Comparative evaluation of aquatic biomass feedstocks for energy application and potential for extraction of plant nutrients from their ash

Abstract Aquatic biomasses have fast growth rate amicable for energy applications. Presence of low melting alkali elements is a major challenge; however they are plant nutrients that enhances the ash utilization potential. The aim of this study was to evaluate aquatic biomasses (Eichornia, Hydrilla, Lemna, and Spirogyra) for potential energy application, and to assess the accumulation of plant nutrients in the ashes obtained at different temperatures (500, 600, 700, 800, and 900 °C). Volatile matter content (wt.% dry basis) was lower in Spirogyra (58.2%) or Hydrilla (56.8%) than Eichornia (68.3%) or Lemna (64.7%), whereas fixed C content (wt. % dry basis) was higher for Eichornia and Lemna (about 11%) and lower for Spirogyra (7.4%) and Hydrilla (1.0%). Carbon content ranged from 25.2 to 37.9%; decreased in the order Eichornia > Lemna > Spirogyra > Hydrilla. Ash content was higher for Hydrilla (42.1%) followed by Spirogyra (34.5%), Lemna (24.0%) and Eichornia (19.9%). FTIR and cluster analysis showed comparable ash characteristics for Eichornia and Lemna; Hydrilla and Spirogyra have typical characteristics. Plant nutrient (except N, and K) contents in the ash increased with increase in temperature. Potassium and phosphorous content was higher in Eichornia and Lemna. Slagging and fouling tendencies could be arranged in the order Hydrilla > Eichornia > Lemna > Spirogyra. Eichornia, Lemna, and Spirogyra feedstock could be used for energy application and the resultant ash has valuable plant nutrients (K and P). Low temperature (600–700 °C) processing is advantageous to conserve plant nutrients in ash.