Application of water hyacinth in wastewater treatment and cellulosic ethanol production

Abstract

Water pollution and depletion of fossil fuels are crucial issues which significantly affect sustainability of water resources and usage of non-renewable energies. Phytoremediation technique is an effective method to treat different types of wastewater using plants in an economical way. Lignocellulosic biomass as a renewable resource can be replaced with fossil fuels. In this research, the lignocellulosic aquatic plant, water hyacinth (WH) was propagated in fabricated tanks to evaluate wastewater purification and ethanol production efficiency. Wastewater treatment was performed in two modes (batch and continuous) and the results were compared with the Interim National Water Quality Standards, Malaysia River classification (INWQS) and Water Quality Index (WQI). The matured plants were harvested at maximum growth rate with the highest sugar content. Then, the WH was dried, and four pretreatments, namely ionic liquid, acidic, alkali and microwave-alkali were performed to obtain optimum carbohydrates content. Scanning Electron Microscopy (SEM) and Fourier Transform Infrared (FTIR) were used for compositional and structural analysis on WH before and after pretreatments. Simultaneous Saccharification and Fermentation (SSF) was performed to obtain a high level of sugars which could be converted into ethanol. In the fermentation process, the inoculation of yeast (Saccharomyces cerevisiae) and commercial cellulase enzyme from (Aspergillus niger) were used. Total reducing sugar and ethanol concentration were measured by Dinitrosalicylic Acid (DNS) method and gas chromatography. In the batch system, some parameters such as pH, chemical oxygen demand (COD), phosphate (PO3 -4), nitrate (NO3 -), ammoniacal nitrogen (NH3) and total organic carbon (TOC) were reduced and the water quality has improved from class III to II. In the continuous system, the removal efficiency 38% to 96% of ten parameters was obtained. The highest ethanol yield was produced by alkali-treated WH with 6.2 ± 0.4 g/L with 0.12 g/g WH/ethanol in 48 hours followed by microwave-alkali, acid and ionic liquid pretreatments.