Razif Harun

Optimization of the microalgae Chlorella vulgaris for syngas production using central composite design

Gasification has emerged as an effective thermochemical conversion technology for generating syngas products from biomass. Process conditions for optimizing the productivity and quality of syngas during gasification vary with the type and composition of the biomass. With escalating research interests in the development of biofuels from microalgae, resulting from its high biomass productivity, agronomical and environmental bioremediation benefits, the current study investigates the optimization of microalgal gasification for syngas production using high temperature horizontal tubular furnace. Four response variables (H2, CO, CO2, and CH4) were optimized under varying conditions of temperature (500–900 °C), microalgal (Chlorella vulgaris) biomass loading (0.6–2.5 g), heating rate (5–25 °C min−1), and equivalent ratio (ER = 0.1–0.35). The optimization study was carried out using central composite design (CCD). Temperature was the most significant process parameter influencing H2 production, followed by microalgal biomass loading and heating rate. An optimum H2 yield of 41.75 mol% was obtained at a temperature of 703 °C, a microalgal biomass loading of 1.45 g, a heating rate of 22 °C min−1, and an ER of 0.29. Statistical analysis showed that the generated models were sufficiently in agreement with the experimental results. It was concluded that the direct gasification of microalgal biomass in the presence of air has significant potential for the commercial-scale production of syngas products.

Analysis of process configurations for bioethanol production from microalgal biomass

Fossil fuel depletion has become a great concern as the world population is increasing at an alarming rate. Current concerns such as global warming, depletion of fossil fuels and increasing price of petroleum-based fuels have forced the search for alternative and costeffective energy sources with lesser greenhouse gas emissions. Research into the development of renewable and sustainable fuels has recognised bioethanol as a viable alternative to fossil fuels, owing to its low toxicity, biodegradability, and the ability to effectively blend with gasoline without any engine modifications (Harun et al., 2009, 2010a). The utilization of crops such as sugar cane, sorghum and corn are considered as traditional approaches for bioethanol production (Harun et al., 2010a). The use of such feedstock for bioethanol production competes in the limited agricultural logistics for food production thus escalating the “food versus fuel debate” (Harun et al., 2010b). There has been a considerable interest in the use of microalgal biomass to replace food-based feedstock for renewable transport fuel production. Microalgae are autotrophic photosynthetic organisms considered as the fastest growing plant species known (Wayman, 1996). They can tolerate a wide range of pH and temperature conditions in diverse habitats including freshwater and sea water (Harun et al., 2010b). Microalgae can store considerable amounts of carbohydrates in the form of starch/cellulose, glycogen, hexoses and pentoses that can be converted into fermentable sugars for bioethanol production via fermentation (Wayman, 1996). Table 1 shows the amount of carbohydrates in various species of microalgae. Compared to existing edible feedstock, microalgae grow easily with or without soil and offer a very short harvesting cycle (1~10 days) (Harun et al., 2010a). Microalgae also have a high capacity of fixing CO2 via photosynthesis and other greenhouse gases, resulting in an overall reduction in the net gaseous emissions during the entire life cycle of the fuel (Wayman, 1996). Majority of the work reported in literature relies on straightforward sequential application of the production process involving pre-treatment of the biomass, hydrolysis, fermentation and product recovery. Simultaneous occurrences or a combination

Subcritical Water Technology for Enhanced Extraction of Biochemical Compounds from Chlorella vulgaris

Subcritical water extraction (SWE) technology has been used for the extraction of active compounds from different biomass materials with low process cost, mild operating conditions, short process times, and environmental sustainability. With the limited application of the technology to microalgal biomass, this work investigates parametrically the potential of subcritical water for high-yield extraction of biochemicals such as carbohydrates and proteins from microalgal biomass. The SWE process was optimized using central composite design (CCD) under varying process conditions of temperature (180–374°C), extraction time (1–20 min), biomass particulate size (38–250 μm), and microalgal biomass loading (5–40 wt.%). Chlorella vulgaris used in this study shows high volatile matter (83.5 wt.%) and carbon content (47.11 wt.%), giving advantage as a feedstock for biofuel production. The results showed maximum total carbohydrate content and protein yields of 14.2 g/100 g and 31.2 g/100 g, respectively, achieved under the process conditions of 277°C, 5% of microalgal biomass loading, and 5 min extraction time. Statistical analysis revealed that, of all the parameters investigated, temperature is the most critical during SWE of microalgal biomass for protein and carbohydrate production.

