Cultivation of microalgae for biodiesel production:A review on upstream and downstream processing

Fluctuating market price of fossil fuel and overwhelming emission of greenhouse gases to the atmosphere have resulted in climate change and have been a global concern in this decade. Hence, biodiesel has become an alternative option to fossil diesel as it is renewable and environmentally friendly. Nevertheless, this alternative fuel that is usually derived from terrestrial oil crops will cause shortage in food supply and deforestation if mass production is realized. In recent years, cultivation of aquatic microorganism(particularly microalgae) to produce biodiesel is considered as a practical solution due to their high growth rate and ability to synthesize large quantity of lipid within their cell. However, the development of energy and cost-efficiency of microalgae cultivation system are the main issues in producing renewable microalgae biodiesel. Of late, wastewater or organic compost has been used as the cultivation medium as it can provide sufficient nutrients to sustain microalgae growth.Microalgae cultivation method and system are vitally important as these factors undoubtedly affect the final microalgae biomass and lipid yield. In this review, the cultivation system of microalgae, nutrients demanded for microalgae production, cell harvesting and drying, microalgae oil extraction, and utilization of microalgae biomass for biodiesel production are introduced and discussed. It is anticipated to convey clearer perspectives in upstream and downstream processes in microalgae-derived biodiesel production.

Advances of macroalgae biomass for the third generation of bioethanol production

In recent years, utilization of renewable sources for biofuel production is gaining popularity due to growing greenhouse gas(GHG) emissions which causes global warming. There has been a great effort in exploring alternative feedstock for bioethanol production. In this context, the production of third-generation bioethanol from macroalgae has emerged as an alternative feedstock to food crop-based starch and lignocellulosic biomass.This is mainly due to the fast growth rate of macroalgae, no competition with agricultural land, high carbohydrate content and relatively simple processing steps compared to lignocellulosic biomass. This review paper provides an insight of recent innovative approaches for macroalgae bioethanol production, including conventional and advanced hydrolysis process to produce fermentable sugar, various fermentation technologies, economic analysis and life cycle assessment. With the current technology maturity, efficient utilization of macroalgae as sustainable source for bioethanol and other value-added chemicals production could be achieved in the near future.

Optimization and evaluation of reduced graphene oxide hydrogel composite as a demulsifier for heavy crude oil-in-water emulsion

The rising production of produced water from oilfields had been proven to bring detrimental environmental effects.In this study,an efficient,recyclable,and environmental-friendly reduced graphene oxide immobilizedκ-Carrageenan hydrogel composite(κCaGO)was fabricated as an alternative sorbent for crude oil-in-water demulsification.Polyethyleneimine(PEI)was employed to form a stable hydrogel composite.The conditions for the immobilization of graphene oxide(GO)on PEI-modifiedκ-Carrageenan(κC)beads were optimized appropriately.An immobilization yield of 77%was attained at 2%PEI,2 h immobilization activation time,and pH 6.5.Moreover,the synthesizedκCaGO is capable of demulsification with an average demulsification efficiency of 70%.It was found that the demulsification efficiency increases with salinity andκCaGO dosage,and it deteriorates under alkaline condition.These phenomena can be attributed to the interfacial interactions betweenκCaGO and the emulsion.Furthermore,theκCaGO can be recycled to use for up to six cycles without significant leaching and degradation.As such,the synthesizedκCaGO could be further developed as a potential sorbent substitute for the separation of crude oil from produced water.