The sago starch industry is one of the major revenue sources of the Malaysian state of Sarawak. This state is currently among the world’s leading producers of sago starch, exporting more than 40,000 tons every year to different Asian countries. This number is expected to rise since starch production and export value have been increasing 15.0%– 20.0% each year. Sago palm is subjected to various processes to obtain starch from its trunk. During processing, a huge amount of residual solid wastes is generated, such as bark and hampas, and in general, is burned or washed off to nearby streams. Along with the rising sago starch demand, the sago starch industry is now facing waste management problems, which have resulted in environmental pollution and health hazards. These wastes comprise starch, hemicellulose, cellulose, and lignin; hence, can be valorized into feedstock as value-added products. To date, these wastes have been utilized in the production of many materials like adsorbents, sugars, biofuels, nanomaterials, composites, and ceramics. This review article aims to summarize the various methods by which these wastes can be utilized besides to enlighten the major interest on sago hampas and bark.
Subcritical water extraction (SCW) was used to extract oil from Chlorella pyrenoidosa. The operational factors such as reaction temperature, reaction time, and biomass loading influence the oil yield during the extraction process. In this study, response surface methodology was employed to identify the desired extraction conditions for maximum oil yield. Experiments were carried out in batch reactors as per central composite design with three independent factors including reaction temperature (170, 220, 270, 320, and 370°C), reaction time (1, 5, 10, 15, and 20 min), and biomass loading (1, 3, 5, 10, and 15%). A maximum oil yield of 12.89 wt.% was obtained at 320°C and 15 min, with 3% biomass loading. Sequential model tests showed the good fit of experimental data to the second-order quadratic model. This study opens the great potential of SCW to extract algal oil for use in algal biofuel production.
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.