Utilizing waste as a feedstock for processes that can produce a variety of bioproducts, recycling nutrients, and reducing waste are the foundations of a circular bio-based economy. Algae-based technologies have emerged as promising solutions in this context, addressing critical challenges such as clean water availability and carbon-neutral energy. This chapter examines the implications of using algal bioreactors in the circular bio economy, with an emphasis on the sustainability assessment of bio-based products derived from algal biomass. A detailed modelling approach is incorporated to evaluate techno-economic feasibility, environmental impacts, and cost optimization of different closed photobioreactor designs. These models highlight the comparative advantages of systems like helical tubular reactors, Green Wall Panel-II, and hanging bag configurations, while also integrating solar-powered closed-loop systems to promote low-carbon, high-efficiency bioenergy production. The chapter contributes to understanding how closed bioreactor systems can be optimized through modelling to support sustainable, scalable biomass production.