Utilization of Acid-Hydrolysed Microalgal Biomass Collected from Eutrophication-Affected Freshwater Pond as a Substrate for Biogas (Biohydrogen) Production by means of Dark- and Photo-Fermentation

Eutrophication-affected waters could be a potential source in providing abundant microalgal biomass which is rich in carbohydrates and can be utilized as a promising substrate for biogas (biohydrogen) production. In the present study, microalgal biomass were collected from the eutrophication-affected freshwater pond and then were treated by acid thermal process. Three dilute acid solution (2.25%) were used as hydrolytic agent, namely sulphuric-, hydrochloric- and nitric acid. Alternate biogas production first by anaerobic bacteria and second by Rhodobium marinum were conducted to convert microalgal biomass into clean energy in the form of biogas (biohydrogen). At first stage, dark-fermentation was carried out by anaerobic bacteria to decompose macromolecular organic matter contained in the microalgal slurry or hydrolysate into organic acids. At second stage, photo-fermentative bacteria, Rhodobium marinum , will utilize organic acids and monosaccharides in the fermented liquid from the first stage to produce (hydrogen) gas. The highest value of biogas evolution (426, 88±26, 88 mL/L) and biogas yield (839, 93±49, 41 mL/g COD) was achieved when sulphuric-acid hydrolysate was used as substrate