To What Extent Can Solids Retention Time Be Reduced Without Deteriorating the Performance of the Thermal Hydrolysis Pretreatment-enhanced Mesophilic Anaerobic Digestion

The solids retention time of anaerobic digesters is one of the most important parameters for operational and design purposes. It has been believed to have the potential for process intensification with thermal hydrolysis pretreatment upstream. To assess the extent and impact of digester solids retention time reduction, the digestibility and dewaterability of three pilot-scale, continuous flow, mesophilic anaerobic digesters operating at 15-, 12.5-, and 10-day SRT were evaluated. These 10-liter digesters were fed with 9% total solids CAMBITM THP-processed primary and wasted activated sludge every day for nearly a year. The study revealed that shortening the solids retention time from 15 to 10 days linearly decreased volatile solids reduction from 60.7% to 53.6%, highlighting the reduction in hydrolysis rate as the major drawback. However, other digester performance parameters such as methane yield, rheology, and dewaterability largely remained unchanged.