Simultaneous waste activated sludge disintegration and biological hydrogen production using an ozone/ultrasound pretreatment

► We examine the optimal level of ozone and ultrasound (US) individual pretreatments. ► We model the reciprocal relationships of the ozone and US pretreatments using RSM. ► The combined ozone/US pretreatment was the first time applied to produce hydrogen. ► Three different pretreated sludge samples for producing hydrogen were compared. ► The combined pretreatment achieves a maximal hydrogen yield of 9.28 mL H2/g DS.