Ismail Rawat

BODIPY staining, an alternative to the Nile Red fluorescence method for the evaluation of intracellular lipids in microalgae

In order to develop feasible production processes for microalgal biodiesel, the isolation of high neutral lipid producing microalgae is crucial. Since the established Nile Red (NR) method for detection of intracellular lipids has been successful only for some microalgae, a more broadly applicable detection method would be desirable. Therefore, BODIPY 505/515, a lipophilic bright green fluorescent dye was tested for detection of intracellular lipids in Chlorella vulgaris, Dunaliella primolecta and Chaetoceros calcitrans. An optimum concentration of 0.067 μg ml(-1) was determined for lipid staining in the microalgae. Compared to NR, BODIPY 505/515 was more effective in staining microalgae and showed resistance to photobleaching, maintaining its fluorescence longer than 30 min.

The optimization of biomass and lipid yields of Chlorella sorokiniana when using wastewater supplemented with different nitrogen sources.

The potential of nitrogen sources supplementing domestic wastewater for the cultivation of microalgae was assessed. Urea, potassium nitrate, sodium nitrate and ammonium nitrate were evaluated for their effect on cultivation and lipid production of Chlorella sorokiniana. Urea showed the highest biomass yield of 0.220 g L(-1) and was selected for further experimentation. Urea concentrations (0-10 g L(-1)) were assessed for their effect on growth and microalgal physiology using pulse amplitude modulated fluorometry. A concentration of 1.5 g L(-1) urea produced 0.218 g L(-1) biomass and 61.52% lipid by relative fluorescence. Physiological stress was evident by the decrease in relative Electron Transport Rate from 10.45 to 6.77 and quantum efficiency of photosystem II charge separation from 0.665 to 0.131. Gas chromatography analysis revealed that C16:0, C18:0, C18:1, C18:2 and C18:3 were the major fatty acids produced by C. sorokiniana. Urea proved to be an effective nitrogen supplement for cultivation of C. sorokiniana in wastewater.

Lipid extracted algae as a source for protein and reduced sugar: a step closer to the biorefinery

The objective of this study was to investigate the feasibility of using lipid extracted algae (LEA) as a source for protein and reduced sugar, and the effects of various procedural treatments on their yields. LEA provided comparable yields of protein and reduced sugars to those from total algae. Oven drying provided highest yields of all products followed by freeze drying, while sun drying significantly lowered their yields. Effective cell disruption by microwave and autoclave increased the lipid yields from algae, but resulted in increased loss of other compounds with lipid extracting solvents lowering their yields during sequential extraction. Relatively inefficient cell disruption by ultrasonication and osmotic shock lowered the amount of cell protein lost to the lipid extracting solvents. These results highlight the complexity of concurrent extraction of all value added products from algae, and the need for proper selection of the processes to achieve the objectives of integrated biorefinery.

Improving the feasibility of producing biofuels from microalgae using wastewater

Biofuels have received much attention recently owing to energy consumption and environmental concerns. Despite many of the technologies being technically feasible, the processes are often too costly to be commercially viable. The major stumbling block to full-scale production of algal biofuels is the cost of upstream and downstream processes and environmental impacts such as water footprint and indirect greenhouse gas emissions from chemical nutrient production. The technoeconomics of biofuels production from microalgae is currently unfeasible due to the cost of inputs and productivities achieved. The use of a biorefinery approach sees the production costs reduced greatly due to utilization of waste streams for cultivation and the generation of several potential energy sources and value-added products while offering environmental protection. The use of wastewater as a production media, coupled with CO2 sequestration from flue gas greatly reduces the microalgal cultivation costs. Conversion of residual biomass and by-products, such as glycerol, for fuel production using an integrated approach potentially holds the key to near future commercial implementation of biofuels production.

Evaluation of operating conditions for sustainable harvesting of microalgal biomass applying electrochemical method using non sacrificial electrodes.

The efficient harvesting of microalgae is considered to be one of the challenging steps of algal biofuel production and a key factor limiting the commercial use of microalgae. To overcome the limitation of metallic electrodes depletion, the application of non-sacrificial electrode was investigated for the electrochemical harvesting (ECH) of microalgae. The effect of applied current, addition of electrolyte and initial pH were parameters investigated. The highest recovery efficiency of 83% was obtained for Scenedesmus obliquus at 1.5A, initial pH 9 and 6gL(-)(1) NaCl with power consumption of 3.84kWhkg(-)(1). Recovery efficiency of ECH process was comparable to literature reported centrifugation, filtration and chemical flocculation techniques but with a much lower power consumption. The ECH process with addition of electrolyte enhanced the lipid extraction by 22% without any adverse effects. The ECH process with non sacrificial carbon electrodes could be a possible harvesting step at commercial scale microalgal biomass production.

