This study reports the contamination of Indian sea salts with different microplastic particles, as a consequence of using contaminated sea water. Samples from all eight brands of investigated sea salts were found contaminated, and concentrations of these particles ranged from 103 ± 39 to 56 ± 49 particles kg of salt. Both fibers and fragments were observed with large variation in size. Eighty percent of the extracted fibers and the fragments were smaller than 2000 μm and 500 μm respectively. Extracted particles were mostly polyesters, polyethylene terephthalate (PET), polyamide, polyethylene, and polystyrene. Their total mass concentration was also estimated as 63.76 μg kg of salt. These results are significant, since India is a leading producer and exporter of sea salts. A simple sand filtration of artificially contaminated sea water could effectively (> 85% removal by weight and > 90% removal by number) remove these microplastics and has the potential for preventing the transfer of microplastics into the salt from contaminated sea waters.

The effects of six different sequential extractions of proteins, lipids, and carbohydrates on their yields and subsequent biomass recoveries was investigated. The maximum yields of lipids, proteins, and carbohydrates were 26.50 ± 1.32%, 28.14 ± 1.97%, and 16.40 ± 0.43%, respectively, in primary extraction of biomass. Compared to the primary extractions, lipid yields were significantly lowered by 20–22% in secondary extractions. The maximum loss of proteins in secondary (post lipid extraction) and tertiary extractions was 34.79% and 56%, respectively. The most significant loss (38–44.5%) in carbohydrates was recorded after tertiary extractions. Among all of the extraction sequences, the sequence of proteins–lipids–carbohydrates extracted algae (PLCEA) showed optimum recovery of individual metabolite. For this extraction sequence, the yields of proteins, lipids, and carbohydrates were found to be 28.14%, 22%, and 10.17%, respectively. It was also characterized by the highest residual biomass available for second (80%) and third (61%) steps of extraction. Finally, the cumulative yields of these metabolites were converted into net value gains. The extraction sequence PLCEA could result in 66.5% net value gain overcoming the cost of biomass generation.

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Microalgal treatment of raw sewage presents many complexities, mainly resulting from the inability of the algal species to sustain increased physiological stresses due to variable nutrient levels and high concentrations of organics. Chlorella sorokiniana and Scenedesmus obliquus have been identified to tolerate higher amounts of organic loading and physiological stresses. Nutrient removal, pathogen removal, and lipid accumulation with secondary or tertiary effluents have been demonstrated independently for these organisms. However, their potentials for accomplishing these objectives simultaneously with raw sewage have not been investigated. This study presents comprehensive investigations of applicability of C. sorokiniana and S. obliquus to wastewater treatment without the requirement for any additional treatment. S. obliquus showed greater potential for removing organic carbon (76.13 ± 1.59% COD removal), nutrients (98.54 ± 3.30% N-removal, 97.99 ± 3.59% P-removal) and comparable pathogens removal (99.93 ± 0.12% total coliforms removal, 100% faecal coliform removal) in comparison to C. sorokiniana (69.38 ± 1.81% COD removal, 86.93 ± 3.49% N-removal, 68.24 ± 11.69% P-removal, 99.78 ± 0.12% total coliforms removal, 100% faecal coliform removal) with 15 days of cultivation with filtered raw sewage, but also encountered increased levels of stress (F v /F m of 0.48 ± 0.03) which accounted for increased lipid accumulation in the cells (23.26 ± 3.95% w/w) but might also affect their biomass productivity and treatment potential in longer applications. In comparison, C. sorokiniana demonstrated better adaptability to physiological stresses (F v /F m of 0.53 ± 0.01) and may be suitable for achieving comprehensive treatment and sufficient lipid accumulation (22.74 ± 3.11% w/w) without compromising these potentials during prolonged applications. These results highlight the importance of selecting algal species with better stress resistance to extend their applicability for comprehensive wastewater treatment and lipid production.

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