A MULTISTAGE GRADUAL NITROGENREDUCTION STRATEGY FOR INCREASED LIPID PRODUCTIVITY AND NITROGEN REMOVAL IN WASTEWATER USING Chlorella vulgaris AND Scenedesmus obliquus
Abstract:-Chlorella vulgaris and Scenedesmus obliquus were grown in artificial-wastewater using a new nitrogen-limitation strategy aimed at increasing lipid productivity. This strategy consisted in a multi-stage process with sequential reduction of N-NH 4 concentration (from 90 to 60, 40, and 20 mg.L -1 ) to promote a balance between cell growth and lipid accumulation. Lipid productivity was compared against a reference process consisting of nitrogen reduction in two stages, where the nitrogen concentration was suddenl… Show more
“…The high light intensity with nitrogen- depleted conditions also found to raise the lipid content up to 54% (dcw) in Nannochloropsis oceanica IMET1 ( Xiao et al, 2015 ). Recently, Chlorella vulgaris showed a lipid content of 63% when grown in municipal wastewater under nitrogen-limitation approach ( Robles-Heredia et al, 2015 ). 61% lipid content in Nannochloropsis gaditana 1049 was observed by Hu et al (2015) , grown in seawater medium with Vitamin B12, thiamine, biotin supplementation and 5% CO 2 sparging.…”
The last decade has witnessed a tremendous impetus on biofuel research due to the irreversible diminution of fossil fuel reserves for enormous demands of transportation vis-a-vis escalating emissions of green house gasses (GHGs) into the atmosphere. With an imperative need of CO2 reduction and considering the declining status of crude oil, governments in various countries have not only diverted substantial funds for biofuel projects but also have introduced incentives to vendors that produce biofuels. Currently, biodiesel production from microalgal biomass has drawn an immense importance with the potential to exclude high-quality agricultural land use and food safe-keeping issues. Moreover, microalgae can grow in seawater or wastewater and microalgal oil can exceed 50–60% (dry cell weight) as compared with some best agricultural oil crops of only 5–10% oil content. Globally, microalgae are the highest biomass producers and neutral lipid accumulators contending any other terrestrial oil crops. However, there remain many hurdles in each and every step, starting from strain selection and lipid accumulation/yield, algae mass cultivation followed by the downstream processes such as harvesting, drying, oil extraction, and biodiesel conversion (transesterification), and overall, the cost of production. Isolation and screening of oleaginous microalgae is one pivotal important upstream factor which should be addressed according to the need of freshwater or marine algae with a consideration that wild-type indigenous isolate can be the best suited for the laboratory to large scale exploitation. Nowadays, a large number of literature on microalgal biodiesel production are available, but none of those illustrate a detailed step-wise description with the pros and cons of the upstream and downstream processes of biodiesel production from microalgae. Specifically, harvesting and drying constitute more than 50% of the total production costs; however, there are quite a less number of detailed study reports available. In this review, a pragmatic and critical analysis was tried to put forward with the on-going researches on isolation and screening of oleaginous microalgae, microalgal large scale cultivation, biomass harvesting, drying, lipid extraction and finally biodiesel production.
“…The high light intensity with nitrogen- depleted conditions also found to raise the lipid content up to 54% (dcw) in Nannochloropsis oceanica IMET1 ( Xiao et al, 2015 ). Recently, Chlorella vulgaris showed a lipid content of 63% when grown in municipal wastewater under nitrogen-limitation approach ( Robles-Heredia et al, 2015 ). 61% lipid content in Nannochloropsis gaditana 1049 was observed by Hu et al (2015) , grown in seawater medium with Vitamin B12, thiamine, biotin supplementation and 5% CO 2 sparging.…”
The last decade has witnessed a tremendous impetus on biofuel research due to the irreversible diminution of fossil fuel reserves for enormous demands of transportation vis-a-vis escalating emissions of green house gasses (GHGs) into the atmosphere. With an imperative need of CO2 reduction and considering the declining status of crude oil, governments in various countries have not only diverted substantial funds for biofuel projects but also have introduced incentives to vendors that produce biofuels. Currently, biodiesel production from microalgal biomass has drawn an immense importance with the potential to exclude high-quality agricultural land use and food safe-keeping issues. Moreover, microalgae can grow in seawater or wastewater and microalgal oil can exceed 50–60% (dry cell weight) as compared with some best agricultural oil crops of only 5–10% oil content. Globally, microalgae are the highest biomass producers and neutral lipid accumulators contending any other terrestrial oil crops. However, there remain many hurdles in each and every step, starting from strain selection and lipid accumulation/yield, algae mass cultivation followed by the downstream processes such as harvesting, drying, oil extraction, and biodiesel conversion (transesterification), and overall, the cost of production. Isolation and screening of oleaginous microalgae is one pivotal important upstream factor which should be addressed according to the need of freshwater or marine algae with a consideration that wild-type indigenous isolate can be the best suited for the laboratory to large scale exploitation. Nowadays, a large number of literature on microalgal biodiesel production are available, but none of those illustrate a detailed step-wise description with the pros and cons of the upstream and downstream processes of biodiesel production from microalgae. Specifically, harvesting and drying constitute more than 50% of the total production costs; however, there are quite a less number of detailed study reports available. In this review, a pragmatic and critical analysis was tried to put forward with the on-going researches on isolation and screening of oleaginous microalgae, microalgal large scale cultivation, biomass harvesting, drying, lipid extraction and finally biodiesel production.
