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• Natural plant extracts were utilized as flocculants to harvest algal consortium. • 8 mg ml−1 of M. oleifera showed 75.5% biomass harvesting efficiency after 100 min. • Natural coagulants have lower costs with lesser environmental and energy impacts. • 95.76% efficiency was obtained in 20 min on combining M. oleifera with chitosan. • Synergistic influence of natural and chemical coagulant formed bigger flocs. The study investigated the ability of plant based natural coagulants from Azadirachta indica; Ficus indica ; Moringa oleifera ; Citrus sinensis ; Punica granatum and Musa acuminata to harvest the microalgal biomass. Influence of eluent type (water and NaCl) and concentration (1–5 N) on coagulant extraction; coagulant dosage (1–5 g) and volume (20–100 ml); pH (6–12) and algal concentration (0.1–1 g l−1) on harvesting were analyzed. The results obtained were compared with alum and chitosan. FTIR and biochemical analysis confirmed the presence of bioactive compounds to aid coagulation. Biomass removal efficiency of 75.50% was obtained with M. oleifera extracts (8 mg ml−1) at pH 7.5–7.8, within 100 min. The harvesting efficiency increased to 95.76% when 4 mg ml−1 M. oleifera extracts was combined with 0.75 mg ml−1 chitosan. The life cycle and cost analysis acknowledged the eco-friendly coagulants as strong alternative for conventional coagulants used in microalgal harvesting, thereby improvising the overall bioprocess. [ABSTRACT FROM AUTHOR]

Graphical abstract Highlights • Biophysical model for assessing algal performance in open ponds was formulated. • Model was based on site-specific light and temperature dynamics. • Light attenuation effects over the microalgal productivity were evaluated. • Location specific optimal pond depth and operating conditions were presented. • Photoinhibition effects declines the algal productivity by 19% at the study site. Abstract Microalgal biomass is currently recognized as a promising sustainable source for biofuel production and carbon dioxide (CO 2) sequestration. Utilization of biophysical models are emerging to access the real-time feasibility of microalgal technology. In this present work, a comprehensive mathematical model based on the site-specific meteorological variables is formulated using MATLAB ODE 45 s solver to estimate the microalgal productivity. The predictive model framework utilized material balance equations with basic laws of physics, known constants and conservative assumptions to evaluate the water temperature that influences the microalgal viability. The dynamic behaviour of algal ponds considering the operating variables like light intensity (including the effects of photoinhibition), water temperature, and design criteria like pond depth, microalgal concentration, was used to estimate the performance of T. pseudonana in open ponds. Maximum growth was projected in September accounting to the biomass and lipid productivity of 170.28 kg (dry mass) ha−1 d−1 and 39.42 l ha−1 d−1 respectively with a CO 2 capture potential of 224.77 kg (CO 2) ha−1 d−1 based on the influence of water temperature. Optimal pond depth and operational conditions to achieve the desired productivity for the specific site were estimated. The maximum annual areal productivity dropped by 19% from 62.18 tons (dry mass) ha−1 yr−1 due to photoinhibition. The simulated biophysical model as a tool could be used to evaluate the biokinetic processes affecting the algal pond performance for further facilitation of effective decision making on scaling up of microalgae cultivation. [ABSTRACT FROM AUTHOR]

• Microalgal growth and nutrient depletion kinetics were simulated in bubble column PBR. • CFD simulations highlight the dependence of microalgal growth on PBR hydrodynamics. • Microalgal productivity of 0.14 g L−1 d-1 achieved with 5.5 % human urine and 4% CO 2. • Phosphate and ammonium removal of 90 % and 84 % was attained in PBR respectively. • Contours of water velocity and turbulent energy gave insights on PBR hydrodynamics. Optimization of microalgae cultivation to reduce the associated costs is one of the major objectives in a biorefinery model. The present study optimized the microalgal cultivation using 4.5–8.5 % v/v of DHU (diluted human urine) as a cost-effective resource, in a bubble column photobioreactor (BCPBR) under real-time conditions. Media with 5.5 % DHU and 4% CO 2 showed maximal biomass productivity of 0.14 g L−1 day−1 with a final concentration of 1.06 g L−1. Phosphate and ammonium removal of 90.70 % and 84.10 % respectively was achieved. The biofixation of CO 2 obtained for 6 days, during the cultivation in 5.5 % DHU, by supplying 4% of CO 2 enriched air was 0.29 g L-1 d-1. Computational fluid dynamics (CFD) simulations were used to study the effects of velocity magnitude, shear stress, turbulent kinetic energy, and irradiance on the microalgal growth inside the BCPBR. The developed kinetic model predicted the biomass concentration and phosphate removal up to 98 % and 82 % accuracy respectively. Such studies would aid in comprehending the large scale commercial cultivation and thereby facilitate the application of microalgae in the future. [ABSTRACT FROM AUTHOR]

• Microalgal extracts as biostimulants were evaluated for tomato plants. • 20-100 % of algal extracts showed positive effects on tomato growth. • Seed treatment with 40-80% algal extracts showed 100% germination in 3 days • Foliar spray of 60% algal extracts showed better yield. • Increased plant growth rate was also correlated with higher chlorophyll content • Lower concentration of algal extracts showed better stimulatory effects. A probable strategy for increasing the economic sustainability of algal technology would involve the utilization of microalgal biomass as biofertilizer by off-setting the high production costs. The present study focusses on the utilization of mixed algal consortia as biofertilizer for analysing the growth rate of tomato plant. Algal extracts (20-100%) in the form of seed primer and foliar spray were used as biostimulants for the growth of tomato plant. Characterization of algal consortium showed the presence of 40.90% carbohydrates and 26.18% proteins that could potentially act as precursors for bioactive compounds to stimulate plant growth. Faster germination percentage was found with extract concentrations ranging from 20-60% in 3 days compared to the untreated seeds. Seeds treated with cellular extracts of 40% concentration also showed faster plant growth rate after sowing in terms of increase in shoot length 19.86 ± 0.51 cm and root length of 14.87 ± 0.63 cm with a fresh and dry weight of 3.47 ± 0.04 g and 0.389 ± 0.036 g respectively after 20 days. Foliar spraying of 60% algal extracts resulted in total plant height of 7.98 ± 0.19 cm with root length of 5.8 ± 0.16 cm, 46% higher compared to the control. 11 ± 0.35 leaves with chlorophyll content of 13.45 ± 0.307 mg g-1 were also obtained after 20 days, with fresh and dry biomass content of 0.416 ± 0.015 g and 0.062 ± 0.005 g respectively. Thus, microalgal cellular extracts could act as an environmental-friendly and economical alternative to synthetic liquid fertilizer for promoting sustainable agriculture. [ABSTRACT FROM AUTHOR]