Optimizing flocculation of digestate to increase circularity in manure treatment

The flocculation of (co-)digested cattle and pig manure has rarely been investigated, leading to a rather intuitive use of flocculants in manure treatment processes, resulting in overdosing and increasing costs. Here, we investigate the effect of molecular weight, charge density and branching of reference and commercially available flocculants by establishing the optimal flocculant dosage and the corresponding maximum organic matter removal. Higher molecular weight flocculants show increased turbidity removal as result of their long chains corresponding to a higher amount adsorption sites. Results presented show that polymers with an increased cationic charge density give moderate and unstable flocculation due to the low amounts of non-charged parts essential for the hydrophobic interactions and hydrogen bonding. Further, the results show that a linear high molecular weight flocculant with a nonionic or a low anionic charge density is the most effective as it reached the highest organic matter removal at a low dosage.