Natural coagulants remove trapped Escherichia coli, suspended solids, turbidity, heavy metals, organic matter, dyes, and harvest microalgae. However, one of the primary drawbacks of using natural coagulants in microalgae harvesting is the lack of full-scale use (Yin 2010; Muhammad et al. 2021). Table 5 demonstrates that biocoagulation technology is a low energy-intensive and ecologically friendly alternative to physical separation techniques or chemical flocculation for extracting microalgal biomass. Even though using natural coagulants for microalgae harvesting is cheaper than chemical one (as depicted in Table 5), the affordability of natural coagulants depends on plant cultivating, harvesting, and extraction of active coagulants, which highly influence by spatial and temporal characteristics (Behera & Balasubramanian 2019). Studies examining the technological efficacy and economics of various harvesting techniques have revealed that plant-based coagulants have the lowest cost of biomass recovery. Since greenhouse gases like CO₂ are mostly to blame for ozone layer depletion and global warming, large-scale biomass recovery systems must be ecologically benign and enable sustained biomass production. Many investigations were conducted to evaluate the unsuitability of using natural coagulants. The results demonstrate that using chitosan has higher energy consumption and high greenhouse gas emissions than alum (Behera & Balasubramanian 2019).