Rapid start-up of anaerobic digestion reactor with rice-straw ash addition for treating high salinity organic wastewater

Anaerobic digestion is an economic method to treat high-salinity organic wastewater (HSOW). However, due to the inhibitory effect of high salinity, the start-up of the anaerobic digestion reactor is slow and easy to fail. In this study, as a potassium source, rice-straw ash (RSA) was used to enhance the HSOW treatment performance and shorten the start-up time of anaerobic digestion reactor under 3.0% NaCl content and high loading rate. The results showed that RSA could provide adequate potassium ion (K+) for alleviating the inhibitory effect of high salinity on anaerobic microorganisms. The rapid start-up of the anaerobic digestion reactor was realized, and the TOC removal rate reached 81.65%. In the reactor with RSA addition, the activities of dehydrogenase, acetic kinase and coenzyme F420 were 25.67%- 89.81%, 19.03%- 50.93% and 35.83%- 944% higher than that of the control reactor, respectively. The addition of RSA promoted the accumulation of acetoclastic methanogen Methanothrix, and changed the methanogenic pathway from hydrogenotrophic methanogenesis in the beginning stage of anaerobic digestion to acetoclastic methanogenesis under high salinity condition. After stopping the addition of RSA, the performance of the anaerobic digestion reactor remained stable, indicating that RSA was only needed at the start-up stage. This study could provide a feasible method for rapid start-up of anaerobic digestion reactor treating HSOW in practice.