“…The maximum values of total lipid productivity are higher than most of the reported in the literature (Table 1), and the trend in increasing lipid productivity under nitrogen limitation confirms the trends observed previously. [33][34][35] Lipid productivity in continuous culture was 0.276 g L -1 d -1 via a closed loop (increase of 31.5 %) over that of the continuous mode in open loop and 81.1 % in batch mode (Fig. 4).…”
Good process control has often been criticized for the economic viability of large-scale production of several commercial products. In this work, the production of biodiesel from microalgae is investigated. Successful implementation of a model-based control strategy requires the identification of a model that properly captures the biochemical dynamics of microalgae, yet is simple enough to allow its implementation for controller design. This paper explores the biodiesel production in a class of continuous culture under heterotrophic conditions via closed-loop operation. A mathematical model adapted from Surisetty et al. (2010) that describe the growth of microalgae in a heterotrophic culture is studied via dynamic analysis. This model is extended to the continuous operation where bifurcation analysis was carried out for the determinate the qualitative model behavior and to analyze feasible operating conditions. This project is focused on the on the use of a mixture of two substrates that are continuously fed into the reactor chamber, and the continuous fermentation process is described by an unstructured mathematical model with a product inhibition on cell growth. In addition, we present the design of a nonlinear control law contains a class of bounded type feedback of the named control error in order to regulate the substrate concentration at maximum value to lead the lipids-diesel concentration indirectly. Lipid productivity in continuous culture was 0.276 g L -1 d -1 via a closed loop (increase of 31.5 %) over that of the continuous mode in open loop. Finally, numerical experiments proved the satisfactory performance of the proposed methodology in comparison with a linear PI controller.
“…When starting the experiments, C. vulgaris was cultivated in an enriched medium at 90 mg L −1 nitrogen; subsequently, the concentration of the culture was reduced to 20 mg L −1 , similarly to that described by Robles-Heredia et al [3]. Of the stock culture, a fraction was taken and transferred to the four bubble column seedlings, adding 200 mL each to one cell concentration of 15×10 4 cells mL −1 (Section 2.1).…”
Section: Cultivation Processmentioning
confidence: 99%
“…The idea of the two-stage cultivation mode is to stimulate the overproduction of intracellular lipids in the microalgae, at the expense of reduced cell growth [3]. are presented in Figure 3 superimposed on the growth curves in both PBRs and at different aeration rates.…”
Section: Effect Of the Aeration Rate On Cell Growth And Nitrogen Consmentioning
confidence: 99%
“…The mixture of saturated and unsaturated fatty acid chains (C 12 -C 22 ) present in many microalgae favors the production of biodiesel [1,2]. Certain species of microalgae tend to reach a high lipid content (20-50% dry cell weight) and may increase it by controlling various biotic and abiotic factors of the crop, such as light intensity, photoperiod, temperature, nutrients, mode, and the intensity of agitation [3]. The total yield of lipids from microalgae depends not only on the concentration of biomass reached but also on the cellular oil content.…”
This research presents the effect of hydrodynamic conditions at different rates of aeration (1.4, 1.8, and 2.3 vvm) and the geometry of two photobioreactors with internal lighting on lipid productivity and other parameters of Chlorella vulgaris. A two-step nitrogenreduction cultivation mode was applied for promoting lipid accumulation. The inoculum was cultivated initially at 90 mg L −1 N-NH 4 + , and at the end of the exponential phase, it was fed to 11 L photobioreactor at 20 mg L −1 of N-NH 4 +. The results showed that with similar aeration rates, the hydrodynamic regime in both photobioreactors was different. However, the increase in shear rate and agitation did not cause cell damage or photoinhibition. The maximum cell growth was 12 × 10 6 cells mL −1. The highest consumption of nitrogen was 19% and shear rates were of 120-340 s −1. The highest lipid productivity was reached in bubble column at 1.8 vvm with 0.650 mg•L −1 d −1 .
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