Characterizing the fluorescent products of waste activated sludge in dissolved organic matter following ultrasound assisted ozone pretreatments

► Ozone/US combined pretreatment achieves a maximal sludge reduction ratio of 40.14%. ► Ozone/US combined pretreatment could induce more DOMs released from WAS. ► This combined-lysis technology provide more DOMs in subsequent biological processes. ► EEM technique was a high available tool for assessing components changed in WAS.