Biofuels from microalgae—A review of technologies for production, processing, and extractions of biofuels and co-products

Abstract

pagesThe main aim of this study was to determine the effects of physical and chemical pretreatments on biogas production from two agricultural wastes (maize straw and cattle manure). The total solids (TS) were 86.1% and 41.2% for the cattle manure and maize straw respectively while the volatile solids (VS) were 82.0% for cattle manure and 51.6% for maize straw (both interms of total biomass). 5% TS was used for both biomasses in the measurement of reducing sugars and the Biochemical methane potential (BMP) test.Solubility was determined by measuring the reducing sugar concentration using the Miller method (Miller 1959). Biomass samples were seeded with sludge seed on a 50:50 biomass to sludge ratio. The pH of the mixture was regulated to between 7.0 and 7.5 and placed in an incubator at 37 o C (mesophilic temperature range). Biogas measurements were done daily and carbon dioxide was measured once in a week.Two chemical pretreatment methods were applied on both biomasses; acid and alkaline pretreatments assisted with heat. The most effective pretreatment method for maize straw was alkaline pretreatment producing the highest concentrations of daily and cumulative biogas with an average increase of 163%. Acid pretreatment of maize straw lasted between 24 to 27 (the fewest number of days) compared to all other pretreatments applied.i Physical pertreatment methods applied on maize straw include; comminution, microwave and liquid hot water pretreatment. The Microwave pretreated samples produced the highest increase in biogas production of about 3 folds.Cattle manure was pretreated with H2SO4, NaOH, microwave and liquid hot water (LHW). Acid pretreatment was more effective for cattle manure than maize straw with both acid concentrations increasing biogas production. Cattle manure samples treated at LHW 135 o C produced the highest cumulative amount of biogas resulting in a 103% increase. Microwave pretreatment was also very effective resulting in 97% increase in methane production which lasted for 32 days.

Surveying techno-economic indicators of microalgae biofuel technologies

“…As stated before, algae can also produce valuable co-products, such as proteins, natural colorants, and biomass after oil extraction, that can be used as animal feed, medicines or fertilizers [3,10], or fermented to produce ethanol, methane or other biofuels [5]. Although this possibility is widely reported, just a few studies [46,[51][52][53]55,57] looked with attention to this question and made financial calculations on the feasibility of producing biofuel and co-products together.…”

“…A set of articles can be found in the literature evidencing the technical feasibility of growing algae for biofuel production [1][2][3][4][5][6][7][8][9][10][11][12][13][14][15][16][17], in which the majority of them demonstrate the absence of the major drawbacks associated with current 1st generation biofuels. For example, the most common drawback pointed out of 1st generation biofuels as being the affect on food prices due to massive arable land use.…”

“…The biodiesel produced from algal oil has physical and chemical properties similar to diesel from petroleum, to biodiesel produced from crops of 1st generation and compares favorably with the International Biodiesel Standard for Vehicles (EN14214) [3].…”

“…These advantages include: (a) capability of producing oil during all year long and with superior efficiency, therefore the oil productivity of microalgae is greater compared to the most efficient crops; (b) producing in brackish water and on not arable land [41]; not affecting food supply or the use of soil for other purposes [2]; (c) possessing a fast growing potential and several species have 20-50% of oil content by weight of dry biomass [2]; (d) Regarding air quality, production of microalgae biomass can fix carbon dioxide [2]; (e) nutrients for its cultivation (nitrogen and phosphorous, mainly) can be obtained from sewage, therefore there is a possibility to assist the municipal wastewater treatment [19,20]; (f) growing algae do not require the use of herbicides or pesticides [42]; (g) algae can also produce valuable co-products, as proteins and biomass after oil extraction, that can be used as animal feed, medicines or fertilizers [3,10], or fermented to produce ethanol or methane [5]; (h) biochemical composition of algal biomass can be modulated by different growth conditions, so the oil yield can be significantly improved [43]; and (i) Capability of performing the photobiological production of "biohydrogen" [22][23][24][25]44].…”

Biochemical evolution in response to intensive harvesting in algae: Evolution of quality and quantity

“…The production of algae in intensive land‐based culture systems is a relatively new approach with significant commercial potential and interest, particularly with regard to algal biochemistry. Algae have been proposed as substrates for a broad range of biofuels (Brennan & Owende, 2010; Elliott, Biller, Ross, Schmidt, & Jones, 2015; Mata, Martins, & Caetano, 2010; Rowbotham, Dyer, Greenwell, & Theodorou, 2012), and as a source of new bioproducts and animal feed (Gosch, Magnusson, Paul, & Nys, 2012; Jiménez‐Escrig, Gómez‐Ordóñez, & Rupérez, 2012; Li, Wijesekara, Li, & Kim, 2011; Pulz & Gross, 2004). A key concern here is the productivity of biochemical components (lipid, protein, carbohydrate) per unit area of cultivation—whether this productivity evolves in response to intensive harvesting remains unclear.…”