Recovery of protein from tofu whey wastewater using protein-based coagulant.

Tofu whey wastewater is the protein-rich liquid by-product of tofu production that has the potential as a source stream for biobased products. Coagulation can be used to recover protein from tofu whey. Biobased coagulants are alternatives for polymer- and metal-based coagulants, particularly if the precipitate is recovered and used for further processes. The tofu whey coagulation performance of three protein-based coagulants, namely soy protein isolate, seed, and isolate of seed protein, was determined with the jar test method. The pH (4, 5, 7, 9) and protein dosage (33-191 mg-protein/L) were varied. The results were compared with chitosan, as a benchmark for biobased coagulants, with similar pH variation and 100-800 mg-chitosan/L dosage variation. Our experiment showed that the optimum pH for protein coagulation was 4 (the initial pH of the tofu whey). Up to 95% turbidity could be removed, with chitosan shown to be the most effective coagulant. On the other hand, chitosan only removed up to 9% of organics as chemical oxygen demand (COD), while soy protein isolate could remove up to 20%. The highest protein removal was obtained by soy protein isolate (35%) followed by seed (34%), chitosan (25%), and seed protein (13%). Meanwhile, coagulation with soy protein isolate could recover 11% protein in the precipitate at 60% protein content. Higher protein removal compared to COD suggests a preference towards protein coagulation compared with other organics. Our results suggest that protein-based materials can be applied to recover proteins from tofu whey.