Sustainable processing of wastewater-associated Chlorella vulgaris: hot-air drying optimization and downstream cost screening for future aquafeed evaluation

Shrimp aquaculture generates nutrient rich wastewater that poses environmental risks but also opportunities for resource recovery. This study develops and evaluates an integrated wastewater to product workflow in which shrimp effluent is treated and the recovered microalgal biomass is processed into a shelf stable powder for downstream evaluation. An Algal Turf Scrubber (ATS) coupled with a membrane integrated High Rate Algal Pond (HRAP) enabled nutrient removal and biofilm based harvesting of Chlorella vulgaris , which can reduce reliance on chemical flocculants and energy intensive pre dewatering. Hot air drying temperature and time were optimized using response surface methodology to support nutrient preservation while maintaining practical processing conditions. Within the investigated design space, a practical operating window at 60°C for 10 h retained 29.53% protein, 40.24% carbohydrate, and 18.54% lipid with low ash content of 5.78%, whereas higher temperatures and longer times were associated with reduced nutrient retention consistent with thermally driven compositional changes. Quadratic models were statistically significant and applied conservatively for comparative trend interpretation and multi response screening within the tested range rather than for extrapolative prediction. A preliminary downstream cost screening, explicitly bounded to drying and grinding, suggested a unit processing cost of 0.01 to 0.02 USD g⁻1 under the stated assumptions. Overall, the study links wastewater treatment, passive biomass recovery, drying optimization, and boundary defined cost screening as an integrated pathway to support circular bioeconomy oriented valorization in aquaculture systems. • Integrated ATS–MHRAP valorizes shrimp effluent into Chlorella vulgaris powder via harvest–dry–mill workflow. • Passive biofilm harvesting provides concentrated biomass (≈12–15% solids, w/w) and reduces reliance on flocculants/mechanical dewatering. • RSM identified an operating window; 60 °C for 10 h retained 29.53% protein, 40.24% carbohydrate and 18.54% lipid (ash 5.78%). • Elevated temperature and prolonged drying shifted composition consistent with thermal oxidation and Maillard-related losses. • Screening downstream processing cost for drying and grinding was 0.01–0.02 USD g⁻¹ under a defined boundary, supporting scale-up assessment.