Studies on power plant algae: assessment of growth kinetics and bio-char production from slow pyrolysis process

ABSTRACT

Algae can simultaneously be used for bio-capture of CO₂, generation of biofuels and biochar. In the present study, the kinetics of autotrophic growth of a power-plant blue–green algae Leptolyngbya subtilis JUCHE1 have been determined along with the assessment of capability of lipid production. The gas phase concentrations of CO₂ have been varied in the range of 5–20% (v/v). Illuminated 250 mL Erlenmeyer flasks have been used as small scale photobioreactors. The temperature and light intensity have been maintained at 37^oC and 2.5 kLux respectively. Substrate inhibition has been observed beyond 15% CO₂ concentration in gas phase. Haldane model explains the growth kinetics. The values of growth kinetic parameters namely μ_max, K_s, K_I have been determined to be 0.6064d⁻¹, 0.0165 and 1.7429 g/L, respectively. The algal oil has been extracted using a mixture of chloroform and methanol 2:1(v/v) and the dry algal biomass has been pyrolysed in an isothermal semi-batch reactor in the temperature range of 300^oC–700°C. The lipid content varies in the range of 4.0–12.5% (wt./wt.) and is strongly influenced by the concentration of CO₂ and the culture period. The yield of bio-char increases from 29 to 44% with the decrease of pyrolysis temperature from 700°C to 300°C.

GRAPHICAL ABSTRACT

KEYWORDS:

• Leptolyngbya subtilis JUCHE1
• 3-G biofuels
• bio-char
• Haldane model
• lipid accumulation

Acknowledgement

The authors are highly thankful to RUSA 2.0 scheme of Jadavpur University, for providing the financial support required to conduct the experimental studies. The authors acknowledge Mr. SukantaLahiri, Senior Manager and Head (Retired), Chemical Laboratory of Sagardighi thermal power plant, Sagardighi, Murshidabad, West Bengal -742237 for providing water samples from waterbodies and solid samples scraped from algal layer deposited on the cooling towers of the plant in 2017.

Disclosure statement

No potential conflict of interest was reported by the author(s).

Additional information

Funding

The present research has been funded by “Rashtriya Uchchatar Shiksha Abhiyan, RUSA, Government of India.