Particulate Size of Microalgal Biomass Affects Hydrolysate Properties and Bioethanol Concentration

Effective optimization of microalgae-to-bioethanol process systems hinges on an in-depth characterization of key process parameters relevant to the overall bioprocess engineering. One of the such important variables is the biomass particle size distribution and the effects on saccharification levels and bioethanol titres. This study examined the effects of three different microalgal biomass particle size ranges, 35 μm ≤ x ≤ 90 μm, 125 μm ≤ x ≤ 180 μm, and 295 μm ≤ x ≤ 425 μm, on the degree of enzymatic hydrolysis and bioethanol production. Two scenarios were investigated: single enzyme hydrolysis (cellulase) and double enzyme hydrolysis (cellulase and cellobiase). The glucose yield from biomass in the smallest particle size range (35 μm ≤ x ≤ 90 μm) was the highest, 134.73 mg glucose/g algae, while the yield from biomass in the larger particle size range (295 μm ≤ x ≤ 425 μm) was 75.45 mg glucose/g algae. A similar trend was observed for bioethanol yield, with the highest yield of 0.47 g EtOH/g glucose obtained from biomass in the smallest particle size range. The results have shown that the microalgal biomass particle size has a significant effect on enzymatic hydrolysis and bioethanol yield.

The Influence of Inoculum to Substrate Ratio on the Biochemical Methane Potential of Fat, Oil, and Grease in Batch Anaerobic Assays

Anaerobic digestion is one of the potential methods widely applied for organic waste recovery to produce biogas. In this study, biodegradability of fat, oil, and grease was tested in biochemical methane potential assays and the effects of substrate to inoculum ratio ranging from 0.2–4.0 were determined. The results indicated that fat, oil, and grease is feasible to produce methane (670 mL CH4 gVS−1) and the ideal substrate to inoculum ratio range of 0.5–1.0 was determined. After 60 days of experiments, maximum methane yield for the ideal ratio was 603–741 mLgVS−1, which corresponds to 81–89% methane production. Increasing substrate to inoculum ratio showed a lag phase phenomena where methane yield may be decreased initially or started slowly, thus delaying the entire digestion process. With a higher substrate to inoculum ratio (2.0–4.0), methane yield was recorded lower than 60% and the highest methane production was 250.2 mLgVS−1.

Bioprocess Engineering Aspects of Biodiesel and Bioethanol Production from Microalgae

Rapid increase of atmospheric carbon dioxide together with depleted supplies of fossil fuel has led to an increased commercial interest in renewable fuels. Due to their high biomass productivity, rapid lipid accumulation and high carbohydrate storage capacity, microalgae are viewed as promising feedstocks for carbon-neutral biofuels. This chapter discusses process engineering steps for the production of biodiesel and bioethanol from microalgal biomass (harvesting, dewatering, pre-treatment, lipid extraction, lipid transmethylation, anaerobic fermentation). The suitability of microalgal lipid compositions for biodiesel conversion and the feasibility of using microalgae as raw materials for bioethanol production will also be evaluated. Specific to biodiesel production, the chapter provides an updated discussion on two of the most commonly used technologies for microalgal lipid extraction (organic solvent extraction and supercritical fluid extraction) and evaluates the effects of biomass pre-treatment on lipid extraction kinetics.

Potential Applications of Nanotechnology in Thermochemical Conversion of Microalgal Biomass

The rapid decrease in fossil reserves has significantly increased the demand of renewable and sustainable energy fuel resources. Fluctuating fuel prices and significant greenhouse gas (GHG) emission levels have been key impediments associated with the production and utilization of nonrenewable fossil fuels. This has resulted in escalating interests to develop new and improve inexpensive carbon neutral energy technologies to meet future demands. Various process options to produce a variety of biofuels including biodiesel, bioethanol, biohydrogen, bio-oil, and biogas have been explored as an alternative to fossil fuels. The renewable, biodegradable, and nontoxic nature of biofuels make them appealing as alternative fuels. Biofuels can be produced from various renewable resources. Among these renewable resources, algae appear to be promising in delivering sustainable energy options.

Process Economics and Greenhouse Gas Audit for Microalgal Biodiesel Production

With the current global drive towards a low-emission economy, countries need to take a stance. For example, Australia, which is one of the world’s largest polluters, has made a commitment that before 2020 its overall emissions would be reduced by 5–15% below the levels registered in the year 2000. To realise these targets, processes which capture carbon dioxide will prove critically important. One of such emerging processes is carbon dioxide capture for microalgae cultivation and subsequent downstream biomass processing for biodiesel production. This chapter will entail engineering scale-up, economic analysis and carbon audit to ascertain the viability of an industrial scale microalgal biodiesel production plant. This will involve the development of an industrial scale model to determine the feasibility of a real large-scale plant. Data from each process step (cultivation, dewatering, lipid extraction and biodiesel synthesis) will be presented individually and integrated into the overall process framework.