Cost-effectiveness for controlling emissions of Volatile Organic Compounds (VOC) in industrial waste gas depend on the characteristics of the gas emitted. SMEs affected by VOC emission Directive 99/13/EC (wood, printing, surface cleaning, dry cleaning, leather, vehicle refinishing) generate low and variable concentrations of several different VOCs in small volumes of waste air. This profile of VOC emissions will be the focus of the new Industrial Emission Directive 2010/75/EU, but it shows the most techno-economic problems for VOC control. GRABGAS will use rhizodegradation to treat small volumes of industrial waste air (1000 m3/h) with low and variable concentrations (30-300 mgC/m3) of several different VOCs with a removal efficiency of >93% to comply with directive emission limit values (20mgC/m3). Rhizodegradation uses plant roots, microorganisms and soil to biologically degrade VOC into CO2 and H2O. It can simultaneously degrade several VOC in very low concentrations or even when they are temporarily absent. GRABGAS will adapt to changing concentration of different pollutants, as well as to weekend and short holiday interruptions without losing removal efficiency. To make VOC mixtures more biodegradable, a solar photocatalytic pre-treatment using doped-TiO2 will be applied before rhizodegradation. To support plant growth and solar photocatalysis with sunlight, GRABGAS will be installed on industries’ roofs, following European green roof standards. Optimal air flow through the rhizofilter will be achieved by a substrate allowing root growth, high active surface for bacterial growth, permeability for air and VOC storage capacity. It will keep the internal temperature and moisture within constant ranges by appropriate sealing, insulation and drainage. Total economic benefits of GRABGAS for the SMEs owning IPR and constructing GRABGAS (LEPRIEURE, AGRIFUTUR and UGN) will be 46 million € in 5 years. Total savings for VOC emitting end users (COLORIS) will be 92,000 € in 5 year