Distribution of protein fractions in tofu whey wastewater and its potential influence on anaerobic digestion

Abstract

Wastewater from tofu (soybean curd) production contains a high organic concentration that might pollute the environment if it is not treated properly. Among the major organic constituents of tofu wastewater are proteins. Degradation of proteins generates ammonia and H2S gases, and if this occurs in an anaerobic digester might hamper the digester’s performance. On the other hand, proteins can potentially be recovered as value-added products. This research aimed to identify protein amounts in different fractions of tofu wastewater, as a basis of designing a process to recover the proteins. Furthermore, the influence of a lower protein concentration to anaerobic digestion of tofu wastewater was calculated. Tofu wastewater was fractionated by gravity settlement and filtration into settleable, suspended, and dissolved fractions. Subsequently, total solids, protein, and COD concentrations of each fraction were analysed. Our results show that tofu wastewater contained 2.9 g-protein/L, equivalent to 4 g-COD/L. While most of the proteins were dissolved, 9% of the proteins were settleable. This might be recovered via a settling chamber. Using the protein-separated wastewater in anaerobic digestion might reduce NH3 and H2S by 10% while only reduce biogas production by 2%.