Biochemical Dynamics during EM4-Assisted Fermentation of Water Hyacinth (Eichhornia crassipes) and Nutrient Characterization of a Potential Liquid Biofertilizer

Abstract

Water hyacinth (Eichhornia crassipes) is an invasive aquatic plant that poses ecological challenges but also represents a potential resource for biomass valorization. This study investigated the early-stage fermentation of water hyacinth using Effective Microorganisms 4 (EM4) at biomass-to-water ratios of 1:4 and 1:5 over seven days. Glucose concentration, oxidation-reduction potential (ORP), pH, and temperature were monitored, while citric acid and gluconic acid concentrations were measured on days 2, 4, and 6. The final liquid product from the 1:4 treatment was characterized for nitrogen, phosphorus, potassium, and organic carbon. Measured glucose concentrations decreased from 3,491.25 to 1,091.25 mg/L in the 1:4 treatment and from 3,228.75 to 953.75 mg/L in the 1:5 treatment, corresponding to decreases of 68.74% and 70.46%, respectively. ORP declined from positive to negative values in both treatments, while pH and temperature fluctuated throughout fermentation. Citric acid was the predominant measured organic acid, reaching its highest concentration on day 4 in the 1:4 treatment. Gluconic acid concentrations also peaked on day 4 in both treatments. The final product contained 1.35% nitrogen, 0.36% total P₂O₅, 1.53% K₂O, and 26.63% organic carbon. These findings demonstrate measurable changes in glucose concentration and fermentation conditions alongside the presence of nutrients in the final product. The results support further investigation of water hyacinth fermentation as a potential biomass valorization pathway, although nutrient recovery efficiency, product safety, and agronomic effectiveness require additional validation.