Pilot-scale validation of floating permeable nutrient uptake system with mixotrophic Chaetoceros for in-situ nutrient recovery in marine shrimp aquaculture.

Intensive marine shrimp aquaculture discharges substantial nitrogen (N) and phosphorus (P) into coastal environments while generating substantial greenhouse gas emissions. Scalable in-situ nutrient recovery technologies that can be integrated with operational aquaculture production systems remain largely absent. This study developed and validated a floating permeable nutrient uptake system (FPNUS) containing mixotrophic Chaetoceros sp. in pilot-scale marine shrimp cultivation. Membrane screening (0.1, 0.5, and 1.0 µm) identified the 0.1 µm membrane, which sustained ammonium (NH4+-N) and phosphate (PO43--P) transfer rates of 55.19 and 17.79 mg·m-2·h-1 with > 95% Chaetoceros retention. Over a 56-day cultivation cycle in 400 L shrimp tanks (five treatments, including the control, suspended microalgae, single-unit mixo-FPNUS (1), dual-unit mixo-FPNUS (1 + 1), and microbial-inoculated, with no inferential statistics owing to the absence of tank-level replication), mixo-FPNUS (1 + 1) reduced the average total nitrogen (TN), NH4+-N, and total phosphorus (TP) by 39.1%, 63.7%, and 40.9%, respectively, relative to the conventional control, outperforming suspended algae, a microbial-inoculated treatment, and the single-unit mixo-FPNUS (1). Recovery efficiency increased with the FPNUS-to-tank volume ratio (TN increased from 24.7% to 39.1%; TP increased from 28.3% to 40.9%). System-level mass balances confirmed cumulative recovery of 4.79 g N and 1.59 g P per tank as harvestable biomass over the 56-day cycle. Carbon-footprint estimation (covering feed production, aeration, water treatment, scenario-based feed replacement, and the FPNUS process) showed a reduction of 26.3% per kilogram of shrimp. These results position FPNUS as an enabling technology for circular, lower-emission marine shrimp production, with particular relevance to the intensifying recirculating aquaculture sector.