Enhancement of the conventional anaerobic digestion of sludge: comparison of four different strategies

摘要

Anaerobic digestion (AD) is the preferred option to stabilize sludge. However, the rate limiting step ofnsolids hydrolysis makes it worth modifing the conventional mesophilic AD in order to increase thenperformance of the digester. The main strategies are to introduce a hydrolysis pre-treatment, or tonmodify the digestion temperature. Among the different pre-treatment alternatives, the thermalnhydrolysis (TH) at 170 WnC for 30 min, and the ultrasounds pre-treatment (US) at 30 kJ/kg TS werenselected for the research, while for the non-conventional anaerobic digestion, the thermophilic (TAD)nand the two-stage temperature phased AD (TPAD) were considered. Four pilot plants were operated,nwith the same configuration and size of anaerobic digester (200 L, continuously fed). Thenbiogas results show a general increase compared to the conventional digestion, being thenhighest production per unit of digester for the process combining the thermal pre-treatment and ADn(1.4 Lbiogas/Ldigester·day compared to the value of 0.26 obtained in conventional digesters). Thendewaterability of the digestate became enhanced for processes THþ AD and TPAD when comparednwith the conventional digestate, while it became worse for processes USþ AD and TAD. In all thenresearch lines, the viscosity in the digester was smaller compared to the conventional (which is a keynfactor for process performance and economics), and both thermal pre-treatment and thermophilicndigestion (TAD and TPAD) assure a pathogen free digestate.