Characterization of Anaerobic Degradability and Kinetics of Harvested Submerged Aquatic Weeds Used for Nutrient Phytoremediation

In this study, eight different submerged aquatic species were screened by batch biochemical methane potential and anaerobic degradability tests to identify a promising/suitable feedstock. Kinetics of the best-screened substrate were studied in a mesophilic semi-continuous experiment. The aquatic species <i>Myriophyllum aquaticum</i>, <i>Egeria densa</i> and <i>Potamogeton perfoliatus</i> showed relatively higher methane yields of over 400 NmL/g-VS (volatile solids). Semi-continuous operation was carried out by feeding <i>E. densa</i> for over 400 days. The achieved results were 33%–53% chemical oxygen demand (COD) reduction and methane yield of 126–231 NmL/g-VS with a short hydraulic retention time (HRT). Additionally, the NH₄⁺ and PO₄³⁻ releases from the biomass to water were found to be low (18%–27% and 2.5%–3.9%) throughout the experiment. Hydrolysis was the limiting step in the digestion of <i>E. densa</i>, regardless of changes in HRT (15–45 days). The acid-phase model indicated that the hydrolysis rate constant (k_h) of <i>E. densa</i> was 0.058 one/day, which was one third lower the k_h value of food waste, but quite similar to cow manure.