Adaptability of growth and nutrient uptake potential of Chlorella sorokiniana with variable nutrient loading

Chlorella sorokiniana can sustain growth in conditions hostile to other species, and possesses good nutrient removal and lipid accumulation potentials. However, the effects of variable nutrient levels (N and P) in wastewaters on growth, productivity, and nutrient uptake by C. sorokiniana have not been studied in detail. This study demonstrates the ability of this alga to sustain uniform growth and productivity, while regulating the relative nutrient uptake in accordance to their availability in the bulk medium. These results highlight the potential of C. sorokiniana as a suitable candidate for fulfilling the coupled objectives of nutrient removal and biomass production for bio-fuel with wastewaters having great variability in nutrient levels.

Prospects, recent advancements and challenges of different wastewater streams for microalgal cultivation

Microalgae are recognized as one of the most powerful biotechnology platforms for many value added products including biofuels, bioactive compounds, animal and aquaculture feed etc. However, large scale production of microalgal biomass poses challenges due to the requirements of large amounts of water and nutrients for cultivation. Using wastewater for microalgal cultivation has emerged as a potential cost effective strategy for large scale microalgal biomass production. This approach also offers an efficient means to remove nutrients and metals from wastewater making wastewater treatment sustainable and energy efficient. Therefore, much research has been conducted in the recent years on utilizing various wastewater streams for microalgae cultivation. This review identifies and discusses the opportunities and challenges of different wastewater streams for microalgal cultivation. Many alternative routes for microalgal cultivation have been proposed to tackle some of the challenges that occur during microalgal cultivation in wastewater such as nutrient deficiency, substrate inhibition, toxicity etc. Scope and challenges of microalgal biomass grown on wastewater for various applications are also discussed along with the biorefinery approach.

Cultivation of Chlorella pyrenoidosa in outdoor open raceway pond using domestic wastewater as medium in arid desert region

Chlorella pyrenoidosa was cultivated in secondary wastewater effluent to assess its nutrient removal capabilities. Wastewaters were obtained from a wastewater treatment plant located in Ouargla, Algeria. The experiments were conducted in winter under natural sunlight in an outdoor open raceway pond situated in the desert area. The highest biomass of the microalgae was found to be 1.71±0.04g/L. Temperatures ranged between 18 and 31°C. The average annual insolation was no less than 3500h with an annual solar irradiance of more than 2000kWh/m(2). Analyses of different parameters including COD, NH4(+)-N and TP were conducted throughout the cultivation period. Their average removal efficiencies were 78%, 95% and 81% respectively. The results demonstrated the potential of nutrient removal by microalgae grown on secondary wastewater in arid areas.

Sustainable Production of Biofuels from Microalgae Using a Biorefinary Approach

Biorefinery has emerged as a new concept to derive more than one utility product from biomass. The products from biorefinery include one or more biofuels (biodiesel, bioethanol, biomethane, and biohydrogen) along with other energy sources (syngas and bio-oil), pharmaceutical products, and commercially important chemicals. Biorefineries, thus could simultaneously produce biofuels, bio-based chemicals, heat, and power. The biomass production and its utilization as biofuel has a higher water footprint (WF) than fossil derived fuel. The biorefinery approach has the potential to bring down the WF. Similarly, biorefinery approach has the potential to bring down the carbon footprint. The value added product derived from biorefinery basket includes pigments, nutraceuticals, and bioactive compounds. The use of industrial refusals for biomass production includes wastewater as nutrient medium and utilization of flue gases (CO2) as the carbon source for culture of microalgae. These processes have the potential to reduce fresh WF and carbon footprint.

Microalgae Applications in Wastewater Treatment

Algal wastewater treatment is effective in the removal of nutrients (C, N and P), coliform bacteria, heavy metals and the reduction of chemical and biological oxygen demand, removal and/or degradation of xenobiotic compounds and other contaminants. Microalgae wastewater treatment technologies have long been in existence; however, uptake of the technology to date has been limited mainly due to considerations of land requirements and volumes of wastewater to be treated. This chapter gives an overview of algal applications in wastewater treatment with specific reference to nutrient removal, phycoremediation of heavy metals, high-rate algal ponds, symbiosis of algae with bacteria for wastewater treatment, and utilisation of wastewater-grown microalgae.