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 37oC 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 μmax, Ks, KI 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 300oC–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