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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]

[Display omitted] • Algal drying characteristics of convective hot air and microwave oven were discussed. • Microwave drying is faster with relatively lower specific energy requirements. • Convective and microwave drying followed thin layer drying models. • 14.4% higher lipid content was obtained in microwave dried algal biomass. • Uniform volumetric heating in microwave drying preserves biochemical content. Conventional microalgal drying consumes huge time and contributes to 60–80% of downstream process costs. With the aim to develop an effective and rapid drying process, the present study evaluated the performance of microwave based drying (MWD) with a power range of 360–900 W and compared with the conventional oven drying (OD) at 40–100 °C. MWD was found to be efficient due to uniform and volumetric heating because of dipolar interaction, with an effective diffusivity of 0.47 × 10−9−1.63 × 10−9 m2 s−1, comparatively higher than OD. Activation and specific energy of 32.43 W g−1 and 42.9–56.07 kWh kg−1 was projected respectively, and a falling rate period with best fit for Newton and Henderson-Pabis model was observed for MWD. Uniform heating from internal sub-surface avoided cell distress, resulting in 14.4% higher lipid yield and significant preservation of biochemical components that can be processed into bioenergy and valuable products in microalgal biorefinery. [ABSTRACT FROM AUTHOR]

Utilization of waste resources is necessary to harness the long-term sustainability of algal technology. The study focused on the use of human urine as the basic nutrient source for culturing native microalgal consortium and further optimized the process parameters using response surface methodology. A full factorial, central composite rotatable design (CCRD) with three variables: urine concentration (1–10% vol of urine/vol of distil water [%v/v]), pH (6.5–9) and light intensity (50–350 μ m o l p h o t o n s m − 2 s e c − 1 ) was used to evaluate the microalgal biomass and lipid content. Results indicated that at 95% confidence limits, the selected factors influence the biomass and lipid productivity. The maximum biomass productivity of 211.63 ± 1.40 mg l−1 d−1 was obtained under optimized conditions with 6.50% v/v of urine, pH of 7.69 and at light intensity of 205.40 μ m o l p h o t o n s m − 2 s e c − 1 . The lipid content was found to increase from 18.96 ± 1.30% in control media to 26.27 ± 1.94% under optimal conditions. The interactive effect of variables over the microalgal biomass and lipid content has also been elucidated. The data obtained were comparable to the BG11 media (control). Optimized diluted urine media in the presence of ammonium ions and under limited nitrate showed better lipid yields. Significant lipid biomolecules were detected in the algal oil extracts obtained from the diluted urine media characterized by Fourier transform infrared spectroscopy (FTIR) and Nuclear magnetic resonance (NMR). Gas chromatography-mass spectrometry (GCMS) revealed the presence of several monounsaturated and polyunsaturated fatty acids in the transesterified algal oil. Such studies would aid in technically realizing the field scale cultivation of microalgae for biofuels. Image 1 • Potential of diluted human urine for microalgal cultivation was highlighted. • Urine concentration, light intensity and pH interactively influences algal growth. • Maximum biomass productivity of 211.63 ± 1.4 mg l−1 d−1 was achieved. • Lipid content was found to increase by 7.31% compared to the control. • Diluted urine media with ammonium and limited nitrate showed better lipids. [ABSTRACT FROM AUTHOR]