• Energy Research

Synchronized growth and neutral lipid accumulation with high lipid productivity under mixotrophic growth of the strain Chlorella sorokiniana FC6 IITG was achieved via manipulation of substrates feeding mode and supplementation of lipid elicitors in the growth medium. Screening and optimization of lipid elicitors resulted in lipid productivity of 110.59mgL(-1)day(-1) under the combined effect of lipid inducers sodium acetate and sodium chloride. Fed-batch cultivation of the strain in bioreactor with intermittent feeding of limiting nutrients and lipid inducer resulted in maximum biomass and lipid productivity of 2.08 and 0.97gL(-1)day(-1) respectively. Further, continuous production of biomass with concomitant lipid accumulation was demonstrated via continuous feeding of BG11 media supplemented with lipid inducers sodium acetate and sodium chloride. The improved biomass and lipid productivity in chemostat was found to be 2.81 and 1.27gL(-1)day(-1) respectively operated at a dilution rate of 0.54day(-1).

Outdoor high cell-density microalgae cultivation is highly challenging due to unavailability of appropriate CO2 feeding strategy under diurnal sunlight intensities. Hence, a novel real time light based CO2 feeding strategy was firstly developed under diurnal simulated sunlight (LED) to test on Chlorella sp. in a 10 L scale bubble column photobioreactor. The strategy yielded a biomass titer of 5.12 g L-1 under simulated sunlight, far higher than existing biomass-density and pH-control based CO2 feeding strategies. In outdoor culturing, the proposed feeding strategy yielded high biomass titers of 6.8 and 9.0 g L-1 in growth-phase of two-stage and single-stage lipid induction studies respectively with same biomass productivity of 0.8 g L-1 day-1. Subsequently, two-stage lipid induction strategy of 6.8 g L-1 titer yielded biodiesel productivity of 120 g L-1 day-1, whereas single-stage strategy of 9.0 g L-1 titer was unable to induce lipid. Moreover, specific light availability affects the lipid production.

AbstractThe study demonstrates a sustainable process for production of bio-crude oil via hydrothermal liquefaction of microbial biomass generated through co-cultivation of microalgae and bacteria coupled with wastewater remediation. Biomass concentration and wastewater treatment efficiency of a tertiary consortium (two microalgae and two bacteria) was evaluated on four different wastewater samples. Total biomass concentration, total nitrogen and COD removal efficiency was found to be 3.17 g L−1, 99.95% and 95.16% respectively when consortium was grown using paper industry wastewater in a photobioreactor under batch mode. Biomass concentration was enhanced to 4.1 g L−1 through intermittent feeding of nitrogen source and phosphate. GC-MS and FTIR analysis of bio-crude oil indicates abundance of the hydrocarbon fraction and in turn, better oil quality. Maximum distillate fraction of 30.62% lies within the boiling point range of 200–300 °C depicting suitability of the bio-crude oil for conversion into diesel oil, jet fuel and fuel for stoves.

Abstract A process engineering strategy was developed for cultivation of high density biomass of Chlorella sp. FC2 with improved productivity under photoautotrophic condition. The process engineering strategy involved a combinatorial approach of: (i) optimization of CO2 concentration in the inlet gas stream & aeration rate; (ii) growth kinetic driven feeding recipe for limiting nutrients; and (iii) dynamic increase in light intensity. The strategy was tested by growing the cells on laboratory grade BG11 medium. With an attempt to reduce the cultivation cost, the growth performance of the organism was then evaluated on commercial grade BG11 medium. Finally, hydrothermal liquefaction was carried out for direct conversion of microalgal slurry into bio-crude oil. Cultivation on laboratory grade BG11 medium resulted in biomass titer and overall productivity of 8.41 g L−1 and 575.9 mg L−1 day−1 respectively. Significant improvement in biomass titer (13.23 g L−1) and overall productivity (731.6 mg L−1 day−1) was observed when grown on commercial grade BG11 medium. Higher fraction of hydrocarbon in the bio-crude oil depicted better oil quality. Thermal gravimetric analysis revealed that maximum distillate fraction lies within the boiling point range of 200–300 °C which is suitable for conversion into diesel oil, jet fuel, and fuel for stoves.

Abstract In this work, potato and sweet lime peels otherwise considered as waste were used as substrates for producing glucose. Different pre-treatment processes were carried out and the best conditions yielding higher amount of glucose concentration were further hydrolysed by enzyme. The pre-treated extract at 80 min in case of dilute acid hydrolysis with autoclaving conditions gave higher glucose concentration amongst all the pre-treatment processes for both the peels and hence considered for further analysis. Rationale for the next step of the experiment was designed based on a central composite statistical design (CCD). To obtain high glucose yield, response surface methodology (RSM) was used to optimize the hydrolysis conditions. The three parameters chosen for the study were; time (h), temperature (oC) and the rotation frequency of the incubator (revolutions per minute i.e. RPM). The optimum conditions in case of potato peel were found to be 56 h, 68 °C and 144 RPM and in case of sweet lime peel, 56 h, 68 °C and 167 RPM. Under these conditions, 46.17 (±0.77) gL−1 and 35.90 (±0.43) gL−1 of glucose were obtained for potato and sweet lime peels respectively. The optimum factors acquired from the statistical model were further confirmed using the experimental results.

The present study demonstrates a promising approach for production of bio-crude oil via hydrothermal liquefaction of microbial biomass grown in large-scale open raceway pond. Three key attributes to achieve process feasibility are co-cultivation of microalgae and bacteria resulting in high biomass titre, utilization of paper industry wastewater as cheap source of nutrients and water, and one-step direct conversion of biomass into bio-crude oil. High biomass titre of 4 g L−1 with 90% of COD removal efficiency was achieved, depicting robust performance of the microalgae-bacteria consortium in industrial wastewater and under fluctuating environmental condition. Statistical optimization resulted in highest bio-crude oil yield of 21.7 (%, w/w) under optimal temperature, biomass loading and reaction time of 299.7 °C, 16.1 (%, w/v) and 65 min, respectively. Bio-crude oil with energy recovery of 43% and heating value of 33.1 MJ kg−1 reflects 81.7% and 73.4% heating value of biodiesel and diesel, respectively. While high percentage of hydrocarbon content in bio-crude oil indicates good oil quality, the presence of significant esters fraction might offer resemblance to biodiesel. Lower H/C ratio and higher O/C ratio in comparison to diesel indicate requirement of upgradation of bio-crude oil before it can be realized at commercial scale.