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[Display omitted] • Mixed Ulva intestinalis and Mimusops elengi oils for biodiesel production. • Optimization of reaction parameters through SPAT and RSM methods. • Simulation of process flow for industrial scale biodiesel production. • Project feasibility study through technoeconomic evaluation. • Minimum selling price of biodiesel was estimated to be 0.81 $/kg. • 0.088 kg CO 2 /kg of biodiesel emission estimated through carbon footprint analysis. The present research explored the sustainable production of biodiesel from mixed oils of marine macroalgae and non-edible seeds using a sulphonated Zinc doped recyclable biochar catalyst derived from coconut husk. The maximum biodiesel conversion of 94.8 % was yielded with optimized conditions of 10:1 methanol to oil molar ratio, 4.8 % biochar catalyst concentration, 54.5 ℃ temperature and 87.4 min reaction time. A techno-economic assessment provided a favourable return on investment (ROI) of 21.59 % and 4.63 years of reimbursement period, with a calculated minimum selling price of 0.81 $/kg of produced biodiesel. The carbon footprint analysis results estimated an annual emission of 752.07 t CO 2 which corresponds to 0.088 kg CO 2 emission per kg of biodiesel produced from the simulated process. The study on economic viability and environmental consciousness of biodiesel production not only paves the way for a greener and sustainable future while also contributing to low carbon footprint. [ABSTRACT FROM AUTHOR]

[Display omitted] • Biodiesel production from marine macroalgae Dictyota bartayresiana oil was studied. • CaO nanocatalyst was synthesized using waste collected from building demolition site. • The reaction parameters for efficient production of biodiesel was optimized. • Investigation on techno-economic aspects was studied for biodiesel production. • Sensitivity analysis was used to study the uncertainty of biodiesel production process. The investigation on utilizing macroalgae for industrial scale biodiesel production is an imperative action needed for commercialization. In the present research work, the biooil from marine macroalgae Dictyota bartayresiana was used for biodiesel production using calcium oxide nanocatalyst synthesized using waste collected from building demolition site. The optimization results obtained were the calcination temperature 573 °C, concentration of catalyst 5.62%, methanol to oil molar ratio 14.36:1, temperature 55.7 °C and time 67.57 min for the transesterification with the biodiesel yield of 89.6%. The techno-economic aspects of biodiesel production were investigated for 20 MT/batch. The return on investment and internal rate of return from the biodiesel production plant was found to be 25.39% and 31.13% respectively. The plant payback period was about 3.94 years with a positive NPV value of about 14,053,000 $/yr. Thus, Dictyota bartayresiana biomass can be efficiently used for the sustainable production of biodiesel. [ABSTRACT FROM AUTHOR]

In this work, granular biochar, Laminaria japonica -derived biochar (LB)-calcium alginate beads (LB-CAB), was successfully prepared by dropping a mixture of powder biochar and alginate solution into a calcium chloride solution for phosphate adsorption. Among different marine macroalgae derived biochars, LB exhibited the best performance, showing a phosphate removal rate of 97.02%, which was attributed to its high Ca/P and Mg/P ratios. With increasing pyrolysis temperature up to 600 °C, the physicochemical properties of LB became suitable for adsorbing phosphate. Experimental results of kinetics and equilibrium isotherms at different temperatures (10–30 °C) showed that the phosphate adsorption process is endothermic and is mainly controlled by external mass transfer and the intraparticle diffusion rate. The maximum adsorption capacity was found to be 157.7 mg g −1 at 30 °C, as fitted by the Langmuir–Freundlich model, which is higher than capacities of other powder form of biochars. [ABSTRACT FROM AUTHOR]

A novel combined electrochemical modification (CEM) method, using a graphite electrode-based electric field and MgCl 2 as electrolyte, was newly developed to prepare porosity-enhanced biochar containing periclase (MgO) nanocomposites (PE-MgO/biochar). During the CEM method, the dried marine macroalgae was immersed in the MgCl 2 solution, and a voltage of 20 V was then applied for 10 min prior to pyrolysis. Morphological and chemical analyses results showed that nano-sized MgO particles with a highly crystalline structure were dispersed and enriched on the surface of the PE-MgO/biochar, which enabled higher phosphate adsorption capability. In an adsorption equilibrium test, among various biochars, PE-MgO/biochar exhibited the highest phosphate adsorption capacity from aqueous solution with a Langmuir–Freundlich maximum adsorption capacity as high as 620 mg-P g −1 . It can be concluded that the newly introduced CEM method is a potent additional technique to effectively prepare modified-biochar in terms of a simple and time-saving modification method. [ABSTRACT FROM AUTHOR]

