Bioplastic Production from Microalgae: A Review.

Plastic waste production around the world is increasing, which leads to global plastic waste pollution. The need for an innovative solution to reduce this pollution is inevitable. Increased recycling of plastic waste alone is not a comprehensive solution. Furthermore, decreasing fossil-based plastic usage is an important aspect of sustainability. As an alternative to fossil-based plastics in the market, bio-based plastics are gaining in popularity. According to the studies conducted, products with similar performance characteristics can be obtained using biological feedstocks instead of fossil-based sources. In particular, bioplastic production from microalgae is a new opportunity to be explored and further improved. The aim of this study is to determine the current state of bioplastic production technologies from microalgae species and reveal possible optimization opportunities in the process and application areas. Therefore, the species used as resources for bioplastic production, the microalgae cultivation methods and bioplastic material production methods from microalgae were summarized.

Outdoor cultivation of Chlorella sorokiniana in third generation biorefinery: Resource savings through medium recycling.

The reduction of resource requirements for the outdoor cultivation of Chlorella sorokiniana using 180 L flat panel photobioreactors through medium recycling was investigated in this study. Without medium recycling, algae grew in 13.6 d from 0.92 to 5.32 gL-1with a productivity of 0.32 gL-1d-1. For the production of 748 g algae dry weight (DW), 152gkg-1 N, 27 gkg-1 P and 231 Lkg-1 water were needed. A realistic cultivation model with the recycling of medium and a productivity of 0.4 gL-1d-1 was set up based on experimental data, in which the requirements decreased to 104gkg-1 N, 24 gkg-1 P and 141 Lkg-1 water. Compared to the production of lutein-containing plant Tagetes erecta, water and potassium requirements of up to 91% less and 96% respectively and higher biomass productivity by the factor 3.7 was achieved.

Biosorption of neodymium on Chlorella vulgaris in aqueous solution obtained from hard disk drive magnets.

In recent years, biosorption is being considered as an environmental friendly technology for the recovery of rare earth metals (REE). This study investigates the optimal conditions for the biosorption of neodymium (Nd) from an aqueous solution derived from hard drive disk magnets using green microalgae (Chlorella vulgaris). The parameters considered include solution pH, temperature and biosorbent dosage. Best-fit equilibrium as well as kinetic biosorption models were also developed. At the optimal pH of 5, the maximum experimental Nd uptakes at 21, 35 and 50°C and an initial Nd concentration of 250 mg/L were 126.13, 157.40 and 77.10 mg/g, respectively. Analysis of the optimal equilibrium sorption data showed that the data fitted well (R2 = 0.98) to the Langmuir isotherm model, with maximum monolayer coverage capacity (qmax) of 188.68 mg/g, and Langmuir isotherm constant (KL) of 0.029 L/mg. The corresponding separation factor (RL) is 0.12 indicating that the equilibrium sorption was favorable. The sorption kinetics of Nd ion follows well a pseudo-second order model (R2>0.99), even at low initial concentrations. These results show that Chlorella vulgaris has greater biosorption affinity for Nd than activated carbon and other algae types such as: A. Gracilis, Sargassum sp. and A. Densus.

Microalgae-bacteria flocs (MaB-Flocs) as a substrate for fermentative biogas production.

Biogas production from the microalgae-bacteria flocs (MaB-Flocs) in batch reactors was conducted in this study. A batch test was performed to determine optimum inoculums that were taken from a running biogas plant (BP), a municipal wastewater treatment plant (MWTP) and a river sediment (RS). The maximum biogas yield (304.83±4.23 mL per gram volatile solids introduced (mL g-VS(-1))) was obtained with the inoculum from MWTP. Subsequently, the effect of substrate-inoculum (S/I) ratios, temperature and pre-treatment methods on fermentative biogas and methane production was investigated. The optimum S/I ratios and incubation temperature were determined as 0.2 g VS(substrate)/g VS(inoculum) and 37±1°C, respectively. The results of the CH4 fermentation show that the methane yields could be increased from 216.72±3.52 mL CH4 g-VS(-1) to 271.34±6.65 mL g-VS(-1) by using enzymatic pre-treatment at the S/I ratio of 0.2 g VS(substrate)/g VS(inoculum) and mesophilic conditions.