Sequencing batch high-rate algal ponds: An alternative approach to sustainable biodiesel and ALE production with microalgae-bacteria consortia cultivated in domestic wastewater

High-rate algal ponds (HRAP) are cost-effective systems for producing microalgal-bacterial aggregates from wastewater, forming a consortium rich in alginate-like exopolymers (ALE) and lipids suitable for third-generation biodiesel. However, the effects of sequencing batch (SB) operation in HRAP remain unknown. Therefore, the present study evaluated the dynamics of algal genera, sewage treatment, ALE and lipid contents, and biodiesel quality of an HRAP (2400 L) operated in SB over 134 days. After the consortium formation (d0-d20), the pond reached a stability period between days 66 and 128, demonstrating a relative abundance of >80% of Cyclotella sp. and nitrogen, phosphorus, and chemical oxygen demand removals of 90.1 ± 3.7%, 40.1 ± 7.3%, and 66.6% ± 7.6%, respectively. ALE content reached 87.4 ± 19.3 mg/gTSS. The most efficient extraction (Soxhlet + chloroform: methanol 2:1) yielded an average lipid content of 11 ± 2 %, and the most abundant methyl esters were C16:0 (35.74%), C18:0 (21.01%), and C16:1 (12.08%). The biodiesel produced met international standards for cetane number, iodine value, kinematic viscosity, and density, while also exhibiting a higher heating value consistent with other renewable energy sources, such as soybean. These results imply increased flexibility in the use of HRAP-MABA systems through SB operation and demonstrate the production of high-quality biodiesel from predictable biomass, even under the adverse conditions of open systems.