Treatment of potato starch wastewater by dual natural flocculants of chitosan and poly-glutamic acid

Abstract

Starch wastewater treatment required extensive optimization because of its high concentrations of organic compounds and concentrated emissions. An environmental friendly dual flocculant, composed of cationic chitosan and anionic poly-glutamic acid, was investigated. Initial mechanistic studies involving independent injections of chitosan and poly-glutamic acid revealed their primary mechanisms of charge neutralization and bridging respectively. The highest removal rates of turbidity by chitosan and poly-glutamic acid were 90.1% and 91.8%. Dosing pattern studies showed that initial chitosan dosing provided the highest removal rate and widest effective pH range. Mechanistic studies using zeta potential and floc measurements, confirmed that chitosan neutralized negative charges, while long-chained poly-glutamic acid aggregated particulates. The effects of wastewater quality storage time, compound ratio, and total dosage were studied, with optimization at 0 h, 1:1, and 80 mg L−1, which outperformed traditional flocculants polyaluminium chloride and polyferric sulfate. The removal rates of chemical oxygen demand, total nitrogen, total phosphorus and turbidity were 44.8, 53.4, 28.1, and 98.3%. The sediment was detected containing 95% of organic matters and 5.6% of total nutrients making it an excellent organic fertilizer. This dual system is promising in starch wastewater treatment and resource recovery considering its eco-friendly and effective flocculation performance.