Effect of glucose concentration and oxygen regulation on biohydrogen yield using microalgae and activated sludge co-culture – A source of green energy and waste energy utilization

The third-generation biofuels include biohydrogen (bioH
2
) production using microalgae is a green source of energy. There are several factors which inhibit the production of bioH
2
such as oxygen (O
2
) production and a sufficient glucose concentration. A sufficient glucose concentration is vital for fermentative bioH
2
yield; however, an insufficient glucose concentration may lead to halt the process. Whereas the production of O
2
during the biophotolytic process is the primary inhibitor of bioH
2
yield using algal biomass. It can be overcome using the co-culturing of algae and aerobic bacteria. For this purpose, activated sludge from a wastewater treatment plant was served as a source of bacteria in order to regulate O
2
during co-culturing with Chlorella vulgaris (CCALA 256). It was observed that the co-culture with 1:1 v/v (algae : activated sludge) produced the highest amount of 1,177 mL/L of bioH
2
with a minimum O
2
content of 82 mL/L in six days of incubation as compared to the previous studies in which pure bacterial cells were used. The rest of the gas composition was mainly carbon dioxide (CO
2
) 34% and Nitrogen (N
2
) 15%, with no methane (CH
4
) production. Furthermore, a continuous supplementation of 1.5 g/L of glucose was also observed to be the enough to produce 1,084 mL/L of bioH
2
. It was also observed that anaerobic conditions, in result of co-culturing, may lead to trigger the hydrogenase activity in living algal cells which enhances the biophotolytic hydrogen production along with photofermentative hydrogen production. The substantial improvement in bioH
2
production indicates the algal-activated sludge symbiosis as an alternative to pure algal-bacterial co-culture, which is source of green energy generation and waste energy utilizing process.