Algal bioprospecting in ecosystems leads to exploring native microalgae and the competency evaluation of economically producing lipids as biofuel or nutritional applications. In this study, ten microalgae species were screened from the saltwater lake. Chlorella vulgaris, Chlorella sorokiniana, Chlamydomonas raudensis, Chlamydomonas hedleyi, Dunaliella salina, Picochlorum bazangan sp. nov., Tetraselmis bazangan sp. nov., Haematococcus lacustris, Nannochloropsis oceanic, and Scenedesmu rubescens were isolated and identified using 18SrDNA and tufA markers. Biodiesel potentials were assayed by the determination of biomass productivity, biochemical components, fatty acid profile, and biodiesel properties. The results showed that the maximum biomass yield (1.22 gL -1 ) belonged to C. vulgaris. The highest protein, carbohydrate, chlorophyll, and carotenoid content were recorded in C. vulgaris, C. raudensis, C. sorokiniana, and D. salina, respectively. N. oceanica accumulated high lipid content and omega-3 fractions (31.09%). However, C. hedleyi had the highest lipid productivity (11.64 gL -1 d -1 ) compared to other microalgae. The best species for biodiesel production was C. vulgaris, with a specific growth rate of 0.36d -1 , lipid productivity of 7.45 gL -1 d -1 , and C16-C18 fatty acid profile of 78.3%. The microalgae C. vulgaris had appropriate biodiesel properties of low viscosity (4.49), high cetane number (55.38), and relatively low cloud point (4.98). Another choice was N. oceanic, with high lipid productivity, cetane number (59.79), oxidative stability (56.43), and low iodine value (47.11). Microalgae T. bazangan sp. nov. had a cetane number (55.24), low cloud point (4.71), and C16-C18 fatty acid profile of 82.34%. Accordingly, C. vulgaris, T. bazangan sp. nov., and N. oceanic can be considered potential species for biodiesel.

Two-stage anaerobic digestion and trace metals (TM) supplementation are promising techniques to improve biogas production. Fe2+ and Ni2+ can improve process stability since they are part of the cofactors of enzymes and microorganisms’ growth. This work attempted to evaluate the effect of Fe2+ and Ni2+ addition on H2-rich biogas production from organic solid waste and the CH4-rich biogas production from the acidogenic effluents (AEs) enriched with TM. The TM concentrations that enhanced the hydrogen yield in the batch were 0.25 mg/L of Ni2+ and 334 mg/L of Fe2+. These concentrations were evaluated in a two-stage system. The substrate for the batch tests and fermentative reactor (first stage) was OSW. The AE generated in the first stage was the substrate to produce CH4-rich biogas in the second stage. In the first stage, the productivity achieved was 1823 ± 160 mL H2/L/day. However, TM supplementation decreased productivity by 65% since the VS removal increased. Megasphaera genus predominated in the first stage. Regarding the methanogenic reactor, the undiluted AE without TM caused the fast decay of the process. Nevertheless, the reactor operated stably after using AE enriched with TM as a substrate, and CH4 yields increased by 42%. The highest productivity achieved in the second stage was 1278 ± 42 mL CH4/L/day, operating with an organic loading rate of 2.8 gVS/L/day. The genera Proteiniphilum, Thermovirga, DMER64, Anaerovorax, and Syntrophomonas predominated in the second stage. In conclusion, AE enriched with TM can be used to recover the stability of anaerobic digesters, increasing methane production.

In the current study, Cheshmeh-Sabz Lake located in northeastern Iran (36°20'N, 59°3' E) with an average minimum annual temperature of -15˚C was screened to isolate native cold-adapted microalgae strains. Various isolation and puri cation methods (different freshwater culture media at 5 ºC, liquid serial dilution with streak plate methods, and then uorescence-activated cell sorting) were used to nd dominant cold-adapted microalgae strains. Three cold-adapted microalgae growth parameters (Scenedesmus sp., Ankistrodesmus sp., and Chlorella sp.) were investigated at 8 ºC and 25 ºC. Among isolates, Scenedesmus sp. (dominant in BG-11) had the same and relatively high biomass productivity (~ 0.54 ± 0.001 g L −1 d −1 ) at low and high temperatures. Fatty acid pro le evaluation of three species at 8, 15, and 25 ºC indicated, the highest amount of α-linolenic acid was produced in Scenedesmus sp., and there was no signi cant difference between the amount of α-linolenic acid at 15 ºC and 25 ºC (10.96 ± 1.5% and 11.07 ± 0.31%, respectively). There were no signi cant differences between palmitic acid amount at 8, 15, and 25 ºC (41.05 ± 5.2, 38.48 ± 4.25, 39.82 ± 1.58% respectively) in Scenedesmus sp. Based on the results, Scenedesmus sp. is the proper choice for outdoor cultivation in different seasons due to its relatively high biomass productivity and the speci c growth rate in low and high temperatures (8, and 25 ºC). In addition, the good ability of polyunsaturated fatty acids production (~27%) and rich in saturated fatty acids at low and high temperatures (~ 66%) makes this species susceptible to work in the biofuels eld and feed supplements.