“… 11 However, there are several constraints such as environmental factors, microalgal species, input/output energy waste, oxygen (O 2 ) regulation, nutrient level, external substrates, light intensity, and pH which might hamper the performance efficiency of microalgae. 6 The co-culturing of microalgae and bacteria, in this case, is a promising technique to regulate O 2 which is one of the constraints during microalgal bioH 2 production. 12 However, using waste resources such as activated sludge as a source of bacteria has also shown a significant enhancement in bioH 2 .…”