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• Pretreatment is an essential step for the breakdown of lignocellulosic biomass. • Combining pretreatment helps to lower the severity of the drawbacks of a single step. • Biological-chemical/physicochemical combined pretreatment strategies were reviewed. • The order of pretreatment in the combined studies affects the overall efficiency. Sustainable biorefinery concepts based on lignocellulosic biomass are gaining worldwide research interest because of their inexpensiveness and abundance. The recalcitrance of lignocellulosic biomass poses a major hindrance to enhance biofuel production. Therefore, a pretreatment step is critical to prepare the substrates for the downstream process. Combining pretreatment steps help to lower the severity of the drawbacks of a single pretreatment step. This paper systematically reviews the combined biological and chemical/physicochemical pretreatment based on fiber degradation and sugar yield. An energy-efficient biological pretreatment method combined with a chemical pretreatment that accelerates the pretreatment times has been seen to be efficient for fiber degradation and sugar yields. However, fungal species, culture conditions, biomass type, the severity of chemical pretreatment and the order of sequential pretreatment influences the relative component contents and sugar yield. Even the same biomass from different sources undergoing similar pretreatment conditions could result in a varying amount of digestibility. [ABSTRACT FROM AUTHOR]

• The individual or dual effect of ultrasound/ozone pretreatment on microalgae were studied. • Ultrasound, released proteins to the aqueous phase and increased lipids viability. • Ozone, induced carbohydrates and phosphorus depolymerization. • Dual ultrasound and ozone intensified microalgae biocompounds fractionation. • Dual pretreatment reduced 95 % the solvent waste and 80 % the extraction time. This study applies individual and combined application of ultrasound and ozone pretreatments for the tandem recovery of microalgae biocompounds (lipids, proteins, and, carbohydrates) and phosphorus from Scenedesmus obliquus cultivated in wastewater. Results of individual application showed that ultrasound released protein to the aqueous phase (99 ± 3 %), and increased microalgal lipid viability from 11 to 90 ± 2 %. Whilst ozone pretreatment induced carbohydrate release to the aqueous phase 28 ± 1 %. Combined ultrasound and ozone pretreatment were studied in sequence mode. Ultrasound was first applied to release proteins and expose lipids, followed by ozone to induce carbohydrates and phosphorus release. The maximum yields of recovered lipids, proteins, carbohydrates and phosphorus by the combined pretreatment were 89 ± 1 %, 91 ± 8 %, 63 ± 1 %, and 75 ± 1 % respectively. In the dual pretreatment best experimental parameters applied for ultrasound were: biomass concentration of 25 g/L and applied energy of 200 kW h/kg dry biomass. Ozone pretreatment used 27 mg O 3 /L, contact time 25 min and pH of 11. The combined pretreatment intensified microalgae fractionation achieving high biocompounds and phosphorus recovery yields; reducing solvent waste by 95 % and extraction time by 90 %, in comparison to biocompounds extraction without pretreatment. [ABSTRACT FROM AUTHOR]