Organic, mostly refractory compounds and ammonium in return liquors from dewatering thermal hydrolysis (TH) digestate were degraded to a large extent using a boron-doped diamond electrode. Electrochemical pre-treatment slightly improved biodegradability of organics but inhibited nitrification. The electro oxidation of biologically pre-treated return liquor at a lower current density was significantly more effective regarding COD degradation and energy demand.