Nutrient recovery from aquaculture effluent via biocoagulation–flocculation and its performance as an agricultural amendment

Abstract

Conceptual diagram showing a closed-loop system where aquaculture effluent is treated via biocoagulation-flocculation, returning recycled water to the industry and recovering sludge as a biofertilizer for plant growth, supporting SDGs 6 (Clean Water), 12 (Responsible Production), 14 (Life Below Water), and 15 (Life on Land). Solid-rich aquaculture effluent treated naturally using plant-based biocoagulation–flocculation produces eco-friendly sludge that can be used as biofertilizer. This study evaluated its effect on the growth of the tomato plant (Solanum lycopersicum L.) over 8 weeks. Five pots (48 cm long × 19 cm wide ×17 cm high) were prepared with different compositions of planting medium (5 kg): 100% garden soil (CGS), 100% sand (CS), 92% sand + 8% sludge (SS), 99.99% sand + 0.01% commercial fertilizer (SCF1), and 99.99% sand + 0.02% commercial fertilizer (SCF2). Five tomato saplings (2 weeks old and 3–5 cm in height) were planted in each pot. Growth parameters included physical appearance, number of leaves, and the height of plants. By week 8, the SS pot presented the highest number of leaves and average plant height (91 leaves and 67.8 cm, respectively). These values were not significantly different (p > 0.05) compared with the CGS pot (78 leaves and 63.4 cm, respectively). Utilizing sludge as a biofertilizer in the SS pot enhanced the growth of tomato plants. The use of sludge from aquaculture effluent treated with natural coagulants enhances crop growth, reduces environmental waste, and creates a valuable, sustainable closed-loop system for the aquaculture industry.