Compound bioflocculant used as a coagulation aid in synthetic dye wastewater treatment: The effect of solution pH

• The effect of solution pH on the aid effect of CBF in dye wastewater coagulation treatment is investigated.
• Color removal performance was enhanced throughout the studied pH range (pH 4–9).
• Floc size was significantly enlarged at acidic condition.
• Floc growth rate was significantly enhanced at neutral and base conditions.
• Floc breakage and recovery factor was improved throughout the studied pH range (pH 4–9).

This study was aimed to study the effect of solution pH on the aid effect of compound bioflocculant (CBF) in dye wastewater treatment combined with widely used alum coagulants. The color removal performance of aluminum sulfate (AS) and polyaluminum chloride (PAC) was significantly improved with the aid of CBF. In addition, the effective pH range of alum salts was also broadened by CBF. Floc properties including size, growth, breakage, re-growth and sedimentation natural were determined by PDA2000. The results showed that floc size was enlarged by CBF, especially at acidic conditions and that floc grew faster when CBF was added, especially under neutral and alkaline conditions. Floc sedimentation rate, floc breakage and recovery factor were also enhanced by CBF throughout the studied pH range. CBF was characterized by FT-IR on which there is abundant –COO− and –NH. It was suggested that adsorption and bridging effect of CBF performed a positive role in dye wastewater treatment.