutral lipid storage.
N+P+
N-PL
Logistic modeling was used for predicting the performance and optimizing future scale ups.
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Transesterification and FAME profile Figure 2: Biomass productivity, lipid productivity, cell size of C. minutissima under nitrogen and phosphorous limited/ starved conditions. Biochemical changes in response to nitrogen and phosphorous
Figure 6: FAME profile of C. mimutissima grown on different nitrogen and phosphorus concentrations. Biodiesel quality
N+P-
(days)
Table 3: Biodiesel quality parameters calculated from FAME profile obtained from C. mimutissima and comparison to standard parameters.
(days)
Figure 1: Experimental and fitted curves of biomass and lipid accumulation in C. minutissima under various N/P concentrations [( ) experimental biomass, ( ) fitted curve biomass solid line, ( ) experimental lipid, ( ) fitted curve lipid solid line].
Table 1: Biomass and lipid parameters. e
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(days)
Parameters used and estimated after fitting the model
where µmax =maximum specific growth rate (d-1); Xmax = maximum algal biomass during batch cultivation X(t)= algal biomass at any time t X0= initial algal biomass at t=0 ho= dimensionless Barayni-Roberts model parameter quantifying the initial state of cells Lag time λ (t) = ho/µmax
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Table 2: Total pigment composition of C. minutissima cells on 10th day.
NLP+
N+PL
Integrating the above equation:
5
(days)
(days)
Logistic equation for growth
4
N-P-
NLPL
Kinetic modeling
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Figure 5: Thin layer chromatography (TLC) Lane 1: Triolein (control), Lane 2-9: Total extracted lipid.
(days)
(days)
Figure 1: Effect of Nitrogen and phosphorous limitation on TAG accumulation
2
N-P+
(days)
Hence in this study, the synergistic effect of N and P on lipid productivity in Chlorella minutissima was evaluated.
1
experimental data used in modeling ; m modelled data calculated using Origin pro 2015
Figure 3: Total lipid, carbohydrate and protein content of C. minutissima cells on 10th day. Lipid accumulation N+P+
NLPL
N-P+
NLP+
N-PL
N+PL
N-P-
N+P-
Figure 4: Nile red staining of C. minutissima on 10th day.
Conclusion • Kinetic modeling of microalgal growth and lipid accumulation indicated results similar to experimental data; R2 0.97, providing a base for better construction of large scale operations for biodiesel production. • The maximum lipid productivity of 49.2 ± 0.41 mg/l/d. was attained in NLPL with biomass productivity of 104.04 ± 0.25 mg/L/d. • N deficiency resulted in more pronounced effect in increasing Chl a/ Chl b, Car/ Chl a + Chl b ratios and biochemical changes as compared to P. • Biodiesel properties were within the permissible limits of ASTM D6751 and EN14214 automobile biodiesel standards.
Authors are thank full to Department of Biotechnology (DBT) and Ministry of Human Resource and Development (MHRD)
