Digestion liquid based alkaline pretreatment of waste activated sludge promotes methane production from anaerobic digestion. (1st July 2021) - He, Dandan
Highlights: The reflux ratio of 20% digestion liquid increased the methane production from WAS by 1.6 times. The digestion liquid promoted the decomposition of WAS and improved the biochemical methane potential. Ammonium and metal ions increase methane production by promoting WAS solubilization or activating enzyme expression. The refractory organics reduced methane yield through suppressing the bio-processes. Abstract: This work proved an efficient method to significantly increase methane production from anaerobic digestion of WAS. This method is to reflux proper of digestion liquid into waste activated sludge pretreatment unit (pH 9.5 for 24 h). The yield of maximum methane improved between 174.2 ± 7.3 and 282.5 ± 14.1 mL/g VSS with the reflux ratio of digestion liquid increasing from 0% to 20%. It was observed that the biodegradable organics in the digestion liquid did not affect the biological processes related to anaerobic digestion but increased methane production through reutilization. The ammonium in the digestion liquid was the main contributor to the increase in methane production via promoting sludge solubilization, but refractory organics were the major inhibitors to anaerobic digestion. It should be emphasized that the metal ions present in the digestion liquid were beneficial rather than harmful to the biological processes in the anaerobic digestion, which may be connected with the fact that certain metal ions were involved in the expression and activation of key enzymes. In addition, it was found that anaerobes in digestion liquid were another potential contributor to the enhanced anaerobic digestion. Graphical abstract: Image, graphical abstract