Photocatalysis and flocculation processes for recycling aquaculture effluent into nutrient-rich irrigation water

This research aimed to create a novel technique for recovering fertilizers from aquaculture effluent to overcome potential non-renewable fertilizers shortages. There are two steps: a photocatalyst technique for nutrient mobilization, succeeded by solids precipitating with two natural and one synthetic flocculants. The photocatalytic degradation of organonitrogen compounds in batch experiments started under the irradiation of sunlight. Following that, photocatalytic breakdown of organonitrogen compounds produces inorganic nitrogen constituents like NH4+, NO2−, and NO3−, which could be used as manure. It was found that, after 12 h of circulation, the concentration of inorganic nitrogen became NH4+ = 17.2 g/L, NO2− = 18.1 mg/L, and NO3− = 15.9 mg/L. The jar test was adopted to assess the capacity of two natural compounds (tamarind kernel polysaccharide (TKP) and tannin-based substance (TBS)) and synthetic water-soluble polymer cationic polyacrylamide (SWP) to reduce turbidity, total suspended solids (TSS), chemical oxygen demand (COD) and colour. The findings revealed that with a dose of 20 mg/L of TBS, 20 mg/L of TKP, and 50 mg/L of SWP, the maximum turbidity reductions were 95, 93, and 94%, respectively. The TBS was slightly better than TKP and much better than SWP in terms of coagulation activities with TSS, COD and colour maximum removal efficiencies.