An advanced biorefinery is effectively a polygeneration facility with integrated, efficient and flexible conversion of wastes, through a combination of physical, chemical, biochemical and thermochemical processes, into multiple products1
. The biorefinery concept was analogous to the complex crude oil refineries adopting the process engineering principles applied in their designs, such as feedstock fractionation, multiple value-added productions, process flexibility and integration
. Enhancing the economic performance of biorefinery is the key challenge during the commercialisation stage. Energy products such as heat, electricity and biofuel are low value high volume products, while biochemicals and biomaterials (e.g. polymers) are high value low volume products. Biofuel or bioenergy production needs subsidies or economic incentives via supportive regulatory frameworks for feasibility. Hence, the aim of this study is to devise a strategy to realise an inherently economically competitive biorefinery system by added-value co-productions using stillage streams including carbon dioxide in offgases or exhaust gases, which can advocate a circular economy. Therefore, waste streams including those containing carbon dioxide from biofuel or bioenergy system must be reused to produce added-value products for achieving sustainability of biorefineries. Carbon dioxide reuse into biofuels, chemicals and biomaterials can be realised via three main routes: carbon dioxide reduction at cathode in microbial electrosysthesis system (MES)
; reusing carbon dioxide from exhaust gas of a thermochemical platform
and carbon dioxide capture by growing algae in algae biorefinery systems1
. The case studies in this paper focus on the production of biopolymer, biochemical, biofuel by CO2
reduction in MES; and biofuel production by trigeneration and Sabatier reactions. The economic performances using techno-economic modelling and environmental performances using life cycle assessment are conducted to result in integrated and advanced biorefineries that can enhance the three measures of sustainability. Producing biomaterial together with biofuels and bioenergy is the route for competitive biorefinery systems.
 Sadhukhan, J., Ng, K.S., Hernandez, E.M. 2014. Biorefineries and Chemical Processes: Design, Integration and Sustainability Analysis. Wiley.
 Sadhukhan, J., Lloyd, J., Scott, K., Premier, G.C., Yu, E., Curtis, T., Head, I. 2015. A Critical Review of Integration Analysis of Microbial Electrosynthesis (MES) Systems with Waste Biorefineries for the Production of Biofuel and Chemical from Reuse of CO2, Renewable & Sustainable Energy Reviews, 56, 116-132.
 Ng, K.S., Zhang, N., Sadhukhan, J. 2013. Techno-economic analysis of polygeneration systems with carbon capture and storage and CO2 reuse, Chemical Engineering Journal, 219, 96-108.