Dewatering fibrous sludge with soy protein

• Soy protein is shown to function as a sludge conditioner.
• It can largely replace petroleum-based polymers.
• High cake solids are obtained upon belt pressing.
• It is approximately five times cheaper that traditional polymers.
• This is the first “green” sludge conditioner described.

Sludge is typically conditioned with petroleum-based polymers such as cationic polyacrylamides (c-PAMs) prior to dewatering. It is shown that soy and whey proteins can function as sludge conditioners. High cake solids are obtained when fiber or fibrous sludge is dewatered after treatment with a crude soy flour hydrolysate. Filtrate turbidity is not reduced by the soy alone, but it can be significantly lowered with a small c-PAM supplement. The approach is demonstrated with wood pulp fiber and several paper mill sludges. The binding of soy protein to sludge solids is much weaker than that of c-PAM, but it still produces a denser cake because charge reversal is reduced. Although soy protein and sludge particles are both negatively charged overall they both contain positively charged groups that facilitate bonding. The cost:benefits of c-PAM supplemented soy protein are attractive when compared to a full c-PAM dose. In addition, the soy product has a green value.