Improving the biohydrogen production potential of macroalgal biomass through mild acid dispersion pretreatment

•The optimized conditions were shown at 12,000 rpm with 30 min under pH 5.•The combined pretreatments yielded 60 mL/gCOD of biohydrogen.•The combined pretreatment increased COD solubilization up to 55%.•Biohydrogen production increased by about 83% at the optimized parameters. Macroalgae is becoming more popular as a viable and promising resource for the production of biofuels belonging to the third generation (i.e biofuels that are made from algae). The high ratio of carbohydrates and lipids, as well as the lack of lignin, make macroalgae a desirable feedstock for biofuel production. However, algal biomass must be pretreated before fermentation to make the carbohydrates trapped within the cell wall more accessible. An effective pretreatment method favors the hydrolysis of biomass and makes the substrates available for hydrogen production. In this study, Ulva reticulata was combinedly pretreated with a disperser and acid to effectively generate fermentative biohydrogen production. The disperser’s rotational speed of about 12,000 rotation per minute and input of specific energy of about 2500 Kilojoule/Kilogram of Total Solids with the dispersion duration of thirty minutes and maintaining the biomass at pH 5 with diluted sulphuric acid were optimized as the experimental parameters for the effective solubilization of the macroalgae. The experimental results displayed that the biohydrogen production increased by about 83 % at the optimized parameters compared to the untreated algal biomass. The combined pretreatment can efficiently disrupt the macroalgal structure leading to a rise in the concentration of organic matters such as SCOD (soluble chemical oxygen demand), proteins, and carbohydrates thereby enhancing the production of biohydrogen. The combined pretreatments yielded 60 mL/g COD of biohydrogen, whereas the biomass pretreated with a disperser alone and untreated macroalgae produced only 30 mL/g COD and 5 mL/g COD of biohydrogen, respectively. Thus, it is inferred that the sample pretreated with the homogenizer (disperser) and acid produced the most biohydrogen. In general, it can be concluded that a combination of disperser along with the addition of acid could be used as an efficient method for disrupting the structure of macroalgal biomass thereby enhancing the fermentative hydrogen production.