Evaluation of a novel seriguela gum (Spondias purpurea L.) based flocculant aid for wastewater treatment: effect of carboxymethylation

ABSTRACT Seriguela gum is a barely explored polysaccharide, whose carboxymethylation reaction can expand its applications for water treatment by the increase of negative charges in the chain. This work aimed to produce carboxymethyl derivatives, under different reaction condition, to apply as a flocculation aid in water treatment. The derivatives were characterized by titration, Fourier transform infrared spectroscopy, nuclear magnetic resonance, and gel permeation chromatography techniques. The reaction condition parameters, sodium hydroxide concentration, and chloroacetic acid molar ratio significantly affected the degree of substitution, with values between 0.35 and 0.51. Optimal results were achieved using lower concentrations of sodium hydroxide and intermediate chloroacetic acid levels. The derivative produced with higher degree of substitution was used as flocculation aid combined with aluminum sulfate for the treatment of contaminated river water. The tests demonstrated that the use of 3 mg/L of carboxymethylated seriguela gum combined with 20 mg/L of aluminum sulfate removed 93.1% of turbidity, showing a 21.0% increase in efficiency and a 60.0% reduction in the use of aluminum sulfate alone. It also exhibited low toxicity to Artemia salina at high concentrations (100 mg/L) due to its biocompatibility. The study revealed that carboxymethylated seriguela gum with increased negative charges can be obtained with a high degree of substitution by a simple and high-yield process, and the tests showed high potential for application as a flocculation aid in water treatment processes.