High solid anaerobic digestion: Operational challenges and possibilities

• The integration of two or more anaerobic digestion technologies can be employed to improve HSAD.
• Leachate pre-treatment and recirculation provide a better option for mixing during HSAD.
• Digestate quality and handling in HSAD are expected to be better.

The process of high solid anaerobic digestions (HSAD) was developed to reduce water usage, increase organic loading rate (OLR), reduce nutrient loss in digestate and avoid or decrease the dewatering of digestate. However, the operation of HSAD is currently constrained by low rates and extents of methane production high operational costs. Several published investigations have been conducted to study the effects of inhibition, temperature, moisture, and reactor design on the efficiency of HSAD. However, low moisture and poor mixing, which are required for the dilution and diffusion of metabolites, have been reported to be the major causes of low methane yield in HSAD. In order to optimize the operation of HSAD, technological integration has to be considered, especially thermo–mesophilic digestion, co-digestion, mixing and integration of two or more reactors. This paper provides a critical review of recent research on HSAD while focusing on how these studies can be integrated to improve HSAD.