The collected roots of Undaria pinnatifida , the main waste in farming sites, accounting for 40–60% of annual production, was pyrolyzed under temperature ranging from 200 to 800 °C to evaluate the influence of pyrolysis temperature on biochar properties and phosphate adsorption capacity. It was confirmed that an increase in the pyrolysis temperature led to a decrease of the yield of biochar, while ash content remained almost due to carbonization followed by mineralization. Elemental analysis results indicated an increase in aromaticity and decreased polarity at a high pyrolysis temperature. When the pyrolysis temperature was increased up to 400 °C, the phosphate adsorption capacity was enhanced, while a further increase in the pyrolysis temperature lowered the adsorption capacity due to blocked pores in the biochar during pyrolysis. Finally, a pot experiment revealed that biochar derived from waste-marine macroalgae is a potent and eco-friendly alternative material for fertilizer after phosphate adsorption. [ABSTRACT FROM AUTHOR]

Various marine sediments were evaluated as promising microbial sources for methane fermentation of Saccharina japonica , a brown alga, at seawater salinity. All marine sediments tested produced mainly acetate among volatile fatty acids. One marine sediment completely converted the produced volatile fatty acids to methane in a short period. Archaeal community analysis revealed that acetoclastic methanogens belonging to the Methanosarcina genus dominated after cultivation. Measurement of the specific conversion rate at each step of methane production under saline conditions demonstrated that the marine sediments had higher conversion rates of butyrate and acetate than mesophilic methanogenic granules. These results clearly show that marine sediments can be used as microbial sources for methane production from algae under high-salt conditions without dilution. [ABSTRACT FROM AUTHOR]

Abstract: In this investigation, Enteromorpha compressa algal oil with high free fatty acids (FFA) used as a feedstock for biodiesel production. Two step process was developed and kinetic study executed to obtain reaction rate constant for the transesterification reaction. The acid esterification was carried out to reduce FFA from 6.3% to 0.34% with optimized parameters of 1.5% H2SO4, 12:1 methanol–oil ratio, 400rpm at 60°C and 90min of reaction time. The maximum biodiesel yield 90.6% was achieved from base transesterification through optimum conditions of 1% NaOH, 9:1 methanol–oil ratio, 600rpm and 60°C temperature for 70min. The algal biodiesel was characterized by GC–MS, HPLC and NIR. This transesterification follows first order reaction kinetics and the activation energy was determined as 73,154.89J/mol. The biodiesel properties were analyzed and found to be within the limits of American standards. Hence, E. compressa serves as a valuable renewable raw-material for biodiesel production. [Copyright &y& Elsevier]

Abstract: This work reports the results of the study for cadmium binding by the dead red macroalga Mastocarpus stellatus. Kinetics sorption experiments demonstrated the high rate of metal biosorption: the system attained over 50% of the total biomass cadmium uptake within 2min of contact and over 90% in the first 9min. The kinetic data were successfully described by a pseudo-second order model with rate constants ranging from 1.06 to 10gmmol−1 min−1, as a function of initial metal concentration and temperature. The equilibrium binding was accurately represented in terms of Langmuir and Langmuir–Freundlich models. The sorption isotherms at constant pH showed uptake values as 0.49mmolg−1 (at pH 2.4), 0.56mmolg−1 (at pH 4) and 0.59mmolg−1 (at pH 6), while the affinity constant values were between 0.6 and 5mmol−1 L (Langmuir fit). The acid–base properties of the alga were also studied, obtaining the total number of acid groups, 2.5mmolg−1, and their apparent pK value, 1.56, using the Katchalsky model. Desorption studies were conducted employing different HNO3 concentrations and desorption times. [Copyright &y& Elsevier]

Abstract: Five different brown seaweeds, Bifurcaria bifurcata, Saccorhiza polyschides, Ascophyllum nodosum, Laminaria ochroleuca and Pelvetia caniculata were studied for their ability to remove cadmium from aqueous solution. Kinetics of cadmium adsorption by all the algae were relatively fast, with 90% of total adsorption occurring in less than 1h. These experiments could be accurately described by a pseudo-second-order rate equation, obtaining values between 1.66×10−3 and 9.92×10−3 g/mgmin for the sorption rate constant k. Several equilibrium adsorption isotherms were obtained for the quantitative description of cadmium uptake. The use of the Langmuir isotherm led to values between 64 and 95mg/g for q max and between 0.036 and 0.094L/mg for b. The effect of pH on biosorption was also studied. Acid–base properties of algae were studied by potentiometry to determine pK values (from 3.54 to 3.98) and the total number of acid groups. [Copyright &y& Elsevier]